Registered users don't see ads

Marine Battery Chargers - Installation Tips & Considerations

Discussion in 'Musings With Maine Sail' started by Maine Sail, Jan 1, 2012. Add this thread to a FAQ

  1. Maine Sail

    Maine Sail Moderator

    Joined Feb 6, 1998
    10,824 posts, 633 likes
    Canadian Sailcraft 36T
    US Casco Bay, ME
    NOTE: This article has been edited, updated and had more information added. I have not had the time to also do that here on SBO. To see the actual article you'll find it on my web site at the link below:

    With battery banks getting larger & larger and battery technology becoming more and more expensive a quality battery charger is not the place you want to skimp on features or quality.

    For this article I am installing a Sterling Pro Charge Ultra. When selecting a marine battery charger there are certain things I find to be important.

    1- The charger should be built to ABYC / UL 1236 standards. These standards are specific to the marine industry, though I think the emergency market such as rescue and ambulance also use UL 1236. This standard is created around safety and isolation of AC & DC. A UL 1236 charger has undergone a 1500 volt test to ensure there is adequate AC/DC isolation inside the charger. 1500 VOLTS !!!!! While there are some non-marine chargers that can do quite well in the marine environment the UL 1236 or "ABYC" compliant statement or logo will be a good guide and won't leave you guessing if the charger you chose can handle the environment or is well suited to a marine application.

    This quote was published in an ABYC referenced article and written by corrosion survey specialist Stanley Konz.

    Ø Burnt and corroded shore power cords
    Ø Improper AC Neutral to DC negative connections
    Ø Reversed battery cables
    Ø The failure of an automatic inverter ground switch
    Ø Oversized breakers
    Ø Wire nuts used
    Ø Undersized wire
    Ø Hard (house type) untinned wires"

    A BATTERY CHARGER INPUTTING 110AC INTO THE BATTERIES!!!!!!!!!!!!!!!! It is critical you choose a well built charger and wire it properly. If you don't fully understand the above points made by Mr. Konz you should consider consulting a qualified marine electrical systems specialist for this install.

    That article goes onto say that nearly 1/3 of the boats in that marina were leaking AC current directly into the water! DIY wiring mistakes, even by those meaning well, can often be a major player in these "leaks". Please be careful and follow acceptable safety guidelines.

    2- The charger should work on varying input voltages and not suffer from output limiting. This Sterling PCU is a "World Voltage" power factor corrected charger and will work on any voltage from 90-260 volts/ 40-80 hz and still supply 100% of its rated output. You can plug this charger in to voltages in just about all countries on the planet. If you're a cruiser this is a critically important feature. If you have a US voltage charger you're stuck charging at US voltage/hz docks.. There are MANY docks out there with voltage drop issues and even at 90 volts AC, with the Sterling PCU, you're still getting the full rated charger output.

    3- The charger should ideally offer battery temperature sensing and come with the sensor as standard equipment, not an "extra".

    4- The charger needs to have a good warranty and the manufacturer should have a good reputation for customer service/support. This charger carries a 5 year warranty and the Support at Sterling Power USA has been outstanding.

    5- The charger should include multiple options for charging voltages/programs.

    6- The charger should be multi-stage with at least Bulk, Absorption, Float. I prefer them to also include a Conditioning/Equalizing program.

    7- The charger should work well with marine generators. Many chargers, especially non-marine units, do not work well with a marine gen set as the generators do not output a pure sine wave.

    8- For charging wet cell batteries I prefer a charger that will revert to an absorption voltage periodically when left in standby/float mode. This programmed absorption voltage cycle helps to minimize electrolyte stratification. Float current alone is often not enough to prevent the electrolyte from stratifying. An absorption voltage, run periodically for a short duration, very often prevents the effects of stratification.

    Stratification is when the acid sinks to the bottom of the battery case and the water rises to the top of the battery case. It creates uneven plate wear and can lead to premature death of the battery. A cyclic absorption voltage will get the electrolyte moving again and minimize any effects of stratification. Not all chargers offer this very useful "cyclic absorption" feature.

    CAR CHARGERS - NO, NO, NO, NO !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

    Okay how do I put this politely with regard to using automotive or non-marine UL chargers on boats? Oh yeah I know..... NO !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

    Still not getting it? Okay.......

    #1 car chargers when used on boats can be one of the worst offenders & cause of stray current corrosion due to their internal architecture which very often does not isolate AC & DC sides like a UL Marine charger will. So this = NO !!

    #2 Most of the car/auto type battery chargers use what is often referred to as an "autoformer" or autotransfomer. These are transformers with just one winding. Cheap, dirty and they can work ON LAND. Because of this single winding they share a common internally. Portions of the same winding act as both the primary and the secondary. This is bad news and not how a "marine" charger is built. With a marine charger all AC source current runs through the AC hot wire of the charger and is fully returned to shore via the white/neutral wire. The "case" is also grounded to the ships DC ground just in case it becomes energized in an internal fault. Again this = a big NO !!!! DO NOT USE AN AUTOMOTIVE CHARGE ON A BOAT......

    #3 If the "car charger" has a two prong plug, many do, especially the older ones we all seem to have lying around the house, these can inadvertently become reversed. This is especially true if your boat has old AC outlets.. Follow me here, if the AC feed neutral & hot are reversed the ships DC negative bus can now become 120V AC with a "car charger"... This is what Mr. Konz observed in my statements in the last photo. You don't want to be a swimmer near a boat with a cheap car charger on-board, trust me. You also do not want to be the cause of an Electric Shock Drowning or ESD.. So again this = a BIG NO!!!!!!!

    PLEASE, PLEASE, PLEASE use a proper marine UL charger not a cheap Wal*Mart type automotive charger..

    Sizing The Charger
    This is a decision that is entirely up to the user, with some caveats. The general consensus is to size a hard wired charger for 10% of the banks capacity. In this case a 400Ah battery bank would get a 40A charger. Sizing at 10% of capacity or less allows thick plate deep cycle batteries to accept the current deep into the plates for a full charge.

    If you size on the low side you must also consider the DC load your boat will use at the dock, when using DC devices. You should consider this load number when trying to get to your 10% sized charger. For instance some power boats & sailboats have small banks under 200Ah. This would suggest a 20A charger. This is well and good except when your dockside DC devices can consume more than 20A, lighting DC refrigeration, computer, TV stereo etc. etc.. In this case you could have a 20A charger sized at 10% of "bank capacity" but still be drawing your bank down, and not charging it, anytime the DC loads exceed what the charger can deliver. As I said, "with some caveats".. Size carefully and don't forget to consider the dockside DC consumption.

    The Sterling PCU chargers have no problem charging a large bank and can run at full output for hours & hours on end. The cooling fan on these chargers is a variable output design to let these chargers run quieter. Chargers with single speed fans are most often louder as the fan is either on or off. I have yet to have the fans kick on very often with the Sterling PCU chargers.

    Some chargers, usually fan-less units, can not charge large banks without suffering from internal heat build up. This can result is a shortened life for the charger if it is not sized correctly. The more efficient the charger is the less heat it will produce. The Power Factor Corrected Sterling PCU is near 90% efficient which is a boost over non Power Factor Corrected chargers of as much as 40%!

    What the heck does that mean? What it means is you'll have a cooler running charger, less noise/fan, a smaller foot print because leas heat needs to be dissipated and you'll use less AC power to charge at the same DC output than a non Power Factor Corrected charger. Even the Sterling PCU 60A model will easily run off a Honda EU2000i generator and leave you with LOTS of left over wattage, about 700W left over, to run other devices while charging your bank at 60A. NOTE: The Honda EU2000i, a popular gas suitcase generator used on small boats, has a constant load rating of just 1600 watts and is not really a "2000 watt" generator for constant loads.

    Sizing to the 10% rule, or better yet, the manufacturers suggestion, is a better choice with non Power Factor Corrected chargers as they develop more heat. The Sterling Chargers are highly efficient so being in the 10% of capacity range is not as crucial with these units or other Power Factor Corrected chargers. The "time" you need to charge can be simply based on just that, "time".

    If you had a 400Ah bank and wanted it charged from 50% state of charge, to full, over one day, you can get away with a 20A charger. Even if the charger is sized at just 5% of total bank capacity your really only drawing your 400Ah bank down to 50% state of charge. By following the 50% max depth of discharge rule for house banks you would only need to replace 200 amp hours, plus charge inefficiencies. If however you need it charged back to full in 10 hours, well that's just not going to happen with a 20A charger.

    Conversely if you power your charger off a generator, when away from the dock as many boaters do, you will want as much charger as your batteries will accept to keep generator run times as short as possible. My one and only real gripe with the Sterling chargers is the largest single charger is 60A. On vessels with large banks or AGM or other types of batteries that have high acceptance rates as 60A charger can limit your recharge times when using a gen set to charge while away from the dock. For larger chargers Victron & Mastervolt make good ones, or simply double up on the Sterling. Using two separate chargers will give you the added benefit of a back up if the other charger fails. In bulk mode, what you'd be doing mostly with genset charging, both chargers will be pumping out to max acceptance of the bank or their limit. Need more, you can go to three..

    Sizing can be a personal preference often based on how "quickly" you need to replenish the bank or necessitated by the charger you choose and its abilities. Deep cycle batteries like to be slow charged, so if your alternator is large, then it may make sense to have a smaller 120V charger for good deep slow charges of your bank. With boats we often don't have a choice but to "fast charge" our banks, especially if off cruising.

    If your vessel is at a dock for long periods of time, or your boat is used weekends only, the added cost and size of a large charger, and the associated wiring, are often wasted if not really needed. Always check with your charger manufacturer to see how long the charger you're considering can be run at full output, especially if sizing on the small side of the charge/time equation. Some won't tolerate full output for very long, and others will barely feel it.

    Adding A Remote
    More often than not your battery charger will be located out of sight and the front control panel may not be easily accessible. To deal with this quirk many quality chargers offer a remote display panel. They are a great feature to look for when choosing a charger.

    The remote for the Sterling Pro Charge Ultra is quite feature packed and offers a multitude of options including monitoring DC output voltage, AC input voltage, DC current output, battery temperature. charger temperature, transformer temperature, total charging time, charging time this event and just about anything the charger is doing or has done. It is one of the most informative remotes I have seen on a battery charger at any price point. It is a very nice piece of gear.

    Wiring the remote is simple, four mounting screws and two plug & play phone jack type connections. It can be flush mounted or surface mounted and both options are included with the remote, plus the cable.

    Marine chargers from companies like Sterling, Mastervolt, Victron, ProMariner & others will often have a remote option.

    11 Pre-Sets and One User Programmable Charge Profile
    The Sterling PCU packs a lot of features into this small form factor charger. Right out of the box it has 11 preset charging profiles. On top of the 11 presets it also has one custom profile that can be tailored for a battery not already met by the preset options.

    There are very few battery chargers, at any price, that currently allow the user to build their own charging parameters. A very cool feature for those who may need it, like the owners of Lifeline batteries.

    As an example Lifeline battery, the AGM battery manufacturer, wants to see 15.5V, temp compensated, for 8 hours to "condition" (equalize/desulfate) their batteries. Many other competitors chargers have an equalization setting of 16 volts for 1 hour or 16 volts for 4 hours or 15.5 volts for an hour etc. etc.. With the Sterling Pro Charge Ultra you can custom build a "conditioning" cycle that matches the Lifeline battery manufacturer suggestions or any other manufacturers suggestions if not already covered by the 11 preset. All equalization charges should be TEMP COMPENSATED so be sure your charger has a temp sensor if you're going to be equalizing.

    Here you'll see the 11 presets, and their voltages, plus the custom user profile.

    DC Charger Outputs
    This 20A charger comes standard with three outputs which can be fed to three different banks. The output is distributed by demand not divided equally as some chargers are. So if a start battery was at 99% state of charge and your house bank was at 60% state of charge the house bank would likely be seeing the vast majority of the charging current 18-19A or so and the starter would be seeing 1-2A or less.

    For owners who have a charge distribution system in place, such as an Echo Charger, Duo Charger, VSR (voltage sensitive combining relay), or in the US often referred to as an ACR (Automatic Combining Relay), the outputs can be "jumped" together as shown to create a simple "single output" charger.

    Technically with this charger you don't need to "jump" the unused outputs if using it as a single output charger. The US distributor feels, and I agree, that it is a wise idea to equally load the output FET's so I chose to jumper than to even load the ouputs. The two red jumpers are jumping output 1, 2 & 3 to load all the output FET's equally. This essentially makes the charger a single output 20A charger rather than a three output 20A charger. All current in this installation will feed to the house bank and the starting bank will be charged via a Blue Sea Systems ACR relay. You would do the same with an Echo or Duo Charger.

    This particular boat has an ACR / Automatic Combining Relay so the charger is being used as a single output. Keep in mind that nearly all chargers, with the exception of some very expensive ones, still only have ONE output setting, in terms of charge profile, so dividing it up is not really necessary unless you don't have an ACR, Echo Charger or Duo Charger type of battery bank charge distribution.

    Also note the location of the green fuse. This is the charger output fuse and it well located and easy to change if necessary.

    The two heat shrink ring terminals are just illustrating where you can connect the neg and possitive battery leads to.

    It should be noted that on 30A and larger Sterling Pro-Charge Ultra chargers they use large studs as opposed to a small terminal strip for the DC output. I really wish the 20A model had these studs too but it does not. For that reason alone I would suggest considering the 30A or larger model if you can.

    Choose A Location
    The location your charger is mounted in plays a critical role in its life span & longevity. Care should be taken to follow your manufacturers instructions of orientation, access to air, moisture or battery gas exposure.

    1 - Mount the charger in a location were it can run cool and air can move around it. An engine space is often a poor location because the engines, and engine bay, remain warm long after the engine has been shut down. Many also have water heaters that can keep the temps in these small areas higher than average. While on many vessels you don't have a choice in this matter, due to space constraints, always look for a location outside the engine space before installing there. If the charger has a fan be sure to mount the inlet and outlet in areas where they will have unobstructed air flow. If necessary, or prudent for your charger, you can cut ventilation holes in lockers, and then cover the holes with pre-made ventilation grills to allow air flow. Ventilation for your charger does not have to look bad. There are many grill options available from teak to stainless steel.

    2 - If your hull is a dark color it is best to avoid mounting the charger directly to the inside of the hull. Topside hull temps, in direct sun, with dark colors, can easily exceed 140F! I have one customer who's AGM's were dead every two seasons use, about 100 cycles, like clock work. He had done everything suggested by the manufacturer including installing solar for his mooring sailed boat to keep them at or near full charge. It was not until I measured the battery compartment temps at 133F, located behind the cabin settee seat back, that we figured out his failure mode. Just as heat is bad for batteries it is also bad for the charger. A cool running charger is a happy charger. If your chargers fan runs constantly it may be trying to tell you something..

    3 - Battery chargers should not be mounted in a battery compartment/space despite being ignition protected. Corrosive battery gas can damage the metals in the charger and lead to shorter life or corrosive damage. All lead acid batteries, WET, GEL and AGM have the potential to vent corrosive gas. Just because your battery is a VRLA design does not mean it won't vent corrosive gas if over temped or over charged. A battery compartment is an absolute last resort location for a charger.

    4 - Try to find a location that is dry and will not have the possibility of water dripping on the charger. If there's even a slight potential of water exposure a drip shield should be constructed to protect the charger. The drip shield should prevent water from damaging the charger, but also allow for proper cooling. This is not always an easy task so mounting in a known dry spot is always the best approach. Generally speaking, higher in the boat is often better than lower in the boat for a charger mounting location. Areas closer to the bilge, or with direct ambient access to the moist bilge air, tend to be more humid and corrosive environments.

    5 - Try to mount the charger as close to the battery bank/banks as possible without mounting in the battery or engine compartment. Shorter wire runs mean less installation cost, less voltage drop can make for better charger performance over the long haul.

    6 - The area on your vessel where the charger is mounted should be clean and free of oils, vapors or other sorts of contamination. While UL 1236/ABYC chargers are "ignition protected" it is not recommend to install them where any gas vapor can accumulate. This includes LPG, gasoline, hydrogen gas or where stored solvents could spill & leak.

    The DC wiring is a very critical part of a chargers performance. Most manufacturers want to see a max voltage drop of between 1% & 3%. Voltage drop is determined by the amperage flowing through the cable over the "round trip" length. This means you add the full length of the negative and positive wires plus the max amperage that will flow to determine to your voltage drop. This 20A charger was wired up for less than a 1% voltage drop using 6GA wire. I personally prefer as little drop as possible. Realistically I could have easily wired this with 10GA wire and been at 2.75% voltage drop but Sterling ideally wants to see less than that and I don't stock 8GA wire, so 6GA it was..

    A 3% voltage drop at 14.6V is roughly 0.44A of lost voltage between the charger and battery bank. This can potentially leave you with a charging voltage at the battery of just 14.14V. With DC charging sources bigger wire is almost always better..

    I very often use this voltage drop calculator: Voltage Drop Calculator

    The Temperature Sensor
    Temperature sensing of your batteries can be very important to the longevity of a bank especially with valve regulated lead acid batteries such as AGM/TPPL or GEL. The hotter the climate you are in the more important temperature compensation is. Temperature compensation is more critical as temperatures rise rather than fall. As the battery temperature goes up, the battery charging voltage must come down. As battery temperatures drop the charging voltage can go up.

    Heat is one of the number one enemies of batteries. If you have them in an engine room, which is not advised, you really do need a charger that has temperature compensation to reduce the charging voltage when the batteries begin to heat up. If your batteries can regularly exceed 80F then you'll ideally want a charger with temperature compensation. Earlier temp compensation on some chargers was sporadically successful at best, bordering on "dumb", as in not very smart. With newer technologies they can be accurate to within a degree or two which is more than enough.

    Battery Temperature Sensor Location
    In the picture below you can see the location of the battery temperature sensor.

    It is important to mount this directly to the battery post so it senses the temperature of the bank correctly. The temp sensor should be mounted to the battery which has the most potential to get warmer than the others. For example, if your battery compartment backs up next to an engine room bulkhead, then the battery closest to that bulkhead would get the temp sensor.

    The sensor also needs to be connected directly to the negative terminal, and not the positive terminal. This sensor has the ability to fry the charger if connected to the + terminal and then accidentally shorted. This sensor CAN NOT be fused and sense temp correctly, so, by ABYC standards, it can not be connected directly to a + post.

    Always keep in mind, when stacking terminals on a battery post, that the highest current potential terminal is always placed on the bottom. In this case the two 2/0 negative cables go below the temp sensor ring terminal. There is also a limit of four terminals per battery post. Use buss bars if you need more than four items on a battery post.

    ABYC standards now also prohibit wing nuts on battery terminals if any wire connected to the battery is larger than 6GA AWG. Use standard nuts with locking washers or nyloc nuts if you have enough thread left for the nylon in the nyloc nut to thread over.

    Charger Feed Wiring
    In this photo you can see how the charger is feeding the bank. With banks in parallel or series parallel it is important that the charger supplies it current across the bank. If you look you'll see that the positive feed and the negative return pull off opposite sides of the battery bank.

    Wiring this way forces the current to flow through the entire bank and helps to minimize any intrabank imbalances. This is one of the most often violated rules of charging I witness on boats. It is important to note that this is not just for charging sources such as chargers, alternators, wind or solar but also for the DC loads. Always connect across your bank to keep intrabank imbalances to a minimum. As banks get larger there are more precise ways of wiring that can lead to better balancing but doing it this was gets you a lot further ahead than pulling everything off one end.

    You will also note the three bussed ANL fuses on the left which protect the ALTERNATOR, HOUSE BANK and CHARGER wiring. The ABYC requires that any device connected directly to a battery be fused within 7" of the + battery post to protect the wiring. These fuses are not intended to protect the devices but rather the wiring in the case of a dead short to ground. While the 7" rule is often very tough to meet always try to get the fuses as close as you can to the battery + post. The wire marked HOUSE BANK + FEED is about 16" long but runs in a conduit for about 9", under the quarter berth, then comes out at the fuse.

    Because the alternator and charger do not use the same size wiring as the house bank feed to the battery switch, they each need their own fuse to protect the wire.

    When you parallel banks you add or combine the amperage as in Ah's, cranking amps or short circuit amperage. These group 31 wet cell batteries can pump out in excess of 1200 cranking amps at 70F. For just two of these batteries that is 2400+ amps of cranking current at 70F. The short circuit current is always slightly higher than CA at 70F. Marine Cranking Amps (MCA) are rated at 32F and Cold Cranking Amps (CCA) are rated at 0F. As temps drop you have less available cranking amps and as the temp climbs the more amps you have to fry things. 2400 amps is enough to weld metal with and that is not even the short circuit rating!

    I have one customer with 4 Odyssey thin plate pure lead (TPPL) batteries with over 20,000 short circuit amps as a bank. If you short this bank the insulation will catch fire in mere seconds. Always fuse devices connected directly to the battery and fuse it for the WIRES ampacity rating.

    Fuse Distribution Close-Up

    This is the fuse distribution buss I talked about in the last photo. The three ANL fuses are bussed together with copper bar stock at the top of the fuses. The source wire from the house bank comes in the top and the ALTERNATOR, BATTERY SWITCH FEED, CHARGER/ACR are protected out the bottom.

    There are many ways to fuse devices and banks like this. For this application I found the bussed ANL fuses a good fit.

    The inverter fuse on the right is controlled via the battery switch and as such it was not "bussed" with the alternator, battery switch and charger/ACR.....

    Close Up With ANL Fuse Covers Removed
    This photos shows the ANL fuses and buss bar. Just makes it easier to see.

    One of the benefits not yet mentioned of a charger like the Sterling is that you can use the charger as a 12V power supply if you disconnect or remove your batteries from the boat during off-season layup.

    Wiring the charger direct to hard mounted buss bars and fuses, and not direct to the battey posts, means it can still power the vessels DC system even with the battery bank is disconnected and off line.

    I use this Sterling charger to power the vessels DC power needs during the off season and it acts perfectly as a 12V power supply. +1 !!!!

    Parallel Batteries - Correct Hook Up
    This illustration will better show how to connect charger sources and loads. Connect "across" the bank and it will force the batteries to charge & discharge more evenly and uniformly. This is the recommended diagram by every battery manufacturer I know of from Trojan, Lifeline, Deka/East Penn to Rolls Battery and just about everyone in-between.

    Parallel Batteries - Incorrect Wiring
    I have used my battery tester many times in scenarios like this and in every example I see the bank unevenly balanced and the batteries show it under testing. I have a battery tester than can show me the differences in a bank of batteries wired like this, and it does matter. Do not just connect your charge sources or loads to one end of a bank.

    Negative DC Wiring
    The bottom negative wire on that buss bar is for the battery charger. If your boat is equipped with a battery monitor the chargers DC negative wire should be placed on the "load" side of the monitors shunt as is shown here..

    As always the DC negative wire should be the same size as the DC positive wire. Using a DC negative buss bar is an easy way to keep the battery posts clean and free of clutter.

    Wire The Temp Sensor & AC Wiring
    In this photo I have plugged in the temp sensor and am testing the charger to see if it recognizes the temp sensor. It did. With the Sterling Remote Panel the charger will tell you the battery, charger and transformer temp to within 1 degree. A pretty cool feature.

    The AC wiring should be sized based on the manual for your charger. For this charger it calls for 14/3 AWG AC colored wire. The input for the AC wiring is marked L - N - G or BLACK/HOT, NEUTRAL/WHITE & GREEN/EARTHING GROUND.

    Your charger should ideally have it's own dedicated breaker in the AC panel sized to protect the AC wire you're using. It is not suggested to share a breaker with any other device for a fixed mounted charger. This one uses a 15A breaker and 14/3 AWG AC color coded wire.

    Always install your AC & DC wiring to acceptable color code standards. For AC and a single phase charger like this it is AC = Black/HOT, White/NEUTRAL, Green/GROUNDING/EARTH

    DC = Red/POSITIVE, Black or Yellow/NEGATIVE and Green/BONDING / EARTHING

    It is not advised to run AC & DC wires together in the same bundle unless sheathed separately. Try to keep your AC/DC wiring runs separate or sheath the AC wires to keep them isolated from the DC wiring.

    Wiring Up The DC Side
    In this picture I have mounted the charger to a back board which will get mounted to the boat. The wires are affixed to the board with sufficient strain relief to prevent inadvertent loading of the attachment point to the charger. The ends of the wires are crimped with ring terminals using the proper tool and then sealed with adhesive lined heat shrink. I also coat the lugs with a terminal grease to prevent oxidation/corrosion at the lug/terminal strip interface.

    One of the more critical aspects of charger installations, that I nearly always see violated, is the green case ground wire shown. If I had to guess I would say that nearly 85% of the installations I see are either not case grounded or the case ground wire is to small.

    This green grounding wire grounds the chargers metal frame to the vessel and allows your over current protection devices to work properly, if there is an internal fault that shorts to the case.

    This green wire gets sized for the DC side of the charger. The green AC ground will not satisfy the ABYC case ground requirement on an AC/DC battery charger. Follow me on this one. If there is a fault on the DC side of the charger the AC green wires size may not be able to handle this fault and could be undersized in having to handle that fault. This is why the requirement for the chargers case ground is for no less than one size smaller than the DC output wires.

    The ABYC standard suggests that the case ground for chargers needs to be no less than one AWG gauge size smaller than the DC output wires. So, if you have 6 GA DC wire then you need no less than an 8 GA case ground wire. Even if your wire is already technically "over sized" your surveyor or insurance company may not know this so it is always best to wire it equal to or no less than one AWG size less than the DC output wires.

    This green wire is routed from the charger to the ships DC earth ground/bonding buss which normally is earthed or grounded to the engine block. Green bonding or earth wires should never have the potential to carry any DC current other than in a fault situation. On engines using case grounded alternators or starters this usually requires the green case ground wires to go right to the engine.

    Test & Program Your Charger
    It is always a good idea to check with your battery manufacturer and obtain the recommended ABSORPTION, FLOAT and EQUALIZATION voltages. You will then program your charger to your batteries using the preset charge algorithms. Some chargers offer very little in the way of "smart" charge programs, sometimes four or less, and others, like this Sterling, offer plenty of options. As mentioned the Sterling PCU chargers also offer a user defined program that you can self program. Very cool for those applications that need it.

    You can always choose to use GEL or AGM settings on wet cell batteries but a good quality charger will not go into equalization mode, and should not, while in AGM or GEL mode. If charging WET batteries with a GEL or AGM program you'd need to switch back to a WET program to equalize your batteries. In contrast you should NOT use AGM or WET settings on GEL batteries.

    Just a note on equalization. Sulfation is like cancer of the battery, once it has set in it is only a matter if time before the battery passes on to battery heaven. Equalization is like Chemotherapy. It helps prolong the life but only prolongs the inevitable for some time. DO NOT over equalize your batteries as it can cause plate decay and lead to shorter life if over done. the best thing you can do for your batteries is keep them at or near 100% state of charge as often as possible. If on a mooring this will require wind or solar as an alternator simply won't do this and the batteries will sulfate prematurely.

    I much prefer to equalize batteries ONE AT A TIME and monitor the progress with a hydrometer or, what I use, a sight refractometer. A good charger with temp sensor should monitor the temp but it never hurts to have a digital infrared thermometer on hand while equalizing. Please DO NOT equalize batteries unattended! It is very wise to be there during equalization. If you are unfamiliar with equalization PLEASE research this before hitting the button. To equalize one at a time simply disconnect the batteries not being equalized.

    Thoroughly test your charger before leaving it to do it's thing. I personally don't like "unattended" charging even with the best built chargers in the world. This is just MY personal preference, so consider it, but don't take it as gospel. For unattended charging I use solar. It works for us, but may not for you.

    Unfortunately for many boaters in warmer climates, with WET cell batteries, the ambient temps require that chargers be left on and most often "unattended". This is due to the exacerbation of battery self discharge in warmer temperatures. Heat kills batteries, cold helps prolong life.

    Sulfation and self discharge greatly accelerate the warmer battery temps are, so do keep your batteries topped up as often as you can. In a perfect world all chargers would perform flawlessly for 20+ years. Sadly for the boating public we don't live in a perfect world and many a charger has taken out a perfectly good bank when it decided to pack it in, I see it OFTEN. When owners leave a charger on constantly when the charger fails it often takes the batteries out with it. This simple charger failure now becomes an entire new bank and a new charger as opposed to just a charger. If you don't need your charger on constantly consider NOT leaving it on and unattended, if you don't absolutely need to. Balancing unattended charging & its potentials for failure modes, versus the potential for self discharge and the resulting sulfation is one you'll have to tackle on your own.

    Good luck with your installation!!

    Good luck with your installation!!

  2. Blitz


    Joined Jul 10, 2007
    521 posts, 2 likes
    Seidelmann 34
    US Atlantic Highlands, NJ

    Thanks again for another thourough and well done post. It is timely since I'm am in the middle of an installation of a Victron Centaur 12 volt / 30 amp charger (replacing my 18 year old Raritan Charger. Yes Raritan used to make charger as well as Toilets. And the Chargers are really heavy!). I will also be moving my Battery Switch to shorten the length of wiring, installing missing Fusing for the batteries which is now the standard but wasn't when the boat was built, and installing the Victron Battery Monitor which I've had for some time but never installed.

    Some questions from your installation notes:

    1 - On your battery charger installation thread it looks like you are using a 280 Amp ANL in a blue seas pn 5005 fuse block. You have shown that at times that a diesel engine will draw over 300 amps (the rating for this fuse block). This was shown on your thread "Battery Fuse Sizing - How?" at around 316 amps. My question is do you ever use or need to use the bigger 750 amp fuse block (PN 5503) or is this block like the ANL fuse in which you can draw over the rated amount for short periods of time?

    2 - Couldn't you have used a smaller fuse on the charger since your Sterling charger is only 20 amps and you used 50 amps. I believe a 35 ANL fuse is available, which is what I was thinking I would use on my charger. I'm assuming the rating from the charger is the DC rating - meaning 30 amp charger would put out the maximum of 30 amps, or a 20 amp charger would put out a maximum of 20 amps. and not that it draws 30 or 20 amps AC respectively.

    3 - Question 2 brings me to a question on the AC breaker - assume 30 amps for a 30 amp charger - or am I messing the whole AC / DC thing up.

    4 - My charger recommends # 5 AWG DC output wiring, which is pretty large in my mind but fully supports your recommendation of less than 1% volatge drop. So due to availablity, it looks like I'll need to use # 4 AWG. Based on this to meet the ABYC standard it looks like I'll need a # 6 AWG case ground. This case ground will go to the neg battery bus, which in turn is connected to the engine/boat's ground (engine block), which is the same place as the #4 AWG neg DC output wiring is going. Do you ever just put a post or bus near to charger for the neg DC output and case ground, which then further leads to the main DC neg bus / boat's ground for a minor reduction in wiring?

    5 - My new Victron Charger also says that each of the three outputs can independantly put out the charger's full output. I'll be using just one, an ACR will be used for charging the two banks. (2 group 27 House + one group 24 back-up battery, all flooded). Do you recommend jumping the three outputs as well? What size wire do you recommend, or used in the sample installation?

    6 - I really like the idea of using copper bar stock to buss the three ANL fuse blocks together. What thickness of copper stock do you use or is this also based on the amps vs milimeter's of the cross section like wire? Have you ever tried or do you think it would be worth while to tin the stock to reduce corrosion? (reason I ask is that I see that Blue Sea has a circuit link that appears to be tinned metal of some kind - but can't find anyone who sells it)

    7 - similar to question 1 but with a positive bus bar. many buss bars are rated as 150 or 300 amps, but in a starting circuit it might find more than this. are they a continuous rating?

    8 - I like your little switch to turn off the ACR. Could you expand on when you would routinely use this? Where can I get one?

    I'm sure I might have some other follow-up questions, but as always - Thanks for your help.


  3. Maine Sail

    Maine Sail Moderator

    Joined Feb 6, 1998
    10,824 posts, 633 likes
    Canadian Sailcraft 36T
    US Casco Bay, ME
    Actually that is a 250A ANL in a 5005 ANL fuse holder. The fuse block does not need to be rated any higher than the fuse you're installing in it. If you have a 325A fuse then you really need to go to the 5003 which is safe for fuses up to 750A. The motor with the 316A in-rush current uses a 225A MRBF, if my memory is good. This thread explains why that can be: Battery Fuse Sizing - How?

    That fuse is always sized to protect the wire not the charger. The charger output should have it's own fuse internal to it. Any fusing close to the battery bank is not to protect devices but rather the wires in the event of a dead short. If you follow the wires you'll see that it also acts as the fuse for the ACR relay which charges the reserve battery. I wanted it at 50A which is above what that battery can every accept but will safely blow in a shorting situation. This fuse is still less than half of what the 6GA wire can be safely fused at.

    Yes messing it up...;) AC & DC are totally different. Your 30A DC output charger can be run on 14GA AC color coded wire and a 15A breaker, which is the standard AC breaker for 14/3 AC wire. The Centaur 12/30 only consumes about 4.4A AC but outputs 30A DC.

    There is no such thing as 5GA wire so you would usually go the next size up. If the wire run is short you can always run the VD for 6GA wire. Case ground should go to the DC earthing buss, or bonding buss, and should not be inserted or connected into DC current carrying circuit wires. Would it work? Technically yes but you really don't want to insert earthing wires into current carrying circuits if it can be avoided. My DC earthing buss goes right to the motor and never carries any current unless there is a fault. If you look close at the DC negative buss you'll notice there are no green wires there because the engine circuit uses the negative wire for the alt and starter current. By connecting the DC earth buss directly to the motor you never energize the earth circuit with DC current, unless it is called into duty for a fault..

    It should not hurt any to jump them but you may want to run it by Chris at Victron as the Centaur may be different than the Phoenix chargers I've installed.. I think the Centaur uses FET outputs like the Sterling and is distributed by demand.. These wires don't need to be big as they are only going an inch and in-theory only have the potential to carry 1/3 of the output each jumper. I use 10GA and that should be fine even on a 30A charger.

    Blue Sea makes nothing that will work for three fuses. Trust me I've been bugging them for a few years on this. I buy my copper stock from McMaster Carr and it is 1" W by 3/16" thick McMaster Carr. I simply coat it with some terminal grease and corrosion has been a non-issue. If it is I can simply unbolt it and throw it on my buffing wheel.. Tin plating would be nice but not entirely necessary.

    Yes with Blue Sea buss bars those are continuous ratings. Remember the "in-rush" for starting is less than 2 milliseconds and the buss bar is unaffected by this in-rush just as the fuse is.

    Some times when I know the start battery is full and I no longer want or need the added "load" of the latching of the relay, when charging off solar, and I want all the current going to just the house bank I will flip it off. Also when working on the system I may choose to shut it off. Or like right now when my start battery is in the barn and the house batts are on the boat I simply flip it off. If there were ever a malfunction it can come in handy too. I simply made the switch with an off the shelf SPST switch and a project box by Velleman. Just drill some holes, mount the switch in the cover, and wire it up...

    Just glad I can help!!

  4. IStream


    Joined Nov 14, 2013
    162 posts, 7 likes
    Catalina 50
    US Seattle
    Re: Marine Battery Chargers - Installation Tips & Considerat

    Great writeup on the charger, Maine. I just installed a Pronautic P2420 (before I found your writeup) and hadn't thought to bridge the outputs but just did so on your suggestion.

    Like you, I was disappointed by the terminal block but I can't justify the extra ~$200 for the stouter studs on the 2430. In fact, the whole unit feels mechanically flimsy but I love its programming flexibility and as long as it keeps on chugging, I don't care so much that it's made of Chinese plastic.

Leaky Lewmar ports?
Start by replacing lens gaskets in stock now
Ready-made sheets and halyards
Now faster than ever, our calculator tells you what sizes you need.
Sail Trim Chart and Guide
When it comes to sailing, as basic as salt and pepper and just as indispensable!
Flexible steel chafe pads
Innovative new product made of flexible, laser cut stainless steel. Must see!