Alternator vs. generator on early A4

Jason K · Post by **Jason K** » Fri May 05, 2006 11:25 am

The 12V generator is dead. Should I replace it with a functional used generator (if I can find one) or with an alternator from Moyer?

I am charging two Group 27 batteries and the generator/alternator is the sole source of charging.

What are the advantages of an alternator? I'm sure it's more efficient and perhaps there are less parts to break as the regulator is internal. I suppose it's more reliable as it is certain to be much newer.

Is it worth the $450 by the time I pay for the alternator, mounting bracket and shipping? Am I missing any pros or cons?

Figment · Post by **Figment** » Fri May 05, 2006 3:39 pm

My generator works, but I switched to a basic motorola alternator when I grew weary of replacing the external regulator time and again. The alternator will probably be more reliable, but even if not, it's a heck of a lot easier to replace or rebuild.

Something goes fluky with the generator, I bring it into the rebuild shop, get a few raised eyebrows, and hear "come back next week".
Something goes fluky with the alternator, I bring it into the rebuild shop and exchange it for a "fresh" one on the spot.

My mounting bracket is a cobbled-together mess. There are times when I'd almost pay the $450 just to have a proper bracket!

I'd shop around a bit for the alternator itself. An alternator is an alternator, nothing really specific to the A4 (possibly the pulley size, but not really), so you can probably find a decent deal locally.

bcooke · Post by **bcooke** » Fri May 05, 2006 6:12 pm

What are the advantages of an alternator?

Alternators produce more power in a smaller and lighter package. Does it matter on an A4? probably not.

My personal preference is for a separate regulator rather than the built in regulators only because if the regulator goes I don't want to replace the entire alternator/regulator unit just because of a cheap regulator component. That said, both units are pretty reliable these days so it really isn't a big issue. The combo units reduce the number of parts you need to keep track of.

I will blather on for a minute concerning the differences between a generator and alternator in case any one really cares...

Electric current is produced by moving a conductor (wire) past a magnetic field. I can explain how this works but I don't think anyone really cares that much.

Generators are an earlier design that incorporates a hunk of magnetic material; hence the higher weight. These magnets can lose there magnetism so that no current is produced. The magnets can also have their polarity (the positive and negative ends) reversed so that the current flows in the opposite direction. Both of these conditions are unlikely but possible.

An alternator has no magnet. Just as an electric current is produced by passing a conductor through a magnetic field, an electric current flowing through a conductor will produce a magnetic field. By running a small current through a wire that is wound around many times, enough magnetism is produced to stimulate an electric current through the main generating portions of the alternator. Without the magnet, alternators are lighter and with more space available (since the magnet is removed) more windings of wire (the conductor) can fit inside the case. Since the magnetism is a creation of an applied electric current the polarity will never be reversed and the inherent magnetism can't be lost (since it was never there to begin with).

The real difference? Generators are just a more primitive and less efficient way of producing electric power. They both get the job done though. You might find it easier to get replacement parts for an alternator than a generator.

-Britton

Post by **dasein668** » Sat May 06, 2006 7:22 am

I was wondering about the difference. Thanks, Britton.

bcooke · Post by **bcooke** » Sat May 06, 2006 2:44 pm

Thanks, Britton.

Don't thank me too soon.

I posted my reply with a nagging feeling that I was missing something. I remembered this morning.

The other big difference is what spins and what is stationary. On a generator, the magnetic field is fixed around the outside of the case and the rotating portion is where all the output current is generated. By the design of the electrical connections which pass the output current out of the rotating portion and into the main bus, the output is DC. Also, passing the output current from a rotating part to a stationary part creates some losses and limitations.

On an alternator, the rotating portion is magnetized and the stationary part carries the output current. The high output current flows from the stationary part directly to the output terminals which is much simpler electrically and the alternator can be designed to turn at much higher speeds. With the proper sized pulleys, much more current can be produced at much lower engine speeds. The output of an alternator is actually AC but diodes built into the alternator convert the output into a pulsating DC. Sometimes you will see a capacitor externally attached to the alternator which is helping to smooth out the pulsing.

Much beyond that I really don't have a clue...

-Britton

Duncan · Post by **Duncan** » Sat May 06, 2006 4:21 pm

A generator can also serve as a "dynastarter", i.e. a combined starter motor/generator. That's about all I know about it, but I shall probably learn more when I try to get the Volvo MD1 set up later this summer.

Jason K · Post by **Jason K** » Sat May 06, 2006 4:35 pm

Thanks Britton -

That was informative. I was wondering why the generator was so inefficient at low engine speeds.

--

A resolution to the problem has presented itself. I was offered an entire Atomic 4 yesterday. It is, like mine, an early model that has upgraded to the alternator. The brackets look fine, too.

The plan is to pull the alternator off and install it in my boat, as I rely on that to charge the batteries. I then need to figure out how to pull the motor (there are a few challenges). I'll do a moderate rebuild on the new one and probably swap out the motor currently in my boat.

Rachel · Post by **Rachel** » Sat May 06, 2006 9:06 pm

bcooke wrote:
I will blather on for a minute concerning the differences between a generator and alternator in case any one really cares...

In *case* anyone really cares? Britton, Britton -- some of us just log in to the forum everyday clinging to the hope that you will have decided to blather on about something ;-)

Really, thanks. It's always interesting to hear about how something works from someone who understands it, and who takes the time to explain it.

--- R.

Figment · Post by **Figment** » Sat May 06, 2006 9:19 pm

bcooke wrote: With the proper sized pulleys, much more current can be produced at much lower engine speeds.

Right, I knew there was another reason I switched to the alternator. 85% of my engine time is spent at putt-putt speeds following the outboard and sterndrive traffic the length of the river. The generator only really did its thing at ramming speed.
When I picked it up after the second rebuild, the guy told me to "let it spin, let it breathe", and I put two and two together.

bcooke · Post by **bcooke** » Sat May 06, 2006 9:46 pm

A generator can also serve as a "dynastarter",

Yes. Generators and DC motors are basically the same thing. If you turn one you create an electric current. If you push an electric current through one it turns. I think each is 'tuned' by design to match its intended function but a basic generator can act as a motor and a basic DC motor can act as a generator.

I was offered an entire Atomic 4 yesterday

Some guys get all the luck...

Britton, Britton -- some of us just log in to the forum everyday clinging to the hope that you will have decided to blather on about something ;-)

Note: no money has exchanged hands...
Really though, it is great to hear from my fan club. Keep sending in those letters and pictures and I will continue to reply with signed publicity photos. Due to the current volume of fan mail received, there could be an unfortunate slight delay with the replies. Don't despair and keep trying.

-Britton

Post by **Tim** » Sun May 07, 2006 7:01 am

I was fortunate to beat the rush and have already received my personalized fan photo from Britton's people. I treasure it dearly, but nonetheless I have decided to share it with you all, to ease the pain of waiting for your own.

I kind of thought he'd have better handwriting, but I guess many famous geniuses have had very child-like handwriting--something about dedicating the brain power where it is needed most, I think.

Duncan · Post by **Duncan** » Sun May 07, 2006 8:34 am

Tim wrote:I was fortunate to beat the rush and have already received my personalized fan photo from Britton's people. I treasure it dearly, but nonetheless I have decided to share it with you all, to ease the pain of waiting for your own.

I kind of thought he'd have better handwriting, but I guess many famous geniuses have had very child-like handwriting--something about dedicating the brain power where it is needed most, I think.

If ever a photgraph was deserving of a caption contest, especially on the 'dedication of brain power' issue, it's this one!

My entry would be - "What are those glasses for anyway?"

Duncan · Post by **Duncan** » Sun May 07, 2006 8:43 am

bcooke wrote:
A generator can also serve as a "dynastarter",
Yes. Generators and DC motors are basically the same thing. If you turn one you create an electric current. If you push an electric current through one it turns. I think each is 'tuned' by design to match its intended function but a basic generator can act as a motor and a basic DC motor can act as a generator...
-Britton

I think you're right (I'm not surprised!). I've found some information from enthusiasts of the Isetta 300/BMW 600 microcars, which had Bosch Dynastarts.
They mention a few key features of their hybrid starter/generator setup:
- the armature has a larger diameter to generate more torque for starting
- there are "field coils" for starting and "shunt ones" for generating.
- power is fed back to reinforce the residual magnetism until output reaches charging voltage
- voltage regulation was accomplished by sort of a "make and break" on the shunt coils, which I don't really get yet.

My Volvo dynastarter only has one set of identical coils, so more to learn.
With luck (and continued tutelage), I will bring my knowledge right up to the start of the art in 1965. It's good to set attainable goals.

Would that qualify for a signed photo?

Edit: Some links from Vire engine owners. It seems that mounting an alternator (and using the Dynastart generator only as a starter motor) results in much better charging:
http://gofree.indigo.ie/~vire7/tips1.htm
http://gofree.indigo.ie/~vire7/add_alt.htm

Rachel · Post by **Rachel** » Sun May 07, 2006 11:11 am

Tim wrote:I was fortunate to beat the rush and have already received my personalized fan photo from Britton's people. I treasure it dearly, but nonetheless I have decided to share it with you all, to ease the pain of waiting for your own.

Thanks Tim! I daresay my pain has been eased considerably, although I'm sure I will not stopping running to the mailbox each time I arrive home. I can only hope mine is personalized too, and that they don't turn out to be merely duplicates, sent out by some large and impersonal agency. Might be understandable though, due to the volume of demand ;-)

bcooke · Post by **bcooke** » Sun May 07, 2006 3:56 pm

Tim wrote:I was fortunate to beat the rush...

Actually Tim, what you have is a rare early edition. Keep it safe.

Today, each letter receives one of eight photos for fans to collect and trade among themselves. Each photo shows a different pose and mode of dress ranging from standard epoxy spattered Carhardt pants and matching sweatshirt to cutoff Carhardt shorts and bare chest. Each letter receives a random photo so keep sending in those fan letters until you have all 8!

- The Big 'B"

Post by **dasein668** » Sun May 07, 2006 4:48 pm

bcooke wrote:cutoff Carhardt shorts and bare chest.

Run for the hills!

Post by **Tim** » Sun May 07, 2006 6:15 pm

bcooke wrote: Each letter receives a random photo so keep sending in those fan letters until you have all 8!

I sent in 21 letters, but I got all the same picture. I'm starting to think I may never complete my collection.

Rachel · Post by **Rachel** » Mon May 08, 2006 7:28 pm

I just had a loooooooong day at work that felt like it would never end (boatyard in spring at a place with a three/four month boating season). Although I wasn't sure anything could make me laugh at this point.... I was pleasantly wrong -- should have known I could count on you all.

Not enough energy to run for the hills; but then there was nothing in my mailbox anyway ;-)