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Old 10-20-2011, 06:06 AM
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How do I check a generator?

Anyone outline the steps on checking the output (volts/amps) of a generator?
Thanx,
Ron

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Old 10-20-2011, 08:01 AM
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repair shop.

Most generator= starter repair shops and some auro parts stores will do it for free
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Old 10-20-2011, 09:23 AM
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Doing it yourself can be done and a good thing to learn, this is electrical basics at its finest. When you say generator I think a 6v system, but I assume this is 12v system and will proceed with it as a 12v.

A proper battery tester is a better way to test because you are able to load the battery and alternator as needed. You can still load the system but will not have the control like a tester will provided. Many ways to skin a cat, this is how I would do it without a tester.

You need a voltmeter.

Battery cable ends clean.

First test the battery, it all starts here. A bad battery will throw off the readings of the alternator. Measure across the battery posts, 12.6V is a fully charged battery. If it is under 12.0V charge it up. Then keep the leads on the battery and turn key on engine off then turn on heater, lights, wipers and radio as available for ~3mins. Battery should not drop below 10.5V. Then turn the key off and all accessories off and measure battery voltage after letting it sit for 5 mins. The battery should recover back to at least 12.0V +/-.6V if it drops below 10.5V during load test or 11.4V on recovery then I would suggest testing the battery with a battery tester at this point, my preference is a carbon pile loader but the testers like a Midtronic are good as well.

Once the battery is verfied, the alternator is much easier. This is just a basic DC voltage alternator test and will not test for excessive AC voltage. This will tell you if it is charging. Start the car and measure the voltage at the battery, 13V at the very minimum 16.5V maximum and rev engine to 1500rpm. If under the alternator is not charging and likey caused of a bad alternator but if PCM controlled then the feild circuit may be the cause. If higher than 16.5V then the issue is a regulator as the alternator can make the juice but nothing is regulating it. If alternator is internally regulated (most vehicles '77 and later with the exception of PCM controlled), replace alternator. If externally regulated, the regulator needs to be tested, but probably a regulator issue. If alternator is between 13V-16.5V then the system needs to be loaded, turn every accessory on, lights, wipers, heater on high, radio, everything then rev engine up to about 1500 rpm and read voltage, same-same as above as far as specs and where to go if out of specs.

Do you have a problem right now? or....?

Hope this helps
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Old 10-20-2011, 12:07 PM
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Thanks 66SSIMP

The engine is a type 1 VW with 12 v generator. I changed my rail over to an alternator, but I would like to get the full life out of this generator on the '70 Beetle before investing in the changeover.
I think I can follow your instructions. In my experience, most of these generators are fairly reliable, but new fields are getting hard to come by. Usually, a good cleaning and brushes help, so I will test it as you described. The regulator is around 3 years old, but that's also suspect at this point. The red gen light only works intermittently at startup, so there are probably other issues too.
Thanx
Ron
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Old 10-20-2011, 08:10 PM
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GENERATOR, not alternator, like you said:

You can test if its working by checking for 12v - 12.6 on the battery before start. Then start the car and rev the motor you should have over 14 volts on the battery which is the generator outputting properly. Similar to an alternator test

If theres no, or little, voltage change then you have things to check.
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Old 10-21-2011, 05:42 AM
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If I remember right.... the VW had external reg and the wire connections were a screw posts with a clamp. Those exposed bare wire connections were very prone to corrosion creeping in. I'd start be cleaning all those connection 1st, then as suggested above .... measusre the voltage across the batt terminals with the eng off, start it and measure again, running you should get 13+ volts. If it's not charging...... decision regulator or gen replacement
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Old 10-21-2011, 06:28 AM
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Thanks to all you guys for the assistance. Generator is no good per the instructions you sent. I'll try brushes first, then, as a last response, I'll have to change it over to an alternator. Two starter shops in this town, but both swear parts for the generator are more expensive than an alternator.
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Old 10-21-2011, 05:30 PM
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There is a way to make the gen go to full charge.......the only real way to rule out the regulator, unless you swap out for a known good one ....... but it's been too long since I worked on VWs and I don't remember how.
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