Queston about charging trolling motor batteries in parallel

[Vecchio]

Currently I have one battery powering my Minn Kota trolling motor, but I am going to buy another of the exact same battery to run them in parallel. I have a dual bank BP charger that I use right now, but I was wondering the best way to use this charger once I have the parallel setup going. I have read you can hook up the charger to the positive on one battery and the negative on the other and charge using one bank, but if the batteries are drained at different levels it wont charge them both fully. My question is can I hook one bank up to the pos and neg on the first battery, and the second bank up to the second battery, and charge them like that without removing the parallel cables between the two? Should I even bother with that or just use a single bank like I described earlier? Thanks for the help.

 

[gm280]

:welcome: aboard Vecchio,...

NO :nono: NO, you can't do it that way. With the parallel wires connected, your dual charger will not work properly. You have to open or remove either the positive wire between the two batteries or the negative wire between the two batteries. Then your dual charger will work as it was designed to work.

 

[mjf55]

Hello Vecchio, and welcome to iboats.
You have an interesting question and I would think would spawn some debate.

First, please elaborate on what the exact make and model charger you have, "dual back bp charger" yields too many different hits.

The main question of using both side of you dual charger, 1 per battery in a parallel setup, the owners manual or a call to the manufacturer can answer that, but my thoughts are that I doubt it will work. I think that each side of the charger will get confused by the voltage from the other side of the charger.

Now as to the question of using a single charger to charge batteries in parallel, although it seems to be controversial, The best answer I see and believe is Yes, it will work. That is because of the internal resistance of each cell will get the current necessary to charge it, provided the charger is strong enough. Eventually, all the cells will equalize and will charge.

However, if there is a battery problem in one battery, it may take down the whole bank. I think i would but in a battery selector switch and charge individually.

This is just the results of my short research in the subject. There are a lot of theads and information on this.

Good luck

 

[spoilsofwar]

How old and how many cycles on the current battery?

To charge this setup you will connect a single bank from your onboard charger, positive lead to the positive terminal of battery A, and the negative lead to the negative terminal of battery B. You cannot charge the paralleled batteries with two banks of the charger unless you first disconnect the parallel connection between them.

There is no reason why it will not charge both batteries fully unless you have a significant imbalance in voltage or capacity between the batteries to begin with, which is why I asked the original question in this post. If your current battery is not virtually new, I would not parallel it with another newer one. Remember in parallel setups, if one battery is stronger then the other, the stronger battery ends up charging the weaker.

 

[Vecchio]

Hello Vecchio, and welcome to iboats.
You have an interesting question and I would think would spawn some debate.

First, please elaborate on what the exact make and model charger you have, "dual back bp charger" yields too many different hits.

The main question of using both side of you dual charger, 1 per battery in a parallel setup, the owners manual or a call to the manufacturer can answer that, but my thoughts are that I doubt it will work. I think that each side of the charger will get confused by the voltage from the other side of the charger.

Now as to the question of using a single charger to charge batteries in parallel, although it seems to be controversial, The best answer I see and believe is Yes, it will work. That is because of the internal resistance of each cell will get the current necessary to charge it, provided the charger is strong enough. Eventually, all the cells will equalize and will charge.

However, if there is a battery problem in one battery, it may take down the whole bank. I think i would but in a battery selector switch and charge individually.

This is just the results of my short research in the subject. There are a lot of theads and information on this.

Good luck

I'm sorry that was a typo, I meant dual BANK charger. It is BPS XPS dual bank charger, and THIS BATTERY. One battery is a little over a year old, and the second battery will be brand new. I was thinking about installing a switch, and when I charge just throwing the switch to battery 1 and then battery 2, but I am starting to think that isn't necessary. If I run a cable between the pos of battery 1 and the pos of battery 2, a cable between neg on battery 1 and neg on battery 2, and then hook one charger bank up to pos of battery 1 and negative from battery two, I will have a parallel connection between both batteries and I can just leave the charger connected and plug it in to charge? Am I right in that thinking?

 

[gm280]

I'm sorry that was a typo, I meant dual BANK charger. It is BPS XPS dual bank charger, and THIS BATTERY. One battery is a little over a year old, and the second battery will be brand new. I was thinking about installing a switch, and when I charge just throwing the switch to battery 1 and then battery 2, but I am starting to think that isn't necessary. If I run a cable between the pos of battery 1 and the pos of battery 2, a cable between neg on battery 1 and neg on battery 2, and then hook one charger bank up to pos of battery 1 and negative from battery two, I will have a parallel connection between both batteries and I can just leave the charger connected and plug it in to charge? Am I right in that thinking?

Vecchio, Unless you disconnect the two batteries in parallel and charge each one with either one battery charger at a time, or a dual charger charging both at the same time, it will not work. If you try to run two battery chargers at the same time with the batteries connected in parallel, you are chancing damaging the charger(s). Battery chargers, at least the more modern ones, sense the voltage on the battery. And when that voltage rises to the proper level, the battery charger either switches off, or reduces the charge to a trickle type charge. But it you have two batteries in parallel with two chargers, the chargers will sense the other battery charger as well as the battery load and not work properly or even damage the internal circuitry depending how they are built. So either separate them and charge, or install a heavy duty switch that separates them for charging. You wouldn't buy two battery chargers and use both on one battery at the same time would you? So attaching a dual charger to the batteries in parallel is the exact same issue. JMHO

 

[spoilsofwar]

If I run a cable between the pos of battery 1 and the pos of battery 2, a cable between neg on battery 1 and neg on battery 2, and then hook one charger bank up to pos of battery 1 and negative from battery two, I will have a parallel connection between both batteries and I can just leave the charger connected and plug it in to charge? Am I right in that thinking?

Correct - to charge your batteries wired in parallel, no switch or other device is needed. Connect the positive lead from the charger to the positive terminal on either battery, connect the negative lead from the charger to the negative terminal on the opposite battery. You just cannot use both banks of your charger to charge this parallel setup unless you disconnect the batteries from one another while you do so. Do not attempt it.

Paralleling a year old battery with a brand new one is not ideal. Ideally, the batteries should be of the same or very similar date code, same or similar number of cycles on them, and exact same make and model.

 

[Vecchio]

Lastly, when I hook up the trolling motor it should go to the pos of one battery and the neg of the other right?

 

[spoilsofwar]

Lastly, when I hook up the trolling motor it should go to the pos of one battery and the neg of the other right?

Correct. It balances the voltage drop between the batteries. Same reason why you charge them with this connection.

 

[Vecchio]

Correct - to charge your batteries wired in parallel, no switch or other device is needed. Connect the positive lead from the charger to the positive terminal on either battery, connect the negative lead from the charger to the negative terminal on the opposite battery. You just cannot use both banks of your charger to charge this parallel setup unless you disconnect the batteries from one another while you do so. Do not attempt it.

Paralleling a year old battery with a brand new one is not ideal. Ideally, the batteries should be of the same or very similar date code, same or similar number of cycles on them, and exact same make and model.

The battery is the exact same make and model, and the year old battery has only been used 5-6 times.

 

[StarTed]

The only reason to go to posts on different batteries is in case there is connection resistance. The same for the trolling motor.

The problem with 2 batteries of a different age is that when the first one goes bad it'll take down the other with it.

Us people that drive diesel vehicles have 2 batteries in parallel for the added current capability. They're charged like 1 battery.

 

[bruceb58]

:welcome: aboard Vecchio,...

NO :nono: NO, you can't do it that way. With the parallel wires connected, your dual charger will not work properly.

Need to read the manual before you know that. Most smart dual bank chargers can have their outputs tied together if there is only one battery or they are in parallel.

I believe the charger he has is made by pro mariner
Go to page 17
http://files.powerprodllc.com/~/medi...sdartitem=true

Veccio, bottom line, read your manual. Lot of incorrect info in these posts.

 

[frantically relaxing]

Battery connections using two 12v batteries:

--wiring in parallel doubles the amperage output, doesn't change the voltage output.
-wiring in series doubles the voltage output, doesn't change the amperage output...

NOTE that you DON'T connect in series unless you WANT 24volt output. However, this routinely done with 6 volt deep cycle batteries installed in 12v boats and motorhomes.

Each of these diagrams is a "bank" of batteries. It doesn't matter to your dual or triple or fourple-bank charger how many batteries are connected in each bank. Houseboaters often have 10 or more in a bank, and 1 battery for each engine- that's 3 banks, and a triple-bank charger will work just fine.

As for the scenario at hand-- if your batteries are connected in parallel as shown, just connect your charger's positive to EITHER battery's positive post, and the charger's negative to either battery's negative post. No need to disconnect them.

As for one battery being older, hey, it's not a perfect world. I have 3 house batteries in my motorhome, all different ages. No problems unless one goes bad, and then it noticeably drains the others. A quick test with a voltmeter will find the bad one- replace it, move on. Even brand new identical batteries will have different charge, discharge and 'wear-out' rates...

 

[Silvertip]

I think everyone needs to read his original post again -- carefully. He specifically stated he will be using only one output of the dual bank charger. With batteries in parallel and connected as he indicated it will definitely work and no dual battery switch is necessary. The down side is it will take twice as long to charge two batteries as it did to charge one. And even then there is a maybe not! Whatever "average" amount of current was used when trolling with one battery, the same amount would be used from two batteries, but only 1/2 as much from each. Therefore charge time would be roughly the same provided usage is the same as I indicated. And even if one battery is a bit more tired than the other they will charge fully. One battery may just not have the identical "capacity" as they other. Over the road trucks may have six batteries in parallel and they charge very nicely from a single source. I'm old enough to have owned brand new 1979, 1980 and 1981 Oldsmobile 350 Diesels and all of them had dual battery parallel setups. Charging those from the single output was not an issue. One bad battery in a parallel setup may prevent fully charging the "good" battery and may also suck the life out of the "good" battery when not on a charger. So the answer to your original question is yes -- with the caveats that I indicated. Use the second charger output for the starting battery. Even brand new batteries with the same date code may not have the same identical capacity so don't fret that unless there is a drastic difference in the two capacities which may indicate one is headed for battery heaven.

The next discussion would be should you run down one battery then switch to the other (switching required) or just run off both by leaving them in parallel. Let the debate begin. We talk about oil and ethanol in future threads -- -)

 

[bruceb58]

He should put them in parallel and use both banks of the charger. His charger manual will tell him if this is acceptable but it likely is.

 

[gm280]

The only probably with charging batteries in parallel is, if one cell in either of the parallel batteries is weak or even shorted, neither battery will ever be charged fully. And while that can happen as well with charging each battery separately, you at least know the suspect battery doing them separately that way. Any battery charger has only so much output current capability. And if a bad or weak battery is draining that supply current, then the other battery will never reach the proper voltage to be fully charged. Does that mean you can't charge in parallel? NO it doesn't. But each situation has its props and cons. The individual owner has to make their determination as to what they want to do. If I had a dual battery charger (two bank charger) and had two batteries connected in parallel, I would install a battery cutout switch that I could easily disconnect the parallel setup and charge both at the same time without worry. But that is just me. To each their own. We are all going to do what we like best anyways. JMHO

 

[mjf55]

I think everyone needs to read his original post again -- carefully. He specifically stated he will be using only one output of the dual bank charger.

..... My question is can I hook one bank up to the pos and neg on the first battery, and the second bank up to the second battery, and charge them like that without removing the parallel cables between the two?

So part of the original question did ask about using both banks of the dual charger on the 2 batteries without removing the cables. I think the overwhelming answer to that is no.
The second part of the question was should he just use one bank of the charger to charge the batteries in parallel. I think that answer is also yes, its is ok, but with some difference of opinion.

 

[fishrdan]

Agree with Bruce, read the charger manual, it will tell you if the charger can be connected to the each individual battery, while the batteries are connected in parallel, it's possible for this to work, depending on charger specs.

If I had a dual battery charger (two bank charger) and had two batteries connected in parallel, I would install a battery cutout switch that I could easily disconnect the parallel setup and charge both at the same time without worry.

I have a dual battery setup and agree with using a battery switch, a Perko 1-2-both-off switch. The battery switch will allow breaking the parallel connection for charging, storage and usage. Eventually, one of those batteries is going to go bad and cause issues, or a ruined fishing trip. If I suspect one of the batteries is going bad I'll run that battery first to see how long it lasts, then switch over to the second battery.

Running the batteries in parallel will give you a bit more run time on the water, since each battery is being discharged slower. Also, the batteries shouldn't be left connected in parallel for storage as they will stabilize at the weaker batteries voltage, and if one of the batteries goes bad it will ruin the other battery.

 

[Silvertip]

Multiple charger outputs bridged to a single battery, dual battery in parallel or a half dozen batteries in parallel will not create an issue for modern multiple output smart chargers and the batteries will fully charge very normally. Since each output sees the same value from the battery bank (because everything is parallel), each output reacts the same. The batteries see one value from the charger and the charger sense circuitry sees one value from the batteries.

 

[gm280]

Multiple charger outputs bridged to a single battery, dual battery in parallel or a half dozen batteries in parallel will not create an issue for modern multiple output smart chargers and the batteries will fully charge very normally. Since each output sees the same value from the battery bank (because everything is parallel), each output reacts the same. The batteries see one value from the charger and the charger sense circuitry sees one value from the batteries.

Silvertip, I absolutely 100% agree with your assumption as well. However, what happens if just one cell in just one of the parallel batteries is shorted. How does the other batteries get fully charged? The shorted cell will never allow the charge voltage to get near the proper voltage level to fully charge all the others in parallel.