Charging batteries in parallel -- can you just use one bank?

[sixstring531]

I have a two bank charger and three batteries -- starter and two 12v for the 12v trolling motor (to last all day) that I've manually switched between when one goes down. I've read you can run two 12s in parallel and will get longer total run time than just the two batteries by themselves - so I thought about doing this.

My question is, with the two 12s jumpered (they are slightly different sizes, mind you) in parallel, do I need two of the banks on my onboard charger, or will one suffice since they are connected?

 

[glenn property of pam]

Re: Charging batteries in parallel -- can you just use one bank?

in parallel they become a bank and that only needs one charger UNLESS the batterys are diffrent size condition then all bets are off as the smaller/poorer one might start to cook off when its full or the good battery wont get a full charge. most chargers have feedback and they adjust the amps to the battery voltage in auto so its sensing the full one first and in manual its overcharging one. not a real expert in how bad this realy is but i wouldnt surgest it unless the batterys were matched on size at least.

 

[Silvertip]

Re: Charging batteries in parallel -- can you just use one bank?

Go ahead and charge them in parallel. It will not be a major issue unless one of the batteries is very different in capacity. Over the road trucks have as many as six batteries in parallel and as they get replaced there will be several different ages and possibly different capacities. A single bank monitors the "system" level, not an individual battery level.

 

[sixstring531]

Re: Charging batteries in parallel -- can you just use one bank?

Due to space we had to go for a slightly smaller one. The older one (3 years older) is a 27 and the new one is a smaller 24. I don't want to cook anything. (unless it's fish when we get back)

 

[Silvertip]

Re: Charging batteries in parallel -- can you just use one bank?

No problem.

 

[halfmoa]

Re: Charging batteries in parallel -- can you just use one bank?

Our racecar has 4 deep cell batterys wired in parallel with no alternator on the engine. We fully recharge them after every pass. No issues.

 

[sixstring531]

Re: Charging batteries in parallel -- can you just use one bank?

Thanks, guys!

One more question:

I've read I should put the positive of the bank on the positive of battery one and the negative on the negative of battery two -- should the electronic hookup be the same? Positive from the trolling motor on positive one and negative on negative two - or does this matter?

 

[GA_Boater]

Re: Charging batteries in parallel -- can you just use one bank?

In a parallel set-up connect + to + and - to - between the batteries. Connect the charger and TM to a + and -. Makes no difference which battery. That will work for you, six.

 

[halfmoa]

Re: Charging batteries in parallel -- can you just use one bank?

Thanks, guys!

One more question:

I've read I should put the positive of the bank on the positive of battery one and the negative on the negative of battery two -- should the electronic hookup be the same? Positive from the trolling motor on positive one and negative on negative two - or does this matter?

That'd be series wiring and give you 24V.

 

[sixstring531]

Re: Charging batteries in parallel -- can you just use one bank?

I think I didn't describe it well - let's try again:

Batteries 1 and 2 are jumpered in parallel ( ++, --)

Instead of placing the Bank One of my charger on Battery 1 + and - (which will still charge both), I place the positive cable of the charger on Battery 1 positive and the ground from the Charger on Battery 2 ground instead of the charger hooked directly to just Battery 1. I read this on several battery sites about charging batteries in parallel.

Since this is recommended for charging with a single bank for two batteries in parallel, I was wondering if connecting the trolling motor + to the + of Battery 1 (B1 and B2 are still connected in parallel) and the TM- to the - of B2 is recommended. This is not 24 volts. Since the Batteries are in parallel the + and - represent a single terminal and are not indepedent.

I included a little diagram and was wanting to know if the TM can or should be hooked up like the charger in the bottom diagram.

 

[GA_Boater]

Re: Charging batteries in parallel -- can you just use one bank?

It makes no difference. Either works the same.

 

[halfmoa]

Re: Charging batteries in parallel -- can you just use one bank?

I think I didn't describe it well - let's try again:

Batteries 1 and 2 are jumpered in parallel ( ++, --)

Instead of placing the Bank One of my charger on Battery 1 + and - (which will still charge both), I place the positive cable of the charger on Battery 1 positive and the ground from the Charger on Battery 2 ground instead of the charger hooked directly to just Battery 1. I read this on several battery sites about charging batteries in parallel.

Since this is recommended for charging with a single bank for two batteries in parallel, I was wondering if connecting the trolling motor + to the + of Battery 1 (B1 and B2 are still connected in parallel) and the TM- to the - of B2 is recommended. This is not 24 volts. Since the Batteries are in parallel the + and - represent a single terminal and are not indepedent.

I included a little diagram and was wanting to know if the TM can or should be hooked up like the charger in the bottom diagram. View attachment 143195

Well I'm no electrical engineer but I don't see the difference.

 

[sixstring531]

Re: Charging batteries in parallel -- can you just use one bank?

Exactly -- the only difference is moving the ground of the bank to the second battery - - shouldn't make a difference right? It was just suggested on a few battery sites I found. Didn't know if anyone did this and if there was any benefit to hooking the trolling motor the same way.

Just read one of the sites again and it suggests the method I've highlighted but says the positive results (no pun intended) are nothing big - though they did not go into the positives of doing it this way.

 

[halfmoa]

Re: Charging batteries in parallel -- can you just use one bank?

Exactly -- the only difference is moving the ground of the bank to the second battery - - shouldn't make a difference right? It was just suggested on a few battery sites I found. Didn't know if anyone did this and if there was any benefit to hooking the trolling motor the same way.

We've always ran our batteries in the same manner you've illustrated in your top diagram with 4 batteries. Replace the trolling motor with the starting system of the car and charging posts. Zero problems ever. I see no issues.

 

[GA_Boater]

Re: Charging batteries in parallel -- can you just use one bank?

Just read one of the sites again and it suggests the method I've highlighted but says the positive results (no pun intended) are nothing big - though they did not go into the positives of doing it this way.

The reason the positive results are nothing big is because there are no positive or negative results. After weighing the plus and minuses between the two diagrams I did see one negative result - The bottom takes about 18" more wire, But that's a positive if you're a wire seller. So it's all a wash in the end. Hook 'em up either way, six. You won't see any difference.

 

[dwparker99]

Re: Charging batteries in parallel -- can you just use one bank?

sixstring, I've read, like you, that when charging batteries in parallel, you should hook the charger positive lead to bat 1 and the negative lead to Bat 2. I'm no expert, but I think it is to put the resistance of the jumpers into play while charging the batteries. If you hook both leads to Bat 1, even if they are identical batteries, the charger will see a difference in resistance of the batteries due to the resistance of the two jumpers. With the modern microprocessor battery chargers, their charge algorithms can be sensitive to the resistance they encounter. For the trolling motor, the resistance of the jumpers is insignificant.

 

[Silvertip]

Re: Charging batteries in parallel -- can you just use one bank?

Current still passes through the same number of battery connections regardless which direction it passes. It isn't a problem either way.

 

[dwparker99]

Re: Charging batteries in parallel -- can you just use one bank?

Current still passes through the same number of battery connections regardless which direction it passes. It isn't a problem either way.

I must respectfully disagree. When connecting both leads to Bat 1, current passes through no jumper to Bat1, but must pass through two jumpers to get to Bat 2. If one lead is connected to each battery, current must pass through one lead to get to each battery. Does connecting both leads to one battery cause a problem? Probably not. Do you get an optimum charge this way? Probably not.

 

[Jlawsen]

Re: Charging batteries in parallel -- can you just use one bank?

sixstring, I've read, like you, that when charging batteries in parallel, you should hook the charger positive lead to bat 1 and the negative lead to Bat 2. I'm no expert, but I think it is to put the resistance of the jumpers into play while charging the batteries. If you hook both leads to Bat 1, even if they are identical batteries, the charger will see a difference in resistance of the batteries due to the resistance of the two jumpers. With the modern microprocessor battery chargers, their charge algorithms can be sensitive to the resistance they encounter. For the trolling motor, the resistance of the jumpers is insignificant.

This is a good response if you have a single battery charger that is able to analyze the battery and then charge it accordingly. I have Shumacher 80 amp and I need to charge the batteries disconnected in order to get a full 100% charge on both batteries. If I don't the first battery that comes up to 100% shuts down the charger and it goes into float mode. I should mention that in float mode it will eventually bring both batteries up to 100% but it takes a lot longer.

That said, I setup another boat with a ProMariner tripple battery charger and put a set of leads on each battery. It worked fine with two batteres in parralel and when the green light came on for the first battery that reached 100% the other ones kept charging until they were full.

 

[Silvertip]

Re: Charging batteries in parallel -- can you just use one bank?

I must respectfully disagree. When connecting both leads to Bat 1, current passes through no jumper to Bat1, but must pass through two jumpers to get to Bat 2. If one lead is connected to each battery, current must pass through one lead to get to each battery. Does connecting both leads to one battery cause a problem? Probably not. Do you get an optimum charge this way? Probably not.

That is very true. However, If you have the POS lead of the charger connected to BAT #1 POS and the NEG on BAT 2 NEG, current must still get to BAT 1 NEG so it must still pass through the jumper. If it doesn't, then BAT 1 would never see a charge. There are the same number of terminals to contend with either way.