Battery charger size

Jan 17, 2013
439
Catalina 310 St. Simons Island, GA
Maine,
I have left two messages through your Compass website with no response so thought I would try the direct approach here. Want to upgrade my 30 amp charger to a bigger one and was going to order the Sterling 60 amp off your website. Then I wondered if I should go bigger than 60 and if so what charger would you recommend? Have a 390 AH bank that I plan to upgrade to the Trojan 6 volts that you recommend which would be 450ah? Want to be able to bulk charge this bank quickly with a Honda 2000. Have a solar panel for much of the charging. Does an 80 amp charger make sense in this situation?
Thanks bob
 

SG

.
Feb 11, 2017
1,670
J/Boat J/160 Annapolis
The "face" rating of the charger doesn't match the real world capacity. IF time is an issue, which it may not be, then you should realize that the output of chargers that I've seen (Inverter-Chargers) is really closer to 2/3rds of the "nominal" capacity. (Internal heat in the charger actually tools the chargers back so that they don't put-out what they nominally list them as.)

Having said that, if you you are going to be limited by the actual ability of the Honda 2000 to put-out "constant" output.

I'd probably be looking for something in the 130 amp rating for that bank unless you want to run that charger for a while. Now if you really draw the bank with only 150-200 AH of draw-down, then the question is how quickly you could expect to bring the bank up to 90-95% of the nominal capacity. You'll have to run the Honda for a lot longer to get the last 10% in vs. the first 30-40% you "drew down". So it you'd like to keep your run time to about two hours, you'll need something that can put-out a continuous 80-90 Amps (real world), in my opinion.
 
Jan 17, 2013
439
Catalina 310 St. Simons Island, GA
I anticipate not getting less than about 80% SOC so maybe needing to put 80-100 AH back worst case...
 

SG

.
Feb 11, 2017
1,670
J/Boat J/160 Annapolis
So how long do you want to run your Honda Generator? What will it really put-out as a load -- i.e., Is the only thing you'll be running the charger? Do you want to be cooking food or heating up the water tank? etc.?

I think you really need to be realistic about the real world derating of the little generator and the charger. You also have the issue of the connection to your shorepower input. You are planning on just connecting into the charger with an extension cord?

I don't know about the dedicated chargers, but for inverter chargers (which are only functioning as chargers for purposes of this discussion), both the Xantrex and Mastervolt units are, in real like, only briefly putting-out their nominal power levels. e.g., our 200 Amp Mastervolt puts out 200 Amps for about a minute or so, then it starts to heat-up internally and it settles down at about 130 - 140 amps. The old 130 Heart (and Xantrex units) that were rated at 130 Amps really put-out only about 60 Amps after a short period. The issue isn't as much ambient temperatures, it has to do with the internal heat within the circuit boards. They automatically "detune" themselves.

It might be that the units that you describe are rated more accurately for real world output -- but that will depend. Also, if you don't have GOOD ventilation in the charger's compartment, it will further reduce the real world output, or cause other issues which the unit actually cuts-out from excess internal heat.

My simple answer would be that I'd go with a charger that is probably rated at least 100 Amps (at 12 VDC) if it were me. As long as it's in the zone that the Honda is okay. It should be okay for a Honda 2000 to work at about 10 - 15 Amps at 110 VAC -- that would work okay for a 130 Amp charger as long as you don't add other major loads (e.g., AC, Hot Water Heater, teapot, Blenders, Hair Dryers, etc. at the same time you're trying to bulk-up your bank.)
 
Jan 11, 2014
11,319
Sabre 362 113 Fair Haven, NY
The limiting factor is how much the battery can absorb. As batteries approach 100% SOC, the charging rate decreases. By the time you get to the last few per cent, the battery may only take a few amps for a very long time. It doesn't matter if the charger is capable of putting out 60 amps, the battery can only take a few amps.

The standard recommendation for flooded lead acid batteries is to size the charger for 10% of the bank's capacity plus some extra for house loads that may be running while charging. For a 450 ah bank, a 50 amp charger would be sufficient. That is what I have, a ProMariner ProNauticP 50 amp charger for a 460 ah bank with 4 GC batteries.

Some battery types, like AGMs can take a higher rate of charge and will recharge quicker. There is a trade off in cost and ease with which AGMs can be trashed with improper charging routines.

That's the reader digest version. Maine can provide data that is more solid.
 

SG

.
Feb 11, 2017
1,670
J/Boat J/160 Annapolis
I think that is an old guideline when Chargers were something you plugged in and came back the following day or week. If you want to bulk charge a battery, you want the bulk phase to be higher. Also, our friend with the Honda generator wants to get his batteries charged and turn the little noisy gas hog off ;^))).

I looked briefly aon dear Web... https://www.westmarine.com/WestAdvisor/Selecting-a-Battery-Charger. 20-40% of 'C'.

Further, the graph and amperage output numbers are the actual output, not "nominal" ratings.

When (some of us were kids) you remember the crazy amps of output ratings on stereo amplifiers -- the advertised output meant little by themselves in the real world.
 
Jan 17, 2013
439
Catalina 310 St. Simons Island, GA
The answer to how long I want to run my Honda 2000 is "as little as possible" and I also know that it will not be able to power anything else while bulk charging the battery. Agree that 100 amps sounds right but am still trying to find a good charger that size.
 
Feb 6, 1998
11,665
Canadian Sailcraft 36T Casco Bay, ME
Maine,
I have left two messages through your Compass website with no response so thought I would try the direct approach here. Want to upgrade my 30 amp charger to a bigger one and was going to order the Sterling 60 amp off your website. Then I wondered if I should go bigger than 60 and if so what charger would you recommend? Have a 390 AH bank that I plan to upgrade to the Trojan 6 volts that you recommend which would be 450ah? Want to be able to bulk charge this bank quickly with a Honda 2000. Have a solar panel for much of the charging. Does an 80 amp charger make sense in this situation?
Thanks bob
Bob,

It all depends upon the charger and its efficiency. I know many 80A chargers that will tap out a Honda 2K. The EU2K is only capable of 1600W continuous but some tap out earlier than 1600W. I know mine can only handle around 1500W and Honda claims this is within "range"...The Sterling's are quite efficient and a 60A can easily run off a Honda 2K. The problem is that Sterling sizing maxes out at 60A so you'd need two if you wanted to go larger. The biggest problem with flooded batteries is the rate at which they can absorb and store the energy. A 60A is about Trojan's "Ideal" at .13C and an 80A is at .17C so were not talking a huge difference in bulk charge capability. Once you poke above 60A on good quality chargers the price tends to skyrocket and you're often better off jumping to a 2000W Inverter/Charger that can be current limited to match your EU2K. Still I think you'll be lucky to get 80A, with most chargers, out of an EU2K..
 
Feb 6, 1998
11,665
Canadian Sailcraft 36T Casco Bay, ME
I anticipate not getting less than about 80% SOC so maybe needing to put 80-100 AH back worst case...
If this is the case then a charger larger than 60A is going to be pretty much wasted $$ except for the occasions where you actually do deeply discharge.. Unless your charger is quite small there will only be a short "bulk" stage (constant current stage) and from 80% SOC the charger will hit the absorption/CV/Constant voltage limit fairly quickly. Once voltage becomes limited or held steady (absorption, float, equalize) the amount of current that can flow into the battery will be continually dropping. In other words your 60A charger may only remain at 60A for a few minutes when starting bulk at 80% SOC...

The duration of bulk depends upon multiple things:

Bank Size in Ah capacity
Depth of Discharge where you begin charging
Battery Type - AGM, GEL Flooded etc..
Output of charger in relation to Ah capacity other wise called the "C" rate
Remote voltage sensing at the battery terminals (most "chargers" do not offer this and only a few inverter/chargers do
Age and health of the bank

If you are curious about how batteries charge and how fast they can be charged this article is focused on AGM. Flooded batteries, especially thick plate deep cycle, charge slower. Note the bulk time differences between the charge rates... Also pay close attention to the "stored energy" the bank was able to capture in the 1 hour or 2 hour charge then discharge scenarios. Flooded batteries simply can't store the energy into the plates (so you could then take it back out) as fast as an AGM can. While bulk is a very efficient stage of charging, as can be seen in the article below, absorption is not.

How Fast Can an AGM Battery be Charged?
 
Jan 17, 2013
439
Catalina 310 St. Simons Island, GA
Bob,

It all depends upon the charger and its efficiency. I know many 80A chargers that will tap out a Honda 2K. The EU2K is only capable of 1600W continuous but some tap out earlier than 1600W. I know mine can only handle around 1500W and Honda claims this is within "range"...The Sterling's are quite efficient and a 60A can easily run off a Honda 2K. The problem is that Sterling sizing maxes out at 60A so you'd need two if you wanted to go larger. The biggest problem with flooded batteries is the rate at which they can absorb and store the energy. A 60A is about Trojan's "Ideal" at .13C and an 80A is at .17C so were not talking a huge difference in bulk charge capability. Once you poke above 60A on good quality chargers the price tends to skyrocket and you're often better off jumping to a 2000W Inverter/Charger that can be current limited to match your EU2K. Still I think you'll be lucky to get 80A, with most chargers, out of an EU2K..
Thank you. This is a key piece of information that I was missing.
bob
 
Jan 17, 2013
439
Catalina 310 St. Simons Island, GA
Thank you for all the feedback - it is very helpful. I think that upgrading to the 60 amp charger is the best route at this point. In a couple years I will upgrade my solar panel to larger wattage and higher efficiency and hope to do most of the away-from-the-dock charging that way but of course it is not always sunny so a 60 amp charger + Honda 2000 will be a good combination.
bob
 
Feb 6, 1998
11,665
Canadian Sailcraft 36T Casco Bay, ME
This one caught my eye on amazon. Has anyone used their products?
AIMS Power 2000 Watt 12 VDC Pure Sine Inverter Charger w/ 6000W Surge $588.00
  • 2000 Watt continuous pure sine power
  • 6000 watt peak power for 20s
  • Built in 70A smart battery charger with 7 selectable battery type settings
  • Auto gen start feature. Multi Stage Smart charger 70 Amp
  • Marine and industrial grade
Be careful when buying inexpensive "marine" inverters or inverters that claim to be "marine". While AIMS generally builds a decent unit, that particular unit is not marine UL, uses a fairly dumb "dip-switch" charge voltage settings & there is no way to set a custom charge profile for absorption & float. Dip switch settings are very old school technology in terms of setting an appropriate and optimal charging profile for your batteries.. The algorithm for absorption duration, while far better than an "egg-timer", is still not as optimal as some other brands. It is basically a voltage rise duration X 10 to set the egg timer. Again, much better than a simple egg timer, but still a pretty basic algorithm. The timer has a min of 1 hour and a max of 12 hours. The case on these is also mild steel. Generally AIMS build good stuff but they build it to meet a price point and for a marine unit it is critical to only buy an I/C that us UL 458 and preferably UL-458-SA or tested to the marine supplement.

The actual marine unit (ETL listed / tested to UL458) runs about $100.00 more and neither come standard with the battery temp sensor.
 

SG

.
Feb 11, 2017
1,670
J/Boat J/160 Annapolis
A question for you Maine Sail: I noticed that some chargers (I assume that might include inverter-chargers) caution that if you intend to use them with a generator, there is switching issue that you need to be mindful of.

One supplier of industrial grade chargers said something like: "Check with us before you order if you plan to use with a generator." Is it's not having AC delivered from utility (sine wave and/or more constant voltage/amperage characteristics)?

The difference in price was not just $100 for a 100 AMP 12V Charger. A unit was was in the $400 vs. $800-1,000 range of cost. IT WASN'T MARINE GRADE, but it didn't seem like a rinky dink product and wasn't intended to be sitting outdoors, either.
 
Feb 6, 1998
11,665
Canadian Sailcraft 36T Casco Bay, ME
Just for grins I was in the shop today so I ran a test on a Trojan T-605 that had just been tested for Ah capacity and was still on the test bench. The battery had just two days ago tested at 196.7Ah and is 210Ah rated.


Because it's a 210Ah rated battery, I discharged it by -42Ah or *80% SOC under a 10.5A load (the 20 hour discharge rate). *Note this is not the actual capacity of the battery so discharge SOC was actually a bit lower at approx 78.6% SOC. Battery temp was 76.4F.

I then recharged the battery at a .2C charge rate (based on the as new rating) or 20% of Ah capacity which for a 210Ah "rated" battery just happens to be 42A.

From 78.6% SOC to an absorption voltage of 14.4V @ 42A/.2C bulk would end at 12 Minutes and current would begin tapering.

Instead I charged the battery correctly at 14.85V, went right past 14.4V, most boat owners don't charge this type of battery at an optimal voltage, and the bulk duration lasted 24 minutes and current began tapering off.

Not a horrible bulk duration from 78.6% SOC but this is a pretty healthy battery delivering close to 94% of its rated capacity. As batteries age & sulfate the bulk times get shorter.
 
Nov 16, 2012
1,037
Catalina 310, 2000, #31 31 Santa Cruz
Bob, what size wire have you got, or will you install? Standard length for the C310 is just over 20’ each way. If you’ve got an ACR or similar you only need two wires, instead of three, so there’s room for bigger gauge in the conduit.
 
Jan 17, 2013
439
Catalina 310 St. Simons Island, GA
Bob, what size wire have you got, or will you install? Standard length for the C310 is just over 20’ each way. If you’ve got an ACR or similar you only need two wires, instead of three, so there’s room for bigger gauge in the conduit.
Don't know the answer to that yet but need to see if existing cables are sufficient or if upgrading is needed.
 
Nov 16, 2012
1,037
Catalina 310, 2000, #31 31 Santa Cruz
Don't know the answer to that yet but need to see if existing cables are sufficient or if upgrading is needed.
Our C310 came with #4, but I know of another C310 that had #10. #10 has the ampacity for 60A (outside the engine compartment), but the voltage drop would be significant. The Blue Sea table shows for a 3% drop with 60A @ 40' (20' each way) you want #1 wire. I'm upgrading to #2, which is good up to 50A (it's only a 30A charger now).
 
Last edited:
Nov 18, 2010
2,441
Catalina 310 Hingham, MA
The "face" rating of the charger doesn't match the real world capacity. IF time is an issue, which it may not be, then you should realize that the output of chargers that I've seen (Inverter-Chargers) is really closer to 2/3rds of the "nominal" capacity. (Internal heat in the charger actually tools the chargers back so that they don't put-out what they nominally list them as.)

Having said that, if you you are going to be limited by the actual ability of the Honda 2000 to put-out "constant" output.

I'd probably be looking for something in the 130 amp rating for that bank unless you want to run that charger for a while. Now if you really draw the bank with only 150-200 AH of draw-down, then the question is how quickly you could expect to bring the bank up to 90-95% of the nominal capacity. You'll have to run the Honda for a lot longer to get the last 10% in vs. the first 30-40% you "drew down". So it you'd like to keep your run time to about two hours, you'll need something that can put-out a continuous 80-90 Amps (real world), in my opinion.
You may have a bad ground or undersized wire. I have a 40 amp charger and will actually see 40 amps before when I am below 85% SOC. I also have a 55 amp alternator and will see 50 amps when running over 1200 rpm and below 85%SOC but wired the alternator directly with appropriate wire and set up an actual ground, not case grounded.