3 or 4 bank charger?

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seasick

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I am not sure how many banks a charger should be for my boat. I have gotten different opinions from dealer, vendors, and internet 'gurus'

I have twin engines and four batteries.
There is one battery for the port engine, a second for the stbd motor and two parallel batteries for the house and accessories.
The engine batteries are each dedicated to the engines and do not 'connect directly to any other loads.
Each engine battery does use ACR that connects and charges to the two parallel house batteries. The two house batteries are hard connected to each other always.

I want to install a charger. The first two banks are obvious, the two engine batteries. My confusion has to do with the two parallel house batteries.
I am an electrical engineer (long retired) and can understand both arguments for a single bank for the two house batteries as well as the argument that the proper approach is a separate bank for each house battery even though they are hard wired to each other.

For situations where batteries are wired in series, for example 2 12v series for a 24v thruster, I completely understand why the correct scheme for a 12v charger is one bank for each battery.

Honestly in my situation I think either approach would be fine with not much if any disadvantage to wiring a only one back to the parallel batteries.

Any thoughts?
 
Treat the parallel bank as one battery. It only needs one charge lead.
The parallel bank should be connected "cross corner" both to Load and to charger.
By that I mean that you use the positive terminal of one battery and the negative terminal of the other.

This balances the voltage drop on the parallel jumper wires. Or in other words, the current travels the same distance from both batteries.
They appear as one battery.
parallel batteries.jpg


I have had my setup like this since 2018. I do not use ACRs though. I use the Aux charging cables from the isolators in the motors
 
Thanks for your advice. I was planning on a three bank with the battery wiring approach you outlined. What threw me was that I saw the same boat but newer year that I have at the NY Boat show and it had a 4 bank charger. I asked the factory rep about the number of banks required and he said three. ( It may have been possible that the fourth bank was not connected, I couldn't trace the wires easily)
This past week, I was at another show and stopped at a booth for a company that was selling lithium batteries. I talked to the rep about my circumstances and he sais that if I had his batteries, I would only need a 3 bank because there is a battery monitoring system built into each battery. He also added that for my flooded cell batteries, he would recommend a 4 bank charger!
 
The "best" way is to go with the 4-bank. But I honestly think the difference between best and good is very slim. If you think, in the future, you'll constantly be thinking about whether or not you should have gotten the 4-bank, get the 4-bank. Otherwise, get the 3-bank and just make sure to fully charge each house battery fully by itself, first.
 
You know, all the talk about chargers...... your motors do most of the charging...almost all of it....they have no special charge sensing circuit...they just put out about 14V and the batteries charge.
When they are fully charged, the motor still puts out 14v.

When you had Grady OEM , a stbd side parallel pair for Start/House, it only had one charging cable.
 
I have 4 batteries but they are all separate (none paralleled). My 3-bank charger takes care of each engine and the house battery. A separate charger services a battery in a forward compartment for the bow thruster, windlass and stereo amp. I have charging shunts on both engines to charge the house and thruster batteries.

If I had your setup I would stick with a 3-bank charger. The shore power chargers load shift. Engine batteries should require little charging so parallel house batteries would be full charging amperage.
 
I once asked Pro Mariner specifically about this question (two charging leads used on a paralleled bank) as I didn't quite understand the need for it, either. They said their chargers (I was asking about the ProNautic at the time) WILL indeed charge each battery in the bank better than if only one charging leads was used for both. I still think it's a minimal gain... but that was right from the horse's mouth.

Also, I do see boat manufacturers doing this - and my thought is that there must be an advantage, otherwise they would use a lower $ amount charger - they typically don't put in higher dollar things for no reason :)
 
Hookup1 said:
I have 4 batteries but they are all separate (none paralleled). My 3-bank charger takes care of each engine and the house battery. A separate charger services a battery in a forward compartment for the bow thruster, windlass and stereo amp. I have charging shunts on both engines to charge the house and thruster batteries.

If I had your setup I would stick with a 3-bank charger. The shore power chargers load shift. Engine batteries should require little charging so parallel house batteries would be full charging amperage.
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You raise an interesting point.
I believe that some charges let's say a 3 x 10 amp can supply more than 10 amps to one bank if the other batteries are charged. It's like load sharing.
I am looking at NOCO chargers and don't see in the documentations that a bank can charge at more than let's say 10 amps for the 3 x 10 amp model.
Any thoughts?
 
seasick said:
You raise an interesting point.
I believe that some charges let's say a 3 x 10 amp can supply more than 10 amps to one bank if the other batteries are charged. It's like load sharing.
I am looking at NOCO chargers and don't see in the documentations that a bank can charge at more than let's say 10 amps for the 3 x 10 amp model.
Any thoughts?
Click to expand...
I'm using a ProMariner ProSportHD 20. They offer higher amperage models too for charging the trolling motor batteries.
  • Distributed-On-Demand™ Technology: 100% of all available charging amps are utilized by distributing unused charging amps to any one or combination of all batteries as needed
I use a single NOCO for thruster battery. I looked at 3-bank NOCO and it doesn't show load sharing. 10-amps per bank x 3 = 30-amp. It just will take longer to bring the house battery back up.
 
seasick said:
You raise an interesting point.
I believe that some charges let's say a 3 x 10 amp can supply more than 10 amps to one bank if the other batteries are charged. It's like load sharing.
I am looking at NOCO chargers and don't see in the documentations that a bank can charge at more than let's say 10 amps for the 3 x 10 amp model.
Any thoughts?
Click to expand...
Try the ProNautic - I have tons of experience with these as they were standard equipment on the Sea Rays that are at our dealership (and my own boats) - they were used for decades and they are very good chargers with a great track record.
 
The engineers at Pro Marier recommend a separate charge lead for each battery regardless of their configuration. Think of it this way, the battery is, in effect, a resistor and probably a capacitor/inductor as well. However, the smart chargers can tell the difference. Two resistors in parallel, do not present the same resistance to a load (charger) as a single battery. Remember the formulas for resistors in parallel versus resistors in series? I opt for one charge lead for each battery. In the long run, it probably doesn’t matter a lot. Smart chargers have different charging curves based on battery parameters. I would assume no two batteries can be exactly the same. R1 + R2/2 = R3 (as seen by the charger) several years back when I changed chargers, I spoke with the engineers at pro mariner, who designed the chargers. They said either will work, but ideally you want a charge lead for each battery.
 
wspitler said:
The engineers at Pro Marier recommend a separate charge lead for each battery regardless of their configuration. Think of it this way, the battery is, in effect, a resistor and probably a capacitor/inductor as well. However, the smart chargers can tell the difference. Two resistors in parallel, do not present the same resistance to a load (charger) as a single battery. Remember the formulas for resistors in parallel versus resistors in series? I opt for one charge lead for each battery. In the long run, it probably doesn’t matter a lot. Smart chargers have different charging curves based on battery parameters. I would assume no two batteries can be exactly the same. R1 + R2/2 = R3 (as seen by the charger) several years back when I changed chargers, I spoke with the engineers at pro mariner, who designed the chargers. They said either will work, but ideally you want a charge lead for each battery.
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That is what I am hearing; three banks is fine but four are preferred. I think I will go with fine.
The electrical theory is that when batteries are wired in parallel, the ground reference used by the charger is the same for both batteries. Since there is a jumper cable between the two grounds, the actual length of the ground connection is different for the second battery, That small error due to current related voltage drop can cause the charger to use a not so perfectly matched charging profile. By connecting the positive terminal of the charger to the second battery a similar error is introduced but it just about cancels the negative wiring error. Fot my physical configuration, cable lengths in the battery bay and the fact that there are separate starting batteries for each engine, the need to sense and charge individual batteries is quite small.
In a situation where there is a physically larger battery bank or more that two batteries in parallel or worse a battery bank with both series and parallel battery banks, the need for individual charging and proper cable routing could be quite critical. At least that's how I see it.

One interesting point that the battery rep made was that if you have different technologies like lithium that have battery management systems built into the individual batteries, the BMS will do all the adjusting and correction of profiles.
 
I suspect that they are covering their ass . By telling you to connect each charger cable to one battery, you cannot F it up.
If one were to connect one charge cable across two batteries that are in series, it would be bad.
Having cables to each battery in parallel banks means you don't need to connect them cross-corner.(you still should have the Load connected cross corner)
They don't know if the customer is clueless. Their tech support needs a known starting point.

Much like marine electronics that tell you to run their included power cable directly to the battery because they have no idea how your boat is wired.
 
seasick said:
The electrical theory is that when batteries are wired in parallel, the ground reference used by the charger is the same for both batteries. Since there is a jumper cable between the two grounds, the actual length of the ground connection is different for the second battery, T
Click to expand...
This is the point about cross-corner connection of the charger and the load. The current to and from both batteries takes the same distance of wire.
 
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