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Old 03-25-2006, 04:50:16 PM   #1
Steve's 74
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multimeter Q? Checking current

I'm feeling dumb right now. I want to measure how many amps my elec fan draws at initial ramp up and then at full spin.
Red lead in 20A (+) and black in COM (-). Meter setting to 20A range in DC mode. Fan NEG connected to ground (-). So far sound right?
Now I thought I should put the meter in series with the power lead; i.e. between the power source and the fan (+). Reading the instructions from the multimeter...
Quote:
Remove power from circuit under test. Open circuit at point you wish to measure current.
this sounds fine so far, but then it says
Quote:
Touch the black test probe tip to the negative side of the circuit. Touch the red test probe tip to the positive side of the circuit. Apply power to the circuit.
Is this reference to the negative side of the circuit referring to the ground or the side of the (+) wire between the power source and the meter?
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Old 03-25-2006, 05:20:46 PM   #2
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_/+

Positve = Power (red)

Neg = Ground (Black)

Just like your battery....
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Old 03-25-2006, 05:41:29 PM   #3
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Connect the power to the red lead, the black lead to the positive input of the fan.
Most likely 20A isn't enough. Got an extra fuse for the meter? Typically the inrush current is three times the running current.
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Old 03-25-2006, 09:46:25 PM   #4
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Quote:
Connect the power to the red lead, the black lead to the positive input of the fan.
That's what I thought. The power goes from the source to the meter (red lead) where the current is read, and then to the fan (via the black lead). That statement from the multimeter manual just had me second guessing.
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Old 03-26-2006, 07:34:30 PM   #5
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GetMore is right... it will pull more than 20A at startup. Other than that, you're on the right track.
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Old 03-26-2006, 07:51:22 PM   #6
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Thanks.
Anyone know if both fans coming on together pull more than 30amps. That's what I need to determine.
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Old 03-26-2006, 08:34:13 PM   #7
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I would guess that they would.
Most likely one fan is going to pull more than 20.

What do you need to know this for? Perhaps we can give you some advice.
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Old 03-26-2006, 08:51:52 PM   #8
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Trying to determine which controller size to get.
http://www.dccontrol.com/
go to fan control section.
Also see this thread: http://www.nastyz28.com/forum/showthread.php?t=43044 especially the post by gmachinz

And I need to know what size wire / fuseable link to use to the controller.
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Last edited by Steve's 74 : 03-26-2006 at 08:58:36 PM.
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Old 03-26-2006, 10:10:39 PM   #9
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You should be fine with the FK-35. By using this unit you will not be dealing with the inrush currents that relays would allow, since it ramps up the speed with temperature.
How far is it from the battery to the control?
You are going to mount the controler as close to the fan as possible, right?

For the wiring I would think that DC Controls would be able to give you all the info you need. I was going to point you to Paniless Wiring or MAD Electrical, but I didn't see the info on their site.
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Old 03-27-2006, 08:54:27 AM   #10
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Thanks. I was planning to mount the control on the driver side radiator support, cause I have some space there (about 3 feet from the BAT), but I could mount it on the passenger side right next to the BAT. The control box will be within 12" of fan 1 and 24" of fan 2.
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Last edited by Steve's 74 : 03-27-2006 at 08:59:12 AM.
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Old 03-27-2006, 02:02:11 PM   #11
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That sounds fine. The thing to remember is that the longer the wire run the thicker the wire needs to be. The lengths you are working with are short enough that you don't need to concern yourself with that issue.
If you were mounting the controller on the firewall and running the battery in the trunk then I would worry about it.
I think you want to keep the unfused wires shorter, so I say go ahead and mount the controller on the driver's side, if that works best for you.
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Old 03-30-2006, 02:58:36 AM   #12
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Don't forget to use a fusible link. Wire size + 4.

8ga wire = 12ga fusible link
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