multimeter ohm reading question
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Junior User
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From: San Diego via Baton Rouge
multimeter ohm reading question
i'm kinda new to using a voltmeter to check different electrical situations (what have i been doing for 10 years of shadetreein'?), but i hav'nt really figured when to use what settings. DC and AC, i'm pretty good, i just start at highest and work down 'till appropriate. resistence, i havn't figured out. i just have a bare essential meter with ohm settings of RX1K and RX10. for example, i'm checkin' resistences through charging system, and readings between both settings are close. which do i use? thanks.
Post Fiend
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From: Central Kali
Use the one that gives a 2/3 of max meter reading. It would be easier if I could show you in person. I don't think your meter will show low resistence. Radio Shack has some cheap digital voltmeters. 
Posting Guru
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From: northern ca
if you're just checking continuity, or something in the 1000s of OHMs , like plug wires, use the Rx1K setting
the Rx10 would be for lower resistance stuff like fuel guage senders, or maybe dim lights, etc.
the Rx10 would be for lower resistance stuff like fuel guage senders, or maybe dim lights, etc.
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From: San Diego via Baton Rouge
thanks ya'll, i've been kinda leanin' toward the Rx1K reading, but jus' on a hunch.
mike the digi's must have alot of ranges, 'cus on mine it'll be like one of 'em will race to 0 (no resistence), and one will be like 0.6
mike the digi's must have alot of ranges, 'cus on mine it'll be like one of 'em will race to 0 (no resistence), and one will be like 0.6
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From: Oregon
Just get yourself a cheap digital. Like, don't spend over $20. I have 3 or 4 multimeters floating around. I use them for work and some cost well over $100, like my Fluke. The one I use the most is the small $12 one that fits perfectly in my toolbox.
Once you start playing around with it you'll get an idea of what an Ohm is. I used my analog meter to check codes before I got my reader, but for most automotive stuff, digital is the way to go.
Once you start playing around with it you'll get an idea of what an Ohm is. I used my analog meter to check codes before I got my reader, but for most automotive stuff, digital is the way to go.
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From: San Diego via Baton Rouge
thanks, i think wally world's got a digi for 20$. its no fluke, but for what i'm gonna be using it for it's plenty.
see i'm checking the field from alt. to ground and i didnt know which reading to go with. i'f i remeber correctly they were both close.also, i've noticed that readings change if you switch the leads. what's up with that?
see i'm checking the field from alt. to ground and i didnt know which reading to go with. i'f i remeber correctly they were both close.also, i've noticed that readings change if you switch the leads. what's up with that?
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Post Fiend
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From: Central Kali
The readings should not change unless you are going thru a diode. A diode will be high one way, low the other.
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From: San Diego via Baton Rouge
o.k., here's the deal. i've been fighting this charging problem the last few days. if ya'll come on here much i'm sure you've seen some of my posts (i know mikew and sparky have)
the last thing i can really figure is i blew something in the regulator during all testing and having field on grd term. of alt. i got another reg., but before i put it on, i checked the ohmage between fld. wire and ground (i had red lead on field and black on battery ground). it shows approximately 1.5 ohms on the Rx10 setting (the Rx1k showed nothing. so i know that ohmage is 1.5).
it says in my chilton that if reading is under 2.4 ohms, service grounded field circuit in wiring harness or altenator. i have all the harnesses tore open and every wire involved in clear view. my questions are:
WHAT AND WHERE IS GROUNDED FIELD CIRCUIT?
COULD I HAVE RUINED MY ALT. BY RUNNING IT A LITTLE WHILE HOOKED UP WRONG?
i don't wanna hook up new reg. until 1 get that ohm over 2.4. thanks for any help.
the last thing i can really figure is i blew something in the regulator during all testing and having field on grd term. of alt. i got another reg., but before i put it on, i checked the ohmage between fld. wire and ground (i had red lead on field and black on battery ground). it shows approximately 1.5 ohms on the Rx10 setting (the Rx1k showed nothing. so i know that ohmage is 1.5).
it says in my chilton that if reading is under 2.4 ohms, service grounded field circuit in wiring harness or altenator. i have all the harnesses tore open and every wire involved in clear view. my questions are:
WHAT AND WHERE IS GROUNDED FIELD CIRCUIT?
COULD I HAVE RUINED MY ALT. BY RUNNING IT A LITTLE WHILE HOOKED UP WRONG?
i don't wanna hook up new reg. until 1 get that ohm over 2.4. thanks for any help.
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From: The best is the U.S.
Check the field lead inch by inch for any breakdown/melting of the insulation. If you cannot find any damage then you most likely toasted your alternator field windings when you unintentionally shorted them to ground. Any time you exceed the rated current for a set of windings you run the risk of damaging the varnish/insulation coating on each individual turn which results in the damaged windings becoming shorted together and in effect removing them from the electrical circuit. Therefore the more windings you damaged the less resistance you will see on the field because alternate paths of lesser resistance have been formed by the shorted windings. 
Post Fiend
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From: Central Kali
If you short the field terminal of the alternator to ground, you will not harm the alternator.
Do this Punchy, pull the field connector off the alternator. Measure the field terminal to the alt case with the ohmmeter. If you spin the pulley by hand, the reading may bounce because you are going thru the brushes to ground. If you are above 3 ohms, you are ok.
Then repeat the test by putting the field connection back on the alt. Pull it off the regulator and check the resistence on the wire. If the wire is grounded you will see it.
Do this Punchy, pull the field connector off the alternator. Measure the field terminal to the alt case with the ohmmeter. If you spin the pulley by hand, the reading may bounce because you are going thru the brushes to ground. If you are above 3 ohms, you are ok.
Then repeat the test by putting the field connection back on the alt. Pull it off the regulator and check the resistence on the wire. If the wire is grounded you will see it.
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From: San Diego via Baton Rouge
thanks, hwford. you really think i could've screw those windings? it's crazy 'cuz tha alt. is brand new and while i had it hooked wrong, i didn't have anything on the fld terminal of alt. the only thing i had screwed up was i had the fld wire from reg. hooked to one of the ground terminals. you obviously know much more about this than me (thats why i come on here).
i checked the field wire all the way down and no problems and it shows good continuency. the only thing is the connection on end is kind of flukey. it's one of those dome shaped plastic casing, with the fitting in the middle that jus' pushes on term. someone who had the truck before me had some of the wire stripped right at the end (obviously for some kind of jump test or something) i'm sure it would be cool for me to just change that to a regular eyelet connection, and use that small nut to secure huh?
that alt. is a kragenator though and if i have to take it back, i'm gonna pay the 10-15$ extra for 70 amp. well, i'm gonna mess with it some more. i'm sure i'll be back on here soon. thanks again, this site is invaluable.
i checked the field wire all the way down and no problems and it shows good continuency. the only thing is the connection on end is kind of flukey. it's one of those dome shaped plastic casing, with the fitting in the middle that jus' pushes on term. someone who had the truck before me had some of the wire stripped right at the end (obviously for some kind of jump test or something) i'm sure it would be cool for me to just change that to a regular eyelet connection, and use that small nut to secure huh?
that alt. is a kragenator though and if i have to take it back, i'm gonna pay the 10-15$ extra for 70 amp. well, i'm gonna mess with it some more. i'm sure i'll be back on here soon. thanks again, this site is invaluable.
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From: San Diego via Baton Rouge
altenator 86'ed
i did the test you said mike (fld. term. to alt. case) and couldn't hardly spin to 2 ohms, and that was gettin' it pretty good. so iguess my alt. is no bueno. i'm gonna take it back to kragen and upgrade to 70 amp. they better not give me any crap. i wish i would have had the extra jack to go to napey in first place. i don't encourage getting certain parts (alt.,starter, etc.) from autozone. kragen is new to me 'cuz i'm from south and we had none, but i'm starting to belive that they're a close first cousin to the autoclone. but, i think i'll get another one and be alright. they put those ridiculous warranties on them so you'll buy, but whats the point if your replacing 'em once a month. i'm done ranting. thanks again everyone, and that test really sealed the deal.
Post Fiend
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From: Central Kali
Hang on a sec Punchy, the resistence won't go higher as you turn it. Sometimes the brushes will show a open circuit from dirt as you turn the pulley. Hold your meter leads together and what do you see? Maybe .3, .4 ohm. Now if you go on the alt field and get 2 ohms, it may be a little low but it is not shorted
For one other test, start the truck with the field on the alt disconnected. Take a test lead and connect it to +12. Slowly raise the rpm while watching the battery voltage. If the alt is good, the voltage will come up. Don't go too high on the rpm.
For one other test, start the truck with the field on the alt disconnected. Take a test lead and connect it to +12. Slowly raise the rpm while watching the battery voltage. If the alt is good, the voltage will come up. Don't go too high on the rpm.