Split-charge relay energised with engine off

[DavidExpert]

Hello

After some work was done on my engine recently (not by me), I noticed the starter and leisure batteries were showing exactly the same voltage which seemed unlikely. Several measurements were taken and in each case this was true. For reference, i have 3 x 110Ah AGM leisure plus one 95Ah starter. Charging is from alternator through split charge relay, Victron (when on shoreline which I am not at present) and MPPT solar.

The voltage across the relay's trigger pins is 12.0V. The solar is currently sticking 13.2V into the batteries which I have also measured across the alternator terminals.

The alternator is getting quite warm which alarms me. Moreover, when the sun goes down this evening, i will presumably be drawing fridge power etc from all the batteries instead of just the leisure ones.

Being very non-expert at this, should I - for ease until someone can look at it next week - simply pull off the blue-capped wire that goes to the alternator earth (number 85 on the relay) overnight so as to de-energise the relay and only drain from the leisure bank?

I also noticed while cruising yesterday that the voltage (being observed on the solar charge controller) never went above 13.2 but I'd have expected the alternator running to shove it up more than that unless maybe the relay de-activated itself while engine running (in which case I'd merely have seen whatever the solar charge controller was putting in which may be 13.2 perhaps)

I have attached a pic of the relay connections. There are three wires going to "86"; one with a blue tip stems from the alternator and I would presume to be the expected trigger for when the alternator is running. The other (yellow-tipped connector) has a (disconnected) Adverc brown wire plus another brown/black wire which disappears off towards the starter motor with the +ve cables from 87, possibly (though I can't see it) onto the starter motor +ve as this is where the cables from 87 attach.

It's all a bit peculiar because I thought it had all been put back the way it started, and it's been like that for the last two years since I had the relay replaced.

Thanks

David

[Detling]

Is it likely that the solar is keeping the voltage high enough to energise the relay. When the sun goes down so will the solar and I would expect the relay to be de-energised separating the two banks. In the morning the sun comes up the solar controller raises the voltage and the relay will energise connecting the batteries.

[DavidExpert]

If it were a voltage-sensing relay then I imagine that would make sense (and indeed be desirable perhaps). It isn't though, it's one of those relays that has a distinct "trigger" across two pins of the relay and that should normally be off unless the engine and alternator are on.

Or, has someone transformed it into a VSR by virtue of connecting up the leisure bank to it? I suppose it depends what voltage the relay needs to trigger but it seems odd in my limited understanding of these things.

[WotEver]

1 hour ago, DavidExpert said:

The voltage across the relay's trigger pins is 12.0V

You really need to find out where this 12V is coming from which I guess means tracing the wires. It’s normally fed by the ignition switch so unless someone has moved the connection (quite possible) it would suggest a faulty switch. 

In the mean time, I suggest you disconnect (and tape up) the relay feed overnight. 

1 hour ago, DavidExpert said:

should I - for ease until someone can look at it next week - simply pull off the blue-capped wire that goes to the alternator earth

Yes. 

Edited September 29, 2017 by WotEver
Clarity

[Sir Nibble]

You have a main +ve diode failed short circuit in the alternator. The alternator is warm because the field is permanently fully energised.

[DavidExpert]

33 minutes ago, Sir Nibble said:

You have a main +ve diode failed short circuit in the alternator. The alternator is warm because the field is permanently fully energised.

Thank you. Is that something I get can get fixed cost-effectively or do I realistically have to buy a whole new alternator?

54 minutes ago, WotEver said:

You really need to find out where this 12V is coming from which I guess means tracing the wires. It’s normally fed by the ignition switch so unless someone has moved the connection (quite possible) it would suggest a faulty switch. 

In the mean time, I suggest you disconnect (and tape up) the relay feed overnight. 

Yes. 

Thank you.

[Sir Nibble]

4 minutes ago, DavidExpert said:

Thank you. Is that something I get can get fixed cost-effectively or do I realistically have to buy a whole new alternator?

Thank you.

That depends upon the alternator type. Disconnect the alternator main +ve and if the relay drops out that proves it. Post a pic of the alternator and I can advise on repair

 

[Tony Brooks]

I do not see how a failed positive diode would keep the relay permanently engaged. I do see it will give a allow charging voltage so you may have two faults BUT:

1. a low charging voltage soon after starting can be normal and caused by the alternator charging at maximum output.

2. an alternator charging at higher outputs does not get warm, it gets very hot, sometimes uncomfortably so. As Snibs says they do get warm when stopped if left with the ignition turned on and it sounds as if yours probably is.

This means that I do not have enough info to draw much of a conclusion apart from you need to sort out that relay

I agree with Wotever for now pull a wire off the relay every night and insulate it but also find out where the wires on the piggyback  blade run to because pulling the pair off in one will isolate the relay coil but may still feed the alternator D+ terminal all night.

I suspect its time for a bi-directional VSR and let it sort out its own energisation.

 

PS further thought means I agree with Snibs, battery voltage will feed through the shorted diode and then via the field diodes to keep the alternator energised. Good diagnosis SirN.

Edited September 29, 2017 by Tony Brooks

[WotEver]

1 hour ago, Sir Nibble said:

You have a main +ve diode failed short circuit in the alternator. The alternator is warm because the field is permanently fully energised.

Nice one Snib

[Sir Nibble]

Current from alternator B+ through shorted diode to stator then out through field diodes to energise rotor winding and relay. Charge light is probably on with ignition off too.

[DavidExpert]

35 minutes ago, Sir Nibble said:

That depends upon the alternator type. Disconnect the alternator main +ve and if the relay drops out that proves it. Post a pic of the alternator and I can advise on repair

 

Here's a not terribly good pic. Am I right in thinking that disconnecting that +ve means I've got to be very careful the spanner doesn't touch any of the rest of the alternator as that'd be ground and then there'd be a big bang?

18 minutes ago, Sir Nibble said:

Current from alternator B+ through shorted diode to stator then out through field diodes to energise rotor winding and relay. Charge light is probably on with ignition off too.

I didn't understand a word of that, sorry but I don't have any lights on anywhere although I'm not sure I even have a "charge light". Ignition is off though inasmuch as the switch is off and the key is out

[WotEver]

1 minute ago, DavidExpert said:

Am I right in thinking that disconnecting that +ve means I've got to be very careful the spanner doesn't touch any of the rest of the alternator as that'd be ground and then there'd be a big bang?

Yes. 

If the alternator is wired via the isolator (and it may well not be) then you can turn the isolator off first. 

[DavidExpert]

1 minute ago, WotEver said:

Yes. 

If the alternator is wired via the isolator (and it may well not be) then you can turn the isolator off first. 

Actually it is - hooray. It's a single switch which has two separate sets of connections, one to the starter motor & battery, and the other pair for the leisure circuits.

I also notice the alternator is wired to the leisure side not the starter battery. So the sequence of wires is: starter battery->isolator->starter motor->relay->alternator->isolator other pair->leisure bank.

presumably this also means that despite switching off the relay (by disconnecting its earth lead to the alternator), the faulty alternator will sit and drain the leisure bank overnight.

Many thanks for the continued assistance.

[DavidExpert]

43 minutes ago, Tony Brooks said:

I do not see how a failed positive diode would keep the relay permanently engaged. I do see it will give a allow charging voltage so you may have two faults BUT:

1. a low charging voltage soon after starting can be normal and caused by the alternator charging at maximum output.

2. an alternator charging at higher outputs does not get warm, it gets very hot, sometimes uncomfortably so. As Snibs says they do get warm when stopped if left with the ignition turned on and it sounds as if yours probably is.

This means that I do not have enough info to draw much of a conclusion apart from you need to sort out that relay

I agree with Wotever for now pull a wire off the relay every night and insulate it but also find out where the wires on the piggyback  blade run to because pulling the pair off in one will isolate the relay coil but may still feed the alternator D+ terminal all night.

I suspect its time for a bi-directional VSR and let it sort out its own energisation.

 

PS further thought means I agree with Snibs, battery voltage will feed through the shorted diode and then via the field diodes to keep the alternator energised. Good diagnosis SirN.

Thank you Tony. The ignition (switch) is off. I have pulled off the wire I mentioned and this appears to have separated the battery banks as they are now at slightly different voltages. The "extra" wire disappears into a wrapped collection of largely brown wires but beyond that I can't easily see.

i was scanning canalworld for VSR info as it seemed like a better solution but there were assorted posts stating various issues with them as well and "for that reason most boaters stick with a regular relay". It's all very frustrating and complicated.

[WotEver]

17 minutes ago, DavidExpert said:

presumably this also means that despite switching off the relay (by disconnecting its earth lead to the alternator), the faulty alternator will sit and drain the leisure bank overnight

Not if you disconnect the B+ connection

[DavidExpert]

10 minutes ago, WotEver said:

Not if you disconnect the B+ connection

I am going to go and do that now. With apologies for the torrent of queries, does this diode fault mean that the alternator might as well stay disconnected because it won't be producing any charge when the engine's running anyway?

[Sir Nibble]

The alternator will continue to make charge, but not much. If you leave it connected it will draw about 3A 24-7 and that amounts to a substantial drain on the battery. Disconnect it and only reconnect it just before you start the engine. The alternator is a type designated "A127" which is cheap and plentiful on ebay so not worth fixing. The connection to domestic battery first is entirely correct.

[DavidExpert]

12 minutes ago, Sir Nibble said:

The alternator will continue to make charge, but not much. If you leave it connected it will draw about 3A 24-7 and that amounts to a substantial drain on the battery. Disconnect it and only reconnect it just before you start the engine. The alternator is a type designated "A127" which is cheap and plentiful on ebay so not worth fixing. The connection to domestic battery first is entirely correct.

Great, thank you. So source a direct replacement and swap it in? (unless one can swap in better alternators,min which case suggestions welcomed). I have disconnected it and wrapped the end of the wire in vast swathes of gaffer tape to prevent any contact with the hull while it lolls around in the engine bay.

[DavidExpert]

1 hour ago, Sir Nibble said:

That depends upon the alternator type. Disconnect the alternator main +ve and if the relay drops out that proves it. Post a pic of the alternator and I can advise on repair

 

I disconnected the B+ wire (from alternator to isolator to leisure bank) and reconnected the relay exactly as it originally was; turned the isolator back on and the relay remained disconnected, the control terminals showing 0V across them, and the starter battery showing 12.5 with the leisure bank at a paltry 12.3. I will leave it disconnected overnight and rewire before plodding on tomorrow - I'm due to have the boat out on Monday for blacking and a BSS so this alternator issue is really badly timed!

Any ideas what on earth would have caused it to fail? It does explain why I thought my leisure batteries were shot when I set out a week ago, they must have been draining nonstop and they're quite ancient anyway!

[WotEver]

2 minutes ago, DavidExpert said:

Any ideas what on earth would have caused it to fail?

The one thing that Alternators hate is excess heat. Other than that it’s just one of those things. 

[Sir Nibble]

Sounds good. The old A127 is a good bit of kit available cheapo and quickly and sufficient for your set up so what's not to like? You may want to stop somewhere close to a garage since the new alternator will come without a pulley and the quickest easy way to swap it over from the old one is to get a friendly mechanic to do it with his impact wrench.

[DavidExpert]

3 minutes ago, WotEver said:

The one thing that Alternators hate is excess heat. Other than that it’s just one of those things. 

It does sit in a hot engine bay with no side slits in the hull for air. Also, for all I know it's the original (17 year old) item so maybe it's just had its time. Anyway, I will order a replacement and many thanks for the prompt, useful and understandable help! Cheers

[Sir Nibble]

3 minutes ago, WotEver said:

The one thing that Alternators hate is excess heat. Other than that it’s just one of those things.

Yes this. Rovers used to suffer badly from this because the alternator was only prevented from drawing it's cooling air straight off the exhaust downpipe by a frequently missing tin heatshield.

[DavidExpert]

2 minutes ago, Sir Nibble said:

Sounds good. The old A127 is a good bit of kit available cheapo and quickly and sufficient for your set up so what's not to like? You may want to stop somewhere close to a garage since the new alternator will come without a pulley and the quickest easy way to swap it over from the old one is to get a friendly mechanic to do it with his impact wrench.

Crikey. I'll have to get it delivered to where I'm having the blacking done but hopefully they'll have a Man With A Wrench who can sort it. Many, many thanks for the help. Now if I could just sort this wretched oil leak and the (new) diesel leak...

[WotEver]

1 minute ago, DavidExpert said:

It does sit in a hot engine bay with no side slits in the hull for air.

There must be some, surely? Otherwise how does the engine breath?