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Old 11-19-2022, 12:04 PM   #1
Cambridgehank
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Default The dynamic braking resistor

The owner's manual for my Tempo with Lithium battery states to clean the dynamic braking resistor. What is this resistor, what does it do and where is it? Thanks for you responses.
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Old 11-19-2022, 03:16 PM   #2
cart12
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Default Re: The dynamic braking resistor

The Dynamic Brake Resistor provides improved safety and control in downhill conditions by maintaining safe speeds and protecting the health of the battery system.

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Old 11-19-2022, 03:34 PM   #3
Fairtax4me
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Default Re: The dynamic braking resistor

If this is on a Lithium cart, what it means to say it it keeps the battery from exploding. By bleeding off excess current from the regen system. It prevents the regen from overcharging the battery which will cause the cells to go into thermal runaway.
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Old 11-19-2022, 09:12 PM   #4
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Default Re: The dynamic braking resistor

Quote:
exploding
That is a powerful word. Maybe more like keeping the batteries from being overcharged and destroyed.
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Old 11-19-2022, 09:56 PM   #5
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Default Re: The dynamic braking resistor

Not really. Batteries don’t slowly burn, and if lithium goes into thermal runaway you generally don’t know it until the case swells up from the pressure inside and the weak part of the case splits open.

Lithium fires are pretty well documented, and are increasingly more common as more and more consumer items use lithium batteries. And we even have a member who had one that he got on video.
https://www.buggiesgonewild.com/show...=184345&page=2
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Old 11-19-2022, 10:33 PM   #6
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Default Re: The dynamic braking resistor

Quote:
Originally Posted by Fairtax4me View Post
Not really. Batteries don’t slowly burn, and if lithium goes into thermal runaway you generally don’t know it until the case swells up from the pressure inside and the weak part of the case splits open.

Lithium fires are pretty well documented, and are increasingly more common as more and more consumer items use lithium batteries. And we even have a member who had one that he got on video.
https://www.buggiesgonewild.com/show...=184345&page=2
Actually, when lithium does run away into a “thermal event” it’s not usually a fast or instant process. Depending on the severity of the failure it could take minutes or it could take days (or longer) before it reaches a critical point of no return. There’s heat and hydrogen and other offgassing ther occurs long before an actual fire. You just can’t see or detect it easily because it is usually within an encasement of some sort. However once ignition occurs, then things escalate very, very quickly from there. This is what gives the general misconception of batteries “suddenly catching on fire”. And the only way to extinguish it is by completely saturating it in water, which is generally nearly impossible due to said encasement preventing the water from immersing as it would need to.

That said, the BMS should react and shut down the pack long before any type of thermal event should occur. In the case of this resistor I’d imagine it is to prevent the BMS from shutting down the pack, which would create warranty claims and general customer dissatisfaction.


And the general maintenance to clean the resistor should be simply cleaning out the fins in the heat sink. Clogged fins would prevent the resistor from cooling effectively, causing the resistor to overheat and fail. Shouldn’t take more than a minute or two to use a nylon brush and clear out and dirt or debris in there.
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Old 11-20-2022, 08:29 AM   #7
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Default Re: The dynamic braking resistor

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Originally Posted by CP241 View Post
Actually, when lithium does run away into a “thermal event” it’s not usually a fast or instant process. Depending on the severity of the failure it could take minutes or it could take days (or longer) before it reaches a critical point of no return. There’s heat and hydrogen and other offgassing ther occurs long before an actual fire. You just can’t see or detect it easily because it is usually within an encasement of some sort. However once ignition occurs, then things escalate very, very quickly from there. This is what gives the general misconception of batteries “suddenly catching on fire”. And the only way to extinguish it is by completely saturating it in water, which is generally nearly impossible due to said encasement preventing the water from immersing as it would need to.

That said, the BMS should react and shut down the pack long before any type of thermal event should occur. In the case of this resistor I’d imagine it is to prevent the BMS from shutting down the pack, which would create warranty claims and general customer dissatisfaction.


And the general maintenance to clean the resistor should be simply cleaning out the fins in the heat sink. Clogged fins would prevent the resistor from cooling effectively, causing the resistor to overheat and fail. Shouldn’t take more than a minute or two to use a nylon brush and clear out and dirt or debris in there.
Thanks CP that answers my questions.
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Old 11-21-2022, 08:54 AM   #8
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Default Re: The dynamic braking resistor

Just to add to the answers, Dealer in WNC mtns where I got mine gave me an example. First he said it protects battery and systems from over charging as others said, by bleeding off excess charging from regen when battery already at capacity. Then when it can't handle the excess, the cart gets shut down. Told me clients who lived on top of steep mtns starting out at 100% charge, had a problem with carts shutting off before they got to bottom of mtn, so system works, but in extreme situations like this they turned chargers down to 90% max charging so cart won't shut off as it gets more juice then it can handle going down hill.
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Old 11-21-2022, 10:44 AM   #9
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Default Re: The dynamic braking resistor

That would be the BMS working as designed, and shutting the pack down to prevent overcharging. That’s certainly a great, and interesting example, however. I hadn’t thought about someone living at the top of a mountain. Thank you
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Old 11-21-2022, 06:22 PM   #10
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Default Re: The dynamic braking resistor

Quote:
Actually, when lithium does run away into a “thermal event” it’s not usually a fast or instant process.
The runaway part is usually pretty fast. Once it starts it progresses pretty quickly. Maybe the condition that leads to it takes some time, but once the right conditions are present, the rest happens pretty quickly.
And being enclosed in a plastic case, you don't know anything is wrong until the case pops open, and all that nasty gas and smoke finds an oxygen source.
Probably just a difference of semantics, but when a lead battery pops open it's almost always described as " it exploded" even though in reality it was just a short combustion event. Not much different IMO when a lithium battery does the same.
The BMS should prevent that, but most of those can only handle so much even if they go into shut-down mode to protect the pack. Which as you said, is going to be a hassle for the customer and garner some complaints for the PR dept to smooth over. Easier to try to bleed that power off as heat from the resistor.
I still say the resistor is there to keep the pack from exploding though.
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