Strange electrickery

[NBDensie]

We have been losing charge on the engine battery whilst the boat has been unused in the marina. I have made some measurements which seem most odd: perhaps someone can explain....

 

Configuration

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The main power cable goes from the engine battery to a large isolation switch A and then to the control panel and Victron inverter/charger.

There are also separate cables from the battery to the bilge pump. This circuit has its own isolation switch B on the main control panel.

 

Measurements

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I disconnected the battery from the cables and measured the resistance between the live and earth cable terminals, the bilge pump and main wires being both connected to the end terminals.

 

Switch A and B isolated - infinite resistance

Switch A isolated and B connected - 60ohm resistance ie short circuit. From a rough calculation this is of the right order of magnitude to explain the loss of charge.

Switch A connected and B connected - infinite resistance

Switch A connected and B isolated - infinite resistance

 

This was checked several times and and the results were always the same.

 

So I am only getting the short circuit if A is isolated and B is switched on. But why should isolating A cause a short circuit???? My first thought had been a fault in the isolation switch, but then it shouldnt have been affected by the setting of the bilge pump switch.

 

Any suggestions gratefully received.

[keble]

My take is this means you have a wiring or similar fault the other side of your bilge pump.

And your wiring is not quite what you think. When you did these measurements was the battery negative connected to boat chassis? If so that's another 'wire'

Edited April 24, 2012 by keble

[WotEver]

Firstly, you're generally much better off when measuring around a boat (or vehicle) by taking voltage readings as opposed to resistance readings. Voltage readings can show poor connections, drops across an isolator etc etc.

 

However, regardless of that, your description of the fault has to be wrong. I don't doubt for a moment that you've measured what you've measured but isolating a switch cannot cause a short. Therefore you're not measuring what you think you're measuring.

 

Any chance of a wiring diagram? These kinds of things are impossible to diagnose at a distance just from a description that "this is connected to that".

 

Tony

[NBDensie]

......

 

However, regardless of that, your description of the fault has to be wrong. I don't doubt for a moment that you've measured what you've measured but isolating a switch cannot cause a short. Therefore you're not measuring what you think you're measuring.

 

Any chance of a wiring diagram? These kinds of things are impossible to diagnose at a distance just from a description that "this is connected to that".

 

Tony

 

That's what seemed obvious to me, and yet it did, repeatedly. That's why I raised the question in case there was something that someone could suggest - thanks for a response.

 

The electrics on my boat, a Polish built Aqualine, seem to be pretty complex but look very neat and impressive. AIUI they were designed by someone with a Polish military background. The wiring diagram is on the boat, I will hopefully remember to retrieve it next time I am there. However, the easiest solution seems to be for me to ensure the bilge pump is properly turned off when I am not on the boat - in 6 years fairly heavy cruising with some 3000 hours on the engine meter the bilge pump has never actually been needed.

[jonathanA]

firstly 60 Ohms is a long way from a short circuit and will only be drawing 0.2A or 2.4w - sounds like an indicator bulb somewhere ?

 

if its only happening when the bilge pump is connected (switch b on)then its got to be the bilge pump, its wiring or any automatic switch/warning lamps associated with bilge pump. so you 'just' need to trace the bilge pump wiring. start by discconecting the pump it self and see if the 60 ohm disappears.

 

just a little thought - its not unusual for the radio (car radios type) or central heating timers to require a permanent live feed and these usually feed off an isolator bypassed circuot like the bilge pump - do you have a radio or central timer that could be conencted to the same circuit ?

[Eeyore]

Any chance of a wiring diagram? These kinds of things are impossible to diagnose at a distance just from a description that "this is connected to that".

Tony

Seconded

The wiring on these is realy tidy, but some things are odd about them.

I specificaly recall having to turn both manual isolators off in order to remove the lead from the B+ on the domestic alternator.

Probably something obvious, but the diagrams weren't on the boat.

Steve

[RobinJ]

I don't doubt for a moment that you've measured what you've measured but isolating a switch cannot cause a short.

I would disagree with that, but it is unlikely!

 

If the bilge pump has a hall effect level detection on it and it is wired to work automatically, this could somehow be cross connected between the two isolators - would that cause the strange effects?

[dccruiser]

Are you sure you are not just measuring the motor windings in the bilge pump?

 

Rick

[nicknorman]

firstly 60 Ohms is a long way from a short circuit and will only be drawing 0.2A or 2.4w - sounds like an indicator bulb somewhere ?

 

 

I think you might have nearly hit nail on head! IIRC Aqualine are prone to installing relays all over the place. Possibly in this case the bilge pump is normally powered by the domestic bats, but with an option to automatically switch over to using engine bat if the former is flat (or switched off) by means of a relay or two.

 

In the short term it looks like the answer is to leave the domestic isolator on and just ensure everything on the boat is turned off. Longer term you could install a bilge pump supply direct from the domestics (or direct from the eng bat if you are confident that it will hardly ever come on) and do away with the relays. This is of course just a hypothesis at this stage, to be confirmed by looking at the wiring diagram.

[NBDensie]

I think you might have nearly hit nail on head! IIRC Aqualine are prone to installing relays all over the place. Possibly in this case the bilge pump is normally powered by the domestic bats, but with an option to automatically switch over to using engine bat if the former is flat (or switched off) by means of a relay or two.

 

In the short term it looks like the answer is to leave the domestic isolator on and just ensure everything on the boat is turned off. Longer term you could install a bilge pump supply direct from the domestics (or direct from the eng bat if you are confident that it will hardly ever come on) and do away with the relays. This is of course just a hypothesis at this stage, to be confirmed by looking at the wiring diagram.

 

Sounds interesting - you are right about the Pole's love of relays. With the rain I havent had chance or the enthusiasm to visit the boat so no diagram yet.

 

 

Thanks for the replies

 

Are you sure you are not just measuring the motor windings in the bilge pump?

 

Rick

 

Could be, but it should still be there when I turn the isolator to let current flow through the main cable. As in the original post this stops the "short circuit".

Edited April 30, 2012 by NBDensie