Understanding a generator

[31nash880]

Have read about problems with generators but info is widespread. 

Questions that need answers in one place

1) It was working and quit, what now?

2) Just bought it, now what?

3) Was removed for whatever reason and now not charging, reverse charging,  over charging. How does one start to fix?

 

Personally I am working on a 1931 Nash 880. Generator was removed for engine access reasons. When reinstalled ammeter seemed to read as a draw on current rather then charge. When engine reverse dash lights became very bright. Now I either blew a fuse or all bulbs. Where does one start? 

Please relate in novice terms.

I have included a pic because I have no idea if box on top is orginal or needed or bad.

[TerryB]

At first look it seems that box on top is a generator cut out relay, possibly a newer replacement type that uses electronic diodes rather than a mechanical relay that was used in the original design. The job of the cut out relay is to disconnect the generator output from the battery when the engine is not running.  If the cut out fails, the battery stays connected to the generator when the engine is not running which discharges the battery rather quickly.  

[Grimy]

Those of us with cutouts (mechanical, not electronic) would be well advised to develop the habit of glancing at the ammeter in the first few seconds after the engine is shut down to ensure that the ammeter is at zero.  If the ammeter is showing a discharge, your cutout is stuck and you're at risk of a fire.  In such case, disconnect the battery immediately.

[Bloo]

2 hours ago, 31nash880 said:

Please relate in novice terms.

 

This system appears to be a third brush generator with a cutout. The system has some fairly large limitations by modern standards, but will work fine when set up and adjusted correctly.

 

They ONLY regulate current (Amps). Current ls like flow. They do not regulate voltage. Voltage is like pressure.

 

One thing I want to get out of the way before going further (and before I forget to say it). NEVER run a system like this (a third brush generator and a cutout) with the battery disconnected. The unregulated voltage will go really high and try to burn out the field coils in the generator. It might also burn out other things that happen to be turned on (lights, etc.).

 

The current is regulated by the position of the third brush. It is adjustable. The brushes are under that band you see on the back. If you move the third brush (small brush) closer to the big brush it is closest to, the generator charges more (Amps). If you move it away from the big brush it is closest to, the generator charges less (Amps).

 

Generators in general, with very few exceptions don't charge much at idle. On a third brush generator, due to the limitations of the third brush regulation, the generator has some particular RPM where it does it's best. Maximum charge is at some particular speed (in high gear) and if you go faster or slower than the ideal speed, it charges less.

 

The next thing to understand, and this is really important, is that since there is only current (Amps) regulation, and no voltage regulation, the generator will keep doing all it can for the particular speed and the particular third brush setting no matter what. When the battery is fully charged, the generator does not know or care. It keeps charging as if nothing has changed. This is why third brush systems have such low output current (Amps). If the systems were really big and had more current available the battery might just explode. As it is, the battery takes quite a bit of abuse.

 

A battery is just essentially a storage tank for energy. Car batteries used to be rated in "amp hours". Many still are if you read the fine print. For instance if you start with a fully charged battery and take 10 amps out for an hour, you'd have to put 10 amps back in for an hour to charge it back to the same level, or 1 amp for 10 hours, or 2 amps for 5 hours... etc. This isn't 100% true, there are losses, and there are limits to how fast you can charge a car battery, you can't just throw it 10,000 amps, and so on. It is mostly true though.

 

The ideal way to have a third brush set, is so that when the person using the car gets home and shuts the car off at the end of the day, the battery is just full. If the car runs longer the battery will overcharge. If the battery is still undercharged when he gets home, the battery will get a little deader over the course of a few days. In practice, batteries had to take some overcharging, and filling station attendants had battery water readily available. The batteries had often been running hot and needed it. Batteries of the era needed water added anyway, but overcharging stresses the battery and makes the situation a lot worse.

 

There was no expectation in 1930 or so that you could drive all night with the lights on without the battery going dead. The reason goes back to the maximum current the third brush is set to. Lets say you have two 21 candlepower headlight bulbs running. That's about 5-1/2 amps, and you've got a tail light, and some dash lights, lets say (just pulling numbers out of the air) 7 amps total with no radio or electric wipers or anything like that. A normal third brush setting is meh... maybe 7 amps. If you add the lighting load to that, you'd have to run the third brush at 14 amps or so to keep it the same at night. That's completely impractical unless you only drive at night. If you set it at some compromise setting, the battery will get hotter than normal at some times in the day and go slowly dead at night. If you get bigger bulbs, the problem only gets worse. I believe this is a reason, probably one of many reasons, the folks who owned these cars when they were new seemed to never want to drive at night, even later on, in more modern cars.

 

Of course, If you were planning to drive all night to get somewhere quickly you could always move the third brush yourself, or have the guy down at the filling station do it.

 

There's the background, some of it anyway, that you need to understand the generator. I have to go now, and probably wont be back for several hours. I imagine by then you will have plenty of hints from others on how to troubleshoot. I might have some hints of my own when I get back here.

 

Edited March 3, 2023 by Bloo (see edit history)

[Oldtech]

Reading the original post. First battery polarity. Is the car negative or positive ground? did sumbuddy hook it up backwards. If so, and that is a solid state cutout, it is toast.  If the battery is backwards you will get a charge reading when you turn on the lights with the engine off, and a discharge reading when it is charging.  Second: make sure there is no draw with the engine off.  Once you have that straight you could jump the 2 contacts on the cutout with the engine running,  and see if it charges. If yes, cutout is bad. if no... we carry on. 

[Dave39MD]

Generators need to be polarized if removed or worked on. Should be something in your manual on how to do it.

 

Dave

[60FlatTop]

As I was going up there were a lot of automotive factory training manual at swap meets. Many were in the $1 pile. I don't think I ever bought one that I didn't sit in the living room and read cover to cover.

 

I remember having this one. I posted a link to one on Ebay for sale right now.

 

An Autolite training book would also be helpful. The introduction of an old engineering book I read advised the reader to study a great diversity of things to better equip yourself to understand the specific items. I took that to mean if it is in the dollar pile take it and read it. And this is $20 information.

 

https://www.ebay.com/itm/285148835763?hash=item426431efb3:g:nq8AAOSw1mBjI5Eb&amdata=enc%3AAQAHAAABADf8PP8loQccGXjvFSW0VhJemrQi1vCcRRlbqMrBao0PtDVpRvvbHAu3q7Fb8JKyoLKRl%2BOW0glrvlYicndXAChlF4PkdJCVjyQu4ClTo95Xt5L1D0hEWGWZU5NYzw8dJC%2BTeskk4P5V%2F6cGPVYNHPSaQK4SuSASvmsJo%2B25mjHHH933gDjkvvfoWCYtd0yBLl5mCc%2Bb5%2B1QZrln7sUEwcJ8bTEZo93C2Oo35okxIg0AQGmQj9sbWbP9qzBntvdD%2FG2VDBTXDTUEs1JbgGULSQhzdtEz5pDJ8LAv%2BPRr%2BfQEgzadqg3oUC4OuxJvA6YsMXJe1zytGZWz3z09YT5209w%3D|tkp%3ABFBMmujAqtZh

 

 

https://www.ebay.com/itm/285148835763?hash=item426431efb3:g:nq8AAOSw1mBjI5Eb&amdata=enc%3AAQAHAAABADf8PP8loQccGXjvFSW0VhJemrQi1vCcRRlbqMrBao0PtDVpRvvbHAu3q7Fb8JKyoLKRl%2BOW0glrvlYicndXAChlF4PkdJCVjyQu4ClTo95Xt5L1D0hEWGWZU5NYzw8dJC%2BTeskk4P5V%2F6cGPVYNHPSaQK4SuSASvmsJo%2B25mjHHH933gDjkvvfoWCYtd0yBLl5mCc%2Bb5%2B1QZrln7sUEwcJ8bTEZo93C2Oo35okxIg0AQGmQj9sbWbP9qzBntvdD%2FG2VDBTXDTUEs1JbgGULSQhzdtEz5pDJ8LAv%2BPRr%2BfQEgzadqg3oUC4OuxJvA6YsMXJe1zytGZWz3z09YT5209w%3D|tkp%3ABFBMmujAqtZh

Edited March 5, 2023 by 60FlatTop (see edit history)

[TerryB]

Generator polarizing 

 

[dodge28]

Grimy has the answer. Look for the solution later. If not attend to and  leaving  the battery connected it can burn the unit in minutes.   

[EmTee]

Look here: https://www.delcoremyhistory.com/trainingmanuals.htm

[31nash880]

EmTee, 

I'm not sure I feel educated enough to read that. Alot of great info. Thank you.

In my case, I had left the battery connected, not the best idea, but when I came back to it a day or so later, everything worked properly.

Thanks to all for your help and wisdom.