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Sort of O/T - Generator versus Alternator

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The other week my son left the radio on in one of the cars and killed the battery which was brand new. I put the battery on a trickle charger (an old battery tender unit) and got it back and charged.

My question is, the car has a generator not an alternator and I don't know enough about electrical things and the differences between the two to know the charging (re-charging) properties of a generator.

I mostly drive the car only around town, so I've been intentionally not shifting to a higher gear (running 40 in second gear or 60 in third gear) with the perhaps naive thought that this will additionally charge the battery.

Does a generator recharge the battery only at higher rpms, or at any rpms?

Is that an unanswerable question because it really matters on the particular electrical design which varies by cars with generators?

Any knowledge / comments would be helpful. I don't really want to purchase a new battery after just buying one, but I also don't want to have a dead or weak battery from driving around town mostly (the car's starter doesn't engage unless the battery is strong).

Any society that would give up a little liberty to gain a little security will deserve neither and lose both.

Benjamin Franklin

73 tii (Verona, survivor, owned since '92)

66 DS21 (most technologically advanced car of the 20th Century)

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YOURE ABSOLUTELY RIGHT = Alternator Or Generator,

your short duration drives should be at higher

rpm so either charging unit puts out the max

during the short time the car is run.

You can see it better if you attach a volt meter

to monitor the charging while you drive,

and test the batteries often with key off to

monitor their state of charge. Every time

you let a battery voltage drop below full charge

you lessen it's life, and it's ability to regain

a full charge.


Is my generator charging?

If you have a voltmeter, here are some easy

tests to make:

Measure the voltage across the battery.

Should be about 12.6 volts with the engine off.

As the engine speeds up, the voltage should increase

to somewhere around 14 volts. If it does, the

generator is working and charging the battery.

If the voltmeter does not go up with the engine

running, first check to see that the generator

brushes are not worn excessively. If you can,

apply a little pressure to the brushes while the

engine is running and see if the gen light goes

out or the voltmeter reading increases.

If it does, the brushes may be worn to the

point that they don't exert enough pressure

on the commutator.

'86 R65 650cc #6128390 22,000m
'64 R27 250cc #383851 18,000m
'11 FORD Transit #T058971 28,000m "Truckette"
'13 500 ABARTH #DT600282 6,666m "TAZIO"

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A simple web search will give you enough info regarding the difference between the two:


Upgrade/update your gen to an alternator. Get it from these guys on ebay:


they're great guys (I picked mine up from them), and the alternators are very well made.



73 tii #2764014

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In terms of design, a DC generator is the simpler

of the two. In fact, a DC generator can be used

as a DC motor by applying power to the shaft,

(this how an Isetta starts ! generator/starter)

while the opposite is also true--turn the shaft

of a DC motor, and it will act as a generator.

This is one of the greatest benefits of a

generator: It will generate power purely

from mechanical motion. As long as you

turn the shaft, the generator

will produce electricity.


'86 R65 650cc #6128390 22,000m
'64 R27 250cc #383851 18,000m
'11 FORD Transit #T058971 28,000m "Truckette"
'13 500 ABARTH #DT600282 6,666m "TAZIO"

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Heh, I agree- but in terms of FUNCTION, the alternator is the simpler design!

Since it can regulate how much power it produces (largely) independently

of RPM, it's more efficient. Since it doesn't use brushes and a segmented commutator

(only slip rings) it's lower maintenance and mechanically robust.

But, then, there's the regulator, and that has to be a bit more clever.

However, you can also bypass the regulator and 'excite' an alternator

manually. Crank up the amps, baby!

As to your question, as long as you're significantly over idle, it should charge

just fine...

If not, might I suggest a nice, sexy.... alternator???



"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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