Solar panel for small AGM battery

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Solar panel for small AGM battery

Postby Vspec » Thu Mar 22, 2018 8:25 am

I have a small 35AH AGM battery (electric wheel chair kind) that I use in my CTC for light and fan. I have been very conscious about turning things off and never ran out of juice for a 3 day weekend - my initial calculations appear to be correct.

Trailer sits idle for days and I usually disconnect the battery (I also disconnect when towing - overkill?). I usually recharge it before any trip.

This got me thinking, since the trailer spends most it its day in the sun, could I get a solar panel that would keep the battery charged and also recharge it.

Before you ask, yes I plan to increase the load by adding a couple more LEDs lights and usb charger. Will I ever run more? Maybe a DC fridge in the future (I know that 35ah battery will not cut it).

I don't mind setting the foundation for the future (larger panel than I need right now) and since my current monitoring system is a multi-meter, I would not mind a charge controller that would tell me what is remaining, how much I am using etc.

What panel size should I be looking at? Is a simple car battery maintainer enough to recharge and and maintain my current battery?

Do I know my consumption, no, because I have no monitoring.
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Re: Solar panel for small AGM battery

Postby Trebor English » Thu Mar 22, 2018 9:05 am

I got a toy rc car battery device.
https://www.amazon.com/gp/aw/d/B00C1BZSYO/
It works well except my inverter powered fridge uses power in pulses and I'm not sure it registers correctly. Otherwise it seems to work well and is a good price.

I crimped 1/4 inch spade quick disconnects. I use them everywhere. To check usage on any particular device like, for example, the thermostat controlled vent fan, unplug the device, plug in the amp hour meter, plug the device into the meter. That makes it the DC equivalent of a Kill A Watt.

I put male spade connectors on the input, female on the output, just like a Kill A Watt. All of the rest of my wiring matches that. I put heat shrink on the female spade connectors.

When I'm not using it for anything else I leave it between the solar panel and the charge controller.
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Re: Solar panel for small AGM battery

Postby rkanz » Thu Mar 22, 2018 9:11 am

I also have a 35 ah battery running led lights and a fan, and phone chargers. I use a 50 watt Grape Solar panel and charge controller. I made a 25 foot extension with 12 gauge low voltage landscape wire. Plenty of power to keep the battery charged. I also installed a battery cut-off switch.

https://www.homedepot.com/p/Grape-Solar ... /206877151

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Re: Solar panel for small AGM battery

Postby tony.latham » Thu Mar 22, 2018 11:27 am

What panel size should I be looking at? Is a simple car battery maintainer enough to recharge and maintain my current battery?


I don't think you want anything less than 20 watts for your current battery and usage. Here's a ($25) 20 watter on my tongue box. I've got a $30 Morningstar Sunsaver controller in the box. It's a little more than a maintainer. (I think 10 watts would be a good maintainer.) Most of what are sold as auto maintainers, I think are marginal.

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Get a GT Watt Meter ($18). That'll tell you how many amps you've used.

Whatever controller you get, read the manual first and make sure it's okay for an AGM battery. I think they are pickier than my lead acid monster.

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Re: Solar panel for small AGM battery

Postby John61CT » Thu Mar 22, 2018 2:15 pm

Yes, monitor first then buy 2-3x your current consumption.

That's for you, just to keep the batt charged 20w is plenty.
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Re: Solar panel for small AGM battery

Postby Vspec » Sun Apr 08, 2018 2:20 pm

So I bought this: http://www.canadiantire.ca/en/pdp/colem ... 2043p.html so I could play around with for a bit and its going back (unless I just keep the panel which seems for 40w panel is an ok price).
Load is 7a
Cut out is 14.2v
Cut in is 13v

Straight out the panel, in full sun, the output was ~22.3v.
Out of the controller, into my multimeter, was over 14.2v.

I connected two batteries to see how it was charging.

First was a 5.0 ah SLA trailer brake-away battery. I connected it to the controller and it went from charging to charged. For good measure I put on my Noco G7200 charger to confirm it was fully charged, which it was. I put it back on the controller, and with the controller showing the battery as charged, I'd see the voltage go over 13v.

I ran the same test with my 35ah AGM battery, and with the Noco confirming the battery was charged, the controller would indicate it was still in charging mode and would voltage at the battery over 14v, even 15.5v. At this point I discovered the mounting posts for the plastic cover were broken and everything went back into the box.

Here are the charging specs for the AGM:

Cycle Applications: Limit initial current to 10.5A. Charge until battery voltage
(under charge) reaches 14.4 to 14.7 volts at 68°F (20°C). Hold at 14.4 to 14.7
volts until current drops to under 350mA. Battery is fully charged under these
conditions, and charger should be disconnected or switched to “float” voltage.

“Float” or “Stand-By” Service: Hold battery across constant voltage source of
13.5 to 13.8 volts continuously. When held at this voltage, the battery will seek its
own current level and maintain itself in a fully charged condition.

Here is what puzzled me, the controller was outputting more voltage then it should, even much more for the larger amperage battery. Is it because the controller is junk (which it probably is) or was it because it was not able provide sufficient amperage to charge the battery?
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Re: Solar panel for small AGM battery

Postby tony.latham » Sun Apr 08, 2018 7:00 pm

As soon as I saw that it was Coleman I began scratching my head. (Great coolers... but...) I think they scrimped on the controller.

I've had great luck with my $35 Morningstar SunGuard PWM.

https://2n1s7w3qw84d2ysnx3ia2bct-wpengine.netdna-ssl.com/wp-content/uploads/2014/02/SunGuardENG2_11.pdf

Regulation voltage is 14.1

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Re: Solar panel for small AGM battery

Postby Vspec » Mon Apr 09, 2018 6:15 am

tony.latham wrote:As soon as I saw that it was Coleman I began scratching my head. (Great coolers... but...) I think they scrimped on the controller.


You gotta start somewhere and learn along the way.

After some Amazon perusing, looks like what would fit needs would be a portable setup, as I don't plant on mounting anything to the CT.
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Re: Solar panel for small AGM battery

Postby tony.latham » Mon Apr 09, 2018 10:58 am

Vspec wrote:
tony.latham wrote:As soon as I saw that it was Coleman I began scratching my head. (Great coolers... but...) I think they scrimped on the controller.


You gotta start somewhere and learn along the way.

After some Amazon perusing, looks like what would fit needs would be a portable setup, as I don't plant on mounting anything to the CT.


Don't get me wrong, I woulda tried that system too.

Portable is good... you won't have to park in the sun.

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Re: Solar panel for small AGM battery

Postby Vspec » Mon Apr 09, 2018 1:18 pm

tony.latham wrote:Portable is good... you won't have to park in the sun.

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Which panel are those? Did they come with a carrying case?

When parking in the shade I usually have access to shore power so it is less of a problem but I don't mind moving the panels around a bit.
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Re: Solar panel for small AGM battery

Postby tony.latham » Mon Apr 09, 2018 1:22 pm

Vspec wrote:
tony.latham wrote:Portable is good... you won't have to park in the sun.

Image


Which panel are those? Did they come with a carrying case?

When parking in the shade I usually have access to shore power so it is less of a problem but I don't mind moving the panels around a bit.


I bought them from Solar BLVD and attached the hinges. The legs came off an old tripod. I’ve got a custom slot in my tongue box for them.

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:beer:

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