Solar Panel/Charge Controller and Dual Battery Question

[coax]

So in my reading about battery chargers, it was fairly clear that using a 3 stage charger to charge 2 12v batteries in parallel is not a great idea, as one battery could be over charged during the boost/absorption stage since one battery will be "full" and the other battery may not be. Which would leave the charger in Boost/Absorption mode for longer than it should be. My question is how this relates to solar panels, and what folks are doing to address this. Or if it even needs to be addressed. I ask because I am looking at putting a solar panel on my Landcruiser that has dual batteries, but also my parents recently bought a small camper with 2 12v batteries, a solar panel, and this charge controller:

http://www.amazon.com/Go-Power-GP-PWM-30-Solar-Regulator/dp/B007KIUDBQ

It is a 3 stage PWM controller, and according to the manual, it states it will do the following for 12v flooded batteries:

• Bulk: 14.4v
• Boost: 14.4v applied for 2 hours if voltage was below 12.3
• Float: 13.7

So my two questions are really this:
1. Is this something to worry about, having one battery of a dual battery system be over charged by the solar panel and 3 stage charge controller? The batteries are identical, but imagine they still have slight differences between the two?
2. In general i understand that 3 stage charging is also bad for unloaded batteries. In a setup such as an overland vehicle with a fridge or a camper with fridge/lights/etc, is a 3 stage solar controller appropriate?


Do they make dual independent outputs on solar controllers and then just put some sort of isolator inbetween? Or use a 2 stage charger and live with the lower effective capacity that it will provide since the batteries wouldn't charge all the way? Use a battery isolater such as the blue sea marine switch and hook up the solar panel to the start isolation so it only charges the house battery off the solar panel?

Thoughts? I did a bit of searching and found plenty on chargers and dual batteries but not much on solar and dual battery setups? Forgive me if I missed a thread where this is explained.

:beer:

 

[teotwaki]

CTEK D250S Dual http://www.amazon.com/gp/product/B005LBCVL4/?ie=UTF8&me=A207GDV8EMU92Y

It will manage the voltage from the alternator and starting battery by turning it into a proper multi step charging regime. If the alternator is off the CTEK will cut out when the voltage on the starting battery drops below 12.8v for 10 seconds. It also has a built in MPPT solar charge controller that will first charge the secondary battery and then the starting battery.

Mine should hit my doorstep tomorrow. :wings:

 

[teotwaki]

Good battery thread at http://www.expeditionportal.com/forum/threads/80568-AGM-Battery-maintenance-charging-for-dummies

DWH can come off as grumpy or sarcastic as I oftentimes do but I'll readily vouch for his technical accuracy. :elkgrin:

 

[dwh]

Answers to OP questions:

1. The problem of a 3-stage getting stuck in absorb mode and overcharging one of a set of batteries is somewhat of a non-issue with solar because the absorb stage is going to end when the sun goes down anyway. It's mostly something you have to worry about with a charger running from shore power.

2. Seems like you got it backwards - 3-stage is good for unloaded batteries, but not for *loaded* batteries because the load fools the charger into thinking that the amp flow is due to the battery not being full, so it sticks in absorb and holds the elevated voltage too long.

There are quite a few charge controllers which are designed to charge multiple batteries/banks. Morningstar SunSaver Duo is one of the more popular ones for small solar rigs.


The Go Power PWM you linked looks to be a 2-stage charger - bulk and float. If the voltage drops below 12.3v it kicks in the bulk stage for 2 hours. They call that boost stage, but it's just bulk stage on a timer.

Same with the EQ stage - it's just a bulk to 14.8v instead of 14.4v, and again, it's on a 2 hour timer. That's not what would normally be considered a proper battery "equalization".

It would do the job, but I'd go with the Sunsaver Duo with remote meter for 10 bucks more:

http://www.solarhome.org/MorningstarSSD25-RMSunSaverDuoChargeControllerwithRemoteMeter.aspx

 

[4x4junkie]

So in my reading about battery chargers, it was fairly clear that using a 3 stage charger to charge 2 12v batteries in parallel is not a great idea, as one battery could be over charged during the boost/absorption stage since one battery will be "full" and the other battery may not be. Which would leave the charger in Boost/Absorption mode for longer than it should be.

Wherever you picked that up from, it's not correct.

Parallel batteries (provided they are the same type & size and were in a similar state of charge when first connected together) should charge & discharge at the same rate together (functionally two parallel batts are the same as one larger batt).

As dwh said, the absorb overcharge issue comes from small loads like a light or your fridge fooling the charger, however some (most?) of your better brand units will simply time out the absorb mode after like 2 hours or so and then drop into Float mode regardless of it having a small load on it (the Morningstar SunSaver MPPT-15 I know does this).

 

[4RunAmok]

Parallel batteries (provided they are the same type & size and were in a similar state of charge when first connected together) should charge & discharge at the same rate together (functionally two parallel batts are the same as one larger batt).

So long as you draw the positive from one end of the bank, and the negative from the other... Essentially treating the bank as one container.

Otherwise if you draw +/- from the last battery in the bank, you will drain that one first, then the second one, then the third one, and so on...

The + and - leads from the charge controller should be connected the same way.

 

[NH Moto Expo]

Slightly off topic...but I have 3 motorcycles that I store during winter. Can I just pull all 3 batteries and hook them up parallel to a "battery tender"? I would rather not buy 3 chargers, especially if this would work the same keeping all 3 topped off for the winter.

 

[HenryJ]

Slightly off topic...but I have 3 motorcycles that I store during winter. Can I just pull all 3 batteries and hook them up parallel to a "battery tender"? I would rather not buy 3 chargers, especially if this would work the same keeping all 3 topped off for the winter.

Not likely to work very well unless they are exactly the same battery and all in the same condition. Differences will cause inconsistencies. The individual battery tenders are a much better choice. If the cost seems excessive you can rotate the charger from one to the next on a schedule.
I have four bikes and had two chargers. I had been rotating the chargers between them. Yesterday I added another tender to the fleet. Now I am just lacking one.
Thin the herd, buy another tender, or be diligent about your rotation of the resources at hand.

 

[teotwaki]

So long as you draw the positive from one end of the bank, and the negative from the other... Essentially treating the bank as one container.

Otherwise if you draw +/- from the last battery in the bank, you will drain that one first, then the second one, then the third one, and so on...

The + and - leads from the charge controller should be connected the same way.

If your jumper wires between the batteries are properly sized for the current draw it should not matter what battery terminals you connect to for charge or discharge.

 

[4RunAmok]

If your jumper wires between the batteries are properly sized for the current draw it should not matter what battery terminals you connect to for charge or discharge.

All traditional knowledge that I can find, and what I've been taught are to the contrary.

http://www.solarray.com/TechGuides/WireDiagrams_T.php

Consider the batteries a glass of water. The end the load is drawn from being the top, and the end farthest from the draw being the bottom. Electricity follows the past of least resistance, just like water, and you will kill that first battery before the second, before the third, etc..

The following is the proper way to wire a bank

 

[coax]

Thanks for the info! Much appreciated.

Answers to OP questions:

2. Seems like you got it backwards - 3-stage is good for unloaded batteries, but not for *loaded* batteries because the load fools the charger into thinking that the amp flow is due to the battery not being full, so it sticks in absorb and holds the elevated voltage too long.

Yep, I did indeed state that backwards. Whoops. Seems like this would also be solved by the timeout on the absorb stage on the solar panels as well?

There are quite a few charge controllers which are designed to charge multiple batteries/banks. Morningstar SunSaver Duo is one of the more popular ones for small solar rigs.


The Go Power PWM you linked looks to be a 2-stage charger - bulk and float. If the voltage drops below 12.3v it kicks in the bulk stage for 2 hours. They call that boost stage, but it's just bulk stage on a timer.

Same with the EQ stage - it's just a bulk to 14.8v instead of 14.4v, and again, it's on a 2 hour timer. That's not what would normally be considered a proper battery "equalization".

It would do the job, but I'd go with the Sunsaver Duo with remote meter for 10 bucks more:

http://www.solarhome.org/MorningstarSSD25-RMSunSaverDuoChargeControllerwithRemoteMeter.aspx

Yep, if this one fails or somehow needs replacing I'll look towards the Sunsaver's. Really just wanted to make sure that the batteries weren't going to fail in an expedited fashion due to a poorly designed system/charge controller. Seems like they should be ok, if not the optimal setup for charging.

 

[coax]

Wherever you picked that up from, it's not correct.

Parallel batteries (provided they are the same type & size and were in a similar state of charge when first connected together) should charge & discharge at the same rate together (functionally two parallel batts are the same as one larger batt).

As dwh said, the absorb overcharge issue comes from small loads like a light or your fridge fooling the charger, however some (most?) of your better brand units will simply time out the absorb mode after like 2 hours or so and then drop into Float mode regardless of it having a small load on it (the Morningstar SunSaver MPPT-15 I know does this).

It's very possible I mis-understood the 3-stage/multiple batteries statement. My understanding was that even if wired properly, the batteries will display slightly different characteristics accentuated by age. So during charging, one battery may be "full" while the other one is not, and then the charge voltage will remain too high during the second stage and overcharge the already full battery??? (Since the second stage is constant voltage instead of constant current)

 

[G35Vortec454]

Wherever you picked that up from, it's not correct.

Parallel batteries (provided they are the same type & size and were in a similar state of charge when first connected together) should charge & discharge at the same rate together (functionally two parallel batts are the same as one larger batt).

As dwh said, the absorb overcharge issue comes from small loads like a light or your fridge fooling the charger, however some (most?) of your better brand units will simply time out the absorb mode after like 2 hours or so and then drop into Float mode regardless of it having a small load on it (the Morningstar SunSaver MPPT-15 I know does this).

X2. So not correct!

When parrallel banks do not charge or discharge alike, and you have a quality 3 or 4 stage charger, the problem is in the other consumable components of the circuit - alternator, solar panels, batteries, isolators, cables, fuses, etc. Fix / replace those rather than blaming the charger. Those components are the most predictable to go bad. To know if a component is bad, one has to use the proper instruments. It's not guesswork.

I have three parrallel banks (660AH) connected to my Prosine 3000W inverter with a builtin 120A 4-stage charger. The banks are also connected to a 220A alternator and 450W solar panels via the SunsaverDuo, and are also automatically charged by the 4kw Onan generator when running, or by shore power when available. The most common challenges with parallel banks are monitoring and maintenance. If you don't monitor, you can't maintan the system timely. Monitoring equipment shows 24/7 the charging/discharging state of each bank and if they are way off each other, maintenance must be performed.

Now to OP questions:
1. no
2. Not bad at all

X2 on SunsaverDuo for your vehicle.
For your folks' trailer, charge them in parallel with a good solar charge controller and monitor and maintain the batteries. The more critical issue is how will your folks fully charge the dual batteries after they're discharged, as the solar charger won't be able to do so?

 

[4x4junkie]

It's very possible I mis-understood the 3-stage/multiple batteries statement. My understanding was that even if wired properly, the batteries will display slightly different characteristics accentuated by age. So during charging, one battery may be "full" while the other one is not, and then the charge voltage will remain too high during the second stage and overcharge the already full battery??? (Since the second stage is constant voltage instead of constant current)

That is why it's important to use batteries of the same type & size, and that they be of similar age (preferably new). As they age together, their charge/discharge characteristics should remain in balance.

4RunAmok's comment about the wiring is also very correct (I should've mentioned that), and becomes especially important during periods of high charge/discharge currents (such as when using a winch).

I probably also should mention just in case, be sure to have both batteries in the same thermal environment if they're wired parallel too. Having one under the hood while the other is elsewhere can create an imbalance between them as well.

When parrallel banks do not charge or discharge alike, and you have a quality 3 or 4 stage charger, the problem is in the other consumable components of the circuit - alternator, solar panels, batteries, isolators, cables, fuses, etc. Fix / replace those rather than blaming the charger. Those components are the most predictable to go bad. To know if a component is bad, one has to use the proper instruments. It's not guesswork.

If batteries in a parallel bank are not staying in balance, almost guaranteed the culprit is some resistance on one or more of it's interconnecting cables. Removing, cleaning, and reconnecting all of it's cable connections should be the first order of business here.

 

[G35Vortec454]

That is why it's important to use batteries of the same type & size, and that they be of similar age (preferably new). As they age together, their charge/discharge characteristics should remain in balance.

If batteries in a parallel bank are not staying in balance, almost guaranteed the culprit is some resistance on one or more of it's interconnecting cables. Removing, cleaning, and reconnecting all of it's cable connections should be the first order of business here.

Corroded and/or loose cables are very common and those are very easy to spot, but you still have to physically check, absent precise monitors from the cabin. Battery Cells could short or open due to vibration, individual cells could be low on water and have the plates exposed, isolators could develop huge drops, charging relays sticking, too many to mention. Without monitoring equipment in the cabin it's cumbersome to make sure your power system is in top shape.

I also wish somebody makes a wireless remote digital SG indicator for each cell of all batteries that are in use, just like tpms you know