# Loss of power and stuttering



## Dougnutz (Aug 22, 2011)

Hi all,
I've been quite for a while, busy driving my ev and working on other projects. I must say first it's been an admirable beast of burden. But the other day coming home from Home depot, lightly loaded on a 90+ degree day I suddenly lost power coming up the hill to my house. It's about 1/4 mile and about 4% grade. I usually climb the hill at about 275-320 amps (battery amps). I'm running a stock Curtis 1231c. and Warp 9.

The power loss was sudden and acted like some sort of overheat limp mode. It was capable of normal acceleration to about 160 amps but more than that it would emit a high pitch sound, similar to the low speed sound of a Curtis controller, and not apply more power despite pedal position. 

the controller does have a good size aluminum heat sink with two 6 in fans on it but I think it may have still overheated due to the heat of the day. Anyway since then the vehicle stutters terribly during low load driving. If I shift into a high gear and use more throttle then the stuttering goes away or is greatly reduced. Which seems backwards to me since the system has to work harder. The batteries seem to be fine and perfectly balanced. All cables and connections look good and are tight.

Anyway I'm a little bit of a loss to diagnose this. My gut tells me the controller may be damaged but I want to figure out how to test it first. I tried testing the pot with an o-scope but it looked to be fine. 

Any help would be appreciated.
Doug


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## Dougnutz (Aug 22, 2011)

Well it seems to be heat related. After a cool morning it drove perfect. I guess the heat sink or air flow is not sufficient.


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## Ziggythewiz (May 16, 2010)

Do you have a temp sensor or at least a laser thermometer? What size is the sink and fins?


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## Dougnutz (Aug 22, 2011)

I do have an infra red thermometer. 

The heat sink is about 2 in wider and longer than the controller. The fins on the bottom are thick (1/4 in) and spaced about 1/4 in apart. There are two 120 mm fans mounted directly to the heat sink. It's made of aluminum


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## Ziggythewiz (May 16, 2010)

What kind of temps are normal for you?

I'd get readings for resting in both hot and cold weather, cool cruising, and stuttering (thermal cutoff). The fins sound pretty small, so that may be an issue...edit, how long are the fins? 1-2" is typical for add on heat sinks, but factory ones are often much smaller.


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## Dougnutz (Aug 22, 2011)

I'll get readings later today. I commute by electric bike so the truck mainly sees weekend duty. 

Anyway the fins are about 1/2" definitely no where near 1"

The heat sink is pretty thick but I'm starting to think it lacks enough surface area to dissipate the heat.


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## Dougnutz (Aug 22, 2011)

I finally took some readings. long story made short; my charger died so I was down a week waiting on parts. In the mean time the weather has turned cooler and the problem has reduced. Further pointing to a heat issue.

Anyway I pulled over at the top of a hill after the stuttering occurred and most of the top of the controller read about 110 (degrees f) and the bottom where the heat sink is read about 120 ish. It took me about < 30 seconds to stop, get out, and read temps. I suspect the temps fell some but this doesn't seem like it's "too hot" to me. 

What sort of temps should I expect?


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