Help charging two batteries from single panel with two controllers

[mtb54703]

I have two pieces of battery operated equipment that I keep in my cargo trailer - one uses a 12v 10ah sealed lead acid battery, the other a 12v 2.5ah sealed lead acid battery. I picked up a 15w solar panel from Harbor Freight and 2 CMP12 charge controllers off of ebay.

I have connected the solar panel to both controllers.

With nothing connected to the battery or load terminals only the green charge LED on both controllers is on. This is what I would expect.

When I connect a battery to one controller, the load LED on both controllers comes on, and the 3 red battery status LEDs on both controllers come (although the 3rd LED on both controllers is initial dimmer, then both slowly brighten as the battery is charged).

Even a bit more confusing, if I disconnect the battery from the one controller, all the LEDs on both controllers flash rapidly from 5-30 seconds, after which just the green charge LED stays on.

Ideally I would like to add a third controller for a third piece of equipment.

[FloridaSun]

I have two pieces of battery operated equipment that I keep in my cargo trailer - one uses a 12v 10ah sealed lead acid battery, the other a 12v 2.5ah sealed lead acid battery. I picked up a 15w solar panel from Harbor Freight and 2 CMP12 charge controllers off of ebay.

I have connected the solar panel to both controllers.

With nothing connected to the battery or load terminals only the green charge LED on both controllers is on. This is what I would expect.

When I connect a battery to one controller, the load LED on both controllers comes on, and the 3 red battery status LEDs on both controllers come (although the 3rd LED on both controllers is initial dimmer, then both slowly brighten as the battery is charged).

Even a bit more confusing, if I disconnect the battery from the one controller, all the LEDs on both controllers flash rapidly from 5-30 seconds, after which just the green charge LED stays on.

Ideally I would like to add a third controller for a third piece of equipment.

Ideally you will understand what you're doing now before getting into more trouble and wasting more money. It's difficult to understand what you're doing from what's stated.... besides screwing up. Hopefully you are not connecting both charge controllers at the same time. ALWAYS connect that controller to battery FIRST so it can determine whether you are charging 12v or 24v battery.

[russ]

I have two pieces of battery operated equipment that I keep in my cargo trailer - one uses a 12v 10ah sealed lead acid battery, the other a 12v 2.5ah sealed lead acid battery. I picked up a 15w solar panel from Harbor Freight and 2 CMP12 charge controllers off of ebay.

I have connected the solar panel to both controllers.

Not sure but it seems like a hopeless case. Stop all you are doing and spend a couple of weeks reading - then ask questions if you choose.

[mtb54703]

Ideally you will understand what you're doing now before getting into more trouble and wasting more money. It's difficult to understand what you're doing from what's stated.... besides screwing up.

I love forums - everyone is so nice!

I have wasted more on other types of projects - so far this is mostly an exercise in learning.

As for what I'm trying to do - I thought it rather clear but.... I have two pieces of equipment that run on batteries. I store them in my cargo trailer. When I'm done using them I would like to plug them into the controllers and have then charged up for the next time I want to use them. One panel + one controller + one battery works just fine. I know I can't charge two batteries from one controller, so I thought I'd try a second controller.

Hopefully you are not connecting both charge controllers at the same time.

So elaborate for me why one can't connect two charge controllers to a single panel? The panel is just a power source to the controller right?

ALWAYS connect that controller to battery FIRST so it can determine whether you are charging 12v or 24v battery.

Okay - so maybe my application of unplugging/plugging the battery from the charger is a little different from what is normally done. Sounds like maybe I should install a switch on the wire from the panel to controllers. When I want to use the equipment, turn the switch off, unplug the equipment, use it, plug it back in, then turn on the switch...

[inetdog]

I love forums - everyone is so nice!

So elaborate for me why one can't connect two charge controllers to a single panel? The panel is just a power source to the controller right?

The panel is not just a constant voltage DC source. It is current limited based on the amount of sunlight.

1. You can charge two batteries in parallel from one CC as long as they are the same voltage and type and can each tolerate the full bulk current of the CC without damage. All of the cautions about parallel charging apply, only more so if the batteries are mismatched in capacity.
2. The electronics of the CC require a battery connection for power before the PV input is applied. To switch a CC from one battery to another you will need to disconnect the PV, move the battery connection and then reconnect the PV.
3. If both controllers are PWM types and the two batteries are the same voltage, you may be able to connect the two CCs to one panel. But the CC connected to the less charged battery may pull the panel output voltage down so low that the other CC cannot work. YMMV.
4. If one or both CCs are MPPT types, you absolutely cannot connect both to one panel simultaneously because each one will try to do its MPPT tracking now knowing that there is another CC which is also taking a varying amount of current from the panel. The result may not harm anything, but will either result in hunting (oscillating current drain) as the two CCs fight for all of the power or will result in the panel voltage being pulled so low that they both lose.

[mtb54703]

The panel is not just a constant voltage DC source. It is current limited based on the amount of sunlight.

Thanks for the helpful reply...

1. You can charge two batteries in parallel from one CC as long as they are the same voltage and type and can each tolerate the full bulk current of the CC without damage. All of the cautions about parallel charging apply, only more so if the batteries are mismatched in capacity.

I understood this from my 'reading' - that's why I have two CCs. I had googled 'charging two/multiple batteries solar charge controller' - but most of what I found that applied to one CC and multiple batteries with the cautions that you've noted.

2. The electronics of the CC require a battery connection for power before the PV input is applied. To switch a CC from one battery to another you will need to disconnect the PV, move the battery connection and then reconnect the PV.

Hooking the battery to the CC first was not noted in the manual that came with the CC. Again, my application is not typical in that the battery will not be constantly connected to the CC. I'll install a switch between the PV and the CC to correct this.

3. If both controllers are PWM types and the two batteries are the same voltage, you may be able to connect the two CCs to one panel. But the CC connected to the less charged battery may pull the panel output voltage down so low that the other CC cannot work. YMMV.

It's not clear to me what type of CC the CMP12 is - my guess would be whichever type is the cheaper given the low cost. I expected that multiple CCs might behave this way, thinking that once one battery was up to charge, the other CC would have enough voltage available to charge the other battery.

4. If one or both CCs are MPPT types, you absolutely cannot connect both to one panel simultaneously because each one will try to do its MPPT tracking now knowing that there is another CC which is also taking a varying amount of current from the panel. The result may not harm anything, but will either result in hunting (oscillating current drain) as the two CCs fight for all of the power or will result in the panel voltage being pulled so low that they both lose.

Okay - got it.

I have now found this CC - which is what I was looking for in the first place (that's usually the way it works):

http://www.yoosmart.com/10a-dual-battery-solar-charge-controller-for-rvs-boats-12-24v.html

Now I have two other CCs for my next project.

My thoughts of expanding my original 2 CC to 3 was to charge another 12v 2.3ah battery runs about 1m of LED lighting in the trailer. From what I've 'read' - it might be best to keep this battery topped off with a smaller < 1w separate panel which sounds like it might not even require a controller.

Thanks again for the input!

[FloridaSun]

I love forums - everyone is so nice!

I have wasted more on other types of projects - so far this is mostly an exercise in learning.

As for what I'm trying to do - I thought it rather clear but.... I have two pieces of equipment that run on batteries. I store them in my cargo trailer. When I'm done using them I would like to plug them into the controllers and have then charged up for the next time I want to use them. One panel + one controller + one battery works just fine. I know I can't charge two batteries from one controller, so I thought I'd try a second controller.



So elaborate for me why one can't connect two charge controllers to a single panel? The panel is just a power source to the controller right?



Okay - so maybe my application of unplugging/plugging the battery from the charger is a little different from what is normally done. Sounds like maybe I should install a switch on the wire from the panel to controllers. When I want to use the equipment, turn the switch off, unplug the equipment, use it, plug it back in, then turn on the switch...

Sounds like a rats nest of wiring and unreliable charging when it all could be done more simply with one battery. Also curious how that harbor fright 15 watt panel will hold up in a 55-65mph wind on that trailer.
Panel, $60. Chargers, $60. Batteries, $50? Wiringx2or3. Battery mounts..... duct tape. Another panel for your 3rd battery experiment.... plugging/unplugging daily=waste of time
Cheap enuff.
have fun!