voltage drops under load but holds 60 Hz, not sure what I’m missing
Hey guys, hoping someone here has experience with these older Yanmar diesel generators.
I’ve got a YDG2000E ( 2kW) that starts easy and runs really smooth. No weird noises, no hunting, nothing like that. Frequency is steady at ~60 Hz (checked with a Kill-A-Watt), and no-load voltage sits around 125–126V.
Problem is as soon as I put a load on it, voltage starts dropping pretty quickly. By the time I’m around maybe 600–750 watts (testing with a space heater), voltage has fallen into the low 90s and the heater shuts off. As soon as I remove the load, voltage jumps right back up to normal. Engine doesn’t bog at all when this happens, still sounds totally fine.
So it seems like the engine side is good and RPM is where it should be, just not able to maintain voltage under load.
So far I’ve cleaned the slip rings, checked the brushes (still decent length and moving freely), and ran it with the rear cover off and didn’t see any sparking. I also opened up the control panel to see what I’m working with.
From what I can tell it’s a brush-type setup with a pretty simple excitation circuit. I’m not seeing a big run capacitor like I expected. There is an inline diode ( I think)in the wiring (covered in heat shrink) and a small transformer in the panel, but I don’t see a modern AVR module anywhere.
At this point I’m thinking it’s something in the excitation/field circuit that just can’t keep up under load, maybe a weak diode or something along those lines, but I don’t want to just start throwing parts at it.
Couple questions:
Do these YDG2000E units actually use an AVR somewhere or are they just diode/transformer based?
Has anyone seen this exact symptom from a bad excitation diode or similar component?
Any good way to test the field side on one of these without tearing the whole thing apart?
Appreciate any help. I feel like I’m close but not quite there yet.