In article ,
Harry Bloomfield wrote:
After serious thinking charles wrote :
They did work - we used them for at least 15 years, running technical
equipment off the second battery.

Perhaps it would, assuming the equipment would be satisfied to work
from a partially charged battery.

Anything car related is designed to work over a wide range of voltage -
say 9-14. The range between starting on a cold day to battery on charge.


The only way you can make diodes work effectively, is by increasing
the input voltage by 0.6 to 0.7 volts to take care of the forward
voltage lost across the junction.

the relay was better.

Of course the relay was much better, the battery would receive a full
charge and the equipment the full voltage.

Apart from starter use, I'd use two diodes to prevent either battery
discharging the other when not on charge. And relays to bypass them for
charging.

But in practice simply fit a larger battery. I've never known any 12v
vehicle that needed two 12v ones. To increase the capacity beyond one 12v
use two large 6v in series. Same as is done with 24v.

--
*The man who fell into an upholstery machine is fully recovered*

Dave Plowman London SW
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