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Old 08-21-2011, 07:10 PM   #1
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Multimeter help

I know you guys probably might not know this one but whatever you guys have should help. How do i use a multimeter to know how much amps my lights put out so i know how big of a fuse and relay to use.

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Old 08-21-2011, 08:05 PM   #2
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Quote:
Originally Posted by bmxanrchy127
I know you guys probably might not know this one but whatever you guys have should help. How do i use a multimeter to know how much amps my lights put out so i know how big of a fuse and relay to use.
You have to remove the positive side of the light and place the red lead of your meter on that wire.then take the black meter lead where the positive wire was connected,you basically put the meter in line with the hot side.put the meter on dc amps,turn the lights on and read your meter

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Old 08-21-2011, 08:11 PM   #3
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Quote:
Originally Posted by bmxanrchy127
I know you guys probably might not know this one but whatever you guys have should help. How do i use a multimeter to know how much amps my lights put out so i know how big of a fuse and relay to use.
Watts divided by Voltage = amperage.
Google Ohms law
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Old 08-21-2011, 08:44 PM   #4
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E over I x R

E being voltage
I being impedance
R being resistance

Basic ohms law
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Old 08-21-2011, 09:04 PM   #5
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Yep, pull a bulb and read the wattage off it and then convert to amps.
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Old 08-24-2011, 03:03 PM   #6
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The above answer to divide the lamp wattage by the voltage is correct and so is the method for inserting an ammeter ----
But a few cautions.
1) Check your multimeter, it probably won't measure more than 10 amps full scale (if that) and will include a fuse in the meter to blow in case of higher current.

2) The test leads on most multimeters are too small to handle high currents and may burn out, plus their resistance will likely affect your readings.

3) Be conservative. If you calculate your current at 12 volts and your alternator is running 14 volts or more, then your current (and wattage) will be be considerably higher.

4) When you first turn your lights on the filaments will be cold and the inrush current will be much higher than that calculated from the wattage.

5) If you are able to determine the current, select a fuse rating 2x to 3x higher or better yet use a circuit breaker----and don't forget to double the rating for 2 lights.

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Old 08-24-2011, 03:12 PM   #7
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Originally Posted by ironmike08 View Post
You have to remove the positive side of the light and place the red lead of your meter on that wire.then take the black meter lead where the positive wire was connected,you basically put the meter in line with the hot side.put the meter on dc amps,turn the lights on and read your meter
Im positive all this would accomplish is a blown meter fuse...
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Old 08-24-2011, 03:15 PM   #8
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Use an amp clamp.... home depot $20
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Old 08-24-2011, 03:16 PM   #9
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wwrap the clamp around the hot leg feeding the light....
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Old 08-24-2011, 04:00 PM   #10
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Use an amp clamp.... home depot $20
^ yes, this...

While your there buying your new amp clamp, pick up a new meter fuse to replace the one you blew trying it the "other" way...
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Old 08-24-2011, 04:12 PM   #11
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They sell DC clamps for 20 bucks? I have seen some, but they were AC only
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Old 08-24-2011, 06:14 PM   #12
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DO NOT USE A MULTIMETER ON YOUR LIGHTS, it will BLOW UP THE METER the amps running in your lights, are way to high for you 10amp fused meter


Seriously don't do it unless you REALLY want a new meter

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