How to read my meter. Please help. - Team Camaro Tech
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post #1 of 5 (permalink) Old Feb 22nd, 12, 11:04 AM Thread Starter
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Tim
 
Join Date: Dec 2010
Location: Lansdale Pa
Posts: 158
How to read my meter. Please help.

Okay guys I just did a test with a meter to see the amp draw of my rear defroster fan because i need to get a switch for it. Let me know if I did this right and if the results sound right.

I set the meter to 10A in the ADC section of the meter (I got this setup info online). I then connected the 2 meter leads "in series" to the power wire and a seperate straight wire to the ground wire on the motor. I connected the ends directly to the car battery, which was not connected to anything else at the time. The draw reads about 2.10 on the meter. So does that mean it's drawing a little more than 2 amps? OR do I have to times that number by 10 because it's on the 10A spot on the meter? If so does that mean it's a 21 amp draw?

Either way it is, please let me know what size switch I should get if you know what these numbers mean. Any help with this would be great.

Thanks!
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post #2 of 5 (permalink) Old Feb 22nd, 12, 11:48 AM
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Jim
 
Join Date: Dec 2002
Location: Saint Louis, Missouri
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Re: How to read my meter. Please help.

With a meter set to the 10A scale (and the leads plugged into the right spots as some meters need the test leads to be moved to the appropriate locations and the selector knob also set right) one of the test leads will connect to the supply of power like a battery positive post, the other lead will go to the power lead of the fan motor, and then the motor is grounded to the battery.

The current or electricity comes out of the battery into the meter through one lead, then out the other lead to the fan motor then out from the motors ground to the battery negative post. You then will get a reading.

If it's under 10A then you should get a reading AND the device should work (in your case the fan motor should start spinning). The meter if it then reads 2.10 then this means the fan is drawing 2.1 Amps of current.

Be aware that some meters measure up to 10A and if this is exceeded then the meter could burn up or it might just blow a fuse inside of it.

Sometimes if I'm unsure if something draws more than my meter I place an inline 10A fuse on the device and if it works and the fuse doesn't blow then I know my 10A meter can measure it. If it blows a test 10A fuse then I know it draws more than 10A and I don't want to put my 10A max meter on it.

If your motor does draw 2.1A of current then get a 10A or larger switch and not some cheap off shore switch but a quality switch. You could get by with a 5A but sometimes motors draw more on startup and the 10A should be a lot safer and longer lasting.

Jim

1974 Spirit Of America Nova (being restored), 1973 Nova Custom, 1968 Chevy II (Garage Find 2012)

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post #3 of 5 (permalink) Old Feb 22nd, 12, 12:13 PM
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Brian
 
Join Date: May 2005
Location: Laurel, In
Posts: 4,872
Re: How to read my meter. Please help.

Jim is spot on. Your motor is drawing 2.1A. 10A on your meter is just the range selected (the most it will read is 10A). Most hand held meters will only read up to 10A before it blows an internal fuse (lucky), or smokes the meter (unlucky). Most of the better meters have the fuse.

Experience...... It's what you get when you didn't get what you wanted.
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post #4 of 5 (permalink) Old Feb 22nd, 12, 02:32 PM Thread Starter
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Tim
 
Join Date: Dec 2010
Location: Lansdale Pa
Posts: 158
Re: How to read my meter. Please help.

thanks guys for all the good information. I figured I could of called my father but decided to ask you guys so I didn't have to hear his long long long explanation.

Btw, you also answered another question I forgot to ask and that is, if it is only drawing 2.1 amps, is it okay if I do get a switch that is recommended for up to 25 amps. so you guys answered that it was okay to use that, which makes me feel better because the switch I looked at is a 25 amp switch.

Thanks again for your help.
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post #5 of 5 (permalink) Old Feb 23rd, 12, 03:38 AM
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Brian
 
Join Date: May 2005
Location: Laurel, In
Posts: 4,872
Re: How to read my meter. Please help.

A 25A switch will be OK, you just don't want one rated for less than your current draw. On the other hand, a 25A switch gains you nothing over a 10A switch provided both switches are of the same quality. Make sure there is a fuse somewhere in the system if you are modifying the factory wiring.

Experience...... It's what you get when you didn't get what you wanted.
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