RE: [DML] Re: Fan current
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RE: [DML] Re: Fan current

Unfortunately, it didn't occur to me to test them while driving, but you're right - the air that is driven through the fans by the motion of the car would have an effect on the amount of current they draw. Unless the weather this weekend is unusally nice, the car is probably "down" for winter projects atthis point, but if the weather is great this weekend maybe we can get it out and run this test.

To: dmcnews@xxxxxxxxxxxxxxxxxxx: joe.dalton@xxxxxxxxxxxxxx: Wed, 17 Oct 2007 10:39:10 +0000Subject: [DML] Re: Fan current

Hi Joe,Good explanation.Have you also tested the draw while driving?The friction in that case may be causing higher consumption.Welmoed.--- In dmcnews@xxxxxxxxxxxxxxx, "joekuchan" <josephkuchan@...> wrote:>> I just uploaded two pictures to the photos section of the DML in a > new folder titled "Fan current". With all the discussion lately > about what various fan designs draw I decided to find out for myself > what stock DeLorean fans really draw. I used a calibrated and zeroed > clamp-on DC ammeter to measure the current of each of the two fans > in 6195. These are original, never been replaced, 26 year old fans, > by the way.> > For this test the Joe Cool was removed and replaced by a fused fan-> fail jumper and a fan relay. The ammeter was clamped first on one > leg of the jumper then the other to measure each fan independently. > The car was started and the AC engaged to run the fans. The photos > show the readings with each fan at its stabilized running current. > Note that one fan draws 9.1 amps and the other draws 9.4 amps. > That's a total of 18.5 amps, considerably less than the 28 to 30 > amps they have been rumored to draw.> > Of course a defective fan, say one with a broken blade, bad > bearings, or shorted windings could draw more, but a normally > functioning fan draws nowhere near the 28 to 30 amp figure that has > been bandied about.> > As for current surges on start up, yes, this is a normal occurrence > with motor loads. Depending on the motor's design it might draw > anywhere from 4 to 6 times it's normal no-load running current on > start-up. This is completely normal and is the result of what is > known as back-EMF (back electromotive force) that is generated in > the motor's windings during startup. The 4 - 6 times rule of thumb > applies to the "no load" current demand of a motor. The fans on a > DeLorean, even in their steady state running condition, ARE under > load by the way. The fan blades are moving air and it takes real > work (i.e. current) to make this happen. So we might not expect the > start up current of a DeLorean fan to be somewhere around 4 ? 6 > times the 9.4 amps running load that I measured on 6195. It will > probably be somewhat less as the no-load current of the motor would > actually be somewhat less than 9.4 amps. > > All of this is the real reason why 15 amp fuses typically won't blow > on normally functioning fans. The fans don't draw 15 amps normally > and the startup surge is of too short a duration for the fuses to > blow.> > The only reliable way to measure the actual current on start up > would be to use a strip-chart recorder, storage scope, or some other > fast-response recording type of current measuring device. Trying to > read the swinging needle of an analog ammeter won't work for this > job as the mass of the meter movement, frictional losses, and needle > ballistics are such that it won't accurately follow the current > profile. A digital meter has none of these problems, but they suffer > from a sampling rate that is too slow to follow the current profile > and the rapidly changing digits are hard to read in any case.> > Hopefully this helps clarify the true situation with respect to the > amount of current stock DeLorean fans really draw.> > Joe> 

Windows Live Hotmail and Microsoft Office Outlook ? together at last.  Get it now.

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