Question about charging in parallel with onboard charger

[AZcamperguy]

I have a Noco Genius 3 bank charger. I have a starting battery that also runs electronics. I have 2 batteries that I would like to use for my 12 volt trolling motor. I was going to hook them up in parallel but was wondering about the ability to properly charge the batteries? I know a lot guys charge them fine when they are hooked up in a series for their 24 and 36 volt trollers but haven't heard anything on doing them parallel. A friend suggested that I use a switch. Any thoughts on this? Thanks

 

[Jlawsen]

Re: Question about charging in parallel with onboard charger

I think I understand what your plans are. You want to charge three batteries separately but run the two in parallel. I think what you'll find is that your three bank charger distributes its max current rating accross all three outputs. That being the case you don't need to use a switch because you can charge the batteries in parallel as if they were one and leave the third output from the charger disconnected. That will distribute all of the chargers current across the two outputs and the charge rate would be the same as if you charged them separately.

 

[AZcamperguy]

Re: Question about charging in parallel with onboard charger

Ok, well what do I do with the third banks connectors then? I was hoping it wouldn't matter and that I could charge the two parallel batteries without issues by hooking up all banks. Thanks for the input.

 

[Silvertip]

Re: Question about charging in parallel with onboard charger

I think I understand what your plans are. You want to charge three batteries separately but run the two in parallel. I think what you'll find is that your three bank charger distributes its max current rating accross all three outputs. That being the case you don't need to use a switch because you can charge the batteries in parallel as if they were one and leave the third output from the charger disconnected. That will distribute all of the chargers current across the two outputs and the charge rate would be the same as if you charged them separately.

Why not use the third output? You can connect two outputs (bridge them) which doubles the charging capacity. By paralleling the batteries you have essentially doubled the size of the battery (looks like one big battery to the charger) so using just one output would take twice as long to charge them as it would if you bridged the two puts. Simply connect them together. The charger doesn't care.

 

[dwparker99]

Re: Question about charging in parallel with onboard charger

I like your friends suggestion to use a switch mainly because I like to occasionally monitor the batteries as they charge to look for anomalies. Either way though, I would use all three banks. If you do use the switch, I would charge with the switch open and operate the TM with the switch closed.

 

[AZcamperguy]

Re: Question about charging in parallel with onboard charger

Why not use the third output? You can connect two outputs (bridge them) which doubles the charging capacity. By paralleling the batteries you have essentially doubled the size of the battery (looks like one big battery to the charger) so using just one output would take twice as long to charge them as it would if you bridged the two puts. Simply connect them together. The charger doesn't care.

So hook both banks to one of the 2 batteries in parallel or just leave one bank (2 total not including the starting battery which would have its own) hooked to each of the two batteries. In other words, do I hook each bank to its own battery then run the two batteries in parallel or do I hook 1 bank to the starter, 2 banks to one of the 2 batteries left and run them in parallel? Also, sine these 2 batts will be for the trolling motor does it matter which battery I hook that too? Thanks for the input. Greatly appreciated.

I like your friends suggestion to use a switch mainly because I like to occasionally monitor the batteries as they charge to look for anomalies. Either way though, I would use all three banks. If you do use the switch, I would charge with the switch open and operate the TM with the switch closed.

Hmm, I would think the opposite would make more sense if I went that route? Run the power off of both at the same time and charge them separately. Also, I was considering the idea of putting a simple switch on the positive lead that runs the two in parallel so that I could simply "disconnect" the two at charging time. Any ideas of a simple switch that could do that?

 

[AZcamperguy]

Re: Question about charging in parallel with onboard charger

Just got off the phone with Noco and the guy told me that you hook each battery to its own bank regardless of set up. He said that's how their chargers work.

 

[dwparker99]

Re: Question about charging in parallel with onboard charger

I think we are saying the same thing. If you use a switch, charge with the switch open (batteries separated) and run the TM with the switch closed (batteries in parallel). As for which switch, it is hard to make a recommendation without knowing which TM you have. Determine the max current for your TM and then Google "battery disconnect switch" or "battery master switch" and select a switch that has a "continuous run rating" that is above the max current of your TM.

 

[Silvertip]

Re: Question about charging in parallel with onboard charger

Don't overthink this. When you parallel two batteries it doesn't matter which battery you hook two of the charger outputs to. Or you can hook each output to its own battery. In the case of the parallel batteries it accomplishes exactly the same thing. Since the two batteries are already "wired" in parallel, having the charger outputs on the same or separate batteries means they are still connected together (the term is bridged). Be aware also that if you insert this "unnecessary" switch in the positive connection between the two batteries, that it needs to be a switch that can handle the full power drawn by the troller. That means in excess of 50 amps. The charger guy obviously didn't fully understand your intent. He didn't give you wrong information. He simply meant the chargers are intended to be connected individually to two separate "but not interconnected" batteries. That does not mean the outputs cannot be bridged. Those three outputs by the way can also be connected in series to charge a 36 volt bank.

 

[AZcamperguy]

Re: Question about charging in parallel with onboard charger

I specifically asked him about charging in parallel when I called. He said it doesn't matter. Hook each bank to its own battery. I did not mention anything to him about a switch though.
So here is what I think I will do.
Hook all 3 batteries to their own bank. Bridge two of the batteries in parallel to run the trolling motor and not worry about switches for now. If it becomes a problem down the road then I will add a switch I guess.
How's that for not over thinking it
Thanks for the point about where to hook what up. I guess I was thrown off a bit by this video http://www.youtube.com/watch?v=bfvLcTxgvzo

Please, let me know if you have any other thoughts on this. They are all appreciated.

 

[Silvertip]

Re: Question about charging in parallel with onboard charger

Excellent choice. Be aware though that if you have one old battery and one new one you may have an equalization issue where the weaker of the two will suck down the good one until they are equal. The switch would prevent that. If both batteries are new or of the same relative age and condition it won't be a problem.