Hot ESC, But Apms Are Below Rating?
 

Last night I took out the E-revo. Running 540C 9XL, Quark Monster 125, and a 4s Lipo setup on 24/66 gearing. I was running it in a open flat short grass field.

I put the Watts Up meter in line with one of the battery packs. I was just trying to get a feel for the amp draw. I was actually surprised at how many amps it was pulling. In first gear I was pulling like 89 amps on a fast start and full throttle puch all the way to top speed. In second gear I was pulling 115 amps! I was really surprised that it would be that high. My question is, the Quark esc was getting really hot after only a couple passes on the speed run, I was not exceeding the 125A constant/300A peak rating on the esc, Why would it be getting so hot. It didn't thermal, but it felt hotter than I was comfortable with. If I kept going Im sure it would have thermaled. The motor was warm, but no where near being hot and the battery packs were both not even warm yet. Bats are rated for 96A constant, 120 peak.

It just bugs me that the ESC is rated for 125A constant, 300A peak, and my set up peaks at 115A and it gets to hot. That burns my butt!!!:mad:1 (so to speak)

So my question is: If my peak amp draw is below the constant rating of the ESC why would it be getting so hot? Would a 5s Lipo be better as far as heat on the esc?

BTW: I just bought a little duratraxx temp meter today(I'm sick of guessing).

It sounds like it is over geared. Go up on the pinion or down with the spur. If the batteries get hot then go back the other way. Under geared= hot esc, over geared= hot battery

undergeared would be hot motor,cooler esc and batteries.

It could be a tad overgeared for general driving,maybe drop to a 20/66 but your main problem is the grass.Try it again with a low rolling resistance (gravel or tarmac)and the temps and amp draw will be dramatically lower.Run a much lower gear on grass.

Edit;does the esc get plenty of air cooling? it will have plenty of heat to dissipate at 115A/14.8v.

Another edit;just a thought but the switching frequency affects the controller efficiency and schulze recommend 9 KHz part load switching frequency for lehner/hacker motors above 8 turns and 19kHz below 8 turns.the quark is fixed at 38kHZ according to the specs.I hope that's nothing to do with the heat.

I know I could just gear it down and reduce the amps that the system will draw. What I don't get is why would the ESC overheat if I am below the specs of the unit?

The 115A I was drawing was peak, under hard acceleration in grass. The constant amp draw could not have bee more than 60 - 70A. The ESC is rated for 125A constant and 300 peak.

If the esc is rated for 125A constant, I shouldnt need to gear down for 115A peak. I should be well within the limits of the ESC. The only reason for gearing down make it easier for the motor to move the truck therfore reducing the amp draw. Am I misinterpreting the ESC rateing?

That frequency thing could be something, but then why wouldn't the ESC manufacturer say that in the specs? They are the ones who set the frequency in the ESC. Its not adjustable in the Quark as far as I know.

And yes there is plenty of airflow over the esc its monuted by itself away from the batts and motor. I could add a fan to the esc, I have it here and actually planned on doing it just for safety, I just haven't gotten around to it yet. But that still doesnt justify the thing overheating when I'm drawing current below the rating. Am I crazy?

Well it will heat up either way. How hot is it getting?

The frequency thing was just me mumbling on.

The controller being rated for 125 amps doesn't mean it can pull that many amps without getting hot,it means it can pull that many without going smoke.
115 amps is still going to produce a certain amount of heat regardless of the amp rating of the controller as it can't be 100% efficient.The quark has a very low resistance but amps still produce heat regardless of the controller rating,simply the heat needs dissipating.that's how i understand it anyway(could be wrong).

My MGM is rated for 160amps constant and that get's very hot if i run it in grass,even at a conservative gearing.The same gearing on gravel or dirt or tarmac and it's more like 120F after 15 mins compared to 150+F on grass after 5 mins.I suspect the grass was the main problem and yes,at that average amp draw(more relevant than peak probably with regard to heat)it sounds like it will need lots of cooling.

I didnt have a temp gauge so I don't know exactly how hot. (I went and bought one today). It was hot enough that I could only hold my finger on it for a 5 count and then I had to pull it off. I know that is still probably OK... But barlely and that was after only 3 minutes. Granted, I was running it pretty hard. Full throttle runs across an open grass field.

I know its going to heat up either way, buy it shouldn't overheat if I'm not pushing it to or past its rated constant amp limit. Should it? It didn't thermal, but thats only cuz I stopped running it before it did. Another miute or so and I gaurantee it would have shut down.

I just dont get the whole amp rating thing. If its going to overheat and thermal at a much lower constant amp draw than the rated 125, why are they rating it for 125? Shouldn't they rate it at 80 or something then?

This doesn't really answer your question about the ESC getting hot, but you can set the ESC so it has a more gradual throttle response. This would keep the amperage down somewhat, making the ESC heat less. I changed this setting on mine and didn't notice noticeable loss in power - if anything, standing starts were more controllable. There is also a setting for the types of batteries you have. One setting pulls more current, the other is a little more gentle on the batts. I would think this would also have the effect of slowing down starts and acceleration. Something to think about anyway.

I agree with Gustav; I think it's the heavier load from the grass. The little heatsink on these things are quite small to dissipate the heat required. If you are pulling 115A @ 14.8v, that's 170 watts being dissipated on the controller assuming a 90% efficiency. Frankly, I'm surprised it's just a little hot. Ever feel how hot a measly 75W lightbulb gets after just a few seconds?

Again, this doesn't address your concern about why it's rated for a certain current, yet gets really hot when you draw less. If you can, maybe mount the bottom part of the case on a piece of 1/8" thick aluminum as a secondary heatsink? If it's big enough and you have some type of thermal grease in the joint, it should go a long way to improve temps.

lots of little changes
 

So it sounds like 125A consant doesnt mean 125A constant witout some help disapating the heat. The electronics won't fry at 125 constant, and you can run it that way IF you can keep it from overheating.

I think I'll try the idea about setting the 'tourque' setting on the esc down a little. I have it on the hightest setting right now. That will probably help a little. Set on high, its a little to touchy. I was thinking about turning it down a little anyway.

I like the idea of maximizing the heat sink with the mounting.:dft003: Right now its mounted to an aluminum bracket, but its mounted with some foam servo tape in an attepmt to isolate it from the small vibrations (probably useless). Im gonna try redoing the mount, get rid of the foam tape and attach the aluminum bracket to the aluminum gmaxx frame and try and get the whole frame to act as a big heat sink. An then of course install the fan that I intended on installing already.

I'm also gonna gear it down, but only a touch. I'm running 66/24 Im gonna go to 68/24. I know its not alot, but all of this combined will hopefully be enough.

One more question, Will a 5s lipo setup run at lower amperage? I'm assuming that a higher voltage will result in a lower amperage for the same speeds. Will this reduce the heat produced? I have a setup for 5s also. I was just running the 4s cuz I figured it was easier on the drivetrain and more than fast enough. If the 5s will run cooler I'll run it that way from now on.

It depends. It's quite possible but I'm not really sure because the motor will probably be more efficient on 5S as opposed to 4S.

Electrically speaking, you will get a certain amperage given a certain voltage and resistance (load). If you increase voltage, amperage increases also assuming the load stays the same. These statements work great for DC. However, these motors are essentially AC driven motors (the ESC converts battery DC into PWM squarish-wave AC), so it gets a little trickier. You have to factor in inductance and to a small degree capacitance , which creates current/voltage phase angles blah, blah,blah. And we can't forget back EMF. As Squee has eluded to, these motors will have the most back EMF at their ideal speed. This is sorta like added resistance, which brings the amperage down. Below their ideal speed, they won't be as efficient. Also, all of this depends on the motor's load (acceleration, vehicle weight, and terrain)

Long story short: higher voltage will increase current draw until the motor gets in its RPM "sweet spot". So if you plan on doing low speed runs for crawling or whatever, I'd go with lower voltage. You won't get the RPM sweet spot, but the lower voltage will help keep current down. If you plan on high speed runs, stick with high voltage. If you plan on doing high speed runs with a lot of standing starts or hard acceleration, you're gonna get heat, so it's up to us to find a way to get rid of it.

Great thread guys , very enlightening, with out going over my head. :p

that is why a lot more heat is generated when you use your system for racing versus using your set up for bashing around,the higher the grass your set up is running ,the greater the heat is generated, using a fan on your system will greatly help to dissipitate your heat in your system, plus proper positioning of your esc,motor, batts, i do really believe that hard launches and acceleration on this system really put more strain on your system as well

Higher voltage normally results in different gearing and if you want to get the same speed, you can tune down your transmitter, and that way, the current will go down to reach the same amount of power to reach a certain topspeed.

Both can be accomplished by either gearing it down or tuning down your transmitter. (that is, if you are happy with the current speed)

And with brushless setups, the current of the batteries are mostly the limiting factor. if a battery can deliver 115A of peak current, it doesn't matter if you use 4 or 5 cells. the peak power stays 115A.

Anyone know if if the battery type setting on the Quark will make a difference? Right now I have it set to Lipo High cuz the batteries I have will handle the discharge rate. If I switch to Lipo normal will that cap the amp draw at a certain level? If so does anyone know what the cap amperage would be?

I'm not sure I'm clear what the difference between Lipoly high and Lipoly normal setting is. The documentation is pretty weak and doesn't really say what the difference is. It just cautions that the batteries should be able to handle %150 of the expected discharge if you are going to use the high setting. Anyone know?