7.2v source with 5v reed relay

troll

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I want to use a 7.2 v power source on my MS20 board.  I have two questions, though:

1.  Could the 5v reed relay take the raw battery power of a 7.2 v power source?  

2.  Is the output of the MS20 board in terms of voltage the same as the input (7.2 v)?

Sorry, my camera is 300 miles away for another two weeks, so I can't put a meter on it.

I figure I can build a voltage divider otherwise and bring down the volts a little if I need to.
 



Archilochus

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Hi troll,
You should be fine with the 5 volt relay - wouldn't go too much more than 7.5 volts though.
Other MS-20 users should be able to answer your MS-20 questions.
You probably could not use a divider on the relay because the resistors used in the divider would reduce the current through the relay and it might not work.

Archilochus
 

troll

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Thanks for the reply.  Is there another way I can reduce the voltage?
 

Archilochus

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Hi troll,
One or two 1N400x diodes in series with the coil would be an easy way, if needed.
You could also just add a low value resistor in series with the relay coil to reduce current through it somewhat - say about 22 to 47 Ohms / 1/2 Watt to start off with - maybe a bit more.

Even cheap relays can typically tolerate about 40 to 50% over-voltage for extended periods.  7.2 volts would be ~ 44% over.  A good relay can typically tolerate about 140% over-voltage.

Archilochus
 

deadcell

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I don't mean to sound stupid but just for the sake of trying .I am using a 5v reed relay on my RS PIR sensor and i power it with a 9.6v battery pack, when its fully charged it measures over 11 volts easy. Am i pushing this relay too hard? Or am i misunderstanding your question? ThanksDC

(Edited by deadcell at 9:22 pm on Nov. 9, 2001)
 

Archilochus

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Hi deadcell,
Well, the life of the relay will depend on what quality of relays Radio Shack had in stock when you bought the parts.  RS usually stocks the cheap stuff - but not always.
The relay might fail in a few months if it's a cheapie, or it could last years if it's a good one.
If it's working OK, just leave it - if it fails soon, replace it with a 9 volt relay.

Archilochus
 


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