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Old 24-11-2015, 19:45   #1
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Charging Batteries in Parallel

Hi Sailors,

I've got a possibly stupid question. I am hooking up a 100w solar panel, via a a control charger panel, to 3 batteries, all the same series, size.

What I am most concerned about is....will the solar charge, if hooked up to the first of the 3 batteries in parallel, continue to charge the 2nd and 3rd after the first has reached capacity.

My #1 batt is the start, #2 and #3 are house so want to prioritize the charging. Just curious how this part of solar charging works, and want to ensure continuity. Note, I motor 3 hours/day at least when cruising.

Thanks, Wes
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Old 24-11-2015, 19:54   #2
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Re: charging batteries in parallel

First to answer the basic question. Yes, if three batteries are in parallel, one charging source connected to any plus and any negative terminal in the set will charge all the batteries. This assumes that there are good connections to all batteries, no loose or corroded terminals, etc.

Now the for the rest.

Are the batteries on a selector switch so you can isolate the start battery from the other two?

Next if you want to prioritize charging you should charge the house batteries first. The start battery, unless you have a problem cranking the engine, uses very little charge so is topped off very quickly when connected to whatever charging. The house batteries usually power lights, fridge, stereo, whatever and are often discharged to a lower state and need more charging. When all the batteries are in parallel the batteries most discharged will take more charge so that issue kind of takes care of itself. The concern is running down your starting battery if it isn't disconnected from the others.
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Old 24-11-2015, 19:56   #3
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Re: charging batteries in parallel

Are you sure all three are in parallel? All in one bank?
Normally one bank would be start bank with one battery and second bank would be house bank with two batteries in parallel.
With a battery switch, set to all or both, all batteries wound be parallel.

How's yours setup?
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Old 24-11-2015, 20:09   #4
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Re: charging batteries in parallel

Hello, thanks for all the info!

I do have a batt selector x 2 for each of the batts (engine and house). But from what I can see, they are all 3 connected via the plus side of the batteries ).

So, I assumed parallel configuration. They are all connected in line via plus with separate charger cables going from each one.

I can switch house or start batt switches to all or both, and the previous owner had all that configured, to work in isolation or together.

I was going to prioritize start batt, b/c I thought that most important, but given that is the most unlikely to run down I am thinking stick with house????

Main question is...if I have all by batts connected, and if I have all my switches on 'all', will my start batt pull from house to get things going if all went south....
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Old 24-11-2015, 20:25   #5
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Re: charging batteries in parallel

Sounds like the previous owner wanted to be able to select one only or both house batteries. Usually only one switch (1-all-2) is used. With the two house batteries parelled together independent of the switch.

Definitely put the solar on the house bank. And I would leave the house switch in the all position. With the solar negative going to one battery's negative and the positive going to the other battery's positive.

And yes, with both set to all, the starter should pull from all three batteries. Assuming I understand the setup of course.

Fair warning, I've never been proclaimed to be one of the forum's experts. One may come along and shoot holes in everything I've posted or suggest there is not enough info to make a solid reccomendation.

But I think I got all the plurals and apostrophies correct. And didn't use any units so I'm safe there.
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Old 24-11-2015, 20:38   #6
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Re: charging batteries in parallel

For your last question of "pull" -- for charging off the motor and for starting the motor we have a switch that goes between house bank and engine start battery and it has a "both" position. If we go with "both" in theory it will pull from both. In practice, since our house bank is much larger in AH than the start battery -- we tend to just go with either/or not both.

On charging using the AC (shore power) we charge 3 battery banks in parallel==>

We happen to have 12V needed for the engine and 36V for the windlass, bilge pumps, spreader lights, etc. Oh, and then there's a 24V shower pump too...So we have a large 800+AH house bank, two 12V batteries in parallel with it (all three together make 36V as needed for those 36V items, and a take-off from the first 2 of the three will give you the 24V), 3 battery chargers, and the engine start battery is a 4th battery that gets charged occasionally when we're on shore power by using the selector on one of our chargers.

No--we didn't go out and buy 3 chargers, we just happened to have that many that came with the boat and decided to use them in parallel to keep the 36V system nicely charged w/o each of the batteries having to be identical to each other. Here's a write up my husband did a couple years ago about the set-up when we had 1/2 the AH of house bank that we have now, and we didn't have a separate start battery then, it was one of the 36V bank. We've seemingly moved "up" in the world. We also have 12V LED lighting now
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Old 25-11-2015, 09:51   #7
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Re: charging batteries in parallel

Quote:
Originally Posted by WesRoge View Post
What I am most concerned about is....will the solar charge, if hooked up to the first of the 3 batteries in parallel, continue to charge the 2nd and 3rd after the first has reached capacity.
If they are connected in parrallel, they are also charging each other. Whichever is your worst battery will suck the charge off the others, and the charger. This is a good way to end up with 3 dead batteries.
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Old 25-11-2015, 10:00   #8
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Re: charging batteries in parallel

Consider adding three diodes to separate/isolate the three batteries from each other but still receive charge from the solar array. Common feed from the positive coming from the solar regulator and then feed each battery with one of the leads from the three diodes. The battery with the lowest voltage will charge until equal to the other batteries. If you have your batteries actually hooked up in parallel it would make no difference as all three batteries would be seeing the same charge potential. All three batteries would also be drained by any usage of the system. You most likely have the batteries on separate systems or switch by some means to use specific batteries for the different functions of lighting and starting. To ensure that the solar system doesn't overcharge the system, you would have to use zenier diodes or provide a high resistance path around the isolation diodes to allow the solar controller to sense the voltage of the batteries and cut off the charge or otherwise you could possibly overcharge/ cook the batteries.
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Old 25-11-2015, 11:43   #9
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Re: charging batteries in parallel

You may want to consult this handy guide: 1/BOTH/2/OFF Switches Thoughts & Musings | SailboatOwners.com Forums

I would suggest keeping things simply by charging only the house bank and using it as a start bank, and keeping the third battery, as the linked piece suggests, quite separate as the "2" switch, charged via relay or echo charger from the house bank. If you have a failure, you have a large single "reserve" battery for get-you-home purposes that is not usually part of the one bank.
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Old 25-11-2015, 12:09   #10
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Re: charging batteries in parallel

Quote:
Originally Posted by WesRoge View Post
Hello, thanks for all the info!

I do have a batt selector x 2 for each of the batts (engine and house). But from what I can see, they are all 3 connected via the plus side of the batteries ).

So, I assumed parallel configuration. They are all connected in line via plus with separate charger cables going from each one.
Hi Wes,

Sorry I'm not totally clear on this point. Are you saying that the plus terminals on all three batteries are connected together or are the plus terminals to the battery switches, like house to position 1 and start to position 2?

A lot of people set up their batteries with house and start to positions 1/2 on a battery switch. Then when charging switch to all, when anchored and running boat systems from the battery switch to the house batteries only so the start is isolated and always charged to start the engine. This system is simple and cheap and works great, as long as you NEVER forget to change the switch from BOTH when you finish charging and start running your lights and such. It only takes once to leave you stranded. Been there, done that.

A simplified description of the idea system for me

- House and start batteries on separate systems.
- All charging goes directly to the house batteries.
- An automatic battery combiner (like this Combiner 100 Sheet but several companies make similar devices) that connects the start battery to the system only when there is charging voltage to the house batteries and automatically disconnects it when not charging.
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Old 25-11-2015, 12:32   #11
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Re: charging batteries in parallel

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Originally Posted by MCOS View Post
Consider adding three diodes to separate/isolate the three batteries from each other but still receive charge from the solar array. Common feed from the positive coming from the solar regulator and then feed each battery with one of the leads from the three diodes. The battery with the lowest voltage will charge until equal to the other batteries. If you have your batteries actually hooked up in parallel it would make no difference as all three batteries would be seeing the same charge potential. All three batteries would also be drained by any usage of the system. You most likely have the batteries on separate systems or switch by some means to use specific batteries for the different functions of lighting and starting. To ensure that the solar system doesn't overcharge the system, you would have to use zenier diodes or provide a high resistance path around the isolation diodes to allow the solar controller to sense the voltage of the batteries and cut off the charge or otherwise you could possibly overcharge/ cook the batteries.

Uh oh, now you have me worried. Doesn't the MPPT charge controller take care of the overcharge possibility? Two 100w panels into 330 AH house bank.
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Old 25-11-2015, 13:37   #12
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Re: charging batteries in parallel

Yes the controller should take care of the risk of overcharging but read the manual for your unit. There is also a downside to using diodes for isolating the different banks. Standard diode will drop 0.7V so you will lose a good bit of your charging voltage and slow the process a lot.

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Old 25-11-2015, 14:41   #13
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Re: charging batteries in parallel

Quote:
Originally Posted by WesRoge View Post
Hi Sailors,

I've got a possibly stupid question. I am hooking up a 100w solar panel, via a a control charger panel, to 3 batteries, all the same series, size.

What I am most concerned about is....will the solar charge, if hooked up to the first of the 3 batteries in parallel, continue to charge the 2nd and 3rd after the first has reached capacity.

My #1 batt is the start, #2 and #3 are house so want to prioritize the charging. Just curious how this part of solar charging works, and want to ensure continuity. Note, I motor 3 hours/day at least when cruising.

Though a correct parallel circuit, "A" setup discharges the first battery the deepest, and charges it the most, it gets the bigger workout and so is treated disproportionately to the others progressively, exacerbating the inbalance in supposedly "balanced" batteries over time.

Thanks, Wes

Slightly off topic, but concerns the effectiveness of parallel charging.

I think the most common way of connecting in parallel is in illustration "A", however I have had it explained to me that connection type "B" is a better solution. "A" solution favours the battery closest to charging source at the expense of the other two batteries progressively, because of resistance in cable and links to other batteries. "B" treats the first and last batteries identically, with a slight disadvantage to the middle battery, because of extra connections and length of cable. It would not seem to be a great disadvantage, but apparently under certain conditions (which I don't fully understand) the difference is significant. The best setup, which treats every battery in an identical manner is "C" . All the leads and connections (therefore resistances) are of equal value so discharge and charge cycles treat every battery identically. I think this doesn't look significant, but it matters when considered over the time factor, when looking at the entire lifetime of the battery. Thoughts??
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Old 25-11-2015, 15:33   #14
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Re: charging batteries in parallel

"C" ensures that the voltage drop in the cables to each battery is equal. That'd be the way to go, with all cables neatly trimmed to equal lengths.


Remember to put a battery primary fuse on each battery, too.
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Old 25-11-2015, 16:14   #15
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Re: charging batteries in parallel

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Slightly off topic, but concerns the effectiveness of parallel charging.

I think the most common way of connecting in parallel is in illustration "A", however I have had it explained to me that connection type "B" is a better solution. "A" solution favours the battery closest to charging source at the expense of the other two batteries progressively, because of resistance in cable and links to other batteries. "B" treats the first and last batteries identically, with a slight disadvantage to the middle battery, because of extra connections and length of cable. It would not seem to be a great disadvantage, but apparently under certain conditions (which I don't fully understand) the difference is significant. The best setup, which treats every battery in an identical manner is "C" . All the leads and connections (therefore resistances) are of equal value so discharge and charge cycles treat every battery identically. I think this doesn't look significant, but it matters when considered over the time factor, when looking at the entire lifetime of the battery. Thoughts??

This came up for some detailed discussion in a previous thread, with some quite detailed opinions posted by some very savvy people. While several experts recommended connections at opposite ends of the battery to compensate for resistance to equalize charging one came in a refuted this with some detailed data that basically the influence is minimal unless you are talking very high currents or very high resistance in the cables (too small or corroded connections). All things considered I think I agree that in a well designed and constructed system the charge difference between the first and last battery in a parallel chain fed from one end will not matter. However I still connected my + and - cables at opposite ends of my bank since it was just as easy and I figured why not.
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