4Springs' Brumby

Post up a thread for your EV. Progress pics, description and assorted alliteration
francisco.shi
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Re: 4Springs' Brumby

Post by francisco.shi »

This is looking good.
Are you making the BMS? I assume you are because it bolts to the end so you would have had to make the board to match the hole spacing.

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Re: 4Springs' Brumby

Post by 4Springs »

francisco.shi wrote:
Wed, 01 Jan 2020, 05:51
Are you making the BMS? I assume you are because it bolts to the end so you would have had to make the board to match the hole spacing.
Yes, this is the second version of this BMS that I've made this year. The other one was for a home storage battery.
That hole spacing is very tight! Looks like I'll have to trim the tab on each cell. The tabs look like they're lined up, but fractions of a mm difference mean that the tabs get chewed up by the bolts.

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Re: 4Springs' Brumby

Post by francisco.shi »

The spacing was a bit tight. I didn't want to end up with a weird spacing.
The screws are generally less than 5mm so they should just clear.
What I found was that getting the tabs to line up perfectly was the problem.
What I did to get around that problem was to make a plastic U shape with the inside of the U at 45mm. Then clamp the cells while the tabs are held by the U. Once I did that it solved the problem.

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Re: 4Springs' Brumby

Post by 4Springs »

I'm just starting to assemble these modules.
I'm used to LFP cells, which have a tinned copper cathode, and an aluminium anode. I polish these immediately before assembly to remove any oxide coating.
I went to polish one of these aluminium tabs, and it got duller instead of more shiny. Perhaps these aluminium anodes are tinned? If so it will make assembly much easier, just give them a wipe down with metho.

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Re: 4Springs' Brumby

Post by francisco.shi »

You just need to polish them to remoce the oxide layer and quickly apply some electrical contact grease and clamp them. That is what I did and it seemed fine the contact resistance was as low as the contact on the copper side.

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Re: 4Springs' Brumby

Post by jonescg »

Yes they will probably be nickel plated so won't need much preparation. The contact grease is always a good move.
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Re: 4Springs' Brumby

Post by francisco.shi »

Only the copper tabs are nickel plated. I had a lot of trouble with contact overheating on the aluminium tabs until I removed the oxide and applied contact grease.

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Re: 4Springs' Brumby

Post by 4Springs »

francisco.shi wrote:
Thu, 16 Jan 2020, 09:20
Only the copper tabs are nickel plated. I had a lot of trouble with contact overheating on the aluminium tabs until I removed the oxide and applied contact grease.
Ah, thanks for the clarification. I'd started assembling without polishing.
IMG_0364.jpg
IMG_0364.jpg (874.07 KiB) Viewed 194 times
This stuff really does look like a plating. If you found it better to remove it though, then that's what I'll do. All 200 cells worth (double sided).

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Re: 4Springs' Brumby

Post by francisco.shi »

I think you are being too aggressive. I think I used some 600 sand paper and did it by hand. Only a few strokes and then quickly applied the contact grease. Then they could sit for a few min while I did the other tabs. From memory I think I folded the sandpaper and did both sides of the tab at the same time.

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Re: 4Springs' Brumby

Post by T1 Terry »

A 3M scotchbrite type pad https://www.ebay.com.au/itm/31Pcs-2-Rol ... SwU1hc20GI and some kero does a great job of cleaning the cell terminals and links. I prefer to use the thin copper links with the hump in the middle because it allows for some movement between the cells without loosening the bolts. I use Alminox to stop the oxidization build up returning and it seems to be good for 3 to 4 yrs before the whole process needs to be repeated.

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Re: 4Springs' Brumby

Post by 4Springs »

So I read Francisco's comment and tested 2000 grit sandpaper. It takes off a bit of the layer, but not the whole lot:
IMG_0366.JPG
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This was very similar to the scourer that I started out with:
IMG_0367.JPG
IMG_0367.JPG (110.99 KiB) Viewed 170 times
So I switched back to the scourer. The things in T1 Terry's link look quite similar, but onna stick. The scourer is what I'm using for the aluminium interconnectors. Then clean them off with metho and apply terminal grease. Then wipe 'off' the terminal grease because I really don't want much on there.
I've assembled 15 of my 200 cells in a day Good thing we bought another car to use while the Brumby is out of action!

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Re: 4Springs' Brumby

Post by 4Springs »

Finally finished a battery module!
IMG_0371.JPG
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Screenshot at 2020-01-20 21-25-14.png
Screenshot at 2020-01-20 21-25-14.png (689.8 KiB) Viewed 44 times
So this is 30 cells, roughly 22 V, 7 kW, 30 kg.
5 cells in parallel, 6 in series.

The main terminals are at the top. Other things you can see are:
  • Black wires going to red/black Anderson connectors connect to the heaters. There are three heaters sandwiched between the cells, connected in series, each with 3 ohms of resistance wire. Connected to a 20V supply (such as a laptop power supply), this provides about 50 W of heat into the cells.
  • Tan-colouored Teflon sheets between some cells. I sandwiched the heaters between two of these Teflon sheets, to provide some heat-resistant electrical insulation. But I noted that where they came out over the terminals at the end, they provided some level of whoops-proofing against shorting terminals when doing up the bolts. So I inserted some even when there was no heater there.
  • Blue/Black wires are BMS communication connections. These run from one BMS board to the next, daisychaining through the six boards.
  • Copper-coloured wires with red terminals are from the BMS (mounted on the negative end) to the positive end of the cell. The two wires are one for current and one for voltage sense.
  • Perspex cover over each end, held on with Velcro. Not exactly IP rated, but enough to reduce the likelihood of accidentally shorting out on something.
The threaded rod means that I can compress the cells somewhat. Nothing like the 15 psi recommended by the link that Francisco gave - that would be 1000 kg worth of compression! But fairly compressed.

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Re: 4Springs' Brumby

Post by jonescg »

One down 7 to go?
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Re: 4Springs' Brumby

Post by T1 Terry »

4Springs wrote:
Thu, 16 Jan 2020, 17:14
So I read Francisco's comment and tested 2000 grit sandpaper. It takes off a bit of the layer, but not the whole lot:
IMG_0366.JPG

This was very similar to the scourer that I started out with:
IMG_0367.JPG

So I switched back to the scourer. The things in T1 Terry's link look quite similar, but onna stick. The scourer is what I'm using for the aluminium interconnectors. Then clean them off with metho and apply terminal grease. Then wipe 'off' the terminal grease because I really don't want much on there.
I've assembled 15 of my 200 cells in a day Good thing we bought another car to use while the Brumby is out of action!
The stick bit is to put in the drill, then you can polish the plates in a wash tub or in a container part way full of kero or metho, or just dip the pad in the kero/metho every so often to wash away the oxide build up and add a bit more fluid to wash away the rubbish as you polish. The scourer pad is probably ok if you don't have a lot to do each time, but I can't imagine how my arms would feel after doing the number we have to do on each install :lol:

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