Perko Battery Switch Trouble
We have been using our boat for six years with no major electrical problems. Stella Blue has 2 banks of single 8D size batteries (Interstate brand, "Workaholic".) In 2008 we noticed that our refrigerator would drawn down the battery banks overnight when anchoring out. We needed to start the genset in the morning to get the engine started. From experience when the boat was newer, we knew that this was not normal. I suspected the batteries were on their way out and entertained the idea of replacing them at winter haul out. The engine, and thruster still worked fine and voltage still came up good when charged. After discussing the matter on Mainship group list, I decided to go one more season on the batteries, but install a link battery monitor to see how many amp hours were actually being cycled.
We always left our battery switch on both or off, depending on whether we using the boat or not. We were never concerned with managing power by climbing in and out of the bilge to cycle switches, and I suspect most users do likewise. It is very inconvenient and you will probable not pay close enough attention to do it properly anyway. One thing to remember if you are managing power using the analog panel mounted volt meter, the voltage will be a value somewhere between the voltage of the two batteries when the battery switch is on both, regardless of the position of the switch position at the panel mounted meter. Another thing to keep in mind is the amp meter only measures what is coming through the 50 amp main on the main panel. Loads that bypass the main breaker, like CO detectors, bilge and shower sump pumps and a variety of other things, are not measured.
I purchased a Link 20 battery monitor in the spring an installed it in June 2009, with the original 2003 8D batteries still in service. Now I could check the actual amp hour capacity left in my batteries. This is where the fun began. With the battery switch still on both, I had about 110 amp/hrs from full charge to discharged. That's about 25% of rated capacity. With a week long trip coming up in a few weeks where we do some time on the hook, I decided to change out the batteries. Not looking forward to moving 8D's around at 130 lbs a piece, I decided to go with 6 volt golf cart size batteries. Two golf cart batteries in a series, closely approximates the capacity of one 8D (130lbs each), in a smaller footprint, with much easier handling (68 lbs per piece.)
On July 11, 2009, I changed the batteries to the new GC size batteries, Rolls EHG 210M, 10 year life rated batteries. I continued to run the battery switch on "both" position as I had in the past. This is when the real problem surfaced. I was barely getting any amp hours out of the starboard battery bank (#2) and the port battery bank (#1) was doing all the work. I knew the batteries were good, so there had to be another reason for this. I started doing a series of checks under different conditions and the results made no sense. The bow thruster would only work on #1 battery, and the house would work on #2 occasionally, only under very light loads. Any heavy load on # 2 position would cause the battery to cut out all together, and cause an error 13 code on the Link monitor indicating an open sense lead connection to #2 battery.
My grounds and battery connections were good on both batteries. That led me to believe that there may be something wrong with the boat wiring, or something was loose behind the panel on the positive leads.
The Perko tech sheet says that "Erratic operation, particularly after very long periods of idleness, can be cleared by rapidly switching back and forth briskly several times without any load connected." Tried that and that did not work for me. I still had erratic operation.
I pulled the back off the Perko switch. There seemed to be more grease on the contacts than I would think should be there. The contact on the number one terminal seemed positive by the shiny wear spots on the plate and clamping finger. Contact on number two seemed very weak by the lack of friction between the rotor and the clamping finger. Any film of grease with be enough to prevent good electrical contact.
I removed the rotor from the switch and wiped off some of the grease. I tapped the fingers down a bit with the plastic handle of a screwdriver, to close the gap a little and make a tighter fit on the rotor, then
reassembled the switch. Before doing this, the switch spun very freely with only the detent causing any noticeable drag. Now I could feel a positive drag as the rotor cycled through all positions and I was confident a positive connection was being made. I double checked all the connections for tightness, and reinstalled the panel.