Current leakage when master switch is off

[oldfatgit]

Carried out a power audit on my boat the other day measuring the voltage drop across a 75mV @ 50 A shunt. No real surprises and, as a result I will take the plunge and replacie my incandescent bulbs with LED replacement lamps and find a low power laptop/netbook to make the most of my generous 2 x 110 Amp Hr batteries.

Anyway, when the master switch is turned off there is a leakage of 75mA at 12.3V. Now, bypassing the master-switch are the VHF (turned off) a Navtex (turned off), bilge pump on a float switch which was not closed and hard wired in the mains charging system . The mains had been turned off for some weeks which is why the batteries were at about 65% charge state. Am I right to think that the 75mA leakage is acceptable and is likely to be back through the mains charging system diodes or does 75mA indicate a fault somewhere? Wiring is good but mostly on un-tinned copper, which, in a future life, I suppose I'll have to change.

Value your thoughts

 

[Playtime]

Am I right to think that the 75mA leakage is acceptable and is likely to be back through the mains charging system diodes or does 75mA indicate a fault somewhere? Wiring is good but mostly on un-tinned copper, which, in a future life, I suppose I'll have to change.

Value your thoughts

I would want to know where 75mA is going. It is 'losing' 1.8Ah a day which soon mounts up.

If it's not too difficult, I would disconnect each item in turn and see when the current changes. It could be the Navtex or even the VHF that, although 'turned off', is actually using a small current to maintain soft settings

 

[Richard10002]

I had a 0.4A draw when the master switch was off - for a few years!! Couldn't find anything that was on.

Anyway, in the end, it turned out that the Navtex didn't actually have an off switch - it had a dimmer and other power reducing things, but no off. Fitted an in line switch and BINGO! No draw.

So there is a strong chance it is the Navtex, even if you think it's off. But it might not be

 

[oldfatgit]

I had a 0.4A draw when the master switch was off - for a few years!! Couldn't find anything that was on.

Anyway, in the end, it turned out that the Navtex didn't actually have an off switch - it had a dimmer and other power reducing things, but no off. Fitted an in line switch and BINGO! No draw.

So there is a strong chance it is the Navtex, even if you think it's off. But it might not be

Thanks but I do have an in line switch which I had turned off. I think I will follow Playtime's advice and start by disconnecting things to see where the current is going.

 

[maxi77]

Earths can be the problem, perhaps some one with more knowledge tha me can indicate how to measure the level of earth leakage onthe system.

 

[Robin]

We inherited an unknown drain on our last boat and traced it to two things. First was the gas alarm permanently wired bypassing the master switch. The second was really hard to find but turned out to be a lead from the master switch to the charge warning light, which I only found after wondering why there was a very slight glow from it one night mid Channel on a totally black moonless night. I disconnected the wire and everything still worked and with no more drain but I asked the Adverc folk at SIBS why that lead and they thought someone had rigged it as an 'excitation' for the alternator, possibly to cure a fault no longer existing.

Another possible culprit is a radio that has power to maintain a clock or preset station memory so is permanently connected.

 

[halcyon]

Earths can be the problem, perhaps some one with more knowledge tha me can indicate how to measure the level of earth leakage onthe system.

Are you talking voltage, or current, please expand earth leakage ?


Brian

 

[charles_reed]

If you have a car radio that has a permanent feed and drains power continuously.
Unfortunately putting in a master switch results in the radio losing all its pre-programming.

 

[maxi77]

Are you talking voltage, or current, please expand earth leakage ?


Brian

If there is leakage it will be both voltage and current. On O boats leakage was measured in volts but clearly if there was a voltage differential there was also an associated current flow. I was not an electrical specialist hence my uncertainty on the details, but we did have earth leakages, which gets potentially exciting when your DC system is at 440 volts.

 

[oldfatgit]

If you have a car radio that has a permanent feed and drains power continuously.
Unfortunately putting in a master switch results in the radio losing all its pre-programming.

Good point, it is "downstream" of the master switch, but draws 270 mA when master switch is on and it is on standby (correcting for the bit leaking that is).

 

[pampas]

make sure that the battery is clean and dry on all sufaces as well, tracking across the battery case is seldom checked.(Including the bottom)

 

[VicS]

If you have 75mA draw ... measured at the battery terminal ????? with the isolator open .... You have something amongst the things that are not switched off by it that is taking current when you don't expect it too.

Physically disconnect them all. Hopefully the current drain will have gone ... if not scratch head harder. Disconnect connection to isolator perhaps.

If Ok with all disconnected reconnect them one at a time until you find the guilty one.

Include disconnecting the mains charger in the above. My automatic charger draws current from the battery when it is not powered up ... but is a portable one not intended for permanent wiring. ( about 60mA IIRC)

 

[VicMallows]

And if you STILL cannot find the cause ... and are using a digital meter ... DO try a different one (or an old fashioned analogue one). I have come across digital meters with very strange offset faults which nevertheless read zero 'at rest'. A useful quick check is often 'does it read the same whichever way around it is connected - apart from the polarity'.

Vic

 

[oldfatgit]

Thank you, it is a very cheap digital mulit-meter, so I was suspicious and did as you suggest; it did read the same voltage, albeit with a negative sign.

 

[oldfatgit]

If you have 75mA draw ... measured at the battery terminal ????? with the isolator open .... You have something amongst the things that are not switched off by it that is taking current when you don't expect it too.

Physically disconnect them all. Hopefully the current drain will have gone ... if not scratch head harder. Disconnect connection to isolator perhaps.

If Ok with all disconnected reconnect them one at a time until you find the guilty one.

Include disconnecting the mains charger in the above. My automatic charger draws current from the battery when it is not powered up ... but is a portable one not intended for permanent wiring. ( about 60mA IIRC)

Thank you, will do as you and the others suggest when I next get down to the boat; not for a while I fear.

 

[VicS]

Thank you, will do as you and the others suggest when I next get down to the boat; not for a while I fear.

Let us know how you get on.

Nice to know if we get things right ... nice to learn when we dont