[Amps] SSR in amp PS not working as expected

David G4FTC g4ftc at hotmail.com
Thu Jan 10 12:31:19 EST 2019


Hi Ulf,

No need to go to the States - try RS Components  - their Swedish Website https://se.rs-online.com/web/ or Farnell - their Swedish Website https://se.farnell.com/

Both are reputable suppliers

David G4FTC
Farnell element14 Sverige - distributör av elektronikkomponenter<https://se.farnell.com/>
NYA Aim TTi TGF4000-serien. Programmerbara funktions-/arbiträra generatorer upp till 240 MHz
se.farnell.com


[https://se.rs-online.com/web/'https://se.rs-online.com/euro/img/home/hero/2019-01/mcc_083_1218ne_rs-pro-homepagebanner_blue_no-textn.jpg'1zR%01]<https://se.rs-online.com/web/>

RS Components | elektronik- och el-komponenter<https://se.rs-online.com/web/>
RS Components är ledande distributör av elektronik-, el- och industrikomponenter. Säker online beställning med möjlighet för leverans från dag till dag.
se.rs-online.com



or


RS Components International<http://www.rs-online.com/>
RS is the leading high service level global supplier of Industrial components and tools, with over 130,000 products despatched same day.
www.rs-online.com



________________________________
From: Ulf Tjerneld <ulf at sm0nor.com>
Sent: 10 January 2019 16:08
To: David G4FTC; amps at contesting.com
Subject: RE: [Amps] SSR in amp PS not working as expected


Thanks for the tip of the D2450. There are quite a few offerings on Ebay for both the D2450 and the D4850, which I guess is the 480 volt version of the same relay. A bit pricey with shipping from the US to take a chance at. I’ll have to rule out all other possibilities first and watch for some EU offerings.





Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10



From: David G4FTC<mailto:g4ftc at hotmail.com>
Sent: den 9 januari 2019 02:29
To: amps at contesting.com<mailto:amps at contesting.com>
Subject: Re: [Amps] SSR in amp PS not working as expected



Hi All,



I use SSRs as a mains input contactor in three HT PSUs. The SSRs are driven from a monitoring circuit which shuts down the PSU in the event of over drive, excessive currents, etc., being detected. The oldest PSU is now over 15 years old and I have experienced no problems with the SSRs.



I place a 1000pF capacitor and a reverse diode across the input to avoid issues from stray RF or reverse polarity. I don't know if either a strictly necessary but I added them as standard practice.



FYI in my W6PO HT PSU I use a Crydom D2450, from the datasheet the main control element comprises of dual back-to-back thyristors. The other PSUs also use Crydom SSRs which I haven't checked for part numbers but I believe are all back to back thyristor units - it was just easier to take the cover off the W6PO PSU to see what I had used!



Hope this helps



David G4FTC









________________________________

From: Amps <amps-bounces at contesting.com> on behalf of Manfred Mornhinweg <manfred at ludens.cl>

Sent: 06 January 2019 22:26

To: amps at contesting.com; ulf at sm0nor.com

Subject: Re: [Amps] SSR in amp PS not working as expected



Ulf,



there are two fundamentally different kinds of SSRs. One type uses

thyristors (TRIACs or SCRs), the other uses back-to-back MOSFETs.



These two (or three!) types have very different behavior. Not only that

MOSFET SSRs can handle AC and DC while the others are usable with AC

only, but also in that their handling of inductive loads is very

different. Generally TRIACs are poor with inductive loads, antiparallel

SCRs are much better, and MOSFET SSRs might be best if rated for

inductive loads, but that needs a special circuit inside them to avoid

damage from inductive kick.



Thyristor SCRs will switch on either the instant you apply a control

signal, or the next voltage zero crossing after that, depending on their

type, and will always switch off at the current zero-crossing. With a

purely inductive load (and the primary of a very lightly loaded

transformer is very close to that), the current zero-crossing is 90

degrees out of phase with the voltage zero-crossing. This leads to some

head-scratching.



TRIAC SSRs will often trigger far more easily in one polarity than in

the other. This is likely the cause for your transformer hum: It's

getting only a semicycle instead of the full grid waveform, so there is

a huge DC component present, and the transformer core gets hopelessly

saturated, with the magnetic flux leaking out of the core.



Another possible reason for hum is that the SSR is switching on too much

after the zero crossing, so that there is a hard voltage step inside

each half cycle. The harmonics contained in such a step tend to be very

loud.



You will need to look for SSRs rated for highly inductive loads, and

preferably of the back-to-back MOSFET type. Or else use old-fashioned

mechanical relays.



One last thing: In some cases you can cure such thyristor misbehavior by

adding snubber networks. You might want to try this first. Simply add a

100 ohm resistor in series with a 100nF capacitor, of adequate AC

voltage rating, directly across the output side of each SSR, right at

the SSR. With some luck that might tame them.



Manfred





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