Author Topic: 48V alternator (ICE driven)  (Read 16041 times)

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oztules

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Re: 48V alternator (ICE driven)
« Reply #27 on: March 08, 2015, 12:35:50 AM »
Everything Flux has said I  agree with from my playing with these things.
I wrote this some time back.. it has 2 parts, and that unit runs 12 or 24v switchable with the regulator that has about 12 parts in it.... fully dial up whatever you want.

http://www.anotherpower.com/board/index.php/topic,492.0.html

http://www.anotherpower.com/board/index.php/topic,500.0.html

I do it a bit different now, but this will give you all you need to know to make it happen..... simple stuff indeed... I now incorporate the little diodes as well.... stops it drawing power into the regulator when stopped, and not turned down......I know... should have done that on the first one too....

...................oztules
« Last Edit: March 08, 2015, 12:39:58 AM by oztules »
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frwainscott

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Re: 48V alternator (ICE driven)
« Reply #28 on: January 09, 2016, 08:37:10 PM »
Ive been using an early ford alt coupled to a 5hp brigs for years to produce over 50 volts on old batteries to rejuvenate them .sometimes works,sometimes does'nt. But the diodes they use are rated over 100v and the alternators will produce well over 120volts .I use a resistor for the field and vary motor rpm for voltage/amperage.
There are three sides to every story: Yours,Mine,& the cold hard truth!

Warpspeed

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Re: 48V alternator (ICE driven)
« Reply #29 on: December 26, 2016, 02:00:21 AM »
Any standard 12v alternator will work fine at 48v.

As rpm increases voltage increases.
In most vehicles the alternator is driven about x3 or x4 engine speed.  The cut in voltage where the alternator light goes out might usually be about 500 to 700 engine rpm.  That is often around 2,000 alternator rpm.

To reach 48 volts the alternator will need to be doing about 8,000 rpm, and a bit more than that to supply full rated current.

That sounds horribly fast, but if your vehicle engine is regularly taken up to 5,000 rpm, the alternator will be x3 to x4 that.  They are quite happy to run at 20,000 rpm continuously for year after year so 8,000 rpm is nothing.

You will obviously need to remove the inbuilt voltage regulator, and home brew something for 48v, but that should not be too difficult.

The diodes will be fine too, most are rated at 200v or more, and you will have zero diode problems with the original diodes at 48v.

Only real down side of vehicle alternators is that they are not very efficient.  They are made to be very small with not much copper and iron inside.  If your vehicle has a 200 Hp engine it does not really matter if the alternator takes 2Hp or 6Hp to charge the battery, so mechanical efficiency was never a strong design goal. 
Small size, reliable, and cheap, yes.  Efficient no.

george65

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Re: 48V alternator (ICE driven)
« Reply #30 on: December 26, 2016, 08:56:27 AM »
withdrawn post
« Last Edit: December 26, 2016, 09:04:06 AM by george65 »

plasmahunt3r

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Re: 48V alternator (ICE driven)
« Reply #31 on: December 29, 2016, 05:45:14 PM »
I have a suggestion.  My understanding of alternator regulators, is that by default, the Field Coil is "ON".  When the desired voltage limit is reached, the Field Coil is switched off.  It switches off/on multiple times to maintain voltage.

So you can test the max voltage of an alternator, by bypassing the regulator, and hard wiring voltage to the field coil.  If the Field Coil is always on, then voltage is controlled by RPM only.

There are examples where people make their alternators into a welder.  They get up to 70 Volts from a standard alternator.  For Welders, they control current by adding a 5 Ohm Rheostat between Battery Positive and Field Positive.
« Last Edit: December 29, 2016, 06:04:13 PM by plasmahunt3r »

Warpspeed

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Re: 48V alternator (ICE driven)
« Reply #32 on: December 29, 2016, 06:26:36 PM »
That is all true,  the field coil is a winding designed to operate at something less than the regulator voltage maximum.

So what happens when you start up your alternator, the regulator connects the field winding effectively to continuous full battery voltage. As rpm increases the field winding continues with full maximum excitation at about full battery voltage until maximum regulator voltage is reached (at usually about 14.2v) where the regulator begins to reduce the alternator output, possibly right down to zero with a fully charged battery.

If your battery is not fully charged, running at for example 13v , the alternator field still receives the equivalent full excitation of roughly full battery voltage, until it reaches 14.2v where voltage regulation commences.

For 48 volt operation, you must ensure that the field winding never sees more than about roughly 14v or it is likely to overheat and possibly burn out.  So the voltage regulator system must be designed to only supply 14v maximum to the field winding until the 48v is reached, where normal voltage regulation begins.

It functions  exactly the same as for 12v, except the alternator rpm needs to be up at about four times the normal 12v speed to reach 48v.

If you had a bike as a kid, you will probably remember, the faster you peddle, the brighter the headlight.
Its exactly the same.  A 12v alternator can easily reach 48v if you spin it fast enough, but you must safely control the field winding voltage to a reasonable maximum to prevent it overheating and burning.

There are several quite different ways to do that. You could power the field winding from a 12v dc supply derived from the main 48v battery somehow. 
Or you could connect a large wire wound resistor in series with the field coil so it drops  around 36v across the resistor.  The voltage regulator then puts the full battery voltage across the resistor plus field, but the field winding only gets 12v of that.

The last method is to design the voltage regulator itself so it switches on and off (most do that already) but instead of switching it on all the time to 100% duty cycle when full battery charging is required, you arrange it so its on only 25% and off 75% when full charging is required.  That effectively does the same thing when powered from 48v as having it on for 100% does at 12v. Its just the usual PWM.

So you usually get to either make or buy a special voltage regulator. 
But the 12v alternator itself will work fine at 48v.

plasmahunt3r

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Re: 48V alternator (ICE driven)
« Reply #33 on: December 29, 2016, 08:57:24 PM »
You can run a pre-Regulator circuit to drop the 48V to a reasonable level for the field coil.  You can use either a NPN or N-ch MOSFET, but the MOSFET can generally handle more current.  I sketched up a quick circuit.

Don't forget the Heatsink.  You can get an Ohms reading on the field coil and figure out how much current it requires.  Then you can figure out watts for dropping 36v.

Warpspeed

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Re: 48V alternator (ICE driven)
« Reply #34 on: December 29, 2016, 09:11:24 PM »
Yup, that is certainly one way to do it.

Pretty sure field current will be in the three to four amp range for most alternators, but it does vary with size and brand.
At 36 volts that is around 100 to 150 watts dissipation.
Both the heat sink and transistor will both need to be very large.

If you decide to use a wire wound resistor instead, it  too will need to be in the same power range.
Best ones to use are the aluminium clad type, bolted onto a large flat heat sink.
Probably something about a foot square should do it.

http://www.ebay.com.au/itm/200W-Wirewound-resistor-Aluminium-Housed-Clad-5-0-1-30K-Ohm-various-1pc-/121767547079?var=&hash=item1c59e950c7:m:mcm5yC8-aiBekXOATnMXCEA


OperaHouse

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Re: 48V alternator (ICE driven)
« Reply #35 on: December 30, 2016, 12:59:18 AM »
But what happens when the wind stops?  You are still dumping current into the field.  I don't remember them being that good at self excitation.  Anyway, the field coil is just a big inductor and you could easily PWM it even with just a simple TL431 circuit, not wasting any heat.

Warpspeed

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Re: 48V alternator (ICE driven)
« Reply #36 on: December 30, 2016, 01:39:12 AM »
This application is being driven by an internal combustion engine, so that its not a problem.
It would not be too difficult to automatically switch off field excitation at zero rpm,  through design of the regulator.
PWM drive of the field winding is an excellent idea in any case.

I would be very surprised if anyone is planning to gear up a wind turbine or hydro to produce 8,000+ rpm.
This application is really only suitable for a gas or diesel engine, where there is no shortage of drive power, as the efficiency of  car alternators is so pitifully low.

george65

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Re: 48V alternator (ICE driven)
« Reply #37 on: December 30, 2016, 08:22:40 AM »

Pretty sure High RPM is NOT a factor. The power applied to the rotor controls the output more than speed. Once the alt is up to it's design speed range, it's the rotor current that controls the output not spinning the bejesus out the thing.

I also believe the Field Voltage does NOT have to be limited to 14V at all.  You can supply it any voltage you like to get the output Voltage you require as long as you watch the AMPS going into the windings which are what determines the heat load they see NOT the volts.

Also the efficiency of car alternators themselves is not low at all. They are designed exactly the same as any other High efficiency alternator. The claw pole design is used in every sort of commercial generation.
What makes car alts inefficient is not the design of the alt but the very crude but robust design of the control electronics.  There are controllers available that will let the alts run to 72V+ and are extremely efficient, right up there with that of commercial power plant generators.

There is a LOT of misinformation parroted about car alts, I suspect mainly by those that have never really used or experimented with them in the applications they speak of.

OperaHouse

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Re: 48V alternator (ICE driven)
« Reply #38 on: December 30, 2016, 10:24:36 AM »
There are adjustable buck converters that will work up to 60V to supply the lower field voltage.  It is also very easy to fool these buck converters, using only one extra wire to the board, that can adjust the field using a TL/LM431 like every line operated supply does.

plasmahunt3r

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Re: 48V alternator (ICE driven)
« Reply #39 on: December 30, 2016, 10:57:14 AM »
Forget about the Field coil.  If I were doing this, I would get a 48v Permanent Magnet Alternator.  They don't need a field coil and they are designed to run at low RPM.  Low RPM means less fuel to operate.  Plus no brushes to wear out.  Overall savings in the long run.

You can buy a Windzilla Permanent Magnet Generator for around $360. 

You can make or buy a regulator to control voltage.  Since you are using an engine, and you can control RPM, your throttle can be you voltage regulator.

Warpspeed

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Re: 48V alternator (ICE driven)
« Reply #40 on: December 30, 2016, 12:53:25 PM »

Pretty sure High RPM is NOT a factor. The power applied to the rotor controls the output more than speed. Once the alt is up to it's design speed range, it's the rotor current that controls the output not spinning the bejesus out the thing.
Quote
George, why does  the alternator light come on in some vehicles if the idle speed is set too low ?
Its because the rpm is not high enough for the alternator to self excite. To reach 48 volts you do need higher rpm than to reach only 12 volts.
Quote
I also believe the Field Voltage does NOT have to be limited to 14V at all.  You can supply it any voltage you like to get the output Voltage you require as long as you watch the AMPS going into the windings which are what determines the heat load they see NOT the volts.
The field winding is an electromagnet. It is the ampere turns in the wire that generates the magnetic field.  Current is determined by Ohms law. As you increase the applied voltage, current also increases in proportion. Power is also dissipated in the winding as heat.  If you increase the applied voltage too far, two things will happen.  First the magnetic path will saturate, and second the temperature of the winding will increase.
Quote
Also the efficiency of car alternators themselves is not low at all. They are designed exactly the same as any other High efficiency alternator. The claw pole design is used in every sort of commercial generation.
by spinningmagnets
Efficiency is relative.
No, there are some huge differences in alternator design. Try comparing the electromechanical efficiency of a really good axial flux alternator to a car alternator for instance.

Quote
What makes car alts inefficient is not the design of the alt but the very crude but robust design of the control electronics.  There are controllers available that will let the alts run to 72V+ and are extremely efficient, right up there with that of commercial power plant generators.
The control electronics cannot increase the output of an alternator, it can only only regulate (reduce) the output by weakening the field excitation.  Voltage regulators are not crude these days. 
Early regulators used vibrating mechanical contacts, later ones an electronic circuit board. Today its all done in a single sealed hybrid chip.  Very robust and reliable.  But the alternator itself has not changed in basic electromechanical design over the last sixty years.
Quote
There is a LOT of misinformation parroted about car alts, I suspect mainly by those that have never really used or experimented with them in the applications they speak of.
What do you do for a iiving George ?

I am a retired power electronics design engineer.
« Last Edit: December 30, 2016, 01:15:56 PM by Warpspeed »

Warpspeed

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Re: 48V alternator (ICE driven)
« Reply #41 on: December 30, 2016, 01:31:16 PM »
Forget about the Field coil.  If I were doing this, I would get a 48v Permanent Magnet Alternator.  They don't need a field coil and they are designed to run at low RPM.  Low RPM means less fuel to operate.  Plus no brushes to wear out.  Overall savings in the long run.

You can buy a Windzilla Permanent Magnet Generator for around $360. 

You can make or buy a regulator to control voltage.  Since you are using an engine, and you can control RPM, your throttle can be you voltage regulator.
That is a much better option than a car alternator for all the reasons you mention.

Its a toss up between controlling the engine throttle, or placing a PWM buck regulator between the alternator and battery.  Either way, it requires a bit of ingenuity and know how to get it all working, but agree its a much better approach.

The main attraction of using car alternators is that they are usually free, and often the IC engine is free too.
So even if the final result is not spectacularly good, its still possible to create something very useful for minimal outlay and a bit of fun.

george65

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Re: 48V alternator (ICE driven)
« Reply #42 on: December 30, 2016, 06:33:19 PM »
What do you do for a iiving George ?

I am a retired power electronics design engineer.

I don't know what you did specifically but I can guarantee it was not working hands on with these type of machines.
My only knowledge is hands on not professional but there are people and products out there that directly contradict much of what you are saying.
It's not a matter of my opinion or qualifications, it's a matter of fact and proof that shows much of your position is patently incorrect. people are out there doing and there are products that allow them to which are known, readily available and do not follow your position of high speed and other statements.

Have you ever worked with Car alts in this way in a hands on, practical application?

From your statements I would say that is a pretty definite NO.  If I'm incorrect, could you show me what you have done that disproves my position?

Warpspeed

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Re: 48V alternator (ICE driven)
« Reply #43 on: December 30, 2016, 06:37:16 PM »
Yes sure I have.
O/k choose any one specific point that I have made, that you consider to be totally and absolutely dead wrong, and let's discuss that in depth.

oztules

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Re: 48V alternator (ICE driven)
« Reply #44 on: December 30, 2016, 08:59:54 PM »
George....
Take it from me. I have written articles on conversion of alternators on this and other sites... I think on  this site it was "playing with alternators" where the theory and practice with lots of pics is covered in depth... down to regulator design and 8 diode units, back MMF and current limiting, rotor design and construction etc etc.

Everything Warp has stated, is fact.... I'm sorry you will just have to live with it.

Until you understand the back MMF in particular for current limiting of the units, you will be seeing things you can attribute to things that are not really driving the result.... it is all inter-related.

I have no qualifications in this, but have put in the practice... and then did the theory to explain what I was seeing.

EDIT It was here for part 1.. not this site
http://www.anotherpower.com/board/index.php/topic,492.0.html

There is a pic of a very very big one too... about 3 tons

and part 2

http://www.anotherpower.com/board/index.php?topic=500.0

Can't say I am excited about perm magets in there... no control means high forcing voltages at high rpm.... I prefer to have total  control and a few losses ( not more than 50 watts at the most...).from the rotor .





..............oztules
« Last Edit: December 30, 2016, 09:14:26 PM by oztules »
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Warpspeed

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Re: 48V alternator (ICE driven)
« Reply #45 on: December 30, 2016, 10:45:51 PM »
Excellent alternator writeup oZ.

There are many ways to skin a cat. 
If you are the average Joe with an old alternator, and a small serviceable gasoline engine, the way you did it is definitely the most logical and best way to go about it.

But someone else might find an F&P washing machine alternator or some other more obscure permanent magnet wind alternator, even a large ex military stepper motor, or maybe a treadmill motor.  All of these are worthy contenders, but there is one slight problem with all of them. 
There is no really simple means of adjusting the output voltage or current, except by  tweaking the drive rpm.
Or alternatively building some clever fairly high power PWM electronics to do that.

My only voyage into the mysteries of home brew gasoline driven standby power have been an only partly finished project. And that has certainly been a very interesting exercise. 

I have a 12Hp single cylinder air cooled Wisconsin driving a 240v alternator. I think its 3.6Kva, but am not absolutely sure of that.
Rigged it up with a 12v car alternator, 12v battery and electric start. I hate pulling a string to start things, especially as I am almost  70, and becoming more and more lazy as I approach middle age, hehehe.

I planned to run it off natural gas, with a home made carburettor, already have all the bits to do that, and operate that carburettor from a radio control model positioning servo to keep it at 50Hz. The original centrifugal governor is an evil thing long ago consigned to the wheelie bin.
The whole thing has been sitting there at the back of my very untidy garage for several years as an unfinished project.
Maybe one day, I will complete it................

Too many projects, too little time.

oztules

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Re: 48V alternator (ICE driven)
« Reply #46 on: December 30, 2016, 11:41:45 PM »
I am right now pondering my next move. I have a 48v unit to do, and so have built the car alt version as above.....

But...... I just got hold of a dead 3kw 240v AVR style 240v generator.... dead alternator, but good motor ( burnt windings )

I think I might rewind it as a 48v stator instead of 240v, and use the original rotor with slip rings, and just whack together a regulator for it, and try that too.... or rewind it as 240v and use a transformer I have laying about for the 48v part.

Decisions decisions......



..............oztules
Flinders Island Australia

Warpspeed

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Re: 48V alternator (ICE driven)
« Reply #47 on: December 31, 2016, 12:11:07 AM »
Three Kw at 48v is around 60 amps.
If you are going to rewind it for 60 Amps, you will need your Superman suit, or if you are Popeye, lots of spinach.
Its not like a car alternator where there are three windings.
A 60 Amp rms single winding is pretty serious stuff.

Even at 240v, that is still 12 amp wire to rewind, but not too difficult. 
I think I would just rewind it as original for 240v, then go the transformer rectifier route.
If later on you change your mind, it allows a few more options.

oztules

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Re: 48V alternator (ICE driven)
« Reply #48 on: December 31, 2016, 12:46:48 AM »
It is this one again

http://www.anotherpower.com/board/index.php/topic,781.0.html

It ran for many months for 24/7 while the drought was on driving water pumps day and night... after many months... the drought stopped. It was left in the paddock beside the dam for a year or 2, and failed not long after it was restarted seasons later... seems the wasps and ants and water had given it a good going over, and managed to short out the fine AVR winding. If you look at that link above you will see the winding info..... so 250 turns over 10 coils or 25 each... for 48v it would be near 40+ turns over 10 windings or only 4 turns each.

I'm thinking 5 in hand will do it@ 1.2mm or so wire. I figure the duty cycle will not be excessive at full power, and most of the time would be closer to 40-50 amps.

However the main windings are sound, and really only need to rewind the  50 turn windings of .7mm wire so am torn between the two.... but a 3kw transformer will weigh a heap too, where as the winding will be air cooled, so can be a bit on the skinny side and survive.

So 4 turns of 5 in hand will probably do just fine as the  cooling is very  powerful........big  fan@3000rpm.


............oztules
Flinders Island Australia

joestue

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Re: 48V alternator (ICE driven)
« Reply #49 on: December 31, 2016, 01:09:31 AM »
one of the problems with cheap single phase generators is the harmonics generated by the non ideal rotor. in my case, the rotor is only 90 electrical degrees wide; if i were to bolt on additional pole pieces and then rewire the rotor's two coils for anti-series, i would have a 4 pole machine.

anyhow: i think single phase generators are more efficient with concentric windings when the rotor is not sinusoidal. this should be the case particularly when the length to diameter ratio of the generator head is approximately 1:1.


much larger motors and generators  have higher length to diameter ratios (approaching 3 or 4:1 length to diameter for large 2 pole synchronous generators), they have sinusoidal flux distribution in the air gap and they are all wound approximately the same way,  lap winding: ~9.5:24 ratio. meaning: 42 separate coils span 17 slots out of 42 slots. other common slot numbers are 54, 60, 72, 84, etc.

so given that information i wound my generator with 24 coils each spanning 10 slots.


if you do want to rewire a generator that will rectify directly to dc at high amps, i might consider something as ridiculous as winding as many separate coils as there are slots, and rectifying each on individually.

if your generator has a rotor that can generate a much more sinusoidal waveform, then it should be more efficient to wind a multi phase machine.

in my case, the 145 volt coil groups are wired in wye to get 230vac. as such, 21 volts worth of third harmonic (rectifiers eat third harmonics for lunch) disappears.

so i might have a more efficient generator if i rectify each single phase 145vac coil group separately and pull power from it at 140 vac*141, rather than pulling power from it at 230vac*1.41.

a couple photos here http://www.fieldlines.com/index.php/topic,149061.0.html
« Last Edit: December 31, 2016, 01:14:17 AM by joestue »

Warpspeed

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Re: 48V alternator (ICE driven)
« Reply #50 on: December 31, 2016, 01:17:39 AM »
I am more used to designing and winding transformers.
Funnily enough, just finished winding a small one myself earlier today.
Its a dc to dc converter should provide  2.5Kw at 30Khz.

Five x 1.2mm sounds like about 30A for a solid standard garden variety bog ordinary 50Hz transformer in free air.
But with a fan and bulk air, and plenty of heat conduction to the outer cast iron frame, its probably conservative for your expectations.
Never attempted a rewind as complex as that one.
You are a much braver man than I  oZ.

Joestue, you posted just ahead of me.
That is an absolutely brilliant suggestion, multi phases  solve a whole lot of problems, and makes some very nice direct current.
Never thought of that, but you are quite right.
There are some pretty bright people here.
« Last Edit: December 31, 2016, 01:25:45 AM by Warpspeed »

joestue

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Re: 48V alternator (ICE driven)
« Reply #51 on: January 01, 2017, 05:35:15 PM »
I suppose I should confess I am now rather curious what kind of power a car alternator will suck up at 20,000 rpm with a full field exciton of 4 amps at 12 volts.

my guess is there will be about 1 hp of air drag and eddy current losses. but at 20,000 rpm the fan might be pulling as much air as a typical household vacuum cleaner, through the alternator. so God knows what the temps will be.  ;D

keep in mind the eddy currents set up in the iron oppose the field coil's amp turns. so the volts per hz will decrease as rpm rises..

Warpspeed

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Re: 48V alternator (ICE driven)
« Reply #52 on: January 01, 2017, 05:59:45 PM »
Yes indeed, but the output power will be pretty considerable as well.

Quote
keep in mind the eddy currents set up in the iron oppose the field coil's amp turns. so the volts per hz will decrease as rpm rises..
Yes, and that is very important.  Its what sets the output current and keeps it constant as rpm rises.
If its a 65 amp alternator or an 85 amp alternator, whatever it is, the designer worked out the volts per hz and inductance of the windings to set a safe maximum current.  We are not changing any of that.  What we are doing is weakening the field at 48 volts not 12 volts to control the output voltage.

If it can deliver 65 amps at 14v (910 watts)  it should be able to deliver 65 amps at 56v (3,640 watts).

It will really be spinning pretty fast, but the dc output current is limited only by the copper wire gauge in the star output winding, so that does not change. The diodes too will be quite happy at four times the output power.

One further thought on all this. 
The original field winding needs around 14v at probably about 4 amps to generate a strong enough magnetic field, just safely below magnetic saturation, for full maximum rated output.

All the previous suggestions above ^^^ assumed we keep this original field winding.
It should not be too difficult to rewind the rotor, as its just a plain simple bobbin winding.

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

And as oZ has already shown us, the rotor halves come apart very easily for a possible rewind.

If you don't have a humongous hydraulic press, your local garage or servo is certain to have one.
A six pack of beer on a hot day should have it apart in seconds.



« Last Edit: January 01, 2017, 06:31:21 PM by Warpspeed »

plasmahunt3r

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Re: 48V alternator (ICE driven)
« Reply #53 on: January 02, 2017, 02:53:04 PM »
Since you have the rotor apart, I think 2 Microwave ring magnets will fit in there, replacing the coil.