Why can't I measure milliamps?

[Scott98]

I've got a Fluke 115 meter. The black lead is hooked to the common on the meter. The red lead is hooked to the one marked "A" which is is fused 10A to the common. I slide the large dial to the very bottom which is A_... for DC not the A _~ for AC. I open the hood on my '87 911 and the battery is connected, underhood light is on, battery is fully charged (I checked it with the meter beforehand). I place the black lead on the negative post and the red lead on the positive post. My meter reads nothing. What am I missing???

Thanks,

Scott

[John W.]

If I understand your description - with your fluke test leads across the battery terminals you are measuring voltage. To measure current you have to disconnect one terminal and insert your meter in series. My fluke has a place for the test lead(10 A) to measure large currents and a place for it to measure milliamps. There is a different place to measure resistance (ohms) and voltage -- hope this helps. I check back to see if you need more help.

[dad911]

To measure current, you need to 'break' the circuit and put the meter in-line. Disconnect a battery cable, and put the meter between the battery and the cable.

BTW, you probably blew the fuse in the meter by hooking it up directly across the battery.

Edit: manual online here: http://us.fluke.com/usen/products/ProductManuals.htm?cs_id=35970(FlukeProducts)&category=MD_AUTO(FlukeProducts)

Page 12 - how to hook up meter to measure current.
Page 16 - how to test fuse.

[scottbombedout]

Voltage across, current through.

[dshepp806]

Yeap,..better check the meter's fuse (s)......

Doyle

[Scott98]

Originally Posted by dad911

To measure current, you need to 'break' the circuit and put the meter in-line. Disconnect a battery cable, and put the meter between the battery and the cable.

BTW, you probably blew the fuse in the meter by hooking it up directly across the battery.

Edit: manual online here: http://us.fluke.com/usen/products/ProductManuals.htm?cs_id=35970(FlukeProducts)&category=MD_AUTO(FlukeProducts)

Page 12 - how to hook up meter to measure current.
Page 16 - how to test fuse.

Thanks to all.

You are right, fuse is blown.

Can anyone recommend a good book for learning basic automotive electricity?

Nothing like beginner's mistakes.

Scott

[Rot 911]

Didn't your fluke come with an instruction manual? Mine did and it does a pretty good job of explaining how to use it.

[Scott98]

Originally Posted by Kurt V

Didn't your fluke come with an instruction manual? Mine did and it does a pretty good job of explaining how to use it.

It got thrown out two days ago while cleaning up stuff in anticipation of a move and getting the house listed on the market....

Scott

[rick-l]

That is an expensive fuse also Allied elect

I avoid using the current feature on my meter just for that reason. I always run into unexpected current surges.

Another thought on measuring current in you car is to wire the terminals of the meter together, let it sit for a while, remove the wire and look at the current. This lets the initial surge settle down.

[dw1]

What the previous posters stated is correct.

Think about potential (units: volts) as pressure, and current (units: amps) as flow.

If you are measuring current from a battery be careful, as 1 milliamp = 0.001 amp, and the battery's current to, for example, run the starter motor can be in the 60 to 150 amp range.

There are LOTS of good references on basic electricity on the web, including
http://www.allaboutcircuits.com/vol_1/chpt_1/6.html
http://www.hvacmechanic.com/basic_electricity_and_elecronics.htm
and many more.

[steely]

+1 on all this input. Based on what the others mentioned, and considering convenience, safety, and whether something is worth the effort for the data you'd get, I usually don't pursue trying to measure the current.

If you really want to however, I'd suggest a clamp on meter.

(PS - lived in albuq over 30 yrs ago - great memories)

[rick-l]

Originally Posted by steely

If you really want to however, I'd suggest a clamp on meter.

A DC magnetic field sensing meter? Now we are talking some big bucks.

[HawgRyder]

If you do use a clamp on meter...an old trick to getting a reading on low current is to wrap the wire being tested several times around the clamp (like winding a wire on a donut).
The numbers of turns will multiply the reading by that amount.
With very small amps, sometimes this is the only way to get a reading.
Bob

[fintstone]

Agree with others here...rarely a reason to measure amperage for auto repair/troubleshooting...in fact, most of the time, one of those $3 voltage testers with a sharp point and a wire with and alligator clip for ground that turns a small light bulb on works very well.
Moving to...or from Abq? Welcome or adios amigo.

[dad911]

Originally Posted by rick-l

A DC magnetic field sensing meter? Now we are talking some big bucks.

Used to be expensive, not so bad anymore.

[spuggy]

Originally Posted by Scott98

It got thrown out two days ago while cleaning up stuff in anticipation of a move and getting the house listed on the market....

Scott

So download the manual from the manufacturer? A Fluke is an investment, not some no-name piece of junk[1]:

http://us.fluke.com/usen/products/ProductManuals.htm?cs_id=35970(FlukeProducts)&category=MD_AUTO(FlukeProducts)


[1] Truth be told, a $20-40 multimeter is perfectly fine for most automotive uses - they just won't last forever like a Fluke or Beckman will in light usage.

[dw1]

For my Fluke 77 & 87, I have an older current clamp.

http://us.fluke.com/usen/products/moa.htm?cs_id=34473(FlukeProducts)&category=HMA(FlukeProducts)

[and scroll down to "Accessories"]

It's not that expensive (typically less than $150 for the Fluke i410 AC/DC current clamp), and worth it if you are trying to diagnose alternator or starter problems. That being said, I agree it is rare that I measure current rather than either continuity (resistance) or voltage when working on a car.

BTW, I find Allied has the better selection, but Newark Electronics and Digikey frequently beat them on price.
http://www.newark.com/
http://www.digikey.com/

For basic automotive electronics, most Bentley and Chilton shop manuals have a "primer" in the first chapter, or in the chapter dealing with the electrical system.

FYI, a good on-line reference is "Autoshop 101":
http://www.autoshop101.com/
and click on the "Online Instruction" link

A web search turns up many others, as well.

[911pcars]

Like others said. A Fluke cartridge fuse is typically around $10. You don't want to blow too many of these, but it happens from time to time. Not sure why they spec'd such an expensive fuse.

Anyone know why one couldn't substitute a more common fast-blo glass fuse (other than adapting to the existing fuse holder)?

if you can find an inexpensive inductive ammeter, let me know. Much easier to troubleshoot some electrical circuits.

Sherwood

[HarryD]

Originally Posted by spuggy

... [1] Truth be told, a $20-40 multimeter is perfectly fine for most automotive uses - they just won't last forever like a Fluke or Beckman will in light usage.

This is all you need



http://www.harborfreightusa.com/usa/itemdisplay/displayItem.do?itemid=90899

less than $5.00

[dad911]

Originally Posted by 911pcars

......
if you can find an inexpensive inductive ammeter, let me know. Much easier to troubleshoot some electrical circuits.

Sherwood

Harbor freight/ Cen-Tech, about $70, will measure DC current, clamp-on.