In article ,
Bill Wright wrote:
On 14/12/2016 21:36, charles wrote:
In article ,
Harry Bloomfield wrote:
charles laid this down on his screen :
You certainly can isolate batteries via diodes. Lucas used to make a
unit -about the same size as an ignition coil specifially for this
purpose. Our tecnical survey vehicles used them in the 70's and '80s.
After then, a hefty relay, which closed when the alternator was
producing enough volts was used.

Because they realised that diodes just did not and could not work?

They did work - we used them for at least 15 years, running technical
equipment off the second battery.

Yes because there was a relay that operated when the alternator was
working. That would be a voltage sensing relay, or if this was years ago
it would work from the ignition warning light circuit.

Bill

No we used diodes without the relay. later we just used the relay. Never
both together,

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from KT24 in Surrey, England