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sacrileger

Proven Member
280
32
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
 

We're on Boost

Probationary Member
1,542
385
Aug 25, 2007
Seattle area, Washington
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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sacrileger

Proven Member
280
32
Jun 26, 2016
Orillia, ON_Canada
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.
 

We're on Boost

Probationary Member
1,542
385
Aug 25, 2007
Seattle area, Washington
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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sacrileger

Proven Member
280
32
Jun 26, 2016
Orillia, ON_Canada
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:
 

We're on Boost

Probationary Member
1,542
385
Aug 25, 2007
Seattle area, Washington
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?
 

DSMPT

DSM Wiseman
2,122
1,682
Jun 12, 2014
Japan / Mexico, Arizona
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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We're on Boost

Probationary Member
1,542
385
Aug 25, 2007
Seattle area, Washington
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?
 

DSMPT

DSM Wiseman
2,122
1,682
Jun 12, 2014
Japan / Mexico, Arizona
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.
 

sacrileger

Proven Member
280
32
Jun 26, 2016
Orillia, ON_Canada
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'.
 

1990TSIAWDTALON

Moderator
9,422
5,247
Nov 14, 2013
Independence, Kansas
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........
 

sacrileger

Proven Member
280
32
Jun 26, 2016
Orillia, ON_Canada
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.
 

DSMPT

DSM Wiseman
2,122
1,682
Jun 12, 2014
Japan / Mexico, Arizona
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.
 

1990TSIAWDTALON

Moderator
9,422
5,247
Nov 14, 2013
Independence, Kansas
I would agree that the main cause for failure is heat and/or fluids in the body of the alternator.
 

sacrileger

Proven Member
280
32
Jun 26, 2016
Orillia, ON_Canada
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 ???
 

We're on Boost

Probationary Member
1,542
385
Aug 25, 2007
Seattle area, Washington
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?
 

1990TSIAWDTALON

Moderator
9,422
5,247
Nov 14, 2013
Independence, Kansas
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.
 

sacrileger

Proven Member
280
32
Jun 26, 2016
Orillia, ON_Canada
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.
 

We're on Boost

Probationary Member
1,542
385
Aug 25, 2007
Seattle area, Washington
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.
 

sacrileger

Proven Member
280
32
Jun 26, 2016
Orillia, ON_Canada
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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We're on Boost

Probationary Member
1,542
385
Aug 25, 2007
Seattle area, Washington
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!
 
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