How to connect two relays to the same PSU - diyAudio
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Old 26th October 2005, 07:58 PM   #1
diyAudio Member
Join Date: Apr 2005
Location: Spain
Default How to connect two relays to the same PSU


Im going to build a loudspeaker switcher (the same pair will be shared by two different amplifiers) using a pair of Fujitsu FTR-F1 sealed DPDT relays (from Mouser). Its specs are:
Contacts: gold plated Silver alloy, 5A switching and 7A carrying only capacity (minimum 10mA)
Coil: 24Vdc voltage and 0.53W nominal power

Ill use a stabilised 24V Switch-mode PSU (Stontronics T25006ST), rated at 0.5A. My doubts are:

1) How to power both relays from the same PSU?. I think the +24V dc output goes first to one of coil contacts and from here to the same contact of the other coil, and the minus output goes the same way to the unused coil contact in the first relay and then to the other relay - coil pin (like wiring the two coils in parallel). Is this correct? Has the PSU (0.5A-rated) power enough to energise both coils?

2) Is it necessary to connect a diode (1N4001?) and a resistor (what value/rating?) between coil contacts on each relay (diode band/cathode to +dc input coil pin) to protect something in the circuit? In my case, there is no more components in it, only the two relays, the PSU and the wiring.

3) The cable from the relay output to loudspeakers would be a 9ft. high-capacitance ribbon type (Goertz MI1). Does it matter? Is it best to use a more conventional type? (BTW, the MI1 sounds superb).

Thank you for your help

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