External alternator regulator for 56 VDC output.

What's the basis for this calculation?

Regulator isn't any different from the one you already have. Just puts more current into the field and senses a different voltage. The problem you're gonna have is RPM. I once tried to build a 110VDC generator from an alternator and lawnmower engine. 2HP engine could just barely spin it fast enough to get to 110V with no load. As I recall, it ran at like 9000 RPM.

mike

Yes. To get anywhere near the original watts out at 4 times the voltage at similar RPMs, you need to rewind the stator with 4 times the turns. Then you are in a position to start thinking about how to alter the regulator to control the field current.

You could cheat:

Use a step-up converter from 12 VDC -> 56 VDC which would probably suck because the losses will be high.

- Or -

Open the alternator and find out how many phases it has got and what frequency it runs at - usually the output windings are on the stator and there are six phases, each with a diode connected in a star configuration. Before the diodes there will be AC at some frequency; maybe as high as 4 kHz - tap that voltage out, then build a multi-phase transformer & rectifier set, that will give you the 56 V.

Use the original regulator, if possible take the feedback from the 56V and divide it down with a voltage divider. The magnetisation voltage comes off the rectified 12 VDC as usual; regulation might be built in here too; experiment. Maybe 56 VDC "open loop" is good enuff.

This should work, it is more involved but saves rewinding of the generator and keeps most of the system "electromechanical".

If you are doing the mechanics yourself had you thought of driving four smaller alternators off the one shaft, and charging each battery separately.

Simpler and far more flexible than shoving the same charging current down a stack of batteries (whatever the state of each one).

A 56V battery pack is also a serious arc welder if ever you have an accidental short.

Didn't think about it till now...Should have three phase output. If you can get at the windings separately, rectify each and put 'em in series. Will need a cap for each cause they're out of phase. mike

Actually, many alternators will provide much higher voltages without much in the way of modifications. This is because they are designed to have a relatively high output at idling RPMs. At higher engine speeds, the rotor input voltage is switched at a relatively low duty factor, although some types of alternators also use inductance to limit the increase in output voltage. Since output frequency is proportional to RPMs, series inductance represents a rising inductance that can be used to counteract rising output. That said, I agree with the posters who argued against charging so many cells in series. Paul Mathews

It is if you have a 48v battery bank.

That is why they invented an "equalizing" charge.

Barrier diodes, eh? I'd put those in series with my 250amp breaker then?

sdb

Charging 4 12V lead-acid batteries in series is not a good idea. Invariably this will lead to charge imbalance and one or more batteries are going to die. Why not just charge all four seperately or in parallel with barrier diodes? Should be enough room for a 2nd alternator under the hood.

-- "We are nothing if not a product of our upbringing." MCJ 200402

In article , Mark Jones wrote: [...]

How about this:

If you build a voltage multiplier, every second tap has a capacitor to ground. These points could be wired to the batteries to be charged. The battery with the lowest voltage would get more current and thus the balancing between batteries would happen with no extra work.

Oh I meant barrier as in "isolation." Whatever the specific name for an automotive battery isolation diode is, it is still a diode. I wouldn't be surprised if there was a standard 250A or even 1000A version either. Don't you think they make big diodes? Check this out:

-- "Pleasantries, aren't they those little apple-filled thingies?" MCJ

Yes, with a forward-voltage-drop tempco crossover at 25kA, where it drops only 1.35V, indicating an ideal diode drop plus 0.2V/25kA = 8 micro-ohms of internal resistance, and a power dissipation of 34kW, which it can handle for one pulse lasting for five milliseconds, raising the junction temp from 25 to 200C, judging from the Thermal Impedance Characteristic curves, IICC. Ahem.

I would dispute that. It may well be the *most_logical*, or *simplest*, approach - but there are sound arguments for not doing it.

Which unfortunately doesn't happen with simple automotive style regulators which are really aimed at CV charging only.

Whwn you have a 400+ volt stack of 2V cells in a UPS, anything othert than series charging is a nonsense. The result is a need to pay special attention to equalisation. At 4x 12V I would look at charging them with four separate chargers. If this needs to be fossil-fuel-driven, then I'd be contemplating an AC output device to feed consumer market chargers x4.

He lost me on that one too.