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Re: [TowerTalk] Gigavac Relays

To: Jim Thomson <>
Subject: Re: [TowerTalk] Gigavac Relays
From: "Richard (Rick) Karlquist" <>
Date: Fri, 31 Dec 2010 11:39:03 -0800
List-post: <">>

On 12/31/2010 8:09 AM, Jim Thomson wrote:

> &&& The K6XX circuit just doubles the OCV when T=0 The 12 vdc across the
> 47 uf cap in his circuit is now in series with the
> 12 vdc OCV... so you end up with 24 vdc... for a split second...until
> the cap discharges..then u down to 12 vdc.
> &&& I don't see any difference between that method of temp obtaining 24
> vdc..... VS using 24 vdc + drop resistor. The 24 vdc
> + drop resistor will def speed up any 12 vdc relay. If you then wire a
> 47 uf cap across the drop resistor, then it's even faster still.

The difference is that the K6XX circuit applies 24V for as long as
is necessary (just size the cap accordingly).  The resistor technique
starts out at 24V but decays at a rate dependent on the coil inductance.
In practice, it is not as effective with the Gigavac relay.  Its turn
on time is about mid way between the K6XX circuit and the stock relay.
I measured both circuits.  The drop resistor with capacitor is 
essentially the same as the K6XX circuit performance wise.  If that 
circuit is more convenient, it makes sense.  For me, I'd rather add the 
handful of components for K6XX circuit and avoid another supply.

> && I did notice that on any of these 26.5 vdc latching type relays..that
> the coil resistance on em is very low..and blows my 5A current limited
> lab supply
> into the red. A quick pulse of 12 vdc is more than ample to operate a
> 26.5 vdc latching type vac relay.
> later....... VE7RF

I used to use latching vacuum relays in my 40/80/160 vertical ( instead 
traps).  I used a capacitive voltage doubling circuit similar to
the K6XX circuit to pulse the relay with 24V for a few milliseconds.
(It ran from a 12V supply).

That worked well, however, the vacuum relays would never last more than
about 6 months.  After replacing them five times, I replaced them with
big air gap contactors as described in May 2009 QST Hinks and Kinks. 
The contractors have been completely reliable through contests on both 
bands.  I still don't know what killed the vacuum relays, but I'm
done with them for that application.  Maybe it was the 1000's of volts
on 80 meters.  We basically don't get lightning around here, so it
wasn't that.

Rick N6RK

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