Building a Small System (some problems)

Supercaravan · December 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.

BB. · December 2021

Regarding battery chargers... For loose cells, it would be better to parallel charge them so they all are charged with the same voltage.

In series, if you have a mix of full and partial charged batteries (or at least those that don't "match" state of charge--SoC), then placing them in series--Then you will have issues charging (high SOC are over charged, low SOC batteries are under charged).

For batteries in series (computer battery packs, tool packs, large batteries for solar power systems, etc.), there are generally using a BMS--Battery Management System--To ensure that each cell is operating within its specified voltage range. Depending on the BMS, they may "turn off' the cell, or "balance the cells" (bleed charging current to low SoC cells).

You can use protected or "raw" Lithium cells... Protected cells are better to use in series connected banks. Unprotected cells are best for single cell (i.e. 3-4 Volt output) applications. And while some chemistry cells such as LiFePO4 (lithium iron phosphate) are relatively safe (generally will not catch fire/explode if over/under voltage), other types of cells can be very dangerous to operate with a BMS (especially in series installations).

For small battery chargers--Candle Power Forums has quite a bit of discussion about them (in great detail):

https://www.candlepowerforums.com/forums/flashlight-electronics-batteries-included.9/ (CPF "battery" forum section)
https://lygte-info.dk/ (one of the folks that does a lot of reviews of chargers and other tools)

Li Ion charger, cells, and packs can have very specific requirements.

It sounds like your panel is fine. I would guess that your Li Ion solar charge controller probably "expects" to see 4x cells in series for closer to 12-14.x volts operating range (again depending on Li Ion chemistry used).

Regarding your solar charge controller... Is this the one?

https://anfiltech.com/products/cmtd-a2420-20a

I could not find a Li Ion version--And this version says:

1. Suitable for solar panels regulation only
2. Suitable for connection to lead-acid batteries only: OPEN, AGM, GEL. Not for nickel hydride, lithium ions, or other batteries
3. Pay attention to polarity at wiring connecting
4. Install the charge controller to the battery as close as possible to avoid losses
5. Connect your controller to the battery first and then to the solar panel and to the load. The disassemble in the reverse order

6. Charge controller heats up during operation. Be careful and install it in the well-ventilated place

No Li Ion support... And only connect solar panels after you have the battery bank connected. If you connect the solar panel(s) first, it can confuse the solar charge controller (controllers "boot" from the battery bank, and can be damaged if connected to the array without a battery bank attached.

Also, this is a PWM type charge controller... Its output current will be the same as the max avaialble current from the solar panel (Imp). And the current into the battery bank will depend on amount of sun hitting the panel, and the state of charge of the battery bank (charge controller will limit battery bus voltage to charging "set point" voltage).

An MPPT type charge controller will take the "higher voltage/lower current" of the solar array and efficiently down convert to the "low voltage/high current" need to charge the battery bank (switch mode power supply--Sort the "DC Equivalent" of an AC Transformer for dropping voltage efficiently).

-Bill

Building a Small System (some problems)

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