Alternator Wiring Testing

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MR2DI4
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Re: Alternator Wiring Testing

Post by MR2DI4 »

Correct but the diodes tend to be kind of "Spot welded" or fused and/or the tab bent over the lead on my new diodes. Solder is not great long term, it has shrinkage with age and is not that strong and fatigues with vibration.

Usually there are some visual signs the diode has gone, that black rubber lifts. They tend to go open circuit, the lead just goes down to nowhere like the diode just evaporated.

The worst part is getting the alternator out of the car, I hated doing it a second time even though it was tested before going in, it just didn't last long.


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Re: Solved: Alternator Wiring Testing

Post by benckj »

UPDATE

Apologies once again for thread pinching.

96NA- Managed to test the wiring circuit from alternator plug to IGN ECU fuse. Found the resistance was 0.4ohms which shows it has good continuity. RE-checked the alternator plugs main terminals, battery and all fuses. Engine starts and runs fine with no belt slipping or other issues. Still no charge to battery without even the slightest increase in voltage as RPM increased. Keep in mind this was a 'new' aftermarket alternator that worked fine until the car sat over winter and battery was re-charged to get started.

96-3sgte- The alternator does work but the voltage is very unstable (logging info using my aftermarket ECU). No real progress on this as waiting for replacement voltage regulator and bridge rectifier to arrive. Speculation that this is the problem as I would hate to drop alternator again!

On request the supplier sent the parts to me at no charge and plan is to change out components without removing alternator. I did check my old alternators and its fairly logical to pull the brushes and other parts from backside without dropping unit. If I can't get access onto screw terminals I'll remove alternator and lower against subframe. Hopefully, this solves the problem otherwise it will need to come out and be replaced. I do notice it makes a funny sort of whinning noise when running and has done so since it was installed. Guess it could be something with slip rings or internal rubbing that I'll need to find.

More to come.
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Alternator Wiring Testing

Post by benckj »

]b]96NA-[/b] Connected up charged battery and tested all 3 leads on alternator plug with IGN on and they were reading approx. battery voltage. All the same so no issues with wiring as far as I can tell. At this point I decided pulling the back cover from alternator was worth trying to view internals. easy enough to pull cover insitu and all internal components looked new and pristine. Only option was to remove alternator so I can bring into local auto-sparky shop and have them test. Before I do that I will use a multimeter today and look for anything obvious with the regulator, brushes or rectifier. Visually they seem perfect but need to confirm.

I can't help but think that both my alternator problems are due to a possible faulty chargers I used when batteries were dead. Electrical problems only surfaced after I did an extended charge (over-night) on each car following weeks of sitting outside over winter. Haven't had problems with charger before but I generally only use for an hour or so until battery has enough strength to start car. What fault could develop with alternator or circuit from charging battery while still connected to car?

98 GT- Once I work out the NA issue I will look closer into this issue assuming they are related to charger. I have a new regulator and rectifier supplied from seller in the case this is the issue. If so, I'll simply remove alternator from bracket and then work on replacement of these parts without completely removing alternator form car. Will be fiddly but much better than removal of alternator bracket.

Alternator as well as the new parts received was dropped off at auto sparky this afternoon. Explained the story and he hope to look at within the next day of so. Hopefully it is a simple fix and turbo alternator can be done without removal. More info to follow.
Last edited by benckj on 27/08/19 5:05, edited 1 time in total.
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Re: Alternator Wiring Testing

Post by MR2DI4 »

Notes:

1.If there is a strange whine, the rectifier diodes are stuffed. They run silent, you shouldn't be able to hear a thing over the engine noise even at idle.I could hear my faulty alternator whine sitting at the traffic lights.
2. I think trying to start these cars with a near flat battery is not good for the old diodes, I think I damaged my rebuilt alternator instantly the second I did this. My car is modified so the current draw on start is high. If its a daily driver then no problem.
3. Unless you have a really good battery charger like the ones I made, Its advisable to remove one battery terminal to charge.
4. I'm not sure I would want to try and work on the alternator while its still in the engine bay. You don't need to drop the sub frame on mine, just remove the stock exhaust bolts from the bottom of the 3inch downpipe to the back of the car, pull it sideways and there is just enough space to get it out if you get the orientation of the alternator right where the exhaust was as it passes over the subframe.

Good luck with it and remember its easier the second time !
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Alternator Wiring Testing

Post by benckj »

Thanks for the words of encouragement Carl. Updated last post to include that alternator & parts dropped off to Sparky along with my long story. Wish dropping my turbo alternator was as easy as you say but afraid not the case due to my aftermarket exhaust and A2W heat exchanger located under rear boot.

On the bright side both alternators have brand new parts installed and look in great condition. Proof will be when testing but initial resistance tests look OK. I'll attach some pics of the NA alternator and turbo replacement parts for reference.
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Re: Alternator Wiring Testing

Post by MR2DI4 »

Use the diode setting on your multimeter if you have it, not an Ohms range setting. Any decent meter will have a Diode setting these days its pretty normal.

Its unlikely any of the windings are stuffed. From memory you have 3 Ohms between the slip rings that the brushes touch on and you need a high current setup to test the actual stator resistance which from memory was 0.018 Ohms for each of the 3 windings but just a very low resistance continuity check to make sure its probably ok may do it. If you know what your doing you can check for shorts between the windings and an insulation test to earth.

Yes the parts already installed look new to me so no idea why you have had failures.
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Re: Alternator Wiring Testing

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I used the diode setting on meter but did not get the results I expected. Would not have thought they are zenors but something doesn’t match the OEM test.

I have the equipment to test stator windings but like you indicated I seriously doubt that is the problem. All the same the Auto Sparky can diagnosis the issue, replace what’s required and actively test alternator on dyno. I’ll get home to measure full output current.

Once I know the fault I can hopefully determine the cause. Still speculating it’s my old Repco charger although it checks out on voltage outputs. Usually I use my 3 stage smart charger but it got left outside overnight and since has an intermittent fault. Might need to chuck both in the bin and buy something decent.
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Re: Alternator Wiring Testing

Post by MR2DI4 »

They are not Zener diodes they are a high current silicon rectifier diodes. Specification wise they are 25 to 50Amp diodes depending on the maximum current output of the alternator. They should be open circuit one direction and something like 0.5V in the other direction.

Find an auto electrician then can put it in their test jig and spin it up and load it. I managed to get both of mine tested for $10 it only takes them a couple of minutes. They know what to look for like a smooth output increase with increasing rpms.

The smart chargers are the go, build two of them probably 15 years ago now before they were even on the market. Chargers are far right, used a commercial 6A switchmode supply and the dedicated board for the charger.

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Re: Alternator Wiring Testing

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Collected the NA alternator and parts removed from turbo (rectifier & regulator) from the local auto-sparky. He was really easy to deal with and more than happy to swap parts around into the NA alternator for testing. Seems checking the rectifier on the bench is easy enough but regulator is not. Also learned that the rectifier may in fact bench test ok but fails under load. I like these parts to be tested as best as possible in the device they are operating.

The final result was a blown rectifier on the NA and a noisy/faulty regulator on the turbo. As the supplier sent over both these parts I was able to ulitise them without buying anything else.

Now comes the fun bits as I have both cars pulled apart. The NA alternator was completely removed but turbo I was able to simply pull backing plate off and un-bolt the internal parts. Couple of pics attached that shows the components which were all new (not refurbished). Note the difference with the regulator and tabs on underside which are joined onto internal pins. Faulty one on RHS doesn't have the tabs connected so not sure what this means.
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Re: Alternator Wiring Testing

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I have stuck to the genuine Toyota Regulators, they have not failed on me yet just the rectifiers.

Yes the rectifiers tend to fail once they get a serious load, thats when mine went because I didn't fully charge the near flat battery before fitting the new alternator. Yes it can handle it when new but some 30 year old parts are just not a good idea.

Wouldn't worry about the wires to the tabs on the regulator, as long as it works your fine. Unfortunately these are full of plastic encapsulated electronic components and they are going to be nowhere as reliable as the Japanese OEM version.

There is a fair chance the rectifier is also going to be "censored" if its made in China, Mine cost NZ$112 and it was made in Germany.

IMO if you factor in your time to fix an alternator in an MR2 its not worth your time using cheap parts. On some cars the alternator is out in 5 minutes, the MR2 can take you hours.This doesn't even factor in the chance that it craps out on you while your in the middle of nowhere and you have to pay to get it towed.
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Re: Alternator Wiring Testing

Post by benckj »

The Denso OEM parts I have from the removed alternators do seem much more robust although are showing their age. The regulators indicate a degraded state with 'white' corrosion evident on all the terminals. Rectifiers look as though they have been through some serious temperatures issues with diodes overheating and bubbling the plastic away. Solder joints look in very poor condition and have a possibly high resistance or even open circuit.

Time will tell how long the new alternators & internal parts will last. I will try and source some good replacement parts in the event I have another failure down the line. The auto-Sparky stated that when they rebuild alternators they use the same brand components I was installing.

Most MR2 owners would have no idea on how well their alternator & charging circuit is preforming. I have voltage displayed on my touch screen and set tight alarm paramters to show any changes. I also data log road runs often to monitor my engine performance and voltage is included on the log. This is what alerted me to the noisy voltage levels and steep charging steps. Old pic of my display below for reference although I've updated and changed quite a bit over the past year.
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Re: Alternator Wiring Testing

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I agree I got away with driving mine in what was a "Faulty" condition for thousands of km's but sooner or later it totally dies on you.

Effectively its a "Three Phase" system and you can loose one phase and it still appears to work in terms of the your warning light not coming on but as soon as you loose the second phase your in trouble.

If you have an oscilloscope you can put it on the battery while the car is running and you can see the three phase ripple Voltage which appears as 14.8V on your multimeter.

The easy check is it should be running totally silent and you should have 14.6 to 14.8Vdc charge Voltage across the battery even at idle or 750-850rpm.

On the way out it also appeared to upset my idle which is usually dead stable. Probably because the unstable Voltage it was affecting the fuel pump.

All in all its the one thing you want working besides the engine itself or about 30 minutes of run time (or significantly less depending on your battery capacity) after it dies your left stranded somewhere.
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Re: Alternator Wiring Testing

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I suspect that I dropped one phase on the turbo and lost all on the NA. As you indicated, monitoring the voltage level at idle is generally a good indication of charging circuit health. Most likely no warning lights will even be shown for this problem and battery will remain charged enough for most people to never notice.

Task this weekend will be firstly install new rectifier & regulator in the turbo and get that up and going. Following that I'll install the alternator back into the NA which happens to have the rectifier that came from turbo. Hopefully, all goes to plan as weather is closing in and there is already snow on them hills..
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Re: Alternator Wiring Testing

Post by MR2DI4 »

Good luck let us know how its goes.

The only problem is that I suspect that these aftermarket alternators only have a design life of 6 to 8 months before they crap out.

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