Motors amps

[matthias]

hi i am just wondering how to tell how many amps my brush-less motor will draw

 

[Tony]

Most accurate way is with a watt meter. Most manufacturers will state what the wattage is, but your other thread, that link does not.

 

[matthias]

is there a mathematical way?

 

[Tony]

Yes there is. Amperage=wattage/voltage. Wattage=amps*volts. As for figuring it out with KV, no there is not. KV is RPM Per Volt which has nothing to do with wattage or amperage.

 

[matthias]

OK so with a meter is the only way?

 

[Tony]

For the unknown chinese motors, yes. And it is the most accurate way as well. This way, you can test what the wattage is with different props.

 

[matthias]

i have a digital multi meter will that work

 

[Tony]

Only if it will read current. Most cheap multi-meters will only go up to 10 amps then you will pop the fuse. Your motors should pull more than that.

 

[ChopDrifter]

Some ESC's have telemetry that tells you the amps/watts draw.

 

[ChopDrifter]

i have a digital multi meter will that work

Tony did a youtube article on cheap Watt meter, i'll see if I can find it

 

[ChopDrifter]

Found it!

 

[Tony]

Yup, sure did. It was donated to Rc-Help by Derek here on the site! Don't need it a lot, but when I do, I'm really happy I have it.

 

[Derek]

I remember getting that meter for you, Tony! Ha ha ha....I was shopping around for one and you, jokingly, said that I should get one for you.....and I did, lol.

I tell you what...I still have my meter today. I bought that thing probably 4 years ago and it's just one of those tools that you won't use often but when you find that you need it, it's an awesome little thing to have around. I got my meter from Hobby King. I just checked their site for the meter and it seems that it's no longer available. However, here is another good looking one and not a bad price, considering what it will do:

Turnigy™ 7in1 Mega Meter Battery Checker/Watt Meter/Servo Tester

Good luck!

 

[Smoggie]

Software such as Motocalc or Propcalc will do a decent job of estimating current draw. This doesn't negate the need for the wattmeter but it's a lot better than guesswork to get in the right ballpark

 

[murankar]

I can track my amps and watts with the Vbar UI sensor. I am not sure how accurate it is but I would guess it's close enough.