Am back again - having solved fuel pump/governor problems two years ago and a broken water jacket pump shaft last year.

This D311 genset (motor SN: 51B5484) has been the primary power source aboard a 1947 boat since at least 1968. Very reliable. Reported to be 30 KW, single phase, 220 VAC (or 208 or 240). Runs at 1800 RPM.

Noticed a problem about two years ago as certain more modern equipment ( e.g., stereo amplifier) cuts out after a couple of seconds when turned on. All works fine on shore power and back-up genset (Detroit Diesel 2-53, 10KW, same age).

Recently, same problem with a variable frequency drive (used to power anchor windlass - converts power to 3 phase, 240 VAC). Tripped 15 am breaker after a second or two. Panel ammeter read 25 amps just before trip.

Output from D311 reads 125 VAC on both legs and steady at 60 cps - which is the only output I know how to measure.

Questions:
1. What else to check, how?
2. What literature available? (have parts book for motor but nothing on electrical/generator end)

Am attaching several pics - to show key data

Problem finding locals who are familiar with the equipment - but suggestions have been clean the brushes, check for easy movement. Could be as working now to clean off 20-30 years of grime in the back end.

Also, trying to tell if letters/numbers in magic marker(?) on cover are genset SN (50TL257?) - I annotated pic to make more readable

All info welcome - thx

50TLxxxx is the Generator s/n for a 7L10 Generator 125-250v 60 cycle 1 phase unit with Exciter 7L4202.
Unit is covered in Parts Book for 51B3140-up Form # UEO36137 Published April 1975.

You don’t mention what other AC electrical equipment in use at the same time as the problem equipment is doing.

I would think if your generator is having a problem you would notice blinking or dimming lights when a heavy load is turned on or possibly brightening when such things are turned off.

As a convenient check on power quality, you may want to buy one or two “kill a watt” units. They’re usually around $25-$30 or so and can be plugged in any 120 volt outlet to display Volts and Hz (CPS) of incoming power as well as amperage and power consumption of anything plugged into the unit.

If you are seeing brown out or black out events, then by all means investigate the generator. If not, I would get an electrician in to check out the wiring, looking especially for connections that have gotten hot in the feeders that connect the CAT generator.

Thx. Replies sent me back to my existing parts book (Caterpillar D311 FORM UE036137) to check out - Old Magnet correct. Turns out generator info included in back of the book - just had not noticed before.

Further - no elec problems noticed in any other equipment - refrigeration, lights, outlets, pumps (110 and 220), battery chargers, etc - when running the D311. Hence, my confusion. Wiring looks good so far in checks.

Will contact local electrician guys, again, figure out what aberration is being generated. Need to figure out what to measure to find problem as voltage and frequency seem to be be fine.

Thx, again

My ups also tripped on my Generac - there was a setting to change something to do with timing or cycle sensing on the back fixed it. Bob

Most common problem is frequency excursions from 60 Hz. Most often happens when a load is applied and the governor response is slow and may overshoot before settling back to set point.

Mechanical governors also have “droop” such that at no load the governor might be set at 62.5 Hz and at half load be spot-on at 60 but by the time it gets to maximum load be down to 57.5 Hz. That would be a bit excessive, but you get the idea of droop. Usually the governor setpoint is set under a normal load, so at least at that condition the frequency should be close to 60.

Unfortunately the governor on the Caterpillar probably isn’t going to be easy to change the droop and sensitivity but it’s possible that you may be able to simply raise or lower the RPM/Hz set point slightly and keep everything happy. The programming of the VFD and the amp might be too restrictive and it’s possible there’s settings that you can modify to let it operate on a wider range of frequency without faulting. However, I don’t understand why the VFD would pull too many amps and trip its breaker because of a minor frequency deviation.

VFDs usually have programming that prevents them from operating overloaded. Is the unit new or has it ever operated successfully on the Caterpillar generator?

Thx, ccjersey - good ideas.

This is a new (replacement) VFD that had a problem the first time we tried to operate it on the D311. The prior VFD was provided by the windlass vendor crapped out after 20 years - but worked fine on the D311.

My VFD guy (versatile electrician - also a special efforts guy for the movie industry) may be able to check out some of the other programming parameters. Will forward the info you provided to him - and will let you know.

Thanks again

Being that old, the old VFD might have been a different design than the new one. Some of them had/have a passive rectifier with plain old diodes to take the 60 Hz AC input to charge the DC bus. Then the active control takes snippets of the DC voltage at the right time and duration to form the desired frequency AC wave

Other designs use an active front end with high speed switching to sample the incoming AC to charge the bus and the control assumes/needs a nice 60 Hz Sine wave to turn on the switches at the right time. These may not play nice with a generator that cannot keep the frequency steady on 60 Hz. Most generators don’t produce a clean sine wave either and the distortion can cause problems.

VFD or other DC power supply on an AC generator can sometimes wreak havoc with voltage regulators. Usually that is more a problem when the DC power supplies are most of the load on the generator like a server building for example.

Since the last post, continuing the search for likely problem and solution - and got quickly diverted into ancillary problems to fix (e.g., hinges rusted thru on door holding exciter components risking pulling out wiring, fastener threads stripped - the usual)

After a sweep of the country side - local long time Cat guy for gensets (different from Mr Go To for engine probs), several marine electricians, a half dozen others, and Quinn who still wants $650 plus mileage to come take a look (4 hour minimum), have decided I can look for a replacement voltage regulator. All the local experts settle in on voltage regulator - as likely source of the problem. Figure I can try at least one (maybe more) as a shot in the dark if the alternative is a $650 tech visit.

So, took apart the unit and found regulator - 7L289 (agrees with parts manual) - now maybe described as 7L-0289 - see pic

No luck after three days of searching on the web - catparts.com recognizes the part but doesn't let me in

Anyone with source for this part or aftermarket ideas?

thx