Help measuring DC Amps with my DMM

[KeyWestBoater]

Hi, Sorry to be asking this in another post but I finally have time to do this and really need some simple instructions. I need to know how to connect my DMM to read DC amps. It has a 10A setting. I found the small wire on the battery which supplies current for the aerator and FF. I tried unhooking all the pos wires on the battery and putting the DMM leads between the pos battery post and the red FF/aerator pos wire. When the FF or aerator are switched on they don't come on and the reading stays at zero. I also only connected the FF/aerator pos wire back to the battery and turned it on (and of course it came on connected like this) and put the DMM leads on the pos and neg of the battery. Still no reading (zero amps) even when the FF/aerator are running. Could someone please tell me what I'm doing wrong? I'm stuck!

Many thanks!
KWB

 

[Proselect]

Re: Help measuring DC Amps with my DMM

When you measure current its just like measuring water pressure so to speak. You need to hook it in series with the circuit. Make sure the aerator is grounded and then hook one end of the meter lead to the positive wire. The other end of the meter lead needs to go to the positive battery terminal lead. Then turn on the aerator switch. You should here the aerator turn on and get a reading. If the aerator does not come on and you get no reading then you may have blown the fuse in the meter. It is fused for a 10 amp circuit, but usually has a 15a fuse in it. If it is blown you won't get any readings. If you hooked it up to a circuit over 10-15 amps then the meter would probably flash OL quick and then back to zero as the fuse blows. Let me know if you have any other questions, I should be able to help.

 

[dchris]

Re: Help measuring DC Amps with my DMM

One quick way to check your meter is to connect it across a small battery like a 9v or AA. Make a short across the +/- terminals with the meter. It should measure a under 100ma. This is the max output of the battery. Don't try it on any large batteries.
You will need to use a lower scale than what you're measuring in the boat, but you can prove out your set up. Like the previous post, check the fuse. Also check your probes with the ohm meter settings.

 

[turbinedoctor]

Re: Help measuring DC Amps with my DMM

QUOTE]and put the DMM leads on the pos and neg of the battery.[/QUOTE]

You should always avoid connecting your DMM meter across the battery terminals, a blown fuse is sure to follow this action. When putting the meter in series with the aerator or FF and they dont work try swapping the DMM leads. Some meters will not work with a reverse polarity connection or if they do it will try to peg the meter needle in the wrong direction.

Durwood

 

[KeyWestBoater]

Re: Help measuring DC Amps with my DMM

I guess I'm learning the hard way. I blew my fuses on my DMM so I will get some new ones tomorrow and try again. Funny thing, before I blew them when I put the lead between the pos cable from the FF/aerator and the pos battery post the FF would not come on regardless of which direction the DMM leads were put. I will try again with new fuses tomorrow night.

Thanks again!
KWB

 

[Moody Blue]

Re: Help measuring DC Amps with my DMM

Most meters require that you move the RED lead from the + terminal of the meter to the 10A terminal of the meter. Your meter may or may not operate that way.

Switch the meter to the 10A scale.

Disconnect the RED wire of the aerator/FF from the battery and connect it to the BLACK lead of the meter. Connect the RED lead of the meter to the battery + terminal.

The meter is now "in series" with the load and will measure the current being drawn when they are switched ON.

 

[bruceb58]

Re: Help measuring DC Amps with my DMM

and put the DMM leads on the pos and neg of the battery.

If you really did that with the leads in the current measuring position, that is how you blew your fuses.

Before you start again, take a picture of your meter and we can let you know what to do.