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sacrileger

Proven Member
288
43
Jun 26, 2016
Orillia, ON_Canada
I am refurbishing my old alternator which most likely failed due to worn out brushes; however, just to make sure, i am testing all the inner components: the rotor, stator and rectifier. Testing the stator and rotor was pretty straight forward but i found testing the md133171 rectifier challenging.

I watched a bunch of vids on how to test alternator components and i found the vid below to be the most comprehensive and concise:
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as can be seen in the vid above, the rectifier which the dude is testing is not constructed in the same way as the md133171 rectifier:
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while i eventually did get all the correct values i was supposed to after a few trials and errors, i'd like to be certain that i tested this rectifier correctly and wanted to ask if anybody here would have a link to resources, such as vids or step-by-step procedure, showing how to test this particular (md133171) rectifier... as well as the ones which are coded as follows:
MD133171
MD136839
MD136838
MD133513
MD169683
MD169683D
MD158495
 
Hmm, what was the problem with testing the rectifier exactly? I've never had one apart but I'd like to try to refurb one of my old alternators some time. Was it hard to get at some of the connections with a probe or something?
When he tested the rectifier In the video, all he did was check to make sure that the "jump-over" voltage of each diode was in the correct range, and the jump-over voltage (forward voltage drop I guess) of a diode always seems to be in the range 0.5 to 0.6 volts or thereabouts. So I wouldn't think you would need any particular value beyond that.

For example, when I tested my "alternator relay" which is actually a diode, I got 0.575 volts in one direction and "OL" in the other direction. So I knew it was ok. That was with a Fluke multimeter like the guy in the video is using.
Is there something else in the rectifier besides diodes that needs to be tested?
 
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Hmm, what was the problem with testing the rectifier exactly? I've never had one apart but I'd like to try to refurb one of my old alternators some time. Was it hard to get at some of the connections with a probe or something?
When he tested the rectifier In the video, all he did was check to make sure that the "jump-over" voltage of each diode was in the correct range, and the jump-over voltage (forward voltage drop I guess) of a diode always seems to be in the range 0.5 to 0.6 volts or thereabouts. So I wouldn't think you would need any particular value beyond that.

For example, when I tested my "alternator relay" which is actually a diode, I got 0.575 volts in one direction and "OL" in the other direction. So I knew it was ok. That was with a Fluke multimeter like the guy in the video is using.
Is there something else in the rectifier besides diodes that needs to be tested?
alternators are super easy to refurbish. there's really not much to fail on the inside other than brushes and rectifier.

as far as testing this particular rectifier, the dude has 6 diodes... three on each side of the plate. i only "found" 3 and i am certain i have 6 as well. i fiddled around testing what i could find and did get 3 values b/w 0.5-0.6V as well as bunch of other values. i cruised thru quite a few vids to find a similar rectifier construction as the md133171 so i could see how to properly test it and not be guessing around. my main suspicion is that the rectifier has to be desoldered completely to test it properly but i just want to make sure that's the way it's done for this particular type of rectifier.
 
alternators are super easy to refurbish. there's really not much to fail on the inside other than brushes and rectifier.

as far as testing this particular rectifier, the dude has 6 diodes... three on each side of the plate. i only "found" 3 and i am certain i have 6 as well. i fiddled around testing what i could find and did get 3 values b/w 0.5-0.6V as well as bunch of other values. i cruised thru quite a few vids to find a similar rectifier construction as the md133171 so i could see how to properly test it and not be guessing around. my main suspicion is that the rectifier has to be desoldered completely to test it properly but i just want to make sure that's the way it's done for this particular type of rectifier.

Yeah, in the 1991 FSM it's a little confusing to me, about "6" or "3". The alternator schematic shows 6 power diodes and 3 exciter diodes just like the one in the video. But then in the step by step rectifier check, their step 3 says "Check 3 diodes for continuity ........".
These screen shots below are the only step by step I can find in the FSM for testing the rectifier.

When you had yours apart, could you see any identification markings on the diodes? Or, do you know what their current rating would be if you bought the same exact diodes per piece from some place like Digi-Key? I'm getting a little interested in the idea of building an external regulator from scratch using diodes that have 2 or 3 times the current rating of the ones in the alternator. Can you think of any reason why it would be hard to build and use an external regulator?


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Yeah, in the 1991 FSM it's a little confusing to me, about "6" or "3". The alternator schematic shows 6 power diodes and 3 exciter diodes just like the one in the video. But then in the step by step rectifier check, their step 3 says "Check 3 diodes for continuity ........".
These screen shots below are the only step by step I can find in the FSM for testing the rectifier.

When you had yours apart, could you see any identification markings on the diodes? Or, do you know what their current rating would be if you bought the same exact diodes per piece from some place like Digi-Key? I'm getting a little interested in the idea of building an external regulator from scratch using diodes that have 2 or 3 times the current rating of the ones in the alternator. Can you think of any reason why it would be hard to build and use an external regulator?


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i consulted the el. manual on how to test rectifier first and found it confusing, i.e the positive and negative rectifier test while not being clear which side was +ve and which one was -ve. i had to go to external sources:

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i have my rectifier on the bench but unfortunately my 25w soldering iron is not clocked high enough to desolder the hard silver solders to take the rectifier apart. needless to say, my rectifier has 6 diodes, 3 on each side of the heat sink. the pairs of +/- diodes are soldered together forming 3 points of contact. i have seen mitsu rectifiers for 3 phase alternators with 8 diodes, such as in the pic above where you can see 4 pairs of diodes but only 3 pairs of diodes connected to the stator with one pair of diodes sitting there idle.

the way i tested my rectifier was to connect -ve multimeter probe to the rectifier terminal leading to battery and checked each pair of diodes with the +ve multimeter probe... and then i repeated the test by reversing/swapping the probes for total of 6 readings.

after that i connect -ve multimeter probe to the rectifier terminal leading to ground and checked each pair of diodes with the +ve multimeter probe... and then i repeated the test by reversing/swapping the probes for total of 6 readings.

... so in total i am looking at 12 readings: 6 readings with voltage b/w 0.5-0.6v and 6 zero volts readings. looking at the values, i am presuming that this rectifier is fine; however, i'd like to be certain that is the case by double checking with a procedure which confirms my findings.

i have no reason to think why having an external rectifier/voltage regulator is not a better solution than built-in rectifier. i guess it's a trade off between utility and convenience and we could argue the merits of each solution till cows come home. anyway, i'd prefer my rectifier to be a separate external unit if i had a choice.

my diodes are rated 30A/200V.. see pics:

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here's the link where this^ info came from:
 
That web page is pretty awesome!
One of the rebuild parts they show for the alternator is, they call it, "Voltage Regulator (f)or Mitsubishi S-L Terminal ......" and it's $15.99.
It says "14.5 Voltage Set Point".
Is that actually the voltage regulator or is that just a terminal block?
Do those things quite often burn out?
If that thing is actually the voltage regulator, and if it is all tied up with the slip rings, it would have to stay in the alternator as designed, I would think.
What do you think about that?
Do you know what is actually in that thing?
 
One of the rebuild parts they show for the alternator is, they call it, "Voltage Regulator (f)or Mitsubishi S-L Terminal ......" and it's $15.99.
It says "14.5 Voltage Set Point".
Is that actually the voltage regulator or is that just a terminal block?
Yes that's the regulator for 1g alternator and the biggest reason why people have kept replacing their reman alternator so often. Low quality cheap regulator and poor soldering often cause the no charge issue. Me too, long time ago I used to replace the alternator from local auto parts store very very often and many times. I was so sick of it, but I completely stopped replacing my alternator after I replaced the regulator with OEM and reinforced the soldering point (where the green circle is).
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Yes that's the regulator for 1g alternator and the biggest reason why people have kept replacing their reman alternator so often. Low quality cheap regulator and poor soldering often cause the no charge issue. Me too, long time ago I used to replace the alternator from local auto parts store very very often and many times. I was so sick of it, but I completely stopped replacing my alternator after I replaced the regulator with OEM and reinforced the soldering point (where the green circle is).

Oh man. So I looked for this part on MitsubishiPartsNow which is an actual Mitsu dealer and they say "no results" for my search of A866X09071. The regulator they do show for 1987-1994 Mitsubishi including our cars is MD611565 and they list it for $165.
No wonder rebuilders use a cheapo part here!
Amayama is worse. They say "permanently out of stock" for A866X09071 and they say "this part is out of production" for MD611565.

If the aftermarket versions of this regulator are more to blame for our alternator failures than the diodes, then I don't see much advantage to beefing up the diodes. Is that what your thought would be?
 
Oh man. So I looked for this part on MitsubishiPartsNow which is an actual Mitsu dealer and they say "no results" for my search of A866X09071. The regulator they do show for 1987-1994 Mitsubishi including our cars is MD611565 and they list it for $165.
No wonder rebuilders use a cheapo part here!
Amayama is worse. They say "permanently out of stock" for A866X09071 and they say "this part is out of production" for MD611565.

If the aftermarket versions of this regulator are more to blame for our alternator failures than the diodes, then I don't see much advantage to beefing up the diodes. Is that what your thought would be?
If you would need one in the future, should try the one in the link below. This one worked really well for me.
 
Is that actually the voltage regulator or is that just a terminal block?
Do those things quite often burn out?
If that thing is actually the voltage regulator, and if it is all tied up with the slip rings, it would have to stay in the alternator as designed, I would think.
What do you think about that?
Do you know what is actually in that thing?
it's a voltage regulator and you would know if it's failing by either overcharging your battery (most cases) or 'no charge' (less likely).
from reading about alternators, it appears that voltage regulators are least likely to fail... brushes or diodes are likely to go before voltage regulators. computer power supply has voltage regulators. my career is in the IT sector, i have been working with computers all my life, i have seen fail many computer parts but i have yet to see voltage regulator fail. i mean, voltage regulators are no longer electromagnetic relays, they are simple integrated circuits (resistor and diode) which act as gateways.

furthermore, when i looked for specs, pretty much most of industrial applications had external voltage regulators and diodes/rectifier. unless i am missing some critical fact, i still see no reason why voltage regulator/rectifier could not be external for automotive applications.

Oh man. So I looked for this part on MitsubishiPartsNow which is an actual Mitsu dealer and they say "no results" for my search of A866X09071. The regulator they do show for 1987-1994 Mitsubishi including our cars is MD611565 and they list it for $165.
No wonder rebuilders use a cheapo part here!
Amayama is worse. They say "permanently out of stock" for A866X09071 and they say "this part is out of production" for MD611565.

If the aftermarket versions of this regulator are more to blame for our alternator failures than the diodes, then I don't see much advantage to beefing up the diodes. Is that what your thought would be?
i would not think that the higher price means better quality. i think it's all marketing shenanigans. i am not convinced that voltage regulators fail more often than diodes since voltage regulators are a combo of resistors and diodes. i still like your idea of building external rectifier/regulator. imagine the convenience of replacing rectifiers/regulators some place close to the harness fuse box as opposed to replacing/refurbishing entire alternator every couple years. moreover, imagine you would buy some cheapo rectifier for $10 and replace it every year... it would take 16 years before you'd be out of $165 for one voltage regulator from 'mitsupartsnow'.
 
In the 1970's and 80's, we would just replace the diode trio, rectifier bridge and brushes and 99% of the time the unit was as good or better than new. Very simple and easy to do. Most of the time, the brushes were just wore down to nubs but we would always replace all 3 parts. Thats been a minute........
 
Yes that's the regulator for 1g alternator and the biggest reason why people have kept replacing their reman alternator so often.
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i am speculating here ...i wonder if the reason for failing regulators in 4g63 applications is the actual location of the alternator in 4g63 setups rather than the regulator itself... the electronics in the alternator are exposed to high temperatures around the exhaust manifold and turbo. moreover, when there's gasket leaks or one has the car oil sprayed for winter or when one needs to unhook the power steering pump, all these liquids are getting into the alternator and will shorten the lifespan of the alternator (ask me how i know).

In the 1970's and 80's, we would just replace the diode trio, rectifier bridge and brushes and 99% of the time the unit was as good or better than new. Very simple and easy to do. Most of the time, the brushes were just wore down to nubs but we would always replace all 3 parts. Thats been a minute........
yes, exactly... i have 3 alternators (2 were seized) which i just busted open and it appears that in all three cases the brushes are suspect... for some reason, in all my cases, one brush is worn down to nothing while the second brushes have still tons of meat on it.
 
i am speculating here ...i wonder if the reason for failing regulators in 4g63 applications is the actual location of the alternator in 4g63 setups rather than the regulator itself... the electronics in the alternator are exposed to high temperatures around the exhaust manifold and turbo. moreover, when there's gasket leaks or one has the car oil sprayed for winter or when one needs to unhook the power steering pump, all these liquids are getting into the alternator and will shorten the lifespan of the alternator (ask me how i know).
The most common alternator's issue on 1g is no charging. Overcharging would happen but much less likely. Most of people who are struggling with replacing reman alternators very often is because the heat, vibration and oil/fluid leak would kill the low quality regulator and soldering easily and having no-charging issue again and again. Many reman alternators often die even in a few days, at the worst in a few hours. One of the most common symptoms on 1g would be like it's charging well while the engine is cold and stops or less charging when it gets hot. Getting less charging and then finally stops charging even at cold start. To avoid this issue, you should have a good quality regulator w/ good soldering (or replace with the OEM alternator). Relocating the alternator is beneficial.
 
I would agree that the main cause for failure is heat and/or fluids in the body of the alternator.
 
Most of people who are struggling with replacing reman alternators very often is because the heat, vibration and oil/fluid leak would kill the low quality regulator and soldering easily and having no-charging issue again and again.

given that the main cause for alternator failures in 1g cars is heat and fluids getting into the alternator and compromising the electronics inside, the idea of external rectifier/regulator, as proposed by @We're on Boost in one of his posts above, is a pretty good idea. there actually are/were businesses which sell that type of solution, i.e. Leece Neville and their external 1111CA rectifier, or these guys here :

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i am not suggesting that this^ solution is viable for us but how difficult could it be to build one like the one above but simpler ???
 
I would agree that the main cause for failure is heat and/or fluids in the body of the alternator.

I'm hoping that my nice alternator heat shield will give me a long alternator life span.
https://www.dsmtuners.com/threads/pics-of-my-alternator-heat-shield.521305/
But at my age these roadside emergencies are not fun anymore! So I'm still thinking about this stuff and glad to be learning a lot from this thread.




given that the main cause for alternator failures in 1g cars is heat and fluids getting into the alternator ....

That regulator is awesome! I see another model that looks simpler and is almost $100 cheaper. I guess I should find the install manual for these things and try to figure some things out from it.
https://hdpsi.com/products/10-401-1...05406&pr_ref_pid=6570693951550&pr_seq=uniform



These regulators in our alternators, is the current going through them only the small current that goes through the slip rings to energize the rotor coil? I mean, it's not the entire 60 amps or whatever that comes from the stator, is it? The rectifier diodes would have that entire ~60 amps going through them, but the regulator would not. Right?
 
Just a 12v signal source to excite it. It usually goes thru a light bulb then to the alternator to excite the coils so not much.

Guys, IDK if it is a cure but it sure does help on my car. I put a flat square of Mr Gasket (Now Cometic) exhaust gasket material between the back of my alternator and my down pipe. It blocks heat transfer and seems to work, it just doesn't look nice. Not easy to see and I don't like it, but its necessary. It is the "make your own" gasket package, about 12x12 and I painted it with high heat black so it's not so noticeable.
Just some things I am doing. :thumb:
It also blocks heat to the oil filter as a bonus but I have to remove it everytime I change oil.
 
I'm hoping that my nice alternator heat shield will give me a long alternator life span.
https://www.dsmtuners.com/threads/pics-of-my-alternator-heat-shield.521305/
But at my age these roadside emergencies are not fun anymore! So I'm still thinking about this stuff and glad to be learning a lot from this thread.






That regulator is awesome! I see another model that looks simpler and is almost $100 cheaper. I guess I should find the install manual for these things and try to figure some things out from it.
https://hdpsi.com/products/10-401-1...05406&pr_ref_pid=6570693951550&pr_seq=uniform



These regulators in our alternators, is the current going through them only the small current that goes through the slip rings to energize the rotor coil? I mean, it's not the entire 60 amps or whatever that comes from the stator, is it? The rectifier diodes would have that entire ~60 amps going through them, but the regulator would not. Right?
that's a very ingenious heat shield you put on the alternator!!

have you tried to check the actual temperature with and without the heat shield on? if yes, what was the delta? i am asking because i would think that the direct heat radiation from the exhaust manifold may not be as critical as the ambient temperature. the alternator has its own fan which draws the air in to cool parts inside the alternator and then forces the air out. the armature can withstand tons of heat but the electronics not so much... and for that reason i like your idea with external rectifier.

i have had good experience with using weather station for checking temp in the various places of the engine bay while driving. i ran the weather station wired probe thru the firewall into the engine bay and then read the changing temp in real time in the cockpit.
 
have you tried to check the actual temperature with and without the heat shield on? if yes, what was the delta?

No I haven't tried to do that!
i am asking because i would think that the direct heat radiation from the exhaust manifold may not be as critical as the ambient temperature.

I don't know which is worse, but I definitely wanted to kill the IR because that is coming at a much higher temperature, hundreds of degrees higher than the air temp near the alternator.
I also shaped the shield to angle the airflow towards the alternator. The airflow is moving aft quite strongly right there because I have a cooling fan on the radiator right in front of the alternator, kind of where the stock AC fan would be.
The shield is shaped to shove that aft moving air outboard towards the alternator. I don't think I mentioned that in the thread. But I spent many hours with the paper mockups to get that shape right the first time when it came time to make it out of aluminum.

BTW I added a post to that thread to show the reflectance of metals graph that I found at the time which helped me settle on aluminum as the material.

i have had good experience with using weather station for checking temp in the various places of the engine bay while driving. i ran the weather station wired probe thru the firewall into the engine bay and then read the changing temp in real time in the cockpit.

That's good to know. I've been thinking about using temp probes more. Partly because when I try to check something with my infrared temp gun, it reads shiny metals way low. So for instance my aluminum radiator, I can't just shoot a temp from the shiny aluminum tank on the top of it. The gun reads low, I'm pretty sure. If the aluminum is very corroded and dirty (like it is on my Jeep) or maybe if it's painted, then the gun reading seems ok.
 
No I haven't tried to do that!


I don't know which is worse, but I definitely wanted to kill the IR because that is coming at a much higher temperature, hundreds of degrees higher than the air temp near the alternator.
I also shaped the shield to angle the airflow towards the alternator. The airflow is moving aft quite strongly right there because I have a cooling fan on the radiator right in front of the alternator, kind of where the stock AC fan would be.
The shield is shaped to shove that aft moving air outboard towards the alternator. I don't think I mentioned that in the thread. But I spent many hours with the paper mockups to get that shape right the first time when it came time to make it out of aluminum.

BTW I added a post to that thread to show the reflectance of metals graph that I found at the time which helped me settle on aluminum as the material.



That's good to know. I've been thinking about using temp probes more. Partly because when I try to check something with my infrared temp gun, it reads shiny metals way low. So for instance my aluminum radiator, I can't just shoot a temp from the shiny aluminum tank on the top of it. The gun reads low, I'm pretty sure. If the aluminum is very corroded and dirty (like it is on my Jeep) or maybe if it's painted, then the gun reading seems ok.
would you be able to guesstimate what temps you're dealing with in your particular application? i'm asking bc the claim is that diodes start dying around 325F:

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i guess your reasoning was that since the front of the alternator is facing the strut tower and inhaling air which is cooler, you wanted to protect the back of the alternator with heat shield behind which all the electronics are mounted on the heat sink which is protruding from the housing? it would be very interesting to know how much heat you had eliminated with your heat shield.

? have you seen this thread yet:
 
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I don't have any kind of guess about how much temperature difference the shield makes.
My thought basically was, given radiation, convection, and conduction, the one I could really do something about is radiation. So that was the main idea, although I hoped it would be a little better for convection too.
And it's the back end of the alternator that gets most of the radiation, so it should help out those electronic components to block the radiation.

That thread and the clip about emergency vehicles is interesting. I'm going to keep the idea of external rectifier and external regulator in my "stack" for possible project someday!
 
Yeah, in the 1991 FSM it's a little confusing to me, about "6" or "3". The alternator schematic shows 6 power diodes and 3 exciter diodes just like the one in the video. But then in the step by step rectifier check, their step 3 says "Check 3 diodes for continuity ........".
These screen shots below are the only step by step I can find in the FSM for testing the rectifier.

When you had yours apart, could you see any identification markings on the diodes? Or, do you know what their current rating would be if you bought the same exact diodes per piece from some place like Digi-Key? I'm getting a little interested in the idea of building an external regulator from scratch using diodes that have 2 or 3 times the current rating of the ones in the alternator. Can you think of any reason why it would be hard to build and use an external regulator?


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the interesting thing is that the FSM shows how to test the original mitsu rectifier which has three terminals yet when i just opened my old original mitsubishi alternator while i was scavenging for useful parts to refurbish the alternator in question, what i found inside was a rectifier with four terminals (see below). i still have to read on how it works with these stators which are wired for four phases but i just thought it was interesting what one may find inside these units.

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i found inside was a rectifier with four terminals (see below). i still have to read on how it works with these stators which are wired for four phases but i just thought it was interesting what one may find inside these units.

I would find that really confusing because I thought all these things would be 3-phase like the guy showed in the video, with 3 large gauge wires coming from the stator windings.

I see the 4 wires in your picture that look like they are coming from the stator. They look funny though. Each one looks like a twisted pair. What's with that?
 
I wonder if this is a difference between the anemic 65A or barely useful 75A from the US cars and the 90A alternators the Canadian Turbo cars received.

Perhaps the 90A has an extra phase to increase the current?
 
I would find that really confusing because I thought all these things would be 3-phase like the guy showed in the video, with 3 large gauge wires coming from the stator windings.

I see the 4 wires in your picture that look like they are coming from the stator. They look funny though. Each one looks like a twisted pair. What's with that?
i was going to speculate if perhaps the extra (4th) phase is the difference b/w various alternator amp outputs and it would appear that @steve in the post above is also entertaining the same theory. i have not read up on it yet and i do not know how it actually works but when i looked for voltage regulators i noticed that vendors sell low and high amp alternators at various prices. i wondered what the difference was and how one would know which alternator he has as the rating is nowhere to be found on any of the alternators i collected (4) over the years plus two currently installed alternators.

i have opened all 4 alternators and all 4 alternators have rectifiers with 4 terminals and stators with 4 'phases'; however, only 2 alternators were wired to all four phases and the other 2 alternators had the forth phase on the stator insulated and not hooked up to the rectifier terminal. i have no explanation and wondered what would happen if i hooked up the 4th phase to the rectifier. i have not done it yet but i am thinking about it and will have to figure out how to bench test it once i get it going.
 
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