Converting a multimeter to a RC amp meter

[sloper steve]

It is so easy to test your amp draw.
Just plug your battery into the female jst and plug the male jst into your speed control. Idle amps are immediately shown. Throttle up and see the amps at WOT.

http://www.slofly.com/images/howto/slofly_amp_tester.jpg

1 Parts needed
Wire strippers
Male and female JST
Meter and leads
Shrink wrap or electrical tape
Optional solder & flux

2 Snip leads
Cut wire leads to 6" to 12" (shorter the better not to lose reading to resistance) from the ends that plug into the meter.

3 Strip wires
Place heat shrink on multimeter leads

4 Twist wires together
Wire the black multimeter wire to the black wire coming from the female JST.
Wire the red multimeter wire to the black wire coming from the male JST.
Twist the two red JST wires together
OR
Wire the red multimeter wire to the red wire coming from the female JST.
Wire the black multimeter wire to the red wire coming from the male JST.
Twist the two black JST wires together

5 Solder optional
Add flux to twisted wires
Apply a small bit of solder to tip and touch to wire
It will jump on the wire and filld the gaps in the wire threads locking them in place.

6 Heat gun or electrical tape
Place shrink over last two exposed twisted wires leaving some extending over the tip.
Shrink them with a soldering iron, lighter or heat gun.

7 Slide JST's
Slide both JST through larger shrink wrap tube

8 Cover connections
Slide wrap over connections being careful not to pull on the wires too hard

9 Shrink it

10 Amp test
Set to 10amp DC setting.
Place black wire in COM
Place red wire in 10ADC

[pda4you]

What type of battery does the meter use?

Mike

[sloper steve]

I am not sure- it comes with it installed and I have never had one run out :)

I'd think 9v and will check.

[pda4you]

Thanks! I just hate it when they use non-standard. I have a towerhobbies tach that takes special button batteries and they cost nearly $20 to replace!?! :eek:

Mike

[sloper steve]

Wow $20 for batteries- maybe compatible ones are available online.

Just checked - Yes it takes a 9v battery.
Also has a replaceable fuse F250mah/250v

[igenius]

Hi Guys,

I've been using the same method to ensure I do not over-amp my Lipo batteries or motor.

But I have one question: Technically how accurate is this type of measure? (Is it a real reflection of the amps pulled from the battery or going to the motor? taking the od waveforms into account, or is it a close enough approximation?)

Thanx in advance.
Rudi

[Joat]

I'm using my craftsman -20 amp on my cp humming bird,and it will be accurate to a point like max draw from a dead stop max pitch,but does not take into account weight-my heli is strapped down so it would be more load than normal,but If you go this route and you still under the max amp rating then you should never really have to worry,as if what ever your using is strapped down and cannot move this would make it the worst case scenerio?

[igenius]

thanx tlyee63

[Joat]

Does it make sense?,there was a big discussion about this at runryder,I have to agree with both sides,unrealistic? somewhat ,most likely you will never see those type of amp draw unless your trying to lift something you can not,but at the same time if your max amp draw is still below your max rating for esc,batts etc then you should pretty much always be safe.

[pda4you]

Well I just got my order with the meter. Wired it up as indicated and it works great!

Shows my Dx-A IPS drive at 1.9a with the radio and that is spot on. Also tested my bn2 islander and it was 7 amps, also just what I figured. Then on to my brushless formosa and it also showed 10 amps at 95% throttle (didn't want to push it past the 10amp max) and I suspect that plane was 8-9 amps in flight so 10-11 static was right on.

I am happy with this for $7!

Mike

[sloper steve]

It depends on your prop pitch.

For instance 'flying with no prop' or moving through the air with no prop you will probably get the same WOT amps because motor load is the same.

The more pitched your prop, the more it is stalling at 0mph tests.

I have often mentioned that motors should have two ratings.
One at 0mph and one every 10 to 20mph (for IPS style)

Why not place another motor in front of it blowing on the prop- inaccuracies/hassle
Like Tylee said it won't be as high in the air.
The amp draw will be less in the air especially if you have a heavy pitched prop since it is stalling at room speed.

If you are drawing close to your batteries max amperage take into acount amp draw for all servos in movement and add that to what is displayed too.

[Joat]

I'm surprized people are only using 10 amp meters,I figured most would rather have a 20 amp,I bought a craftsman 20 amp for like 40 bucks -but that was a while ago.

[EddieNewYork]

Great! This was just what I was looking for. Thanks Steve. :)

[EddieNewYork]

Will this measure KV too?

[sloper steve]

Just amps because the meter needs to be spliced into one wire for amps.
For volts it needs to be tapping into the + and -
A volt meter can be added in addition but going all the way and getting a more expensive amp/volt/watt meter could be for you.
KV can be figured by taking your battery voltage and doing an RPM measurement I believe.
There may be something out that plugs into one of your brushless motor wires to get measurements.

[EddieNewYork]

Just amps because the meter needs to be spliced into one wire for amps.
For volts it needs to be tapping into the + and -
A volt meter can be added in addition but going all the way and getting a more expensive amp/volt/watt meter could be for you.
KV can be figured by taking your battery voltage and doing an RPM measurement I believe.
There may be something out that plugs into one of your brushless motor wires to get measurements.

IC, thank you very much Steve. :)

[Microbatman]

What if I am using deans ultra connectors?
Can I substitute female JST=female deans? in the instrustions
male JST-male deans?

I have a female deans on the battery and male deans on esc

[EddieNewYork]

What if I am using deans ultra connectors?
Can I substitute female JST=female deans? in the instrustions
male JST-male deans?

I have a female deans on the battery and male deans on esc

Yeup. ;)

[fnnwizard]

be careful using that kind of meter, it seriously constricts current as there are lots of resistance in the meters, your setup will pull more amps than actually shown on the meter... use one of the astro whatt meters or similar...

if you absolutely have to use this kind of meter, keep the test leads short as possible and use thicker (16G) wires.

[Microbatman]

Just did this.
hooked it up and motor only goes to %25 throttle and cuts out
hooked it up regular motor runs fine
Is the multimeter sending a signal throught the speed control
Castle Creastions 25
that would cause cutooff at 1/4 throttle? :confused:

[sloper steve]

How many amps is the motor?

Make all wires as short as possible for more accurate readings above 5 amps.
Do not use meter for draws over 10 amps or for burst guestimate a few more amps.

To get a good feel for it just give her full throttle without the meter.
Attach the meter and give her full throttle. The lower rpm is the amount of resistance.
Cut the wires shorter to lower wire resitance. I'd like to know how much the meter itself is losing to resistance and if it is - is it linear or predictable. So far I just add 10-30% to the amps shown above 5 amps.

If you know of any meters on any sites please post a link to it.
Perhaps some lower cost ones have emerged since the start of this thread.

How I've used it-
Use meter to make sure amp draw isn't way over what is right.
Fly plane short distance and check motor for heat and battery for any warmth.
A well done setup will hardly get the battery warm by keeping it under its max amp output and the motor will run cool because it is not losing your flight time as heat.

[Microbatman]

Thanks for the info

Also

Asked Castle creation how long wire could be and they told me approx 6 inches.

Right now I have approx 2 feet.

Will try cutting down the lenght and see what happens

[olmod]

shows you how to solve the long wire problem and also how to increase the range of amps. ;) cheers.

http://www.allaboutcircuits.com/vol_1/chpt_8/9.html