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Continuity or infinity on a starter?

Discussion in 'General Electronics Discussion' started by noquacks, Dec 15, 2013.

  1. noquacks

    noquacks

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    Jun 26, 2013
    People,

    This may be more "auto" than "electronics", but Im confident the people here really would know this stuff better than car guys- Rebuilding a starter, which did work before dismantling (wanted to put in new brushes). I put it all back together and test motor by applying 12v to the positive stud, and I get sparks, no start.

    Then, thinking there may be a short circuit, I put an ohmmeter on it- one terminal on the body(ground), and other terminal on the positive terminal. I get continuity. isnt this bad, people?? Shouldnt there be no continuity(infinity)? If so, I screwed up somewhere.....

    Thanks
     
  2. Six_Shooter

    Six_Shooter

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    Nov 16, 2012
    There should be some resistance, not one extreme or the other. It is usually measured as a low resistance, due to how the windings are made.

    What car is this for? I have some extenive experience with cars, and have had to diagnose and repair my share of starter systems.
     
  3. jpanhalt

    jpanhalt

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    4
    Nov 12, 2013
    Was the resistance really "zero" ohms, or a very low reading? If it is a one-stud starter, designed to take 100 to 200 A, at 12V, then the resistance will be <0.1 Ω.

    Did you seat the new brushes properly? And of course, there is always the possibility that you messed up something. Pictures of the brushes and commutator might help, but I am not optimistic.

    How bad was the sparking? Did you try to turn the armature shaft to see if it could be started?

    John
     
  4. flippineck

    flippineck

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    Sep 8, 2013
    Bear in mind that some starters have an integral solenoid - in this case if the integral solenoid isn't energised, the resistance between the big fat power terminal and the case of the starter, should be very high?

    If it doesn't contain a solenoid, some continuity isn't bad, you've got a path like carbon brush - commutator - fairly heavy winding - commutator - brush. As per what Six_Shooter said.
     
    Last edited: Dec 15, 2013
  5. noquacks

    noquacks

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    Jun 26, 2013
    you guys respond so fast! Wow- thanks! Will get the exact ohms in a few minutes- gotta go in garage........other answers will follow too.....
     
  6. noquacks

    noquacks

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    Jun 26, 2013
    0.4 ohms. Its from an alfa romeo spider 1987, Bosch. Seated the brushes by just popping them on the commutator. What else should one do to pop on brushes?

    sparked a tiny bit, but was afraid to hold it on there- saw some smoke.
     
  7. duke37

    duke37

    5,191
    704
    Jan 9, 2011
    The starter will take a very large current. You will need a big battery and fat cables to feed it.
    It will take off like a scalded cat and spin off the bench unless you tie it down.

    A headlight bulb in series with the starter can be used to see if it is taking current and probably indicate whether there is some torque there.
    Can you measure brush voltages when assembled?
     
  8. mursal

    mursal

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    Dec 13, 2013
    If you look at the wires coming from the positive brushes (2) to double check they aren't touching the body of the starter (short). I think some of those Bosch starters have a screw holding the brush wire on the terminal, so its easy when tightening to pull the eyelet round until it hits the body.
    No sparks around the top of the battery, so do your last connection away from the battery.
     
  9. noquacks

    noquacks

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    Jun 26, 2013
    thnaks, duke. how could one measure v from brushes? By touching probe to braided copper wire exiting the case and other touching ground? Brushed are now burried inside case, of course, cant access them directly. dont have bulb set-up.......
     
  10. noquacks

    noquacks

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    Jun 26, 2013
    good tip- I will double check about that eyelet contact. But I suspect it is not the issue, as I actually put back the original chewed up brushes just to see, and same problem. (remember- BEFORE I dismantled all to rebuild, the starter did start- no problem, no short, no spark)
     
  11. flippineck

    flippineck

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    Sep 8, 2013
    aye good advice - lead acid batteries are capable of producing a mixture of gaseous hydrogen and oxygen inside the tops of the cells, a nearby spark can turn the battery into a bomb that throws fairly strong sulphuric acid over everything nearby
     
  12. jcurrie

    jcurrie

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    Feb 22, 2011
    if the starter was working before you started i will ask did you replace the brushes with factory brushes or generic set some brushes requier a islotar of some kind , if its correct you will get sparks by hooking up the stud on starter and body as break away amps can be up to 500 amps on small startes most of the time though it will be under350 amps.also on reassembly did you hold brushes back or just slide armeture back in , if the later is the case you could be shorted to ground . what is the amp draw when you hook up leads ?


    jcurrie
     
  13. noquacks

    noquacks

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    Jun 26, 2013
    Thanks, j. They are generics, I believe, but specs are to OEM, (Ive been told). They do state they are for that model Bosch starter. Now,

    1) can one short an armature while putting on brushed "sloppily", by bumping into the side of the case, etc? If so, I think we're onto something. I put on brushes with armature inside case, and pushed down around the brush "holder' until all 4 brushes slid down. Man, that was so clumsy/awkward/distasteful. Maybe I did something there.

    2) Puzzling- how can one short out an armature without voltage/current, by just "touching" the brush assembly/holder to the grounded case?

    3) Bigger question- I went through the following steps to test armature (1-6), and tests all passed!:
    http://www.ehow.com/how_8197179_test-dc-armature.html

    So, if the test methods above link passed, how could we be dealing with a shorted armature? man, Im comfused......Pls help.
     
  14. jcurrie

    jcurrie

    128
    1
    Feb 22, 2011
    never worked with bosch starters but from what i know about starters mostly MT25 and larger that it wouldent short out the armature but you can cause the brush holder to short out to the case i have used a growler in the past to test armatures but havent seen one for years. another question i'll ask can you rotate the armature in the case, it is possable to push a armature in too far on some starters causing the commuintar to short to he case don't know if that would be the case here though.

    jcurrie

    ps if you did have a shorted armature you would smell it i'm shure
     
  15. noquacks

    noquacks

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    Jun 26, 2013
    Yes, j, it does turn pretty easily with fingers. One way, of course. I thought of that- it turns.
     
  16. noquacks

    noquacks

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    Jun 26, 2013
    No smell. But, how can the brush holder short out to the case? Just by "bumping" it to the case, without any current being applied?? Man, I need some learning.......

    If so, Im cooked for good, and will dump the whole apparatus.
     
  17. jcurrie

    jcurrie

    128
    1
    Feb 22, 2011
    found a vido on utube just goggle bosch starter repair that takes you through repairing a bosch starter after looking at it never seen one but it has some good points that may help you
     
  18. noquacks

    noquacks

    44
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    Jun 26, 2013
    I'l look at it- thanks man. You guys tried very hard to help me- I appreciate it big time. I will always come back here.
     
  19. noquacks

    noquacks

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    Jun 26, 2013
    It works. Sheesh- mech I know brought me to his buddy, a starter shop, and at first they were puzzled, as they tested the armature, and all was well but still, shorted out. So, they dismantled it again, blew out some faint dust, and BOOM- starter starts!!

    Man, I was sooooo close. Now we know. Thought Id share with yous. Thanks!!
     
  20. jcurrie

    jcurrie

    128
    1
    Feb 22, 2011
    aha dirt is a bad thing , reminds me of some years ago i worked at a motor rebuild shop this copmpay brought in three large motors that they just had rebuilt by a fly by night place upon dissambley it was found that the coummantors had been turned to true them up but the edges of the coms werent rounded slightly and as soon as the motors went in service the sparks started to fly because the sharp edges of the com filled the gabs with brush material shotring out the sections. some times its the simple things that get overlooked
     
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