Re: Convert battery powered to battery backup

jasen wrote:
On 2007-04-20, ehsjr <ehsjr@xxxxxxxxxxxxxxxx> wrote:

As I said in the first two lines of my post:
"I suspect that you cannot do it. It is likely that the
24 volts is not a supply, but rather just a switched
loop that the tstat closes when it calls for heat. "


if it runs for years on batteries, you could probably get enough power from a current transformer to run the unit while the switch is closed.

Bye.
Jasen

Possibly. And as an alternative one could charge supercaps
while the switch is open, to provide power when it's closed,
or modify it at the other end with a lower voltage relay and a
resistor in the closed tstat circuit at the tstat end so there
would be voltage available, or add a wall wart power supply, etc.
It can be Rube Goldberged to get it to work. But that is not
the point.

He assumed a 24 volt supply in the wall. He cannot do it based
on that assumption if the assumption is wrong, which is highly
probable. It is almost certainly a switched loop, not a supply.
He cannot simply regulate it to 3V, as he mentioned, and use it
in place of the batteries. Additionally, it is almost certainly
AC (as it would have to be for your CT idea to work), not DC, so
that's another reason I suspect he cannot do it. He would need
to not just regulate it, he'd need to add a rectifier and filter
first to get DC. His idea makes no mention of converting AC
to DC.

Ed
.

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