looking for cheap, true mppt solar charge controller

[joestue]

i recently took my chances and bought a 67$ 20 amp unit off vevor.

https://www.vevor.com/mppt-solar-charge-controller-c_10732/vevor-20a-mppt-solar-charge-controller-12v-24v-auto-dc-input-solar-panel-regulator-charger-with-lcd-display-temperature-sensor-cable-for-sealed-agm-gel-flooded-and-lithium-battery-charging-p_010254593392

looks like this one was cheaper.
https://us.easunpower.com/products/easun-power-20-40a-mppt-solar-charger-controller-12v-24v-battery-and-solar-panel-solar-charge-regulator-pv-input?variant=46747612053811
then there is this one

https://hqsolarpower.com/20a-mppt-solar-charge-controller-with-parallel-charging-bluetooth/

or this one
https://bateriapower.com/products/mppt-solar-charge-controller-20a?variant=46991413838116

any thoughts? i'm not expecting much.

i have 3 panels but will get a 4th one from my brother which should give me, in theory, 50-60 volts at 7 amps, from 4 panels in series/parallel.

its unlikely i'm in a good enough solar region to justify buying 16KW of used solar panels for 6-7K usd delivered.

[dnix71]

The Vevor unit comes with lightning, reverse polarity and other internal protections that I would not want to be without. It looks like a deal.

HQ Solar's LiFePO4 12v 100ah battery looks good, too. The price matches eBay prices and is about 1/3 of what Home Depot wants. I wonder if you can start a small car with one of those and what the life expectancy would be if used for that purpose. If it would power a small car, it would be cheaper in the long run in hot climates like south Florida than a lead-acid wet battery.

[tanner0441]

Hi

100Ah I would think will start any  car you put it on, but I don't give much for the batteries life unless you do something with the alternator which is set for lead acid charging parrameters.

Over chargind a lead acid battery will initially boil off electrolite and may kill the battery. Overcharging a Li battery may kill the battery and the battery may take the car with it.

I had a Li tool battery and coudn't lay my hands on the correct charger so I fiddled a couple of wire onto it and connected it to an old world 8A battery charger the first I was aware of a problem was a very loud hiss followed by a louder bang and the battery case split.  18650 batteries have a rupture pressure of some 450psi. Ryoby were more than happy to sell me a new one. I was told I was lucky it didn't catch fire.

Brian

[clockmanFRA]

Have a look at these chaps for a good cost home built MPPT controller.

Its the whole story so sit down and get comfortable.

https://www.thebackshed.com/forum/ViewTopic.php?FID=4&TID=12027

150V 45A MPPT - roll your own

And yes some really know what they are talking about.

[bigrockcandymountain]

its unlikely i'm in a good enough solar region to justify buying 16KW of used solar panels for 6-7K usd delivered.

You might want to check out skid prices on new panels.  I see some offers of 50c Canadian per watt, which is about 35c usd.  That's new, mono, tier 1 panels. 

The last skid I bought was 56c per watt cad.

At those prices for solar, you don't need to be in very good solar country for them to work out.

[joestue]

https://imgur.com/gallery/HnqdwHc

I have not hooked it up yet but this looks like something that can be improved upon relatively easily.

Needs much larger input capacitors and it should be relatively easy to parallel more mosfets and then tweak the shunt resistors to get more current out of it.

The 100 volt maximum input will work fine with the three solar panels i have in series. (30v oc each, 8 amps short circuit, 25v mpp at 7 amps)

Im not sure what it has reverse polarity protection on. It appears to have 2 mosfets in parallel on the output. (Probably over discharge protection for the battery), (it has separate load and battery terminal blocks)

The input appears to go through 2 mosfets in parallel (which would make sense for a 20 amp buck converter) with a third to220 for the diode.

[joestue]

Currently it is somewhere around 94 to 97% efficient at 50volts and 2.4 amps from the panel, and 8 amps into a 14.4v battery