Please help understand the relay interface of the surge protection module - Page 1
Forum section: electronics / beginners

author: max.wwwang
author_rank: Frequent Contributor
timestamp: March 09, 2020, 07:53:18 am
content: I salvaged this board - a good standalone mains surge protection module - from an EATON UPS. There are 2 relays between the two sets of the terminals which are normally open. It's handy so I'm not planning to remove them and short the terminals to make it permanently connected.I have difficulty understanding the should-be-simpler (to me) relay interface which I have drawn up as below. I have tested by directly connecting pins 2 and 3 with 12V DC; it worked with a current of about 0.3A. My questions:What are all the 4 pins supposed to be used? Is my way of driving the 2 relays correct without making use of the triode, resistors and the zenar diode?Thanks.

author: MarkF
author_rank: Super Contributor
timestamp: March 09, 2020, 05:49:16 pm
content: Here is my quick look:+/- Voltage, Status and Control pins

author: max.wwwang
author_rank: Frequent Contributor
timestamp: March 11, 2020, 08:02:42 am
content: Quote from: MarkF on March 09, 2020, 05:49:16 pmThanks. You are exactly right. I tested and it worked perfectly.I like the idea of colouring the connected wires (of the same potentials). I'm using Fritzing, can this be done (semi-)automatically?

author: MarkF
author_rank: Super Contributor
timestamp: March 11, 2020, 03:27:01 pm
content: I used Photoshop to color your original schematic for clarity.I use DipTrace for my schematics and PCB layouts.It is possible to assign wire colors in Diptrace.Even so, I don't color the wires.I don't know anything about Fritzing.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: March 12, 2020, 08:19:07 am
content: simplified the power from +12V/+5V to one single +12V supply --Only one thing, when the relays are on, the constant current is around 0.3A. Is this the right level? The whole power consumption to maintain the relays are around 3.6W.

author: MarkF
author_rank: Super Contributor
timestamp: March 12, 2020, 03:44:17 pm
content: Relay specs: 832A-1A-F-C-BH-12VDCcoil: 12V / 92.3mA / 130ΩApprox LED current: 11V / 2KΩ = 5.5mATotal current: 92.3 + 92.3 + 5.5 = 190mA

author: max.wwwang
author_rank: Frequent Contributor
timestamp: March 13, 2020, 05:27:46 am
content: That's in the ball park range. Thanks.In your diagram the Crl pin is not used. it's is intentional and would this work?

author: max.wwwang
author_rank: Frequent Contributor
timestamp: March 13, 2020, 07:20:46 am
content: Seems like that would work. Bang!!!Then what’s the purpose of pins 1,4 and the rest of the circuit?Oh, basically you are getting back to my original direct connection solution. So only 2 pins are needed. There would be much greater current through the switch. But it's not a big deal I suppose. So why bother this extra circuit?

author: MarkF
author_rank: Super Contributor
timestamp: March 13, 2020, 03:42:55 pm
content: The transistor and its supporting circuitry are there to allow a low voltage signal to control the relays.Imagine switching the relays with an Arduino or other microcontroller.