Author Topic: 48V alternator (ICE driven)  (Read 12868 times)

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Warpspeed

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Re: 48V alternator (ICE driven)
« Reply #54 on: January 02, 2017, 03:31:16 PM »
That would certainly work, and so would several rare earth magnets placed around in there, instead of the bobbin winding. Whatever you decide, once the steel has magnetically saturated, there is no further increase in alternator output.  So there is no way to lower the rpm requirement for higher required voltage, at least not without rewinding the star output winding.

The disadvantage of a PM rotor would be that the output voltage could not then be so easily controlled.
Something that will work really hard then pull the charging current right back to zero once full battery voltage is reached is an absolute necessity. Its pretty important not to boil the battery !

It could certainly be done with some kind of buck regulator on the output, but that would have to carry the full alternator output power, perhaps a couple of kilowatts.  Its much more convenient to control the much smaller current in the field winding, the power required to do that is only roughly about fifty watts, not kilowatts.

Controlling the IC engine  throttle opening is another possibility, but it is not a very nice way to do it. 
And if something goes a little bit  wrong, once again you might cook a battery. 
The original automotive voltage regulator worked fine at 12v, it just needs something very similar to work in the exact same way, but designed to work at 48v.

OperaHouse

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Re: 48V alternator (ICE driven)
« Reply #55 on: January 02, 2017, 03:43:24 PM »
Not without a non magnetic shaft.

Warpspeed

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Re: 48V alternator (ICE driven)
« Reply #56 on: January 02, 2017, 03:53:16 PM »
Yes, I see what you mean. 
It could still be done, but the steel shaft is a definite problem to be overcome for PM operation.
A permanent magnet modification would still be a backward step IMHO.

oztules

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Re: 48V alternator (ICE driven)
« Reply #57 on: January 03, 2017, 12:31:40 AM »
In practice I think a n45 neo that big would possibly saturate the shaft it would behave as a non-magnetic shaft anyway......plenty of lines left for the job I suspect

But I agree with Warp, it would be a backward step, particularly seeing how simple a regulator for it is ( in those links to playing with alts). I use a 7 dollar 7amp buck off ebay to get the 12v for the regulator to drive the rotor... works perfectly stable.... and totally controllable with a pot so you can choose your charge rate if your motor is not powerful enough to drive full power out of it when the battery is flat... and your only running a 4 or 5 hp motor from the dump.

It is not wildly efficient..... but is eminently doable for free most times.


...........oztules
« Last Edit: January 03, 2017, 12:42:58 AM by oztules »
Flinders Island Australia

Warpspeed

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Re: 48V alternator (ICE driven)
« Reply #58 on: January 03, 2017, 01:06:06 AM »
Have to agree, anything rescued free from the tip at zero cost is definitely a bargain.

I suppose if you desperately wanted to try a PM alternator, a brass shaft might be  up to the job.
If I was doing this myself I would just rewind the field for 48v. Its probably  a 15 minute job.
« Last Edit: January 03, 2017, 01:14:01 AM by Warpspeed »

Ungrounded Lightning Rod

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Re: 48V alternator (ICE driven)
« Reply #59 on: January 08, 2017, 06:41:36 AM »

So what would be needed would be to rewind the rotor with wire of half the original diameter (one quarter the cross sectional area) but with four times as many turns.
So instead of having X turns and four amps, we have 4X turns with one amp.
Same ampere turns, same volume of copper, and sixteen times the ohmic resistance.
But we can now operate our home made voltage regulator at 48 volts output instead of 12 volts output.
Much more efficient., especially as its now only one amp required

Alternatively, if you don't mind wasting up to 144 watts (at startup, though somewhat lower during run) you can put 9 ohms of (high-power!) resistance in series with the field coil.

You might try that for a quick conversion, to get it running and test it, then rewind it when you get around to it and/or are tired of wasting the fuel to make heat in the resistor, rather than delivering it to the load as power.

Another possibility (if the alternator is wye rather than delta) is to find a point on each winding that is 1/4 of the turns up from the wye point, carefully clean off the insulation, solder on a lead, and use these to feed the regulator's AC sampling inputs in place of the ends of the wye.  (You'll also need three more 5A diodes to provide a "virtual 12v circuit ground", rather than leaving the regulator's negative terminal connected to the now-48V winding's rectifier's negative terminal, and the "alternator light tickler circuit" will need a rework.)  Then the alternator operates about as designed and no extra power is wasted.

You could also do this with external 4:1 transformers, even if the alternator is a delta (the transformers can still be connected wye), though your regulation accuracy would suffer slightly.  Get some cheap Radio Shack transformers and rewind them as autotransformers.  You'll need at least enough core to handle 48 watts multiplied by the transformer's original rated frequency and divided by the alternator's frequency at cutin.  Automotive alternators run at a high frequency compared to grid mains (to reduce the amount of core and wire required) so that's a pretty small core.
« Last Edit: January 08, 2017, 07:31:04 AM by Ungrounded Lightning Rod »

plasmahunt3r

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Re: 48V alternator (ICE driven)
« Reply #60 on: January 09, 2017, 07:54:15 PM »
I was looking at DC-DC converters on Ebay, and I noticed encapsulated golf cart 48v to 12v converters, 10A & 30A.  For around $14 bucks, you can get the 48v to 12v 10A converter and run your field coil off this converter using your 48v battery bank.  Then RPM will get the voltage you require.  Simple.
« Last Edit: January 10, 2017, 12:21:46 PM by plasmahunt3r »

bergmanj

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Re: 48V alternator (ICE driven)
« Reply #61 on: January 16, 2017, 10:08:47 AM »
Folks: Just "thinking out loud".

What about a hybrid field consisting of a ring magnet capable of, say, 50% power output excitation (or 10%, or 100%, or anything desired); and an electromagnet that would buck / boost the actual working field strength to control actual output needs?

Yes, I recognize that this would not be "fail-safe" with regards to field control failure.  but, what control scheme IS totally "fail-safe"?

This kind of hybrid field would be self-exciting, and controllable.  It could also "save" the "waste" of output power at peak loads when needed most (if, say 100% power PM excited, then countered by electromagnet at max. equivalent opposite field when no external load is present).

I know that there are probably "cracks" in this thought!  But, want to hear other's thoughts anyway.  Makes for good conversation that may continue to move things forward.

Regards,   JLB

p. s. Not on here very often due to lowly dial-up internet connection at home; am at a high-speed connection right now.

joestue

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Re: 48V alternator (ICE driven)
« Reply #62 on: January 16, 2017, 01:48:51 PM »
one way to field weaken an automobile alternator would be to stack two of the stators as in figure 7 http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.569.5759&rep=rep1&type=pdf the same method is shown in figure 16.

a coil of wire in the stator is what regulates the flux density.

it seems to me you could cheaply build a centrifugal governor to adjust the phase between two sets of magnets. getting the cams (or non linear springs) correctly built to get constant volts with rpm would be a bit of a fun challenge.

OperaHouse

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Re: 48V alternator (ICE driven)
« Reply #63 on: January 16, 2017, 03:04:14 PM »
If you are willing to make a non ferrous shaft so the magnets can be installed there is no reason to add a field coil.  Electronics can be added to make it do anything you want.  I'm confounded by all these Rube Goldberg attempts to avoid electronics which in the end involve as much electronics as doing it right.

Warpspeed

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Re: 48V alternator (ICE driven)
« Reply #64 on: January 16, 2017, 03:13:01 PM »
Definitely agree with that ^^^^

A brass shaft should not be too difficult to make.