Hello -
I may be in the wrong type forum but will try anyway.
I'm rebuilding a 94-95 LT4000 lawn tractor. Having so much fun I can hardly stand it!

Today I decided to check out the charging system - and let me say up front it is working. Maybe a bit overtime. With the throttle about half-way, I measure about 15.3 VDC on the battery posts. If I speed up the motor, it goes a bit higher.

Then I decided to check for proper diode operation (make sure it isn't shorted) so switched to the AC volts position. With the red positive meter lead on the + post and black ground lead on the - post, I read right at 32-33VAC. I was NOT expecting this reading!

Reversed the meter leads and read 0VAC. Got two more meters and tested with them - got the same results.

I then shut the motor down and unplugged the alternator output connector to check the diode - reads good. Conducts in one direction, shows open in the other. See attached Schematic.

Note: I was using cheapo Harbor Freight DVMs and an older Radio Shack analog meter. In order to see the forward bias on the diode, I had to reverse the meter lead connections between the analog meter and the DVMs. Obviously a difference in the circuitry of the meters.

So, why would I read 32-33VAC during the initial test and 0 when I reverse the leads?

Note: This motor has two alternator windings producing AC voltage - one to charge the battery and the other to power the headlights.

 

if you want to test diode, disconnect it from circuit and use diode test of your multimeter

if you want to measure voltages while circuit is in operation, stick with test points and values that are indicated on schematics.... such as highlighted:

 

if you want to test diode, disconnect it from circuit and use diode test of your multimeter

if you want to measure voltages while circuit is in operation, stick with test points and values that are indicated on schematics.... such as highlighted:


View attachment 117518

Thx for the replies. Finally got tired of screwing with these meters and put my 4-channel Iwatsu to work - got some sensible reading then.

At engine idle after 1-2 min of 'recharge', scope showed about 15.3 VDC and approx .1 - .2 VDC ripple. Ripple was about what I would expect. At full throttle, scope showed right at 15.8 VDC with a very slight increase in ripple voltage - but not much.

The scope was showing maybe a .2 volt less difference than the meters. The clock reference on the scope is a .6 volt 1Khz signal, and it was right on the money on that scale. No matter, .2V ain't gonna shake any trees in this case.

My only concern now is the high charging voltage - cooking the battery. This is a Briggs engine, so called their Tech Support line for info on this but they decided to take the week off, so it'll be next week before I'll find out if this is typical for this engine or not. Not sure what I could do about it other than maybe add a sizable wire wound resistor in series to drop a couple of volts.

Any other thoughts?