MPPT Recommendations to Charge 12V AGM Battery from 455W / 36V Solar Panel?

[DaveFix]

Someone on Facebook gave me a free solar panel. It's brand new but the glass is fractured. I'm planning to superglue the cracks so that it can be used outside without corroding the panel.

I would like to use it off-grid in the garden with my old 12V AGM car battery.

The panel is a DMEGC DM455G12RT-B48HBB. I understand the max. watts are 455 and max. volts 36.

What's the cheapest MPPT I can use with this panel and 12v battery?

 

[jj4091]

Look for a 12v charge controller for solar panel

 

[ericmark]

Most people only do it once, even electricians rarely return to see how they have worked, so really down to guess work as to good and bad.

Could try a narrow boat or caravaning forum.

 

[DaveFix]

I've checked a lot of MPPT controllers on eBay, but the problem I'm finding is that their specs. state that they can only charge a 12v battery if the solar panel voltage is below about 25v and wattage below about 200w. For panels with a higher output, you can only charge a 24v battery.

My panel outputs 36v / 455W and I have an existing 12v battery I would like to use.

 

[ericmark]

36 volts at 455 watts = 12.5 amps, so a bit more to what a zenor diode can handle.

So somewhere somehow you need to have some way to reduce amps and volts. There are units to run CB's from a wagons 24 volt supply but what you are looking at is doing it on the cheap.

So I have two ex-car AGM batteries, plus the one on the car, but that hardly matters, and I have found the smart charger has set stages of 5 amp, 3 amp, 0.8 amp and 0.1 amp, and when old it may stay at 0.8 amp, but when new would switch on about once a day for ½ hour at 0.1 amp. So the battery needs very little to maintain it, so more looking at what is used.

So we can get a reasonable priced zeror at 10 amp,

at 14 volts. Back years ago I used a 2N3055 NPN transistor and what I did was take the excess rather than try to regulate output, and turn it into heat. I used a 12 volt voltage regulator and a red LED to boost the volts to around 13.8 volts. The regulator turned on the transistor, and the transistor was in series with a 36 watt bulb, so the heat shared between the two. But clearly very wasteful, so although one could design and build a simple regulator, same idea as used with early motorcycles, most the energy would be lost as heat.

So be it a resistor voltage divider or any other method, much depends on how much energy you want to gain, and how much you want to spend.

So a trade-off, amount spent to watt/hours gained.

 

[davelx]

If you want a proper job:

SmartSolar MPPT 100/30 & 100/50 | Victron Energy

Maximize the energy-harvest, driving it intelligently to achieve full charge in the shortest possible time using the SmartSolar MPPT. Learn more now.

www.victronenergy.com

but it's about £75 plus VAT.