Leisure battery not charging via starter battery (T5)

[JukeBox]

My starter battery (SB) is 3 months old; my leisure battery (LB) is less than 12 months old. Using a multimeter, the readings are as follows:

SB voltage with engine off: 12.85
SB voltage with engine running: 14.15
LB voltage with engine off: 12.43
LB voltage with engine running: 12.43
Leisure battery not charging via starter battery (T5)

With engine running:

When the terminal clamps are disconnected from the LB, testing the voltage across those terminal clamps gives a reading of 14.05V

When those same terminals clamps are connected to the LB, the voltage then tested across the terminal clamps reads 12.43V. Obviously this needs to be up at the 14V range.

Does this sound like there’s a problem with the LB? Even if it’s less than 12 months old? I'm guessing the voltage sensitive relay is working ok since the voltage across the terminal clamps when disconnected from the LB is reaching 14.05? Or could it be another issue I’m missing?

Many thanks for any advice, I’m at a loss now ¯\_(ツ)_/¯

 

[Pete C]

A high resistance anywhere in the link between SB and LB or a poor earth somewhere could give those symptoms.

I would check all connections carefully - live side and earth.

Posting some photos could help us too.

Pete

 

[oldiebut goodie]

voltage can show where current will not pass, my money is on poor earth connection - this is invariably the problem with heaters with these symptoms.

 

[Pete C]

The high resistance could of course be in the VSR - how old is it ?

Pete

 

[Lightrofit]

What year is your van?

Have you earthed your LB?

 

[JukeBox]

Thanks for your replies. Here are some answers to some of the questions:

It's a 2010 T5 diesel.
I don't know the exact age of the VSR, but it most likely dates to 2015.
Attached are some photos of where the LB sits under the driver's seat.

As you can see, there are some cables which lead into cavities so I cannot tell where some of these go. Not sure about the earthing. And there are three cables which seem to go nowhere - the red one rising from the floor and connected to nothing; the black cloth-covered cable leading from the VSR but connected to nothing; the black cable with a yellow end coiled immediately above the VSR and also connected to nothing. Hoping you can make these out from the photos.

Hope this helps? Thanks again.

 

[Pete C]

One question - has it ever worked OK in your ownership, or is this new to you ?

Pete

 

[IestynD]

you could always bypass the relay for a test... That would then tell you if that was at fault or if it is the battery (leisure).

Clearly the alternator is working as expected as you see good charge to the SB once its running.

Bypass the relay and then report back.

 

[JukeBox]

@Pete C - no, I don’t believe it has ever really worked properly. I’ve had it for 1.5 years and have generally relied on charging the LB from the mains before each trip, which works ok. But I’d like it to charge properly through driving too.

@lestynD - thanks. However, wouldn’t the fact that the voltage across the terminal clamps, when they’re disconnected from the LB, gets to 14.05V, suggest that the relay is working ok? Happy to be told otherwise though!

 

[Pete C]

Getting 14.05v suggests that the relay is physically moving the contacts closed, but if there is a high resistance between them (burnt and pitted over the years), then you would only notice this when current was drawn, hence the suggestion of carefully bridging the VSR to see what happens.

Pete

 

[IestynD]

Another option is to swap the batteries... its either the battery thats faulty or the relay. (my money is relay).

If you swap the batteries around then the LB will be given a direct charge from the alternator... does it accept this charge and report 14+V?

The starter battery is now connected via the relay... is this receiving 14v when the engine is running? If not, its almost certainly the relay (or wiring) that at fault as the problem stayed with the location of the leisure battery.
If the starter battery once in the position of the leisure battery is getting 14v then perhaps its the battery thats at fault - Although it could still be a temperamental earth!

Good luck and keep us informed how you get on

 

[T6ChrisO]

Maybe a daft question but lets say your LB was on 11v, how long would you have to drive for to get your LB up to say 12.5v? I was driving for 4 hours last week and only saw a minor increase. Only item being used was the Fridge whilst I was driving. Im just wondering if I too have an issue

 

[Samro]

My starter battery (SB) is 3 months old; my leisure battery (LB) is less than 12 months old. Using a multimeter, the readings are as follows:

SB voltage with engine off: 12.85
SB voltage with engine running: 14.15
LB voltage with engine off: 12.43
LB voltage with engine running: 12.43
Leisure battery not charging via starter battery (T5)

With engine running:

When the terminal clamps are disconnected from the LB, testing the voltage across those terminal clamps gives a reading of 14.05V

When those same terminals clamps are connected to the LB, the voltage then tested across the terminal clamps reads 12.43V. Obviously this needs to be up at the 14V range.

Does this sound like there’s a problem with the LB? Even if it’s less than 12 months old? I'm guessing the voltage sensitive relay is working ok since the voltage across the terminal clamps when disconnected from the LB is reaching 14.05? Or could it be another issue I’m missing?

Many thanks for any advice, I’m at a loss now ¯\_(ツ)_/¯

Is your LB Lifepo4 with BMS? My BMS cuts off charging at 0 degrees and does not allow charging until 10 degrees. (It still allows discharging and operates normally other than failing to accept charge.)

 

[JukeBox]

I haven't yet had chance to bridge the VSR (I have Reynauld's in my hands and so my fingers won't work outside in these temperatures!). However....

I have an "intelligent pulse repair charger" which I used to fully charge the LB last night. Now, when I connect it to terminals under the driver's seat, and with the engine running, the readings are as would be hoped for:

When the terminal clamps are disconnected from the LB, testing the voltage across those terminal clamps gives a reading of 14.15V

When those same terminals clamps are connected to the LB, the voltage then tested across the terminal clamps reads 14.08V.

I won't really know if this has solved the problem long term until I go out and use the LB in the van for a few days and see whether it recharges again.

Could it be that the LB itself was providing the high resistance mentioned before (rather than the VSR), and that by repairing the LB by fully charging it from the repair charger has reduced this resistance and solved the problem?

 

[JukeBox]

Is your LB Lifepo4 with BMS? My BMS cuts off charging at 0 degrees and does not allow charging until 10 degrees. (It still allows discharging and operates normally other than failing to accept charge.)

Thanks, but I don't think so - I was having the same problems during the summer.

 

[Samro]

Thanks, but I don't think so - I was having the same problems during the summer.

Oops! If I read your post properly, I'd have realised that you are charging with a VSR!

Could it be that the LB itself was providing the high resistance mentioned before (rather than the VSR), and that by repairing the LB by fully charging it from the repair charger has reduced this resistance and solved the problem?

A pulse charge can recover starter batteries to allow them to last a good while longer, but I have noted that leisure battery banks don't fair so well following desulfation.

In my experience leisure batteries are generally reaching the end of their life from the point that an initial loss of performance is noted.

Desulfation is less beneficial for a LB bank than starter batteries due to the higher depth of discharge that you would experience from a bank used for engine start.)

I'd let your recovered battery rest for 48 hours, and drop test it before doing too much else. (It could be that its voltage will significantly drop, although if this were the case I'd have thought you'd notice that the battery case has been getting warm?)

If it holds its voltage and passes the drop test, then it is likely that there is a problem with the charging system.

 

[Pete C]

I haven't yet had chance to bridge the VSR (I have Reynauld's in my hands and so my fingers won't work outside in these temperatures!). However....

I have an "intelligent pulse repair charger" which I used to fully charge the LB last night. Now, when I connect it to terminals under the driver's seat, and with the engine running, the readings are as would be hoped for:

When the terminal clamps are disconnected from the LB, testing the voltage across those terminal clamps gives a reading of 14.15V

When those same terminals clamps are connected to the LB, the voltage then tested across the terminal clamps reads 14.08V.

I won't really know if this has solved the problem long term until I go out and use the LB in the van for a few days and see whether it recharges again.

Could it be that the LB itself was providing the high resistance mentioned before (rather than the VSR), and that by repairing the LB by fully charging it from the repair charger has reduced this resistance and solved the problem?

I don’t think you have solved the problem, just charged the LB.

Pete

 

[JukeBox]

I don’t think you have solved the problem, just charged the LB.

Pete

Even if now, with the engine off, the LB reads 12.43V but then with the engine running the LB reads 14.08V? Doesn't that suggest that the VSR is working correctly? And that the resistance of a very depleted LB may have been the problem?

Thanks for the continued suggestions. I'm away now for a few days, I'll be back at the weekend to see how it's working then. If still not right, I'll look at replacing the VSR.

 

[Pete C]

It's likely that the LB is now full, so is not drawing any current, so the voltage remains high as any resistance in the circuit is irrelevant under those conditions.
As you say, see what happens now you start to use the LB.

Pete