For all you electrical geniuses ... Denso Alternator Mod?

Hey ... here's a question:

Normally, a Denso alt has a rectifier that looks like this:
http://store.alternatorparts.com/images/products/detail/11730.jpg

If that goes bad, can it be replaced with an external, post-mounted generic rectifier that looks like this:
http://www.xsforsale.com/media/cata...5/s/t/stud_mounted_do-5_rectifier_s30760_.jpg

???

Assuming that the amperage and volt ratings are the same, of course.

Would that work, or is there some other function built into the Denso rectifier?

Thanks.

The stock Denso rectifier pack contain several diodes and cannot be replaced with a single diode. Nice try!

lazyxj said:

The stock Denso rectifier pack contain several diodes and cannot be replaced with a single diode. Nice try!

Click to expand...

Can you tell me more about how the several diodes perform in a way that is different from the single? I'm not challenging your answer, just want to learn more about this now, and enjoy getting more info.

There are three different phase windings in the alternator. You need a diode per phase. You could wire three of those together in the right way and replace the ones in the alternator, but you have to heat sink them and connect all the different connections as well as make sure they have the right ratings. The diode you show is most likely not high enough current and maybe even voltage.

Those alternator diode packs are pretty cheap and can be had in various amperage ratings. I can see no advantage of converting the pack to individual diodes.

old_man said:

There are three different phase windings in the alternator. You need a diode per phase. You could wire three of those together in the right way and replace the ones in the alternator, but you have to heat sink them and connect all the different connections as well as make sure they have the right ratings. The diode you show is most likely not high enough current and maybe even voltage.

Those alternator diode packs are pretty cheap and can be had in various amperage ratings. I can see no advantage of converting the pack to individual diodes.

Click to expand...

Hi Old Man: Thank you for that informed response. Do you know a good source for the packs you described? Maybe a link? You are right it would definitely make things easier than external

The link I provided was just for a picture. Here's a link to a stud rectifier rated to 85 amps max & 600v max:
http://www.xsforsale.com/index.php/s30760-silicon-power-rectifier-600v-85a.html

I wanted to convert to external diode because I want to rewind the stator for increased output ... especially at idle. So ...

- Increased output amperage should be accompanied by higher-rated diodes. I think three external diodes, each rated at 85 amps & 300 volts max, should cover the amps/volts requirements.
- Removing the internal diode would make a little more room in there for the larger stator windings? I'm not sure about this because I haven't opened it up yet, but it couldn't hurt.
- Moving the diodes outside the alt would reduce internal heat, which can only be good for the unit -- especially the rear bearings.
- It would save a few bucks
- And most importantly ... it would be fun to do.

Your point about heat sinks is a good one ... I was thinking I could use one of the old PC heat sinks I have lying around ... would certainly be larger than the little sink on the OEM diode trio.

Another point of concern would be making sure the external diodes had avalanche capability to protect the computer. This would be less important if we changed the alternator power feed directly to the PCM, with an external Voltage regulator.

I'm picturing 3 wires inside a plastic wire loom going to the diodes, then from there 1 wire going to external voltage regulator, then from there to the hot post on the PCM. This would basically bypass the computer for voltage regulation.

Any holes in that idea?

Thanks to everyone for the input, and please keep 'em coming. But I think old man's idea about just getting a higher-rated diode trio might be a good idea.

.

old_man said:

There are three different phase windings in the alternator. You need a diode per phase.

Click to expand...

Actually, since each of the three windings produces A/C, each winding has two diodes so both halves of each sine wave is rectified. This means the main rectifier pack has 6 high-power diodes.
Depending on the design, there may be another rectifier pack called the 'diode trio' or 'isolation diode'.

It might be a lot easier to get an higher output alternator that already has the beefed up components. 160-amp alternators (2003 Dodge Durango) are available off the shelf that fit with a little modification.
I prefer to use off the shelf parts for easy replacement. Parts always seem to go bad when I'm on a trip and far away from my garage.
I suspect you would have a much easier time finding a replacement Durango alternator as opposed to finding replacement 85-amp, 300-volt diodes when out in the back-country of Montana.

Thanks for the reply.

Here's an interesting link:

http://www.alternatorparts.com/quicktifier-remote-bridge-rectifier.html

They use this with all of their upgraded alternators. They keep the oem rectifier inside the alternator, and add this external for extra capacity.

I'm aware of the durango alt ... but sometimes I just like to dive into this sort of project ... strictly for the fun of it, and for knowing exactly what you've got. A new durango denso alt would cost at least $200. Rewinding and rebuilding your own should cost no more than $50-$60, and that would include heavy-duty bearings, better performance at low rpm, etc.

montanaman said:

Here's an interesting link:
http://www.alternatorparts.com/quicktifier-remote-bridge-rectifier.html
They use this with all of their upgraded alternators. They keep the oem rectifier inside the alternator, and add this external for extra capacity.

Click to expand...

You might be able to do the same using one or two OEM rectifiers mounted outboard of the alternator and wired in parallel with on board rectifier.
Mount it/them in spot with good airflow or use a 12-VDC computer fan for cooling.
Let us know how it works.

lazyxj said:

You might be able to do the same using one or two OEM rectifiers mounted outboard of the alternator and wired in parallel with on board rectifier.
Mount it/them in spot with good airflow or use a 12-VDC computer fan for cooling.
Let us know how it works.

Click to expand...

Thanks ... I've been looking into this, and apparently there are troubles with running diodes in parallel -- especially if they are not perfectly matched. The hottest one takes the most current ...

Also ... the link above says they are non-avalanche diodes ... if they are wired in parallel, that could also be a problem, couldn't it?

montanaman said:

Thanks ... I've been looking into this, and apparently there are troubles with running diodes in parallel -- especially if they are not perfectly matched. The hottest one takes the most current
Also ... the link above says they are non-avalanche diodes ... if they are wired in parallel, that could also be a problem, couldn't it?

Click to expand...

Looking at the instructions and schematic, it appears that the Quickifier is wired in parallel. If you use the same model outboard diode pack as the in board one, they should be fairly closely matched.
Using off the shelf diode packs should make it a lot simpler to build and more dependable. It should be easier to make the connections using the OEM packs.
Not sure about the 'non-avalanche diodes' but would suspect that the OEM diodes would be the same since the control of radio noise is a problem in all cars and trucks.
You might want to contact 5-90, on this forum, for more info, he is the resident Cherokee electrical expert.

Well ... after reading more about all of this, I don't think I really like the idea of external diodes in parallel. This Quicktifier thing hasn't been on the market for too long, so I'll hold off on the whole idea of parallel diodes.

I have a '91 HO XJ, so I guess I'll get a 136 amp alt from a '98 Grand Cherokee with the 5.9L motor (Denso part# 12100-4170). The back of that alt is almost exactly the same as 91-98 XJs. The B+ insulator is clocked differently, but that's an easy remedy.

And grinding the bracket isn't a problem, as long as I don't need to grind the block.

So ... I'll get one of those at the jy, and rebuild it myself ... new brushes and bearings, clean the rectifier, clean and re-shellac the stator coils, hit the slip rings with 2k paper, and put it all back together.

For now, that will have to be enough DIY fun. And this is probably huge overkill, since my current alt (Denso 12100-3440) is only 75 amps, and I've never had a problem with that. I have no power anything, only 1 mechanical fan, and don't really plan any electrical add-ons in the near future. Even my headlights are stock halogen, although I'm planning a fatter lighting harness with relays to make them brighter.

Of course, once I have that alt, I might need to get a decent winch, just to put it to work LOL.