Building a Small System (some problems)


New Member
Dec 1, 2021
Hi All, new to the forum and the technology. My short question is, can someone recommend an inexpensive Li-Ion charge controller for a 100W panel?

I was out camping with friends and several people had a 45W portable solar kit from Harbor Freight. I almost bought one until I looked on ebay and discovered 100W panels delivered for less than the HarborFreight kit.

I bought a NewPowa 100W panel and an Anself CMTD solar charge controller (the 20A Li-Ion version, Adam Welch made a youtube video of him testing the controller), and I ordered a bunch of 18650 battery packs. I'm waiting for the batteries to arrive, but have started testing my kit with three loose 18650 cells that I wired in series.

My panel seems good and measures ~24V open circuit and ~6A short circuit (is that bad for the panel to directly short it out?)

With the system set up in full sun, I measure ~300mA from the panel and ~150mA into the battery pack. When I add ~600mA load (on a USB port), current runs from the battery until the battery voltage gets low enough that the charge controller shuts off the load and returns to charging the batteries, and this cycle continues. I also noticed that current from the panel toggles between something lower than the load and 0mA.

I think the charge controller is defective, but want to verify that this setup would work the way I think it should. Shouldn't the charge controller pull full current from the panel before it starts draining the battery? Also, shouldn't the charge current be higher than 150mA? Now that it'll be cloudy, can I test the controller with a bench supply instead of the panel?

I had two ideas: Maybe this controller needs two panels in series? It's panel voltage rating is <50V; Maybe I am not using enough battery capacity?

I tried an industrial 11.1V, 85Whr battery pack and have a similar experience, but saw just a little more charge current. Someone said I should not use that kind of battery because it needs a smart charging system that can communicate with the battery circuitry (and maybe a microcontroller via connectors -TDC+). I used a decent hobby charger to charge up both of my battery systems (charging as series 3S to +-) and it worked just fine.

Another curious thing is that I one of my two AC inverters does not turn on when connected to the charge controller Load terminals. I measure ~12.5V and the inverter works just fine when connected to the batteries and I tested it on a bench supply down to 10V where the alarm started to sound. It does need >11V to initially turn on.

Thanks for any tips and advice.


Happy Breffast!
Oct 26, 2021

That charge controller is a steaming pile of garbage. It's behavior is consistent with it not functioning properly.

First, it's PWM, that means that you MUST use only 12V panels ONLY in parallel with it. Only true MPPT allow for higher PV voltage.

Li-ion makes for crap 12V systems.

You need a 3S BMS for the battery to prevent fire/explosion.

You NEVER connect an inverter to charge controller load terminals. They are not designed for that.