Marginal excess AMP draw?

[Harry Glover]

I am in the process of learning how to set up twin motors as follows:

2x brushless 22x12 1400kv motors with 8x6 props

1x 3s 2200 35c Lipo

2x 30A ESCs

 

Using a Power Meter the amp draw is 35A on full power

My question is the 35A draw the sum of both motors or the draw of each motor.?

Ran motors at full power for very short periods. No smoke, no smell, no heat.

 

Also occasionally from No1 or No2 motor (not sure which) I  hear a not very loud 'crack' sound similar to an elecrical short. No heat. No smell. No smoke. No change in motors performance.

Can anybody educate me as to the above. Please keep it simple. I am 82 and minus a few brain cells (joking)

 

 

[Geoff S]

Assuming you have the power meter connected directly to the main battery, then it's the sum of the 2 motors.  To check each motor individually the meter needs to be in the feed to just one of the escs.

[Phil Green]

I depends where you're taking the current measurement Harry - if its from the battery then yes its the sum of both motor currents.

To test individual motor current, put your power meter between one ESC and the Y connector, then between the other ESC and the Y connector.

Dont worry if whilst doing this you notice a slight imbalance.  Be very careful, with a twin you're in danger of losing twice as many fingers!  🙂

 

Edit: Sorry Geoff - doubled up there 🙂

Edited July 24, 2023 by Phil Green

[Cuban8]

What's the model they're in Harry?

As for the loud crack sound.......maybe something coming loose and catching? Need to find it in case something jams solid and you do get heat, smell and smoke! Check the motor magnets are secure.

Maybe run one motor at a time to at least narrow it down a bit.

[Simon Chaddock]

My only concern is the 2212 1400kv like this is only rated for a continuous 10A so if you are pulling 35A in total you are overloading the motors a bit at 17+A each full power. The motor will get hot unless it is very well cooled or you don't use full power for more than a few seconds.

The amps a motor draws is down to the voltage (the number of cells), the 2212 1400kv is ok for 3s, or the prop. Perhaps a 8x6 is just a bit too big (either diameter or pitch). Either a 7x6 or a 8x5 would reduce the full power amp draw to the motors continuous rating.

 

How much and for how long you might need to use full power will depend on what the model is and ultimately its weight.          

[Cuban8]

4Max do rate their motor which looks to be the same as the Ebay one at quite a bit more than 10A. Presumably they've tried it and it's OK. https://www.4-max.co.uk/value-power-package-1400kv.htm

Suck it and see I guess.

[Harry Glover]

Thanks Gents for your prompt replies. As both ESCs are conected to the battery on a Y lead, I shall test each motor seperately to determine their draw on the test rig.

The motors, ESCs, props are from 4Max Value Pack x2 and I note that the motors are rated at 10A. I ran them for probably less than a minute each time. I shall get some smaller props and try them, and if I can get the total draw down to 20-25A and  all works out ok, I shall then figure out a suitable twin motor model to put them in,

Once again, thanks gents for all the help and advice you have given me.

I shall let you know how I go on in due time. Thanks

[RottenRow]

This is the data on 4-Max's website for that motor / prop combination, so 34A for two running together would seem appropriate. However I would still check them individually for the very unlikely possibility that one is drawing a lot more current than the other.

 

Thrust/Speed

810g/1.79lbs Using the supplied 8x6 prop at 11.1V (17.5A). Est Speed 55MPH

 

Brian.

 

[Harry Glover]

Thanks Brian, I suspect that a change of props may do the trick to bring down the Amps, and thanks for the data.

[Peter Jenkins]

Harry

 

I've found that taking current draw readings with the aircraft tethered gives an artificially high current draw as the motors are kept stationary.  If you have on-board telemetry, that will be the best way to find out what is being drawn while airborne.  

 

As an example, my set up has a 10S power pack and a Hacker Q80 motor rated at 2,800 watts.  I use a 3rd party on-board telemetry module (Link) that can be set up to talk to almost any radio, and this gives me my data.   When I did a ground power check, I briefly saw 3,600 watts and 99 amps at full throttle.  Needless to say, I closed the throttle pronto!  However, in the air, the maximum power I have seen, and then only once after slowing the aircraft down to almost stalling speed then applying full throttle and flying a vertical upline, was 2850 watts and 80 amps.  The normal maximum I see is 2750 watts.  I conclude therefore that using on-board telemetry will be far more useful than trying to check current draw/ power with the model tethered.  The UnisensE is very light (10-20 g) and small and well worth the money.  You can move it from model to model to check all your other models as well.

 

Whilst you can test on the ground and reduce the power draw to not exceed 10 amps, once in the air, your power train will be up to 25% below what it is rated at.  If the performance you get is fine then that's OK.  If power is less than expected the best way forward is to check the power/current with  airborne telemetry.

 

Peter

[Harry Glover]

10 hours ago, Peter Jenkins said:

Harry

 

I've found that taking current draw readings with the aircraft tethered gives an artificially high current draw as the motors are kept stationary.  If you have on-board telemetry, that will be the best way to find out what is being drawn while airborne.  

 

As an example, my set up has a 10S power pack and a Hacker Q80 motor rated at 2,800 watts.  I use a 3rd party on-board telemetry module (Link) that can be set up to talk to almost any radio, and this gives me my data.   When I did a ground power check, I briefly saw 3,600 watts and 99 amps at full throttle.  Needless to say, I closed the throttle pronto!  However, in the air, the maximum power I have seen, and then only once after slowing the aircraft down to almost stalling speed then applying full throttle and flying a vertical upline, was 2850 watts and 80 amps.  The normal maximum I see is 2750 watts.  I conclude therefore that using on-board telemetry will be far more useful than trying to check current draw/ power with the model tethered.  The UnisensE is very light (10-20 g) and small and well worth the money.  You can move it from model to model to check all your other models as well.

 

Whilst you can test on the ground and reduce the power draw to not exceed 10 amps, once in the air, your power train will be up to 25% below what it is rated at.  If the performance you get is fine then that's OK.  If power is less than expected the best way forward is to check the power/current with  airborne telemetry.

 

Peter, your last paragraph probably describes perhaps the way to go for now, I would have to learn more about telemetrey before diving into that aspect of our hobby.

Thanks Peter

 

[Harry Glover]

1 hour ago, Harry Glover said:

Peter, your last paragraph probably describes perhaps the way to go for now, I would have to learn more about telemetrey before diving into that aspect of our hobby.

Thanks Peter

 

[RottenRow]

Harry,

 

If the data provided by 4-Max on their website is correct, as I mentioned previously, the motor and prop. combination that you already have and which was supplied by them as a complete set, is rated at 17.5A maximum current. As that is what you have measured using your 3s battery (35A for two of them working at the same time), I can't see where you feel a problem exists. I can't see anywhere, on the 4-Max website, that they are stating that the maximum current for the motor you have is 10A. If they do state that somewhere then it is directly contradicting their own 17.5A rating, and the purpose of supplying a matched set of parts (motor, prop and ESC).

 

If you're really worried about it, you could give 4-Max a call and ask them directly.

 

As Peter says, once in the air the current will drop anyway, plus you will be unlikely to be using full throttle for most of the flight.

 

I would install the motors and props as supplied into the model and go and fly it.

 

Brian.

[Harry Glover]

Thanks Brian for your view. I shall still try to get the Amps down by changing props, and if that does the trick, and eventually fly's the model I select, then that will be sufficient for me, and I would still have a Amps "reserve/buffer" if things do not turn out as hoped. A sort of Max/Min envelope.....mebbe.

Harry

[MattyB]

 

8 hours ago, Harry Glover said:

Thanks Brian for your view. I shall still try to get the Amps down by changing props, and if that does the trick, and eventually fly's the model I select, then that will be sufficient for me, and I would still have a Amps "reserve/buffer" if things do not turn out as hoped. A sort of Max/Min envelope.....mebbe.

Harry

Sorry, but you are trying to solve a problem that doesn’t exist. If you didn’t have any intention of listening to the responses people post, why ask in the first place? Even if you don’t believe posters here, call 4-max and get his view - £5 says he’ll tell you all is well, and go fly as is…

[Harry Glover]

Brian, dont assume that I have no intention of listening to advicefrom posters, and as I said in my post, I'm 82yo, and prefer to keep things relatavely simple, and follow a simple 'learning curve'. Your advice has been noted (amongst others).

BTW I dont bet (if that was the meaning of the £5.

Harry

[RottenRow]

3 hours ago, Harry Glover said:

Brian, dont assume that I have no intention of listening to advicefrom posters

 

Harry, I haven't assumed that..

 

Brian.

 

 

[Simon Chaddock]

Harry

I would point out that many web sites selling exactly the same motor quote "10A max efficiency and a max 12A/60s".

I am not saying the Emax figure is wrong but it a lot higher.

Unfortunately I do not have a 1400kV version (only a 2200kV one) of that motor to actually test.

I can only suggest you run one of your motors with an 8x6 prop at full power for up to 60 seconds on some sort of test stand using a fully charged 3s and stopping periodically to see how hot it actually gets. If the outside of the motor is getting too hot to touch then stop! Remember if the motor is inside a cowling it will not be so well cooled as "sitting out in the open" 

This is a home built test stand I use, in this case to test a similar but slightly more powerful motor with a 9x6 3 blade prop.

 

 Sometimes actually doing your own tests gives you the most confidence.  

 

[Cuban8]

Uncomfortably hot to the touch is definately a no no. Not efficient and damaging to the windings over the long term. None of my leccy motors run any warmer to the touch than luke warm - even my largest 1200W unit after a thrashing. The little 400W motor in my Yak remains quite cold even after six or seven minutes of spirited flying. It's all in the numbers. Overheated insulating lacquer on the windings has a unique odour as well.

Edited July 26, 2023 by Cuban8