Are my multimeters knackered??

[Ray Pooley]

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

 

[Pete999]

Have your meters been calibrate recently? how are you measuring the current with your multi meters? Are you measuring the current in series with the load?

 

[Squid]

No help at all but take me back a good few years.......

 

[davesparks]

I doubt that the battery is capable of delivering 11amps.

 

[telectrix]

check meters by measuring resistance ( of a known resistor) and voltage ( on a variety of batteries. sod trying to measure current with a multimeter. as dave sparks, cAN'R=T SEE 11 a BEING DRAWN FROM A BATTERY UNLESS IT'S A CAR BATTERY OR SIMILAR.

why the bllody hell is caps lock right next to A. whre fat fingers hit it.

 

[ian.]

Are you using a power source capable of delivering the expected current, try it across a car battery but your resistor will need to dissipate 180watts

 

[telectrix]

Are you using a power source capable of delivering the expected current, try it across a car battery but your resistor will need to dissipate 180watts

fried resistor?

 

[Ray Pooley]

Have your meters been calibrate recently? how are you measuring the current with your multi meters? Are you measuring the current in series with the load?

Hi Pete

Thanks for the response.

No. I haven't gone through any kind of calibration process. I will check that out.

It'a a straight forward battery to resistor, resistor to meter, meter to battery loop. Nothing fancy.

 

[Ray Pooley]

fried resistor?

No. I have 10 resistors all new and all the same. They all read 0.1 ohms so the meters don't have a problem reading resistance.

 

[Ray Pooley]

Are you using a power source capable of delivering the expected current, try it across a car battery but your resistor will need to dissipate 180watts

Ah yes. You may have a point there. I need a source that can actually deliver the current that Ohm's Law predicts. Makes sense. I need to review my test equipment. 11.6A is probably a little ambitious from a 9V battery. Duhhh.

 

[Ray Pooley]

Thanks everyone. I think I have my answer now. It helps to reach out. I need to rethink my experiment. Cheers

 

[ian.]

The DM09 looks a cool DVM, got meter envy now

 

[Ray Pooley]

The DM09 looks a cool DVM, got meter envy now

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.

 

[Ray Pooley]

The DM09 looks a cool DVM, got meter envy now

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.

 

[littlespark]

A 9 volt battery that gives out 11 amps???
I’ll never test one on my tongue ever again!!

 

[DPG]

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]

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]

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.

 

[DPG]

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]

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.