Watt meter question

[john66]

When testing my motors on a watt meter how long should I WOT for to get as accurate reading as possible?

Thanks, John

PS they will be firmly screwed to a bench this time.

[john66]

Results in so far XYH 35-36 1100kv motor with Hobbywing Pentium 40A ESC

MA 9x6 WOT = 21.3A

MA 10x6 WOT 25A

I ran them on WOT for a cpl of secs while the reading stabilised.

John

[flydiver]

All you need for a reading is a few seconds. It can be useful to run for 15-30 sec when you think you are close to what you want and then check for component heat. OK for things to get warm but not HOT. No air cooling on the bench so don't run longer-the center of a prop wash doesn't really provided much cooling and if things are stuck in a plane there can be almost zero cooling.

Take several seconds to ramp up. If you jam the throttle you get an unusually high peak reading from acceleration.

[john66]

Cheers flydiver, as you can see with the fresh impatience of a noob with a new toy I went ahead and took the readings for my cub build motor before a response. It was more the draught on various plants and bits of paper in the room that made me stop WOT after a couple of seconds, I did ease it up gently though. A good point letting run WOT for several more seconds to check the temps of the electrics. Will clear up a bit more and try this.

Thanks, John

[john66]

Can anyone confirm if the readings I got in the 2nd post are aprox right for a brushless 1100kv motor, with the props concerned?

John

[flydiver]

Unless has exactly the same setup you have to go to the motor specs for that info. Be aware that the Chinese lie about their specs, a LOT. Until proven otherwise I degrade all specs about 20%. That's where the heat check comes in. If it gets hot, it's being pushed too hard.

Also, quality control is poor on stuff. The cheaper > the worse. On a lot of towerpro motors the winding is so erratic that motor with the same designation will have entirely different KV and thus have different load capabilities.

If you got a motor without out specs (a LOT of cheap RTF come that way)....well, you are on your own.

[ginginho]

Jun 1, 2010 16:25:03 GMT 1 @john66 said:

Can anyone confirm if the readings I got in the 2nd post are aprox right for a brushless 1100kv motor, with the props concerned?

John

John, IIRC I get around 260W (~26A) in the Gem with the 1100Kv motor spinning a 10x5 APCe clone. So your readings are not far off the mark. Which pack amd prop make did you use?
The stock LIPO will be pretty much flat out delivering 25 or so amps, so if that was the one you used, that's probably what's the limitation. The LM (2250 20c IIRC?) will be more than capable of dumping what you prop and motor combo will try to extract, the Twinny pulls 32A out of those without the pack missing a beat.
Does your meter show voltage (look at the drop under load) and watts in as well as amps?

[john66]

Jun 1, 2010 17:07:04 GMT 1 ginginho said:

Jun 1, 2010 16:25:03 GMT 1 @john66 said:

Can anyone confirm if the readings I got in the 2nd post are aprox right for a brushless 1100kv motor, with the props concerned?

John

John, IIRC I get around 260W (~26A) in the Gem with the 1100Kv motor spinning a 10x5 APCe clone. So your readings are not far off the mark. Which pack amd prop make did you use?
The stock LIPO will be pretty much flat out delivering 25 or so amps, so if that was the one you used, that's probably what's the limitation. The LM (2250 20c IIRC?) will be more than capable of dumping what you prop and motor combo will try to extract, the Twinny pulls 32A out of those without the pack missing a beat.
Does your meter show voltage (look at the drop under load) and watts in as well as amps?

I used the stock battery and both props were the Master Airscrew electrics.

Good point about the battery, I didnt consider that. Yes meter shows voltage which dropped by about 1.8v at WOT and the watts went up to 184w from a stationery 22w I just rechecked now. I will recheck with my 2250 next time I take it up from storage charge.

Thanks, John

[john66]

My main concern is that even if the meter isnt the best out there is that it is close enough to prevent me overpropping, particularly with a 3 blade set up on the 1250kv motor.

John

[flydiver]

Sure, unless it's grossly inaccurate it should be fine. Propping is not measured in 10th of an amp.
More important is the approx output and battery voltage drop as gingho indicated. If the battery drops voltage badly and warms up fast then the battery isn't keeping up with the requested draw.

It's good policy to not exceed 80% of the C-rating of lipos. To do so regularly guarantees a short life. Remember, those cheap lipos are over rated too.
So stock lipo: 1300 x 1.5 > ~ 18A x. .8 (over rate) > 14A .
You are WAY WAY over the top of the stock lipo. Guess what happens to it? Plus it can't feed that power pack to it capability so you really don't know what it can do with that battery.

[john66]

Im slowly begining to understand it, though I have read alot of stuff about it in this and various other websites, I find it quite difficult to grasp stuff until im putting it into action myself.

Thanks chaps for your input so far. getting a chance to see it in action on the meter while reading the posts is helping loads.

I will stick to using my stock battery on my stock motor.

John