Does this sound like a DC ground fault?

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BAD ORCA

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Nov 6, 2020
222
Mariner 36 California
I have a Blue Seas fuse block https://www.bluesea.com/products/5026/ST_Blade_Fuse_Block_-_12_Circuits_with_Negative_Bus_and_Cover with a few branch circuits connected to it. This fuse block is turned on/off manually via a circuit breaker on my DC distribution panel.

With the breaker turned off, and both battery banks turned off, if i put my multimeter probes on a positive stud of the fuse block and a negative stud, (fuse block has a built in negative busbar) i get an approximate 1.3 volt reading. This voltage changes slightly but remains around 1.1 - 1.4 volts. Why am i seeing voltage on this fuse block with the positive side disconnected?

I know some multimeters give a 1 volt reading when they are out of range but this seems like an actual reading. Is it just my multimeter and the way it works maybe? Is this a symptom of a DC ground fault? Is 1+ volts leaking somewhere from my positive side to the negative ground somewhere?

My batteries do not drain at all when im away from the boat. I leave them switched on and have not noticed anything unusual aboard. The only wires aboard that bypass any on/off switches are two wires for the two battery monitor shunts and the negative side of my DC system of course.
 
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Davidasailor26

Davidasailor26

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May 17, 2004
5,392
Beneteau Oceanis 37 Havre de Grace
What types of devices are connected to the fuse block? My guess is one or more of them have some capacitance, possibly in a filtering capacitor or something like that. The capacitors might just be holding some residual charge after the breaker is turned off. You could try pulling individual fuses while continuing to check the voltage across the bus to see if one particular branch is causing that.
 
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BAD ORCA

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Nov 6, 2020
222
Mariner 36 California
Davidasailor26 said:
What types of devices are connected to the fuse block? My guess is one or more of them have some capacitance, possibly in a filtering capacitor or something like that. The capacitors might just be holding some residual charge after the breaker is turned off. You could try pulling individual fuses while continuing to check the voltage across the bus to see if one particular branch is causing that.
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A VHF radio, two computer cooling fans, two temperature sensors for the fans (each sensor is on its own programable circuit board), the 12 volt plug and a small Rule bilge pump that has internal float switch.

I will be back at the boat today so will do this and check again before anything is turned on. That circuit was turned on for a couple of hours that morning so this may be plausible.
 
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BAD ORCA

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Nov 6, 2020
222
Mariner 36 California
Ralph Johnstone said:
Use an analog voltmeter to introduce a small load into the circuit.
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with the intention of the small load to drain any residual stored energy from capacitors or the like?

I dont currently own one. Do you have one you would recommend or would anything from local Home Depot/ Harbor Freight suffice?
 
walt

walt

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Jun 1, 2007
3,519
Macgregor 26S Hobie TI Ridgway Colorado
solar panel and charge controller "could - depending on a bunch of things" do something like that with the battery completely switched out.
 
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shemandr

shemandr

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Jan 1, 2006
7,335
Slickcraft 26 Sailfish
I really shouldn't post on any electronics thread because I barely understand electronics. But it occurred to me that the VHF probably has a station pre-set low voltage memory circuit. The positive comes directly (Bypasses the circuit breaker) from the battery fuse and the negative would go to the negative bus bar. Or something like that.
I don't know if that would fit your observation but I'll throw it out at risk of being thought an idiot - which I am in electricity. So, nothing's lost.
 
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BAD ORCA

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Nov 6, 2020
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Davidasailor26 said:
What types of devices are connected to the fuse block? My guess is one or more of them have some capacitance, possibly in a filtering capacitor or something like that. The capacitors might just be holding some residual charge after the breaker is turned off. You could try pulling individual fuses while continuing to check the voltage across the bus to see if one particular branch is causing that.
Click to expand
Thank you, this worked. First thing i did when getting to the boat today was re-test. There still was voltage present but it had dropped to .3 volts. I started pulling fuses and when i pulled the VHF fuse everything went to zero.
 
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BAD ORCA

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Nov 6, 2020
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Mariner 36 California
shemandr said:
I really shouldn't post on any electronics thread because I barely understand electronics. But it occurred to me that the VHF probably has a station pre-set low voltage memory circuit. The positive comes directly (Bypasses the circuit breaker) from the battery fuse and the negative would go to the negative bus bar. Or something like that.
I don't know if that would fit your observation but I'll throw it out at risk of being thought an idiot - which I am in electricity. So, nothing's lost.
Click to expand
You would be correct. The VHF was the culprit. My VHF doesnt bypass the fuse block though but it must store energy in capacitors that slowly drains over time or some such scenario. I'm pretty weak on electronics myself.
 
Ralph Johnstone

Ralph Johnstone

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Jan 4, 2006
6,925
Hunter 310 West Vancouver, B.C.
shemandr said:
I don't know if that would fit your observation but I'll throw it out at risk of being thought an idiot - which I am in electricity. So, nothing's lost.
Click to expand
I wouldn't worry about that.

I find it's time to worry when we've just pulled into a transient slip, we're getting set up, and one of my crew members yells out loud enough for the entire dock to hear, " Hey, plug in the electric hose will ya ?"

It's at that time that I slink below deck and hope to hell I never see any of the people on this dock again, as long as I live :facepalm: .
 
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BAD ORCA

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Nov 6, 2020
222
Mariner 36 California
Ralph Johnstone said:
I wouldn't worry about that.

I find it's time to worry when we've just pulled into a transient slip, we're getting set up, and one of my crew members yells out loud enough for the entire dock to hear, " Hey, plug in the electric hose will ya ?"

It's at that time that I slink below deck and hope to hell I never see any of the people on this dock again, as long as I live :facepalm: .
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Its from all those youtube electricians comparing electricity on boats to water going through hoses. I must have heard that comparison twenty or thirty times by now :p
 
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shemandr

shemandr

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Jan 1, 2006
7,335
Slickcraft 26 Sailfish
BAD ORCA said:
Its from all those youtube electricians comparing electricity on boats to water going through hoses. I must have heard that comparison twenty or thirty times by now :p
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Amen. I’ve heard my quota of those and they leave me short of understanding.
 
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