Low cost DIY Lithium camper batteries.

very cool. I see I will have to add a BT dongle to my 75/15 MPPT controller, but that means I can't have the MPPT Control (physical guage) hooked up too. Maybe if/when I upgrade to a bigger/newer MPPT controller with built in BT, I can do this then.

Nice feature tho!
 
Unless you want it for the lithium low temperature cut off - I think this makes a pretty minor difference to charging. Great if you can add it through software for free, but not worth paying for.
 
Went at it again... I am nothing if not persistent.... wife would say stubborn.... my problem was my reticence to heat the battery top fearing damage to the cell. The battery wasn’t hot enough for the solder to stick. I have done one block of 30 both sides and though not pretty all I want is solid connection. BTW I check volts and got 3.32 from the block. IMG_5038.JPG
 
rando said:
Another quick update - 7 months in. My camper has been sitting for the past couple of months (busy with work travel) but now I am getting ready for some spring road trips. My battery has been sitting in the camper on the solar charge for the past couple of months (13.4V absorb, 13.1V float, so not really charging, just not discharging). I did notice that the cells had drifted (slightly) out of balance. The first cell in the chain was about 50mV lower than the other three cells. I turned on my balancer, but as K6ON pointed out, its balance function is very slow, and it had to pull three cells down to meet the 4th cell. So I plugged in my TB6 balance charger, and in a few hours, all the cells were at the same voltage (13.3V). I just checked today, a week later, and they are all still within 10mV of each other.

What I think happened is that I left the balancer plugged in over the past months, and it seems that it may draw the power it needs to operate off just the 1st cell - leading to a slightly increased draw on that one cell, and pulling it down relative to the other cells. Moral of the story, if you are not planning on using it, unplug the battery balancer!

Otherwise all seems to be well with the batteries.
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Rando, have you done or are you interested in doing another capacity test? It would be interesting to see if there has been any change.

I'm still "playing" with my individual cells; haven't built any packs yet. I've noticed that all the cells will all settle at 3.33v after a full charge, and stay there for several weeks anyway. I haven't recorded the amount of time they've been sitting unfortunately. But recently I've been cycling some of these cells again, and they not only have self-discharged a fair amount (~10% typically), they also fail to acheive their earlier capacity (~5% degradation).

I'm in no hurry to build the packs, so I think I'll do a proper experiment on cells that haven't been cycled yet to see what's up.
 
I would say that looks pretty good (well at least as good as my effort and I was an EE in a former life).

buckland said:
Went at it again... I am nothing if not persistent.... wife would say stubborn.... my problem was my reticence to heat the battery top fearing damage to the cell. The battery wasn’t hot enough for the solder to stick. I have done one block of 30 both sides and though not pretty all I want is solid connection. BTW I check volts and got 3.32 from the block.
attachicon.gif
IMG_5038.JPG
Click to expand...
 
I have not rerun my capacity test, as I would need to pull the pack out to do this. But I haven't seen any changes my installed pack that would cause me to be concerned - they idle at around 3.3 -3.4V when charged, and only really drop to ~3.2V when I have pulled about 40% of their capacity out.

I am still a little suspicious of the test methodology for the results below - they really don't make any sense. There is no way that one cycle will cause a 5% degradation, and self discharge on these batteries should be super low (1-3% per month, max). Are you sure your test set up really has the accuracy to make this sort of measurement?

rruff said:
Rando, have you done or are you interested in doing another capacity test? It would be interesting to see if there has been any change.

I'm still "playing" with my individual cells; haven't built any packs yet. I've noticed that all the cells will all settle at 3.33v after a full charge, and stay there for several weeks anyway. I haven't recorded the amount of time they've been sitting unfortunately. But recently I've been cycling some of these cells again, and they not only have self-discharged a fair amount (~10% typically), they also fail to acheive their earlier capacity (~5% degradation).

I'm in no hurry to build the packs, so I think I'll do a proper experiment on cells that haven't been cycled yet to see what's up.
Click to expand...
 
I'm using the Imax B6, same as before. Set at .5a charge and discharge. It tapers the charge current til it hits 3.6v, but the discharge runs at .5a until voltage hits 2v. When it stops discharging the voltage bounces back to ~2.8v after a couple hours.
 
Rando appreciate the positive encouragement. I am learning and when done will have an acceptable grasp. I am happy that that hurtle is over. Once done soldering I hope I will be able set up the battery monitor cell adjuster so that I can keep this investment running right. As is my two AGM batteries will suffice for this season and hope by fall to have this new one installed. I built a cabin in the woods and will move the 2 old batteries there with a 90 watt panel to keep phone freaks charged (god forbid they go silent for a few days!) some folks just feel safer... funny I feel safer in the woods then in the city but that’s me.
 
Rando
Started to think of soldering my ‘series’ wires between the four packs. In the attached 2 photos, the battery monitor clip (5) wires... how do I know if they are in the right place in the clip or does it not matter? IMG_5365.JPGIMG_5366.JPG
 
Buckland,

You need to follow the little diagram silkscreened on the back of the board - the orange (?) wire goes to the negative side of the whole pack, the yellow goes to the junction between the first and second set of cells (ie the +ve terminal of the pack with the orange wire on the -ve), the white wire goes to the junction between the second and third set of cells and so forth.....

It doesn't matter where on the junctions between the cells you attach the balance wires. The yellow wire could either go to the +ve terminal of the 1st pack or the -ve terminal of the second pack. The way I did it is to have all the heavy gauge wires from all the packs come to a junction block, and then tap the balance wires in there. You can see in the photo below - the wires on the right are from the individual cell packs, and the yellow wires on the left go to my protection PCB (my specific pcb only needed 3 as it used the main +ve and -ve wires to sense those voltages). You can also see the metal jumpers between the screw terminals that put the cells in series.

[sharedmedia=core:attachments:29381]
 
Okay I will suss this out. I think if I read it over a few times and "dry fit" it the logic should make it apparent. (one hopes!) Thanks...
You might remember I have the two battery monitors ...one that allows you to adjust voltage... I assume these wires also attach at the same points as the other balancer? I'll recheck that post and edit this if I put a photo. Yes the two 'balancers' are in post #64.
 
The connector for the balancer should be the same as for the protection PCB. Orange to overall -ve etc.
 
It has been about a year since I built this battery pack, so I wanted to give a quick update. I have camped ~30 nights using the lithium pack, but I have also left the fridge and fans running in the camper for a good part of the summer - so I would estimate the equivalent of 60 nights of use. In that time there have been no issues, with the deepest discharge around 60Ah (or down to about 60% SOC).

I was working on a camper project this weekend so I took the opportunity to run another capacity test on the camper battery. This was similar to the first test I ran right after building the pack (which yielded 150.3Ah) but I ran the discharge rate slightly lower at 7A, just in case the battery had degraded. After 20 hours at 7 A (so 140Ah), the battery was still > 12V under load, and jumped back up to 12.4V once the test completed, indicating to me that there was at still at least some capacity left. In retrospect, I should have run the test at 8A rate, but from what I can see the battery is still performing the same as it did last year.

Over the last year the pack has stayed in balance to within ~0.1V per cell, but I did activate the balancer once or twice, mainly just because I could.

I have made a few minor changes to my setup since first installing the battery:

1. I reduced my charging voltages - float is now 13.2V (really just offsets the loads), and my bulk charge cuts off at 13.6V. This probably only charges the battery up to 90% SOC, but that is still more than enough power for me. It should also keep the battery in balance longer.

2. Victron has added a remote battery temperature/voltage monitor to their lineup. This, coupled with a firmware update to the MPPT solar controllers, allows you to set a minimum charge temperature (3C in my case) so as to avoid the issue with charging below freezing. You can also view the battery temperature on the Victron app on your phone. In the winter I leave my ACR isolated when driving, and check the battery temperature before switching on the ACR. Low temperatures have not really turned out to be an issue - we keep the camper well above freezing when we are using it - so the only time it has ever been a concern is on the first day of a trip when the camper has been in the driveway unheated overnight and we are going to drive first thing in the morning.

So far this project has been an unqualified success, but I will try to remember to update this thread again in a year or so with how the system is holding up.
 
That sound real hopeful and glad it is performing well. I have not completed it yet as a number of serious things got in the way... just rolling with it as I can. BUT.... was wondering if my being in New England where I store the camper presently in the winter with the AGM batteries on board and an external solar panel keeping things charged up.... has worked fine for 7 years.... it gets down to 15 below zero sometimes at zero for a few weeks. But when I change to the lithium pack.... will I need to remove the battery and store in the house (basement is 50 during winter)? I have a 'battery tender' 4 amp I use for another project...should I keep it on that?
 
If you don't use the camper over the winter - just charge up the battery to ~80% SOC before it gets cold and then switch everything off (solar included). One of beauties of lithium is that is doesn't mind just sitting there at a partial SOC. In fact they prefer to sit at somewhere between 40 - 80% SOC than at 100% SOC. These batteries don't need or want a 'maintenance' charger.
 
Thanks on that ...that is good news. I think this will be great ....as soon as The cold weather sets in people will leave me alone enough to get back to the project. Thanks for thinking this one up!
 
Hi...thanks for the information. Hobbyist RC chargers and even my simple Fluke 87V multimeter rarely ever show any cell-cell difference larger than .015v - even when taken well down into the discharge knee beyond their recommendation, nor at the top when I charge with a voltage of about 14.6 and the absorb current is essentially zero. Neither of these is not good on a regular basis, and probably due to factory matching, they are still in balance. The components and their pcb assembly can also impact the value of knee voltage value. So, always consider the components rating when calculating the knee voltage discharge.
 
cwdtmmrs said:
What about using these if the price was comparable?

https://www.alibaba.com/product-detail/LFP75190S-high-power-Cylindrical-Rechargeable-Lifepo4_60559526654.html?spm=a2700.7724838.2017121.5.3eca3db0iE2lR8&s=p

cwd
Click to expand...
I am thinking of diving into the LiFePo deep end, with the above batteries.... unless there is less expensive option available? CWD, I have never dealt with Alibaba before... how does the negotiation process work?

Any suggestions on a BMS to use with these? I am thinking of building a 200AH (maybe 250) battery bank.

Rando, you use a BMS and the Victron BMV as well, right? What does the BMV get you that a BMS doesn't?
 
Vic,

Julian OH8STN, a ham in Finland, has built and documented DIY LifePo4 battery pacs. His larger one is 45 aH and he has links to supplier for the BMS and other parts that may be of interest.

Bestech makes his BMS.

rando is likely your best source for information on design and build.

Paul
 
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