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Safely use DIY powerwall in van?
#1
I'm planning to move into a van for University and I really like the idea of creating a battery pack from used lithium-ion batteries instead of paying 5 times more for something on the market. I've read a lot and I'll read a lot more about it if I decide to do it but it seems like it's generally seen as a big fire hazard. Is there any way to make a battery pack from used lithium-ion cells that would be safe enough to consider having in a motorhome? I haven't heard a lot of stories of these projects catching fire but I've seen a lot of posts about how unsafe it is even with a BMS and people saying not to do it.
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#2
I would use LiFePo4 instead. They are generally safer including alot more cycles. With that said they also only have half the total capacity.


Would i build one myself? Yes i would build with lithiumIon but only if i cannot get LiFePo4 instead. If i would do Liion that would be an encapsolated insulated box that have double sides and venting is to the outside of part where you sleap. This if i use 2nd hand.
If using new cells i would only do a normal encapsulation but still venting to outside.

The reason is rather simple. they can catch fire if misthreated. They are violent if they do it. There arent any good tests for 2nd hand cells like we do it.
Korishan and leftthegan like this post
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#3
(01-28-2020, 11:07 AM)daromer Wrote: I would use LiFePo4 instead. They are generally safer including alot more cycles. With that said they also only have half the total capacity.


Would i build one myself? Yes i would build with lithiumIon but only if i cannot get LiFePo4 instead. If i would do Liion that would be an encapsolated insulated box that have double sides and venting is to the outside of part where you sleap. This if i use 2nd hand.
If using new cells i would only do a normal encapsulation but still venting to outside.

The reason is rather simple. they can catch fire if misthreated. They are violent if they do it. There arent any good tests for 2nd hand cells like we do it.

Thank you for the educated opinion! LiFePO4 is definitely my second choice moving towards being the first. It's just the cost and added weight keeping it back but it seems relatively cheap compared to other options if you get the cells individually and much lighter than options like AGM. I'll look into those some more.
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#4
(01-28-2020, 11:26 AM)leftthegan Wrote:
(01-28-2020, 11:07 AM)daromer Wrote: I would use LiFePo4 instead. They are generally safer including alot more cycles. With that said they also only have half the total capacity.


Would i build one myself?  Yes i would build with lithiumIon but only if i cannot get LiFePo4 instead. If i would do Liion that would be an encapsolated insulated box that have double sides and venting is to the outside of part where you sleap. This if i use 2nd hand.
If using new cells i would only do a normal encapsulation but still venting to outside.

The reason is rather simple. they can catch fire if misthreated. They are violent if they do it. There arent any good tests for 2nd hand cells like we do it.

Thank you for the educated opinion! LiFePO4 is definitely my second choice moving towards being the first. It's just the cost and added weight keeping it back but it seems relatively cheap compared to other options if you get the cells individually and much lighter than options like AGM. I'll look into those some more.
And - the LifePo4  'Y' versions can handle lower temps than non-Y and 18650.   Not sure where you'll be driving - but if you're driving in cold areas this might be a consideration.
Here's an example of a Y: https://www.ev-power.eu/Winston-40Ah-200...-40Ah.html
Notice "Operating temperature -45°C up to 85°C (discharging)" which is -25C lower than non-Y which typically bottom at -20C.
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#5
I would agree with the recommendation to use LiFePO4; however, my usual comments still stand - it's best to not use DIY battery packs inside your home.
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#6
LiFePO4 all the way if at all possible to do so. The simplicity and the easier matching of equipment to voltages is so much easier. And you can use more of the full capacity because of the voltage matching
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#7
I've only had one fire and that was with lifepo4, and its as violent as li-ion when it goes off. I've been using both li-ion and lifepo4 as house batteries in my van going on 4 years, as long as you don't overcharge them or short them out they are fairly safe. Just make sure you never puncture one, that is guaranteed to cause a fire everytime. 

Always use an overvoltage protection relay to disconnect the power source/solar panel as a deadman switch. Use some sort of overvoltage/undervoltage audio alarm on your battery also. The only bms I recommend is one that uses contactors (to mechanically disconnect the power source or solar panel) , I use the chargery bms8 for that reason its never let me down and you can quickly program on the lcd screen what voltage you want the power to disconnect at. The chargery bms8 works with any cells li-ion or lifepo4 up to 8s, they also have 16s model for larger packs. 

And for building the pack I would do it right the first time and get a 12 volt tab welder, the best tool I ever bought for building battery packs, gets you a good professional job everytime, the reason I got the 12 volt tab welder was cost and also to build the packs inside my van. The first couple of pack I built I solder and that was very time consuming. I use the maletrics welder (cost in 100 dollar range) and it makes quick work of the job. Double check all your wiring especially the balance wires. Use as many fuses as you need, you can never have too many fuses.

Right now inside my van I have a 220ah 4s lifepo4, 2x 30ah 3s lion, 1x 65ah 3s li-ion, another 30 ah 4s lifepo4, 4x 10ah 4s lifepo4 jump packs, and I even keep a 28ah agm lead acid battery to run my tab welder and as a spare engine start battery.

The only fire I had was due to complacency, I was taking a lifepo4 pack apart and I shorted out a cell which punched a hole in the side, I heard lifepo4 was a safer cell so I was rushing, I learned the hard way that lifepo4 is as dangerous as any other lithium when mistreated.

Over the years I was more scared of my propane heater catching my van on fire then my lithium batteries, I got rid of propane heater.
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#8
An idea I just had: how about placing the batteries inside a roof box? IF something should happen, that's probably the place that will cause the least harm/damage as fire and fumes would rise up and away.
And cover it with solar panels to keep it charged as well as in the shade.
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