I recently installed an alternator in my 49 flathead engine (2 actually) which had an 300 cca AGM battery installed. The alternator is a Powermaster Shorty. While the gauge showed 14 vdc, my multimeter showed really wild voltages: -3 to 100 vdc and erratic vac. I discussed it with Powermaster and Speedway. Thinking there was a problem with the alternator, I sent it back under warranty and got a replacement. Same issue. I called Powermaster again, the guy I talked to this time helped me troubleshoot it. I ran the alternator output to my pickup's standard battery and the problem went away. I'm OK with running the pickup battery for now, but really liked the AGM for it's size and mounting flexibility. Besides, the pickup needs it's battery back. I know others are running AGM batteries with no issue, so am looking for advice and maybe a recommendation.
my new pickup has an AGM. Our 56 uses lead acid with a PowerMaster alternator. My LSR roadster uses an Odessy and mini 60 amp alternator and has for 15 years so has my sons circle track car identical system.
Op check out PowerHouse Performance https://www.powermastermotorsports.com/racing_alternator_features_a.html For Technical requirements and usage . There From what I understand some AMG & Lithium Batteries , the alternators are specific and adjustable to the battery requirement. Some battery specs and information below https://braillebattery.com/
When trying to measure voltages on a car with a "standard" ignition system (copper or graphite leads, points, coil, etc) some digital meters will be all over the place as a lot of interference is generated by the ignition system. Usually the closer to the engine that the meter is operated at, the worse it is. When I strike this PITA, I revert back to an ****ogue meter.
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