Voltage sensitive relay

[Boldly]

Half way into our trip to southern Spain the leisure batteries stopped charging from the alternator. Not a problem in itself as wall to wall sunshine. Got round to having a look this morning and the relay seems to be doing what it should.with the cables disconnected from the leisure battery 14.33 volts. As soon as the cable is put on the battery it immediately reads 12.9 which is the state of the battery.
I have disconnected the solar in case that was interfering with the reading.
Can any electrical guru explain what is happening?

 

[Jev88]

Put cables on battery. Engine running. Now what voltage do you see directly on battery?

 

[headlight]

Half way into our trip to southern Spain the leisure batteries stopped charging from the alternator. Not a problem in itself as wall to wall sunshine. Got round to having a look this morning and the relay seems to be doing what it should.with the cables disconnected from the leisure battery 14.33 volts. As soon as the cable is put on the battery it immediately reads 12.9 which is the state of the battery.
I have disconnected the solar in case that was interfering with the reading.
Can any electrical guru explain what is happening?

Where are you getting the reading of 14.33v from ?

 

[Boldly]

Put cables on battery. Engine running. Now what voltage do you see directly on battery?

That is what I did.
Everything connected as should be 14.3 at starter battery 12.9 at leisure battery. Removed cable from leisure battery terminal and reading end of cable 14.3 again.

 

[Boldly]

Where are you getting the reading of 14.33v from ?

Reading across terminals on starter battery engine running. Also end of split charge cable when removed from leisure battery.

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[DBK]

How do you know it has stopped charging from the alternator? If the sun is shining while driving that could be doing all the charging.

 

[Boldly]

The figures on the screen generally rise to about 14 volts when the engine is started now they are static at the leisure battery voltage. It is not significantly important as the sun is enough. On my return journey through always wet France in November however.....

 

[headlight]

Reading across terminals on starter battery engine running. Also end of split charge cable when removed from leisure battery.

14.33v is a charge voltage so if you are seeing that from the split charge cable with solar disconnected then the split charge is working.

 

[Boldly]

14.33v is a charge voltage so if you are seeing that from the split charge cable with solar disconnected then the split charge is working.

It doesn't seem to be putting it into the battery though as voltage drops as soon as reconnected to leisure battery. Even with the meter on the end of the cable rather than the battery terminal as soon as it's reconnected the voltage is only 12.9 again.
I think there must be a problem with the -ve side of things but am struggling to find it.

 

[Boldly]

Added a jump lead from -ve terminal to earth point got 13.5 volts. Loosened bolt and retightened now 14.17volts so all good for tomorrow's trip to Sevilla and beyond.

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[Jev88]

That is what I did.
Everything connected as should be 14.3 at starter battery 12.9 at leisure battery. Removed cable from leisure battery terminal and reading end of cable 14.3 again.

That is what I did.
Everything connected as should be 14.3 at starter battery 12.9 at leisure battery. Removed cable from leisure battery terminal and reading end of cable 14.3 again.

Dodgy earthing maybe?
Common on old vans. Add a new earth from neg to engine bolt/block.

 

[autorouter]

Everything connected as should be 14.3 at starter battery 12.9 at leisure battery. Removed cable from leisure battery terminal and reading end of cable 14.3 again.

So as I understand it, you are getting 14.3V at the starter battery when the engine is running. With the wire connected to the leisure battery you are getting 12.9V at the leisure battery, but the voltage at the starter battery stays at 14.3V. That means there is a voltage drop of 1.4V between the starter battery and the leisure battery.

A voltage drop means there is some resistance somewhere. Could be anything - clamps not tightened, bad connection, oxidised fuse, something like that probably. If you are measuring at the battery terminals, you could measure at different points like the clamp metal, fuse terminals, any connections etc to see where the voltage drop is.

Edit - sorry, a bit late, you already fixed it, as you said, the resistance was in one of the earth connections.

 

[pappajohn]

13.6v is the battery float voltage.
As the hab battery is fully charged the voltage from solar and split charge will not bang anymore into the battery.
If it constantly pushed 14.4v into the battery it would boil in no time due to overcharge.
Disconnecting split and solar will again show 14.4v on the leads as theres no load.