Low Voltage and a "Pop" Sound ...

15 posts / 0 new
Last post
Kocho
Offline
Last seen: 7 years 6 months ago
Joined: Friday, March 21, 2014 - 21:05
Points: 488
Low Voltage and a "Pop" Sound ...

After my usual daily commute a few days ago, my battery got hot: 44C when I arrived at work. This has never happened before - temp is usually just a few degrees higher than when I start, u below 30C at the end of the trip. I've done the trip many times even in warmer weather than when the 44C temp happened.

To the office it is 12 miles, perhaps 8 of them highway where I could go up to top speed if desired (and I do for portions of these 8 miles, but never below 50mph, usually around 60 most of these 8 miles). Slightly uphill overall. When I arrive at work, I would usually have enough battery charge to make the trip back without charging (the return trip is easier, as it is slightly down-hill. I know that as I've done the return trip and at the end of it I have a bit of charge left and don't dip below 120V in use. However, I usually don't do the full round trip on one charge. Instead, I charge the half-empty battery at work, so I can make the return trip with no need to slow down.

That day, of course, I could not immediately charge, because the charge temp limit is 40C. So I had to wait for a few hours, turning the bike on and off several times to trigger the fans to cool off the battery. Once the temp went below 40, I started the charge. The temp went down slowly during the charge and I let the charge go to about 143V or so and I went on my way home.

143V are usually more than enough to get me home. Not this time. Half-way through the trip the voltage was already hovering around 120 even though I was riding at 30mph (normally I could maintain full speed in that section with voltage well over 120V). Something was not right. I kept slowing down to keep the voltage around 120V and soon was crawling at 15mph. I was way too far from home to even consider pushing the bike. Voltage dropped to as low as 101-103V and I was doing perhaps 5mph (walking pace) on a gentle uphill. On flats, perhaps 115V at walking speed. Then, something made a "pop" noise under the seat and my voltage climbed to 127V and I got more power instantly. Not much, but enough to get to 30mph without dropping below 120V.

Any theories as to what happened? Yes, pretty sure I've damaged some cells. One bank was at 44C while the rest were in the high 20s during my ride to work. And, a subsequent charge, on the day after I came home (after all banks have equalized their temperatures to ambient), took 8+ hours to complete. I wanted to see if finishing the equalization cycle will revive the cells. The bank that got hot while riding to work the day before did not heat-up abnormally during this charge. If anything, this bank was cooler than the rest by a couple of degrees during that charge.

That long charge brought the battery up to 146V, with most banks beginning to warm slightly, just a couple of degrees above ambient (below 29C). That tells me they were equalizing and full.

Took the bike on a ride to check the range, and, with easy riding at 30mph, I only made it perhaps 4 miles far and I noticed my voltage was dropping down to the upper 120s, which is not normal. Turned back and got home. Effective range seems to have dropped from around 30 miles to less than 10...

Any thought on what might have caused the bump in voltage after the pop noise during my ride home? I will be taking the battery apart soon to visually inspect it for bad cells, just curious of what you think.

Could a damaged cell have had high resistance, got hot, vented (the pop sound), and then somehow shorted itself, thus reducing its resistance, thus increasing the pack voltage, thus fiving me s bump in my speed?

Kocho
Offline
Last seen: 7 years 6 months ago
Joined: Friday, March 21, 2014 - 21:05
Points: 488
Re: Low Voltage and a "Pop" Sound ...

I should also mention that, at the end of the short and low-speed test ride after the last charge, no cell group's temperature was reported higher than the rest (unlike the ride that I think caused the damage, where one group of cells much warmer than the rest).

antiscab
Offline
Last seen: 9 months 3 weeks ago
Joined: Saturday, July 7, 2007 - 23:55
Points: 1686
Re: Low Voltage and a "Pop" Sound ...

Voltage dropped to as low as 101-103V and I was doing perhaps 5mph (walking pace) on a gentle uphill. On flats, perhaps 115V at walking speed. Then, something made a "pop" noise under the seat and my voltage climbed to 127V and I got more power instantly. Not much, but enough to get to 30mph without dropping below 120V.

Ah, I have seen this before - one of your cells has failed short circuit

when you were having low voltage, the difference was being disipated across that one cell.
It has likely become hot enough to vent

anyway, it's now a low resistance short - it's probably worth bypassing now

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km

Kocho
Offline
Last seen: 7 years 6 months ago
Joined: Friday, March 21, 2014 - 21:05
Points: 488
Re: Low Voltage and a "Pop" Sound ...

Yup, took the batteries out today. Your videos were of great help - thanks!

I hand-lifted the rear battery pretty easy. I rigged a very simple handle for the rear battery: a 1" wide nylon strap (the shoulder strap from some old camera bag, I think). Took about 40cm length, folded about 2cm on each end and with a hot screwdriver melted a hole through the double fold at each end. That made a nice flex handle - attach like you attach your rig, with a pair of washers and nuts to the two metal rods in the battery pack.

To take the rear battery out, first, position a sturdy knee-high table or chair near the bike. Then, straddle it, facing towards the seat, lift the battery out and with just a little motion place next to the bike on the chair. I guess it helps I'm tall and, but it was quite easy this way - I did not have to bend down, so used my legs to lift and swing to the side. Still, that could injure the back, so others should do that at their own risk!

Anyway, as I was taking the front battery out I did manage to create a nice little short between the lose battery terminals, which resulted in smoke and smell of burned plastic by the time I noticed the short. It lasted just a couple of seconds, I guess, and luckily, I separated the flex leads from each other and there was no fire or explosions :)

One cell had swollen badly and heated and burned a bit on the sides. The CelsiDot near it was dark (all others were white). Probably this was the already bad cell that I managed to fully cook today with the brief short-circuit.

A kind local VX1 owner who converted to lithium gave me his old NiMh front pack to use as a source of spares. In it I can see most of the cells in each group of 8 are visibly gently swollen. Only a few look much worse than the rest (and one has high resistance at no load and at 0.8V, lower voltage than the rest, which are all at about 1.17V). Perhaps 1 or 2 cells in each group appear to not be swollen visibly - my guess is these are the better cells (based on what Mik wrote in his posts here). So I have a few good spares it looks like.

Back to my bike. On my front pack, most cells are either square or ever so slightly swollen - looks like it is in better overall shape than that old donor pack. I have not broken-up the rear pack yet, hopefully the situation with it will be the same as with the front pack - few if any bad cells. I'll probably replace what I see being bad, reassemble, then see how it goes.

Though, going Li right now, when I have the packs out, looks very appealing! With Leaf cells it will be also much easier to put the bike together! Choices...

Kocho
Offline
Last seen: 7 years 6 months ago
Joined: Friday, March 21, 2014 - 21:05
Points: 488
Re: Low Voltage and a "Pop" Sound ...

Can anyone speculate if one bad cell can be all it took for my voltage drop? That cell is toast (0V), and visually I don't see any others that appear too swollen. I have only taken apart the front pack so far, and there only this one cell is bad. I will take apart the rear pack soon too to visually inspect. I don't have the time and patience to check cells one by one electrically under load...

antiscab
Offline
Last seen: 9 months 3 weeks ago
Joined: Saturday, July 7, 2007 - 23:55
Points: 1686
Re: Low Voltage and a "Pop" Sound ...

one bad cell can either be a low resistance short (in which case you don't really notice it) or a high resistance short (which is very noticeable)

I would replace any cell that has bulged - they all have higher self discharge and/or reduced capacity

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km

Kocho
Offline
Last seen: 7 years 6 months ago
Joined: Friday, March 21, 2014 - 21:05
Points: 488
Re: Low Voltage and a "Pop" Sound ...

If I look at the cells in the area just above the compression strap, all of them bulge out gently to some degree, none are totally flat. Very few bulge more though. Is that what you observe too? Bulge is slight but pretty clear if one uses a flat object to better feel it. The bottom third of each cell has very little bulging, the top third has more.

That's on my pack. Comparing to the cells from a salvage pack from another VX1, they are similar, perhaps slightly better on average. I'll probably just replace the one burnt cell for now. I'm curious, so I'm doing one capacity test on one cell group that has the most bulging cell in it (from the donor pack) to see if the capacity of that cell that bulges out more is lower compared to that of those that bulge less. If I see a considerable difference, I'll probably replace a few more cells on the new pack that appear to bulge the most, without further tests - don't have the time and patience to spend days testing each group of cells (that would be weeks for the whole pack!)

R
R's picture
Offline
Last seen: 2 months 1 week ago
Joined: Thursday, June 18, 2009 - 09:46
Points: 1768
Re: Low Voltage and a "Pop" Sound ...

"Before the vectrix makes POP, you must stop!"

I must admit, I'm simply amazed. That USA design of those NIMH cells is incredible. Inside every cell there's a gas chamber which prevents a metal plate to lift and short-circuit the terminals. If the inner pressure increases and the upper chamber is finally vented through the valve, (POP!) the metal plate lifts, makes a short-circuit, and automatically bypasses the cell. This explains why after the Pop sound you recovered range and voltage. The energy was diverted from heating the cell to the motorcontroller.

Then, something made a "pop" noise under the seat and my voltage climbed to 127V and I got more power instantly. Not much, but enough to get to 30mph without dropping below 120V.

Without this safety system, your vectrix would have catch a fire!

If you have MC1014b installed, I suggest you never ride under 115-120v.

Now comes the tricky problem of the Malayan clone design, wich morphed the NIMH cells to GP lithium. They look smartly alike, but without wearing any perimeter reinforcement geometry at all. The metal case is thinner, and 3x times taller: If any problem arouse, the cell gets fat, then the gas is vented, but the metal plate is not lifted to bypass the cell. The safety system does not work at all! Whats more, the hot gas is directly vented on the BMS board, damaging it. The vast majority of battery problems in V lithium versions is caused by damaged BMS, because they loose the ability to read correct temperatures and voltages. The BMS board becomes partially blind, and kills the battery.

Kocho
Offline
Last seen: 7 years 6 months ago
Joined: Friday, March 21, 2014 - 21:05
Points: 488
Re: Low Voltage and a "Pop" Sound ...

The front pack is back together (replaced the one popped cell and the one next to it, which was deformed by the excessive swelling of the popped cell). I managed to do it without breaking the compression strap, reusing it - again, thanks for postings here (by Mik, I think). The rest of the cells seem visually OK. Hopefully will have time to put the rest together in the next day or two and see if this was enough to revive my range.

R
R's picture
Offline
Last seen: 2 months 1 week ago
Joined: Thursday, June 18, 2009 - 09:46
Points: 1768
Re: Low Voltage and a "Pop" Sound ...

Kocho, can you make a longitudinal cut and split the swollen cell into two parts, and post the pictures of that cut?

Kocho
Offline
Last seen: 7 years 6 months ago
Joined: Friday, March 21, 2014 - 21:05
Points: 488
Re: Low Voltage and a "Pop" Sound ...

Probably not... But anyway, which way would you like it cut, just in case I do decode to do it? Top to bottom in the middle of the wide side or the narrow side vs. Side to side across the middle?

R
R's picture
Offline
Last seen: 2 months 1 week ago
Joined: Thursday, June 18, 2009 - 09:46
Points: 1768
Re: Low Voltage and a "Pop" Sound ...

Thanks for considering... About the way, have a look at the picture. It is a pity I've sold all nimh cells of my first vectrix, I'm really curious about the metal plate that bypasses the cell in case of failure.
slice of Cell.jpg

There is an electric tool called in Catalan "amoladora" which may do the job, with a thin metal-cutting disc.
amoladora-bosch-gws26230jh.jpg

elevatorguy
elevatorguy's picture
Offline
Last seen: 3 years 8 months ago
Joined: Thursday, July 12, 2012 - 20:13
Points: 87
Re: Low Voltage and a "Pop" Sound ...

Gloves goggles and outside. That cutoff tool is probably not the best choice, I would go with a band saw or recipricating saw with a fine tooth blade.

Kocho
Offline
Last seen: 7 years 6 months ago
Joined: Friday, March 21, 2014 - 21:05
Points: 488
Re: Low Voltage and a "Pop" Sound ...

I got plenty of cells, most of them look good. But I may try a can opener on one of the bulged cells :) Yes, protective gear... And I got power tools too, but they are more for woodworking. I think a hacksaw with a metal blade will do the trick just fine, though I may try the jigsaw with a metal cutting blade too. By feel (tapping them with my finger) I don't think the walls are attached to anything on the wide sides and probably on the other sides too on the inside - only at the top where it looks a can opener might just work to separate the top.

Any idea about the electrolyte consistency used inside? It is not liquid, probably some type of gel...

heathyoung
Offline
Last seen: 6 years 11 months ago
Joined: Wednesday, July 27, 2011 - 21:11
Points: 90
Re: Low Voltage and a "Pop" Sound ...

Electrolyte is NaOH - sodium hydroxide, used in drain cleaner.

Wear PPE, gloves and glasses, this stuff is nasty. It saponifies (turns to soap) organic matter, this includes fingers.

Log in or register to post comments


Who's online

There are currently 0 users online.

Who's new

  • xovacharging
  • stuuno
  • marce002
  • Heiwarsot
  • headsupcorporation

Support V is for Voltage