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Re: (ET) motor current


On Thu, 27 Jul 2006, Elie, Larry (L.D.) wrote:


Don't you have a Hall clip-on meter?  They are fine for this
application.


Nope. I've never found them to be very accurate, so I don't use them.
I realized last night that the approach of using the leads as a shunt to measure voltage across (to calculate current) won't work, since the resistance along the leads is essentially zero (tested to confirm) - it's on the order of milliohms, and the leads from the multimeter probably add more resistance than the 14 Ga motor lead wiring itself. I'll just use my multimeter in ammeter mode, and short across it when the blades first start up, so the startup current doesn't fry the fuse. 

Mike



Larry Elie


-----Original Message-----
From: elec-trak-bounces cosmos phy tufts edu
[mailto:elec-trak-bounces cosmos phy tufts edu] On Behalf Of Michael S
Briggs
Sent: Thursday, July 27, 2006 4:32 PM
To: steves
Cc: elec-trak cosmos phy tufts edu
Subject: Re: (ET) motor current



On Thu, 27 Jul 2006, steves wrote:


I thought the motors were more like 1 HP. I have measured the current
with a DVM (if I recall correctly) and it can get over 10A (I think).
Problem is if you blow the DVM fuse - the replacement fuses are
expensive. I'm pretty sure 'idle' current is < 10A so you could

measure

each motor running but not cutting and see if the suspect motor pulls
excess current.


I have gobs of fuses for DVMs here at work (students are constantly
blowing them in our labs), but I think I'll still just try measuring the

voltage drop along the leads to the motors instead.

Mike


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