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Still Stymied

1548 Views 19 Replies 6 Participants Last post by  MattsAwesomeStuff, 
jswallow
Since I apparently “stumped the panel” with this one, I thought I’d try again, now that I’ve rewired the charger receptacle, found that the charger is fine and that the problem is in one of the modules in the battery pack. After removing a couple of modules (Tesla 21V, 5.2AH) I found that one measured zero voltage! The other four all measure 19.5V - pretty much “nominal” for these modules. So, THAT’S why I couldn’t charge the pack - charger didn’t sense the presence of the pack.

Looking closely at the bad module, I can see that three of the tiny wires that connect the cells to the current collector we’re fried.

So, now - I remember reading somewhere that part of the “genius” of these Tesla modules is that if a cell or two go bad, it doesn’t ruin the whole module, but my latest finding is that one bad cell renders the module useless.

Does anyone have experience with this, and can it be fixed or do I buy a whole module replacement? And, how do I “balance” a repaired or new module with the rest of the pack?

jswallow said:
Before I start clipping wires and pulling components, I thought I should run this by you to see if you have any ideas or suggestions.

I finished a restoration and EV conversion of a 1990 Miata almost three years ago, using EV West's AC-50, Curtis 1238 system with five Tesla battery modules and the Elcon PFC2500 charger. I followed their wiring diagram exactly and didn't stray from the component set-up. Everything worked great and I've been happily tooling around here with no problems at all - probably putting on 15 - 20,000 miles in the past almost three years - until the conjunction of two serious problems recently.

First, the white wire from the J1772 receptacle to the charger fried itself, apparently shutting off the charger internally, unbeknownst to me. Next, due only to my stupidity in miscalculating how far I was able to go on a drive, I ended up at the dreaded 5% capacity cut-off where the DC system shut down completely.

Despite replacing the burnt-out charger wire, the charger will not turn on and start charging my depleted batteries for some reason. My reading of the charger manual and what I can find on-line indicates that once the "short" is corrected, plugging in the J1772 will turn the charger on again. So, I am at a loss as to where to go from here. And by the way, I'm using a no-frills Level 2 charger on a dedicated 50 amp 220V line.

Do I pull the charger out, open it up, and hope to find something I can fix or replace? Could the charger be toast already and I'll have to buy another? Is there some kind of "reset" button or process that I'm not finding? Is there something in the system somewhere else that is not letting the charger come on?

Hoping that I'm not the only nincompoop out there that has done this, I wonder if you have seen this before and have some words of wisdom as to where to go from here.
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MattsAwesomeStuff
Not exactly sure what you're picturing. You're saying on one of your tesla modules, you found 3 broken cell fuses? That's a really odd circumstance, those should almost never blow unless a cell fails shorted (rather than open). Regardless, the pack itself is blind to those fusible links blowing, so no, it wouldn't have deactivated the pack.

My hunch is that there was something going on with the BMS intermittently connecting, or failing, and draining that pack to zero. If that pack suddenly got voltage, maybe that caused the individual fuses to blow?

If the pack is truly disconnected from the others, then there must be a module-level fuse that blew. I'm not familiar enough with Teslas to offer better advice. But, it's possible that module is just discharged, not blown.

You could try testing voltage on the pack and seeing if there's continuity, and seeing where the voltages are. And if so, perhaps manually charging them to see if they're still okay. Then maybe you'd only have to replace the module-level fuse, but, we're getting down a pretty long chain of IFs.

Can't make good decisions with bad information. Find out more information.
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kennybobby
what about the fuses on the "bottom", look at the other side
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jswallow
kennybobby said:
what about the fuses on the "bottom", look at the other side
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They’re all fine.
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jswallow
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kennybobby said:
what about the fuses on the "bottom", look at the other side
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MattsAwesomeStuff said:
Not exactly sure what you're picturing. You're saying on one of your tesla modules, you found 3 broken cell fuses? That's a really odd circumstance, those should almost never blow unless a cell fails shorted (rather than open). Regardless, the pack itself is blind to those fusible links blowing, so no, it wouldn't have deactivated the pack.

My hunch is that there was something going on with the BMS intermittently connecting, or failing, and draining that pack to zero. If that pack suddenly got voltage, maybe that caused the individual fuses to blow?

If the pack is truly disconnected from the others, then there must be a module-level fuse that blew. I'm not familiar enough with Teslas to offer better advice. But, it's possible that module is just discharged, not blown.

You could try testing voltage on the pack and seeing if there's continuity, and seeing where the voltages are. And if so, perhaps manually charging them to see if they're still okay. Then maybe you'd only have to replace the module-level fuse, but, we're getting down a pretty long chain of IFs.

Can't make good decisions with bad information. Find out more information.
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Yes, just the three fuses and as the questioner below wondered, all the fuses on the bottom are intact. Here's a closeup image. This is right at the negative "terminal" (part of the whole connector plate, but it's where you bolt in your connection). The three "blown" fuses are circled.
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There is NO continuity when measuring between the main positive and negative terminals.

Pictured below is the module on its side with the positive terminal down. "Blown" fuses are indicated by the arrows.
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There are four current collectors on the top. You can see the borders clearly. There is no continuity or voltage between the collector with the blown fuses. All the others show continuity and voltage. Voltages in the individual cells under the "bad collector" vary a lot, and tend to be in the 3.5V range right next to the negative terminal and quickly drop to millivolts as you test farther away from the terminal. Voltages of all the rest of the cells under the other collectors measure at 3.27V.

What this tells me is that this is a dead module and I'm going to have to replace it, but I'm tempted to see if I can put any charge into it if I attach my 12V trickle charger. Do you think that is a very good idea? Any other possibilities?
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kennybobby
i don't know what you mean by No continuity between the + and - terminals of the module--that makes no sense to me; you can measure voltage on a module, but i've never heard of measuring continuity on live cells, seems it would blow your meter.

The block of cells with the blown fuses:
somehow that block of cells wasn't sharing the load and those 3 blew their fuse due to the current >25 Amps.

If the cells in that block are at various voltages and not the same, then there has been something bad happen in that block.

Not a very good idea to try to charge that module.
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R
I'm from the opposite School of Nothing to Lose.

This is very risky, but I would try to charge each of those bad cells to see if they will take a charge, assuming they aren't discharged below the minimum rated voltage.

If it was my module, I'd test those blown cells to see if they still have their minimum voltage levels to be chargeable and try to bring them up to the voltage everybody else is at. If they do charge up, then reconnect them, keeping a length of the fuse wire in place.

It's possible those locations were proud and they were shorted on a metal bench or on a stack of modules with the polycarb insulator off them. That's where my optimistic head is at.

You don't want to do this anywhere where a module fire can do damage and it is risky.
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jswallow
I am pretty sure that I’ve found the problem. Testing each cell individually (well, not EVERY, since there are hundreds of them) I get 3.7V for the vast majority of them and same as those in the unaffected module. A few, and not necessarily the ones with the blown fuses, measure less than 1V. So, probably not rechargeable.

Finding that I measured 20.2V when the module was on its side, but just millivolts when laying flat, I “poked & squeezed around” and found that the current collector of the block of cells that makes up the negative pole was a little LOOSE! Fiddling with it a little more, I unwittingly (and VERY easily) separated part of the collector from whatever it was glued to. Now, I can only measure voltage in this cell if I clamp the loose collector onto the module with a fair amount of pressure.

So, this spot must have been gradually loosening over time - maybe because of how it was mounted? My battery management system shuts down the high voltage system when the pack charge gets down to 5%. I don’t know why, but that must have been the coup d’grace for that negative terminal in the middle of the pack.

I have put everything back together, sans bad module. Each of the four modules measures 19.7V, and the whole pack measures 78.3V. The chargers now recognizes t battery pack and will charge. All I need to do is come up with the bucks for another module.

These few blown cell fuses and several “dead cells” were a red herring, as someone suggested earlier: one of the strengths of this battery module design is that if a few cells go bad it doesn’t shut down the whole module.
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MattsAwesomeStuff
jswallow said:
A few, and not necessarily the ones with the blown fuses, measure less than 1V. So, probably not rechargeable.
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Ehn, 50/50.

2 kinds of failure:

- High self discharge, will always plummet even if you try to charge them, and if left to charge unsupervised may become scalding hot (because they higher their voltage gets, the faster they want to turn that into heat and get back to their lower voltage).

- Discharged cells. Just needs charging.

You don't know what kind of failure has led them to being 1 volt. Maybe they just got discharged to 1 volt. That's not great for a cell, but it's not a disaster, if it charges up without getting too hot, and, more importantly, maintains its voltage, it's fine. Fuse it back into circuit and she's good.

So, this spot must have been gradually loosening over time - maybe because of how it was mounted? My battery management system shuts down the high voltage system when the pack charge gets down to 5%. I don’t know why, but that must have been the coup d’grace for that negative terminal in the middle of the pack.
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Well, all your modules are in series. Like a chain. When you break one link, the whole chain is broken. Makes sense to me.

All I need to do is come up with the bucks for another module.
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Ehn, even without the few cells with blown fuses, you're fine. It's not rocket science to fix the negative terminal that's broken off of wherever it was connected.
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jswallow
MattsAwesomeStuff said:
Ehn, even without the few cells with blown fuses, you're fine. It's not rocket science to fix the negative terminal that's broken off of wherever it was connected.
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Oh, really? What do I do - go out and get some glue and glue it back? :oops:
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R
If you don't know how it can be done, don't mess with it. The kind of repair Matt suggested on the module terminal requires skills and experience.
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MattsAwesomeStuff
remy_martian said:
If you don't know how it can be done, don't mess with it. The kind of repair Matt suggested on the module terminal requires skills and experience.
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To some degree, that's a reason to avoid doing anything. You don't get experience by avoiding things, and if you avoid things until you have experience you'll never do it.

That said, Remy's advice is solid. If even the thought of repairing it leads you to bewilderment that it could be possible, it's probably a few steps ahead of anything you should attempt.
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jswallow said:
I “poked & squeezed around” and found that the current collector of the block of cells that makes up the negative pole was a little LOOSE! Fiddling with it a little more, I unwittingly (and VERY easily) separated part of the collector from whatever it was glued to. Now, I can only measure voltage in this cell if I clamp the loose collector onto the module with a fair amount of pressure.
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It's pretty evident that this module is DAMAGED (in a few different ways)
...& as such IMO should NOT be used in (or to power) a passenger vehicle (for a few different reasons)

I would now, only use it as a learning tool to dissect & learn more from
...so, you (& if you post/share the info, we/us) can better understand better "how" the modules (that you are working with) are designed & function ;)
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Functional Artist said:
It's pretty evident that this module is DAMAGED (in a few different ways)
...& as such IMO should NOT be used in (or to power) a passenger vehicle (for a few different reasons)

I would now, only use it as a learning tool to dissect & learn more from
...so, you (& if you post/share the info, we/us) can better understand better "how" the modules (that you are working with) are designed & function ;)
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Well, here’s what I’ve come up with. I find that this works on my bench, but the only way to see if it works inIN THE CAR is to wire it in and try it. Although it’s hard to get the modules in and out, it seems like it might be worth a try, especially since another module will cost $1500. Attached are pictures that I’ve taken of my “fix”. It’s a stainless clamp put on the end of the module and presses down on the bolt that attaches the wire terminal (projecting to the side and down to the positive pole of the previous module in the series).

What do you think? Is this a bad idea?
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R
I think the contact resistance will be too high. You don't have the equipment to measure single digit milliohms accurately.

Another approach is to dump current at 750 amps and measure the sag, but you don't have the gear there either, though I suppose the car might be an option. Realize if the contact resistance is high enough, your "connection" will get extremely hot awfully fast and could light off a cell. You might thermocouple it and gradually increase the current.

I suggest you take it to a competent (and brave) shop to get it welded...ideally spot welded at a body shop that does aluminum cars, or a shop that knows its poop TIG welding. The tab going to the cells is going to need major heat sinking, which they should be able to understand.

It is a risky repair. 160F max cell temperature or it may light off...this they need to know.

My gut feeling is that clamp likely won't work given the high currents a car will see.
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P
Imho, the case underneath the clamp melts way before the battery lights off and you loose contact Mit spitzen sparken und das blinkenlights.
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jswallow said:
Well, here’s what I’ve come up with. I find that this works on my bench, but the only way to see if it works inIN THE CAR is to wire it in and try it. Although it’s hard to get the modules in and out, it seems like it might be worth a try, especially since another module will cost $1500. Attached are pictures that I’ve taken of my “fix”. It’s a stainless clamp put on the end of the module and presses down on the bolt that attaches the wire terminal (projecting to the side and down to the positive pole of the previous module in the series).

What do you think? Is this a bad idea?
View attachment 136651 View attachment 136650 View attachment 136651
View attachment 136650
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Creative repair (y)

IMO you're going to have to ask yourself
...is "my" car & all of "my" efforts worth (another) $1,500.00?
...& (more importantly) if this "goes bad" how dangerous could it be for me, any passengers &/or first responders?

Maybe you could use it for a PowerWall (so you can still put it to use)
...it could be in a "safe" sturdy & stationary location
...& the current demand, should be less too
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jswallow
Yep. I finally came to my senses and ordered a module and a BMS.

BTW: What’s the difference between a 5.2kwh module from eBay for $750 and one from EV West (or other commercial supplier) for $1500 . . . . besides, of course, $750?
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R
The ones for $750 are usually damaged in some way.

How many of those clamps do you have? 😂
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MattsAwesomeStuff
jswallow said:
BTW: What’s the difference between a 5.2kwh module from eBay for $750 and one from EV West (or other commercial supplier) for $1500 . . . . besides, of course, $750?
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EV West bought the eBay ones and doubled the price to be your middleman. Same as everything they sell.

I mean, who knows but... it's not like EV West is ordering them brand new. They too are buying them out of crashed vehicles, they're not going to get much better prices than you will.

The good news is that EV West has a great warranty and stands by their products so you can buy with confidence will ghost you for month after month if the garbage they sold you never works even right out of the box, and send you down wild goose chases about not using gold plated wires until you give up and stop bothering them and accept that you wasted thousands of dollars (real example, screw EV West).
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