APL's Pressure Contact Battery box

[fechter]

It might be possible to nickel plate the ends. I’m not sure how much current it takes or how long but I think it’s pretty easy. For sure bare steel will get rusty fast.

[APL]

The rust will come, but not before I get some tests done in the short term.

I also thought of plating the ends,.. the bottoms would be easy, but the tops are a problem because they have a positive charge and are so close to the neg can. It involves acids, and would be time consuming for hundreds of batteries. (But it's not ruled out if I can get over some hurdles.)

Otherwise, I'm still thinking that a dielectric grease or conductive paste is about the best I can do in this situation in the long term, but I have no experience with it. (I always thought that it was an oxymoron to use 'grease' and 'conductive' in the same breath.)
The manufactures all have great claims, and the forums are divided, as usual.

I did find this article about silicone dielectric grease that seems informative. But I still need to look into it more,.. might have to just try some various things out this summer.

Silicone grease; https://www.w8ji.com/dielectric_grease_ ... grease.htm

[john61ct]

Great article, really hard to get a handle on that topic.

Silver Paste is truly conductive...

[spinningmagnets]

dielectric grease is an insulator. It does not conduct current so that using it on electrical connections will not cause a short if it drips or oozes.

It prevents corrosion on battery terminals and electrical conductors by sealing everything away from the oxygen in the air.

Conductive paste (possibly with silver in it) will improve the electrical connection on pressure contacts, since the surfaces may not be perfectly flat.

When using connectors with silicone dielectric grease, the metal contacts "push through" the grease to make metal-to-metal contact.

[APL]

Thanks for chiming in on that guys, those are the two things I'll be trying out this summer,.. dielectric grease, and the silver paste.
Just a thin film on the contacts, enough to keep the oxygen off. Hopefully one of these will work well enough.

In the article he says that he uses dielectric directly on battery posts, which are high current, but it was still unclear to me if he means before or after assembly. If it pushes it out of the way, then I guess that's how it works.

Neither the batteries or contacts are very flat, so there's only one spot that makes contact. I assume that this is always the case.
Even with very flat contacts only one place on the surface will likely handle most of the current, since it always finds the shortest possible route. Welded cells only pass current through the weld spots, so I also assume that it doesn't take all that much actual contact area to at least work well enough? (could be wrong about all that)

[fechter]

You can put the dielectric grease on before assembly. It will squeeze out where the contact points are. I’ve used it on several projects and it doesn’t impede current flow.

[ZeroEm]

From cars to ebikes most of the connections are pressure contacts. All connections are not welded or soldiered. Corrosion has and will be a problem. Don't need to rethink it all just need to look at what has been used and is being used. Autos after installing a battery then sprayed an inhibitor on the posts, computers used dielectric grease before the connection. Seems to come down to before or after the connection. Seems it's all about keeping air and water from interacting with the metals.

Have not gave this as much thought as now. Seems to all start out at the design level to prevent air and water from reaching the connection if no cover is provided then they move to spray on or grease. Both can be used.

Sorry guys just doing a brain dump here.

[SafeDiscDancing]

Has anyone tried laying the cells flat (and in series) rather than upright before compression?

Seems to me that if the cells are flat and you hit bumps which are mostly up and down movements that the weight of the battery would be directed away from the contacts towards the sides of the cell.

This would allow a light pressure from end to end since you aren't worried about any bouncing effect.

In the case of parallel cells you could have copper strips with little dimples on both sides (not sure how) which could then be the attachment point for balancing wires.

A set of four parallel cells stacked 2x2 could then be inserted into a square tube made of plastic or fiberglass.

Then you just have springs on each end to bind up the series. Maybe each series is six cells. Two of these is 12S.

This project is far along and looks good, but it's just a different perspective on the problem.

[TorontoBuilder]

Has anyone tried laying the cells flat (and in series) rather than upright before compression?

Seems to me that if the cells are flat and you hit bumps which are mostly up and down movements that the weight of the battery would be directed away from the contacts towards the sides of the cell.

This would allow a light pressure from end to end since you aren't worried about any bouncing effect.

In the case of parallel cells you could have copper strips with little dimples on both sides (not sure how) which could then be the attachment point for balancing wires.

A set of four parallel cells stacked 2x2 could then be inserted into a square tube made of plastic or fiberglass.

Then you just have springs on each end to bind up the series. Maybe each series is six cells. Two of these is 12S.

This project is far along and looks good, but it's just a different perspective on the problem.

I've designed and mostly built 6 compression batteries where the batteries lie flat parallel to the grade being travelled, the pack slides tightly into an aluminum extrusion with moulded in retention slots. The entire pack is compressed end to end. I use end plates and cell spacers on each set of cells and I have two groups side by side and 4 end to end for 64 cells. I just need to solder the tabs together and add bms to complete them.

I'm working on a bigger arrangement for my flying merkel build that fits into round fuel tank.

[SafeDiscDancing]

I was thinking you could go in series for maybe six or more cells all laying flat.

Then the only springs are on the ends.

You are doing only two in series.

Do you see my idea?

Basically the separators become the place where the balance wires attach.

[APL]

Interesting, I guess it depends on the space and orientation needed. Batteries should always lay flat to the road for sure.
Hard to see without a picture, but one thing about series would be the tensioner length depending on how it's designed.

Internal parallel wiring and contacts might get tricky with any more than two cells long. I guess it depends on how your separator's are placed and your method for getting cells in and out.

[APL]

Nice job TorontoBuilder, hope it works out for you. Are you using any spring mechanism with the contacts?

[APL]

Finally have a few hundred cells refurbished and ready to go. Not my favorite thing to do, that's for sure.
Anyway, I loaded up the box and took a pic, nice to see at last.

Loaded box.jpg (105.68 KiB) Viewed 537 times

A few more tweaks and some rattle can and I think she's ready to rock. Bulk balance, then a small voltage drain,
and check if the cells stay balanced.

[APL]

Somehow missed the fact that I need a charger for this pack, focused on too many other things I guess.
Looked around and found these guys that look OK,.. reviews seem good. 60v 3A for $60.

Any enlightenments? Just don't want to buy a lemon.

Yarlan 240w 60v charger.jpg (24.73 KiB) Viewed 513 times

[john61ct]

Make sure your charger auto terminates, try to find out how it measures pack is Full.

60V is just a nominal label

You want 66V termination in normal cycling for longevity, ideally stopping right at hitting voltage not holding a long CV/absorb stage.

Certainly stay under 67V, unless benchmarking capacity, or to engage poorly designed balance gear.

Below 65V, you start sacrificing capacity without benefit.

So make sure your charger lets you user - adjust the voltage without hacking

ideally would be over 1C current rate, but let you adjust that as well, half that is best for longevity but slow if you're in a hurry.

[APL]

Thanks for the info john61ct, there doesn't seem to be a lot of offerings out there for basic chargers. I haven't been paying too much attention to that side of the battery equation either.

Since I have an 11p pack at roughly 29ah,1C would be 29A? That sounds a bit high,.. I thought that 5A was pushing it!
Not in any hurry to charge, so 6 - 8 hours is fine. Probably should compromise at 5 -10 amps, since slower is easier on the cells.

All of the 60v chargers I have looked at usually give 67v as the output V, I assumed that the BMS cuts it off at about 65v.

Thanks for the help,.. wasn't ready for the charger thing, thought maybe there was a common go-to unit that folks have been using.

[agniusm]

Somehow missed the fact that I need a charger for this pack, focused on too many other things I guess.
Looked around and found these guys that look OK,.. reviews seem good. 60v 3A for $60.

Any enlightenments? Just don't want to buy a lemon.

Yarlan 240w 60v charger.jpg

I would look into meanwell hlg series. Heavier but far more reliable than these aluminium cans.

[john61ct]

Since I have an 11p pack at roughly 29ah,1C would be 29A? That sounds a bit high,.. I thought that 5A was pushing it!

Yes as you say half that is much healthier but sometimes we are in a rush. 2C is even OK so long as only once in a while, with healthy well balanced cells, and OTP.

> All of the 60v chargers I have looked at usually give 67v as the output V, I assumed that the BMS cuts it off at about 65v.

Never rely on a cheap BMS as charge control, it should be set higher than the charger cutoff, so it never engages unless the charger has failed.

A good charger is Grin Satiator, in your case #7205 20-103V 4-5A (360W)

can adjust both voltage and current

About $300

[Vbruun]

The charge cutoff john61 is talking about is not real and not an issue. See other threads where it has been discussed extensively and shown that this does not matter. At this point it is borderline fact resistance.

The max voltage can matter if you really care about longievity. On most chargers that can be disassembled, it can be adjusted via an adjustment pot.
So just buy whatever floats your boat
I have a few of the alu bricks and they work just fine, but it's probably true that they are not as reliable as other more expensive options.

[APL]

Thanks guys, I looked at the Meanwell's which were good quality, but didn't notice a plug and play unit,.. also looked at the Grin Satiator, which is the Cadillac, as usual. Love the Satiator, but not ready for the $300. price tag at the moment.
Obviously the best choice in the long run with it's programmability and famous Grin quality.

Also found the Sur Ron chargers which are also good and not too expensive for $125. from Luna, but the 10A output seems a little harsh for these tired old batteries,.. so I think I'll hold off on that one until I get some fresh cells.

Since I need something like 'right now', and I'm not even sure that this compression pack is going to work yet, I'll probably settle on
one of the 5A aluminum cans at $60., and upgrade later once I see how this all works out.

Thanks for all the help and info., it's been an interesting week of learning and searching the subject. There's a lot more options at
lower voltages, but when you go 60v -72v - and up, seems like they get more scarce.

[APL]

Ran into a snag on the battery box project,. I put a little too much stress on the top phenolic plate when I lifted the full pack, and
the epoxy glue let go. Evidently the phenolic sheet doesn't take epoxy very well, even though I sanded it well. Good quality 3hr glue too. (3000+ psi)
There's about 20 sq inches there, so it should begood for 60,000 lbs!

I sanded it back with some 30 grit and bonded it again, which should be good enough as long as I don't try to lift it again. Just a heads up, and I won't be using this sheet for anything but dash panels and bolt on stuff anymore. Strictly fiberglass from now on.

Also still trying to figure out how to connect the BMS without frying the board. They weren't intended to be remote, so I have to be careful here. The negative balance wire has to be connected first before any of the positive wires, and I can't do that with a cheap
JST connector reliably. So it looks like I'm going to have to go back to the dual 8 pin connectors and a single negative with a spade.
Spade first, and then the two 8's in order. Anyway, I'm still trying to figure it out.

I don't need a BMS to do the drain test though, so at least I can continue on with that.

[john61ct]

can you link to that sheet material?

[APL]

Same stuff from the same vendor, different add. "Paper" phenolic, (I didn't notice that before), "XX" is the lowest grade,.. I bought
it because it was cheap and stiff for the experiment, but it turned out to be a little too much so. Glue was Permatex 3hr epoxy.
https://www.ebay.com/itm/Garolite-Micar ... 19d87ea2a9

Phenolic sheet (1).jpg (42.14 KiB) Viewed 375 times

Should just 3D print the whole center section and sides,.. would save a zillion hours of work.

[APL]

All pimped out and look'n bad. Screws are all snug'd up and I've got 65v, so that's better than not. Just closed it up, so I'll re-torque the screws over the next few days. 

Volt test 1.jpg (119.27 KiB) Viewed 333 times

 
I had to strip the shrink wrap off of the cells because they were binding in the holders. Seems like the two plastics just don't get along.

Anyway, I need to figure out a way to drain the pack down a volt or so. The bike is in between mods, so that's out. The old controller is low volt, and the new one want's halls in the motor,.. yada, yada.

[spinningmagnets]

Looks fantastic!