Building a Small System (some problems)

[ctwo]

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.

[sensij]

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?
.

It doesn't sound defective. That is a super-generic PWM charge controller, programmed for Li voltages instead of lead acid. The USB ports won't be powered by the panels directly, only by voltage conversion from the battery. When the battery gets low enough, it trigger the flow of charge current from the panels (and apparently disconnects the USB output when charging).

The current that is delivered will be based on the battery voltage, and what the battery can take. If the battery is only lightly discharged, it may only be able to take a little bit of current.

[ctwo]

It doesn't sound defective. That is a super-generic PWM charge controller, programmed for Li voltages instead of lead acid. The USB ports won't be powered by the panels directly, only by voltage conversion from the battery. When the battery gets low enough, it trigger the flow of charge current from the panels (and apparently disconnects the USB output when charging).

The current that is delivered will be based on the battery voltage, and what the battery can take. If the battery is only lightly discharged, it may only be able to take a little bit of current.

Maybe I did not explain the problem very well. When I connect a small load, even a 30 ohm power resistor to the 12V output, there is no more charging the batteries at all. The batteries drain until 9V where the load is turned off, then the batteries charge to 11.1V where the load is turned back on, and the cycle repeats.

If that is normal behavior for a PWM solar charge controller, I don't see how people can run things like water pumps all day. The batteries would only charge to 70% of their capacity, and never any more.

I read this article before posting my question: https://www.solarpaneltalk.com/forum...ing-or-selling

I had thought of connecting my load direct to the batteries, but that seems to defeat the purpose of the SCC and I'd need another circuit to protect the batteries from over discharge (which would be an unusual condition if the system is sized properly).

[littleharbor]

Have you gone through and set and/or verified all parameters? There should be no way your batteries are allowed to discharge this low unless the settings are way out of whack, or you have a very long distance of teeny, tiny wire (that's a technical term) between the controller and batteries.

[SunEagle]

It depends on the charge controller. Some do not have very high amp rated "load terminals". They can easily be overloaded and hurt the CC.

My guess is that CMTD CC is really not set up to charge Li chemistry batteries so they are not getting to 100% SOC based on some limiting factor.

Based on my experience with LiPo batteries it takes a balancing circuit to get all of the cells to the correct voltage. My guess is that is not happening

[Sunking]

First problem is your batteries are dead from what you describe. You did not say what 18650 cells you have, example LFP or LCO. All you said is 3S.

If LCO full charge voltage would be 12.6 volts, and if LFP would be 10.8 volts. Anyway if you measure 9 volts under load means your batteries are not charge up and makes no difference what kind they are.

Assuming bright noon sun, and batteries are discharged you should be seeing at least 8 to 9 amp of charge current, and that would be a huge problem for 18650 cells resulting in thermal runaway and possible fire. Most 18650 cells max charge rate is C/2. Again not knowing what type of cells you have and capacity I can only guess the capacity is as low as 1900 may up to 4000 mah. That would mean max charge current you should be applying is around 1 to 2 amps. I highly doubt your charge controller can limit current current to a desired value less than the spec rating.

To conclude, your system is not properly designed, not is it functioning correctly. That is what happens on You Tube.

[sensij]

Maybe I did not explain the problem very well. When I connect a small load, even a 30 ohm power resistor to the 12V output, there is no more charging the batteries at all. The batteries drain until 9V where the load is turned off, then the batteries charge to 11.1V where the load is turned back on, and the cycle repeats.

Yes, this is how it is designed to behave. The 9 V is the "low voltage cut-off", and the 11.1 V is the "low voltage recovery". When you hit the low voltage cut-off, it cuts off all load output until the recovery voltage is hit. If you want behavior that allows you to power a load and charge at the same time, you need to hook up your load to the battery terminals. As you said, you'll need some other method of protecting your batteries from over-discharge. This is standard for these very low end style PWM controllers.

If you don't connect a load at all, it looks like it should eventually get your battery to 12.6 V before discontinuing the charge.

[ctwo]

Well, that seems like an odd way to intentionally make the system, so I am glad I did not buy a hundred dollar controller. I may design my own if none exist for Li-Ion. But of course I would rather buy one.

I was using 3 cells in series LG LGABC21865, 2800mAh Lithium-ion Battery Cell, max charge 4.2V, cutoff discharge 3V, charge circuit 0.5C are some specs I found. I was planning to build up the size pack I'd need for my power needs. This was just a test of a small load to see how the system is working.

The parameters on the controller are not settable, but show 9V cutoff, 11.1 load turn on, and 12.6V is where it goes to float charge. This would seem to be the right kind of controller for the batteries I'm using, and it is rated for 20A. There are 6 power FETS total, I assume a pair of 10A each for the battery and load, one for the USB ports, and one for the panel input circuit.

Dead batteries would draw 8+ amps when the charge voltage is limited to 12.6V? If that is the case, there will be a lot of problems because I'm sure there are millions of these devices out there, or soon to be...

Thanks for all the insights.

[Sunking]

Well, that seems like an odd way to intentionally make the system, so I am glad I did not buy a hundred dollar controller. I may design my own.

I was using 3 cells in series LG LGABC21865, 2800mAh Lithium-ion Battery Cell, max charge 4.2V, cutoff discharge 3V, charge circuit 0.5C are some specs I found..

OK if you have a 100 watt panel, and 20 amp cheap controller; how in the world do you plan to limit charge current to 1.4 Amps? With a 100 watt panel and PWM controller your charge current is 5.5 amps or 300% more than the battery can safely be charged at.

That is bad planning on your part. Simple enough to fix, use 3S4P. Now each string receives 1.377 amps. At 3S4P LCO gives you a nominal 10.8 volts @ 11.2 Amp Hours.

[ctwo]

I just wanted to test it while I wait for the rest of my batteries to come in, but the batteries were charged before I started and I was monitoring the panel and charge current, 150mA.

The main problem I had was not expecting that the load and charge could not happen at the same time. Maybe I'm an odd duck, but that is still puzzling to me. You are also right that I should have been expecting a charge current setting if I was going to use such a small battery. It was just an afternoon test so I wasn't really planning on using that as my system battery, and I was putting load on it to see some free electrons powering something.

I had already ordered 100 cells and planned to build packs around 450Whr as that seems to be the max expected daily output from my panel where I am. That seems like more than I'd need given efficiency, and I'd be using power too. Maybe three 3S11P packs that I could rotate would be about right? I was going to think more about that once I established some numbers through testing.

I'm going to try again with the loads on the battery and try a few different packs I have and see how the system responds. I guess I won't be using the USB ports anytime the sun is up though.

BTW, is there a better controller I should consider?

Thanks again.

[Sunking]

I just wanted to test it while I wait for the rest of my batteries to come in, but the batteries were charged before I started and I was monitoring the panel and charge current, 150mA.

Charged batteries will not take any charge current unless you set the voltage to high. Nor should fully charged LCO batteries crash if charged up unless the load is excessive.

You might want to rethink all of this. I do not know your goal, but if the goal is to make a 12 volt battery of say more than 10 AH, you are using the wrong form factor (18650), and wrong type of Lithium battery. Lithium Cobalt i snot compatible with 12 volt battery systems, and using a bunch of parallel 18650 cells is just not practical. On top of that you are paying way to much money.

If your goal is to make a 12 volt battery of say 10 AH or more. use a prismatic Lithium Iron Phosphate (LFP) cells. A 4S LFP is a drop in replacement for 12 volt lead acid batteries. They come in 10 to 1000 AH and about everything in between at 1/3 to 1/4 the cost of LCO 18650 cells. You do not have to build or buy anything special. They charge at the exact same voltage Lead Acid batteries use. You can buy and use with off the shelf solar charge controllers. Use a CALB cell as CALB is the best of the Chi-Com LFP batteries. They are also the lowest price of the Chi-Coms. You are paying roughly$2.00 per wh for those cells. A LFP is 1/4 that price at 45-cents and last have 3 times the cycle life. You are paying up 1200% for something not compatible with a 12 volt world.

[inetdog]

...You do not have to build or buy anything special. They charge at the exact same voltage Lead Acid batteries use. You can buy and use off the shelf solar charge controllers. Use a CALB cell.

But, and it is a large but, make sure that the charger you use does not have temperature compensation or automatic Equalization charge periods enabled. Small cheap solar controllers probably will not have either feature, but more expensive ones might.

[Sunking]

But, and it is a large but, make sure that the charger you use does not have temperature compensation or automatic Equalization charge periods enabled. Small cheap solar controllers probably will not have either feature, but more expensive ones might.

Good point and true. Seeing how he has a 100 watt panel a No Brainer CC is a Genasun GV10. They will handle up to a 140 watt panel and can charge any 3S and 4S LCO or 4S LFP battery. Completely Plug-N-Play. You just have to order the right model for voltage of 12.5 (3S LCO), 14.2 (4S LFP), or 16.7 (4S LCO). Exact same models as the Lead Acid versions. Lead Acid models just cost more for the extra code to make 3-stages.

High quality stuff made for Marine environments.

[ctwo]

That GV10 looks like a nice controller and there is a version that supports 11.1V Li-Ion, not that I have to married to that type. I'll have to save some pennies for a while. Thank you.

[Sunking]

That GV10 looks like a nice controller and there is a version that supports 11.1V Li-Ion, not that I have to married to that type. I'll have to save some pennies for a while. Thank you.

You are welcome.