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Old 04-25-2008, 07:41 PM
Stoney Stoney is offline
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Join Date: Feb 2007
Posts: 176
Same method my co worker came up with...


Are you connected to a turkish engineer named Hussein by telepathy?
He said the EXACT same thing and showed me a method using an DM O Scope to do it.

But the problem is I don;t have time to rip it all apart and do it.

A simple test using same method as answer #1 (which I had intended to do anyway) came up with Left Fan DFM (dead as an Efing Mackerel) and Right Fan at maybe 30% of max power and also kinda intermittent. This is with 12V direct from the battery using 12 ga test leads. I figure that the feed from the Aux Fan Relay was not eniough amps to kick on the Right fan and the Left is doing nada. When I applied power it took a few seconds until the Right fan came on, the Left fan will not come on even with a little help (starter spin in correct direction of rotation).

I have a supplier who is shipping a good tested used assembly (whole shebang of fans, shroud, and all fasteners) on Monday. the price is 25% of new (he's an old College bud).

When I get the time I will tear into the dead fans and do the brushes and see what is what..

Thanks for the help and the education!
Originally Posted by stevebfl View Post
The quantitaive answer in the evaluation of a working fan, would use the technique called current ramping.

Current ramping is the plotting of the instantaneous current over time with an oscilliscope. It would be done mostly with an inductive amp probe. Using such a technique current rises as the brush enters the commutator post. It builds till it leaves the post. This happens quickly but is easily caught on a scope. This technique is usually used on fuel pump motors and a quick google of "current ramping" shows this example:

The amount of current, the uniformity, and individual sector issues can be addressed.
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