Using an old car alternator to generate electricity...

[RebelRider.Mike]

I have an old alternator off a 1981 Civic Wagon. The engine is kaput, but it still has lots of good parts. Like the alternator.

I made a note of each color wire was attached to the alternator before removing it, and also found a wiring diagram so I could identify the function of each connection:

F: field coil +
E: field coil -
B: power coil +
N: power coil -

For anyone who doesn't know, (I sure didn't) alternators don't have permanent magnets in them. So in order to generate a magnetic field, power must be applied to the field coil. This means you have to put power into the alternator to get power out. This took a while to wrap my brain around.

By the way, "field coil" and "power coil" may not be the proper terms for these components. I'm still learning this stuff. But at least they're descriptive, right? Also note, this alternator has no voltage regulator. Second Generation Civics have an external voltage regulator, which I won't be using.

So a 12V battery on the field coil terminals will generate the magnetic field, and a multimeter or light bulb on the power coil terminals will tell me if its working. Also, its seems like a good idea to ground everything to the alternator casing, since that's how it's done in the car. Here's a diagram of how I plan to wire it:

There's a couple features on this diagram that I haven't used yet. The switch to the battery, and the jumper from B (power coil +) to F (field coil +). Those I'll add later to try to make the field self-sustaining. For now I just want to see if I can make it work. Here's my actual wiring:

Well, the wiring is a mess, but I used a motorcycle battery for the field (which drew about 1.5A) and a hand drill to for rotation. It worked! The multimeter read around 15V, and when I hooked a light bulb up to it, nice and bright. Next is to clean it up better and put it on some kind of jig and replace the jumpers with proper wiring. Also, I need to find out at what RPM the alternator is meant to be used, and how many Amps can be safely drawn from it.

 

[Harold in CR]

Don't know if you are capable, but, if you take the alternator apart and carefully/forcefully separate the 2 halves of fingers/claws on the rotor, you can remove that field coil inside and replace it with 2 ring magnets and press it back together. Then you don't need the brushes that will eventually wear down AND, you won't need a diode in line from the low voltage source to the field winding, which will use energy and then drain energy once the alternator is not functioning.

Look up the year and model of the car and see what the alternator rating is. Should be between 25-50A depending on accessories, AC, etc. If you go the magnet way, you will get a variable floating voltage and the battery will control the voltage part. You will still need a way to control current flow for charging and top off of batteries, IF batteries are your end goal.

Post more info for more assistance.

 

[Dauntless]

Don't know if you are capable, but, if you take the alternator apart and carefully/forcefully separate the 2 halves of fingers/claws on the rotor, you can remove that field coil inside and replace it with 2 ring magnets and press it back together. Then you don't need the brushes that will eventually wear down AND, you won't need a diode in line from the low voltage source to the field winding, which will use energy and then drain energy once the alternator is not functioning.

Is this good while you're still using it on a car? If so why do they build them the way they do?

Do they still make cars with as little as 25-50 amp alternators? I read that my Mustang is 135a and my diesel pickup is 143a.

 

[Hwy89]

Fun to play around with. What do you plan to use to spin the alternator?
As is, it will probably need to spin around 1000 RPM to produce a useable amount of power. If you strip the wire off the stator and re-wind it with 20 or 22 gauge magnet wire you can start producing at much lower rpm.
A few years back I modified several old Delco alternators into PMAs (permanent magnet alternators) and installed them on home built wind turbines. They worked well and produced some decent but unreliable power. It all came to a halt when after a storm my neighbors found one of my hand carved pvc pipe blades sticking up in their garden 400 feet away and on the opposite side of my house. I never located the other two blades. Needless to say, I quit putting up wind turbines. Solar panels are not as exciting and much more reliable.

 

[Harold in CR]

Dauntless, he stated it was a 1981 auto and he posted under alt energy section. According to my search, it's a 50A alternator.

OEM wants to build stuff as cheap as possible.

 

[spinningmagnets]

There is a website called "Otherpower.com", which is about alternative methods of generating electricity for an off-grid home. they have a chat forum called "fieldlines" which has some older posts in their archive for using car alternators. These posts have quite a bit of conversion detail, and there is also quite a bit of information about swapping-in permanent magnets, if you like.

 

[billvon]

Is this good while you're still using it on a car? If so why do they build them the way they do?

Because the field winding allows you to regulate voltage without a separate buck/boost converter. With a permanent magnet, your output voltage is set by alternator speed.

 

[spinningmagnets]

One of the curious features of the common car alternator construction is, the way that they provide 12V.

In the older style of simple and in-expensive generators (often found at 6V before the 1960's), they only made their designed voltage at the highest RPMs. When the motor was at idle, the voltage would sag, and for instance...the headlights would dim slightly. After WWII, higher quality gasoline at a higher octane became readily available. One way to make more horsepower from the same size of engine is to raise its compression ratio. Of course, that requires a higher-octane gasoline (which was just then available) but it also meant that the starter motor had to work twice as hard to spin the engine fast enough to start the engine.

You could either double the size of the 6V generator and wires, or...double the voltage and keep the starter the same size. This was such a big change, that manufacturers decided to also include a design feature that would improve the low-RPM voltage. Modern alternators are designed to provide 14V at idle, and when the RPMs start to climb, the part that directs some of the current to the excitation electromagnets will begin to 'weaken' the voltage, so instead of the output voltage climbing, it stays at around 14V at all RPMs.

This is relevant because...if you bypass that voltage controller, and feed the output voltage directly into the excitation electromagnets?...the output voltage will rise with the RPMs.

Some 120V devices require AC to work properly, but charging a 48V off-grid battery, or powering a 120V incandescent/filament light-bulb will work fine on 120V DC. If you bypass the bridge rectifier (which converts the native AC of the "alternator" into DC for the car) you would have 120V AC.

Since the output voltage is dependent on the RPMs of such a converted car alternator, this could be useful to someone in a remote location where you needed a portable generator for a 48V ebike battery. I am of the opinion that if you want to make a generator based on a car alternator, one of the easiest engine conversions is a gasoline-powered grass edger, specifically the style which uses a vertical blade and is driven by a fan-belt (HORIZONTAL-shaft engine, example below is a random pic taken from the web). These are also easily converted to running off of propane, natural gas, moonshine, and wood-gas...

 

[RebelRider.Mike]

Don't know if you are capable, but, if you take the alternator apart and carefully/forcefully separate the 2 halves of fingers/claws on the rotor, you can remove that field coil inside and replace it with 2 ring magnets and press it back together.

Thanks, I looked into that, and the rotor is packed together so tight, I can't get it apart, even with a wheel puller, without damaging it. If I can come up with a new shaft, there's lots of different designs I've seen of rotor magnets. I'm not ready to dismiss the idea just yet.

 

[RebelRider.Mike]

Is this good while you're still using it on a car? If so why do they build them the way they do?
Do they still make cars with as little as 25-50 amp alternators? I read that my Mustang is 135a and my diesel pickup is 143a.

I initially thought that the voltage regulator takes the output from the alternator and limits it to around 14V. That's how my motorcycles work.
But on a car its different. The voltage regulator controls the intensity of the electromagnetic field, which in turn regulates how much Voltage the alternator puts out. By doing this, the alternator can put out a constant voltage regardless of RPM. A permanent magnetic field would not be variable, and so there would be a huge difference between Voltage at idle, and voltage at top RPMs. How much? I don't know, but I imagine that the Voltage bucker needed would be huge. Compared to a little thing controlling the magnetic field.

I've only just got my brain wrapped around this in the last couple days. See: this is stuff I wouldn't know if I wasn't playing around with this thing!

My little car has very little power requirements compared to modern cars with their fancy electronics and sound systems, and safety systems, and heated seats, and door locks... etc. I haven't found specific specs for the car, but the remanufactured alternators all seem to put out around 45A or so. Makes sense, as there's a 55A fuse protecting the rest of the electrics from the alternator. Apart from the ignition system, my car has just a few lights, wipers, and a radio with two tiny speakers. Just doesn't need much power.

 

[RebelRider.Mike]

Fun to play around with. What do you plan to use to spin the alternator?

For now, I'm thinking of putting it on a stationary bike. Maybe charge batteries or something. I could certainly use the exercise! I can see that for a wind turbine, it would pretty much have to be modified to a PMA, or you'd forever have to be figuring out how to initially excite the field coil between bouts of wind! I'd like to have a wind generator someday. Solar is nice, but its cloudy and rainy a lot where I live, and usually the rain brings wind, so both would be much better for me than either one. I've seen folks building these vertical blade things more like a squirrel-cage on its side rather than the traditional fan-blade type. Seems like it would be more stable and safer if it goes down in a windstorm.

Back to exercise though, I wonder if I could convert my treadmill to make power instead of using it. To me, exercise seems like a whole lot of work without getting anything done. Maybe if I were producing electricity...

 

[Hwy89]

I hooked up one of my DIY PMA alternators to a Schwinn stationary exercise bike and mounted a 12 V portable TV in front. You will be amazed at how much work it is to pedal enough power for even a small TV. Sold that contraption in a garage sale right away.

 

[RebelRider.Mike]

There is a website called "Otherpower.com", which is about alternative methods of generating electricity for an off-grid home. they have a chat forum called "fieldlines" which has some older posts in their archive for using car alternators. These posts have quite a bit of conversion detail, and there is also quite a bit of information about swapping-in permanent magnets, if you like.

Thanks, I've started reading through that forum.

 

[amberwolf]

To me, exercise seems like a whole lot of work without getting anything done.

You could leave the motors turned off on the ebikes, and ride them as pedal bikes to your destinations. That would get you more exercise while getting something done.

 

[RebelRider.Mike]

I hooked up one of my DIY PMA alternators to a Schwinn stationary exercise bike and mounted a 12 V portable TV in front. You will be amazed at how much work it is to pedal enough power for even a small TV. Sold that contraption in a garage sale right away.

That's a good point. With the electromagnet, the field could be made weaker and therefore the rotor would be easier to turn. No sense in putting work into electricity I don't need. Sounds like PMA vs. EMA would depend on the application.

If I do get this working on a bike, I think I'd hook up a momentary switch to get the magnet started, and then a variable resistor between the output and the field + to vary the field intensity. Put both of those on the bike handlebar, along with a charge controller for a battery. So much stuff to think about!

I can envision the house at night, with the lights going on and off every time I push down on a pedal, LOL.

 

[RebelRider.Mike]

To me, exercise seems like a whole lot of work without getting anything done.

You could leave the motors turned off on the ebikes, and ride them as pedal bikes to your destinations. That would get you more exercise while getting something done.

Hm...
Perhaps I'll charge the eBike with the "power bike".

 

[billvon]

That's a good point. With the electromagnet, the field could be made weaker and therefore the rotor would be easier to turn. No sense in putting work into electricity I don't need.

There ain't no such thing as a free lunch. You get the power out that you put in, minus efficiency. Changing field strength just changes the RPM vs voltage relationship.

 

[RebelRider.Mike]

That's a good point. With the electromagnet, the field could be made weaker and therefore the rotor would be easier to turn. No sense in putting work into electricity I don't need.

There ain't no such thing as a free lunch. You get the power out that you put in, minus efficiency. Changing field strength just changes the RPM vs voltage relationship.

That's exactly my point. Less power needed means I can get away with a weaker field. Which means less resistance to turning the rotor. No point working hard to generate 630W if I only need 30W.

 

[billvon]

That's exactly my point. Less power needed means I can get away with a weaker field. Which means less resistance to turning the rotor. No point working hard to generate 630W if I only need 30W.

What I'm saying is that you load the alternator (or generator) less the resistance goes down. You don't need to muck about with the field - just draw less from the output.

 

[RebelRider.Mike]

Ok, I see what you're saying. The thing is though, that the resistance goes down with less power draw because the regulator is mucking about with the field automatically. A PMA can't be regulated that way, so the resistance would be the same regardless of power usage.

 

[billvon]

Ok, I see what you're saying. The thing is though, that the resistance goes down with less power draw because the regulator is mucking about with the field automatically. A PMA can't be regulated that way, so the resistance would be the same regardless of power usage.

Sort of. The PMA has the added issue that output voltage is directly proportional to speed. So you'd have pedaling resistance based on your load.

If it's a light or LED or something, then resistance felt will be proportional to speed.
If it's a battery, you'll feel zero resistance below the battery voltage and then a lot of resistance past the battery voltage.
If it's a switcher then you will feel very odd things. Below LVD no resistance. Then when you get above LVD you will suddenly feel a LOT of resistance. It may cut in and out suddenly as you go above and below the voltage. The pedaling resistance will the drop as output voltage increases, because the switcher will keep output voltage (therefore power) constant.

 

[RebelRider.Mike]

Well, it doesn't look like I can get the rotor apart without breaking it. If I want to experiment with magnets I'll have to make my own shaft and magnet assembly. I'm leaning back towards keeping the original rotor anyway. A fellow from the old Honda Civic forum suggested I use the original external regulator rather than messing with resistors and switches and such. That struck me as a pretty good idea. Although, it means learning how the regulator works so I know how to wire it.

Starting with blowing up the wiring diagram to a horribly blurry size, I took a look at how the internal wiring is done.

I also took a really close look at the actual regulator.

I'm amazed at how clean and new the upper half looks. Anyway, with that stuff to look at, I've come up with what I think is an easier to understand diagram of my own.

It looks like one coil/switch is for the field coil, and the other coil/switch provides power to the first coil/switch.
The first coil/switch operates based on how much voltage there is in the system, and the second coil switch operates based on current returning through the negative back to the power coils.

I think the blue wire is only there for the dashboard warning light. See, the light already has a positive and ground on it, as well as this blue wire. So as long as the second switch is connected to power, voltage across the bulb will be the same, so no current. If the second switch is grounded, now the other wire on the bulb will send current to this new ground through the blue wire. Letting you know that there is no current getting back to the power coils through that coil/switch. That's my best guess anyway.

So with all that figured out, I can add the regulator back onto the alternator and have some nice automated power regulation. Here's what I've come up with for wiring so far:

Well, my parts are all clean and painted up nice, so time to put some of this guess work into practice and see what blows up.

 

[RebelRider.Mike]

Sort of. The PMA has the added issue that output voltage is directly proportional to speed. So you'd have pedaling resistance based on your load.

Interesting. I didn't know that would be the case. I'm thinking at some point, if I can come up with a good way to make a new shaft or two, I'll experiment with different magnets, configurations, loads, and see how it all works.

I got the alternator and regulator reassembled, and wired according to the diagram I posted earlier.

It works! The battery starts out sending about 1-2A to the field coil, and the voltage sags to around 12.9V (I think this battery is on its way out.) I used a hand drill to spin the alternator up to around 1100 RPM, and the Voltage increased to around 13.1V, and I measured around 0.5-1A heading back into the battery.

On the regulator, the second switch, the one affected by the current to the power coil ground, behaves exactly as it should. The first switch, which regulates current to the field coil, didn't get a chance to perform, as the Voltage never got high enough. But pressing the switch manually, did cause the magnetic field to be reduced. I was able to observe this as a reduction in Voltage, Amps, and rotational resistance.

So I'm pretty pleased with these results! I'm thinking though, that bypassing the 11 Ohm resistor in the regulator will allow more current to flow to the field coil, and allow the alternator to produce more power at lower RPM. Sure, it would turn with more difficulty, but I don't know what kind of RPM's I can expect from attaching it to a bicycle wheel. Well, it won't matter until I get a belt in the mail and a bike set up to run the thing. I read somewhere, that alternators can spin up to 5000 RPM. 1100 certainly doesn't make much more than what's needed to run the coil.

 

[billvon]

So I'm pretty pleased with these results! I'm thinking though, that bypassing the 11 Ohm resistor in the regulator will allow more current to flow to the field coil, and allow the alternator to produce more power at lower RPM.

Two potential problems:
1) You might burn out the field coil
2) The field coil might take so much power that you are net negative (i.e. it takes more power than it generates.)

 

[RebelRider.Mike]

I got the alternator attached to the bike. Its ugly, but its all just stuff I had laying around. The only expenses so far have been a spring and the belt.

It's hard to pedal and look down at the multimeter at the same time, but I think I'm getting a little over half an Amp back into the battery at top gear. If I pursue the project further, I'll add an On/Off switch, variable resistor (for the field coil) and a V/A meter to the handlebar. A nicer looking platform with a battery mount would be good too.