Low cost DIY Lithium camper batteries.

[rruff]

I'm planning to just glue my cells together. Would take up less space.

 

[buckland]

That’s a good idea. Using a hot glue gun?

 

[rruff]

Maybe. It's paper so anything would work.

 

[rando]

Did you have the issue of the copper being high due to the plastic battery cage?

IMG_4219.JPG

Mine was a little high, but once I started soldering the wire just melted a little groove into the plastic between the cells. It actually works out pretty well, because one things cool down the groove locks the wire into place. I used needle nose plyers to position the wire as I soldered it down.

 

[buckland]

That sounds good... I was mulling over the ways to do this. Glueing would not get them that closer ... maybe a 1/4” overall. Again thanks for your feedback. Just got a ten week old rescue puppy and dang she says she’s the center of the universe so it is hard to stay on a job for more ham 8 seconds.... man do they like to chew everything.

 

[rruff]

I finally got my batteries today. The paper cover pulls right off, and there is a plastic disk that covers the top (+) terminal. Thinking I'll remove the paper covers and hot glue them in a staggered formation to take up the minimum space. Does that seem risky? It doesn't look like I'd have much chance of causing a short, but I haven't done anything like this before.

 

[rando]

As long as you are extra careful during assembly, I don't think removing the paper cover would be an issue. One idea I had for assembling in a staggered formation was to make some dummy 'half cells' out of HDPE or wood or something. You could use these half cells to fill in the recessed end of each row, so that you end up with a rectangular brick of cells. That way you could circumferentially strap the whole pack with strapping tape before you heat shrink it to really solidify the pack.

 

[buckland]

I was wondering if the battery, when done will require me to change my SunSaver 20L controller? I have a 160 W panel on the roof and was also considering with swapping this out or adding to it, the 120 W flex panel:

https://www.solarblvd.com/products/solar-cynergy-flexible-bendable-120-watt-12-volt-solar-panel-3/

Do I need to get a different kind of controller?

 

[rruff]

I'm certainly no expert, but I wouldn't trust the batteries to the BMS alone. I'd get a programmable controller that allows me to set parameters just the way I want them. Particularly high and low shutoff voltages and no float. I'll probably also add a temperature switch to prevent charging when it's below freezing.

rando mentioned earlier that a cheap way to boost alternator charging is to use a device that boosts 12v to 24v. Then use 24v solar as well, and an MPPT controller for your batteries.

I've hear nothing but bad things about flexible panels. I don't know if issues have been fixed at all (cell cupping, surface degradation), but I wouldn't consider one unless it had an aluminum backing, which is rare.

 

[rando]

I was wondering if the battery, when done will require me to change my SunSaver 20L controller? I have a 160 W panel on the roof and was also considering with swapping this out or adding to it, the 120 W flex panel:

https://www.solarblvd.com/products/solar-cynergy-flexible-bendable-120-watt-12-volt-solar-panel-3/

Do I need to get a different kind of controller?

You don't need to get a different controller, but one with adjustable voltages would be preferable. I use a Victron MPPT controller and have set all my charge voltages to be quite low, particularly for when the camper is not being used. I have the bulk charge set to terminate at 13.6V and float at 13.0V. This actually doesn't charge the battery all the way up, leaving it around 90 - 95% charged, which is good for keeping the cells in balance and for the life of the battery. If we are on a trip and need maximum battery power I will up the bulk charge cut off to 14V which helps bring the battery back closer to full, and the float to 13.3V which allows the solar panels to provide the power to any loads once the battery is fully charged. With the bluetooth charge controller and the app this is quick to do.

It is generally a good idea to have matched solar panels in terms of voltage and current. So either add another panel the same as your existing panel or get 2 of the Solar Cynergy panels. I am currently using 2 of the solar cynergy panels, and so far so good.

 

[Vic Harder]

rando, I'm curious about not wanting to fully charge the batteries. Is this a lithium chemistry thing?

 

[PaulT]

I'm curious about the same. While Li Ion is different chemistry than LiFePO4, my laptop recommends keeping the battery at 50% charge for maximum life if normally running on AC and I've read that Li Ion batteries should be stored with a 50% charge.

Paul

 

[rando]

I am doing it for two reasons - the first is cell balance. If you don't run your battery all the way down or charge it all the way up the series cells are less likely to get out of balance. In the 4 months or so that I have had the lithium battery the cells have stayed in balance on their own. It is is no huge deal if they do get a little out of balance, I can either rebalance them manually by pushing the balance button on the balancer or the BMS will take care of it on its own if I set the charge voltage higher. But if they stay in balance without any balancing required, why not?

The second reason is the storage issue. Supposedly it is best not to store lithium batteries fully charged, however from reading the literature this is a minor effect particularly for short term storage. In my case it is really a non issue because we are using the camper at least once a month, all year, if you put the camper away for 9 months out of the year it maybe more of an issue. But again, it is easy to adjust the charger so why not?

 

[rruff]

Rando, I've been checking my cells and noticed a pretty big voltage variation. 3.02-3.37v in the first box. Did you balance them before wiring? Thinking there might be some big current flows....

 

[rando]

I didn't do any balancing before making the packs. However I had about 10 extra cells (I bought a test batch before buying a large batch) and I put aside any cell that was more 0.1V away from 3.2V, about 5 cells out of 120. My original thought was that maybe these cells were bad, but I tested a few of the 'rejects' on a battery analyzer and they were fine. Once you wire them all together they will self balance to the average voltage. I wouldn't worry about large currents - the dV is not large enough to drive much current.

 

[rruff]

I put aside any cell that was more 0.1V away from 3.2V, about 5 cells out of 120.

I think I was less fortunate. I bought 180 cells.

115 were between 3.20-3.37v. Good. Most very close to 3.30v.
49 were between 2.80-3.19v. Probably ok.
10 were between 2.0-2.79v. Marginal.
6 were ~1v. Dead.

I heard somewhere that these have been sitting around for a few years. They were probably initially fully charged and then allowed to self discharge. I'll probably do a 4x40 cell battery for ~200ah @12v. There are enough in the 1st two categories for this.

You were right! I tested wiring the 3.37v battery to a 3.01v and there was no overheating.

 

[rando]

Anything over 2.5V is likely OK, just needs a charge. You can charge the individual cells with an RC plane style charger, or a lab power supply with some care. My cells had a 2015 manufacture date.

 

[rruff]

Thank you, I do not have a charger. Does this look like a good option? https://www.amazon.com/HOBBYMATE-Battery-Balance-Charger-Adapter/dp/B01NB9A36R/ref=zg_bs_2234135011_11?_encoding=UTF8&psc=1&refRID=AYJCQWW8NCSDQ6F0DT3A

I just checked the Chinese stickers on the sides of the boxes. Oct 2013.

 

[rando]

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.

 

[buckland]

Which controller would you recommend for current 160 watt panel but want to in eventually increase this to around 300 watts. And the phone app dongle to monitor?