Using car alternators

OK, so I've got an alternator from an old BMW I want to direct couple to my little JAP, the plan was to cover it up & make it look old, but as you can probably guess there is quite a lot of work involved.

I dragged it out of storage & offered it up to the engine last night, there's a small sticker on the side with amperage, voltage & a little arrow on it, I'm guessing the arrow is direction of rotation. Now, without checking under the bonnet of my car (also an old BMW) I don't know for sure which way it's supposed to spin, but if the arrow is right, then the alternator is wrong.

So my question is: Can I reverse the rotation of an alternator???

I have dismantled the unit as much as was immediately possible last night, mainly just because I like taking things apart, but I reckon I may be able to take off the stator windings & turn them round, would this be any help???

Like I said, it's a lot of work, getting it coupled up to the engine, I'm not too worried about the cooling fan, as the engine will be drawing it's cooling air past the alternator, which will keep it cool, but I would like it to produce some charge & run a few lights.

I see there's another thread on alternators, but it's in the general chat section, if anyone else has any other alternator issues by all means feel free to use this thread as a general "using car alternators" thread (as the title suggests), but I would like an answer to this question as well please.

Anyone know??? (think I can guess one or two who might, but I will mention no names, yet )

from the basic principles of an alternator it will make no diference which direction you rotate it, why?

by its nature it will generate AC, AC when generated is only given Live and Neutral by which end of the coil you choose to use as a reference to earth if you so desire to.

Ie: in a generator (or at the transformer in a sub station) for one single phase supply you will have 2 wires for your output, if you wish to provide an earth, flip a coin and choose one wire, bond this to earth via a stake and it becomes labled as neutral, use the other wire instead and that would become neutral either way leaving the second as Live. Therefore taking off your stator winding and reversing them is a pointless excercise.

As said by the nature of the alternator, it always starts off as AC, whichever way you turn it the curent will always push-pull, no good for running the dc circuits in a car let alone charging the battery which is of course DC by nature and things would get rather messy if you introduced AC to a battery. This is where the rectifire then comes in converting the AC to DC, converting the push-pull to a constant push in one direction, followed by the regulator which then regulates the voltage to keep it with the range required for the application.

Any help?
Andy

I heard you could use in either direction (old thread on here somewhere) the only problem is it could damage the brushes as they are set to turning the opposite direction and could break up turning in reverse. I think that's right it's a while since i read the article LOL and after that I don't know alot about sparks.

Stu.

stationary stu wrote:I heard you could use in either direction (old thread on here somewhere) the only problem is it could damage the brushes as they are set to turning the opposite direction and could break up turning in reverse. I think that's right it's a while since i read the article LOL and after that I don't know alot about sparks.

Stu.

usefull point Stu, but they aren't set to go in one direction, they wear in that direction much like the flint in a lighter, I wouldn't worry too much though personaly and would take my chances, or if that concerned fit a new set of brushes before use. Or run it slowly for a while in the direction you want to run it in with a vari speed drill for a while.

On some alternators the bushes are offset so those are designed to run in one direction. Not that it won't work the other way, but the bushes may bind and/or wear quickly.

Most have the bushes mounted straight though so they'll mind even less which way they turn. The only issue could be the wear on them (as blackvanman stated) but this can be sorted with a bit of fine wet-and-dry to deglaze and remove any lip - I'd give the armature the same treatment too.

Depending on the design, the fan might be directional too. I've not heard of any problems but in theory it could cause a problem if you are running near capacity. I'd say to keep a sensible speed and not too much of a load and it'll be fine.... (The preceding view is the sole opinion of the author of this post and no responsibility can be accepted for any damage caused or any wildlife injured!)

pauldg wrote:On some alternators the bushes are offset so those are designed to run in one direction. Not that it won't work the other way, but the bushes may bind and/or wear quickly.

Most have the bushes mounted straight though so they'll mind even less which way they turn. The only issue could be the wear on them (as blackvanman stated) but this can be sorted with a bit of fine wet-and-dry to deglaze and remove any lip - I'd give the armature the same treatment too.

Depending on the design, the fan might be directional too. I've not heard of any problems but in theory it could cause a problem if you are running near capacity. I'd say to keep a sensible speed and not too much of a load and it'll be fine.... (The preceding view is the sole opinion of the author of this post and no responsibility can be accepted for any damage caused or any wildlife injured!)

yes I like feeding pigeons to mechanical fans also

i would of thought it will be an old pattern bosch alternator..there bomb proof..if its a big one 130 amp it will take some driving..the only problem i can see of running it backwards is the the cooling fan will be wrong..but if its just going to run a few light bulbs i recon it will last a long time...

lister warwick wrote:..if its a big one 130 amp it will take some driving..

It'll only take as much effort to drive as you want to get out of it - if you are only pulling 10 amps it won't be any harder (mechanical disadvantage aside) to drive than a 35 amp one giving 10 amps.

I would have thought the cooling fan wouldn't have made that much difference as it will be pushing air into the alternator rather then drawing it out, may run a little hotter but not that much and running it out doors you'd hardly notice any difference in my opinion.

Stu.

pauldg wrote:

lister warwick wrote:..if its a big one 130 amp it will take some driving..

It'll only take as much effort to drive as you want to get out of it - if you are only pulling 10 amps it won't be any harder (mechanical disadvantage aside) to drive than a 35 amp one giving 10 amps.

yes i agree. but you cant just take the load from the bulbs9or what ever you want to run) into consideration.he will need a battery to energise the alternator and that will take an initial load from the alternator..i guess if he uses a 7 amp dry cell battery it cant demand much power..

OK, thanks for the replies, I did wonder why this direction arrow was on a little sticker & not cast into the machine itself. I know all about AC & DC & the difference between the two, but I really appreciate the thoughtful explanation there from Blackvanman, as this is an information post & not just for me, hopefully this will be of help to others as well

I did say, but will re-state, the cooling fan is of little consequence, as this engine pulls it's cooling air through the generator, so if I do direct couple & encase it I will probably remove the fan altogether as it will do little more than impede the flow. I believe when running in the correct direction these fans should pull air through the alternator, not push it (as I found when I had to rig up some ventilation to one I fitted in a boat some time ago) but this will be of little consequence here either, as it will be under very little load & will only have a very small sealed lead-acid battery (from a lantern or fire alarm panel or something) to excite it. I do intend to "use" it though, I seem to be in the habit of running down my caravan battery very quickly when at these rallies, so it will be used to replenish supplies there, as well as running some lights for display.

As for the brushes, this one is missing a regulator, which also houses the brushes, so I will very likely be starting from new anyway, so they'll wear whichever way it happens to be turning. I actually thought, if anything, it would be the regulator which was different for the direction of rotation on these things.

BTW, the sticker on it says "14v 65amp" which when converted into watts & then converted into Horsepower is way over what my little engine can produce, so I won't be running it anywhere near capacity anyway.

TBH I'm not even sure I want to go down this route, it's going to be very difficult to rig this up as a direct coupled unit. It would look good when done, & will make a nice little exhibit, if done well, but it's a lot of work & I don't think I have the workshop facilities available to me, & you should all know how I feel about farming work out to people, I've spent too much on this engine as it is!

If I can think up a simple way of getting the 2 bits together I will do it, but direct coupling is quite a precise business, even with flexible couplings, & I really don't want to go down the belt drive route if I can possibly avoid it.

I'll take a few pics & put them up on the JAP resto thread this week, see if any ideas come in. At least the alternator didn't cost me anything

If it's any help, an alternative is to mount the alternator in opposition to the engine like on my old Villiers with alternator. Hopefully the pic will explain.

Can I just say that anyone thinking about what to use alternator or dynamo yes the dynamo is old so it would look better but using an alternator you don't have to worry about regulators as most are built in and I think I'm right in saying (sure I'll get corrected here) you need to conect a battery when using a dynamo.

Stu.

You will need a battery to provide the initial excitation. This is usually done by wiring it through a warning lamp. After it gets up to speed it will self excite via it own rectifying diodes

Yeah, you need a battery with both types I think, although in theory you could get a dynamo to self excite.

Also, you don't necessarily need a regulator with a dynamo, you can set them up to regulate on engine speed, then the engine governor will regulate for you. But this will require some rewiring. My Tarpen has a simple dynamo on it, that is only regulated by engine speed.

You can easily make a modern alternator look old though, I've seen people put them inside an old motor case, with just the shaft & pulley sticking out, so it just looks like any other old motor/generator.

A simple tin plate surround is easy enough though. I've even seen people put them in wooden boxes (with adequate ventilation, of course).

Dynamo's will self excite because of the remaining magnetism in the armature. The alternator has such a low value that it needs the few milliamps of current through the alternator warning lamp to get it started. Running them without a regulator is not a good idea unless you have a constant load and speed or limit the field current by some means. Any change could cause the field current to rise and then the magic smoke gets out and it finished.

Yes, my Tarpen is a simple shunt wound dynamo, which has no regulator apart from the engine speed governor. But car dynamos are (I believe) a compound wound unit, so in order to run without a regulator you would need to do some rewiring, or add a resistance into the field circuit (which could look nice if it was a big sliding variable resistor with brass ends).

Probably best to stick to a regulator if you don't know what you're doing (& probably even if you do know what you're doing )