Are my multimeters knackered??

Ray Pooley · Jan 16, 2019

Hello everyone.

New to the forum. Just want to run this by someone who might be able to provide some input.

Far as I know Ohms Law hasn't changed since 1827. Right?

It has been a while since I engaged with this stuff. Retired now and thought I would re-engage as a hobby.

So I have two multimeters and I just thought I would check them out.

I have a 9.3VDC battery. I connect it across a 0.1 ohm stock 4 band carbon film resistor. (brown, black, silver and gold if you're interested).

Total resistance in the circuit is 0.8 ohms including the meter cables.

So according to Ohm's Law i = V/R = 9.3/0.8 = 11.6A.

Is that right?

One of my meters is a 35 year old Fluke with a new battery.

The other is 12 months old TackLife DM09 with a new battery.

So why do my meters read 0.55 amps (Fluke) and 0.2 amps (TackLife)?

Any ideas what's going on here? What am I missing?

I could understand the Fluke being tired but not the TackLife.

Thanks

DPG · Jan 17, 2019

Ray Pooley said:
It does. It seems to be ok. Only problem is that there doesn't seem to be any way to calibrate it. Can't open it and there's no way on the outside to adjust it.

It's unlikely that you will have the necessary source equipment to enable accurate calibration of the meter anyway to be honest. If in any doubt I would get it professionally calibrated - it won't cost much and you will have confidence that all ranges are reading correctly.

DPG · Jan 17, 2019

Ray Pooley said:
Actually, I'm going to need a car battery and a rheostat. Something like a 200W rheostat. That should enable me to test my meters over a range of currents. I got it now.

Watch your cable sizes!

Ray Pooley · Jan 17, 2019

DPG said:
Watch your cable sizes!

Yes. Probably gauge 16. Maybe 14. I am thinking of using the actual 36V ebike battery pack. I now that there is nothing on the bike that's heavier than that. Just got a data sheet on the bike and the power is 250W to 350W not 350W to 500W as previously thought. Battery pack is 12Ah. So I calculate between 7 and 10 amps using 5.2 to 3.6 ohms. Waiting for the rheostat to be delivered. Going to take up to 5 weeks apparently. That's a long time. Still got to get my neighbour's old battery pack and borrow his charger. There are some estimated travel distances in this data. I can use that to extrapolate run times.

[ElectriciansForums.net] Are my multimeters knackered??

DPG · Jan 17, 2019

I would prefer to use a bank of aluminium clad high power resistors rather than a rheostat.

Don't forget, as Lucien mentioned above, that you won't necessarily get the full Ah capacity out of the battery. It will depend on the current you are drawing.

Ray Pooley · Jan 17, 2019

DPG said:
I would prefer to use a bank of aluminium clad high power resistors rather than a rheostat.

Don't forget, as Lucien mentioned above, that you won't necessarily get the full Ah capacity out of the battery. It will depend on the current you are drawing.

Not my bike so I don't want to spend any money on this project. Just spent £10 on a rheostat. I consider that hobby money so I won't be asking the bike owner to pay for it. But that's enough.