telephone line relay

DickCappels

Joined Aug 21, 2008
6,005
Yes, if you have a 6V power supply with which to drive it, if you only +5V then answer would be "probably". Make sure the contacts are rated for over 150 VAC so then can withstand the ringing voltage.
 

absf

Joined Dec 29, 2010
1,942
Make sure that the 6V supply only goes to the relays and not the CM8870 DTMF decoder & PIC mcu. The decoder supply only works from 4.75V to 5.25V. The absolute max Vcc is 6V. Check the datasheet of the max supply voltage for the PIC too.

cm8870 cct.png
Allen
 

Thread Starter

abc77

Joined May 10, 2017
59
i don't actually need the decoder. I just want to switch the line using call accept/end function.

there is BC547 transistor feeding the relay via 1kOhm, do you think lowering this resistor value will increase voltage for the 6V relay?
 

Thread Starter

abc77

Joined May 10, 2017
59
Yes, if you have a 6V power supply with which to drive it, if you only +5V then answer would be "probably". Make sure the contacts are rated for over 150 VAC so then can withstand the ringing voltage.
I have SC5-S-DC6V relay. It says 7A, 240VAC,50Hz and coil:6VDC. Then again after a long separating line, there is 10A/125VAC. Will this do?
relay.jpg
 

DickCappels

Joined Aug 21, 2008
6,005
i don't actually need the decoder. I just want to switch the line using call accept/end function.

there is BC547 transistor feeding the relay via 1kOhm, do you think lowering this resistor value will increase voltage for the 6V relay?
The BC547 should have much less than a volt from collector to emitter when the relay is on if it is working correctly, so in that case lowering the 1k resistor would have very little effect. The best thing to do is to measure the collector-to-emitter voltage.

upload_2017-5-12_22-35-46.png

If the collector voltage is over 0.6 volts with 5 ma of base drive (close to what you get with 1k and a 5V power supply) then either the transistor is bad or the relay is pulling too much current. The maximum collector current of a BC547 is only 100 ma.

If you know or can find out, what is the coil resistance?
Do you know the pull-in voltage?
 

DickCappels

Joined Aug 21, 2008
6,005
Yes. It means that you are good to go with that relay and that voltage. If this were a high volume production design we would require more margin but since this is a one-off and you have a very high chance of success with this relay, go for it!
 
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