Small Frame 12V alternator Examination.

[glort]

As promised in the 12V battery charger thread, I picked up a couple of Mitsubishi 12V/ 80A alternators and torn one down for a look see in refrence to them being suitable for battery bank charging.

The question was if these alts were suitable for long hours at full output.
I have taken pics that I will post up shortly but my non qualified opinion from what I have seen so far is that I have no doubt these things would handle their rated loads no problem.

The alt I am referring to is a twin internal fan model off a Subaru but is fitted to a number of other makes as well and I have also seen in my curiosity that the Bosch alts of the same style should be just as capable.

The significant thing in the design of these alts is they have 2 internal fans and the rearmost one cools the Diodes and regulator.
To this end, in pulling one of these things apart, the rectifier is of a finned heatsink design that the fan sucks the air right through the middle of.  The regulator is also placed in a position that would get a very strong airstream which would also afford great cooling ability.l

The coils have their own fan and in addition, the coils themselves are also in a rather open design that would have to help with cooling.
The case is lightweight alloy and very well ventilated itself. I was wondering if cooling could be helped by the drilling of extra holes but that seems to be well covered by the manufacturer. Anywhere there would be airflow is already ventilated as far as I can see.

In referencing Bob's paper on the leece units, pretty much all the differences apply to these alts in the battery charger config as he noted. The main one I can see being the things operating outside a heated engine bay.  Pulling ambient air through the electronic side of things would have to be a huge advantage to the longevity of these units and given the under bonnet temps of modern vehicles, in a stationary application they would have to be 50oC better off. That's a significant amount in heat dissipation ability.

I also noticed that the brushes are real easy to get to on these units with just the removal of a plastic cap. I plan to drill a hole in the casing to feed a couple of wires through and attempt to solder a couple of wires so I can full feed the rotor. Removing the reg wouldn't be easy but taking it out of the equation by drilling a hole through it or similar would be a piece of cake. One could then use something like a simple tail lamp to control the rotor current and switch them in parralell for different current outputs if one wanted to limit it.

My goal is to see what the things will take flat out however.  So far I see no reason these couldn't be externally controlled exactly the same way Bob did his. While the output on these units may be lower in some cases, the giveaway prices they go for mean a person could run 4 of the things with spares and still be way in front.
I see no reason efficiency couldn't be increased the way Bob bettered the leece units.

I'll have a crack at a flat out test of one of these things next week. I have got all my inverters up and running and can pull a load on the alt over its rated capacity with no trouble. I'll try to add in load till the volts drop and then see if I can hold the alt there and give it a good long run to see if any magic smoke escapes.  If it survives that, I'll try giving the rotor all the juice it wants and see how I go there.

I'm feeling confident these units will stand up to all the abuse that can be thrown at them.  The internal design seems aimed at keeping everything cool and when removed from the environment of an engine bay, I really think they will just be cruising even when giving all they have.

When going through the pile of alts at the yard, I noticed that even though they are all the same, the part numbers changed. They seemed to get higher the later the vehicle they came off.  I noted previously that of the 2 on my lister, one runs hotter than the other. I'm now wondering if this is due to the alts being a different series/ part number. I haven't looked to verify they are but given how many I went through in the yard to find a matching pair, I'd say its possible.
As such I'll just re-assemble the one I have taken apart and us one of the others for the testing in case I do blow the snot out of it.

I'll put the matching number pair on the lister and see if they run more evenly temp wise or maybe what I am seeing is just a manufacturing tolerance thing.

[Ronmar]

The temp difference is probably due to tollerance as you surmised.  A very slight difference in the internal regulator voltages could cause one to be pulling a little harder than the other which could result in the temperature difference you noted...  How were you measuring the temperature, IR thermometer?  If so, sometimes the surface being measured can effect the reading due to emissivity.  When using the IR to compare temps on items, I shoot a little spot of flat black spray paint everywhere I am testing to level the playing field.  it also gives me a consistent place to measure from...  

Too bad you don't have a high amperage shunt you could put in circuit to measure the actual DC current comming off the test alt...  looking forward to what you find.

[glort]

The difference in the alts was significant enough to be felt just with my hands.

I was upgrading the wiring and setup on the lister last night and  had a significant Duuuh! moment as to why this is happening.
I have the alts on a metal bar on the other  flywheel side of the head to the fuel pump.  As they are, one of the alts, the one that runs hot, has the exhaust pipe about 1 inch behind it.  Obviously it's sucking heated air off the pipe that has just exited the head!  The cool alt sits in front of the airbox so obviously no excess heat there.

While I'm a twit for not picking this earlier,  ( I did have the engine the other way round in my weak defense) it is very interesting  in the comparative heat the alts run.
The one on the cool side is significantly cooler than the one in front of the exhaust.  The cool one gets no where near as hot as the other one and if this is the difference that cool V's heated air makes to the things, then I'm more confident than ever of their ability to pump out full power over long hours in a stationary application.

I'll have to try and insulate the pipe behind my alt as I don't really want to change the config. Might also try and angle or offset it a bit as the clearance is limited atm.

[Carlb]

a sheet metal baffle between the alt and the exhaust pipe should make a big difference.  Just don't get the baffle too close to the pipe.

[Ronmar]

That or an air duct to the alt from a cooler location...