alternator current regulator

You picked a hard place to start. The field circuit of an alternator is not a good friend to transistors. It is very inductive. Stopping and starting the current quickly needs a highish voltage.

If you want very slow values of "quickly", you can do this:

D1 ---!

Timely question. A non-technical neighbor asked for help with a bicycle-powered stationary generator project a couple of weeks ago.

After a little Googling and thinking, I proposed an automotive alternator, SLA battery, and a microprocessor regulator that would both keep his physical workload within his comfort level and properly charge the battery. (I'm kind of proud of that "contolling the physical workload" idea. Reading about this stuff on the net, it doesn't seem to be something that anyone else has considered.)

Never having driven an alternator, your real-world experience is a great help. Frankly, I hadn't even considered this part of the problem, so you undoubtedly headed off a big 'gotcha!'

Any recommendations for the diode? I take it a 1N4004 probably isn't the one I want. (I was hoping to build the regulator out of junkbox parts. I have some nice logic-level-drive , errrr..., "MooseFETs" that would serve, but probably would have to mail-order the diode, doggone it.)

(Whether or not I pursue this is dependent, of course, on said neighbor getting off his butt and driving down to the junkyard to buy an alternator...)

Many thanks!

Tom

I believe that alternator field/rotor coils have a high-side control, so I suggest you look at "Top-FET's". HexFet's have a substantial parasitic diode too, whice eliminates the need to a serarate one. If you are serious about this, think about incorporating a permenant magnet into the rotor too. Automoticve alternators use about 25% of their output just to energise the coil !.... not good for windgenerators.

True before solid state regulators. Now most fields are low-side controlled.

Don't do that.

What planet are you from? A 70-80A alternator will use a 5A field.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
         America: Land of the Free, Because of the Brave

Somewhere around 1970 I helped a company design a "bicycle" exercise machine that used an alternator to power the electronics AND serve as a variable exercise load.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
         America: Land of the Free, Because of the Brave

Ooops auto stuff usually doesn't bring out the bottom end of the field lead Modified:

You need a "high side driver" chip or the like to drive the MOSFET.

I have with others involved. The project didn't go anywhere.

Our idea was to use a DC motor as a generator and a clever bridge booster to raise the voltage because the motor was moving too slowly to make enough voltage.

I have some nice MUR1660s in my bins of parts. If IIRC, the resistance of the coil is 4 Ohms or so. The current will be about 4A max so a heat sink will be needed.

You want a diode that can have a good het sink attached. The MUR1660 is in a TO-220 package so it would do. It has two diodes. I would parallel them.

A human can make a peak power of about 1 HP. Running aerobic, a person can make about 1/4 HP.

1HP = 746W

This tells you how much power the output side needs to handle. That is a peak current of about 65A.

The MOSFET's diode is pointing so that it will never conduct in this circuit. If you leave the diode out, you will eat the MOSFET the first time it tries to turn off.

If

GM (Delco) controls the field from the low side. I think Chrysler does too.

An automotive alternator comes with a device that "quickly and dynamically adust(s) the field current." It's called a voltage regulator. What do you want to do that a voltage regulator can't do?

Last time I did alternator regulator designs, Ford was low-side also.

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

| 1962 | America: Land of the Free, Because of the Brave

Well, I figured there was a pretty good chance the alternator he'd wind up with would have a built-in regulator, so I was planning on some surgery on it anyway. I was sorta hoping to bring out leads from both slip rings while I was at it and driving it low side.

However, if he manages to find one without a regulator and no surgery required, I guess I could use a P-channel MOSFET and optocoupler. I have those on hand.

I have absolutely no idea how to select or apply a high-side driver chip.

Which is why I chose an alternator in the first place. The ability to control the drive torque requirement was a very welcome fringe benefit.

Outstanding! Many thanks! That part isn't anything at all what I would have found on my own. You have *really* saved my bacon on this project.

That's sort of what I told him when he asked me how much power I thought something like this could produce. I used Lance Armstrong as an example of someone who could produce one HP. However, since both neighbor and I are old dudes, I told him to expect something like 50 watts sustained.

(And I'll let him see if he can maintain that level for three hours. Me? I'll hook up the data recorder, open one of his beers, sit on his couch, and watch a baseball game on his fancy new TV. And laugh at him. :-)

MooseFET, once again, many thanks. This is just terrific information. Now I'm really anxious to try my hand at this project. Think I'll put a hurry-up on the neighbor.

Tom

Cool idea!

Thanks everyone for your feedback. I really appreciate it.

-James

DQoiTW9vc2VGRVQiIDxrZW5zbWl0aEByYWh1bC5uZXQ+IHdyb3RlIGluIG1lc3NhZ2UgbmV3czow YjdhNTc2Yi1mYjY2LTQ0YzktODBmMS1kYmE2NDQ2Y2Q0NmZAczhnMjAwMHByZy5nb29nbGVncm91 cHMuY29tLi4uDQo+IE9uIEZlYiAyMiwgMzoyMSBhbSwgc2tlbm5faWUgPHNrZW5uLi4uQGVpcmNv bS5uZXQ+IHdyb3RlOg0KPj4gSSBiZWxpZXZlIHRoYXQgYWx0ZXJuYXRvciBmaWVsZC9yb3RvciBj b2lscyBoYXZlIGEgaGlnaC1zaWRlIGNvbnRyb2wsDQo+PiBzbyBJIHN1Z2dlc3QgeW91IGxvb2sg YXQgIlRvcC1GRVQncyIuICBIZXhGZXQncyBoYXZlIGEgc3Vic3RhbnRpYWwNCj4+IHBhcmFzaXRp YyBkaW9kZSB0b28sIHdoaWNlIGVsaW1pbmF0ZXMgdGhlIG5lZWQgdG8gYSBzZXJhcmF0ZSBvbmUu DQo+IA0KPiBUaGUgTU9TRkVUJ3MgZGlvZGUgaXMgcG9pbnRpbmcgc28gdGhhdCBpdCB3aWxsIG5l dmVyIGNvbmR1Y3QgaW4gdGhpcw0KPiBjaXJjdWl0LiAgSWYgeW91IGxlYXZlIHRoZSBkaW9kZSBv dXQsIHlvdSB3aWxsIGVhdCB0aGUgTU9TRkVUIHRoZQ0KPiBmaXJzdCB0aW1lIGl0IHRyaWVzIHRv IHR1cm4gb2ZmLg0KPiANCg0KDQpOb3QgYWx3YXlzIHRydWUsIEkgaGF2ZSBpdCBvbiBpdCBzdGls bCBkaWVzLiAgVGhlIENhcCBpcyBpbXBvcnRhbnQgdGhhbiBkaW9kZSBpZiB5b3UgZGVhbCB3aXRo IGtpY2tiYWNrIGFjLg0K

I think you are right. My first version of the circuit would be correct in that case.

The wiring I was remembering was for an alternator with build in regulator. There was a wire for charging the battery and another for, I guess, powering up the regulator circuits.

g

=A0 =A0 ...Jim Thompson

=A0 =A0 | =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 =A0 =A0 |

=A0|

=A01962 =A0 =A0 |

uoted text -

yes, this is what I am trying to build: An exercise device load where the reactive force is proportional to the speed of the movement.

Thanks, James

A aluminum (copper if you're rich) disk and some old hard drive magnets. If you don't need power out, works well with no fuss - just eddy currents in the disk (ultimately resulting in heat). To make it variable beyond "faster is harder), make some of the magnet pairs able to be moved away from the disk.

If you want power out, better to glue magnets to a disk, and spin it in coils, avoids brushes, commutators, and such-like failure-prone moving electrical parts. Some home wind-power folks have nice web pages about building moving-magnet generators/alternators (and the rest of the wind generator).

The page about what they've learned over time (Wind turbine evolution) is well worth reading.

--
Cats, coffee, chocolate...vices to live by

...

[10 line sig snipped]

He doesn't listen. Most of us just trash the junk.

Cheers! Rich

GM used to be low side, with a secret "ground here for a full field test" tab. Ford was was the other way, as I recall.

-- A host is a host from coast to snipped-for-privacy@nrk.com & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433