[MAMS] relay driver

[Danny Pease]

I wonder if I can simply put a rather large capacitor on series with each
coil and switch the DC from one to the other when going from TX to RX? The
discharged cap should look like a short for a few milli-seconds, allowing
the pulse to activate the coil and then when the cap is charged, no more
current. Of course there would have to be a discharge path to bleed the cap
off. The coils are about 60 ohms and the specs say the relay takes 15
milliseconds to switch, so maybe a 470 uF cap with a 610 ohm resistor in
parallel?

Danny NG9R



-----Original Message-----
From: mams-bounces at mailman.qth.net [mailto:mams-bounces at mailman.qth.net] On
Behalf Of Zack Widup
Sent: Friday, September 07, 2012 4:15 PM
To: Mid-America Microwave Society
Subject: Re: [MAMS] relay driver

No, not if it continues to draw current. In the HP33311C I've been
mentioning, there is evidently an internal relay or switch that disconnects
the pin that was just grounded when you switch it. It draws no current as
long as that pin is grounded. When you ground the other pin, it switches the
relay and also disconnects that pin. So it's a whole different arrangement.

Zack W9SZ


On Fri, Sep 7, 2012 at 3:40 PM, Danny Pease <dpease at adams.net> wrote:

> I see 225 mA of steady current when 13.6 VDC is applied. The case does 
> warm up noticeably after 20 seconds or more and is almost hot after 90
seconds.
> I
> don't think I will want to leave the DC applied all the time.
>
> Danny NG9R
>
>
> -----Original Message-----
> From: mams-bounces at mailman.qth.net 
> [mailto:mams-bounces at mailman.qth.net]
> On
> Behalf Of Dr. Gerald N. Johnson
> Sent: Friday, September 07, 2012 1:30 PM
> To: mams at mailman.qth.net
> Subject: Re: [MAMS] relay driver
>
> There are at least a couple two coil latching relay schemes. One is 
> just two coils tha you only need to apply a pulse to for a short 
> period and the relay mechanically or magnetically latches. I don't see 
> a restriction in the catalog that requires power be removed from the 
> coil right away except that the current of some latching versions at 
> 12 volts is 230 ma and the same relay not latching (fail safe) is 195 
> ma, so there's more heat in the relay with continuous coil power. 
> Then, of course, it takes applying power to the other coil to change 
> the relay position. Coils often have one wire in common and are 
> polarity sensitive so that prevents some simple drive circuits based 
> on conventional relay drive.
>
> Some Dow-Key also have a self cutoff circuit, so keep the power 
> consumption low by taking care of interrupting the coil current on 
> their own to make the drive circuit simpler.
>
> I have portions of a recent Dow-Key relay catalog on my other computer 
> but need a model number to know what you have and how to drive it.
>
> 73, Jerry, K0CQ
>
> On 9/7/2012 12:47 PM, Danny Pease wrote:
> > I picked up a two coil 12 volt latching DowKey SMA relay and am 
> > looking for simple suggestions for using it or I would be glad to 
> > trade it for a non latching SMA relay, 12 or 24 volt.
> >
> > Danny NG9R
> >
> >
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