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  1. #1

    Low voltage from 120 side

    One AC unit is 120, the other (3) 220. The 120v unit is only getting 107 volts, as are the outlets throughout the vessel. Where do I even start trying to figure this out? I really feel like this is beyond my ability, any recommendations who’d be qualified to diagnose?
    '88 55'C hull 394 ​BEATs Therapy
    12-71 TA's ZF BW190 1.5:1 gears

  2. #2

    Re: Low voltage from 120 side

    Most likely a bad receptacle or plug to the boat, or a bad connection somewhere in the circuit that has low voltage, like where the cable connects to the plug or receptacle on the boat side. It could also be bad connection on the breaker dockside.
    Your best bet is to start at the line side of the breaker then the load side and work down to the power panel from there.

  3. #3

    Re: Low voltage from 120 side

    Are you plugged into 240 or 208?
    1966 34c
    1982 46 HP

  4. #4

    Re: Low voltage from 120 side

    Start at the source and measure voltage at the pedestal. On a 120/240-50 you should find 120 between each leg and the neutral as well as 240 across the hots.

    There could resistance in one of the shore power cord connection causing voltage drop under load
    Pascal
    Miami, FL
    1970 53 MY #325 Cummins 6CTAs
    2014 26' gaff rigged sloop
    2007 Sandbarhopper 13
    12' Westphal Cat boat

  5. #5

    Re: Low voltage from 120 side

    This is dock power and/or gen-set?
    If dock power, Do you have a transformer?

  6. #6

    Re: Low voltage from 120 side

    If it doesn't have the issue on Generator, it is a dock power issue or a power cable issue between the dock and the boats power panel.
    That should be an east test.

  7. #7

    Re: Low voltage from 120 side

    An 88 boat will have transformer. 208 (approximately, never exact) will poop out 104 volts rather than 120 240 would poop out. Unless modified with a boost switch that swaps taps to account for lower shore power voltage. This is Sky's area of expertise on the boost switch. But transformer windings are simple math.

    I deal with this all the time with stats on AC units. The BMS stats we install need good voltage or they won't power up. Previous battery stat worked fine and would run the unit. But ours has too low a voltage to power up. Why? Because the AC units 24 V transformers will always come tapped for the highest voltage they will see. 240V. Power it with 208 which is typical on a commercial site and the normal 27-28V output is now about 23.5 volts with zero load on it.

    My guess is incoming shore power voltage is around 214 volts. If this is a resistance/bad connection issue it must be solved ASAP. Potential fire issue.
    Last edited by madhatter1; 02-03-2023 at 06:32 PM.
    1966 34c
    1982 46 HP

  8. #8

    Re: Low voltage from 120 side

    With the transformer, if you feed it 3-phase 208v, which is 120 degrees out of phase, it will output 208v single phase that is 180 degrees out of phase. This gives you 104v between each leg and neutral or ground instead of the 120v that you would normally get with 208.

    SO the question is, what is the input voltage to the transformer?
    Sky Cheney
    1985 53EDMY, Hull #CN759, "Rebecca"
    ELYC on White Lake--Montague, MI

  9. #9

    Re: Low voltage from 120 side

    The voltage remains 107/108 on the gen. I recently installed new light switch’s/outlets and GFCI outlets and will be checking all those connections. Interesting finding…ONLY IN THE MASTER HEAD, the GFCI won’t “trip” but it resets, 2 NEW receptacles tested.
    '88 55'C hull 394 ​BEATs Therapy
    12-71 TA's ZF BW190 1.5:1 gears

  10. #10

    Re: Low voltage from 120 side

    I have checked all the connections to the new outlets and switch's, found a loose ground on a GFCI, this correction didn't change anything, voltage today is reading 102.6 on shore power.

    Riddle me this......rear salon lights are on a 3 way switch. I forgot this when ordering switch's so I'm still searching for a matching 3 way. That being said, one side has an "open" jumper wire, could this cause the voltage drop?

    I had a revelation today, do you think my lack of hot water is coming from voltage too low? Gave that a little check, sure enough 207 volts.
    '88 55'C hull 394 ​BEATs Therapy
    12-71 TA's ZF BW190 1.5:1 gears

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