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Home > Archive > Electrical Engineering > July 2005 > Using 12v kit on 24v supply
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Using 12v kit on 24v supply
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| colinstone@hotmail.com 2005-07-26, 10:21 pm |
| I have a gas detector which it has not been possible to determine the
supply voltage - it is either 12 or 24v. While I wait for any
manufacturer info, can I add a resistor to the unit if it is a 12v unit
to operate it on 24v - a safety device I'd rather have it operating off
the base 24v supply rather than through a DC converter.
Tech details from the info I have 12v version uses 240ma, so I make
that a 50 ohm resistance. So can I add a 50 ohm resistor in series
with the 12v unit to run on 24v - and a 6 watt value should do. BTW
the 24v version uses 120ma, so is a 200 ohm resistance.
TVMIA
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| colinstone@hotmail.com wrote:
> I have a gas detector which it has not been possible to determine the
> supply voltage - it is either 12 or 24v. While I wait for any
> manufacturer info, can I add a resistor to the unit if it is a 12v unit
> to operate it on 24v - a safety device I'd rather have it operating off
> the base 24v supply rather than through a DC converter.
> Tech details from the info I have 12v version uses 240ma, so I make
> that a 50 ohm resistance. So can I add a 50 ohm resistor in series
> with the 12v unit to run on 24v - and a 6 watt value should do. BTW
> the 24v version uses 120ma, so is a 200 ohm resistance.
>
> TVMIA
If the detector *always* draws the same amount of current, this works.
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| Palindr☻me 2005-07-27, 6:21 am |
| colinstone@hotmail.com wrote:
> I have a gas detector which it has not been possible to determine the
> supply voltage - it is either 12 or 24v. While I wait for any
> manufacturer info, can I add a resistor to the unit if it is a 12v unit
> to operate it on 24v - a safety device I'd rather have it operating off
> the base 24v supply rather than through a DC converter.
> Tech details from the info I have 12v version uses 240ma, so I make
> that a 50 ohm resistance. So can I add a 50 ohm resistor in series
> with the 12v unit to run on 24v - and a 6 watt value should do. BTW
> the 24v version uses 120ma, so is a 200 ohm resistance.
>
> TVMIA
>
Presumably this gas detector does something when it detects
gas? In which case, its current consumption probably will
not be constant but will rise, perhaps by a lot, when it
detects something. Which may, if fed via a resistor and if
the unit has an alarm sounder, cause it not to sound or to
sound like an unhappy mouse rather than a very annoyed coypu..
A resistor as a voltage dropper is fine if the unit always
draws the same current and the source voltage is always
fixed or if the unit isn't that fussed what it gets.
Only use one if you are sure that the unit draws the same
current under all conditions and the voltage source is constant.
In this case, I would suggest using an inexpensive three
terminal regulator, with a couple of capacitors as in the
manufacturer's application notes, or a resistor/zener diode
combination.
--
Sue
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