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RPM: What tool to measure?

ron in charleston on Mon July 11, 2005 8:58 PM User is offlineView users profile

What specific tool or gauge can I use to measure rpm. I want to check the rpm of my generator.

I know some of the Flukes can with an inductive pickup, but I did not want to go that route since I have a Fluke though it doesn't offer that option.

Chick on Mon July 11, 2005 9:48 PM User is offlineView users profile

A tachometer, and then you have to figure the ratio of the pully...Never tried tried that...Sounds interesting though...

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Chick
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Freedoms just another word for nothing left to lose

ron in charleston on Tue July 12, 2005 8:15 AM User is offlineView users profile

I should have been more specific about the generator. It's a Mutliquip GA-3.6RZ which is a small emergency generator used to produce electricity when power is out due to storm damage.


The motor is a Wisconsin Robin W1-280, has 273cc and makes I think 7 hp.

ron in charleston on Tue July 12, 2005 11:54 AM User is offlineView users profile

Quote
Gather you want 60 Hz output

That correct's, I do want 60 hertz, when it's under full load of about 27-30 amps. But I don't really have a way of being certain of the load I apply. RPM should be 3750 with no load, that maybe about 61 hertz and then 60 hertz at 3600 rpm when under full load.

Voltage, which I can measure should be between 115 volts and 125 volts, this would be from no load to full load, that sounds like the easiest way to test output. That's actually how I've done it in the past, when I had the unit under the load I was using I would just check the voltage and adjust idle speed accordingly.

I know the Fluke 78 measures hertz and rpm with the induction pickup as an option, I might should spring for one of those.

bohica2xo on Tue July 12, 2005 12:52 PM User is offline

Well, if it was a larger generator you would install a dedicated frequency meter - many larger units include one.

Nothing wrong with a good old vibrating reed frequency meter. Been pretty much the same insided since the 1920's....

The downside is cost. Stichco still makes a good unit, but it is about 125 bucks. Nice units, OEM in large Multiquip gensets.

Of course you could put the 125 toward a new Fluke, but you won't leave the fluke connected to the genset all the time either.....


Your call. If the genset is connected with a transfer switch (permanent installation) I would recomend a dedicated frequency meter as well. Makes a good 'quick check' along side a voltage meter. Kind of like having a manifold set.

.

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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

ron in charleston on Tue July 12, 2005 7:56 PM User is offlineView users profile

Thanks to all who responded.

Looks like I have lots of options. I like that idea of the Hertz meter since circuit breaker box is set up to have generator connected to it so generator will power anything I want except 220. No A/C Of course with the full power 120 volt output of 27 amps and 3400 watts I have to select what I want to use and can not use that much at the same time. But when you don't have power for a couple of weeks or more you're are more than happy having light switches that actually will make the light bulbs go on and a refrigerator and freezer that function.

I bought this generator in September of 1989 two days after Hurricane Hugo. Below is a photo I just took, with the new wheel kit I installed after making sure it's in perfect running condition and ready should the need arise.

ron in charleston on Tue July 12, 2005 10:06 PM User is offlineView users profile

My whole neighborhood has underground cable but, but after Hugo we still didn't have power for 2 1/2 weeks. I guess all the big high tension stuff is all above ground. I remember the towers that brought power from the other side of the river where gone and had to be replaced.

I remember it was real wierd to go over one of the bridges by my house 2 nights after the storm and look towards downtown Charleston and it was completely dark, you turn 360 degrees and wherever you looked it was dark, that's the way it looked in 1670 when the first settlers came here.

k5guy on Wed July 13, 2005 10:45 PM User is offline

Quote
Originally posted by: NickD

My cheap Timex wristwatch runs about 2 seconds fast per week that translates to a 2 divided by 604,800 or a 0.00033% error, plenty good enough for measuring speed. That is 3.3 ppm.

You guys are living in the dark ages timewise. GPS, oh yeah, that's the ticket. I actually bought one of these for work. It is nice to have really accurate time (within 2ms in actual use.) The one problem is that the thing thinks I'm 23 meters below sea level. LOL. This GPS device has a 1 pps output, so you can get the time within 50ns. Thats just a tad too accurate for what I need.

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Edited: Wed July 13, 2005 at 10:47 PM by k5guy

k5guy on Thu July 14, 2005 10:09 PM User is offline

You guys know I'm joking with the GPS. Actually, I like the inductive pickup idea. They sell these really cheap for use on bicycles. They are supposed to connect to a spoke of the wheel. I suppose that you could tape it to the shaft somewhere on the generator. The ones that I have for my bikes are adjustable for distance. If you know the distance of 1 rev, then its easy to get accurate rpm from that.

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