12V Parallel charging

[ECHO 1]

I'm going to hook up 2 batteries in parallel for my 12V trolling motor. Meaning + to + and - to - . My question is when charging can I hook the charger to just one batterie to charge them both or do I need to charge them seperatly ?

 

[ddennis]

Re: 12V Parallel charging

I'm going to hook up 2 batteries in parallel for my 12V trolling motor. Meaning + to + and - to - . My question is when charging can I hook the charger to just one batterie to charge them both or do I need to charge them seperatly ?

I have heard people doing it both ways, but to me it seems to work better if I do it seperately.

 

[Bondo]

Re: 12V Parallel charging

Ayuh,..........

There's nothing Wrong with daisy chaining the batteries together,+ Charging them.......
Except,........
Electricity is Very Lazy,.......
The Batteries closest to the Charger will be Hotter, Sooner.........

 

[rebuilt]

Re: 12V Parallel charging

Maybe this'll help. I drove 18 wheelers for 6 years. They have a bank of huge 12v batteries-typically 4, hooked up in paralell.. The cables were connected like this..........






/////////////// + - //////////////
/////////////// + - //////////////
/////////////// + - //////////////
/////////////// + - //////////////

Hook the positive lead to the top left postive terminal, the negative lead to the bottom right negative terminal. Make sure your charger will push both batteries. KR

 

[Silvertip]

Re: 12V Parallel charging

Look at it this way -- two (or more) batteries when connected in parallel are essentially one giant battery. Charging them means it will take much longer to charge that "big" battery than any one of them individually. A 2A charger will charge them but it will take forever. A 20A charger will also charge them, but 10 times faster.

 

[ECHO 1]

Re: 12V Parallel charging

Thanks for the responce. My charger is a 12 /24 10Amp, auto or manual, but I am planing on installing an onboard system. What would be the recommened Amps to charge both batteries hooked together? And one more question if the 1st batterie got hotter quicker than the 2nd would this confuse the charger in auto mode and not complete the charge on the 2nd?

 

[rebuilt]

Re: 12V Parallel charging

Can't speak for how your charger is scec'ed. But if you treat it like one big battery, IE top left, bottom right, when the charger senses a reduction in total amperage load, it will shut itself down. If you were to hook your charger up to the first battery only, it would treat the second battery just like a jumped car battery. The first would get "full" sooner. KR

 

[Silvertip]

Re: 12V Parallel charging

There is an equalization sequence that will occur. If one battery in a parallel string is fully charged and the others aren't, the weaker batteries will draw down the fuller of the bunch until all is equal. At which time the charger fires up again and the sequence continues until the entire pack is equally charged. No big deal! That's why a weak battery in a parallel string will draw down the good one. Connect the charger and let it work.

 

[rebuilt]

Re: 12V Parallel charging

Can't go wrong with that one. KR

 

[ECHO 1]

Re: 12V Parallel charging

Work's for me. Thanks

 

[Rancherlee]

Re: 12V Parallel charging

10 amp is perfect for 2 12v deep cycle's, you really don't want to feed them more than 5 amp each for a long life.

 

[ddennis]

Re: 12V Parallel charging

I never parallel mine. simple reason is that I fish a lot of electric only lakes...If I parallel them, there is a chance I could kill both and not make it back without the paddle. If I connect only one and it dies...I know I have enough juice to make it back on the other without risking a big ticket by starting the outboard.. but then again I only have a 12v trolling motor.

 

[Silvertip]

Re: 12V Parallel charging

It doesn't matter what the output is of a battery charger is. Batteries "accept" a charge -- you don't "force-feed" them. In makes absolutely no difference if you use a 5A or a 35A charger. If the batteries will "accept" a charge rate of 35A thats a good thing. If they won't the charger cannot "force" them to accept that rate. The charge rate will taper automatically so there is no problem with harming the battery. If this was not true, every vehicle owner would be buying a new battery daily as the alternator in most cars today has an output of well over 100A.

 

[QuadManiac]

Re: 12V Parallel charging

Charging parallel batteries is fine, with one caveat: It is best to start with same brand, type, age and useage pattern. This is most easily accomplished by starting fresh with two new batteries.

If you have two different batteries (brand, type, age, frequencey of use, etc) they will require different charge rates and periods to reach full, proper charge. When charging different batteries in parallel, one will always overcharge and one will always undercharge, leading to premature failure of both.

When starting with fresh, new batteries, you can assume that they have charging characteristics that are nearly identical, and so will both charge correctly, and provide you with a long lifetime.

You certainly can use two less similar batteries, but their lifetime will be reduced, in most cases siginificantly.

Good Luck.

 

[Rancherlee]

Re: 12V Parallel charging

It doesn't matter what the output is of a battery charger is. Batteries "accept" a charge -- you don't "force-feed" them. In makes absolutely no difference if you use a 5A or a 35A charger. If the batteries will "accept" a charge rate of 35A thats a good thing. If they won't the charger cannot "force" them to accept that rate. The charge rate will taper automatically so there is no problem with harming the battery. If this was not true, every vehicle owner would be buying a new battery daily as the alternator in most cars today has an output of well over 100A.

Actually Most chargers that people have in there garage will force feed batteries if you let them. Automobiles have a regulator which limits them to around 14.4v at the most which will only effectively allow the average battery charge at ~15amps. If you take a normal battery charger and check the voltage settings the 10amp setting puts out roughly 13.5-14 volts max but if you have one with a quick 40-50 amp charge option its will put out ~16volts with a single battery hooked up which WILL boil the water in a battery if you use this option too long (mainly used for a quick 5-10 minute charge to get your vehical started) My charger even has a 200amp "start" mode which is over 18 volts force feeding the battery to start it instantly. That being said, Deep cycle batteries are designed for a low draw slow charge situation with tightly packed plates and are alot more prone to damage and shortened life do to excessive heat from too much current draw OR charge.

 

[Silvertip]

Re: 12V Parallel charging

I though we were talking about smart chargers which are very well regulated I do agree however that an unregulated charger, one that is not well regulated, or those with the "boost" function will boil a battery if left on continuously.

 

[bruceb58]

Re: 12V Parallel charging

If you have two different batteries (brand, type, age, frequencey of use, etc) they will require different charge rates and periods to reach full, proper charge. When charging different batteries in parallel, one will always overcharge and one will always undercharge, leading to premature failure of both.

I disagree...as long as the chemistry of the two batterries is the same, they will charge fine when in parallel. Both will have nearly identical full charge float voltages and both will have similar internal resistances.

 

[QuadManiac]

Re: 12V Parallel charging

I disagree...as long as the chemistry of the two batterries is the same, they will charge fine when in parallel. Both will have nearly identical full charge float voltages and both will have similar internal resistances.

Ahh, Bruce... you have NOW hit the nail on the head, sort of.

THe whole problem is internal resistance. Even if they are of the same chemistry, different brand, size and/or age batteries WILL have different cell resistances. That is the basis of my whole argument. Since the resistances are different, charging in parallel will pass more current through the battery with lower cell resistance, overcharging it, and less current through the battery with higher cell resistance, undercharging it. The charger (even if 'smart') thinks it's charging one big battery, and provides the charge curve appropriately, which is too much for one and too little for the other. You can't beat Ohm's Law or physics.

Same brand, type and age will have resistances close enough that there is no noticeable difference in charge rates. Same brand and type, but one has been used and recharged many times, the other has just been trickle charged to keep it's voltage up - will have VERY different cell resistances. The cell chemistry dictates this.

I'm done arguing this point. You can believe science or you can assume what ever you wish.