Amp-Probe question

[PineRidge]

Have a circuit that I'm trying to figure the running amp draw for a small 12 volt DC air compressor. There is no information on the motor itself and my Amp-Probe indicates 1.5 amps. Don't think this instrument is all that accurate for low readings. But think I remember someone saying years ago to take one of the load wires from the compressor and wrap it around the Amp-Probe jaws 5 full revolutions, take a reading, then divide by 5 to get a better average. Is this the correct way to take a low amp measurement?

 

[Inspector507]

Mike,
I awlays used a meter that will read the lower scales. But keep in mind that some typical Amprobes will not have a scale for DC. Make sure yours does.

 

[kennyd]

Mike,
Why not just put the DVM inline to check the current draw? My Fluke will read up to 10 amps safely inline.

 

[PineRidge]

Inspector507 I checked and you're correct, it was on the AC amp scale. It has no DC amp scale which might account for the low reading that I initially got.

KennyD I don't have a digital volt meter. Think to be on the safe side I'll just power this little guy up using a 30 amp dc relay. That should cover whatever the amp draw may be.

 

[John47]

Amp-Probes aren't designed to measure DC current, they are an AC instrument that operate off the "transformer" principle. (Mutual Inductance) What you need is an "in line" DC ammeter of some sort, like a multi meter with 10 or 20 amp ranges.

 

[slowrev]

Clamp on DC Ampmeters are available, just fairly expensive. I used them in Telephone central office work years ago.

Ben

 

[kennyd]

KennyD I don't have a digital volt meter.

Well that sounds like the perfect excuse to buy a new tool!

Speaking of new tools, I just bought a small vertical mill to play with When I get it all set up I will get some pics posted.

Are you making chips yet on the lathe?

 

[Charolais]

I have an Amprobe brand amp clamp that's for AC and DC. Bought it back in 89 and if I remember correct, it cost $485 back then. I use it in at my work place on DC motors,ele. DC brakes and DC relay coils and such. It's digital also. Don't remember right off hand but I think it's rated for 500 amp DC. It also reads in tenths so it is usable for smaller 12 volt systems too.

For the price it's not your everyday home shop tool. But in my line of work it comes in handy at home sometimes.

 

[Bird]

I have an Extech Digital Clamp Meter that's for both AC & DC and has a temperature probe. It only cost me $180 in April, 1990.

 

[PineRidge]

Bird by 1990 standards that was a lot of money for the Extech Digital Clamp Meter.

Kenney no, no chips yet but we are much closer.

 

[Soundguy]

Amp-Probes aren't designed to measure DC current, they are an AC instrument that operate off the "transformer" principle. (Mutual Inductance) What you need is an "in line" DC ammeter of some sort, like a multi meter with 10 or 20 amp ranges.

I used to use my expensive VOMs as inline amp testers.. but tired of taking them aprt and replacing hard to get to fuses when i fould a circuit that pulled 11 amps.. etc..

So i hit the local auto store and bought a cheapy sunpro ampmeter.. 9$.. I added wires with gator clips to it. It is now a great inline ammeter.. polarity indicative due to meter swing.. and good for 60a.. etc.

Soundguy

 

[PineRidge]

So i hit the local auto store and bought a cheapy sunpro ampmeter.. 9$.. I added wires with gator clips to it. It is now a great inline ammeter.. polarity indicative due to meter swing.. and good for 60a.. etc.

Soundguy

I haden't even thought of an automotive amp meter and there just may be one around here lurking in the pole barn. Thanks for the tip SoundGuy!

 

[kennyd]

That is excellent advice Chris, I think I will steal that idea in the future as well

 

[PineRidge]

That's the real beauty of this site KennyD. Members teaching other members.......

 

[Farwell]

Don't remember what resistor I used but I once built a 50 amp dc meter out of a not to expensive Radio Schlock amp meter, a resistor and some alligator clips.
Farwell

 

[Soundguy]

Considering an ammeter is on;t a 'shunt voltmenter' It's easy to measure a voltage drop from a known load, if you also know system voltage, then make a comparison, and calculate amps.. etc..

soundguy

 

[mrutkaus]

Get a few fuses and put them in line. When they stop blowing, you found yoru value!

Mike