PWM Solar Charge controller and smaller batteries

[oxydog]

Good day all,

Wow, haven't been here in a long time!

Quick question: I have a 20A PWM Solar charge controller installed on my Hilux to charge my deep cycle. I have 2 hinged 40W PV panels for charging.

Can I use the same controller and panels to charge my small 7Ah (garage motor type) batteries? How do I connect them, directly to the connectors that currently go to the deep cycle and just disconnect the deep cycle?

Regards,
Jarus

[dax021]

Hi Jarus, that will work, but just be careful. A rule of thumb for lead acid batteries is never charge at more than 10% Amps of the AH rating, i.e., max 10A for a 100AH battery. So, check what voltage your panels are putting out and work out the Amps that they can supply (A=W/V). Bear in mind that your controller can supply 20A if your panels can push that. Connecting multiple 7AH batteries in parallel could solve the problem.

[Family_Dog]

As Peter says, there should be no problem, just keep an eye on the voltage that it stays at around 13.8v for a flat battery, then stabilises to around 13.2 - 13.5v for a steady charge and no more than 13.1v for a float charge. The 7A battery will draw what it needs so no problem if the SP can supply more but it should not ever draw more than 1A initially and tapering off to less than that as the charge builds up.


-F_D

[oxydog]

Thanks Peter and Eric.

So I suppose I could also try to limit the current by covering part of the panels? Surely a 7Ah battery can't take that long to charge in any case, but I like the idea of charging them in parallel - never thought of it. (Electronic engineering studies aside... )

[Family_Dog]

The Solar Panels cannot "force" amps into the battery, the battery will draw what it requires, so no need to cover any panels. The most important thing to check for is the voltage from the SP array, it should read 12.8-13.8v maximum off-load or on-load.


-F_D

[dax021]

Eric, I respectfully disagree with you. Current cannot be pushed, only drawn, agreed, but if that battery has been depleted overnight, it will try to draw the full 20A that the controller can supply. Most PWM controllers can take a 50V input from the panels, although I doubt his panels will produce such a high voltage, even in series. The charge parameters can be set, so panel voltage is a non issue

[oxydog]

Hmmm. Interesting conflicting arguments here. Obviously, covering part of the panels can't do any harm, but in some cases one would want to charge the battery as quickly as possible without causing damaging to the equipment.

I'd like to see what others say.

[dax021]

I'm pretty sure you will never need to shade your panels. That is the job of the controller. Post a photo of the stats sticker on the back of one of your panels. Your setup will work, no question about it, all that concerns me is maybe overcharging, which can be pretty much overcome by careful monitoring. If everything goes pear shaped, the worst that can happen is that your battery swells and loses half its life. Not a big deal, when you consider the other option of not having any power to your alarm/garage door.

[dax021]

I have 3 x PWM controllers, one on a 120W panel, one on a 50W panel and the other on a 10W panel. I have 5 old motorbike batteries (12Ah) which I shuffle around between chargers and use for powering modems, LED lights and whatever else is needed for loadshedding. Also use the system to keep my 48V 170Ah solar batteries topped up.(they are not connected to an inverter at the moment, so is just trickle charging)..I do keep an eye on things and disconnect when full.

[oxydog]

I have 3 x PWM controllers, one on a 120W panel, one on a 50W panel and the other on a 10W panel. I have 5 old motorbike batteries (12Ah) which I shuffle around between chargers and use for powering modems, LED lights and whatever else is needed for loadshedding. Also use the system to keep my 48V 170Ah solar batteries topped up.(they are not connected to an inverter at the moment, so is just trickle charging)..I do keep an eye on things and disconnect when full.

Thanks Peter, I think that answers my question. I'll simply monitor the battery status myself and trust my controller to do its job.

Thanks guys, that's why I love this forum!

[oxydog]

Update: I've built some cables over the weekend and tested the setup. Works like a charm. Thanks for the advice guys!

[dax021]

Great, glad to hear it is working