Watt meters

[Racer09]

Can someone tell a good watt meter to buy. Have a Funtana 125 with a 160 exceed motor and castle 100 amp esc turning a 20x11prop with two 5000 mah batteries 14.8 volt.

[kenchiroalpha]

Hi
Welcome aboard
Pleased to meet you
I and many others use "Watts up" meters
Easy to use and quite accurate
http://www.hobbyking.com/hobbyking/s...idproduct=6380
Take care
Yours Hank

[JetPlaneFlyer]

If your system pulls considerably more than 50A continuously (and with your hardware I suspect you probably do) than you might want to get a meter that's got a higher amp rating than the Watts-Up

Steve

[rcers]

For above 75amps you really need a clamp on type or shunt meter. Look for the Sears clamp meter that does DC volts (important!). It works very well at higher power levels.

Mike

[Racer09]

Thank everyone for your help and nice to meet you all.

[dditch66]

are you running series or parallel?
I have an 11S setup and I just used the watt meter hooked up to one of the batteries then extrapolated the Wattage once I new the current and wattage across the 6S pack. I have both a P0 and P1 watt meter from Hobbypartz.com
I compared them to an Eagletree and a clamp on Fluke meter and they were within 1%.

[kyleservicetech]

Originally Posted by Racer09

Can someone tell a good watt meter to buy. Have a Funtana 125 with a 160 exceed motor and castle 100 amp esc turning a 20x11prop with two 5000 mah batteries 14.8 volt.

The Astroflight wattmeter will read to 50 Amps. But the Sears Craftsman #82369 digital clamp on multimeter will read 0-40 AND 0-400 amperes DC. Its fairly accurate on the DC current ranges. That Craftsman meter will measure the starter current of a diesel truck. Nice thing about these clamp on meters, you do not need any adaptor connectors, just "Clamp" the meter around ONE of the battery leads.

Note that most digital clamp on meters are AC only, the #82369 is AC and DC.

Of course if you need watts, you need a second meter to measure the voltage while the clamp on meter is measuring current. That second digital voltmeter can be an inexpensive digital meter that everyone sells, including Walmart nowdays.

(Watts equals volts times amps, so an example: 29 VDC and 85 Amps is 2465 watts.)

http://www.astroflight.com/index.php...lc0th5bmefk19q

[Racer09]

Thanx for everyone's help. I did buy a clamp meter and it worked great pulling 61 amps at 100% and only 22 at 50%.

[kyleservicetech]

Originally Posted by Racer09

Thanx for everyone's help. I did buy a clamp meter and it worked great pulling 61 amps at 100% and only 22 at 50%.

You'll like that clamp on meter. Makes it easy to check anyones current pulled out of the battery. As well as vacuum cleaners, automotive alternators, you name it. Thats a quick way to check an alternator in your car. If it puts out DC current with all your headlights on, it's working!

Did you get an RPM reading out of your setup? Just curious.

[Racer09]

No rpm readings I broke my gauge so waiting on new one.I will let you know what I got though I'm going do some prop changes and see what I like the best. The 20x11 I'm running has very little ground clearance so I'm going to a 18x12.

[kyleservicetech]

Originally Posted by Racer09

No rpm readings I broke my gauge so waiting on new one.I will let you know what I got though I'm going do some prop changes and see what I like the best. The 20x11 I'm running has very little ground clearance so I'm going to a 18x12.

Sounds good.
I ran your numbers through www.motocalc.com. Motocalc suggested your motor would be running pretty hot with a 20X11 prop on it. That program indicated your motor would be turning that 20X11 prop at only 4600 RPM, with an efficiency of 56%.

To me, that doesn't sound right. That would be one kilowatt of heat dumped right into the motor.

[Racer09]

I tried the motorcalc but i didn't really understand. It's new to me can you possibly show me your read out.

[Racer09]

this is also my first scale electric and im still learning so any help would be great.

[kyleservicetech]

Originally Posted by Racer09

I tried the motorcalc but i didn't really understand. It's new to me can you possibly show me your read out.

Certainly, take a look at the attached JPG. Motocalc suggests this motor is really going to run hot with your setup. Motocalc is predicting 70 Amps full throttle, with 2384 watts input, and 1041 watts lost in the motor. Motocalc is predicting only 56% efficiency. Could be the Monster motor specifications are a little off, don't know.

That's why I asked for the RPM, to see if motocalc is even close on the predicted RPM values, based on the Monster Motors specs provided by Monster motor.

If you can provide the weight of your model without motor and battery, wingspan, wing area, that can be added to the motocalc spreadsheet.

I've got a Hacker A60-16M motor that is running at 2500 watts, with 3000 watts peak. Per motocalc, this motor is running nearly 90% efficiency. With a 12S2P A123 battery, it turns a 19X12 wide blade APC-e prop at 7000 RPM, pulling 72 Amps at about 33 VDC.

[Racer09]

weight is 8.5# wing area is 1108" and span is 69.5"

[Racer09]

plane is a Funtana 125G by hanger 9

[Racer09]

batteries are blue lipo 5000 mah 14.8 volt 40c and castle creations pheonix ice 100 esc

[kyleservicetech]

Originally Posted by Racer09

batteries are blue lipo 5000 mah 14.8 volt 40c and castle creations pheonix ice 100 esc

OK, now we have good info to work with.

www.motocalc.com suggests that the best prop to use on your Monster 160 motor and 10 LiPos, is a 17X10. That setup will result in about 2200 Watts, 7800 RPM, a prop pitch speed of 74 MPH, and thrust of 295 ounces. Thats also about 170 watts per pound, very good numbers. The good thing about this setup is the motor efficiency, predicted at 89%.

As previous setups with that 20 inch diameter prop showed, motor efficiency drops like a rock, producing heat in the motor, rather than power to the prop.

That model should be able to fly vertical out of sight. Your model should fly very well with this power setup. As always, be certain to verify your results with one of those wattmeters, such as Astroflights wattmeter to make certain all is OK.

[JetPlaneFlyer]

Kyle,
I'm confused... where did the 10 cells come from in your motocalc analysis?

The OP said 4 cells (14.8V) but with such low Kv motor I'm assuming he's got of these packs in series to make 8 cells which is still undervolting the motor but would at least get usable performance.
A single 4 cell pack would of course be a total waste of time with a 245kv motor.

Steve

[Racer09]

thank you Kyle thats alot of help im going to try the motcalc some more and learn how to use.

[kyleservicetech]

Originally Posted by JetPlaneFlyer

Kyle,
I'm confused... where did the 10 cells come from in your motocalc analysis?

The OP said 4 cells (14.8V) but with such low Kv motor I'm assuming he's got of these packs in series to make 8 cells which is still undervolting the motor but would at least get usable performance.
A single 4 cell pack would of course be a total waste of time with a 245kv motor.

Steve

Geeze, good catch, thought I saw 5 series cells somewhere.

That will make a BIG difference in power output with only 8 cells.

[kyleservicetech]

Originally Posted by Racer09

thank you Kyle thats alot of help im going to try the motcalc some more and learn how to use.

OOOPS
Jetplaneflyer caught the fact that your battery packs are 4S, not 5S. That is going to make a big difference in propeller selection, more like a 19X12 APC-E Wideblade unit. Try the 8s battery pack in motocalc and see what you think.

[Racer09]

Will do and thanx again for all your help

[Racer09]

Kyle got the motocalc working and I found that a 18x12 prop is going to the best for the 8 cells. Getting about 1600 watts to the prop and 88% eff. With about nine min. of flight time. Thank you again for all your help.

[kyleservicetech]

Originally Posted by Racer09

Kyle got the motocalc working and I found that a 18x12 prop is going to the best for the 8 cells. Getting about 1600 watts to the prop and 88% eff. With about nine min. of flight time. Thank you again for all your help.

Sounds good!

Let us know how your first flights go. As for the 9 minutes of flight time, it would be a good idea to limit your first flights to perhaps 6 minutes. Then charge your battery with a charger that records total milliampere hours put back INTO your model.

IMHO, its not a good idea to fly more than perhaps 60% of your battery capacity on any given flight. So if you need to go around on a landing, if someone is on the field, its a bad day, you don't have to deal with a dead stick model, and the possible battery damage that might go with it.