Electric/Battery gremlins

[hoopdriver]

1 minute ago, Tony Brooks said:

 

Through a shorting diode(s), quite possibly. The alternator should also be warm to the touch

But this would not be a normal thing with a healthy system?

[nicknorman]

8 minutes ago, hoopdriver said:

Thank you! Im remembering now that when the guy checked the alternator he checked the connection at the BMS (I might not be phrasing that correctly) and was puzzled about why there would be current there with the engine off. 
 

I mentioned this to the guy who installed it and he said it would be current coming from the battery.  Could that be right?

 

 

"The battery" - but which battery! In your screenshot of the BMS after engine shut down, you can see that the alternator voltage is slightly higher than the Lithium battery voltage. It might be concievable to put that voltage down to back-leakage from the lithium battery if the voltage on the alternator terminal was slightly lower, but not feasible since the voltage on the alternator terminal is slightly higher. Current always flows "down hill" ie from higher to lower voltage.

 

A lead acid battery, just having been taken off charge, will have a voltage of around 13.5v. Seems an unlikely coincidence!

Edited December 11, 2024 by nicknorman

[hoopdriver]

Just now, nicknorman said:

"The battery" - but which battery! In your screenshot of the BMS after engine shut down, you can see that the alternator voltage is slightly higher than the Lithium battery voltage. It might be concievable to put that voltage down to back-leakage from the lithium battery if the voltage on the alternator terminal was slightly lower, but not feasible since the voltage on the alternator terminal is slightly higher. Current always flows "down hill" ie from higher to lower voltage.

He definitely meant the lithium battery.

 

I may not be tech savvy but even I wondered how you could flow “uphill”

[nicknorman]

4 minutes ago, Tony Brooks said:

 

Through a shorting diode(s), quite possibly. The alternator should also be warm to the touch

But only if the alternator is connected directly to a battery, which we are told it isn't.

[hoopdriver]

Just now, nicknorman said:

But only if the alternator is connected directly to a battery, which we are told it isn't.

It’s connected to the BMS 

[nicknorman]

Just now, hoopdriver said:

He definitely meant the lithium battery.

 

I may not be tech savvy but even I wondered how you could flow “uphill”

 

There has got to be a connection to a lead acid battery in there, even if the installer doesn't realise it! If there isn't a domestic lead acid battery, it must be the starter battery.

Just now, hoopdriver said:

It’s connected to the BMS 

Yes, hence I said "directly". And as you said, current doesn't flow up hill so it can't be the Lithium battery that is holding the alternator terminal voltage up.

[hoopdriver]

Just now, nicknorman said:

 

There has got to be a connection to a lead acid battery in there, even if the installer doesn't realise it! If there isn't a domestic lead acid battery, it must be the starter battery.

Not comforting to think the installer doesn’t realise it….

 

there is only the starter battery and the lithium - that’s it. Nothing else 

[Tony Brooks]

2 minutes ago, nicknorman said:

But only if the alternator is connected directly to a battery, which we are told it isn't.

 

but the diagram sows the start LA battery directly connected to the alternator, so current could flow from the start battery through the alternator.  I think we need a diagram for the system as installed.

[nicknorman]

Just now, Tony Brooks said:

 

but the diagram sows the start LA battery directly connected to the alternator, so current could flow from the start battery through the alternator.  I think we need a diagram for the system as installed.

But don't forget that diagram is for a vehicle with a single alternator.

[hoopdriver]

Just now, Tony Brooks said:

 

but the diagram sows the start LA battery directly connected to the alternator, so current could flow from the start battery through the alternator.  I think we need a diagram for the system as installed.

Yes - I wish I had one …. 
 

 

[Tony Brooks]

1 minute ago, hoopdriver said:

Not comforting to think the installer doesn’t realise it….

 

there is only the starter battery and the lithium - that’s it. Nothing else 

 

For clarity, how many alternators? If it is two then perhaps the start alternator is charging it's own LA battery, while the domestic alternator feeds he Victron BMS, but if so that is not what the diagram shows, I would expect another LA battery.

[nicknorman]

Anyway all this chit chat is speculation! What we need is a categoric check and (almost certainly) repair of the domestic alternator. The rest is of less consequence other than perhaps the much smaller starter alternator is doing all the work at present and may thus have a short life if the domestic alternator isn't repaired pronto!

2 minutes ago, Tony Brooks said:

 

For clarity, how many alternators? If it is two then perhaps the start alternator is charging it's own LA battery, while the domestic alternator feeds he Victron BMS, but if so that is not what the diagram shows, I would expect another LA battery.

There are 2 alternators.

Edited December 11, 2024 by nicknorman

[hoopdriver]

Just now, Tony Brooks said:

 

For clarity, how many alternators? If it is two then perhaps the start alternator is charging it's own LA battery, while the domestic alternator feeds he Victron BMS, but if so that is not what the diagram shows, I would expect another LA battery.

Sure - for clarity there are two alternators.  One fir the starter battery one fir the lithium/domestic. There are only two batteries involved - starter and lithium. There is no extra LA. The guy who installed it specifically said he didn’t think such things were necessary since there was a BMS 

[Tony Brooks]

3 minutes ago, nicknorman said:

But don't forget that diagram is for a vehicle with a single alternator.

I agree

 

3 minutes ago, hoopdriver said:

Yes - I wish I had one …. 

 

At this point, a totally unhelpful comment would relate to a three letter acronym.

 

3 minutes ago, nicknorman said:

Anyway all this chit chat is speculation! What we need is a categoric check and (almost certainly) repair of the domestic alternator. The rest is of less consequence other than perhaps the starter alternator is doing all the work at present and may thus have a short life if the domestic alternator isn't repaired pronto!

There are 2 alternators.

 

Agree with that as well. Ideally we need a diagram from the boat. or a start, only the thicker cables and what hey connect to would help.

[hoopdriver]

2 minutes ago, Tony Brooks said:

I agree

 

 

At this point, a totally unhelpful comment would relate to a three letter acronym.

 

 

Agree with that as well. Ideally we need a diagram from the boat. or a start, only the thicker cables and what hey connect to would help.

Would photos help? I was originally promised a laminated schematic but that never happened (and to be fair I didn’t pursue it as I should have - and will now!)

[Tony Brooks]

2 minutes ago, hoopdriver said:

Sure - for clarity there are two alternators.  One fir the starter battery one fir the lithium/domestic. There are only two batteries involved - starter and lithium. There is no extra LA. The guy who installed it specifically said he didn’t think such things were necessary since there was a BMS 

 

Well, I think that he may be wrong. The Victron diagram seems to show the LA start battery being used to prevent a voltage surge from the alternator when the BMS stops charging. It presents a load to the alternator at all times. Without such a load, then a BMS disconnect may well blow a diode or two in the alternator.

[hoopdriver]

1 minute ago, Tony Brooks said:

 

Well, I think that he may be wrong. The Victron diagram seems to show the LA start battery being used to prevent a voltage surge from the alternator when the BMS stops charging. It presents a load to the alternator at all times. Without such a load, then a BMS disconnect may well blow a diode or two in the alternator.

That would explain a lot 

[Tony Brooks]

5 minutes ago, hoopdriver said:

Would photos help? I was originally promised a laminated schematic but that never happened (and to be fair I didn’t pursue it as I should have - and will now!)

 

I am not sure if photos would help unless the batteries, alternators, the BMS and the wiring was clearly visible. I suspect that if you sat down and started drawing what you can see, you would learn a lot. Go by wire size and wire colours where they go into and out of the wiring loom. It may not be 100% correct, but it would at least be a start.

 

 

 

3 minutes ago, hoopdriver said:

That would explain a lot 

 

Remember, take more notice of Nick and Peter F than me. They are probably far more conversant with that BMS and how it works than I am.

Edited December 11, 2024 by Tony Brooks

[hoopdriver]

11 minutes ago, Tony Brooks said:

 

I am not sure if photos would help unless the batteries, alternators, the BMS and the wiring was clearly visible. I suspect that if you sat down and started drawing what you can see, you would learn a lot. Go by wire size and wire colours where they go into and out of the wiring loom. It may not be 100% correct, but it would at least be a start.

 

 

 

 

Remember, take more notice of Nick and Peter F than me. They are probably far more conversant with that BMS and how it works than I am.

You are all being incredibly helpful! I have learned more this morning, and advanced the possibility of this being resolved, than in the past three months 

[nicknorman]

20 minutes ago, Tony Brooks said:

 

Remember, take more notice of Nick and Peter F than me. They are probably far more conversant with that BMS and how it works than I am.

 

Nevertheless you had a valid point. It was something I had thought about earlier, if you remember the original problem was that the green "allow alternator charging" LED on the BMS was not illuminated when it should have been, due to a fault in the BMS which was then replaced, and now the green "allow alternator charging" LED is on, but the alternator is only producing limited power. Both the BMS failure and the alternator problem occurred at the same time, which suggests they are linked. Once scenario is that a fault in the BMS caused a sudden interruption of alternator current which generated a transient which blew diodes. The only contrary indication to that is the presence of 13.5v on the alternator input terminal of the BMS, a voltage higher than the Li battery. And thus I can't see how that could come from anything other than a lead acid battery (the starter battery) being in parallel with the alternator. Alternators, since that would suggest both alternators were paralelled.

 

What Mr hoopdriver could do is to get his mate to check the voltage on the starter battery, the starter alternator main positive terminal, and the domestic alternator main positive terminal - with the engine switched off. If they are all exactly the same voltage (to within 0.1v) it tells us that the alternators and starter battery are all paralelled. Which would not be a bad way to install the system, it's just not the way we were expecting.

Edited December 11, 2024 by nicknorman

[hoopdriver]

I’ll do that 

[nicknorman]

Is this a new built boat, or a second hand one that originally had lead acid batteries and you then had modified for the lithium system?
 

If the latter, it is conceivable that previous owner decided to connect the starter and domestic alternators together, either directly or via some sort of relay, to increase the maximum charging current. And when your Lithium installer came along, he wasn't aware of that and didn't realise they were already connected together. I am just hypothesising of course!

[hoopdriver]

No, it’s a new build. A year old - I moved in last year at this time. 
 

The same electrician did the entire installation 

Edited December 11, 2024 by hoopdriver

[nicknorman]

10 minutes ago, hoopdriver said:

No, it’s a new build. A year old - I moved in last year at this time. 
 

The same electrician did the entire installation 

 

Then I don't understand where the 13.5v is coming from!

[hoopdriver]

This just gets weirder …

 

I’ve just looked at the app and in the BMS it us showing 13.44v from alternator starter current - and this more than three hours since I shut off the engine 

Edited December 11, 2024 by hoopdriver