Hi, never used this service before, thanks for donating your time.

I have a Briggs 12hp #284707-1026E1 model engine in my rider. When running, I measure around 18 volts across the battery terminals at full throttle, 12.5 at idle. This is an unregulated charging system. I confirmed the voltage readings at the battery terminals with both a digital and analog meter. Why is it so high? What, if anything, besides the diode in the charging wire restricts voltage to the battery positive side? Does this mean the alternator is shot?

Thank you for any consideration of my questions, sorry it was a long explanation.

Eric

How long did it run ? Are you having trouble with it charging ?
In order to get a proper reading on a unregulated system you have to hook in a thing called a shun .
18 volts is normal after a start it would take about thirty minutes to get to normal,
Luck

Yeah, the battery in it is worn out, so maybe that is the cause of the crazy voltmeter readings. It reads only 9 volts across the terminals engine off. I jumped the tractor and that's when I saw my in-dash voltmeter pegged at 18+ vlts. Shunts are $50, so I've never thought to use one. I need to buy a new battery as this one sat for a few years and is probably sulfated and useless. Once I get another one and install it, 18 volts on my in dash voltmeter (which is brand new) is OK for awhile? It won't gas the battery or boil the acid right out of it?