# Alltrax SPM72400 issues.



## akseminole (Jan 5, 2014)

What are you using as a heatsink and can the controller get decent airflow?


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## Jayls5 (Apr 1, 2012)

I'm not using a heatsink. I was told that Alltrax is very good about being realistic with their claims. I specifically bought the SPM series over the AXE because they advertise, "Thermostatically fan cooled, no external heatsink required. Dramatically increases continuous power compared to conduction cooled drives."

I have it in a large box. It's not getting free airflow from the outside, though it has plenty of space in the box to circulate air. I'm not even sure if the bottom of the SPM controller is thermally conductive like the old model is  I'd happily throw one of my aluminum plates under it if it would help.


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## akseminole (Jan 5, 2014)

Is it possible that the air in the box gets hot and doesn't adequately cool the controller? Can you route an inlet and outlet air duct to your controller?

Isn't the box your controller is in the same one that your batteries are in? Do you have a temperature gauge to monitor the inside of the box air temp? Aren't RC batteries sensitive to heat?

(Not related to this post; have you updated your build thread recently? When I tell people about the build that I am planning, I like to whip out your youtube videos as an example. People usually make impressed sounds.)


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## akseminole (Jan 5, 2014)

It seems to me that a closed metal box with an active electrical heating element inside it and a fan running would tend to act like a convection oven. 

The controller pumping out 72v 200+ amps at what, 90-95% efficiency needs to shed like 1,500 watts or more of waste heat at a pretty constant rate in order to not overheat, right?

If you Can route air to it, I bet that would be cheaper than adding a heatsink and adding the extra mass of a heatsink to your car.


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## akseminole (Jan 5, 2014)

As for you 5v signal problem, it is my understanding that desktop computers by and large use an internal 12v DC power supply, so why couldn't you simply kludge together a desktop USB port as a 12v to 5v adapter?
http://m.ebay.com/itm/361192538489?nav=SEARCH

(I'm only an expert at coming up with off the wall ideas, not at implementing them, idk if this will work or how difficult it would be.)


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## Jayls5 (Apr 1, 2012)

akseminole said:


> As for you 5v signal problem, it is my understanding that desktop computers by and large use an internal 12v DC power supply, so why couldn't you simply kludge together a desktop USB port as a 12v to 5v adapter?
> http://m.ebay.com/itm/361192538489?nav=SEARCH
> 
> (I'm only an expert at coming up with off the wall ideas, not at implementing them, idk if this will work or how difficult it would be.)



I like this idea. I'll give this a shot and break out the connections from the chip if it comes down to it. My roommate and I put the "bad" 5v converter under an oscilloscope today and found a 300mV variance on my crappy Chinese 5v converter. My USB port on my laptop that gave the smooth throttle response was around 60 mV voltage variance. The chinese model was also a sawtooth wave while the USB was smooth enough to look linear. Long story short, we took some random capacitors from my junk bin and put them in parallel with the crappy unit I had, and it reduced variance to 90-100 mV. I'm going to retest it when I'm off work in 3 days.

Regarding heat, I speculated that the closed box might have something to do with it. I did a single run with the box open to free air on a nice day, and it didn't give me too many problems... but then again, I had also adjusted the current down to 220A out of frustration. I don't know which variable improved the situation, but it still seemed weird: the current wasn't constant at 100% throttle even at the start. It had to climb up to the 25-50% rpm range to build the current up to what I had it set at. Of course as RPM peaked it understandably dropped current due to back EMF, but it just didn't make sense that "off the line" was so weak. I have to do a few more test drives.

I have huge update coming for the main build thread. I didn't want to clog up the forum with a bunch of trivial updates. I'll try to get something out tonight or tomorrow.


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