Low cost DIY Lithium camper batteries.

Thanks Vic... I continue to be so thankful at how freely folks offer advice and direction on this WTW site. It is such a civil place to be!
I am biting at the bit on this project...everything is laid out on the bench ready to go... and life keeps pulling me elsewhere. (a 12 week or puppy in training is a major distraction as is the New England weather... oh yeah and work!).
Even though that controller looks pricey I decided to dedicate my snow plowing money (do the neighbors road) toward this in the Spring. I want this to come out good. I have faith in others with solar electrical knowledge.
 
what’s the lowest voltage your battery bank will see? assuming 12 v, add .5 v to that as the “extra “ needed to push current into the batteries then divide 300w by 12.5 to get the max current flow possible = 24amps that’s more than the controller can put out, but as rando has pointed out before, you are usually only to see 80% of max power that’s 19.2amps you should be good then
 
My understanding (which I haven't really tested) is that if the solar panels produce more power than the controller can handle, it just caps the current at what ever the design limit is - so in this case 20A. Your extremely unlikely to ever get more than 20A out of a 320w array, but if by some fluke you do, the controller will just max out at 20A. The spec sheet just states that Isc for your panels should be less than 20A, with two 160W panels, your Isc should be around 17-18A. Of course if you think you may ever want more than 320W of solar it would be wort investing in a bigger controller now.

Is that your experience Vic?
 
rando said:
My understanding (which I haven't really tested) is that if the solar panels produce more power than the controller can handle, it just caps the current at what ever the design limit is - so in this case 20A. Your extremely unlikely to ever get more than 20A out of a 320w array, but if by some fluke you do, the controller will just max out at 20A. The spec sheet just states that Isc for your panels should be less than 20A, with two 160W panels, your Isc should be around 17-18A. Of course if you think you may ever want more than 320W of solar it would be wort investing in a bigger controller now.

Is that your experience Vic?
Click to expand...
I undersized mine too, and have two of the 75/15 controllers - one for the roof and the other for the portable panels. The 75/15 has errored twice on me with an "overcurrent" error. In both cases, that meant it shut down until I could disconnect all power from the controller to get it to reset. Annoying to say the least.

I have 265W on the roof, and using the same math I just did for Buckland above, that's 265/12.5 = 21.2A * .8 = 16.96. So at least twice I have exceeded 15 Amps and it did not "blow up" but it did shut down. If that happened while I was away from the camper for a day or three (backpacking) it would result in a battery drain situation.

Now they might have upgraded the firmware by now, but that's my experience.
 
Vic, that is kind of what I remembered, so I guess there is a caveat to undersizing the controller.
 
rando said:
That charger is a great option - it the same one or a clone of the one I have. It is useful for lots of things as it can charge, discharge and balance just about any battery chemistry. Looking at the boxes on my shelf, the first box I got was 2014, and the later boxes were 2014 and 2015.
Click to expand...
I wired 3 of the <1v cells together in parallel and they took 18ah before hitting 3.6v. They then settled to 3.33v. I thought that was promising.

I want to cycle them a few times, but the charger refuses to discharge them. It's set to 2A and 2.0v minimum. When I run the discharge, it will ramp up to 1.5A discharge and then drop to zero. The charger measures ~3.12v when this happens, but I multimeter shows the actual voltage only drops down to 3.28v. And then it goes back to 3.33v.

Any ideas?

EDIT: NVM. I set it to 1.4A and it works now. I read somewhere that max discharge is 5w, so that must be the limit with these.
 
Bigger cells are certainly easier to deal with. Just make sure you use caution dealing direct with China. I'd look for a company that people in the US have had successful dealings with for starters.

You would need 8 of those cells to make a 100ah 12v battery. You can get that capacity battery from a US retailer for ~$650. If they will really sell them shipped to you for $50/ea that would be $400. Doesn't look that enticing to me.

Here is the manufacturer site with more info: https://gebattery.en.alibaba.com/product/1855335861-0/GEB_lifepo4_battery_50ah_3_2v_lifepo4_cylindrical_battery_cell_50ah_55380.html

They want $100/ea with a 50 cell minimum. Not cheap.
 
rruff. I deal with suppliers on alibaba all the time and never have had an issue yet. I sent a request for pricing on 12 pieces. The link I attached above only required a 5 piece min. Of course if the quote comes back @ $50, that wouldn't be very cost effective.
 
I'm slightly bummed. As I posted earlier I bought 180 cells with the following initial voltage results.

115 were between 3.20-3.37v.
49 were between 2.80-3.19v.
10 were between 2.0-2.79v.
6 were ~1v.

I've tested 5 cells that were <2v including 2 that were over 2v when I first tested, but dropped to ~1.7v after I got them. All were charged to 3.6v and discharged to 2v at least 3 times. The best was 4.5ah and the worst 3.9ah. But I wasn't expecting a lot from these.

I just finished cycling one of the "good" cells that was 3.30v. Only got 4.7ah out of that one. Testing another one now.

I wasn't expecting the full 5.4ah, but based on what others have gotten I was hoping for ~5ah. One thing that concerns me is what the degradation means for cycle life. If they are initially 5.4ah cells capable of 2000 full cycles when manufactured, does it mean I can expect 2000 cycles at a slightly reduced capacity, or are they displaying end of life behavior and going to be dead in 200 cycles?
 
On the same concern... I got the 120 cells. And there there sit. I checked the box and they are 2013. I do not have a "battery analyzer" but have a Fluke ... any way I can check these cells out before soldiering them all up? Mayhaps I am out of my league! Is there a way to test each one as is with the Fluke?

Then....Here's a silly question...once I get them into a four packs of thirty and soldered together into a big single unit.... I do have a battery tender that says it charges lithium batteries (BatteryTender)... should I hook it up and charge them?
 
What does your Fluke do?

EDIT: Also, I'd be curious what your voltages are. That is an easy and quick thing to check. I'll probably see if I can get my low voltage cells replaced.
 
buckland said:
Just a fancy volt/ohm meter
Click to expand...
You can check the voltages then.

Your charger will probably work, but I'd cycle the 4 packs of 30p first before you do the whole thing. That way they will be balanced when you start.
 
I wouldn't stress too much about the results you are seeing. My 120 cells give me a measured 150Ah of capacity (20 hour rate) without pushing things (charge to 14.4V (3.6V/cell) discharge to 10V (2.5V/cell). All I did was set aside a few cells that measured low voltage, I did not capacity test individual cells. There very well maybe a few weak cells in my pack, but even a totally dead cell only drops the capacity by 3%, and if the weak cells are distributed across the pack you can even have 4 dead cells and only drop the capacity by 3%.

In your case, I would probably not use the cells that were < 2V, but use the rest. If you were running you battery test with a single cell a 1.4A, and you got 4.7Ah out of the cell - that is actually pretty good. At 1.4A you were discharging the cell over 3 hours or at a rate of 0.3C. In practice you will be discharging the battery over 20 or more hours - which will lead to a higher effective capacity. As for the longevity - 80 - 90% of capacity after 5 years of shelf life is not something I would be upset about.

It is good to think about these things, but it is also possible to over think things.

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