Volts drop with RPM increase?!?

[geoffm70]

Good day all, after all the headaches with the engine swaps and the oil leaks after. Had about 3 to 4 hours of trouble free cruising. Then, last time out, after say 20min at 3500rpm I notice the volts on the engine batts down to around 10 on the dash, throttled back and once under 2000rpm the volts started coming up. Around 1200 rpm, dash was back to 13 in a few minutes and as I increased RPM, as soon as it got over 2000, it started back down again.

I run batteries on BOTH for both switches and the house volts stayed the same (13). I have new since the engine change electric fuel pumps to go with the 5.7 Carbed Vortexs now in the boat. The Alternator on that engine is almost new, maybe a year old. Batteries are 2.5 years old and water levels are all good.

Could it be the fuel pumps are too much of a drain as RPMs increase?

[mmwjr]

This is only on one engine; correct? Can you temporarily wire a volt meter right to the alternator output to verify the voltage is dropping with rpm. Did you check for loose wires? You could also take the alternator to a shop or auto store that tests them.

[geoffm70]

even thought I run with both switches set to both, only 1 side drops under speed. noted the tests, will try that tonight.