Multimeters - What Features To Look For.

[Therapy]

Originally Posted by transmitterdan

This unit is available under more than one brand name. Extech is one brand but there are others with differences only in the color and labeling.

If you are referring to the DC function I may be able to shed some light on it as I have an Extech 730 800A AC/DC meter. The DC current function relies on a Hall Effect device. The AC mode uses the same device. It is possible to magnetize the probe so that it has a permanent fixed magnetic offset. Usually it is small on the order of 1-5ADC. Some users think this offset error means the unit is not accurate. That is not the case. The Hall Effect device can measure residual magnetism in the clamp jaws left there from a previous DC measurement. It is possible to demagnetize the jaws and reduce the built in DC offset but the procedure is a bit complicated for the typical user who just wants to measure something. So they included a DC ZERO button to do just what it says. Using this button does not decrease the accuracy much unless the DC offset is a lot of amps (say >100).

On my unit the AC function has a bit of offset too (about 1A out of 800). But I don't think it means the unit is not accurate. I have checked it several times and found it to be correct within about 0.5A at 50A. If I want to use an 800A meter to measure milliamperes of current accurately then I would have to spend a lot more money than these little units cost. For what they are they are a pretty good deal and accurate enough for working on most boat electrical systems.

I want a meter too that will measure DC current. I looked up this one you have and did not see how much DC it can measure.

I also noted it ain't no 50 buck meter.

I don't mind paying but the Fluke was like 330.00 something. EEK! Too far for me.

If the Radio Shack one is the "same" how much DC current can it measure and also I should be able to find it (with different cosmetics) on Amazon for a lot less.

This is more complicated than I realized.

[transmitterdan]

Originally Posted by Therapy

I want a meter too that will measure DC current. I looked up this one you have and did not see how much DC it can measure.

I also noted it ain't no 50 buck meter.

I don't mind paying but the Fluke was like 330.00 something.

The unit i have can measure up to 800A either AC or DC. It costs around $125 US in retail stores. The Fluke is far better in performance and costs 3-4 times the price.

[Therapy]

Originally Posted by transmitterdan

The unit i have can measure up to 800A either AC or DC. It costs around $125 US in retail stores. The Fluke is far better in performance and costs 3-4 times the price.

Thanks.

[foggysail]

You can trust that he is not putting 800 amperes through any hand held meter!

I don't know what it is you're trying to measure and how much you can upset the circuit that you want to measure current. For large currents, a shunt is almost always used. For example if you put a 0.01 ohm resistor in series with the the current and then measure the voltage drop across the resistor, you can calculate what the current is. Shunts are designed to measure a wide range of currents.

Meters-- good quality meters such as Flukes are designed for laboratory use. Sure, they can be used anyplace just as a sledge hammer can drive tacks. I personally use a $50 Greenlee (sp) which is more than adequate for my applications. Save your money, purchase what you require and leave teh expensive toys to big company laboratories. JMHO

[Therapy]

Originally Posted by foggysail

You can trust that he is not putting 800 amperes through any hand held meter!

I don't know what it is you're trying to measure and how much you can upset the circuit that you want to measure current. For large currents, a shunt is almost always used. For example if you put a 0.01 ohm resistor in series with the the current and then measure the voltage drop across the resistor, you can calculate what the current is. Shunts are designed to measure a wide range of currents.

Meters-- good quality meters such as Flukes are designed for laboratory use. Sure, they can be used anyplace just as a sledge hammer can drive tacks. I personally use a $50 Greenlee (sp) which is more than adequate for my applications. Save your money, purchase what you require and leave teh expensive toys to big company laboratories. JMHO

I want to be able to measure low DC amps. Say to 80 or so.

[hellosailor]

A clamp meter is probably best bought. But don't forget, the resistance of most cable and wire is posted online. You can take a foot, or a meter, of some convenient gauge cable (i.e. zero gauge, two gauge) and simply use that as a shunt. Measure the voltage drop across it with your $20 multimeter, do a little math, and you've got your reading without an expensive shunt or meter.

Maybe not accurate to four decimal places but sometimes, one percent or even ten percent is good enough.

[s/v Jedi]

A clamp meter is accurate enough. When the current to measure is small, you can give the wire a second wrap through the clamp and divide measured current by 2.

[goboatingnow]

Nobody measures current , in a test environment with shunts !!! , Hall effect clamps have totally taken over this area from 100mA ones to over 1000A

Dave

[foggysail]

Originally Posted by hellosailor

Measure the voltage drop across it with your $20 multimeter, do a little math, and you've got your reading without an expensive shunt or meter.

.

Expensive shunts??? Minimum bid $3.99 plus $10 shipping including a digital panel meter? Note, will need a power supply of some type for the meter

DC 100A Red LED Digital Amp Ammeter Panel Meter with Current Shunt | eBay

And Dave--

I know Halls are popular especially for lower currents but the cheap old shunt is here to stay.

[transmitterdan]

Originally Posted by foggysail

You can trust that he is not putting 800 amperes through any hand held meter!

And you know this how? I measure nearly 800A all the time with it. In fact I just did that today. I never said I only use it on a boat though.

There is nothing wrong with having a high current meter like this. When you need to measure inrush current of a starter it is very handy. You can measure smaller currents very easily. Just wrap a few turns of the wire into a loop and measure the current in the entire loop. Then divide the result by the number of loops in the wire. You count the loops as the number of times the wire passes through the clamp jaws. So a complete loop will have 2 wires passing through the jaws so you divide the displayed number by 2. Another loop and you divide by 3 and so on. If you use exactly 10 loops of wire through the jaws your meter will read ten times the actual current. So 10 amps reads as 100 amps. Easy as pie when you know how they work.

[DotDun]

Originally Posted by foggysail

I know Halls are popular especially for lower currents but the cheap old shunt is here to stay.

Here to stay?? In a museum, maybe. There is no reason to open a circuit and install a shunt for the purpose of measuring current flow (or inrush) in a main or branch circuit on a boat.

[foggysail]

Sure--- and just how much does a Hall cost? Therapy stated $300 or so for a Fluke was too much. Don't assume everybody has big bucks to spend on special tools to read DC that may only be used once or twice. Shunts have their place in the world, they are simple, inexpensive and the work with a cheap mulitmeter even outside of museum. There are applications for them and they are not going away.

[Lake-Effect]

Originally Posted by foggysail

Sure--- and just how much does a Hall cost? Therapy stated $300 or so for a Fluke was too much. Don't assume everybody has big bucks to spend on special tools to read DC that may only be used once or twice. Shunts have their place in the world, they are simple, inexpensive and the work with a cheap mulitmeter even outside of museum. There are applications for them and they are not going away.

A Hall effect sensor costs... less than a dime in bulk. Any clamp meter that cam measure DC current as well as AC has such a sensor.

My experience with inexpensive clamp multimeters is that they aren't always great at currents lower than 5 amps. And, how often does the average cruiser have to measure high currents? Especially if they already have a battery monitor with a shunt permanently in the circuit?

If a cruiser is buying just one meter, I would say to just get a good basic multi meter and forego the clamp current measurement. I've had good luck with house-brand meters that are in the $40 to $100 price range. (even better when such models go on sale for $20 ). I have a $99 Radio Shack meter, a close copy of a Fluke 77, that's going on 20 years old.



My list of necessary features:
- robust construction with a rubber or plastic boot
- uses common batteries
- auto off
- DC and AC volts
- DC and AC current to about 10 A
- resistance, diode test
- 'beeping' continuity test

If you can afford something like a Fluke, by all means do so; with care it will last a decade or longer, which means you're paying about $20/year for a top-grade meter.

[DotDun]

Originally Posted by foggysail

Sure--- and just how much does a Hall cost? Therapy stated $300 or so for a Fluke was too much. Don't assume everybody has big bucks to spend on special tools to read DC that may only be used once or twice. Shunts have their place in the world, they are simple, inexpensive and the work with a cheap mulitmeter even outside of museum. There are applications for them and they are not going away.

How much is reasonable for one spend on readily available cables, connectors, compression tools to open a circuit and install a 800A shunt? How many DIYers have the knowledge to do that properly? How many shunts should a DIYer have? 100A?, 500A?, 800A? How accurate is a low end multimeter at measuring <50mv? How accurate is a $3.99 100A shunt purchased on Ebay?

How does one measure inrush with a shunt and a cheap multimeter?

The ability to measure inrush for my AC units properly using a Fluke gave me the knowledge to size my generator correctly. The cost of the meter was more than paid for by the savings in being able to purchase the correct generator vs. the one the 'experts' were recommending.

There is more to it than owning cheap shunts.

[goboatingnow]

The 'cheapies' are cheap and virtually disposable.

however a little up the scale and some features are useful on boats

* Peak hold
* RMS AC measurements
* Inrush capture
* latched continuity


other features while exotic Ive found useful

* data logging ( useful for power profiling)
* averaging


Having said all that the one meter in my boat kit , always is my old fluke 77 , unbreakable , infinite battery life, it just works and works . My lab is full of fancy gear, but that one has a place in my toolbox.

dave