Cannot take the reading of the amps

[chris0147]

Hello guys,

I need a little help, because I cannot be able to take the reading of the amps through on clamp multimeter. I can only read the amps on digital multimeter, but not on clamp.


Here it is the clamp multimeter I have got:
http://www.bargainhomeuk.com/products/Professional-1000-Amp-Digital-Clamp-on-Multimeter.html



Can you tell me why the clamp cannot take the read of the amps? I guess that they should be able to read either current of AC or DC. If you guess that the clamp multimeter should be able to read, then why I couldn't take the reading and what's gone wrong? :confused:



Any advice would be much appreciate it!

[Philldpapill]

Are you using a PWM with your setup? If so, the most probably reason is in how the two work. A clamp-on meter works by measuring the magnetic field produced by the wire as current flows through it. The multimeter probably measures current by measuring the very small voltage produced across a small section of wire as current flows through it.

If you try to measure using a clamp on, and you're using a PWM, the current is changing VERY rapidly. This change in current can screw with the mechanisms that measure the magnetic field(I say CAN... not WILL). A typical multimeter can sample the voltage at a much faster rate, so it should be pretty good.

All this is ASSUMING you're using a PWM. If not, hell if I know......

P.S. that meter is intended to measuring HUNDREDS of amps. If you're trying to measure 20A, good luck getting any kind of accurate reading. Just because something CAN measure really high currents, doesn't mean it can measure small currents very well. It's like trying to pick up a B.B. with a crane that's designed to pickup large objects weighing tons. Precision...

[chris0147]

Yes, I am using PWM for my setup. So I can't see why I couldn't take the reading of the amps for the DC current. When I tried to take the reading of DC and AC current, it said there was no amps in the current. Do you know why I couldn't take the reading? :(

I have tried to measure the amps between the battery positive post and the cell positive post, so it said there was no amps. And I have tried to use with the digital multimeter as well which I was on the same boat.

However, I have changed the wire on a different port on the digital multimeter and I got the reading!

So the real reason could be why I couldn't take the reading for the amps on the clamp meter, is it could be the wire that has not plugged in the right port on the meter?

And can you guess that if I could be able to take the reading for the amps of the DC current using with the clamp meter?

In this case, the site said that the clamp meter I has got can only take the reading of the amps for the AC current. I'm not sure if it could take the reading for the DC current? :confused:

[Philldpapill]

The way the clamp on meter works, is the current going through the wire makes a magnetic field. If the current changes, it makes a changing magnetic field. This changing magnetic field induces a voltage in the clamp that the meter reads.

Sounds like you got the traditional AC clamp on meter. They work entirely differently than the newer DC clamp on meters. DC clamp on meters use something called the "hall effect" to directly measure a magnetic field, and extrapolate the current based on that. Sounds like you just wasted some money... You won't be able to get an accurate current measurement if you're using an AC clamp on meter.

[chris0147]

Yeah, looks like I have wasted some of my money. I doesn't realise that I should always use DC current to measure the DC amps :(

Are there any ways to use that clamp meter to measure AC current amps for the circuits?

[Bhart]

Yeah, looks like I have wasted some of my money. I doesn't realise that I should always use DC current to measure the DC amps :(

Are there any ways to use that clamp meter to measure AC current amps for the circuits?

Chris, I made the same mistake as you did, and bought a cheap meter from ebay thinking I could measure dc amps.
Look up the information as how to measure dc current with a shunt arrangement, that will be my next step..

[Bhart]

Chris, I goggled diy for dc shunt and found this youtube site:
http://www.youtube.com/watch?v=65EiiE4NoDI

[Philldpapill]

You'll need some knowledge of electronic circuits in order to build an amplifier to take a tiny microvolts signal, and boost it to volts that you can read accurately.

[rcflyn]

In this case, the site said that the clamp meter I has got can only take the reading of the amps for the AC current. I'm not sure if it could take the reading for the DC current? :confused:

You answered your own question... I went and looked at the site you provided, and didn't see any DC AMP specs...
It only reads AC AMPS....

[chris0147]

Thanks for the advice guys, I have learnt my mistake. So what amp meter is the best things for me to buy?


I want to buy amp meter similar as the clamp meter I has got.



Thanks!

[Philldpapill]

It really depends... There's a common misunderstanding out there about "amps". There are two types of "amps" - RMS and Average. When you talk about gas produced per amp, you are talking about the number of electrons that have passed through your cell, so you would be interested in average current. On the other hand, you need to consider RMS(Root Mean Square) amps when you are using a PWM to ensure that you aren't dumping HUGE spikes of current(large spikes of current means excess power loss). Ideally, your RMS current reading and average current reading would be the same, like in the case of DC when you just use a direct connection to your cell from your battery. Your RMS reading will ALWAYS be greater than or equal to an average current reading.

If you go with an analog current meter, then you will definitely be getting an average current reading. If you go with a digital meter, you could be getting either one...

[chris0147]

Well, I don't want to spend more than $40. I am thinking of buying this product:

http://cgi.ebay.co.uk/Uni-T-UT203-Current-Digital-Clamp-Meter-DC-AC-400A-/260654213980?pt=UK_BOI_Electrical_Test_Measurement _Equipment_ET&hash=item3cb033ab5c


Does it looks good for hho production if it does match in my needs?

[Bill Foote]

Check Ebay for DC ammeter. It will have a digital read-back panel and a shunt. Mine has a 75A=75mV shunt, it's stamped on the shunt.
You need a separate power supply for the ammeter than the power supply you are reading. You can't use your car battery to power the ammeter because you are measuring the car battery current. It seeks ground through the ammeter and smokes it good!
I use a 9VDC battery to power my ammeter. It has an aqua blue background and black numbers.The connection is battery, breaker, solenoid, shunt, PWM, dry cell positive, then negative of dry cell to negative of battery or good frame ground.
My ammeter and shunt was $25.00 with free shipping direct from Japan in one week.
The solenoid is to turn on the system safely, I built a box with temp read-back,current read-back, time to fill reservoir led, on/off switch and a Eurotherm PLC with a normally closed relay that will open if the temp goes to 165F. Remember to use a 9 volt battery for your ammeter/shunt circuit.
Have Fun, Bill

[thedore]

Most meters have a 0 to 200 mv volt range. This can be used with a shunt like this one
http://www.google.com/products/catalog?q=50+a+shunt&hl=en&cid=220722003728512553&ei=M1m2TL3YG6jQiQTYh5SzBA&sa=title&ved=0CDkQ8wIwBTgA#p

to provide a 0 to 50 amp meter. 50 mv = 50 amps