GM Volt Forum banner

1 - 20 of 22 Posts

·
Registered
Joined
·
5,188 Posts
Discussion Starter · #1 · (Edited)
How does GM propose to drain a damaged battery?

In light of the recent NHTSA fires... GM has proposed a procedure for draining the coolant and discharging the battery. (Which they say could have prevented the fires.)

How do you drain all the cells in a damaged battery is some of the cells are open circuit? The cells in a Volt battery are hooked up in a parallel/series configuration. If some of the cells are damaged or the interconnecting wires are damaged you will not be able to drain the charge in the battery because the circuit will be open? This means you would have to pull the entire pack out of the car and discharge each cell individually. (And that's not easy.)

I guess the coolant would be somewhat easier to drain. Perhaps there could even be an automatic "purge" valve installed that would drain the coolant after the airbags were deployed. Of course that's not easy if the car has rolled over. Then where does it drain?

I think that GM simply putting out a procedure that states the battery should be drained after a crash ignores the likelihood that the battery might be so severely damaged it cannot be drained through a single connection because the circuit is also likely damaged.

It may not be an easy problem to solve.
 

·
Registered
Joined
·
2,694 Posts
Isn't this the reason why GM sends out a team to deal with a severely damaged Volt/battery?
 

·
Administrator
Joined
·
20,776 Posts
GM has "plans to propose to a damaged battery"? I doubt a corporation can legally marry an inanimate object :) You can use Edit Go Advanced to fix the typo in your headline Fulgerite.
 

·
Registered
Joined
·
3,165 Posts
Here is my SWAG:

First, the fires are believed to be caused by the coolant, and draining (most) of that should be easy. If there is an "open circuit" in the coolant circulation it will likely just leak out if oriented properly. (Up a flip would delay that for a while).

An open circuit could stop draining from a single point. I will observer that if the circuit is open it also reduces the chance that you can feed as much current into any short-circuit (which is what it takes to get the fire, a short that gets hot enough).

In addition each of the three battery modules could have its own fail-safe that it get an open-circuit condition they shunt the power to resistors to self-drain. (Could even have that type of fail-safe every few cells,but that pushes up the cost).
 

·
Registered
Joined
·
5,188 Posts
Discussion Starter · #5 ·
GM has "plans to propose to a damaged battery"? I doubt a corporation can legally marry an inanimate object :) You can use Edit Go Advanced to fix the typo in your headline Fulgerite.
Thanks Steverino. (Too much coffee = typos.) ;-)
 

·
Registered
Joined
·
60 Posts
I have owned 5 laptop computers and nobody has told me how to prevent it from catching fire if dropped on a hard floor. Several Sony laptops caught fire a few years ago, not in a destructive test, but in normal usage and NOBODY made such a fuss as they are making about a battery catching fire 3 weeks after being seriously damaged in an engineered test.
 

·
Registered
Joined
·
5,188 Posts
Discussion Starter · #7 · (Edited)
Isn't this the reason why GM sends out a team to deal with a severely damaged Volt/battery?
I think that's a great plan under the circumstances. But that's going to get costly when they have a million Volts on the road. (I hope they sell a million.)

All I am pointing out is that the problem is not as easy as connecting a "dummy load" to the output terminals and draining the charge. You can't always drain a damaged battery as a fully functional battery does. I am wondering what the engineers are proposing as a solution.
 

·
Premium Member
Joined
·
14,156 Posts
At Christmas time they just connect lights to it! Only kidding of course, but it was described to me as attaching what is essentially a large light bulb to the battery. Obviously you want to take the chemical energy and turn it into light or motion. Heat is another option of course but that's what they're trying to avoid.
 

·
Registered
Joined
·
5,188 Posts
Discussion Starter · #9 ·
I have owned 5 laptop computers and nobody has told me how to prevent it from catching fire if dropped on a hard floor. Several Sony laptops caught fire a few years ago, not in a destructive test, but in normal usage and NOBODY made such a fuss as they are making about a battery catching fire 3 weeks after being seriously damaged in an engineered test.
Syrenab...

Don't get me wrong... I love my Volt... But a laptop battery is a lot smaller than a Volt battery. You can probably just walk away from a laptop battery if it catches fire and eventually it goes out. I think the concerns here might be: After a crash a parked vehicle might catch fire in a garage somewhere and set a building on fire. Or worse... After a crash the occupants might be physically unable to exit the car and the battery might catch fire with people in the car. (As unlikely as that might be.)

Frankly I am more concerned about the gas tank leaking and catching fire but... The battery is one more source for a fire and I think the engineers at GM need to find solutions that will put this issue to rest so we can all go on enjoying our Volts.
 

·
Registered
Joined
·
5,188 Posts
Discussion Starter · #10 ·
At Christmas time they just connect lights to it! Only kidding of course, but it was described to me as attaching what is essentially a large light bulb to the battery. Obviously you want to take the chemical energy and turn it into light or motion. Heat is another option of course but that's what they're trying to avoid.
Don...

The question was not what kind of dummy load to connect. (I do understand that light bulbs, resistors and motors can drain a battery.) The question is how do they plan to drain battery with open circuit damaged cells without completely disassembling the entire battery and individually draining each cell. (Which would be extremely difficult & costly.)

I am not saying it can't be done. I am just curious to hear the proposed solutions. (Like the shunting idea tboult suggested.) It's a technical question. (Not a political one.)
 

·
Registered
Joined
·
716 Posts
"How do you drain all the cells in a damaged battery if some of the cells are open circuit?"

I would consider the situation where some cells are open-circuit a GOOD "failure mode," and in that case draining the electric charge would be less important. Considering the strong metal jacket of the battery module, I think the greatest concern is for situations where ALL the cells, or a large number of cells, are still connected together and pushing the sum total of all their charges into a short circuit. Then you get the massive heat buildup that can overcome the large module metal jacket, or cause a fire if the short is outside the battery module.

In short (oops, pun..., "short" ... sorry), a few isolated cells inside the module that aren't discharged may not be a significant threat. And if enough cells become disconnected to the point that there are no plausible complete circuits left, that would be a good outcome, (even if all the individual cells are still charged).
 

·
Member
Joined
·
247 Posts
I would consider the situation where some cells are open-circuit a GOOD "failure mode," and in that case draining the electric charge would be less important.
Right - infact what tesla does is to have a fuse with each cell to manage their discharge. If thermal runaway is detected the fuse opens.

It is possible in some distant future, EVs will have cell fuses that open up after a crash automatically.
 

·
Registered
Joined
·
255 Posts
Take a deep breath and relax everybody. Remember all the fear and doubt about stale gasoline a couple of years ago on this web site? So many problems stated, so many fears expressed, so many armchair engineer solutions put forth. And yet, the GM engineers were working on the solution for a pressurized fuel tank and to generate electricity from the old gas before it became a problem.

I'm just going to guess that the GM battery engineers know how to discharge an undamaged battery, a lightly damaged battery, a severely damaged battery, and an entire shredded wad of Volt in the middle of a 64-car pileup on a foggy freeway.

JMHO.
 

·
Registered
Joined
·
5,188 Posts
Discussion Starter · #14 · (Edited)
Right - infact what tesla does is to have a fuse with each cell to manage their discharge. If thermal runaway is detected the fuse opens.

It is possible in some distant future, EVs will have cell fuses that open up after a crash automatically.
Actually that would be a problem. The potential energy would still be trapped in the cell. If that cell had a bad seal coolant or air can leak in and you still have a fire hazard. Lithium + water = Fire. Lithium + Air = Fire.

The heat does not always come from a short circuit. The heat can also come from the chemistry in the cell.

A simple fuse would only solve one part of the issue. Not the chemical heating issues.
 

·
Registered
Joined
·
5,188 Posts
Discussion Starter · #15 ·
I'm just going to guess that the GM battery engineers know how to discharge an undamaged battery, a lightly damaged battery, a severely damaged battery, and an entire shredded wad of Volt in the middle of a 64-car pileup on a foggy freeway.

JMHO.
I hope you are right.
 

·
Registered
Joined
·
3,165 Posts
Actually that would be a problem. The potential energy would still be trapped in the cell. If that cell had a bad seal coolant or air can leak in and you still have a fire hazard. Lithium + water = Fire. Lithium + Air = Fire.

The heat does not always come from a short circuit. The heat can also come from the chemistry in the cell.

A simple fuse would only solve one part of the issue. Not the chemical heating issues.
The Lithium in the battery is not in metallic state (which is when lithium +water = fire or Lithium+air=fire).
It is an in a chemically compound, with different batteries using slightly different chemistries. I most cases its in a liquid or gel-like compound.

There are various studies on the air/water exposure of the raw materials used in batteries
(e.g. http://event11.ise-online.org/online/meeting/infiles/pdf/ise110433.pdf)
and they are, at least in the short term, not a major concern for fire or explosion. Admittedly, sitting for a while mixed with other chemicals may allow separation and formation of different compounds which may be more violative.
 

·
Registered
Joined
·
5,188 Posts
Discussion Starter · #17 ·
The Lithium in the battery is not in metallic state (which is when lithium +water = fire or Lithium+air=fire).
It is an in a chemically compound, with different batteries using slightly different chemistries. I most cases its in a liquid or gel-like compound.

There are various studies on the air/water exposure of the raw materials used in batteries
(e.g. http://event11.ise-online.org/online/meeting/infiles/pdf/ise110433.pdf)
and they are, at least in the short term, not a major concern for fire or explosion. Admittedly, sitting for a while mixed with other chemicals may allow separation and formation of different compounds which may be more violative.
I did not realize the LG battery chemistry in the Volt was LiFePO4. I thought it was closer to a LiPo type battery. (LiFePO4 is a more stable compound that is not supposed to burn.) Although my statement that Lithium + water = fire is technically correct... It does not apply to the Volt's battery. I did not realize the LG Volt chemistry is very different than the Lipo batteries used in cell phones and laptop computers.

This article explains it well:

http://www.popsci.com/cars/article/2011-01/gm’s-new-battery-chemistry-it’s-already-chevy-volt

I am surprised that there is a fire problem at all with this type of battery. As you suggest...it must be a secondary formation of compounds that lead to overheating & fire.

Knowing that the Volt's battery uses LiFePO4 chemistry is reassuring.
 

·
Registered
Joined
·
3,165 Posts
I did not realize the LG battery chemistry in the Volt was LiFePO4. I thought it was closer to a LiPo type battery. (LiFePO4 is a more stable compound that is not supposed to burn.) Although my statement that Lithium + water = fire is technically correct... It does not apply to the Volt's battery. I did not realize the LG Volt chemistry is very different than the Lipo batteries used in cell phones and laptop computers.

This article explains it well:

http://www.popsci.com/cars/article/2011-01/gm’s-new-battery-chemistry-it’s-already-chevy-volt

I am surprised that there is a fire problem at all with this type of battery. As you suggest...it must be a secondary formation of compounds that lead to overheating & fire.

Knowing that the Volt's battery uses LiFePO4 chemistry is reassuring.
Actually I don't think its LiFePO4, that was just one of many article's I've read. I don't think the exact formula is public. I was really just trying to say its not raw lithium but some far more stable compound.

Compact power (which was co-founded here in CO) was part of the LGChem fomulation team. They were definitely was working with lithium manganese, and the pop-sci article above say at least the cathode is LiMi?? but also says they are using the Argone lab mixed in.
 

·
Premium Member
Joined
·
14,156 Posts
I did not realize the LG battery chemistry in the Volt was LiFePO4.
It's not. It's Manganese Spinel. Not as stable but a long way from the lithium cobalt. FWIW my guess is the coolant is shorting out the battery, not that the chemistry is unstable.
 

·
Registered
Joined
·
5,188 Posts
Discussion Starter · #20 · (Edited)
It's not. It's Manganese Spinel. Not as stable but a long way from the lithium cobalt. FWIW my guess is the coolant is shorting out the battery, not that the chemistry is unstable.
I don't think it is Manganese Spinel yet. The Popular Science article says GM may use the Manganese Spinel in the future. I believe the Volt's current battery technology is manufactured by LG Chem Power Inc. It is a Lithium-Ion Polymer battery. You can read about it here:

http://www.lgcpi.com/lithium.shtml

http://www.lgcpi.com/faq.shtml
 
1 - 20 of 22 Posts
Top