Renewable Energy Questions/Discussion > Solar (heating or electric)

Mppt Brand Comparison Suggestions

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MadScientist267:
Lithium doesn't quite bulk all the way up but the absorb rolloff we're all accustomed to with lead is definitely much shorter lived.

As for testing output of MPPT, because of how they do their thing, you really need the batteries there and not a dummy load. This is frustrating of course because the batteries have to settle out somewhere for this to work. The way I got around this with the truck system was to pull them down either to a specific point the previous night (which requires some faith in forecasters) or hitting them hard to get them somewhere just before the sun is where you want it to run the test, and then letting them rebound and hold them with a known load. Neither way is ideal but the only real way I found to replicate conditions for PV "health checks".

This is where of course the Isc metric comes in on the labels.  With the strings isolated, measure the shorted current in as quick succession as possible so sky conditions are as close as possible, and note what you get back. I combined mine with Schottky diodes in the truck, one benefit of doing so being that each string can be shorted for testing without taking anything offline. If you use a regular combiner, it's more involved obviously.

Hope that helps.

Steve

solarnewbee:
When you say short with a diode you mean actually short? I’m at 90-125v depending on sun position. 36x3 open circuit (37.8?) 3 in series divided into a total of 18 panels. 3 strungs on front roof, 3 strings  on back roof.

Been some debate as to whether (48v bank) 58v or 57v or 56.5v or 54.7v Is the best float point for lfp’s. I saw a study that said with most lfp 18650 brands in the study that stopping at 3.5 or 3.6 per cell seemed to make little difference in capacity. 56v or 57.6v I have some used 24v lfp packs and when they get up to 57v the mv differences start to get wonky so I don’t charge them past 56.5v. They only have 85% life left in them but for 200ah packs they were cheap. At 168lbs they were hell getting in the cabinet. I have pics in my Philippines project. Used a server cabinet.

Cheerios!

solarnewbee:
kWh produced since January 2019

solarnewbee:
kWh produced since January 2019

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