Charging voltage?

[Phantom]

After a rare night on EHU and the leisure batteries being charged by the onboard charger I noticed that the battery voltage stayed higher for much longer during later off grid use than usual, like they had more charge in them so I checked the alternator output voltage. At the starter battery it was 14.2v but only 13.5v or less at the leisure batteries. All batteries are wet lead and connected by a VSR but are about 5 metres apart so guess the 7 metres of cable may be causing the voltage drop. I'm now wondering if this lower charge voltage is denying the leisure batteries some degree of charge? Is it worth running another cable to cure the voltage drop as not much solar?

 

[SquirrellCook]

This is a very old problem when trying to charge a second batter. You really need a battery to battery charger to do it properly. You just won’t get enough volts by simply connecting the two together.

 

[wildebus]

Pretty much as Squirrelcook says.

What would be interesting to do is the following:

With the engine on and so VSR activated check the following points:

1. Starter Battery +ve Post
2. Input to VSR
3. Output from VSR
4. Leisure Battery +ve Post

That will tell you the losses on the two cables and the VSR itself.
You are reporting a 0.7V drop between the two batteries. Apparently there are some VSRs that have a 0.7V drop internally - you may have one of those?

 

[Phantom]

You are reporting a 0.7V drop between the two batteries. Apparently there are some VSRs that have a 0.7V drop internally - you may have one of those?

Thanks, it's a Durite VSR. I'll check those readings tomorrow.