On 13/04/2014 12:03, Tim+ wrote:
wrote:
Following on from the thread about second use for old electric car
batteries: surely as end of life is reached for any cell the self
discharge increases and thus a higher proportion of the charge gets
expressed as heat?

I need to provide hot washing water in one of our vans, about 10
litres is enough and these basin units are readily available for £250.

I can see a split charge system will only charge the second battery
when the main vehicle battery exceeds 13.5V, and even a facility I'm
told that will only charge it on overrun.


Really? Why? Surely it'll charge whenever the engine is running?

It depends on the split charge relay in use. Some just connect the
batteries in parallel with the engine running, some sense the charge on
the starter battery, and connect intelligently.

As for how do you stop the leisure battery discharging too far, it's
done by sensing the battery voltage. As all lead acid batteries have the
same (Roughly) discharge curve against the percentage of available
charge used, even ones which are approaching their end of life, there's
no need to calculate amp hours used and put in.

These problems were all solved long ago by the boaters and motorhome owners.

One slightly more expensive way to get quicker hot water is to use a
well insulated calorifier heated by the engine, which has a high power
alternator fitted to run an small immersion heater as well. If you have
room, that is.
--
Tciao for Now!

John.