Understanding / Tearing down a 48V Starter/Alternator

[threeReefs]

As part of building an inverter-generator setup I am looking into 48V alternators.

I realised that cars increasingly have such things built in to provide a "mini-eco" function. They effectively have an entirely separate 48V electrical system comprising a 48V starter/alternator, and a 48V battery. The alternator mode puts energy into the battery during braking, and the battery can use the "motor" mode of the device to both provide the stop/start function and also provide a bit of extra power when accelerating.

So, these are pretty interesting devices and available relatively cheaply on the 'used' market, and I figured I would see if I could use one as the basis of my generator. I bought a "salvaged but servicable" one from a Ford Focus (a 1-litre petrol car) which is a 48V 150A unit - it was cheap enough I reckoned if I broke it while dismantling, I would at least have learned something. I found a slightly strange setup and I'm wondering if people here can shed some light on it. Obviously things will be complicated by the Starter functionality, and it might even be possible to use that, but let's see.

First weird thing is the stator has 5, (yes five) connections. It's densely packed, 80 slots :

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The five leads come out onto the back and are labelled U, V, W, X, Y. There is no Z like I was expecting (well actually I was hoping for just 3, but you can't have everything). They do not seem to be isolated pairs, and there is about half an ohm between every combination / pair of terminals. Here's the backplate :

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The wires are led through fat copper tracks to spade-type terminals which are spot-welded onto tags from the electronics package, in the visible groups of 2, 2, 1. This is turns out is so they can be led into the regulator/manager in the right places. The regulator package is large! and heavily potted/sealed so was a devil to get apart. It looks like this :

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Forgive the fragments of plastic from my ham-fisted and exasperated attempts to open things up. There was a LOT of potting, spot-welding, and sharp-edged connectors and my pain levels got to a point where the red mist descended and the hammer and screwdriver came out. I was reflecting that I didn't really want the control package, just the main body of the device, so I wasn't concerned about re-using it.

You can see five small boards with golden components on them - this is where the five stator leads come in. The prominent gold components are precision resistors, so something is monitoring current very precisely. I can't see the rectifiers but I think they're potted-in up the top of the picture.

The rotor has a small magnet attached to the end, which I suspect is driving a hall-effect sensor in this package so the system knows where the rotor is, rotationally - it needs this for the Motor mode, I think ? Because it has to generate / synthesize a waveform to move the rotor around based on where it is relative to the stator coils. Some controllers do this by sensing the change in inductance as the rotor moves past stator coils, but this appears to use a sensor. I guess that gives it more control.

The control harness comes in at the top-right, it's a six-way connector but only four of them are used, you can just see four little loops of wire coming onto the central processor board.

So it is WAY more complex than I need, but if I could figure out the stator windings I could perhaps use it. The sliprings/rotor connections are very accessible. So I'm posting this (a) because people might like to see inside these things and (b) to ask if anyone knows what the five stator tags signify and whether it's possible to three-phase rectify this.

I might try tearing-down the manager a bit more to try and find the heavyweight rectifiers, and there must be some chunky switches in there (FETs or a relay maybe?) to switch between Motor and Alternator modes.

Thoughts appreciated !
Richard

[threeReefs]

So I've done some more digging and maybe answered some of my own questions.

There are 80 slots, and 16 poles on the rotor, which gives this alternator a pole pitch of 5. Since there are 5 connections coming out, this seems to be a 5-phase alternator (!)

Each phase would then have eight coils (80 divided by five (phases) and then by two (sides to a coil)), and since each connection crimp has eight wires into it, it seems those eight coils for a phase are connected in Parallel, not in Series as seems more common. I've no idea why you would do this but it must put the emphasis on current not voltage ? And the more phases you have, the smoother the operation in motor mode, and possibly the more torque on startup ?

The fact that I find similar resistance between all pairs of connectors then suggests that this is a star-wound alternator and there is the mother of all star points (with 5*8 or 40 wires joining up) somewhere. Given that number, the star point could be more a star "ring" running around the other end of the stator. I will take the back (slip-ring end) of the casing off and look.

Still very interested in peoples' thoughts on the suitability of this for an inverter/generator setup. It looks well made and solid.

[Tom Reed]

My thoughts are to spin it up and apply 12vdc to the rotor and then measure what the voltage is across the winding's. With an interesting bridge rectifier setup you might get a nice smooth 48vdc out of it.

What did you pay for this motor/generator??? I'm interested for charging my 48vdc LiFePo4 off grid battery bank.

[keith71]

Did it have an extra long front pulley on it? Like this one.
  https://www.ebay.com/itm/116094352017?itmmeta=

[threeReefs]

I paid about USD120 for it. It's about five years old so has some rust etc, but that would clean up and it looks good. If I was going to use it long-term I would probably replace the bearings with some good ones, and get some spare brushes.

Keith, that's an interesting pulley ! Must put a lot of load on the front bearing. But I think that's the 12V alternator from the same car - it has just one large terminal so must use frame as ground, whereas I'm getting the feeling the 48V subsystem is run completely isolated from the main 12V circuit, so my 48V alternator has two large terminals, like this :
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If I put the part number off your listing into a search I get 14V units.

I've done some more checking and actually now think this is a delta (or pentagon!)-wound unit - I can find no star-point. The coils for each phase are wound with a group of four wires, and it's the start and end of that skein (so 4+4=8 wire) that I can see bring brought out to the terminals. With four wires in the skein for any given winding, the resistance is so low that my simple multimeter can't resolve the difference in resistance between different points on the outputs.

I am going to try running it up and seeing what happens. I should be able to use a couple of three-phase bridge-rectifier units, right ? Just only part-using the second one. All you're doing as you add phases is to add more diode-pairs, so I can link the outputs of the two units in parallel, and attach each phase to one of the inputs, leaving one unused. I think that should work OK.

Thanks for the feedback !

[threeReefs]

Reassembled without the Management unit, and with the backplate brought out so each phase can be led out, and a connection into the sliprings.

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Now awaiting the arrival of some large bridge rectifiers. I had planned to use an old washing machine motor plus speed controller to build a test rig that would enable me to spin it up at different speeds and put a little electrical load on it, but the pulleys have different groove sizes :-( Rethink required.