Motor Controller Temperature Correction 1

[rteich]

I am working on testing some different heat sink setups on a motor controller. We are forced to test outside and since the daily temperature varies it becomes difficult. Does anyone have any ideas or ways to correct the data for varying ambient temperatures.

 

[machmech]

Hello rteich

Most motor controllers are built with adequate cooling for the intended process unless you are building one your self then you are given options. I don't think you can over cool a motor controller, Why not adjust for the extreme and go with that?

You might want to post some specs so you can get a better answer. I hope this helps some.

Getting older is inevitable
Acting your age is optional

 

[itsmoked]

rteich; Generally all this stuff is handled as temperature rise . So if your test shows some device reaching 140F and the ambient is 90F your system is obviously running a 50F rise. This lets you and/or customers make assessments like, "what happens if my ambient hits 100F?". So you could make all your testing based on rise verses some fixed ambient allowing you to essentially stop worrying about a changing ambient. What you can't ignore would be wind as this will screw up everything.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[CJCPE]

To put it slightly differently, you design based on a maximum expected temperature rise above a desired rated ambient temperature. Your test data should include the actual ambient temperature plus the critical component temperatures so that you can calculate the actual temperature rise and the projected component temperatures at the desired rated maximum ambient temperature.

 

[IRstuff]

Up to a point. The absolute ambient temperature affects the gain of analog devices, so the inherent efficiency can can change, which does require an additional layer of correction or at least, control.

TTFN

 

[rteich]

I appreiciate everyones quick response thank you!!

itsmoked,

What we are trying to do is test for the most effective yet simply designed and adaptable heat sink configuration.

What i have is about 4 sets of data (individual tests) all with different heat sink configurations. If i plot the difference between the data point and ambient for each set of data will i then have excluded ambient temperature from my testing? Or do i need to have multiple sets of data with the same heat sink configuration to find a trend before i compare to the other data?

You also mentioned somthing about wind. Some of these heat sink configurations have different fans included in them. Is this the type of wind you were refering to that will screw everything up?

Thanks again

 

[itsmoked]

Hello rteich;

First-order effects of heat sink performance versus ambient can generally be ignored. If you're talking about, 32° F. versus 90° F. then yes ambient should probably be taken into consideration. What I'm led to believe, with regards to your case, is you're just doing tests on possibly different days and the local ambient is subject to being several degrees different.

Understand that your heat sinks are using two techniques for ridding themselves of heat. One is radiation the other is convection (fan driven though it may be). If your design is heavily dependent on radiation then the ambient makes a much larger difference and will possibly even be a first-order effect. If air circulation is fan forced then radiation will likely be a second order effect.

Most heatsink studies aren't worried about low temperature operation as the high-temperature operation will be the thing causing the product a problem.

So yes, if you are making comparisons between different heat sinks in the the same approximate ambient, plotting the difference between a data point and ambient for each set of data will exclude your ambient temperature from your testing. Keeping in mind what I said previously!

If you're running fan forced air across your heat sinks, the radiation component is pretty much overridden.

By wind, I meant if you're running a fan forced system or a non fan pure convection system and it's out in the open or in a breezy area those breezes will make a large difference in the performance of the heat removal system and so would have to be taken into account.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com