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Old Jun 27, 2012, 11:17 PM
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HoosierGuy's Avatar
United States, IN
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Need a Wattmeter

Tonight I flew my FPV Raptor (with no FPV equipment, don't have any yet). This is my first flight with my new ESC and UBEC and I had a lot of soldered wires in it. I guess my soldering held up since I did not crash and flew fine.

Anyway, now I want to get a wattmeter so if I try different motors and props, I can make sure they will work and not burn up the motor.

What wattmeter do you all suggest that is cheap but works? Do they measure everything on an R.C. plane? Motor and servos? Do you usually use a wattmeter while the plane is on the ground and you run the motor and servos? Are there any that monitor the watts while you fly?

Thanks!
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Old Jun 28, 2012, 12:33 AM
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United States, AK, Fairbanks
Joined Aug 2009
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I bought this meter awhile back. It's been excellent for me. Seems to be plenty accurate and precise. Functionally it does everything I'd want it to, and the screen is nice and readable with its blue backlight.

I soldered my regular Deans connectors to it for power system use, but then I also added some servo-type leads so I could put it between a receiver and power supply to check servo draws, BEC performance and other things like that. I made up some alligator/Deans adapters to use it for a variety of oddball purposes as well.

It wouldn't really be practical to mount it in a plane and fly it around unless the plane was pretty big. There are things like the EagleTree eLogger that'll ride around in the plane and give you all the info you could possibly want, but they do get expensive.
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Old Jun 28, 2012, 01:45 AM
222 km/hr Parkjet flyer
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Latvia, Ventspils pilsēta, Ventspils
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I bought my Wattmeter of Ebay ... it came with the power adaptor lead to alow it ton connected into the battery to ESC cable, it has the 1 - 6S balance board and connect cable.

It was cheap enough ... about $20 I think. Does the job ... I use it to a) check my LiPo's after flights, before and after charging, to balance LiPo's that are detected out of balance .... etc.

Your question about checking with servos etc. - the amps display is not that deep into decimals, so light load of 1 - 2 servos barewly changes the displayed figures ... but have 4 servos and start throwing those sticks around and you see the numbers change ... interestingly nowhere near the horror stories that some write about ! Well that's my observation with cheap servos anyway !

The real benefit for me is the charge state of the LiPo ... and then secondary the wattage / amps / volts level of motor / prop or EDF combo etc. That can be frightening when you see what you are really doing !!
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Old Jun 29, 2012, 01:13 PM
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United States, GA, Perry
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i got a ''WattsUp'' watt meter. you can get it on ebay,Hk,...
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Old Jun 29, 2012, 09:36 PM
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Quote:
Originally Posted by solentlife View Post
I bought my Wattmeter of Ebay ... it came with the power adaptor lead to alow it ton connected into the battery to ESC cable, it has the 1 - 6S balance board and connect cable.

It was cheap enough ... about $20 I think. Does the job ... I use it to a) check my LiPo's after flights, before and after charging, to balance LiPo's that are detected out of balance .... etc.

I think I bought the same one you have. It was $19.99 and I believe comes with a balancing board and cable with a deans connector on each end.

This is what I want it for, so tell me if I understand this right. I can buy a motor and lets say its max watts is 500 watts. I get it and want to try a prop I have. So I put the prop on the motor and run the watt meter between the battery and ESC.
Then run up the motor to full blast and see what it reads. If it's under 500 watts then my motor and prop should be OK to try to fly with (nothing will get burned up). Is this all correct?
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Old Jun 29, 2012, 09:55 PM
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C₄H₁₀'s Avatar
United States, AK, Fairbanks
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This is what I want it for, so tell me if I understand this right. I can buy a motor and lets say its max watts is 500 watts. I get it and want to try a prop I have. So I put the prop on the motor and run the watt meter between the battery and ESC.
Then run up the motor to full blast and see what it reads. If it's under 500 watts then my motor and prop should be OK to try to fly with (nothing will get burned up). Is this all correct?
You've got the idea... The number you really need to pay attention to is current (amps) rather than power (watts). Current is what'll fry the motor.

A wattmeter can tell you a lot more than that, though. It'll also show you how much your battery's voltage sags under load, which gives you an idea of pack condition. It lets you compare performance with different props; some props give more thrust and speed while using less power than others. It can be used to quickly check resting battery voltage, ensuring that you don't accidentally store a charged battery and that you don't drain packs too much in flight.

Once you have a meter, you start scratching your head wondering how you made it without one
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Old Jun 29, 2012, 10:11 PM
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Here is what I have and it is cheap and works great for me. I bench test with it when I build a new plane or if I want to try a new prop or make any changes to a plane so I know I will not fry a component.

http://www.hobbypartz.com/aeo-p0-watt-meter.html
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Old Jun 29, 2012, 10:16 PM
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United States, GA, Perry
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Originally Posted by john50049 View Post
Here is what I have and it is cheap and works great for me. I bench test with it when I build a new plane or if I want to try a new prop or make any changes to a plane so I know I will not fry a component.

http://www.hobbypartz.com/aeo-p0-watt-meter.html
Iv heard bad reviews about that. people say the amp rating can be way off.
Quote:
Originally Posted by HoosierGuy View Post
I think I bought the same one you have. It was $19.99 and I believe comes with a balancing board and cable with a deans connector on each end.

This is what I want it for, so tell me if I understand this right. I can buy a motor and lets say its max watts is 500 watts. I get it and want to try a prop I have. So I put the prop on the motor and run the watt meter between the battery and ESC.
Then run up the motor to full blast and see what it reads. If it's under 500 watts then my motor and prop should be OK to try to fly with (nothing will get burned up). Is this all correct?
the one I have is 59.99. it just has 2 wires coming out each end
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Old Jun 29, 2012, 10:29 PM
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Iv heard bad reviews about that. people say the amp rating can be way off.

the one I have is 59.99. it just has 2 wires coming out each end
I can only say what I know about mine. It has always worked great and never failed. Maybe I have the only one that works but I would not trade it for your 59.99 watt meter.

This is just my personal experience. I could care less if he buys one or not. I get no commission when one is sold. I have 40 planes and it does a great job helping me set up all my planes. I have actually went about 2 months without buying a plane. That is a record for me. I think I have enough to make it through the summer so I am going to try to wait to black Friday before I buy anymore planes. I might get the shakes if I wait that long though because I am addicted and can not find a addiction program for buying to many planes. My bedroom is full of planes and it is missing a bed!!
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Old Jun 30, 2012, 03:40 AM
222 km/hr Parkjet flyer
solentlife's Avatar
Latvia, Ventspils pilsēta, Ventspils
Joined Jan 2010
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Quote:
Originally Posted by HoosierGuy View Post
I think I bought the same one you have. It was $19.99 and I believe comes with a balancing board and cable with a deans connector on each end.

This is what I want it for, so tell me if I understand this right. I can buy a motor and lets say its max watts is 500 watts. I get it and want to try a prop I have. So I put the prop on the motor and run the watt meter between the battery and ESC.
Then run up the motor to full blast and see what it reads. If it's under 500 watts then my motor and prop should be OK to try to fly with (nothing will get burned up). Is this all correct?
That's about it ... plus of course make note of the AMPs draw ... as the voltage will dip significantly as you go WOT ... so amps will climb higher to make the watts .. Volts x Amps = Watts.
It's not unusual for amps to go higher than ESC is designed for in so-called matched packages because of the violtage sag.

Nigel
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Old Jun 30, 2012, 03:48 AM
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Originally Posted by Pyrofan View Post
Iv heard bad reviews about that. people say the amp rating can be way off.
Quick check of maths will show that ... Volts x Amps = Watts unless meter uses displayed figures to calculate others.

I know my Watts-Up cheapo of Ebay has a lower volts result in balance display than a mates checker - but the above equation works out ...

Quote:
the one I have is 59.99. it just has 2 wires coming out each end
Fine ... each to their own .... my $20 item gives me all I need and more.

The only modifiction I wish they would make is to incorporate the balance sockets into the case like the B6 range of chargers ... the adaptor board and cable has failed on my original and had to buy another ... which had wrong plug on end - so I had to cut and join to the old ...
Have to admit - I did consider opening the case and soldering the balance board direct and fix it to the meter rear-face.

Nigel
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Old Jun 30, 2012, 01:48 PM
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That's about it ... plus of course make note of the AMPs draw ... as the voltage will dip significantly as you go WOT ... so amps will climb higher to make the watts .. Volts x Amps = Watts.
It's not unusual for amps to go higher than ESC is designed for in so-called matched packages because of the violtage sag.
Woefully incorrect, but that's what we're here for

Watts (power) is only a mathematical product of current and voltage. When the voltage sags, the motor slows down. This means that the current draw (and thus total power) will actually drop. There's nothing in the system that's trying to attain a specific watt number.

This is why running batteries with higher discharge abilities will result in more overall power. The lower internal resistance means less voltage sag, so the motor spins a bit faster and you get more thrust and speed as a result.
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Old Jun 30, 2012, 09:21 PM
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If you buy a motor and it recommends a 3cell and 1000mah to 2000mah battery, It's Ok to try a battery with bigger mah, correct? As long as you don't mess with the volts, you can increase the mah (not counting the extra weight of the battery of course). I'm correct on this, right?
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Old Jun 30, 2012, 09:37 PM
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United States, CA, Roseville
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Right. mah is simply a number assigned to the amount of capacity a battery can hold. You.can go as high as your plane can carry the weight and size of the pack. Going smaller however is an issue when you go beyond the c rating and pull more out of the pack than can be safely delivered.
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Old Jun 30, 2012, 09:38 PM
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Hoosier Guy

Putting in a battery with higher mAh capacity is mostly like putting a bigger gas tank on a car. The spec is Amps drawn X time run, so a 2000 mAh battery can put out 20 Amps for 0.1 hours or 6 minutes. The 3000 mAh one will put out 20 Amps for 0.15 hours or 9 minutes. There is a complication about the Amp draw limit of the battery called C. The 2000 mAh battery rated 10 C can put out 20 Amps as its max current, while the 3000 mAh battery rated 10 C can put out 30 Amps as its max current.

Hope this helps

Joe
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