Xenu's small powerwall build.

lordxenu

Member
Joined
Aug 17, 2018
Messages
61
Hey all,

I came here after finding several YT vids that turned out to be members here and I've decided to join in on the fun.

As chance would have it, I happen to have about 312-320 brand new cells including

92 x Panasonic NCR18650B @ 3400mAh
100 x Panasonic NCR18650BE @ 3200mAh
120 x LG B4 @ 2600mAh

So since I already have these cells, and they were doing absolutely nothing on my shelf I've decided to use them to build a powerwall. I am by no means an expert, nor an electrician ... but I do like DIY and electronics and I have built some off-grid systems in the past with lead acids and currently have a 4kW grid tie solar PV system at home with hot water diversion unit.

So I've decided not to go grid tie with this system, but instead to use an independent set of solar panels already mounted on the roof that provide (in theory) 960W - with 3 x Canadian Solar 320W panels all in series, one reason is that here in the UK we don't do net metering, instead we provide what the goverment calls the feed in tarrif; which is basically a system that says I get paid about 0.14 per kWh that my system produces ... and they just "assume" 50% of it gets exported, so I get another 0.04 on top of that. But this tarriff says you can have a maxmium of a 4kW system... so for that reason, and because I want a backup system that can operate when the grid goes down I have decided to go for a hybrid inverter that will charge batteries from solar (and AC if necessary) and includes a transfer switch to transfer loads to AC when the batts are dead.

I have a few devices that I'd like to stay on in the event of a grid failure (which to be fair is rare, but has happened about twice in the last two years for about 10 minutes) so I'll hook them into the inverter and let them run from that and they can swap back to grid AC if the batteries don't get charged enough.

I have decided that I'm going to use a 14s system and i'm going to arrange my packs like this

84 x NCR18650Bs in 14s6p = approx 20Ah at 58v (going to charge them to 57.4v ~ 4.1v per cell)
98 x NCR18650BEs in 14s7p = approx 22Ah
112 x LG B4 in 14s8p = approx 19.2Ah

All in all i should have somewhere close to 3.5kWh pack to play with. I'm going to mount it outside my house and bring the wires in (only on the wall outside, 1-2 metres max) to the inverter which i'll then connect to my stuff inside.

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What I have not decided yet is if I should make one giant battery pack, or split them into three. Splitting has the advantage that all the same type of cell will be bonded together. One large cell means it's easy to use a BMS like batrium with only 14 longmons ... not 14 x 3...so that point I'd like to ask if anyone has any advice on?

Today I purchased the 48v 3000W hybrid inverter. Not really heard of this brand but it looks very similar to the MPP Solar style ones.
This one is 230V AC (I live in the UK) not sure if links are ok so i'll just post a pic. With today's ebay discount, I saved 50 on the total price of it.. so I'm really hoping this one works ;)

Let me know what you think of my proposed design and I'll be updating and adding images as the stuff arrives.
 
Some updates:

Not buying batrium (as It's out of my budget for now) so I'll use some Chinese BMS' and hope they don't burn me.
Therefore I don't care too much about large packs or multiple small etc... so I've decided actually to build two packs:

1 x 14S13P 2.4kWh pack
1 x 14S8P 1.3kWh pack

and eventually i'll replace the LG 14S8P pack because they're a bit low capacity compared with the panasonics. but for now it's all i have so... yeah.

I have not decided how to wire up the batts still. I would like to spot weld, but I also like the idea of fusing so as not to destroy the pack... yet I have done a little bit of research here and both LG and Panasonic say "do not solder the battery" in their data sheets. But yet it would seem pretty much everyone does this. Watched one of the UK guys doing a build in his shed and he's like "uh .. i don't think I'm putting too much heat into the batteries" but makes zero attempt to actually take readings .. meanwhile ebikeschool video actually bothered to do a proper test and saw that holding the iron onto the battery for just 2 seconds produced temperatures of up to 100C. So I'm really really not keen on soldering brand new batteries but what to do? I want fuses .. so I tried an experiment to see if I could spot weld nickel strips and solder fuse wire to that.... but I simply cannot get the solder to stick to the nickel.. any idea why ? Even with flux.

Picture time:

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yeah PCBs nice. i've seen your thread earlier and i saw some vids of jehu doing PCBs. It's certainly an interesting approach. are you selling your PCBs ? I might give a few a try.
 
I spot weld 1.5A fast blow glass fuses direct to the battery positive end and then spotweld the other end of the fuse to nickel strip. The nickel strips are hotglued to the battery pack inbetween the cells as to not contact the battery terminals. On the negative side, I don't fuse. I just spotweld nickel strip straight to the battery. I do not like the idea of soldering batteries either.
To connect battery pack ring terminals, I run a length of 2.5mm2 copper wire along the main section of nickel strip and I solder it to the strip. I use standard electrical rosin core solder from screwfix. I rarely have a problem with it flowing onto the nickel and that's with just a 40W iron.

Good luck.
 
Some more updates:

Purchased some BMS. One works, other one doesn't work at all. Not going to bother to try to diagnose or repair it.. instead the seller will send another.
In the mean time I've been practicing my spot welding. Not going to go down the fuse route. They're all the same battery, brand new, I'll stick with what the manufacturer told me to do and spot weld. I would have really liked fuses ... but whatever... maybe next time.

I ran out of nickel strips so here's a semi-finished one


Also does anyone know what I should cover these batts in ? As in i want to contain them so that terminals cannot be touched , things dropped on it etc.... should I use card/paper ? I can't find a heat shrink large enough.
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Nice work. Though, I assume you're not done spot welding(?)
Those cells with only a U connection, like the left half, should be finished like the ones on the right half. Otherwise you'll potentially have heat spots as current is flowing around the cells.

I'd personally just plot the pack on a piece of plywood and make a box for it. Or just tape heavy cardboard around it. Then paint the box
 
Keith on eBay sells Nickle, MASSIVE heat shrink & Kapton tape all will help you out https://www.ebay.com/sch/18650ed/m.html?_nkw=&_armrs=1&_ipg=&_from=&rmvSB=true

Kapton Tape - https://www.ebay.com/sch/m.html?_od....TRC0.A0.H0.Xkapton.TRS5&_nkw=kapton&_sacat=0
Nickle - https://www.ebay.com/sch/m.html?_od...TRC2.A0.H0.Xnickel.TRS0&_nkw=nickel+&_sacat=0
Shrink - https://www.ebay.com/itm/Large-Pack...hash=item1ee7ba293f:m:m2EZrmLaFh8KVgyS4MfMIXQ

New cells should be good for a long while with out fuses, all the ebike boys do it this method..

Pete
 
Korishan said:
Nice work. Though, I assume you're not done spot welding(?)
Those cells with only a U connection, like the left half, should be finished like the ones on the right half. Otherwise you'll potentially have heat spots as current is flowing around the cells.

I'd personally just plot the pack on a piece of plywood and make a box for it. Or just tape heavy cardboard around it. Then paint the box

Yeah not finished because I ran out of pure Nickel strips. More on the way.

Plywood seems fine.

Today I got this enclosure :cool: not sure if i will mount the inverter in there as well with some fans .. or not.


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hbpowerwall said:
Hey Pete.... love your videos !!!

Thanks for the tips buddy this is very helpful.
Did a back of a napkin calculation vs Tesla Powerwall 2 (UK one)
Price per kWh:
Tesla: 538
Mine: 425
 
personally I'd save the enclosure for your breakers and fuses and other switching as well as the battery and have the inverter outside as it looks goooood
 
jdeadman said:
personally I'd save the enclosure for your breakers and fuses and other switching as well as the battery and have the inverter outside as it looks goooood


Yeah I'm also concerned about proper ventaliation. Guess I won't mount it inside there. I'm the kind that likes to play with equipment regularly so it would be a pain to have to unlock the cabinet each time. I think you're right. Mount it on the wall...
 
Thanks for the tips buddy this is very helpful.
Did a back of a napkin calculation vs Tesla Powerwall 2 (UK one)


Pete can't even napkin math :Dbut numbers look good lol
 
Some updates. The day approaches !!

1 of 2 batteries completed. BMS tested (cheap Chinese bluetooth BMS is really nice actually)

I'm going to complete battery number 2 this weekend and then power the inverter up.
So stay tuned for a weekend bonanza. Any tips for first builds ? Going to timelapse film it I guess i'm not much of a host when it comes to videos.

Anyway, enjoy these pics of my completed battery number 1




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Some more updates.

Unfortunately life got in the way (as it often does) and didn't get to complete it last weekend.
Then my sparky cancelled on me as he had an all-day job to go to.

But today, I've managed to mount the hybrid inverter, hook up the solar PV panels and crimp and attach battery cables.

Next steps, hook up the batteries and get the sparky in for the AC connection.
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sorry about the rotation... they appear the right way up in my photo editor ?!
 
If your images are still getting rotated, please zip the original and add it as an attachment to this thread: Image Rotation Issues
 
Thanks Korishan. They seemed to come out ok when I posted it but after uploading a few were sideways. But if it happens and it posts like that then I'll make a note of it in that thread.

Cheers
 
and calling it quits for today. safety features fitted... 100A fuse disconnect... 80A DC breakers... auto fire extinguisher :D


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lordxenu said:
All in all i should have somewhere close to 3.5kWh pack to play with. I'm going to mount it outside my house and bring the wires in

It is not wise to charge lithium ion cells below freezing so you may need to think about insulation, heating for winter and cooling in summer.

Panasonic NCR18650B datasheet specifically says not to charge below0'C and for temperatures below 10'C to limit charge current to 0.25C.
 
w0067814 said:
lordxenu said:
All in all i should have somewhere close to 3.5kWh pack to play with. I'm going to mount it outside my house and bring the wires in

It is not wise to charge lithium ion cells below freezing so you may need to think about insulation, heating for winter and cooling in summer.

Panasonic NCR18650B datasheet specifically says not to charge below0'C and for temperatures below 10'C to limit charge current to 0.25C.


yes agreed. I am keeping them inside the house for now... then they will be moved to a log cabin structure that I intend to build in my back yard. But for now, they are in my house. Hence the automatic fire extinguisher to keep the missus happy ;)
 
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