Building a Small System (some problems)

[ctwo]

I simply ordered the lead acid version of the same PWM controller I was using and connected a 10Ah sealed lead acid battery. I connected my phone to the USB port with one of those USB power monitors and observed about 1 amp going into the phone, and about 200mA going into the battery at 13.7V. There was partial shade as the sun was behind trees.

This does what I was expecting. I also expect that, with a larger (30Ah?) battery, this panel will allow me to run a continuous ~15W.

How I get that number is from PVWatts that says I can expect 450Wh average per day in my area with my setup parameters.
80% efficiency / 24h = 15W

[ctwo]

The battery packs all measure 36.x volts. They are 10S2P. They are for an e-bike or such.

I was using a cen-tech DMM to measure battery current since the controller PV values were jumping around, about on a 1sec interval. I do not know how the DMM would respond to PWM.

[Sunking]

I sure hope he did not receive his batteries at 3 volts. I would have sent them right back. They should be around Storage voltage of 3.4 to 3.5 volts. 3.0 volts is fully discharged and you do not ever want to go to 3.0 volts rested.

[sensij]

Based on how quickly it sounds like the battery voltage was going from 9 to 11.1, I'm not so sure that whatever was monitoring the charge current was accurate when it was reporting only 150 mA.

[Sunking]

To be completely honest, when my panel and controller arrived on the same day, I first drug out an old 10Ahr SLA I've had sitting for a couple years. I first measured 12.5V and that was the first battery I connected to my cheap SCC. I was disappointed to see only a couple hundred mA,

OK you mentioned in your opening statement you were not observing much current with the 18650 cells, and now saying not much with a Pb battery. That is telling me you have either a bad controller or incorrect wiring. Another remote possibility is you do not have the panel in direct sunlight around noon hours on a bright sunny day.

OK let's make things simple. All batteries have minimum and maximum charge current requirements. Lithium is not real picky as they can be charged quite slowly, or quite fast up to C/2 is what most manufactures recommend. So how do you control the charge current on a solar system?

It is stupid simple and when you hear the answer will make you wonder what you were thinking. You just match the panel wattage and battery AH capacity to work together. As an example lets say you have a 3S 40 AH LCO battery and want to charge it at C/2 or 20 amps. You could use a PWM controller if you want to throw a bunch of money away using low voltage battery panels. With PWM Controllers Output Current = Input Current. Makes life simple, you look at solar panels Imp current rating. You have to use 36-cell low voltage 12 volt battery panels like you have. A 100 watt panel has an Imp of 5.5 amps. You would need 4 x 100 watt panels wired in parallel. That would give you 22 amps of charge current. Close enough.

MPPT Output Charge Current = Panel Wattage / Battery Voltage. Using that formula and rewriting it we can find that the panel wattage needs to Panel Wattage = Charge Current x Battery Voltage. A 3S LCO charge voltage is 12 volts for the calculation so, 20 amps x 12 volts = 240 watts. All you would need is a single inexpensive 240 watt high voltage panels with 72 cells and a 20 amp MPPT controller.

See it is Stupid Simple. So consider yourself lucky you have a defective charge controller or wiring issue. If it had worked correctly you would hit your 2800 mah cells with 5.5 amps or a 2C charge rate which is 400% over the safe limit.

I assume you intend to use the 100 watt panel which is fine, but you trap yourself with limits on battery capacity. If you use a PWM controller charge current is going to be 5 amps. That means you minimum size battery is 10 AH. You can go higher, but even that has limits because if it is too large will take forever to charge. If I had to put an upper limit would be C/6 and that would mean a maximum capacity of 30 AH. That would take two full days to recharge from a fully discharged sate.

With a MPPT controller Charge current is 100 watts / 12 volts = ,8.3 amps, just call it 8 amps. Using the above limits is a battery of 16 AH to 50 AH.

Now this will piss you off and it should. If you had bought 4 x 40 AH Calb Batteries would have cost you $200 to $240 depending on supplier.

[ctwo]

Wow, I need to work on my Google Fu. I concede, this was somewhat an impulse buy, but these devices you all are presenting are in a different class than the lion's share I was able to find.

1. I had already accepted that I would need to move all my loads direct from the battery and would need my own protection, but there is a little more to it than that...and that is my cheapie does not cut charge voltage and will float. Given regular use and the sun cycle, that might not matter, but would need manual attention or an additional circuit. I suspect the GV10 would handle that properly, but I've already been surprised.

2. I really had planned on using a number of cells in parallel, so the panel would not be capable of over current. The details were not worked out yet, and I will admit that at the point when that was mentioned here, I had not considered it for what I was doing at the time. Dumb luck perhaps, but I did expose myself to risk with my anxious testing that I presented earlier (it was outside in the grass, so no worries). I also failed to discover the different battery technologies and the best option. My choice was one of opportunity and familiarity. To be completely honest, when my panel and controller arrived on the same day, I first drug out an old 10Ahr SLA I've had sitting for a couple years. I first measured 12.5V and that was the first battery I connected to my cheap SCC. I was disappointed to see only a couple hundred mA, but that was an obvious conclusion once I gave it a thought! So, I then went to the industrial 85wHr "laptop" battery pack and was getting confused about the load switching and the potential of some sort of BMS activating. That's when I went searching and found some videos showing three 18650 cells in series with my controller...I think I'm boring you now.

I should regroup and properly define what I really want to accomplish - that is to have light-weight, portable solar power when tent camping (not hiking), that was the initial drive anyway. My whole system was t be bolted to the back of the panel for ease of use. I soon realized that would not be a constant use of the system and would like to be able to use the panel at home to supplement power needs (to lessen the cost of the system), maybe to run water pumps, lights, or some appliance within the capability of the 100W panel I have. That was to be an auxiliary use and a learning experience as I consider the longer term plan to install a complete solar home system (with windmill).

The good news is that my battery packs arrived today and I am not nearly as anxious to start putting them to the test this weekend. No casualties :thumbsup

[sensij]

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.

It is a nice controller, but I'm not sure it solves any of the problems that you've expressed with the model you own now.

Problem 1: The load terminals (and USB output) shut off when in voltage recovery mode, and the USB port is always 100% powered by battery.
The Genasun controller doesn't even provide load terminals, and offers no protection against over-discharge. If you just moved your load on the cheap PWM controller from the load terminals to the battery terminals, you cut all the goofy load control logic out of the picture (as Genasun has done).

Problem 2: Your controller has no ability to limit charge current to 0.5C, or even limit charge current to within the rating of the controller.
The Genasun is mppt, and is probably smart enough to limit charge current to the rated output by moving off of the maximum power point with the charge current rating is reached. However, it offers no ability to further reduce the maximum charge current, so that if you are using a battery that can only take 1.4 A, you are still at risk of hitting it with more than that. In fact, the Genasun is slightly worse in this respect, because as an mppt, it would convert your 100 W to 100 / 12 = 8.3 A, instead of the ~5.5A Isc that the PWM controller would pass from a 100 W panel (under STC conditions).


I think "The Kid" by Midnite Solar offers all the functionality you are looking for (and more), but at ~$300, you'll need a few pennies to get there.

[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.

[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]

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.

[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]

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.

[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]

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]

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.