Engine Extractor Runs Briefly at Night

[Paulfireblade]

So, I have an extractor fan in the engine bay running from a fused relay and the signal line comes from the red wire going to the ecu, so when engine is running relay runs the fan and when engine is turned off the fan goes off so all good except at night after we turn off the two pole battery isolators for the engine.

With all power disconnected from engine the extractor will run randomly for a few seconds repeatedly from time to time.

I replaced the relay but it still did it, so I removed the signal wire from the relay and there is generally 0.8 - 1.0 volt on the wire coming from the engine electrics when the neg and pos from engine battery isolated and sometimes it climbs briefly to 1.7 volts which is then enough to operate the relay.

So I appear to have one or two stray volts flowing around my engine electrics which doesn’t sound great.

Could it be a problem with the Split charger feeding voltage back through alternator?

It is a VP D1-30, where should signal line for extractor be taken from.

If it wasn’t for the extractor I wouldn’t even know about the random voltage in my engine circuit when supposedly disconnected.

Any ideas anyone, please.

 

[Zing]

I thought it was a special sort of thief.

 

[coopec]

You don't have a humidity sensor in your fan do you?

 

[ChromeDome]

My engine room fan relay is controlled by the ignition switch. Never had an issue.

On a petrol engine I'd want the blower on several minutes before, during and minutes after running the engine, as a safety measure.
Would need to be a manual switch, then.

 

[coopec]

Why Does My Bathroom Fan Turn on by Itself?

 

[Paulfireblade]

You don't have a humidity sensor in your fan do you?

View attachment 147826

No humidity sensor and presumably if it did it would need a permanent live but is switched through the ignition circuit.

 

[Paulfireblade]

My engine room fan relay is controlled by the ignition switch. Never had an issue.

On a petrol engine I'd want the blower on several minutes before, during and minutes after running the engine, as a safety measure.
Would need to be a manual switch, then.

The fan uses a live from the engine to trigger the relay so once engine panel turned on fan starts straight away before engine is started and carries on after engine stops and runs until engine electrics power off, but fan stays off until we turn off the positive and negative engine battery isolators.

 

[Paulfireblade]

Why Does My Bathroom Fan Turn on by Itself?

Double checked and fan does not have a humidity sensor and pretty sure it would need a permanent live if it did.

 

[ChromeDome]

To overrule ECU's and other digital ghosts just make it manual
Edit: Aka connected outside Volvo controls.
You, not Volvo, then decide what's going on.

That would improve things also in the way that your main concern is your own welfare. Can't grant that for Volvo's concern$.

 

[Paulfireblade]

To overrule ECU's and other digital ghosts just make it manual
Edit: Aka connected outside Volvo controls.
You, not Volvo, then decide what's going on.

That would improve things also in the way that your main concern is your own welfare. Can't grant that for Volvo's concern$.

Fair point with manual switching but that still means I have one to two volts floating around in the engine wiring with the engine battery isolated!

where is it coming from?

 

[Alex_Blackwood]

So, I have an extractor fan in the engine bay running from a fused relay and the signal line comes from the red wire going to the ecu, so when engine is running relay runs the fan and when engine is turned off the fan goes off so all good except at night after we turn off the two pole battery isolators for the engine.

With all power disconnected from engine the extractor will run randomly for a few seconds repeatedly from time to time.

I replaced the relay but it still did it, so I removed the signal wire from the relay and there is generally 0.8 - 1.0 volt on the wire coming from the engine electrics when the neg and pos from engine battery isolated and sometimes it climbs briefly to 1.7 volts which is then enough to operate the relay.

So I appear to have one or two stray volts flowing around my engine electrics which doesn’t sound great.

Could it be a problem with the Split charger feeding voltage back through alternator?

It is a VP D1-30, where should signal line for extractor be taken from.

If it wasn’t for the extractor I wouldn’t even know about the random voltage in my engine circuit when supposedly disconnected.

Any ideas anyone, please.

Again, almost impossible to diagnose on line. No idea where your stray, if it is stray, voltage is coming from. As far as the intermittent running is concerned, is it possible that there is a capacitor that is charging and then discharging at a certain level? You say the relay operates at 1.7 volts? Seems strange value. what is the operating voltage of the fan? It must be getting that level from somewhere. If it is 12 volt then it may run on anything from about 9volts. Does it get warm, when not running, with everything disconnected as you describe? can you measure any voltage across the fan connections when all off?
If you could connect a meter appropriately so that you can monitor the "stray" voltage, then disconnect everything associated with the engine until the voltage disappears or changes.
Sorry not much help. I am not familiar with the engine or ECU so basically just flying a couple of kites!
I certainly wouldn't muck about with the ECU and installation if not sure what is what.
Edit: - Should have said, there must be a common source of supply to both the relay, via the ECU, and the fan motor. Probably the ignition switch. Are there any voltages present on the switch when isolators off?
Just a thought. You do have your meter on d.c. Volts?.

 

[NormanS]

I have an extractor fan in my engine space. It's the engine.

 

[Boater Sam]

Inverter still connected with isolator switches off?

 

[roaringgirl]

You have a theory about the VSR. How could you test out that theory? Did you observe the polarity of the stray current?

 

[Alex_Blackwood]

You have a theory about the VSR. How could you test out that theory? Did you observe the polarity of the stray current?

As I said work back from where you know the voltage exists. Is it a VSR ? He just said "charge splitter"

 

[Paulfireblade]

Again, almost impossible to diagnose on line. No idea where your stray, if it is stray, voltage is coming from. As far as the intermittent running is concerned, is it possible that there is a capacitor that is charging and then discharging at a certain level? You say the relay operates at 1.7 volts? Seems strange value. what is the operating voltage of the fan? It must be getting that level from somewhere. If it is 12 volt then it may run on anything from about 9volts. Does it get warm, when not running, with everything disconnected as you describe? can you measure any voltage across the fan connections when all off?
If you could connect a meter appropriately so that you can monitor the "stray" voltage, then disconnect everything associated with the engine until the voltage disappears or changes.
Sorry not much help. I am not familiar with the engine or ECU so basically just flying a couple of kites!
I certainly wouldn't muck about with the ECU and installation if not sure what is what.
Edit: - Should have said, there must be a common source of supply to both the relay, via the ECU, and the fan motor. Probably the ignition switch. Are there any voltages present on the switch when isolators off?
Just a thought. You do have your meter on d.c. Volts?.

Your thoughts appreciated. There is only voltage going to fan when relay operates, and the triggering voltage going to the coil terminal on the relay (normally pin 86) is fed from a red/live wire in circuit to ECU (tapped into) and it is that voltage which seems to fluctuate and occasionally goes high enough to pull in relay. It is a 12 volt relay and I agree 1.7 volt seems a bit low to pull in the relay and it may well go higher but that is the highest I have seen (I have a peak hold AVO which I will take to use next time.

The twist in the plot for me was that with engine turned off but 12 volts available from engine battery to engine the fan only runs when it is supposed to but once positive and negative isolators from engine battery turned off then fan relay will pull in and turn extractor on briefly from time to time.

I just wondered if anyone had had a similar issue and as you say a process of elimination is required and regarding meter, I certainly hope it was on DC

 

[Paulfireblade]

Inverter still connected with isolator switches off?

Good thinking but don't have one fitted

 

[Paulfireblade]

You have a theory about the VSR. How could you test out that theory? Did you observe the polarity of the stray current?

It is a positive voltage and the split charge system came to mind as it connects the engine charge system and house batteries so seemed a possible means of stray volts flowing around the engine when the engine battery isolators are turned off.

 

[Paulfireblade]

As I said work back from where you know the voltage exists. Is it a VSR ? He just said "charge splitter"

The engine definitely charges the house batteries and it is a 20 year old French boat so presumably something would have been factory fitted but I am not remotely familiar with how my system is wired but looks like I will need to investigate and try disconnecting it and see if that stops the presence of voltage in the engine when engine battery isolated.

I presume even a 20 year old system would have some form of voltage sensing relay or have they improved since that time?

 

[PaulRainbow]

I presume even a 20 year old system would have some form of voltage sensing relay or have they improved since that time?

They have improved, by fitting VSRs instead of diodes. Yours will almost certainly have a diode pack. I don't recall a diode pack ever doing what you describe, but still worth checking. Look for something like one of these :

split charge diode - Google Search