Four battery series/parallel wiring configuration

[PJordan]

Hey folks, loving this forum so far - great store of information that has been invaluable.

I recently came into a new (to me) pontoon boat for use on the lake that I live on. This lake allows only electric motors. I am in the beginning stages of overhauling this thing, and starting with wiring which is a dangerous mess right now.

The existing setup in this boat has 4 - 12v batteries and a dual motor Minn Kota EP130 that is 24v. The batteries are currently wired in banks of two batteries in series to step up to 24v, then paralleled together to increase total capacity. There is a perko battery selector switch (which I believe is wired incorrectly as-is) between the batteries and motor controllers.

I found the service manual online which shows a different wiring setup by putting the two battery banks in parallel, then connecting the banks in series:



I am having trouble conceptualizing how this configuration would work for me. It seems that 1: I would not be able to switch two batteries of the four in/out with a selector switch, right? and 2: I currently have a single-bank 24v charger - would I just attach that to negative on battery one and positive on battery four? 3: What about my 12v accessories - just run those say from battery 3 negative and battery 4 positive? 4: What about fusing in this situation? Where and how?

Is there any reason to go with this type of configuration instead of how it is currently wired? The batteries I have now are pairs of different ages - 2 are 3 years old and 122ah, 2 are 5 years old and 115ah. I would think that the above configuration, they would all need to be identical for charging purposes correct?

I don't know if all you guys with the gas engines have it easier or harder....

 

[PJordan]

This is basically the current configuration. I think the selector is wired incorrectly although I haven't opened it up yet, because if you switch from 1 or 2, to both, the thrust increases. It would seem to me that this should not be happening.

 

[UncleWillie]

Current config (Post#2) is 2 Series Banks in Parallel. Proposed (Post #1) is 2 Parallel Banks in Series.
It is like asking which is larger 2x12 or 12x2. Both give the same results.
Your current configuration with the switch in the BOTH position is equivalent to the proposed configuration.
The current configuration gives you more options.

When you parallel the banks with the switch in the BOTH position, you effectively Lowered the Source impedance and the Power delivered to the Motors will increase.
Not a huge amount, but enough to be noticeable.
In the second drawing....
You are sourcing your 12 volt supply from a point that is essentially GND = 12v and 12v = 24. The difference is 12 v and OK as it stands.
If anything were to go wrong in the wiring it will go horribly wrong. All 12v equipment could suffer a 24v meltdown.
Give me a few minutes and I'll update your drawing.

 

[UncleWillie]

Try it this way!


Remember that supplying the ACC from one side of a series bank is not ideal.
Once the ACC Battery goes flat, the other battery in the bank will kill it by placing it in a reverse charge.
As long as you are careful to not deplete it you will be OK.

Is your Battery Switch a 3 Terminal or 4 Terminal?
Battery Selection = Off,On,Combine ...OR... 1,2,Both,Off ???

 

[PJordan]

Wow Bill, that's servicey! :tea:

It is a 4 terminal switch.

Is there a sensible alternative to wire the 12v leg other than a fifth battery? I'm not coming up with anything.

 

[UncleWillie]

No!
The 12v leg is typically take off the Starting Battery of the Gas Engine. (That you do not have!)

The Best way is a 5th Battery.
If the 12 volts is for a Stereo Sound System and Nav and Party Lights on long evening cruises, it would be highly recommended. (>5amps)
If it is just running a sonar in Daylight, not so critical. (<3amps)
A Dedicated voltmeter on the dual use battery would allow you to call it a night when it got below ~11.5v.
Another 1,2 Switch would allow swapping the 12 load over to the bottom battery in the other bank to extend the outing.
Fishing Barge? or, Party Barge? Both?