$3 Wattmeter - Page 2 - RC Groups
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Nov 13, 2008, 12:17 PM
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Thanks Rich. Heading for the workshop now.

BTW, the only resistor close to 1K I can find in my parts box is 2.2K. I'm going to use that one. If you know of any reason it won't work, please post back.

Thanks again,

Bill
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Mar 02, 2009, 06:46 PM
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Magnumpi's Avatar
OK what did i do wrong??? Heres the way it went together, the 2 negative wires soldered together, then a 1k Resistor soldered on the ends of the negative wires, then i soldered the end of the resistor to the middle hole. then one red wire to the 10ADC, and the other red wire to the COM or bottom hole. I think i did it right , but when i check AMPS at WOT it says 8.32 i know that is not right. Can someone tell me from the pictures what i did wrong??
Mar 02, 2009, 07:15 PM
Registered User
Here's how I have mine wired and it works just fine.

Maybe you should check your DMM current with a known source.

EDIT: While looking at your pictures in more detail it seems you may have the two outer bananna plugs plugged in reverse order.

Bill
Mar 02, 2009, 08:03 PM
Registered User
Magnumpi's Avatar
OK i switched the plugs to look like yours, it still shows 8.83 WOT as before, except before it was a negative number. I soldered the 1k resistor straight to the middle hole is that OK? I check for the amp draw with the meter set on 10A is that right?
Mar 02, 2009, 08:10 PM
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Magnumpi's Avatar
BTW it tested a 9v battery ok.
Mar 02, 2009, 08:31 PM
Registered User
It seems to be wired right.

Why do you think the reading of 8.34 amps is incorrect?

Bill
Mar 02, 2009, 08:58 PM
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Magnumpi's Avatar
Well im testing my Typhoon 3d with a 3700k motor running on a 2200 15c lipo. With a 13.5 7 prop. I would think it would be at around 15 to 20 amps draw at WOT. Am i wrong?
Mar 02, 2009, 09:11 PM
Space Coast USA
hoppy's Avatar
CAUTION
Most DVM's have a limited time spec for current measurements on the high range.
Be sure to limit the time you use the meter for current measurements to the limits of the meter. Some are as short as a couple of minutes.....others 10 min..etc.
Mar 02, 2009, 09:14 PM
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Magnumpi's Avatar
It starts at 0.04 ( Need to recalibrate) and stays at around 8.49 but below 9.00
Mar 03, 2009, 10:58 AM
7000mw of raw power!
rich smith's Avatar
Quote:
Originally Posted by Magnumpi
It starts at 0.04 ( Need to recalibrate) and stays at around 8.49 but below 9.00
Magnumpi,

It looks correct to me. To double check just forget my adapter and use the unmodified meter inline between battery and ESC. I suspect the read will be the same. These meters are cheap but usually dead on.

0.04 means nothing. I don't think you need to recalibrate unless you go over 10a. In that case add heavy wire in parallel to the shunt inside the case until it reads exactly half what it did w/o the wire. Max scale will then be 20a instead of 10a or add more for even higher current. One guy has set his up to read 100a!

Keep in mind the higher the scale the less accurate it will be though.
Mar 03, 2009, 11:03 AM
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Magnumpi's Avatar
I think it is right, i just tested my FW F-35 with a 3s 1500 25c and it showed

16.87 so i thank its working OK...Is there a way to convert the AMPs to tell how much Watts your getting???
Mar 03, 2009, 11:12 AM
Registered User
Watts = Amps x Volts

It's going to be difficult getting both those figures at the same time without using a wattmeter. If you have 2 meters you can set one to amps and the other to volts.

Bill
Mar 03, 2009, 11:13 AM
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Magnumpi's Avatar
Thanks for the info, i love this site.
Mar 03, 2009, 11:18 AM
Registered User
Quote:
Originally Posted by Magnumpi
It starts at 0.04 ( Need to recalibrate) and stays at around 8.49 but below 9.00
If there's other equipment connected to the meter, ie, ESC, receiver, servos, etc., that could be where the 0.04 amps is coming from.

BTW, 0.04 amps is 40 milliamps which is just about right for the idle current for those items I mentioned above.

Bill
Mar 03, 2009, 09:58 PM
Registered User
Rich
I just saw your post on setting up a harbor fright multimeter to check your amps and volts. Great Idea
the multimeter from Harbor Fright show the amp range from 20 ma to 200 ma
is this the same one you used?
I would like to use two multimeter's so I could check the watts I guess I would
use one meter to check the voltage and one to check the amps.
I would not have to use The 1 k resistor with this set up right. what would the wiring diagram look like. Thanks for any help ahead of time
Earl


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