Generator load questions for the resident panel


#1

so went to run all the machinery on the DAUNTLESS today and finding an issue with one of my gensets which I hope my fellow mariners here can give me some insight into…

with one genset, when connected and hit with a load, its rpms sag down but then suddenly bounce back and then it will do this over and over and over again. I have noted that it is caused by the load put on the generator by the battery charger. At times it seems as if the generator is about to die but all of a sudden, wroom…off we go again! With the other genset I am getting none of this occurring. So I am wondering if this is caused by the Woodward Speed Switch on that particular generator and if this is a sign of it finally failing?

ideas?


#2

First guess would be governor issues. Has the DG been sitting awhile? Might be the governor is failing or just needs an oil change and flush


#3

The specs say the gens are 3-71s. I’m assuming hydraulic governors. A common problem of hunting can be cured by moving the droop adjustment wedge a fraction of an inch.


#4

indeed they are…I realize now I omitted that bit of important info

and where might I find this adjustment? I assume on the governor itself? I try not to fiddle with any knobs, etc… if I do not know what they are controlling.


#5

Just pull the cover off the top of the governor. You’ll see a screw with a slotted wedge. Loosen the screw slightly and move the wedge. Crank it back up and see if you moved it in the right direction. In some configurations, this can be done while running. On some, the speed control motor is mounted on the cover.


#6

This can also be caused by the rack sticking on one of the injectors. This is common on engines that have been dormant for a while. It normally clears up after running a while.


#7

before it gets complicated, is it starving for fuel, no load it runs, with load it dies?
Time for a fuel pressure check


#8

with no load it runs fine at 1800 rpm but with load rpms drop then recover back to 1800 and it does it repeatedly. I do not feel it is a fuel supply issue but a governor one.


#9

The easy way out, and in the end probably the cheapest and fastest, is just to hire a good local mechanic with a lot of experience with 71 series generators to come aboard and fix it properly the first time.


#10

Most likely the problem if it’s bogging. Several times over the years, I’ve found the hose between the primary fuel filter and suction side of the fuel pump collapsed internally. A vacuum gauge on the inlet of the pump will tell.


#11

except if that was the problem I would expect it to not recover rpms like it does but just bog down and then die if the fuel flow was restricted…recall that the rpms drop then bounce back.

I am pretty much convinced the issue is in the governor and likely that droop setting you are taking about however does that explain the cycling it does?


#12

Does the RPM recover under load or after it’s taken off line? What’s the cyclic rate of the bog?


#13

no, the load is not taken off however as the genset slows, I notice the amps coming out of the battery charger falling. as soon as the generator recovers, the amps coming out of the charger go back up and then down goes the generator again. as far as frequency goes, I would say 20 to 30 seconds total for one cycle to complete itself.

mind you as well, the same charger does not cause the same to occur with the other genset…it is steady as a rock


#14

I can’t remember the symptoms but we had to change a speed controller on the one at KP. You might try switching the speed controllers between the two and see what happens.


#15

aha…the plot thickens

so maybe not the demon governor but perhaps that evil speed switch afterall…


#16

So both gensets are electric start with only one charger between the two, and no alternators?
I’m not following on how the charger is being affected…i am assuming these were purely mechanical DGs …


#17

both electric start (24v) but neither have an alternator

what set off the worse of the fluctuations was when I went to start one of the main engines…that put a big draw on the batteries which then caused the charging amps to spike and the online genset to almost crash


#18

Does each genset have its own battery charger? Are the mains electric start or air start? If they are electric start, do they each have their own battery charger?
I know the answer to these questions most likely isnt tied into this issue, but best to troubleshoot even the less likely.
The other suggestions about the speed control and the governor are probably the culprits by the sound of things…


#19

all engines are 24v electric start and all starting batteries share a single La Marche Constavolt 100amp charger


#20

To me that’s an unorthodox arrangment and would explain the excessive load on the charger…but then again i know its an old vessel and i am assuming if its worked all these years with no problems, why would there be an issue now?
How old are the batteries? Newer batteries wouldn’t require much from the charger assuming they are in good health.
If the other DG is supporting everything fine like you said, maybe the issue could also be the actual generator and not the engine ? Something electrically is wrong with the genset. I’d go that route after you try the governer and speed control which obviously would be the easiest to check at this point.