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  1. #1
    meco3hp is offline Hot Rolled
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    Hello,
    I'm trying to rebuild a 1 wire Delco alternator, on my 83 1 ton Chevy and have replaced everything new, except the bridge rectifier and the stator. Does anybody know how to test these with a multi meter?

    Thanks!
    Richard

  2. #2
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    Hi Richard,

    I'm not familiar with alternators, but all rectifiers work the same way.

    To test an individual rectifier (diode), use a multimeter set on a high ohms scale. You should read zero ohms with the test leads connected one way, and very high (infinite) resistance with the leads reversed. For reliable readings the diode(s) should be completely disconnected from the circuit.

    A bridge rectifier normally has four connections, two for the AC input plus outputs labeled + and -. Using the ohmmeter set as above and measuring across the two AC terminals, you should get an infinite reading regardless of which way the leads are connected. (I just replaced a bridge yesterday which measured 0.13 ohms AC to AC. Talk about shorted )

    You can measure the four diodes inside the bridge separately as described in the first paragraph. Two diodes are connected to one AC input, and two to the other. Two are connected to the + output, and two to the - output.

    One variant you might encounter is a three-phase bridge, which has six diodes rather than four. There are three AC input terminals, with two diodes connected to each. Three diodes connect to the + output and three to the - output.

  3. #3
    mobile_bob is offline Stainless
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    on your bridge rectifier (after removal)
    you will note three posts that the stator is nutted down to.

    connect your ohm meter from each post to the little copper tab on one side and note the reading, reverse your leads and recheck, one way is very high resistance the other very low resistance, check down each side at each post
    all six positions both ways.

    if you don't get these readings replace it.

    basically the bridge is made up of 6 diodes, this is the way to test each of them.

    the stator is a bit more of a problem with an ohm meter, check it visually for burnt coils, and obvious shorts. then connect the ohm meter from one of the eyelets to the stator core for shorts.
    if shorted replace it. bare in mind that this is only a very low voltage test and the stator could still be faulty at higher voltages.

    on a delco, if the stator looks good it probably is. whereas a rectifier bridge may look like new and be bad.

    bob g

  4. #4
    mobile_bob is offline Stainless
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    Leigh mentioned the bridge being made up of 4 diodes which most bridges are comprised of, the delco uses 6 because the stator is wound as a 3 phase unit, as are most all automotive alternators.
    bob g

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    Hi Bob,

    I did mention the three-phase configuration. I seemed to remember that alternators used that configuration. I'm not an auto electrical type

  6. #6
    CharlieBiler is offline Hot Rolled
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    If you are talking about the 10SI alternator, the one with four bolts holding it together, I can help.

    The rectifier is tested by placing one end of the meter on the ground plane, the side that goes against the case. Touch the stator contact posts, one at a time, with the other lead. All should have no path, or closed path. Reverse the leads and the results should reverse. Now repeat the procedure using the power output side versus the three stator posts. The path results should reverse because the three diodes are opposite polarity from the ground side diodes.

    The stator is tested by making sure each of the three leads has contunity to the other with no resistance. Then make sure there is no short to ground by setting your meter to the 100,000. ohms and make sure there is no contunity from the leads to the frame of the stator stack. Keep your fingers out of the path or the meter will read you as a ground short, at this setting.

    You need a dynamic tester to go further, but for all practical porposes, this test is not needed to be done at your level of parts checking. I doubt someone slipped in a different draw stator while you were not looking.

    Just why would you use a one wire unit on a pickup? One wire units are for primitive systems without battery ignition. They also suck for turn on at slow speeds and cold kick in. I personally use one wire regulators in all 10SI units, but still hook up the excite and idiot light plugs. If you rebuilt the alternator; you must use the excite and idiot light functions once to excite the circuit so it can magnetize and align itself for future self turn on. Is the air gap less than 0.005 inches between the rotor and stator? If not, the thing will never self excite.

    Charlie Biler
    www.molineparts.com

  7. #7
    meco3hp is offline Hot Rolled
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    Hello,
    Thanks! I'm weak when it comes to electrics but I like to rebuild alternators any time I can with the kits from NAPA, alot cheaper that way, than buying a new alternator. But this one has me stumped. I'll get into it tommarrow and see what I can find out. The sator looks really good so I'm thinking its the bridge rectifier. I'll get'er done one way or another!

    Thanks!
    Richard

  8. #8
    meco3hp is offline Hot Rolled
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    Hello,
    Charlie, I've not heard of having to "exite" the circut to get it to work. I know the one I put on my 1961 IHC 1/2 ton didn't need that unless I missed it when the alternator guy built it for me, right infront of me. Do you have a schematic of what to hook up and where? This one wire is the first one that I've rebuilt myself. Usally I do the "regular" 3 wire alternators, but NAPA only had the single wire kits, so I said fine I'll take it. Maybe I should've held out for a "regular" kit.

    Thanks
    Richard

  9. #9
    mobile_bob is offline Stainless
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    i got distracted when i did my first post, so i made an omission (sp)

    if you lay the bridge so that the three posts are vertical to you, such that they are in a line toward you...

    each of the six diodes are connected by the little copper straps to the diodes, the other side of each diode is connected to the heat sink

    three on the right side as viewed connect to the right heat sink

    three one the left side connect to the left half of the heat sink

    using your meter, connect the black lead to the left sink and the red to each of the left diode straps, then reverse the leads, one way there is high resistance, the other low resistance,

    duplicate the procedure on the right side of the heat sink

    if you find any of the six diodes to be open(high resistance both ways) or shorted (low resistance both ways)then replace the rectifier bridge.

    the ohm meter check on the stator is usually a good enough test, you can check the winding to the stator core with a 120 volt light, but this is not for the novice. sometimes stators will light the bulb showing a defective or leaky stator winding to ground.

    most times the problem will be found to be with short brushes (worn out) or a bad regulator.

    hope this clarified the answer i posted earlier

    bob g

  10. #10
    440roadrunner is offline Hot Rolled
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    Howdy. I'm new here, but not new to alternators.

    Guys, you CANNOT reliably test diodes and stators with an ohmeter. Diodes often test OK with an ohmeter, and are really bad. If they DO test bad, they are. If they test good, maybe they're good and maybe they're bad. Most modern digital meters have a "diode test" function, and if so you should use it. Some sensitive meters have enough "leakage current" that using the ohmeter is basically unreliable.

    The stator can have shorted turns and test "OK" with an ohmeter. This means that it may charge but heatup (a few turns shorted) or be vastly degraded (many turns shorted) The same is true of rotors. I learned the hard way, once, on and old external regulator type. After having the thing apart several times, I finally swapped rotors, and away we went. What I had earlier was a 55amp or so Delco that wouldn't put out more than about 30--partly shorted rotor.

    The best way to test diodes is to get a REAL heavy load---like a 4537 landing light, or a resistive tester that you can limit to 20 amps load or so. Testing diodes with a heavy load will show up the ones that are "weak". The only place I've seen this in print is some older Motors manuals back in the AMC/Motorola section. Basically, with a heavy lamp or resistive tester, you want a good current draw through the diode one way, and none the opposite polarity. After you've "done" a few you'll see.


    Some of you mentioned "4 diodes" I didn't realize there were any alternators that were other than 3 phase, with 6 diodes.


    Looking for loose/ worn insulation (interturn vibration) and burns is a good way to see stator trouble.

    A unit that has suffered bad mechanical vibration, such as damaged belt/pulley, running with loose hardware or bad bearings is a candidate for a bad "vibrated armature"

    (I used to blow these up pretty regular on my old 70 six pack Roadrunner---the alternator turned some 20K with the engine at 6K

    On the single wire--I'm fuzzy anymore, but Iused to replace the idiot lamp circuit with a series diode to the key. On a mag ignition, you can wire it to an oil pressure switch. The second term. can be jumpered right to the bat. I don't have much experience with single wire--they were just coming out when I went on to other things.

    I was told once that some replacement regulators "act" like single wire no matter what--in other words, one lead did nothing but a dummy.


    Also, most Delcos I've seen had a little tab and slot on the rear--you should be able to "short" from the case to the tab inside to "full field" the unit and bypass the regulator. This should of course give you full tilt output.


    (Incidently, I finally ran Delcos on my 340 Dodge because I'd had it with the Chrysler units. In my opinion, Delco is among the best, and easiest to repair, on the market.)

  11. #11
    CharlieBiler is offline Hot Rolled
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    Yes it is true that you can ground the secondary brush on a 10 SI Delco to make it give full output. The little tab behind the "D" hole grounds the brush lead and causes full output. The rotor is always hot and the regulator just supplies a ground path on a 10 SI. Appling power to a the excite lead on a 10 DN gives the same results.

    I really advise against running full loads, especially reverse, through a 10SI diode. At a Delco Remy tech seminar we were shown the results. Picking bits of crap out of your face is not my idea of fun. The Delco service manual has definite warnings against trying that stuff that is done to Motorola units. Delco used six different types of diodes in the ten series. Unless you are real sure of the diode type; leave the high reverse load checking out. The CS type threw in the avalanche diodes and that gets even harier.

    There are special units to check diodes, and the rear sub assembly, and they are expensive. I have one on my bench. I did not blow a week's profit for nothing.

    10DN (external regulator) Delco can diodes are not the same animal as the button pack type SI units. The parts look similar in some cases, but mixing parts makes the day exciting. The diodes are totally different in both type and use. Type S can diodes will not normally blow while type B can diodes normally pop at similar loads. Button diodes in more modern units, and those Pontiac transition models, are even screwier.

    Just hook up the #1 lead to the battery positive post and the #2 wire to a 12volt bulb that is grounded, while the alternator is turning. This will magnetize the rotor and orient the stator. The self exciting units use residual ground to start the turn on cycle. Something must power the rotor magnetic bobbin first. After you excite the unit, you can then plug the hole and it will self excite.

    The only difference between a self excite and a regular unit is the tight rotor to stator air gap and the regulator. You can install a self excite regulator in any unit and it behaves normally. With no close air gap; the self turn on does not work and the regulator just behaves like the cheaper OEM type unit.

    A short from winding to winding is checked dynamically on a test fixture. In real life, without a high frequency tester, these kinds of shorts always show up as hot windings or pulsing output. They are easy to spot on the final spinup test.

    I agree that the old Delcos were the most reliable units ever built. When GM spun off Delco Remy; they also killed off quality alternators too. Now the Delphi units are even crappier than the competition. Delco Remy America had not built anything in years. Delco is now just a name slapped on Korean and Chinese scrap. They subbed out everything to the aftermarket suppliers for years before that. Now that most of the aftermarket is even gone, we are left with nothing.

    I hope to be suppling quality Delco Remy parts, through my buisness, soon. Getting supplies set up is getting tricky because I refuse to sell import scrap, with my name on it. Even Echlin (NAPA) has gone the route of cheapo substitution. You might as well just buy the junk because the name brand stuff is just a difference in cardboard boxes.

    Charlie Biler
    www.molineparts.com

  12. #12
    Tom1 is offline Stainless
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    I havent done this in a while, but. The diodes are a just a service part, they were $3.50 (last time I bought one). If you are going to all the trouble to take the unit off, open it up, I would matter of fact put in a new bridge and be done. Nothing worse than a week later having the "alt" lamp glow...


    One wire systems, the ones I had, just had a jumper wire from the Batt term to the Ign term. Most of the time you had to rev it to 2500 rpm to get it charging. The draw back is that the alternator stays ON and has a load on the battery. Things that werent used regular would go dead. Are we talking the same thing?

  13. #13
    440roadrunner is offline Hot Rolled
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    I'm sorry to hear that Delco has decided to "play" with diodes. The main diodes SHOULD be the very "basics" of diodes---high current, robust diodes, aka "a welder"

    I do disagree that checking them with an appropriate load should be hard on HEALTHY diodes, and if they fracture while testing, well, they weren't good, anyhow.

    I do agree that wearing safety goggles and shielding them behind a barrier might just be a good idea. I've tested hundreds, however, with no ill effects. I certainly found bad diodes this way, that tested good with an ohmeter.

    Life just ain't simple......

    I hope none of us want to return to generators, though.....

  14. #14
    CharlieBiler is offline Hot Rolled
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    A true one wire system has no other wiring, save for the charge wire coming from the power post. There is absolutely no difference to the electrical system on a one wire unit. The regulator will monitor the voltage level and keep pulsing the rotor to maintain a 14.7 volt level at the power post. Amperage output and horsepower draw are exactly the same.

    One wire systems are just a cop out for people that do not know how to wire equipment. On industrial systems we always used either an oil pressure switch, or ignition lead for the #1 exciter. The ground lead or idiot light #2 hookup should always have a resistor in parallel to the light. GM always included this on all cars. With this setup; you have the best of both worlds. The oil pressure switch setup will allow the alternator to 'soft start' and not load the engine too soon. The cut in on the alternator need not be some game in gunning up the throttle. There is always a small 'load' on an electronic system that uses diodes. The full time energized #1 systems have about three times as much standing load. Only mechanical generators have no reverse leakage.

    Diodes are not cheap. I can still order diode bridges for $3.50 or even less. The problem is that the replacement part is not worth two pennies. Ten amp diodes and injection molded plastic are not as good as what you removed. Cheap diodes also are like a leaky faucet. They let your money go down the drain. It is so much fun to see some cheapskate bitch when his battery discharges from setting for a week. He saved so much on those cheaper diodes. He forgot that the alternator must also eat gas to replace that battery power that leaked away. Heat resistant insulators and fifty amp diodes cost serious money. They are also the cheapest way out.

    I would pay gladly to get a truckload of 63 Chevy generators. They are the very best charging units ever made. The early 10 DN Delco was a drop in replacement for the generator. They even used the same regulator. I have guys willing to buy real charging systems. Most of today's crowd just forgot the simple things that Dad told them. They treat the electrical system as a black box.

    Charlie Biler
    www.molineparts.com

  15. #15
    Mike W is offline Stainless
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    I drove a truck with a 60 amp Ford alternator for several years with 3 of the 6 diodes blown open. I finally noticed it when I installed a voltmeter and noticed some funny jumps in the voltage. I opened it up and saw them. The front bearing is the same for some GM and Ford alternators.

    Years ago I had a Datsun truck with a bad alternator. The best price I could find one for was $185. I modified the brackets and put a Ford alternator on it. I like the external regulator. You can easily test to see if the problem is the regulator or the alternator.

  16. #16
    meco3hp is offline Hot Rolled
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    Charlie,
    Do you mean that I could just take the little plastic plug out that is filling the hole on a true, original, 1 wire unit and plug my other 2 wires in and it'd act like a normal 3 wire? I went and looked and the 2 terminals on my rebuilt alternator are there. Could I just plug my 2 other wires in and go?

    Thanks
    Richard

  17. #17
    CharlieBiler is offline Hot Rolled
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    Mr. meco3hp,
    You are correct. That little plastic plug is just marketing and eye candy. I normally never plug the two extra 1/4" spade terminals, unless it is for some really dense individual that can not follow instructions.

    Charlie Biler
    www.molineparts.com

  18. #18
    CharlieBiler is offline Hot Rolled
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    Mr. Mike W,
    ninety-nine percent of all the alternators, and generators use one front bearing. If you have a #6203 double sealed bearing; you have them mostly covered. The rest of the drive end bearings are just for large tractor trailers and aftermarket replacements with the oversize bearings being substituted. That would be two other bearing numbers.

    Generators used the #6203 bearing with no seal on one bearing side. A seperate seal was used and cup oilers were used to provide the lube.

    The back bearing on generators and alternators is another story...........

    Charlie Biler
    www.molineparts.com

  19. #19
    meco3hp is offline Hot Rolled
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    Charlie,
    LOL! I might just fall under that catagory!
    Thanks for the info, I think I'll just plug the 2 spaded plug back in and go with the 3 wire unit.

    Thanks
    Richard

  20. #20
    440roadrunner is offline Hot Rolled
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    Actually, the only real downside I have to Ford units is the fiddling with soldering/unsoldering diodes when servicing. To me, that alone made the difference between Delco and "all the others."

    I once had a Yamaha street bike, and THREE parts engines, ALL 4 had blown/damaged alternator rotors--and were very expensive. I belt drove a Nippo unit through a slot in the left side case

    Also, you can use the older (??-69) Chrysler one wire regulators on just about any system. On a few with "ground lead" regulating, you may have to reconfigure the brushes. The heavier (square, twice as big) Dodge truck is also a versitile unit, and there are aftermarket solid state replacements.


    Also, on Delco "conversion" units with a center tap stator, you can get 6V out of the center to run 6V gauges in a 6/12 conversion. I would NOT hook any heavy loads up to it, only the gauges, which are difficult to deal with at times.

    Also, I disagree that QUALITY diodes have appreciable reverse current. Sometimse the car's other accessories (clock, alarm) draw far more on older systems, IE mechanical clocks. I've left my old '70 Roadrunner parked ALL WINTER at times and only started it once midwinter for a "warmup" with no problems. This is with some sub zero days, too. Good diodes should leak no more than a few milliamps. Sometimes the "dirt" leakage across the top of the battery is more. this of course you can't easily measure

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