Restoring the Generator Set

11/30/2007

1300 After launching the boat in the morning, John attempted to start the generator to test it out. Unfortunately, the battery was too weak to start the engine. Some extended cranking in July while bleeding the fuel system after maintenance and then sitting all summer without being charged depleted the battery. We borrowed jumper cables from Leonard on Vallé Caché and jump started the generator from the port main engine, only to have it shut down only a few minutes later, presumably on high temperature.

12/1/2007

John checked and cleaned the sea water strainer. It was only slightly dirty and did not look like it could have caused a significant restriction to seawater flow. He pulled the cover off the seawater pump and pulverized rubber fell out. He replaced the impellor with an onboard spare and restarted the machine. Besides having to do all the extra repair work, John was embarrassed for not remembering to prime the pump before starting the generator engine, especially after the issues he had just experienced with the main engines. Mechanically the generator ran fine but would not put out any voltage on the installed voltmeter. When the main output breaker was closed, the engine lugged momentarily then came back to no load speed.

12/3/2007

John inspected and checked all components in the control box for the generator. No problems noted.

12/4/2007

0400 While trying to get back to sleep after an early morning head call (nautical term for a bathroom break), John suddenly realized that he had not actually measured the generator output voltage with a meter separate from the one in the system. He decided to do so first thing.

Late in the morning after taking care of some other boat duties, John checked generator output voltage but had the digital meter on the wrong scale so he saw 35 VDC instead of 240 VAC that was expected and was probably actually there. Greg Mallory (greg@hattonmarine.com) at Hatton Marine recommended cleaning the slip rings and then measuring output voltage again. John spent the afternoon cleaning slip rings. (That is a job that would have been much easier with a rubber arm!)

1600 Restarted the machine.  It put out 240 volts at the output but that dropped to zero when the main distribution breaker was closed.

1630 Another call to Hatton Marine revealed that a dead short across the output can collapse the field in a small generator like this one without tripping a breaker.

12/5/2007

John began the witch hunt for a dead short across the output leads of the generator. He opened the main distribution switch box and checked continuity from U1, V2, and ground in the generator control box to their respective terminals in the switch box. All were 0 W (ohms). Resistances between all leads were essentially infinite after disconnecting wires from U1 and V2 to remove the stator winding from the circuit. The resistance between leads on the load side of the switch was 0 W. Removed the leads from the load side terminals to split the loads (one set of wires went to a 240/120 VAC transformer that supplies house loads, including the main battery charger, and another set went to the air conditioning [A/C] main breaker panel). The A/C panel had about 67 KW across its leads because of an installed voltmeter and ammeter. The dead short across the other set of leads to the transformer turned out to be the "smoking gun". That short cleared when the input breaker to the transformer was opened.

Pulled the cover off the transformer under the aft port bunk. The problem was immediately apparent. The unneeded wire connector shown hanging down from the top input lead in this picture had spun around to contact the lower conductor, causing a direct short.

Inputs shorted.

John removed the errant connector and measured 8 ohms resistance across the leads, about what would be expected for a transformer of that size.

After short removed.

1500 Ran the generator to successfully power 110 volt loads.

12/6/2007

1935 Started the generator to recharge batteries that had slowly discharged over the past several days and to make ice. It ran under load but shut down after about 5 minutes, presumably on high temperature again. Let it cool for a few minutes while checking obvious things like the hull valve being open and the strainer. It then operated for almost an hour under lighter load but once again shut down on high temp.

12/7/2007

John reviewed the owners manual and discovered a sentence that says to flush the heat exchanger yearly or after 2400 hours. Also received a suggestion from Clarence on Lotus who said to check the heat exchanger seawater discharge elbow for clogging. Pulled the inlet elbow and several chunks of the old seawater pump impellor fell out. Apparently those chunks combined with a couple of moderately clogged tubes and some fouling at the discharge elbow reduced flow enough to keep the engine from carrying full load. Attempted to remove the heat exchanger core through the front of the machine but could not get enough clearance. Removed the control box from its mounts on top of the generator to slide the core out the back of the machine. Cleaned the core with cuticle sticks since my one steel rod was a fraction of a millimeter too large to go through the tubes. After reassembling the heat exchanger, the machine put out only 20 VAC across U1-V2.

Another phone call to Greg at Hatton Marine suggested checking the high temperature shutdown sender – it should read 0W unless in a high temp condition. If it shows any resistance, it has failed. Checked resistance: 0W.

Greg also suggested cleaning up the copper slug on the automatic voltage regulator because if it does not make contact, the machine would produce only about 20 volts. Upon reinstalling the slug, John noticed one of the contacts was bent out slightly, breaking contact with the slug. He VERY carefully bent it back into position and started up the machine, which put out 240 VAC. The fuse holder contact must have been bent while relocating the junction box to extract the heat exchanger core.

Basically the generator restart was complicated by three unrelated problems:

1. Weak battery, which was not surprising considering the excessive cranking and lack of recharging all summer.
2. Burned up seawater impellor – our fault for not priming the pump before starting the engine.
3. The unused and unneeded wire connector in the transformer left from initial installation.