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Semi dopey question

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large_ghostman

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If this was a tractor question I know the answer, but for some reason I am not convinced it works the same way on a car, it should do but just in case..........

On old tractors you have a generator to top the battery up (really old tractors), on modern cars you have an alternator. Main difference being a generator is basically a back to from motor knocking out DC, an alternator is different phases in sine wave. Alternator goes into a bridge rectifier and produces DC?

Now at 800 RPM you get ~14V and at 6000RPM you get ~14V, my assumption is the voltage regulation and rectifier is inside the alternator??? Or is the regulation external?

I am asking because I have a variable speed device I want to turn an alternator, its just to keep a battery topped up like it would on a car. But Do I need to build the regulation circuit and current limit or do alternator already have them?

I am converting a 5KW 3 phase wind turbine (QR5 type) to a measly 14V 2A trickle charger.
 

tcmtech

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It would depend on the generator/alternator unit itself.

A typical automotive or even heavy commercial type nowadays most often have the voltage regulators built into them and many are designed to self excite and run as 1 wire units too even if they don't say it outright.

However they are still some that use external regulation as well and that wont self excite (either regulation system) no matter how fast you spin them.
 

large_ghostman

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Ok thanks, so I need to find out which UK cars have which type, then go and get a scrap one.
 

MrAl

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Hi,

There are no dopey questions there are just dopey people :)

If i remember right the old generators had brushes for the main current so they spit out DC.
In the alternators, the brushes are for the light current while the main current is AC three phase and goes into a three phase bridge that rectifies it into DC. The idea is that the brushes/commutator last longer due to the much lighter field current.

In autos maybe 10 or so years ago and earlier, the alternators had a regulator built right into the alternator body and so no external regulator needed. The downside, as i have found many times, is that you can not adjust the max charging voltage. It is preset at the factory. You can sometimes buy new regulators to replace the one inside, but it may also have the same voltage with no adjustment (without some extreme modding that is).

Todays autos are starting to use the computer to regulate the voltage, but i dont know if that is the primary regulator or a secondary regulator of some kind. I guess it depends highly on the type of automobile it came from these days.

The older alternators do in fact run on a standard electric motor that turns at the normal speed of 1200rpm or whatever it is. That's with a pulley of about 2 inch diameter with the standard maybe 3 or 4 inch pulley on the alternator itself. So there is some gear down there but it still charges a battery. I've actually done this long time ago so i know it works. You just need a pulley on the motor and a belt, then mount the two using a plate of some kind. I used a thick fiberglass plate maybe 1/4 to 3/8 inch thick. This was probably back in the 1970's. Today however battery chargers are easy to build so you dont have to go through all that trouble anymore.

You can get lots of interesting things from junk cars. I did the same thing with an old Cadillac air conditioner compressor. Mounted it to a plate with a 1200rpm 120vac motor and old water tank, used it as a air compressor for paint spraying cars and stuff. Activated the clutch with a full wave bridge rectifier in series with a 120vac light bulb (that engages the compressor).
Used it for some 10 or more years.
 

JimB

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From the little that I do by way of working on cars these days, maybe new cars are more reliable, or I can afford new(er) ones!

So I just had a look at my two cars, Mazda MX5 and Mitsibishi Shogun, the alternators are well buried and cannot see the connectors, but I suspect that they need control signals from one of the ECUs.

Looking at old manuals from cars which are now long gone, the Austin and Rover Metro had simple alternator with controller built in, as did the VW Golf Mk2. I don't know about the Golf Mk3 or later.

At a quick guess, if you look for something from the 1980s or 1990s, the alternators will be simple and easily adapted for your intended use.

JimB
 

tcmtech

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Personally if you need to ever generate any amount of power for extended period consider visiting your local heavy equipment salvage yard and getting a commercial application alternator like a large frame type Delco, Prestolite, Bosch, Leece Neville, Motorola or such european brands equivalents.

Reason being most of the bigger units for such applications are high capacity continuous duty rated one wire capable units that will run circles around any automotive units for similar costs.

Plus unlike so many automotive units they are rated for their full output specs at 3600 RPM or less (many self excite at under 1000) whereas most automotive don't heat their peak rated power until 6000+ RPM.
 

KeepItSimpleStupid

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LG:

In the simplest for the role of the rotor and stator are effectively reversed. The rotor is a variable controlled rotating magnetic field. The stator, is 3 windings 120 degress apart. They all are combined to get DC out. The diodes are usually heat sinked to the body.

Which side of the rotor is grounded is at the whim of the designer. Some are even isolated.

A GM alternator had a nice "drop in" regulator that went inside of the alternator. You have a large post (output) that the goes to the battery and ground. Two other wires from the regulator, go to a source of +12 and the other is designed for the idiot light,

Out of those two wires, it's where the +13.8 V sense takes place and battery discharge through the regulator is prevented. There has been some changes that have occurred that through battery chemistry has altered the "float voltage", but you cannot select this.

There's very little residual magnetism and a battery is required to excite the rotor.

In AC generators without a battery, it's a requirement that the rotors are "flash magnetized", so there is some magnetism to get the AC alternator to do it's thing and start the control circuitry.
 

large_ghostman

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Great info guys thanks alot. Its just to charge a leisure battery when their is wind around (a fair bit up on our hill). The 5KW turbines have been decommissioned, I didnt want the agro of the actual turbine itself, but I have the helix type rotor. This will easily turn a alternator by a pulley.

Knowing the rough age of car to scavenge from is helpful, should also make it cheap, The battery itself is only running a 10W water pump, its a large deep cycle battery, worse case I can take it in to charge, but wind charging would be alot easier due to its site.

I had a look on my car.......Big metal case covering the engine (I assume there is an engine under it, might be a hamster). Cant even get to the light bulbs without taking the engine covers off!
 

large_ghostman

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I want a MX5!! Really nice looking cars, I would love a British racing green one.
 

dr pepper

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Hi Lg, if you only need to run a 10w pump a little alty will be enough, pretty much any nissan micra has a 55amp or so alty, regs have been built in most alty's for a long time.
There are 3 wires, bigun from the case of the alty to battery -, the larger of the 2 spade connectors is batt +, (if there are 2 large spade connectors look closely one of them will be linked straight to ground, you can usually see this from the outside of the alty), then the small terminal is for the charge indicator light up in the dash, you need to switch this to battery + through a 12v 1.2W bulb when you want the battery to charge, it'd be a waste of power to leave it there all the time, so maybe rig up a relay that closes when the mill is going quick enough to charge.
Some have actually modded a car alty so it starts on its own without the 1.2W bulb, by bunging a magnet behind the rotor, but thats a bit tricky to do.
Some later cars have a silly can bus interface to the alty using 2 wires, sometimes yellow, probably not worth bothering with one of these, even the rev counter works from this.
 

large_ghostman

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Hi Lg, if you only need to run a 10w pump a little alty will be enough, pretty much any nissan micra has a 55amp or so alty, regs have been built in most alty's for a long time.
There are 3 wires, bigun from the case of the alty to battery -, the larger of the 2 spade connectors is batt +, (if there are 2 large spade connectors look closely one of them will be linked straight to ground, you can usually see this from the outside of the alty), then the small terminal is for the charge indicator light up in the dash, you need to switch this to battery + through a 12v 1.2W bulb when you want the battery to charge, it'd be a waste of power to leave it there all the time, so maybe rig up a relay that closes when the mill is going quick enough to charge.
Some have actually modded a car alty so it starts on its own without the 1.2W bulb, by bunging a magnet behind the rotor, but thats a bit tricky to do.
Some later cars have a silly can bus interface to the alty using 2 wires, sometimes yellow, probably not worth bothering with one of these, even the rev counter works from this.
Cheers thats really useful. The actual rotor blades for the wind turbine are massive!! But they are free :D. The pump isnt running all the time, but I might stick a few 1-3W leds in the poly tunnel as well. The leisure battery is large and heavy, so I dont fancy carrying it into the work shop to charge it up :D.
 

dr pepper

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Sounds like a 110ah battery, another consideration with alty size is charge rate, a 55ah alty at full tilt would be C/2, that might be a bit much for some leisure batts, if you have the technology you can pull the reg from the alty and make your own and then implement current limit.
 

large_ghostman

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I will need to go check the battery, but from memory its way over 110ah. I got it ages ago for the boat, I think it was around £240 at the time but not sure now.

I dont mind adding current limit, I could also use any excess output for something else.
 

alec_t

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large_ghostman

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Sub-soil heating for the polytunnel? Scottish grown bananas, pineapples! :D.
And there was me thinking reading light
 
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