How hot is hot

[David Soper]

Been flying couple of years and still consider myself as a novice. I have a 40A esc running on 4s battery with 11x5.5 prop. (Ruckus) they say it will run happily on 4s with either 11x5.5 or 10x6 prop. ( I only running 4s because i crashed the Riot XL and have 4s batteries spare)

I have not maiden flight yet, so running out of flight is proberbly not a true reflection on how hot or how much current the esc is drawing, as no true air flow for cooling. It does seem to get quite hot, cannot easily hold esc in hand after 5 mins at 50% throttle.

I guess the only thing is to see what esc is drawing in current... im not sure how to do this.

If i discover the esc is drawing close to 40A would changing to 50A esc be better?

 

Edited By David Soper on 01/02/2019 13:19:07

[Martin Harris - Moderator]

I'd be worried that those sorts of temperatures would reduce component life. ESC maximum power figures shouldn't really be taken as a guide to continuous power - I would aim somewhere in the range of 2/3 of the rated power for full throttle operation (counterintuitively, accepted wisdom is that more heat is produced while switching at part throttle) and do make sure that you have a good cooling airflow over the heatsink side of the ESC.

[Allan Bennett]

Posted by David Soper on 01/02/2019 13:06:31:

. . . I guess the only thing is to see what esc is drawing in current... im not sure how to do this.

If i discover the esc is drawing close to 40A would changing to 50A esc be better? . . . .

You check the maximum amps draw using a wattmeter like this one. Just connect it in line with the battery, restrain your model, and then run it at full throttle on the ground with a prop on and a fully charged battery, and observe the maximum amps. Like Martin, I like to have an ESC that is rated for somewhat more amps than the motor, or at least, more than the maximum amps your battery/prop combination produce.

A wattmeter will also show you the volts, which you will notice will reduce as the throttle is opened, and the power in watts. It will also allow you to try different props to determine which ones give the optimum power for your setup -- smaller prop is an option that will reduce the amps, and the stress on your ESC, but it will also reduce the power.

[David Soper]

Thank you for your advice, Century also advised me to reduce prop to 10x6, which will reduce load on esc. I understand it will reduce power/thrust, I got a lot of vibration on this prop, i suspect its a not well made prop and is unbalanced. I guess you get what you pay for... i think i should maybe get more into prop balancing!!

I still ask if i can upgrade to a higher Amp esc so keep my lovely balanced prop and power should i ever need it

[Geoff S]

When I had a day job designing measurement systems for aero engine rig and bed testing we would run full mil spec electronics at 125 degrees C for some jobs (ie on engine radio telemetry) but it's not a good idea generally. If your esc was too hot to hold comfortably then it was around 50 deg C and the semi conductors inside were almost certainly higher. The components in there are almost certainly not full mil spec and in any case higher temperatures accelerate failure. Best to keep things as cool as possible.

First thing is to measure the current from the battery using a so-called watt meter as others have said. For an electric flyer it's a very important tool and should be used to check all electric power systems. An esc should be run at no more than 2/3 its rated maximum - a few seconds of maximum on a vertical say shouldn't be a problem but on landing the esc should be only warm to the touch.

As for your vibrating prop - it just needs balancing and there are lots of balance tools available and probably YouTube videos explaining the procedure. You can either balance by removing material from the heavy end or add weight to the light end with paint.

Geoff

[David Soper]

Thanks Geoff

I suspected the prop was unbalanced and i will invest in a watt meter, this is where aero models gets beyond the 'novice' and into a lot more 'stuff' !

[Martin Harris - Moderator]

Don't overlook the possibility that any spinner fitted could be causing imbalance. Run the prop without a spinner to check this.

Edited By Martin Harris on 01/02/2019 15:35:52

[Peter Beeney]

David,

I’m probably being a bit pedantic here, and maybe it really doesn’t matter much anyway, but the power at the prop is not necessarily that as seen as the reading of the watt meter. In fact, it can never be exactly equal, it’s always going to be modicum less, due to amongst other things, the power used overcoming the inertia of the motor; however, reducing the prop size might not always reduce the power/thrust.

There is a rational explanation for this, but one simple short answer might be is to be prepared to try a variety of prop sizes and see which one performs best; changing diameter and pitch, with a combination of both. Keep an eye on the current flow but the faster the prop turns the better, it will be using less amps; and as an added bonus will thus give a little more duration. I invariably use ACP i/c sport props; in general I’ve had better performance from these than the E types…

Hope this is of some use…

PB

[David Soper]

Hi Martin i of course ran prop without spinner and the vibration was the same .. thank you Peter i will look into you suggestion

[MattyB]

Posted by Geoff Sleath on 01/02/2019 15:01:28:

...First thing is to measure the current from the battery using a so-called watt meter as others have said. For an electric flyer it's a very important tool and should be used to check all electric power systems. An esc should be run at no more than 2/3 its rated maximum - a few seconds of maximum on a vertical say shouldn't be a problem but on landing the esc should be only warm to the touch.

Choosing ESCs with 50% headroom is a safe strategy, but I think overly conservative and sometimes impossible if you have a very slim fuselage as in many electric gliders. I used to be more cagey, but now work on 10% or 10A headroom, whichever is lower. Examples:

• If powertrain draws 40A at full throttle, ESC rating should be minimum of 45A (i.e. 1.1X 40 = 44A)
• If powertrain draws 80A at full throttle, ESC rating should be a minimum of 88A (i.e. a 90A one)

The only exception to this should be if you are very unsure of how much power you may actually need and the motor has the headroom to run at significantly more. In that instance I would spec based on the max current of the motor + 10% or 10A, whichever is lower. This then gives you the ability to prop up without replacing components if you find your inital prop choice does not give enough thrust.

Edited By MattyB on 01/02/2019 17:04:51