Low level DC Amp-Clamp

[ATSman]

I am in the market for a low cost DC clamp-on AM to measure parasitic current flow in vehicle battery
systems. It would measure in the range of a few ma to 80A DC and was looking at the one in this link.
It claims to have a 1 ma resolution on the low scale.
Has anyone ever used this model or can give some insight on what you use or recommend for low level measurements?
Thanks


http://www.testequipmentdepot.com/e...tm?ref=gbase&gclid=CPT3iarW4tECFRBxfgodeoUA0g

 

[gar]

170128-0900- EST

ATSman:

I am hesitant to respond because I can not answer the question you asked. But you are not a newbie so possibly I won't drive you away.

Note it is 22 hours since you started this thread and no one has responded, not even a moderator.

I have no experience with Extech meters except to have asked questions about capability at a show. Others on this forum have in the past made some comments on this company.

You have not indicated how low a DC current you want to measure, and with what accuracy. Just some thing like in the mA range.

Is a clamp-on essential, or can you break the circuit?

I believe many clamp-on DC current meters will use a Hall device as the magnetic field sensing element. These are noisy and have drift problems at mA current levels using a one turn input. Further is the problem of the earth's magnetic field, sensor position and zero setting.

With an old Fluke Hall current probe that I have it's low range is 2 V out with a 20 A one turn input. That is 0.2 V / A. On AC the noise level is about 2 mV, or 10 mA. On DC I have a hard time doing a zero adjustment with the Fluke adjustment for low currents. On DC I can get a 5 to 10 mV (or 100 mA) change from orientation in the earth's magnetic.

Try to get an Extech and play with it.

.

 

[milldrone]

Has anyone ever used this model or can give some insight on what you use or recommend for low level measurements?
Thanks


http://www.testequipmentdepot.com/e...tm?ref=gbase&gclid=CPT3iarW4tECFRBxfgodeoUA0g

I have used the Extech meter in the link. We find it to be a very useful addition to our test equipment. Yes it does measure down to a 1ma resolution, which is very useful when trying to measure ranges above our fluke 771 (4 to 20 clamp on). My only complaint is that it has an auto shutoff (15 minutes) that cannot be disabled. We use a DVR video recorder and several Simpson 260's & pilot lights as long term data logging equipment.

Edit: just noticed Gar's post. Yes it is very sensitive to magnetic fields, but it has a very handy "zero button". A DC coiled contactor 12 inches away will affect the reading, and if that contactor is cycling you will need to constantly be "zeroing" .

 

[big john]

Any digital display with 3 decimal places can say 1mA resolution, that is not the same as being accurate down to 1 milliamp.

If you only care about getting within a few dozen mA of the truth, that meter will probably work fine. I tried to find a cheap DC clamp for process loops and was disappointed every time.

Short answer: You will not get accurate low-milliamp readings cheaply. Expect to pay $300+.

 

[zbang]

Short answer: You will not get accurate low-milliamp readings cheaply. Expect to pay $300+.

That's been my experience, too. FWIW, I usually consider Extech to be second-tier test equipment (functional but not always that accurate and not extremely robust).

 

[Electric-Light]

If this is the only purpose you're needing, I would recommend breaking the circuit and slipping a high wattage (20w or more) 1 ohm resistor through and measure the mV across the resistor. It will be 1mV per mA. You can get accurate enough reading while surviving things like accidentally opening a door or leaving on a small lamp without blowing the mA range fuse. You might cook the resistor if you leave the car on "run" when you connect the battery but this shouldn't happen often.

 

[Cascode3]

If this is the only purpose you're needing, I would recommend breaking the circuit and slipping a high wattage (20w or more) 1 ohm resistor through and measure the mV across the resistor. It will be 1mV per mA. You can get accurate enough reading while surviving things like accidentally opening a door or leaving on a small lamp without blowing the mA range fuse. You might cook the resistor if you leave the car on "run" when you connect the battery but this shouldn't happen often.

At 80Adc (see OP), that would 80Vdc, probably more than the battery can supply. Not to mention the 6,400W. That might be a bit much for a 20W resistor don't you think?

 

[milldrone]

For this application I'm thinking accuracy is not an issue, but ease of measurement is. An amp clamp is the perfect form factor. Start at the battery + then proceed down the wiring until you loose the parasitic draw, then back up. The parasitic draw will be where the current leads you.

An alternative if you have a bluetooth meter with a remote display like the Keysight brands or some of the Flukes you could place the resistor like Electric light suggested, put the bluetooth meter there and use the remote display near the fuse box and the start pulling fuses until the reading disappears.

 

[Electric-Light]

At 80Adc (see OP), that would 80Vdc, probably more than the battery can supply. Not to mention the 6,400W. That might be a bit much for a 20W resistor don't you think?

The OP said that's the capability of the meter. I don't believe he plans on cranking over while measuring parasitic draw.

Got to be real careful with modern cars. The current can be very high like 100mA for a few minutes after the last activity before everything goes to the deepest sleep. Influence of magnets and coils will also throw off DC current.

 

[Cascode3]

The OP said that's the capability of the meter. I don't believe he plans on cranking over while measuring parasitic draw.

I was simply commenting on the practcalities of inserting a one ohm resistor.

 

[infinity]

At 80Adc (see OP), that would 80Vdc, probably more than the battery can supply. Not to mention the 6,400W. That might be a bit much for a 20W resistor don't you think?

I thought that you were given a short recess from the forum?

 

[ATSman]

Thanks Everyone

Thanks Everyone

First of all I want to thank everyone for all their insight and comments.
This meter was recommended to me by a friend of mine that does startup testing on large utility scale PV solar farms.
I bought the meter and have played around with it and as others have mentioned
it does have its quirks like having to zero it a lot and the meter position with respect to other devices in the circuit.
But for the money it suits me fine for what I will be using it for and can recommend it as a low cost non-intrusive ammeter.

 

[gar]

170130-2026 EST

ATSman:

What was the smallest current level you wanted to look at, and was this something that you could easily cycle on and off?

.

 

[ATSman]

170130-2026 EST

ATSman:

What was the smallest current level you wanted to look at, and was this something that you could easily cycle on and off?

.

Hi GAR,
I was looking for values in the 25ma and above range and with some playing around this meter can achieve it. If you search you tube for parasitic current leakage you will find that any draw above 25 - 30ma may be considered a problem in the vehicle's electrical system. It is important that the t-shooting be done without opening the battery connection since this turns on things along with the ECM that interferes with what you try to measure and takes time for these systems to go to sleep. This was the reason for choosing a clamp-on AM.
It turned out that my problem was caused by a defective alarm module (Derringer II) that I am still trying to isolate. I am trying to get the wiring diagram for this puppy.

 

[Electric-Light]

Hi GAR,
I was looking for values in the 25ma and above range and with some playing around this meter can achieve it. If you search you tube for parasitic current leakage you will find that any draw above 25 - 30ma may be considered a problem in the vehicle's electrical system. It is important that the t-shooting be done without opening the battery connection since this turns on things along with the ECM that interferes with what you try to measure and takes time for these systems to go to sleep. This was the reason for choosing a clamp-on AM.
It turned out that my problem was caused by a defective alarm module (Derringer II) that I am still trying to isolate. I am trying to get the wiring diagram for this puppy.

30mA is still way too high for my liking. If you don't drive often or go out of town for a bit, you're going to lose 10Ah in 2 weeks.