[Amps] Noisy relay

[MU 4CX250B]

Tim, if I understand your question correctly, the diode will have no
effect on the closing time of a d.c relay, because the diode is always
back-biased, with its cathode tied to the positive terminal of the
relay coil. In effect, the relay coil is unaware its presence,
inasmuch as the back resistance of a small signal diode is typically
hundreds of megohms or more.

When  the relay coil opens, however, the inductive kick forward—biases
the diode so its effective resistance is only an ohm or two. The
current in the relay coil decays slowly through the diode, which is
why the relay release time is slowed.
73,
Jim w8zr
Sent from my iPhone

> On Dec 12, 2022, at 12:38 AM, Tim Duffy <k3lr at k3lr.com> wrote:
>
> Thanks Jim
>
> My concern is with the diode(s) across the relay(s) coil (or Zener diode combo) does it affect the timing on the front end closure of the relays?
>
> As in TX delay settings? So when the relays "settle" before RF is applied?
>
> Three relays involved. Input, output and bias
>
> 73
> Tim K3LR
>
> -----Original Message-----
> From: MU 4CX250B [mailto:4cx250b at miamioh.edu]
> Sent: Monday, December 12, 2022 1:48 AM
> To: Tim Duffy
> Cc: Steve London; amps at contesting.com
> Subject: Re: [Amps] Noisy relay
>
> Hi Tim, Yes a clamping diode will slow down the release time of a dc
> relay. The time constant (release time) is approximately L/R, where L
> is the relay coil inductance and R is the coil resistance. If the
> release time is objectionable, it can be shortened by adding a zener
> diode (typically with a zener voltage roughly equal to the power
> supply voltage in series with the clamping diode.
> 73,
> Jim W8ZR
> Sent from my iPhone
>
>> On Dec 11, 2022, at 7:00 PM, Tim Duffy <k3lr at k3lr.com> wrote:
>>
>> Hello Jim
>>
>> Does that clamping diode across the coil affect the TX key up delay time? As in "slow it down"?
>>
>> 73
>> Tim K3LR
>>
>> -----Original Message-----
>> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of MU 4CX250B
>> Sent: Sunday, December 11, 2022 5:49 PM
>> To: Steve London
>> Cc: amps at contesting.com
>> Subject: Re: [Amps] Noisy relay
>>
>> Steve, you might be hearing the induced voltage kick caused by the
>> inductance of the coil. Try putting a clamping diode. A small signal
>> diode like a 1n914 will work fine,
>> 73,
>> Jim w8zr
>>
>>
>> Sent from my iPhone
>>
>>>> On Dec 11, 2022, at 9:39 AM, Steve London <n2icarrl at gmail.com> wrote:
>>>
>>> Commander HF-2500..
>>>
>>> Every time the T/R relay goes back to receive, I'm getting a pretty big RF
>>> spike that I can hear in the receiver. This has nothing to do with the
>>> transceiver hot switching or RF stored in the tank circuit. I can reproduce
>>> it just by cycling the T/R relay in the amp with a separate cable, not
>>> connected to the transceiver, and not transmitting.
>>>
>>> Suggestions ?
>>>
>>> 73,
>>> Steve, N2IC
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>