Datsun Roadster Forum-311s.org

david premo wrote: Thu Feb 10, 2022 1:22 am FYI the alternator is an AC generator rectified to DC, however there is no place to measure AC voltage in the system. I’ll try to keep this simple, on 12 volt automotive electrical system the battery voltage is about 12.5 to 13 volts at rest and with a property operating charging system it should read around 13.7 to 14 volts when the car is running. Sometimes it’s slightly less until you rev up the engine. AMP’s is a measurement or flow, and with current flow as high as 30 AMPS at idle on a 30 AMP system tell me the alternator is over charging the system.

my thought was to test for burnt diodes during his meltdown see if any AC in the system

agree with the rest of your post.

No when you lose a diode it just half’s the output of the alternator. The diode’s are there to rectify AC to DC in pairs like a set of check valves. The big problem with alternator systems is if the regulator fails it just keeps climbing in current and voltage. An alternator on a 12 volt system can put out over a 100 volts in theory if the regulator fails and it cannot get a voltage reference from the battery. It just keeps putting out current and voltage like a runaway truck with no brakes. A generator on the other hand is a motor running backwards and is limited to its current output and cannot runaway as it’s limited to it’s 12 volt and what ever amperage it is.

Thanks all for the possible remedies, after market parts suggestions and 30 amp circuit breaker addition.

The Duralast VR728 arrived today and was the issue. Infact my ammeter has never been this stable.

Thanks again all. It's 80 degrees so off for an afternoon cruise by the ocean

Mahalo Bruce

glad it was simple. odd that your backup had the same issue but sometimes they throw you for a loop like that.

Glad it's fixed and didn't cause a Meltdown! Car looks great, and you're in paradise... enjoy!

????? So you cut charging current from the alt ?
Via circuit breaker , guess you waiting on the VR
You need a pro to assess the charging system
With a VAT machine at some point, batt, alt , draw ,load test