Building a DC Electrical Foundation

[Maine Sail]

Every boats DC electrical system needs to start with a solid foundation. The foundation of any electrical system includes the battery system, charging system, switching and all the associated wiring and over-current protection.

This was a simple design I did for a boat the owner had already gutted to the bones. I say "simple" because the boat had no inverter, no windlass, no electric winches and only a very basic 120V system powering outlets, a charger and a water heater. This, by today's standards, is pretty simple.

When I am asked to make a drawing of the installed system I will ask the owner if they want an electrical layout drawn using standardized electrical symbols or an electrical layout using images of the actual installed products. Most boat owners, unless they are electrical engineers, simply don't understand electrical schematics or know what the symbols mean so they usually opt for a drawling like this one. There is no sense handing someone a drawing for their boats system if the language it's drawn up in is foreign to them.

Battery Banks:
The batteries for this boat were chosen by the owner based on his desired engine run time, which he wanted to be very minimal. AGM batteries do charge a bit faster. His house needs included refrigeration and the desire to run two-three days on the hook before needing any engine recharging. While the bank wound up being 440Ah instead of 500Ah (shown) he can certainly do that with his Firefly AGM batteries which can be cycled to 80% DOD.. Of importance is the manner in which the house bank is wired. The negative comes off the right side of the bank and the positive off the left. This helps to keep the bank well balanced. Also note that nothing in the DC negative side connects to the battery negative terminal before the shunt for the battery monitor.

Busbars:
Busbars are a very good way to wire batteries on most boats larger than about 27'. This keeps the number of terminals on the battery posts to a bare minimum and allows for a clean, neat, orderly and well labeled installation. Off the positive side of the house bank the first thing we hit is the unswitched/charge busbar. This busbar wound up within 7" of the battery terminal thus the fusing was off the multi ANL fuse bus. If the busbar is more than 7" a fuse between the busbar and battery would be a good idea and an ABYC requirement unless you sheath the positive wire. The only fuses suitable for a bank of this size are MRBF, ANL or Class T.

The unswitched/charge bus is just what it says. It is used to power bilge pumps, this boat had three, (not all are shown) and collect all the charge sources. If an inverter, inverter/charger or windlass were installed this would be the take off for that large gauge wiring as well. On this busbar are:

Alternator
Bilge Pumps
Solar
Battery Charger
House Bank On/Off Switch
ACR Combing Relay

The negative side busbar collects all DC negatives on the system or "load" side of the shunt. Of importance is the position of the engine negative cable. I purposely place the engine negative cable on the ear of the starter motor. This removes rusty, corroded and multiple dissimilar poorer conducting metals in the negative path and leads to better cranking performance.

Safety:
Anything connected to either battery bank is over-current protected including the ACR, alternator, solar, battery charger and DC panel. You will note that the fuse going to the HOUSE ON/OFF switch is 300A. This is so that when or if the house bank needs to be used to start the motor it won't trip. Immediately after the HOUSE ON/OFF switch there is another fuse where the wire gauge steps down to feed the DC panel. This fuse is after the emergency parallel wiring so that starting the motor does not affect the house panel fuse.

Another safety feature is the Alternator Service Disconnect Switch. Because the alternator is fed direct to the house bank for optimal charging performance this switch is a worthwhile investment in safety. This is a switch clearly marked and labeled inside the engine room so that techs or the owner working on the engine can turn off the alternator feed when working on the engine. I use the Blue Sea mSeries switches for this.

The "emergency switch" can serve to parallel banks, use house for everything use start for everything and isolate either start or house in the event of a bank failure. It can also be used to charge both banks should a fault occur in the ACR.

Charging:
On this boat the alternator is the prime mover of bulk charge current. It is set up to deliver about 125A of charge current, a .28C charge rate, to the house bank. The regulator (not shown in diagram) is a Balmar MC-614 with battery and alt temp sensors. The shore charger is only used for equalizing and charging when the owner visits a dock. The boat is also equipped with a 200W solar array with the panels wired in parallel to minimize shading issues. The starting battery is charged via the ACR and activates whenever a charge source is present. The ACR is also wired for start isolation. The start isolation feature "SI" isolates the START bank from HOUSE the split second the starter switch is depressed and reverts to normal operation once the engine is started. With solar the banks could be in parallel during starting so start isolation is a good feature when you have a three ON/OFF switch configuration. The ACR also has an ON/OFF toggle switch in the negative so the owner could turn it off if he so desired (not shown)

Switching:
This owner was starting from scratch and as such I chose to use the three ON/OFF switch configuration. HOUSE SWITCH<>EMERGENCY SWITCH<>START SWITCH. Normal use isolates the house loads from starting loads however the middle emergency switch can be used to do starting and house loads from either bank while isolating the other. The emergency switch is purposely place on the load side of each ON/OFF so that either bank could be 100% isolated in the event of a bank failure. I use a "keyed" ON/OFF switch with the key on a lanyard. This little key on a lanyard trick stops most guests from using the middle switch.

Hidden House Bank Isolation Switch (lower left of image):

For this installation a battery switch was installed (lower left) to completely isolate the house bank from all charging and loads in the event of a failure. The switch is physically located inside the battery compartment right next to the bank.

In the event that there were a house bank failure, the owner can isolate the house bank then turn on the emergency parallel switch and all charging previously feeding directly to the house battery can now be used when relying on the start/reserve bank. Default position for this switch is always on...

This owner also added a Balmar Smart Gauge to the boat when he realized how much work the Ah counter was to keep calibrated.. There are many more options one could change, modify or add but this is a pretty typical cruising boat foundation for a 27-40 +/- footer these days..

 

[Charles Erwin]

Buss bars immediately after the battery bank are the key to making a messy wireup into a simple and neat one.

If you cannot do a whole boat revision right away start by adding the negative bar which will clean things up rather well. Moreover usually there is not much effort involved in adding a negative bar.

The reason is that DC negative terminations always wind up bolted to the motor - usually in more than one spot on the motor block. That arrangement makes for an unreliable DC system and may also contribute to stray current corrosion problems. The threat is multiple DC negative bolt ups on the motor block (other than all at a buss bar) means you are using the motor block as a conductor. Very not reliable.

The better more reliable way is shown in the diagram MaineSail posted. Note all DC negative cables or leads pass first to the negative buss bar and the buss bar connects to the motor at one place only - at one of the starter mount bolts.

All in all very skookum.

Charles

 

[Maine Sail]

The better more reliable way is shown in the diagram MaineSail posted. Note all DC negative cables or leads pass first to the negative buss bar and the buss bar connects to the motor at one place only - at one of the starter mount bolts.



Charles

Charles makes an excellent point and it is something I often just take for granted that everyone is aware of.

The alternator for this motor is "isolated ground" meaning the alternators case is electrically isolated from the DC negative current path. With a case ground alternator it is best to wire a substantial gauge wire from the alt case directly to the engine negative connection and physically stack the alt lug on top of the main DC neg cable. This keeps the resistance path all copper. You want to avoid using the engine block for carrying DC current and as Charles points out one main negative connection point then off to the engine which is most often your ships "Earthing" point..

 

[berner73]

Maine,
Please forgive my ignorance. What is the reason for the fuse between the DC neg bus and the neg terminal on the ACR? Is it fault current protection?

 

[Maine Sail]

Blue Sea recomends it.

 

[Charlie98117]

Maine,
Please forgive my ignorance. What is the reason for the fuse between the DC neg bus and the neg terminal on the ACR? Is it fault current protection?

I bought a boat with an ACR but noticed it didn't have those fuses as shown in the Blue Sea literature so I called Blue Sea to ask the same question. I was told the ACR couldn't handle starter current so the fuses are needed to protect the ACR if somehow someone had switches configured wrong and the starter current was routed through the ACR.
Edit: Sorry, can't delete the post. I thought the question was about the fuses on the positive side...

 

[gettinthere]

My diagram didn't look like that! How purty.

On mine, there's no fuse between the primary pos bussbar and the secondary pos bussbar. The items on the secondary pos buss are fused. The run from bar to bar is about 4 feet.

The primary pos bussbar is 7" from the house bank so no fuse there.

 

[rgranger]

Is the shunt simply a "T" connection allowing current to pass around the negative buss or does it actually perform some other function?

 

[dlochner]

Some questions and comments.

The engine is a Yanmar 3JH2E. The starter is grounded to the block by virtue of being bolted on. Does this need an additional ground to the grounding bolt on the engine block?

Is the stock Hitachi 80 Amp Alternator a case grounded alternator? If so where would the ground attach to the alternator?

The Blue Seas ACRs have an LED status light. The LED draws current off the positive connection between the batteries but needs a grounded connection to complete the circuit. Blue Sea determined that it was better to put a fuse in the negative wire rather than try to fuse the positive connection to the LED, thus the recommendation for the fuse on the negative lead. Without a fuse if the ACR failed in some way and allowed current to pass through the negative wire the wire would have to be way oversized for the LED's current draw or it needed an appropriate gauged wire with a fuse. Cheaper and easier to throw an inline fuse on the negative wire.

After studying MS's posts on this forum and his website, my boat was re-wired in a manner very consistent with this schematic. I think I was 2 years early in my project. One thing I did differently was to add a 6 fuse Blue Sea fuse panel where MS has the bilge pump take offs on the positive bus bar. My thinking was that there will be several things I want directly connected to the battery; bilge pumps, CO detectors, propane detectors, and the stereo's memory circuit. The fuse panel provides for these connections.

Nice Shout Out in the latest Practical Sailor. PS takes the whole author/tester anonymity too far. Every article doesn't need a byline, but it is good to know who's testing what.

Now there was one more thing I wanted to say when I started, but that damn CRS reared its ugly head again!

 

[Davidasailor26]

Is the shunt simply a "T" connection allowing current to pass around the negative buss or does it actually perform some other function?

The shunt is used to measure the current into/out of the batteries. It's essentially a very low resistance resistor. The amp hour counter measures the voltage across the resistor and then uses the formula V=IR to calculate the current in the circuit.

 

[Maine Sail]

Some questions and comments.

The engine is a Yanmar 3JH2E. The starter is grounded to the block by virtue of being bolted on. Does this need an additional ground to the grounding bolt on the engine block?

By forcing the starter motors current to pass through a rusty engine block this can lead to voltage drops at the starter which can then lead to anemic cranking. When I am working on major wiring near an engine I will almost always move the engines main neg connection to the physical starter ear. This creates a direct electrical path to the starter motor and removes dissimilar poor conducting metals, corrosion, paint and rust from the circuit..

Is the stock Hitachi 80 Amp Alternator a case grounded alternator? If so where would the ground attach to the alternator?

The typical LR-180 is isolated ground and has two isolated negative studs. It is best to bus these together then run the negative either straight to the bank or directly stacked on top of the starter motor neg lug.

Blue Sea determined that it was better to put a fuse in the negative wire rather than try to fuse the positive connection to the LED, thus the recommendation for the fuse on the negative lead.

The fuse in the neg lead has nothing to do with the LED, it is for a potential fault condition as Blue Sea explains below.. Also both positive wires require fusing to meet ABYC standards. Fusing is about protecting the wires from the battery in the event of a fault, short etc..

Blue Sea:
"Fuses installed between ACR terminals A and B and each battery positive are to prevent a hazard if there is damage to the wires from the batteries to the ACR. Therefore, the fuses should be placed as close as possible to the batteries so that most of the wire is protected.

Since these fuses connect directly to batteries, choose fuse types that have sufficient AIC for your battery bank. Appropriate fuses for this application include ANL, MRBF(Terminal) and MIDI/AMI.

Automatic Charging Relays (ACRs) are connected to engine and house battery banks through large conductors. In the unlikely event that there is a fault in the ACR internal circuitry that allows fault current to flow from the high powered positive leads to the negative reference wire, the negative reference wire may have to carry more current than it is capable of and can overheat. The wire is typically rated for 20A; the normal current in this wire is less than 1 ampere. A 10-15A fuse in the negative wire can prevent excessive current from flowing in the wire leading to overheating or possible fire."

One thing I did differently was to add a 6 fuse Blue Sea fuse panel where MS has the bilge pump take offs on the positive bus bar.

This is another excellent option. Blue Sea has many ATC type fuse blocks that can also be right off the main busbar for "always on" small loads.

Nice Shout Out in the latest Practical Sailor. PS takes the whole author/tester anonymity too far. Every article doesn't need a byline, but it is good to know who's testing what.

Ed Sherman wrote that article on battery monitors. I was asked but I wanted to do more scientific testing rather than a feature/benefit piece. The testing involved, for the pay, was simply not even in the realistic range. It would have been many, many hundreds of hours of work or about 2¢ per hour... (grin)[/QUOTE]

 

[Charles Erwin]

ATC blocks are indispensable so as to consolidate low value fused circuit protection. In the picture below (use some imagination) the fuse block - lower right - protects both EchoCharge leads to the battery banks, the Victron battery monitor sense, the alternator voltage regulator sense, the always on bilge pumps, etc. Some positions are switched and the rest are always on. The neat thing is you get to choose which.

If it were not for this central fuse block (and the labels) every one of those several leads would have to be protected by separate inline fuses which will be necessarily scattered everywhere. It can be a stone bitch to find the one that goes bad - moreover some inlines will be ATC, some glass tube, and surely none will be the right value for your back up inventory. So all in all not a good arrangement when it comes time to do some fixing.

Installing a fuse block with labels assures fuse changes will be the correct value and that the types are all the same. That is a blessing for sure but it also means that these six or more fuse protected leads are all in one place - thus no need to hunt through a bunch of inline fuses to find the culprit.

This may not work for everyone but the more often you can consolidate fuses in a block - instead of inline - the easier it is to find and fix the fuse that has tripped, the more likely your back up fuses will work because they are all the same type and probably the right value.

Buss bars and ATC fuse blocks - I am a fan. You will be too.

Charles

 

[Don Crowther]

Could someone tell me what those 3 symbols are? One is under the bilge pump, one is in the starter isolation circuit and the last one is under the voltage sensing relay.
Thanks

 

[Maine Sail]

Could someone tell me what those 3 symbols are? One is under the bilge pump, one is in the starter isolation circuit and the last one is under the voltage sensing relay.
Thanks

They are not symbols but images of an in-line ATC fuse holder. I find my customers, those wishing to pay for a diagram, understand the diagrams better with actual images than they do electrical symbols..

 

[rgranger]

The shunt is used to measure the current into/out of the batteries. It's essentially a very low resistance resistor. The amp hour counter measures the voltage across the resistor and then uses the formula V=IR to calculate the current in the circuit.

Ah

So there are two poles on the shunt. I get it now.

 

[rgranger]

So where can I buy one of these?

I've rewired three older sailboats and the bus and fuses were always physically separate components ... something like this would save a LOT of crimping and extra spaghetti .....

 

[jssailem]

RG Blue Sea makes them. Not sure about the SBO website store. Likely Defender. Blue Sea has a link on their site to find a retail outlet.

 

[berner73]

So where can I buy one of these?

https://www.bluesea.com/products/category/16/Fuse_Blocks

 

[Charles Erwin]

Right here at Sailboat Owners

http://shop.sailboatowners.com/prod.php?931

Charles

 

[Scott T-Bird]

Did you include an AC diagram? I'm particularly interested in the AC ground to DC ground connection.