Polarity insensitive

[KC]

I just bought an analog runtime hour meter. Specs state the operating
voltage should be 10-80vdc. Installation instructions state to
connect positive to one terminal and negative to the other terminal,
polarity not necessary since the unit is polarity insensitive.

Since the unit obviously has a motor that needs to run in one
direction only to increment the time, I'm having a hard time
visualizing what they've done inside the sealed unit to make polarity
a non-issue. Any ideas?

KC

 

[Sylvia Else]

I just bought an analog runtime hour meter. Specs state the operating
voltage should be 10-80vdc. Installation instructions state to
connect positive to one terminal and negative to the other terminal,
polarity not necessary since the unit is polarity insensitive.

Since the unit obviously has a motor that needs to run in one
direction only to increment the time, I'm having a hard time
visualizing what they've done inside the sealed unit to make polarity
a non-issue. Any ideas?

KC

Bridge rectifier?

Sylvia.

 

[David Nebenzahl]

Bridge rectifier?

Bingo.

 

[Arfa Daily]

Bridge rectifier?

Sylvia.

Agreed. That's the usual way if the circuitry following can tolerate 2 x
diode drops on the voltage.

Arfa

 

[z]

Agreed. That's the usual way if the circuitry following can tolerate 2 x
diode drops on the voltage.

Arfa- Hide quoted text -

- Show quoted text -

in which case, it ought to run on ac?

 

[Arfa Daily]

Agreed. That's the usual way if the circuitry following can tolerate 2 x
diode drops on the voltage.

Arfa- Hide quoted text -

- Show quoted text -

in which case, it ought to run on ac?


Usually not if it has been designed just as a universal polarity DC device,
as it will have no filter cap etc. It does, however, often work the other
way round. Back in the day, some cordless phones had AC power supplies. When
these failed, or got lost in house moves etc, a DC supply could be used
instead, provided you picked one with about 50% more DC output than the RMS
value of the original AC supply. This allowed for the 2 diode drops, and the
fact that the filter cap would have brought the rectified DC up to
approaching the peak value of the original AC.

It doesn't always work though. Many guitar effects pedals use AC supplies,
and the effect doesn't work when the owners try to substitute a DC supply.
This is because the pedals often have supplementary supplies inside which
rely on having an AC input, to generate negative rails for opamps etc.

Arfa

 

[Baron]

KC Inscribed thus:

I just bought an analog runtime hour meter. Specs state the operating
voltage should be 10-80vdc. Installation instructions state to
connect positive to one terminal and negative to the other terminal,
polarity not necessary since the unit is polarity insensitive.

Since the unit obviously has a motor that needs to run in one
direction only to increment the time, I'm having a hard time
visualizing what they've done inside the sealed unit to make polarity
a non-issue. Any ideas?

KC

I'm curious ! Why do you think it has a motor ?
I've seen similar devices that are purely chemical and require DC to
function. You can wind them back by reversing the polarity of the
supply.