Re: latching relays?


No problem, Colin. I didn't know if you were aware of the latching relay history.......
We have kept clear for a good reason!


On 25 Mar 2021, at 17:33, Colin Ranson <g8lbs@...> wrote:

I knew Sam would pop up and put me straight, thanks Sam.


I had seen PQL’s design but never associated it with Dave RIP.


I’ll go back to sleep.


Colin de G8LBS.


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From: SAM JEWELL via
Sent: 25 March 2021 16:26
Subject: Re: [UKMicrowaves] latching relays?


AFAIK, Dave had permission to use the  basic PQL design. The rights are still PQL's, hence no one has taken up the design in the UK.

Dave was in the process of amending the design to use MOSFETS, rather than Darlington bipolars, in the output stage. He prototyped the new design but never got as far as having PCBs made. 


Time for a new design?


Sam, G4DDK




On 25 Mar 2021, at 15:57, Colin Ranson <g8lbs@...> wrote:

Ben, Neil, all.



I have a  pic of completed board, should be easy enough to replicate..... unless someone has bought rights to Dave’s designs of course.


Please e-mail me for a copy if you are interested.      



Colin de G8LBS.


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From: Colin Ranson
Sent: 25 March 2021 15:45
Subject: Re: [UKMicrowaves] latching relays?


Hi Ben, I have a number of these in use......



Someone was supposed to take over production (DX Shop ?) when Dave died but I think it never happened, I may be wrong though.


I got one spare for future use.    Attached is the configuration PDF in case it goes walkies into a data black hole one day.


Been looking for a PCB layout but no luck yet.


Colin de G8LBS




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From: Neil Smith G4DBN
Sent: 25 March 2021 12:34
Subject: Re: [UKMicrowaves] latching relays?


If they don't have tellback contacts, there is a bit of a problem in knowing the current state of the relay following loss of power for instance. I've just bought some HP latching jobs with 3.5 mm connectors and no tellbacks, so I have the same issue as you.  This one I have on the bench at the moment is rated at 15 V and pulls about 170 mA.  The others I have all come with separate tellbacks or internal contact so the current drops to zero once the relay has flipped.

The way I'm dealing with these is to use a PIC as a sequencer and just send a half-second pulse to a low-side FET switch.

Not exactly low-tech. How about a small double pole relay with two resistors and two electrolytics? Electrolytics sized to give a 200ms pulse on the relay and a resistor with 10 times the value of the coil resistance to recharge the cap?  You'd end up with a small current through the active coil all the time on rx and tx, but only 10 mA.

Neil G4DBN

On 25/03/2021 11:10, militaryoperator via wrote:

There was a thread a while back about lathing relays. 


The ones I had required a voltage, they latched then pulled no current.


One's I have just got need volts to latch then pull about 100mA if volts left on. As they don't need volts all the time, what's the best way, circuit etc, to pulse them, common goes to ground and a 12v pulse on 1 or 2 needed to latch etc. 


Just trying to avoid over-straining my few remaining brain cells, and not re-invent the wheel again. 







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