- Category: Electrical and Electronics
- Published: Saturday, 26 July 2014 09:56
- Written by Super User
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Old Delphi forum notes on Galvanic Isolators
I slept onboard last night and heard the galvanic isolator buzzing at random intervals (5 to 15 minutes) all night long, and this morning too for a really short, single burst of less than a second. I tested the outlets with a polarity tester and they all check out normal, polarity apparently ok. There's been no change in the boat's AC wiring, and no new accessories. The marina is completely rewiring (a project that has been underway for three years) but the workmen say there's been no change in my end of the facility; they are working on a different dock. Since this happened at night when no workmen were present, I don't really think anyone was messing with ground or other wiring.
Do you experience buzzing like mine did, a quick staccato burst (to be gross, like a short f*rt). If the signal were continuous, I'd agree on a bad power cord somewhere nearby on the dock. But since it occurs sometimes at intervals of 15 minutes or more, I would be there all day pulling another guy's power cord and waiting for the event. My cords look ok. Again, I would think if there were bad, the buzzing would be continuous.
My isolator sounds like a tuning fork vibrating against another piece of metal. It sounds very metallic. The noise was random but I did notice is only when there were people around me. I spent five days a week on the boat and I knew it only buzzed when there were others near by. It would buzz for less then 2 or 3 seconds maybe once a week if that. Then one day it began buzzing constantly. I looked around and the only person near me was the marina mechanic working on the boat 2 docks down. This boat was suspect, but I never got around to investigating until that day. The mechanic had taken the boat for a test ride that morning, came back and plugged the cord back in. He turned on a fan in the cabin. Apparently his repositioning of the shore cord and turning on the fan was just right to create a constant short. I asked him to flip the breaker while I listened to my buzzing turn on and off. He pulled the plug from the dock post and it was brown and melted at one prong and the outlet looked a little melted. The mechanic contacted the owner and then replaced the outlet. I would look for anyone near you when this happens or if anyone is running their A/C while they are gone from the boat.
Perhaps a boat is moving around enough to jiggle the shore cord and create the short to ground or maybe a shore cord is dropping in and out of the water?
This happened in my experience when the air conditioner in a nearby boat would turn on. That boat was wired in such a way that the neutrals (white) were connected to its grounds (green) at the shipboard electrical panel when connected to shore power. Unless an isolation transformer is used this a no-no as it can cause AC currents to flow through water. Part of this boat's neutral current was passing through the ground wire (and possibly the water) all the way back to the marina's main breaker panel where the neutrals and grounds are supposed to be connected. This current causes a small AC potential difference between the ground (green) at the boat and the ground (green) at the main panel or transformer feeding the dock to develop. Unless there is a ground fault, there should be no current flowing in any ground wire and hence no potential difference. Prior to general acceptance of ABYC guidance, several boats were wired with the grounds (green) sharing the same shipboard panel bus as the neutrals (white). As soon as the boat described above made the change and separated the neutrals from the grounds, the problem went away. I have also seen several boats with neutrals connected to grounds that left the factory with neutrals separated from grounds. In these cases, owners or workman who were unfamiliar with the need to keep them separate joined them together.
What you describe is entirely possible in my case. I didn't check to see whether any of them had A/C's running when the buzzing occurred.
But here's the update: we spent the last two nights aboard and the isolator buzzed only twice. Go figure.
I would conjecture that it takes a certain amount of voltage or current through your boat's green wire to trigger your galvanic isolators alarm. If this voltage difference is due to currents flowing through the green grounding wire, then this voltage difference will increase or decrease with the amount of electrical load aboard the boat (or boats) which have neutrals (white) connected to ground (green) at their panel (s) or whatever fault is causing your alarm to trigger. This load can vary greatly over the course of a day.
I'm going to head off at about 90 degrees from the rest of this thread for a minute because what you described sounded like something I heard on mine - but it was not the galvanic isolator or, for that matter, even electrical except in the most general terms. I only noticed it at night presumable because it had to be real quiet. I would hear a short "brrzzzzzzzt" every 10 or 15 minutes. It drove me nuts for a while but I finally figured out that it was my raw water wash down pump cycling on to restore the pressure in the line. The boat was new (for me) and I didn't realize that I had left the pump circuit powered up. Apparently the pressure would bleed down a bit on about 15 minute periods. I think it was bleeding back through the pump because I couldn't find any leaks or drips. It does not do it now even though nothing was changed other than ensuring that I normally leave the pump off (something everybody should do I would think). Coincidentally, I heard the sound again this past weekend while anchored out. Jumped out of bed to turn off the wash down pump and SPLASH! Talk about a sinking feeling! Well, the wash down pump was already off. It was the main house plumbing pump. It turns out the ice maker water supply had broken and the "refill" of the ice tray and the water had just saturated the carpet in the v-berth area. I've replaced the line and now water apparently is overflowing into the ice bucket (then freezing) so there is something else wrong with it. Anyway, I don't want to divert attention from your issue but just wanted to mention the pump cycling because your description of the sound (short staccato) reminded me of the sound I was hearing.
Glad you were able to wake up in time to avert a worse disaster. Flooding is the thing you always pray against (along with hemorrhoids) I know the difference in sounds. I, too, get an occasional burp from the fresh water pump. Especially right after it runs for a legitimate purpose (like toilet flush or hand-washing)--as if it didn't fully charge the system and it needs another burst or two. The isolator (at least that's what I think is causing the noise) has a different sound; a little more metallic and closer but not the same as the engine alarm. The water pump has a slight rushing air quality to its sound. This annoyance (I hope it's at that level only) is definitely not water pump.
The only time to date that we've heard the isolator buzzing was after a severe rainstorm. I figured out what it was after a bit by unplugging the shore power cord (and leaving it unplugged for several hours). The problem eventually went away.