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Old 06-11-2003, 08:53 PM   #16
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Ok this would be interesting, what if you took the motor out of the car and put a fan on it as a load?
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Old 06-11-2003, 10:44 PM   #17
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Quote:
Originally posted by fatdoggy
...what if you took the motor out of the car and put a fan on it as a load?
Good suggestion fd, but it might not be enough load to replicate normal racing condition - you'll need some pretty big prop to do that.

Have a 6" prop setup to bolt onto a 540 shaft from long time ago (haha, "air-car" experiment); last time that we used it we had it running at ~10,000rpm on a silvercan 540 @ 7.2V, it drew only about 5A. Small props don't have much pitch so think the motor wasn't really loaded... still lots of wind though!


I was thinking of the bulb array in lieu of motor as that can at least draw 20-30A.

Will wait till next bad-TV day...
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Old 06-12-2003, 01:27 AM   #18
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apologies, i didn't explain that all that well.

I was under the impression normal racing conditions were going to be replicated. (braking and accelerating). running at constant speed even at partial throttle is not going to warm the brake fets up at all.

in which case the contant acceleration and deceleration of steel wheels would IMO provide sufficient load.

I have access to a fair amount of test equipment, in fact the motors on my reviews are subjected to waht i would class as normal race conditions. a computer does the controlling not me, so its subjective.

I shall run a small test this morning and get back to you.

have a nice day

sanj
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Old 06-12-2003, 01:43 AM   #19
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Quote:
Originally posted by schumacher
I was under the impression normal racing conditions were going to be replicated. (braking and accelerating). running at constant speed even at partial throttle is not going to warm the brake fets up at all.
Yes you're right on the brake FETs, they got no work at all.

Replicating racing conditions is good idea for motor testing no doubt. High-mass wheels would have an effect here; better still would be a rolling-road dyno. Needless to say, you'd also have arranged appropriate speed-scaled cooling for the motor on test? (btw good work on the ol' Clara pages, Sanj. good reading)



Re: the Test, I was just wondering how hot the drive FETs got, between Full-On 100% speed and approx Half-On speed; that was the whole point of the original discussion, so that's all I went for. I didn't even scan the brake FETs' temp, only the drive FETs.

Throttle was pegged down appropriately with a cabletie...


If you've got some good test equipment, how about rigging something up re: FET operating temp @ 50% vs 100% drive?

Just wanna find out...
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Old 06-12-2003, 03:22 AM   #20
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okay, i spent a bit of time rigging up a rather crude test.

here's what i did.

1. ambient temperature is 20C (its regulataed in our building)
2. setup track simulation with 50% throttle (50% brake) and 100% throttle (100% brake). total run time was 5 minutes each.

speed control was a keyence zero (it has onboard fet monitoring).
and load was a centrifugal clutch device that squares the load as speed increases (similar to a proper car). Motor was Integy Matrix 12 triple

anyway run 1 with 100% throttle, temperature was 44C after running.

let both motor and speedo cool and repeated it with 50% throttle and temperature got to 54C.

let it cool

Repeated 100% throttle got, 46C

let it cool again

repeated 50% throttle got, 54C

based on that it is clear that running partial throttle heats the fets up more.

its a fairly basic test but since the only thing i changed was the throttle position i think it is conclusive.

sanj
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Old 06-12-2003, 03:48 AM   #21
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Cool results, so it does heat up under real load - interesting!

Now just gotta go find out *why*...



Sanj: any idea what the current draws were @ 50/100%?
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Old 06-12-2003, 04:04 AM   #22
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Hey all, here's more confo too.

Quote:
Asked
"Do ESCs heat up more when driven at half-throttle only, compared to full-throttle? "

**** LRP replied ****

Yes, all speed-controls do indeed run slightly hotter at half-throttle then at full-throttle!
The reason are the switching looses during the PWM of the Fet's, the gate-capacitor of the Fet has be switched on/off more then 1000-times per second on a Sprinter for example! No possibility to get rid of that...

Hope that the explanation is understandable and not too technical.
--
RetoKoenig-LRP
R&D Manager
LRP electronic GmbH
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Old 06-12-2003, 05:40 AM   #23
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average 26A at full and 13A at partial. thats a bit misleading as at half throttle the motor doesn't spin at half speed. if that makes sense?

LRP don't really like me, but still its glad that we actually agree on something!

sanj
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Old 06-12-2003, 06:52 AM   #24
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Quote:
Originally posted by WC
You started it my friend... with your "I'd rather not waste my time explaining" remark. Rather arrogant answer to a innocent query, don't you think? This is a chatboard, and differing opinions make the community what it is.


As all good engineers do, I'm constantly learning & always open to new ideas & concepts.

Increabily short memory you have...if you scroll to your first reply, it was you that came out with the "sarcastic" comments...let me quote it back to you...

" Huh?

Why should a switching FET cause more heat?

This would always be *less* than full duty, in which case Ohm's Law (heat = resistance of FET X voltage) applies.


If what you were saying is true... my ESC would be hottest when its doing nothing or running at 1% throttle, yes?


We're talking ESC here, not MSC."

I merely reply in the same manner of your response. As if I did not know the CS Rocket is a ESC and not an MSC....you insult my intelligence!

You also made the assumption that I did not know what I was talking about. Well now that you realise you were WRONG in the first place perhaps you should be careful about being so "scarcastic" in the future.

Yes, this is a public forum, if you are nice to others they will be nice to you. If you are scarcastic, they will be the same back!
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Old 06-12-2003, 06:54 AM   #25
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On the subject of what the ESC manufacturers say...there is also this on the Novak site;

http://www.teamnovak.com/Tech_info/m...fo/pol_drv.htm
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Old 06-12-2003, 06:57 PM   #26
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Quote:
Originally posted by dtm
re: original assumption...
This would always be *less* than full duty, in which case Ohm's Law (heat = resistance of FET X voltage) applies.[/B]
Original speculation went along lines of:
a) at full tilt, full current goes thru (= X amt of heating)
b) at partial throttle, only a fraction of current goes thru (=X/? heating)
Now appears that, at the high loads racing ESCs run at, the (C) heating-from-switching effect causes enough heat to overcome the lesser current going through and also (D) any FET's resistance is nominally rated @ 25degC, resistance rises as it gets hotter - catch22.

But at lower loads... the switch-heat effect must be lower...?
Hmmm...

(sigh... this would be a great topic for a uni paper. Pity we're all out in real world already, sometimes I miss those boozin' days.)
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Old 06-12-2003, 08:00 PM   #27
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Quote:
Originally posted by schumacher
average 26A at full and 13A at partial. thats a bit misleading as at half throttle the motor doesn't spin at half speed. if that makes sense?
Thanks. Yup, makes sense. Motor's RPM is more proportionate to voltage than the current, but that'll also depend on size & nature of the load.

Quote:
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Haha, I won't probe... but if you don't trust them Germans
here's one from none other than Charlie Suangka, "King of Orange"?
Quote:
(excerp)
Very good questions, for once something other than setup. Thank You!

When the ESC is at full throttle, the FETs are turned on completely.

At half throttle, or any partial throttle for that matter, the ESC does get hotter than at full throttle. This is because of the high speed switching on and off, and the current being handled at the same time. The FETs are being turned on and very fast, and a lot of current is being pulled across them.

As far as efficiency goes, the heat effects that more than anything else, mosfets loose performance as they get hot, so the "hotter" the ESC temp is at any point is the main effect on how efficient it is.

Power capacitors and schottky diodes all have major effects on the components that contribute to the heat build up or lack of it. The Power Cap will absorb the ripple current that is generated by the "switching". Also, the cap will feed the voltage it received back to the motor on the off cycle. The result is higher motor RPM at partial throttle. You can actually hear the motor change if the power cap is taken on and off at partial throttle. The ESC also operates much much cooler.

The Schottky stops voltage the motor generates when it is free spinning from going back into the ESC. This always happens when ever you lift the throttle and the car coast. The schottky seems to have a very great effect on the temperature of the ESC, today's motors create such large "EMF" stuff that the ESC's are getting a lot hotter.

We are also able to switch the ESC's much much faster than in years past. This contributes to some of the need for the Caps and Diodes. But performance is significantly better across the board.

Charlie Suangka,
Novak Electronics
1935 Deere Ave
Irvine CA, 92606
The Lord has spoken (I'm an ORANGE freak).
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Old 06-12-2003, 10:43 PM   #28
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i didn't go through the threads,so not sure wat the guyz have said...
but it seems like a temperature shutdown...could have been caused by several factors...weather,etc and not forgetting ur gearing...check ur motor recommended gearing,make sure u r not over-gearing...
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Old 06-13-2003, 03:33 AM   #29
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ijnek - one thing i am sure of is that his gear ratio was fine, chris (oasis) is one of the top drivers in Aus and certainly knows what he's doing in terms of gearing.

all the posts above basically say that a possible cause for the temp shutdown is that esc's get hotter under partial load than at full throttle and he would have been using partial throttle msot of the time in the wet conditions, thefore the speedy would have been hotter.
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