How do you guys measure Amps?

You just order dedicated electronic device ... http://motorbicycling.com/f9/nimh-battery-build-17318-12.html#post178125 ...for example.

I have found that if you let your dog mark his territory on exposed wires you can guage your amps by how far he jumps.

I read the manual that came with the electric bike,lol.

george_n_texas said:

I have found that if you let your dog mark his territory on exposed wires you can guage your amps by how far he jumps.

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actually the first law is it takes 1 volt to push 1 amp through 1 ohm of resistance. Then its volts x amps = watts. I don't measure amps yet. I should I know that but the relationship between volts and amps is such that for my purposes which are not exact at all, the volts tell me enough I think. I may have to go for an amp meter one day soon.

HJ - The link was to a device called a wattmeter. not a simple multimeter or voltmeter. I'll be honest with you I don't know how it works but it measures (or maybe calculates) amps, amp-hours used, voltage in the pack, etc. There are 3 out there - Turnigy wattmeter ($24), WattsUp ($50) and CycleAnalyst (more expensive). Here is a link to the Turnigy HobbyKing Online R/C Hobby Store : Turnigy Watt Meter and power Analyzer $23.95 and the specs from the site:

Operating voltage: 4.8~60V (0V with optional auxiliary battery)
Measures;
0~130A, resolution 0.01A
0~60V, resolution 0.01V
0~6554W, resolution 0.1W
0~65Ah, resolution 0.001Ah
0~6554Wh, resolution 0.1Wh
Screen: 16x2, backlit LCD display
Size: 85x42x25mm
Weight: 82g

- jd

Heres what i do, get 10 feet of solid core 10 gauge wire and put it in a peanut butter jar with two holes drilled in the top. Use two nuts and bolts to make two terminals that come out of the peanut butter jar going through the holes in the top. The resistance of 10 guage wire is almost exactly one(.9989) ohms per 1000 feet, so a 10 foot can be concidered a .01 ohm resistor. you can use this along with a multimeter to measure the voltage drop over the wire. Multiply your voltage drop by one hundred and you have a current reading.

only small problem is the whole current squared times resistance will get you when you measure currents over 20 amps or so. So the reason you have this all in a penut butter jar is so you can fill it with mineral spirits or kerosene. It wont conduct electricity and will keep the wires from getting too hot and changing the resistance skewing the readings.

I have an old super computer power supply that can put out 5v at 120 amps before blowing a fuse. Ive measured over 70 amps using this method.

PS. you can use any size wire but larger currents are going to require larger wires.

i forgot to mention you hook this up in series just like you would the meter

Im so lost my peanut butter jar is plastic would it melt.

Just buy the Turnigy watt meter mentioned, and use Anderson connectors for the connections and you'll be able to monitor all the usages during charging and discharging.

That's the easiest way and the cheapest. Just use a minimum of 12awg wires for most accurate measurements.

I don't get into political debates...

If you use the meter you (almost) mentioned, I would suggest against it because the use only 16awg wire which skews the results because of resistance issues with that gauge wire.
If price is not an issue, then I would deinitely go with the Cycle Analyst, because they use a shunt wired at the battery side which uses extremely low resistance to measure everything.
I use those (yes I have two of them, because I have two motors).
The Turnigy comes in at a better price (about half of the WU) and uses 14awg wire.

Yesterday I tried a test...
I rode one direction on a 16awg wire till battery depletion, (after recharge) I went a second dir on a 14awg wire and after a last recharge removed the Meter i was using and went on a 12awg wire....
(all flat, no wind)

Results (on a 36v 15ah LiFePO4 batt)
16awg (10' of wire and meter attached) = 15miles
14awg (10' of wire and meter attached) = 19miles
12awg (No Meter, 2' of wire from Battery to ESC) = 26miles!!!!

And that's only using one motor..

I use two motors normally, 36v 15ah (front) and 36v 25ah (rear), in conjunction and using the cycle analysts..
Top distance achieved?
With no wind and a flat surface, I was once able to max out.....
(drum roll, please)
An Amazing, 117miles averaging 20mph..
When I first started with the motors I was using WU meters and was only able to get MAX 80 miles distance..
So obviously for distance ability, the best choice is the Cycle Analysts, excpet for the fact that just those two meters cost me over $300.
16

no the jar wont melt from the mineral spirits. If you mean by the heat, you don't want to measure more than 20 amps continuously.

hey here is ohm's law A=V/R but hey who gots time for that.....but its a good way of figuring about an amp draw....i use an amp clamp to figure my draws in real life....ohms llaw works for things that do not have a motor cause as the motor winds up it draws less power

I'm just not scientific enough for this discussion lol. All I know is that life is better on a bike, be it electric, gasoline, or pedal. All the rest is just added fun and mental exercise. The old bent Deacon is now leaving the discussion quietly because he has nothing constructive to add.

I was off a guage...
WU uses 14awg
Turnigy uses 12awg
CA uses a shunt.

Most people would set their meters on the handlebars which adds length of wires and added resistance.

WU good for those who want to by an American made item, for a good price.
Turnigy good for those who want a better price and better meter.
Cycle Anaylst is for those that don't care about price and want the best meter out there.
(It's the only one that also measures regen and has MANY other useful features that the other ones don't - it's also made in USA, I think.)