Small powerwall build

Headrc

100 W
Joined
Aug 11, 2015
Messages
169
I am building my first powerwall for a friend. It is a 14S24P using Boston Power Swing 5300 cells and the Batrium BMS system.

Here is how I am building the packs for this small powerwall. Since this is for a home application for safety I wanted to fuse at the cell level. I actually went with 6.3A fuses. They should blow about 13A or a dead short and as such provide what I want ....which is protection against a dead short or some other catastrophe ....and not impede current in normal use. This is going to be a 14S24P powerwall with Boston Power Swing 5300's, all new batteries and the Batrium BMS. It is meant to be able to be moved around if need be and for all individual parallel packs to be able to be removed in case of any problems with that pack. Additionally if I want to expand it I can just add packs in parallel at the bottom of it and not have to invest in more Batrium longmons. Regular continuous current has been analyzed to be 60 amps with possible spikes of 150 amps so this configuration should handle it with no problem.

I fabricated brackets out of steel and then wrapped them with silicone tape to prevent shorting with the Batrium Longmons that will be mounted on the top of the batteries with ziptie holders. This is so the packs can be mounted vertically on a wall. I am also building a box for all of them and the batrium. The box is painted with intumescent paint which is supposed to form a foam barrier and be at the very least a fire retardant in case something like that might happen. There is 1/4" ABS plastic in between each pack. I think I may cover the front of the box with 1/4" acrylic and have ventilation ports on the sides of the boxes and probably hook up some fans but I really don't expect this pwall to be experiencing significant heat issues as the normal load will only be about 60 amps. The intumescent paint is by Firetect and you can check it out here: https://www.firetect.com/

The packs are spot welded to the batteries on the positive side with 1.5MM pure nickel which is then soldered to the busbars. The negative side has the 6.3 amp fuses soldered to the battery as well as the busbar. I tried a setup where I spot welded nickel tabs to the negative side of the battery then soldered the fuses to it and the busbar but it was just too messy for my taste so I went with just soldering on the negative side. My spot welder is the Kweld and good welds can be accomplished at as little as 15 joules with it.

I want to implement a shunt trip breaker with this powerwall but still need to either buy the expansion board ....or figure out how all that works with just the mosfets on the Watchmon4.

That's it for now .....comments are always welcome.

Richard

Powerwall parallel pack #1.jpgPowerwall Parallel pack #2.jpgPowerwall Parallel pack #3.jpgPowerwall Parallel pack #4.jpgPowerwall Parallel pack #5.jpgPowerwall Parallel pack #6.jpgPowerwall Parallel pack #7.jpg
 
Headrc said:
It is meant to be able to be moved around if need be . . This is so the packs can be mounted vertically on a wall. I am also building a box for all of them and the batrium. The box is painted with intumescent paint which is supposed to form a foam barrier and be at the very least a fire retardant in case something like that might happen.

Glad you are thinking about safety.

My #1 suggestion - use this ONLY OUTSIDE. Again, use this ONLY OUTSIDE. And put it far enough from the home that a fire will not put the structure at risk. We have had people's homes burn down from perfectly good battery packs lighting off. We even have someone right here on ES lose their garage from a battery fire. And no, some fire retardant paint won't keep this from happening if a cell lights off.

It's great that you are helping your friend with this. But I am sure you would be very upset if something you built for him contributed to him losing his house - or his life.
 
Thanks. Yes these will be installed in a small outbuilding holding all of my friends solar equipment. It is located about 30 feet from his house. The link to the fuses is this:

https://www.ebay.com/itm/100pcs-Glass-Tube-Fuse-Axial-Leads-3-6-x-10mm-6-3A-6-3Amps-F6-3A-Fast-Quick-Blow/290945050705?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

It took about 3 weeks to get them.

I have a large supply of the Boston Power batteries ....and have found them to be great batteries for many applications. They should perform very well in this situation in my opinion. LFP or LTO would be a lot more $$. The Boston Power batteries are also cost efficient when compared.

I appreciate everyone's comments.

Richard
 
Thanks, 10A version here, what I'm after.

https://www.ebay.com/itm/100x-Glass-Tube-Fuse-Axial-Leads-3-6-x-10mm-10A-10Amps-F10A-Fast-Quick-Blow-250V/300932931000

Have you tested how sensitive / fast / reliable they are?
 
I did try to test the 6.3A using the method of the hair dryer coil etc. I do not have a bench power supply to test with at this time. The hair dryer coil method only got me up to 10 amps (and hot there!) So I could not really get the 6.3A to blow at what I expect to be 13A judging by testing some lower rated ones from the same seller. They usually blow at about double their rating from just an applied current. However a dead short was instantaneous of course ....which I think more of a real world scenario for this application. The current draw is going to be very low compared to what these batteries can produce. These batteries are rated to go up to 13A continuous discharge ...so 24P means the battery could handle over 300 amps. No where near what the load calculation indicates it will be. But of course things can happen which is why I am fusing these packs. I also did not want to limit the current capability of these batteries as a result of fusing.
 
Well they will have resistance and cause some voltage drop of course, as every connection / transition does.

I'd love to see a side-by-side test but as you say that takes precise gear
 
Yep I know they will induce some resistance which is why I wanted to use as big a fuse as I thought applicable. But the safety factor offsets that.
 
Yes I have had a garage fire . The fire department first truck couldn't get the pump to work and 20 minutes later the second truck oh they did ask me where the closet fire hydrant was . Then before they left one fireman looked at my 100 ft of garden hose and said we could have just used it { as the fire was very small but the damage was very great}. The water from the hose made the heat rise and melt all ski"s fishing poles hanging from the ceiling. If it didn't melt the black shoot can"t be removed the brick wall had to be sand blasted. Want a 18650 pack but ? Now live with the weight of lifepo4 but long life and level discharge 1,390 cycles. Where"s the next great battery ? Sorry I had to vent.
Let us know how many cycles these pack goes and balance.
 
The batteries are rated at greater than 3000 cycles with an 80% DOD. That is at .5C. I plan to discharge to 3.1 so so we shall see depending on all the variables. Balancing should not be a problem being that they are new batteries and I will be using the Batrium system. But of course this is for a friend and it will be up to him to really manage everything properly ...but he should have all the tools to do it.
 
Nice cells too, but wish they'd put proper post/bolt terminals like Headway.

For a powerwall I'd have gone LFP, safety more important than energy density, and cost goes to nothing when you can make them last decades.
 
OSN has a post spot welder machine but theheat to spot weld a post after cell is made is questuionable. It would have to be done before in production
 
The Headways/LFP are nice ...but again there were reasons for using these cells. The Boston Power cells really are great batteries ...and of course I have a good quantity of them. I have done a number of projects with them and have several others build batteries for things like Ebikes and they are really happy with them. And no problems that I have heard ...in fact I had one person state they were like Zombies and would never die. LOL Then the LFP/Headway cost was an issue. All in all I am quite comfortable with the build ...especially with the safety I am adding. And yes the Batrium is quite a BMS system ....not cheap but very capable. It also adds another level of safety.
 
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