# Converting automotive alternator to put out 48V?



## cbcansurvive

Apparently (if you're an electronics whiz) it's fairly easy to get an automotive alternator to put out as much as 120VDC by modifying the voltage regulator. This could be very useful for charging large banks (48V, etc...) of batteries via an alternator coupled to a small engine. Has anyone seen a good FAQ out there of how to do this? I just don't know enough about resistors, diodes, etc...to make sense of it all without pictures or very detailed step by step instructions.


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## wy_white_wolf

Besides the voltage regulator it also needs to be rewound. Smaller wire so you can make 4 times wraps. Doing so also cuts down the amperage it is capable of putting out.

WWW


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## Bottleneck

+1, generally not worth the effort.

is charging a battery bank what your looking for?


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## cbcansurvive

I am, but not for an off-grid energy system. It will be to power a 48V electric outboard and charge the 48V battery bank supplying it. Sort of a hybrid system, so something small and light (ie: an alternator coupled to a small engine) is needed. I've read that simply removing the regulator altogether and simply dialing in the voltage needed via RPM with pulleys is possible, but I'd worry about voltage dips and spikes when turning the motor on and off, but does that matter if I'm only charging batteries and running a motor (no sensitive electronics, aside from the speed controller)?


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## Harry Chickpea

Without a voltage regulator, you can overcharge and destroy batteries.


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## Bottleneck

i have a gingery book somewhere about changing the voltage. i'll try and find it. I know that a regular 120v genset, you adjust rpm to adjust hertz, not voltage. i'm pretty sure that voltage is determined by the amount of turns in the coils.


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## Bottleneck

http://www.windbluepower.com/articles.asp?ID=128


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## JeepHammer

What SPECIFICALLY are you using for an alternator?

Alternating Generators ('Alternators') produce 'Watts'.

Watts = Volts X Amps.
Raise the Volts, the Amps drop, its still the same Watts.
Raise the Amps, the Volts drop, its still the same Watts.

Some 'Alternators' produce more Total Watts than others.
Starting with a high output Alternator in the first place will allow you to convert Watts more easily.

An 'Industrial' Alternator will me MUCH longer lived.
First off, the 'Rectifier', the part that converts Alternating Current (AC) into the Direct Current (DC) has to cool itself,
The Rectifier MUST be kept cool, and 'Industrial' Alternators have better cooling of the Rectifier.

'Industrial' units also have things like full roller bearings, rebuildable brushes, and nearly bullet proof voltage regulators.
Big trucks have VERY high output alternators, heavy duty units that work day and night without failures, and when they do finally fail, they are easily rebuilt.

Turning a high output alternator takes power.
The more output you expect, the more input power you will need.

Engine driven alternators are all about the same, you can do about anything you want to, from making welders, to producing high voltage...
No rewinding required.

Rewinding usually comes in when you slow the unit down.
Rewinding is required when your power source is under powered or under speed.
More Stator Windings (more windings of smaller wire) will increase Voltage, but decrease Amperage.
Smaller gauge wire won't carry Amperage, but more of it will produce more voltage.

So, is this theoretical/planning stages,
Or do you have a specific alternator already?

Pick the right Alternator to start with, there are 48 volt Voltage Regulators right off the shelf.
For every battery made, there is a charging system.
There are 48 volt vehicles with 48 volt batteries, so there are 48 volt Alternators.
The 'Trick' is to find an application that uses a 48 volt alternator, and use that base model.
The 48 volt unit off the shelf, plus core charge, will be prohibitive in most cases,
But a common 12 or 24 volt unit, base model, with an added 48 volt regulator will give you a cost effective 48 volt unit.


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## JeepHammer

cbcansurvive said:


> I am, but not for an off-grid energy system. It will be to power a 48V electric outboard and charge the 48V battery bank supplying it. Sort of a hybrid system, so something small and light (ie: an alternator coupled to a small engine) is needed. I've read that simply removing the regulator altogether and simply dialing in the voltage needed via RPM with pulleys is possible, but I'd worry about voltage dips and spikes when turning the motor on and off, but does that matter if I'm only charging batteries and running a motor (no sensitive electronics, aside from the speed controller)?


Electric boat propulsion isn't my specific field of expertise,
But its catching on!
There are several residential lakes areound here that won't low a gas engine of any kind.

I did a couple of pontoon boats with a local marine sales place, small, just 'Lap around a small lake' builds, and it was an eye opener!

A 20 foot pontoon with a hard sun roof, replaced the sun roof with solar panels.
Best charge to weight ratio you will get is with solar panels.

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I'm not to sure about the Hybird idea...
You can use a smaller engine, vertical shaft,
And mount a good size industral alternator vertically (don't try a verticle mount with an 'Automotive' alternator, the bearings won't live)
And keep it compact, but it will need to be WELL VENTED for heat!

I'm seeing pretty large losses with converting gasoline to heat,
Carbs aren't efficient in the slightest,
Then converting that heat to stright line recriprationg motion, the piston,
Then converting that to rotary motion, connecting rod/crank,
Then to belts to the generator,
Then converting mechanical motion into alternating current,
Then converting the AC into DC via a rectifier,
Then converting the DC into chemical energy at the batteries,
Then dragging the chemical energy back out, converting it to DC electrical energy again,
Finally winding up at the electric drive motor, converting it back into rotary motion for the impeller or prop...

Losses everytime you convert that power that started out as gasoline, diesel or propane...
Just getting that out there, not trying to discourage you since I don't know your situation.

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Gasoline engines are cheap, there is one on every lawn mower.
Large frame, high output industral alternators are cheap, there is one on every large piece of equipment, like big trucks.

The frame to mount is easy, so are pulleys and belts.

The wiring is a snap if you start with an alternator that will support a 48 volt regulator to start with, its basically two wires to the batteries and an On/Off safety switch... Maybe a fuse or breaker...

The big deal will be charge over time, how long will you need to run the charging unit?
If you want to direct drive a 5 HP electric outboard DIRECTLY, you are going to need 12 to 15 HP motor and a string of alternators,
Or one BIG, heavy, expensive generator.

If you are willing to listen to a little engine rattle for hours on end to charge the batteries, you can run off batteries...
But the alternator won't keep up with motor demand.


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## JeepHammer

The efficiency from Hybrid cars comes from,

1. Fuel injection on a constant speed engine.
The engine is sized and only turns at the optimum speed for the generator,
Virtually no throttling up or down,
And fuel injection compensates for altitude, air density, humidity, ect.

2. The Hybrid cars use an AC generator, and many use AC motors to drive the vehicle.
This takes away a lot of the conversion losses,
And many have a supplemental DC generator attached to charge batteries, if its a battery powered Hybird.

An inverter converts battery DC to motor AC in some cases, other times the wheel motors are DC and direct driven.
Its all in the design/application...

The idea behind boats is, 
The fuel weight is replaced by battery weight,
Which doesn't translate well for small craft that don't carry a lot of fuel.

You will also be trading a powerful (weight to power ratio) 2 stroke engine for a heavier, less powerful 4 stroke engine (less powerful for the weight).
2 stroke outboards are very fuel/weight/power efficient, and that's why they have been used for so many years...

4 stroke fuel injected engines are cleaner, and the fuel injection adds some of he power back when switching from 2 stroke to 4 stroke.

They are by no means 'Clean', but 'Cleaner'...

I've looked into LPG outboards, which are much cleaner running, no fuel contamination issues, but they are expensive, so I haven't had one to 'Tinker' with yet...

-------

I have to say, the idea of a silent running outboard, or inboard for that matter, is something I'd like to try for myself!
Smaller pontoon or houseboat, hard deck on top with some serious solar panels,
And a battery bank that would let you get someplace...

If you ran low on battery, a day off to fish or sight see while the batteries charge, then piddle on down the river or coast line to the next place I want to screw off awhile!
With a house boat or pontoon, there is no rule saying you can't plug a gas out board back there when you need extra runtime beyond the batteries, or help with strong currents...

I'm too broken down to water ski anymore, so drowning bait and poking along is just fine with me...

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If you don't mind my asking, what is your intended application?
And what kind/HP of outboard do you have?


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