fv1609 Posted June 23, 2011 Share Posted June 23, 2011 Is your multimeter digital or analogue? first multimeter giving resistance across probes as 25 across the terminals on a new alternator Sorry I don't understand where you are measuring i am getting nothing as in the two probes are not connected. Sorry I don't understand what you mean I am in the process of expanding & clarifying the generator tests for a new version of ACU4. The basis of these tests were from Field & Base Repair EMERs. The impression it gives is that the diodes can tested individually as it describes tests that appear to subject individual diodes in turn to scrutiny. The problem is that the stator windings are very low resistance in the order of 0.05 ohms this in effect joins the cathodes of all three low power diodes putting them in parallel with each other. So when you do tests to P, T & R you are just testing 3 parallel diodes & should get identical readings. A failure in one will give the impression of failure in them all. By moving between P,T & R you are testing the continuity of each of the 3 main stator windings & at the same time repeating the tests on the paralleled diodes. Despite what ACU4 says the only way of testing an individual diode of any of the 9 is to remove the section of the generator that houses the diodes & the large connector. Then unsolder the soldered terminal of one diode at a time. You will also need to remove the end cover plate so that when you assemble it again the carbon brushes can be aligned into place. So I'm sorry it is not as easy as EMERs & ACU4 first indicated. I have spent 8 hours so far on the new version, but a long way to go yet. The points you raise are not a nuisance but help in fashioning improvements. In fact all of ACU articles have been in response to trying to help people & the queries arising help focus my mind:) Quote Link to comment Share on other sites More sharing options...
emmetgilgunn Posted June 23, 2011 Author Share Posted June 23, 2011 thanks for the reply ill elaborate. the first point was that i was checking the resistance of my leads before i started to try and rule out multimeter (digital) problems. the reading i got by touching the two probes +ive and -ive was around 25 oam so the meter reads low reistance. now what happens specificly when i test the (supposed recond) genny on my bench is that when i do the tests that should result in low resistance -ive W + ive X i get a infinite reading (as if they are not connected) at all settings on my mutimeter up to 2000K ohms when i do the tests that should read a high reading ie +ive W -iveX i get the expected high readings im getting a headace Quote Link to comment Share on other sites More sharing options...
fv1609 Posted June 23, 2011 Share Posted June 23, 2011 That's the problem with digital meters is that there is no way of off-setting the resistance in the leads & prods. At least with an analogue meter you can adjust it to zero ohms with the prods connected. The other problem is that it can just display gibberish when you are not measuring anything! But in these generator test the overwhelming problem is that the ohms range on a digital meter is useless for testing diodes & it will give very high readings. A silicon diode needs to be forward biased with about 0.7 volts before it will conduct & demonstrate the properties of a diode. An analogue meter will bias it sufficiently to test it but I'm afraid digitals are a waste of time for these sort of tests. Quote Link to comment Share on other sites More sharing options...
emmetgilgunn Posted June 23, 2011 Author Share Posted June 23, 2011 sorry if i am thick i understand the high reistance readings being off the scale but the low reisitance ones i cant figure out why am i getting a 0______ as i do when they are not connected? Do you think i am right in saying this genny is not working? should i put it into my truck and see? Quote Link to comment Share on other sites More sharing options...
fv1609 Posted June 23, 2011 Share Posted June 23, 2011 Before you do anything drastic to yourself(!) or the generator, I would abandon the multimeter & get an analogue meter. Even a new £5-£10 will be quite adequate. Maplin & others have these budget meters. Quote Link to comment Share on other sites More sharing options...
emmetgilgunn Posted June 23, 2011 Author Share Posted June 23, 2011 thanks for the clear advice. i think ill leave this as experence has taught me again and again if you are getting annoyed leave it Quote Link to comment Share on other sites More sharing options...
fv1609 Posted June 23, 2011 Share Posted June 23, 2011 thanks for the clear advice.i think ill leave this as experence has taught me again and again if you are getting annoyed leave it I often find that if at first you don't succeed give up! Then come back to it the next day when there is less adrenaline flowing & you have had a chance to reflect on things. Very often when I am waking up I can see my way round problems that were such a challenge the day before. I would ditch that that digital meter. I even have an expensive militarised Fluke digital meter & despite all the fancy features I rarely use it because it is such a pain. I prefer an Avo 8 & 12. But this is perfectly adequate for most tests & is unambiguous in performance. http://www.maplin.co.uk/general-purpose-analoguemultimeter-25414 Quote Link to comment Share on other sites More sharing options...
emmetgilgunn Posted July 1, 2011 Author Share Posted July 1, 2011 sorry relised i was very rude in my lack of closier to this problem. long story short i got hold of a new multimeter and all was well as it turned out. olive is running fine again Quote Link to comment Share on other sites More sharing options...
fv1609 Posted July 1, 2011 Share Posted July 1, 2011 Excellent news Quote Link to comment Share on other sites More sharing options...
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