Thermal shutdown in Alltrax controller?

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reikiman
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Thermal shutdown in Alltrax controller?

I've had this happen a couple times now and am curious over y'all's thoughts. In my VW Karman Ghia sometimes it get into a mode where it's literally crawling. The battery voltage reads ~ 72 volts, and the amps read very low (say, 30A). Each time it's happened after a few miles of modestly hard driving.

First time it happened I thought, oh, the batteries are really crapped out. But it was very puzzling why would the voltage be reading at 72 volts? A completely discharged pack under load would be reading, say, less than 50 volts. In any case I pulled to the side of the road and waited awhile - the "growing amps" strategy that's known to let a battery pack recover a bit so you can limp home. I limped the car home and put it on the charger. The AH's used weren't very high. Hurm?

The second time it happened I thought to get out and feel the motor. It was very hot. But I didn't think to feel the controller. The last time it happened I felt the controller - and it was so hot my hand involuntarily leaped away. Any hotter and the controller would have given me a burn.

The controller is not mounted in the air flow, and doesn't have a heat sink. It's an Alltrax 72 volt 450A rated controller - this is the one with the longer case. It doesn't have much innate heat sink capability. It is bolted to the engine compartment firewall, but there's a sheet of rubber in-between.

It seems obvious the controller is overheating. I haven't checked whether Alltrax designed in to detect high temperature and go into shutdown, or whether it's simply being less efficient due to the heat and getting damaged. The controller obviously needs to be on a heatsink or else have a cooling fan.

Spaceangel
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Re: Thermal shutdown in Alltrax controller?

What is your current while driving just before thermal? My controller does the same thing except I am using a 36 volt motor with 48 volt applied and motor get excessively hot and then current folds back and battery voltage goes back up. If I continue the beetle does a crawl. I am pushing nearly a full 600 amps a lot of times. I don't have the big Trojans you are using just Optimas and they die rather quickly but it is just a NEV. Yes the Alltrax gets hot too. Or I should say warm. What is rated controller continuous current 450 is not continuous?
How long do you stay at fairly high current? I do believe mounting controller on heat sink does help me for the fins on other side are still warm with white thermal compound too. Do you have an ammeter in motor circuit too? You can have an easy 450 or more amps on motor side while doing 250 to 350 amp battery pack side. Mine is always doing big motor amperes.
I think you do need a heat sink! On Alltrax with thermal compound. Also glue a Radio Shack thermal sensor to controller. It will give you an indication of getting warm before shut down.

KB1UKU

antiscab
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Re: Thermal shutdown in Alltrax controller?

the trick to avoiding overheating is to drive in the lowest gear you can to maintain the speed.

heat build up in both motor and controller is proportional to the square of motor side current.

say you are driving in 4th, rather than 3rd.
say the difference in ratios is 1:1.2
that means, heat builds up 44% faster when running in 4th, than in 3rd.

do you have a second amp meter you can put on the motorside, to see how many amps are going through?

Matt

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2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst 2 x TC Charger & MC
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reikiman
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Re: Thermal shutdown in Alltrax controller?

Hm, interesting .. I've been shifting up to 3rd quickly .. the thinking is that a) in 2nd speed is limited to 25ish b) ..uh.. this is a little more complex. If I stay in 2nd for awhile before shifting to 3rd there is two cycles of 200-300 amps. Whereas if I stay in 2nd just long enough to get moving, then shift up to 3rd, there's only one period of 200-300 amps plus the speed where the car settles in at 100 amps cruising is in the 35 miles/hr speed rather than the 25 miles/hr speed I'd be at in 25.

No second amp meter.

- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki
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antiscab
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Re: Thermal shutdown in Alltrax controller?

with your foot to the floor:
if battery amps are low, it means the controller is operating in motor current limit.
so the motor would be operating at around 400A (assuming it has sufficient inductance, which i think it does).

when accelerating as fast as possible, big amps on the battery side is a good thing (at least as far as keeping things cool).
use the accelerator to reduce acceleration rather than shifting up.

out of curiosity, whats your top speed in 1st?

going 1st -> 2nd -> 3rd will keep things cool if the motor/controller is a bit marginal.

how good is the heat sinking on the controller?
how thick is the bit of steel its bolted to?
you could try putting a thick (1/2") steel spacer in between the controller and mounting to increase the thermal mass.

Matt

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst 2 x TC Charger & MC
conversion

reikiman
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Re: Thermal shutdown in Alltrax controller?

I rarely drive in 1st.. it works to start in 2nd. What I found last night on the way home is I could STAY in 2nd and still get to 40mph. And it wasn't terribly painful, even, to get there. I did have to ignore my instinct from 30 years of driving stickshift to shift up based on the sound of the ..er..uh..engine..uh..motor.

Somewhere recently I read a claim that these electric motors are more efficient at high RPM? In any case at the end of the ride the motor and controller were hotter than warm but not enough to call it "hot". The total AH used was over 25AH whereas normally that same trip takes 22-23AH, and 1800WH versus the more normal 1500WH.

There is no heat sink on the controller.. it's a metal box with the barest of finning built into the box, but you're probably familiar with alltrax controllers. As said above it's bolted to the firewall but there's a sheet of rubber in-between. Just went to check, the rubber is relatively thick.

- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki
- Electrified Electra To

antiscab
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Re: Thermal shutdown in Alltrax controller?

yup, aren't electric motors wierd?

max power is in the middle of the rev range, so to increase acceleration, sometimes you have to shift *up* :)

at higher rpm:
a series DC motor is less efficient, as more of the power is gong to running the shaft driven cooling fan.
on the upside, the extra cooling flow, and lower current through the motor means it runs cooler.

the controller should run cooler due to the lower motorside current.

battery current is higher due to having to run the fan.

one thing to watch out for: what is the rpm in 2nd @ 40mph?
you do have to avoid running the motor above ~4000rpm (or 5000rpm for a few seconds)

the rubber between the controller and firewall suggests the case is live (which is unusual).
when the car is on, measure the voltage relative to the various traction batteries.

if it is live, you can still put a thick piece of metal between the controller and rubber to increase the thermal mass.

Matt

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst 2 x TC Charger & MC
conversion

reikiman
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Re: Thermal shutdown in Alltrax controller?

I've posted some info, pictures, and thoughts here: http://visforvoltage.org/forum/9065-some-thoughts-redesigning-karmann-ghia

Basically - In the medium term I'll be replacing the motor, controller and battery pack so I don't want to invest too much into fixing issues on the existing setup. But obviously there is an immediate overheating problem. I am thinking that swapping the motor now for the new one will help with motor overheating, and that will leave the controller overheating. Maybe there's a way to do a temporary heatsink ?? I'm gonna go by the electronics surplus place tomorrow 'cause I know they have random heatsinks and mebbe something will look like it can be mounted on this controller.

- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki
- Electrified Electra To

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