• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Newbie question about charging system

Share this page

M

mgless

Senior Member
Country flag
Offline
Hi all. So my "new" Sprite has the ignition light on at all times while the motor is running. Battery registers about 12.2v when the car is off and 12.2v when the car is running.

The PO told me he had the original generator rebuilt last year, but he suspected that it still wasn't working. I tested the generator using the procedure in the Bentley manual (run a wire between the two terminals, then run a multimeter between that and ground.) It came out at .23v.

So... I ordered a new generator from VB. I'm wondering if I should get a new voltage regulator as well. It says Lucas on it, so it might be original. He also gave me a few buckets of parts, one of which contains a old corroded looking regulator, so I'm not sure.

I don't plan on ever adding a radio or anything so didn't see the need to go to an alternator at this time.

Once I get this tackled, I'll move on to figuring out why most of my guages don't work. /bcforum/images/%%GRAEMLIN_URL%%/smile.gif

Also, I assume that "new" generators need to be polarized?
 
It's probably a good idea to check out the regulator and replace it with a new one. Also make sure the fanbelt is okay.Generator will need to be the same polarity as the car.

Stuart. /bcforum/images/%%GRAEMLIN_URL%%/cheers.gif
 
Pay close attention to the new regulator if you buy one. There may (or may not) be a notice on its case telling you to use a solvent soaked rag to clean BETWEEN the contact points inside. It's a good idea to do this even if there is no label. Apparently the new units from some sources are shipped with a Cosmoline type coating on the points and failure to remove it is effectively the same as installing a non-functional regulator.
 
Now that is an excellent idea, will try that for sure.
 
Okay, so I got the new generator in the mail today and have the old one pulled off the car for future refurbishing...

The new generator has "neg earth" stamped into the metal housing. I thought generators didn't care one way or the other?
 
Generators are polarized. One of the steps in converting an BE to Negative ground involves polarizing the generator.
 
I just thought it odd that it had neg ground stamped into the side of the metal when it can be used either way. I guess that just means it comes polarized negative from the factory.

I'll give it a shot.
 
In any case polarize it when you put it on.
 
A generator will put out a positive voltage with a positive voltage on the field coils, or a negative voltage with negative on the field coils. The field coils simply generate the magnetic field that runs the generator; reverse it, you reverse the output.

Now, the problem is this: you need generator output to power the field coils, but you need powered field coils to get generator output. So, how do you start the whole process? The field coils tend to magnetize the metal in the generator, so you have a weak magnetic field in the coils at start-up. Then, as the generator builds up voltage, it energizes the field, which allows more voltage, and so it goes. So, that original magnetic field HAS to be right, or you get the wrong output. The easy way to assure this is to "flash" or polarize the generator by briefly connecting the battery output to the field. So, it seems that this is worth doing for any new generator. Won't hurt, in any case.

By the way, when you flash the coils, keep your pinkies away from the terminals. When you disconnect the wire, you generate a momentary large voltage at the terminals, which is why you get an inordinately large spark. Same principle as the ignition system.

It's always seemed to me that you could get the original current in the field coils from the battery, and then you wouldn't need to worry about this. Probably would require an extra relay or something, or switching the highly inductive load might burn the ignition switch. I can imagine the Lucas guys being so very proud of themselves for getting the thing to start up without any initial power, so the generator could even charge a virtually flat battery! Let 'em feel happy, I guess.
 
Back
Top