On 2016-06-12, Jeff Liebermann wrote:
On Sun, 12 Jun 2016 11:33:39 -0500, Ignoramus13864
wrote:

I have a forklift with a Detroit Diesel 3-53 engine.

Unfortunately, the alternator on it does not charge at engine idle.

At idle it rotates at 1,250 RPM (measured with my tachometer).

That may be normal:
http://www.thesolar.biz/Balmar%2070-SeriesDIMENSIONS.jpg
Notice that it starts charging at about 1200 RPM.

Right

If I push on gas, it charges.

This alternator is a rebuilt alternator.

Oh-oh. Was this a rebuild, or an exchange? If exchange, was the
pulley diameter the same as the original? Methinks you should check
if it's the correct diameter pulley (including the belt depth and
fit).

It was an exchange. I did not check closely when it was exchanged (my
guy went to that shop, not me).

What I know is that the pulley that I have right now is the smallest
practicable pulley.

Someone told me that I should change the regulator on this alternator
to make sure that it does charge at idle.

Nope. If it's charging normally at higher RPM's, and it's not over
charging the battery, it's probably working normally. Minimum
charging RPM is set by the pulley diameter ratio, typically 3:1 for
a gasoline engine. No clue what it might be on a diesel. The idea
is to set the RPM so that it barely charges at idle, where the added
load of charging the battery and running the lights does not put an
excessive load on the engine causing it to stall at idle or have
difficulties starting.

Well, I know that it does NOT charge at idle.

I know that by simply measuring voltage on the battery. It is about
11.76 volts when at idle. Goes up to over 13 volts if I push the gas pedal.

Could someone comment on this, and also how can I find different
regulators?

The regulator is inside the alternator and possibly looks something
like this:
http://store.alternatorparts.com/ProductImages/35-103.jpg
Before attacking, you might want to pull the alternator and drag it
down to an auto electric shop and have it bench tested. Or do it in
the forklift:
https://www.google.com/search?q=alternator+test&tbm=vid

I do think that I have a good understanding of it using the
multimeter.

On a different forklift, I was able to solve it by making the pulley
diameter smaller, but here the pulley is already very small.

What problem did that solve and what problem are you trying to solve
here?

The problem was exactly the same, the other forklift also had a DD53
and the replacement alternator did not charge at idle. I was able to
make the pulley diameter smaller on a lathe and that helped.

Here, the pulley diameter is already small and even smaller diameter
will ruin the belt.

Sounds to me like it's working normally. If it doesn't charge
at idle, does it need to charge at idle, such as it might need to
charge the battery just after starting? Does it deliver any current
when you turn on the lights?

It definitely needs to charge at idle.

Note: The dashboard ammeter might be giving you a false impression
that the alternator is not charging. It's connected to the positive
wire going between the battery and the alternator. The various loads
in the forklift go to the battery. If the engine is at idle, the
battery is fully charged, and you have perhaps a 5 Amp load
(headlights), if the alternator is delivering 5 Amps to the lights,
the meter will read zero because the battery is not delivering any
current or being charged.

I was looking at changes in battery voltage.

At idle, the battery voltage is exactly the same as when the engine is
off.

Basic test. Put an inductive ammeter:
http://www.stuttgartperformanceengineering.com/inductiveammater.html
on the battery (not the alternator) positive wire and see what it's
doing. At idle, it should barely charge (less than 5A). Turning on
the lights, will make it charge more. Revving the engine should
charge even more, but only if you have a battery that needs charging.
If the battery is fully charged because the forklift has been running
for a while, you won't see much charging current. Moving the
inductive ammeter to the alternator positive wire should should what
the alternator is doing.


I just bought an ac/dc clamp ammeter, it might help me in the future,
but I do feel strongly that the DC voltmeter is telling me all I need
to know.

i