cyborg1

Hi, I just bought a watt meter in the LHS, it's a knockoff of the TENERGY meter. i was testing it on a setup that I'm preparing for a 46 sized aircraft. It's a 560kv motor controlled by an 80amp ESC, powered by a six cell 22.2v 2200mah battery. the readings I got at full throttle were:
Amps:33
Watts: 650
This is with a 13x8 apc e prop. I don't have the rpm figures, but is the watt meter reading correct? It seems pretty low to me. I just wanted to know if the watt meter I got is correct or not, as I may have to change it if it isn't. Thanks for helping out, I'm a newbie at electric flight.

DaveFlynn

Need more info: what motor (4120/560?), volts (650W/33A=19.6V ???

opjose

What you've discovered is WHY watt meter's are so important.

Assuming that you've overspec'd your ESC by 80% as you SHOULD(!!!!)

60A x 22.2v = 1332 watts of power ( GOOD!!! )

However you are only using a battery pack capable of sustaining about 15C ( 20 C BURST )

So 22 x 1.5 = 33A EXACTLY what the watt meter is telling you!

So bottom line, you need higher capacity packs.

At the least 4000mAh or HIGHER 22V packs...

Or you can use two of your existing packs in Parallel.

cyborg1

Hi Opjose,

So, in this case, if I use a 4000mah pack rated at 30c, the amp figures should go up? My concern with the current setup is to ensure that the entire combo works, and that it will not be detrimental to any of the components. As it is, bench testing shows that there should be enough thrust and torque to power a 3 kilo Katana s comfortably. It was suggested that I should keep the amps below 60amps by another thread, so theoretically I should be ok? Electrics is quite confusing, as there are so many variables involved....[X(]

cyborg1

Hi DaveFlynn,

The motor is a chinese motor available off ebay. the specs provided are:
Rotational Speed 560 RPM/V
Continuous Current 60A
Max. Current 70A
Input Voltage 8 - 23V
Max. Efficiency 96%
No Load Current 1.4A
Internal Resistance 56mΩ
Motor Dimensions (Diameter x Length) 37.1mm x 59.2mm
Shaft Diameter 4.97mm (Front and Back)
Shaft Length 14.6mm (Front) 11.2mm (Back)
Input Battery Types NiCd/ Nimh/ Li-po Battery
Recommend Model Airplane

The specs for the esc are:
Dimensions 67.8mm x 38.2mm x 12.5mm
Sustaining Input Voltage 6 - 30V
Continuous Output Current 80A
Max. Output Current 90A/12s
Internal Resistance 0.0018mΩ
Cable Type 14 AWG (Battery & Motor)
Cable Length 105mm (Battery)
70mm (Motor)
190mm (Receiver)
Input Battery Types NiCd/ Nimh/ Li-po Battery
Recommend Model Helicopter / Airplane

Yes, the batteries were not fully charged, and I didn't get rpm figures as of yet. By guesstimate, I should be getting about 11,000 rpm with this setup. When you say normal 12x6 prop, I'm assuming that you're referring to glow engine props?

Rey

cyborg1

Here's a picture of the motor and esc combo

opjose

Yes they'll go up, because the batteries will be able to sustain the load the prop and motor is putting on them.

You don't necessarily need a 30C pack if the capacity is higher though.

A 20C 4000mAh pack will put out 80A. 60A is within your margin of safety.

Instead of spending the money on a 30C pack I'd suggest upping the capacity instead, and invest in say a 5000mAh 20C pack.

Not only does this handle 100A output ( which exceeds your draw specs by a very decent amount ) but the capacity will provide much longer run times. You'll also not tax the packs this way, they'll be loafing along while giving you more flight time.


One of the problems is that manufacturers overstate their electronics specifications.

There is another thread here which talks about derating the manufacturer's info... EXCELLENT thread!

If you leave a 20% or MORE margin in your estimates, you'll be better off, and it seems you are doing exactly that.

But ALWAYS test with a watt meter.

You'll be surprised at the difference you'll get from the same setup once you switch to higher capacity packs.

opjose

Yeah I've used those motors.

Be careful! The motor is intolerant of currents above it's rated continuous current.

I've pushed one to destruction to see how tolerant it was. It does ok up to the max continuous current but not beyond.

cyborg1

so in essence, the watt meter is only measuring the load output from the battery then? Please correct me if I'm wrong, so that I can get a clearer understanding of how the watt meter works, and what applies to what.

DaveFlynn

The ESC may be limiting the amps because of a low voltage cut-off. Need to plot the RPM vs Amps. I don't use "E" props for high wattage setups, they break.

opjose

The watt meter displays watts, amps and voltage states.

It sits between the battery and the ESC, so it reports the status of your power system.

If your battery is not up to the load placed upon it, you typically will see low wattage output, and a depressed voltage level.

If the battery is up to the task, the voltage will not drop so precipitously and the watt and amp figures should then more closely reflect what your power system is doing or is capable of.

Then these figures can be used to see how your actual power consumption relates to what the ESC and Motor tolerate or are capable of.

Sometimes you may find that your packs are not up to the task, then you switch packs to more capable ones, only to find that you may be cranking out more current than what your ESC or motor can safely sustain... or that the prop you are using is not pulling as much current as you would like, and you need to step the size up, etc.

A Watt meter is a VERY important tool for electrics.

John 38

its possible that the prop is on the small side and the motor is simply not loaded enough. if the watt meter shows good voltage - 20 plus - while still only showing 33 amps etc then this will confirm that motor has insufficient prop load.

the Kv of 560 at 22 volts will give a maximum 12300 rpm turning a tiny prop.

once the motor is loaded with a larger prop, the back emf generated drops the max revs down to about 80/75% of max revs. therefore if the motor is not loaded sufficiently by the prop it will simply max out on revs at whatever current is needed to get there.

6s lipos and low Kv motors equate to bigger props to develop the load without going way over the top on amperage.

try a 15 x ? prop and see what the watt meter says.

john

cyborg1

ok, thanks for the updated info. I have another question...the motor in the photo above accepts until 24 volts input. A 6 cell pack fully charged is at 25.2. My question is...can I use a 6 cell pack with this motor, or is it going to fry the motor? Will I have to use a 5 cell pack to keep it within the limit? If I do, I'll have to reorder battery packs to make up for the difference[:@] ouch! I already have 2 4000mah 11.1v packs and 2 3300mah 11.1v packs to make up 2 six packs...bummmer[]

DaveFlynn

I don't know why mfg's put voltage numbers on motors. Motors only care about amps and watts. If you want more rpm, run a higher voltage. It's the ESC that must be selected to handle the voltage. If you want to run a 9S pack and an 9x4 or 9x6 prop, go ahead. Castle's HV-30 would be a good ESC for that motor.

cyborg1

So in essence, even if the volts of the battery pack exceed the recommended input voltage of the motor, it doesn't matter. So long as the esc selected manages to keep the amps and watts under control, which is also done by the proper selection of prop/motor for the intended purpose. That's where the watt meter comes in then. When propping the motor with an oversized pack, I should then make sure that the amps and watts don't exceed the recommended ratings for the motor at max efficiency or max throttle.

DaveFlynn

Correct. And, many times the amps the mfg's recommend are higher than the motor can handle, or the number is the instantaneous current not the RMS current shown by the watt meter. I like to plot a graph of amps vs rpm and see for my self how many amps a motor can put to use. Many times the value I fine is only a little over half the value given by the mfg.

cyborg1

I just finished tinkering with my setup. On a freshly charged 2200mah 6 cell pack, the acceleration is terrific (bench testing). However, I could only rev it to half throttle, because after half throttle, the motor begins to change in pitch, becoming very high pitched and screechy, so I didn't dare to go any further. Does this mean that the volts are too much for this motor? I was getting 600+ watts, 22 volts, and about 30 amps at half throttle. Should I go down to 5 cells or opt for a larger prop to create more load? Boy, this is confusing...[&o]

opjose

So you were at .8+ Horsepower at half throttle.

At full throttle you'll be getting close to 1200 watts and 60 amps assuming a linear increase ( which is probably not accurate ).

I'd use high throttle very sparingly.

What prop were you using?

It may well be that the prop is windmilling at high revs.

Of course it could also be the ESC timing.

Did you check to see how it was set?

Dr Kiwi

The screeching is usually an indication of timing being too advanced.. try the lowest timing setting on the ESC and see if that makes a difference.

Oldbob

How do you change the timing on an ESC?? I have a PZ T-28 and had to change the ESC, (first one fried a phase). the replacement ESC works fine for awhile (2 or 3 minutes) and then the motor growles and come to a stop. I have to go to low throttle and back up to get it to run. could this be a timming problem?

I have in the hobby for a long time but very new to this electric stuff.

Bob

opjose

Yes it could indeed be a timing problem.

I had a similiar problem with my Typhoon.

A search turned up the programming info for the Parkzone ESC, but I don't remember where I found it.

Oldbob

Jose, thanks for the response. If you remember let me know.

Bob