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Crawlers, Dozers, Loaders & Backhoes Discussion Forum

testing ammeter

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135 Fan

07-26-2007 22:36:47




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Is there a simple way to test an ammeter? Bob/Ont said current goes through the ammeter to charge the battery. It is on a 931B Cat and the ammeter used to work fine and now doesn't and I need to boost the machine everytime I start it. I took the ammeter out and was just wondering if it can be tested easily. Also what else would cause the ammeter to stop working? It hasn't worked for a little while but I didn't have to boost the machine all the time either. Now I do. Could the reset switch on the dash be bad? Any thoughts? Thanks. Dave

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AJK

07-27-2007 14:04:55




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 Re: testing ammeter in reply to 135 Fan, 07-26-2007 22:36:47  
The most likely reason that the ammeter is not working is because the machine is not charging,test the voltage between the positive cable and ground,note the reading,start the engine,increase the engine speed and check the reading again,if the alternator is charging the voltage will be considerable higher, to test the ammeter go to the link where I put a crude sketch.
AJ

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Bob Plumadore

07-27-2007 08:28:03




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 Re: testing ammeter in reply to 135 Fan, 07-26-2007 22:36:47  
if it is an alternator aquick check ofthat is to take a small wrench nd hold near the rear near the center, if it is putting out it will attract the wrench. does your ammeter show discharge when you are using the starter? it should



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135 Fan

07-27-2007 09:11:30




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 Re: testing ammeter in reply to Bob Plumadore, 07-27-2007 08:28:03  
I will try that test on the alternator. I'm not positive but I don't think the ammeter showed discharge when starting although I wasn't really looking at it. Before when everything worked, the ammeter would show a fairly high charge rate for several seconds after starting and then show just a low rate of charge. Now the ammeter shows nothing. Dave



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RAB

07-27-2007 00:11:14




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 Re: testing ammeter in reply to 135 Fan, 07-26-2007 22:36:47  
Your symptoms lead me towards thinking your charge circuit is at fault. I would think, therefore, that checking the output from the generator would be the place to start. It may be dead or dying. If you must check the ammeter, just use Ohm's Law to find a resistance suitable to deflect it sufficiently, but not excessively, and connect them in series across a suitable battery.
Regards, RAB



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