Low cost DIY Lithium camper batteries.

[rruff]

Just finished cycling the 2nd "good" battery (3.31v initially) and only got 4.2ah out of it. I got more out of the 1v batteries.

I know that a slower charge and discharge would get a little more out of them, but not much. Plus the testing I've seen posted on the internet regarding these and the Tenergy batteries is always ~5.0ah charging and discharging them similar to how I'm doing it. Actually I'm discharging them further (to 2v). Wish I could adjust that to 2.5v but it doesn't appear I can on the Imax B6.

It looks like I'll be lucky to get 4.5ah on average. Which would be fine, but I wonder about cycle life.

Do you understand my question about longevity? Usually they spec 2000 cycles to 80% capacity. What happens then? Do the next 2000 cycles drop you another 20% to 64% of initial? Or are the batteries about dead? Since I'm already at ~80%, I don't want to bother with them if I can't expect them to last.

 

[rando]

What are you are seeing is called 'calendar aging', in that it is due to the age of the batteries, not the number of cycles. Your cells still have effectively zero cycles on them. My understanding is that the two effects are largely independent - ie should still get 2000 cycles on your battery, it will just be starting from whatever the capacity you are at now. Also realize that you will never actually put your batteries through 2000 cycles. In ~60 nights of camping I only put ~10 cycles on my previous battery, with 'a cycle' defined by my BMV-700 as a discharge below 60% SOC. At that rate, even 200 'cycles' would last me far longer than I am going to own the camper, and calendar aging will dominate. With my new large lithium pack, I normally only use 20-30% of it's capacity, so it is likely that calendar aging will be a bigger factor than cycle life going forward.

I am also a little surprised that you got such different numbers with back to back cycles on the same cell - makes me wonder if your charger/discharger is really measuring what it should be. Can you take one of your 'good' cells and run a few charge/disacharge cycles and look at he variability.

 

[rruff]

Thanks! I'm fine the lower capacity if they will last. I have a buffer. It will probably be enough even if I get a fridge later. I'm going to be nearly full time, but even then 100 eq full cycles/yr would be a lot. So 20 year cycle life.

I don't get much variation on a specific cell after a couple cycles. There is a big variation between cells, however. I'm on the 3rd "good" one and it looks close to the 1st, which came to 4.75ah discharge. The 2nd was 4.19.

Efficiency is >90% which seems pretty good.

 

[buckland]

Okay back to kindergarten. Here is a shot of my horrendous first attempt at soldering. It ain’t sticking. Strangely enough the solder gun tip is also soft and bending w/o much pressure. But as you can see it isn’t working. I cleaned with alcohol, cue tipped each with a dab of flux (water soluble) then pre-tinned the copper... then sat the iron on the wire touching the solder to wire. Any idea with in the world I am doing wrong?
No pain no gain.

 

[buckland]

Photo one

 

[photohc]

IMG_4484.JPG
Photo one

Make sure the area of solder is clean. Apply a small amount of flux prior to solder. I used a Qtip. Apply solder to cell without the wire first. Then apply solder to wire, separately. Next touch the wire (with the pre-soldered area) and apply heat. It looks like you don't have enough heat applied. You shouldn't have to apply pressure. The solder needs to flow with just the heat. Good luck.

 

[rruff]

Okay back to kindergarten. Here is a shot of my horrendous first attempt at soldering. It ain’t sticking. Strangely enough the solder gun tip is also soft and bending w/o much pressure. But as you can see it isn’t working. I cleaned with alcohol, cue tipped each with a dab of flux (water soluble) then pre-tinned the copper... then sat the iron on the wire touching the solder to wire. Any idea with in the world I am doing wrong?
No pain no gain.

I thought you had acid core solder? If so, you need acid flux. Or you need different solder.

I'm using rosin core solder and a 60W iron. I sand and clean (with alcohol) the cell and wire. Then I just melt the solder on the iron, slop it on the cell and wire, and rub it around with the iron for a few seconds. I know this isn't good technique, but I got good adhesion.

 

[Vic Harder]

No offence rruff, but I think photohc's technique is neater and perhaps will get more consistent results.

 

[rruff]

No offence rruff, but I think photohc's technique is neater and perhaps will get more consistent results.

I agree!

I'm planning to do it the "right" way, but was experimenting with how careless I could get. And my flux hadn't arrived yet. I'm going to use that as well.

I think sanding the cell surface is a good idea, since it is the toughest part to adhere.

 

[buckland]

Okay ...I guess I was anxious about applying the soldering iron tip on the battery terminal... it is a 100 W iron. I will try and pool a blob (technical term) on the terminal ...the copper wire is tinned. then place iron on top of wire and the blob should liquify.

I am using rosin core solder 40/60 and I am using a water based plumbers flux (as Rondo suggested) ...I do have regular flux (plumbers) if the water base is causing the problem.

Oh BTW... thanks for the steerage.

 

[rruff]

I cycled a couple batteries before and after soldering, and there was no change. I think these big batteries are fairly tolerant of heat.

Pretty sure regular plumber's flux will be acid, so don't use that unless you have acid core solder.

 

[buckland]

I believe I will buy some 'no-clean' rosin flux tomorrow. I'd like to get good at this... a good skill to develop. Probably like 'mudding' though... as soon as the job is done you're really good!

 

[photohc]

For clarity, here are some shots of my build. Using tinned copper wire (easier to apply solder)

 

[buckland]

Thanks looks great.... a tad prettier than my glob fest. Pre tinned wire ... that is nice. I will get some flux and retry tomorrow

 

[rruff]

For clarity, here are some shots of my build. Using tinned copper wire (easier to apply solder)

Looks great! Did you happen to check your cells for voltage or cycle them?

I just discovered that the cells I got that had low voltage are rapidly degrading in voltage. There were 10 in the 2.0-2.8v range and now they've all dropped by about .5v. Only 1 is still above 2v. The ones in the 2.8-3.2v range have dropped a little, but not as much. The higher voltage cells (3.2-3.3v) show no degradation. They are being stored at room temperature.

Does anyone know why this would happen?

 

[photohc]

When I received my shipment, I only did a quick voltage check. I discovered 3 that fell below 3v. If I held the meter to the cell, I could see the voltage continue to diminish. I asked the vendor to replace those cells and they quickly shipped me 5 replacements. I did not do a long term cycle. It would have taken a long time to complete. Ask them if you could get replacements.

 

[Vic Harder]

Looks great! Did you happen to check your cells for voltage or cycle them?

I just discovered that the cells I got that had low voltage are rapidly degrading in voltage. There were 10 in the 2.0-2.8v range and now they've all dropped by about .5v. Only 1 is still above 2v. The ones in the 2.8-3.2v range have dropped a little, but not as much. The higher voltage cells (3.2-3.3v) show no degradation. They are being stored at room temperature.

Does anyone know why this would happen?

wow, that sucks. Is it still price competitive?

 

[rruff]

wow, that sucks. Is it still price competitive?

I'm not sure it's even a problem. Just odd that cells that have been in storage for 4+ years would be showing any rapid changes at this point.

I've cycled a few of the low voltage cells and they seem to perform almost as well as the high voltage ones.

 

[rando]

Sounds like maybe you have a relatively low impedance (ie resistance) meter. The meter itself is loading down the batteries and causing the voltage to drop. Otherwise you are right that it makes no sense that a battery that has sat for 4 - 5 years would suddenly start dropping voltage quickly.

 

[rando]

Very nice job! This is should be the 'how it should be done' example.

For clarity, here are some shots of my build. Using tinned copper wire (easier to apply solder)