110v-230v AC to Mysensors PCB board
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Hmmm. I got the 5.5V DC varistor from another AliExpress seller and I'm a bit puzzled as to why it starts smoking after a few seconds. Tried several of them. The HLK gives a solid 5V output. I'm assuming I got some lower voltage varistors by mistake?
@bjornhallberg Maybe I've missed reading something, but why use a varistor for 5 Vdc and not a zener diode?
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@shabba Right... if you look at the schematics
you can see that the two capacitors can be swapped without consequences
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@bjornhallberg Maybe I've missed reading something, but why use a varistor for 5 Vdc and not a zener diode?
@m26872 You're probably right, I just followed the BOM. I'll see if I can stock up on some diodes from AliExpress for future use.
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Just a stupid question, the "G3MB-202P DC-AC PCB SSR In 5VDC,Out 240V AC 2A " What happens if I forget and plug something more power-hungry like a toaster or a microwave-owen? does any of the fuses blow or does the relay break ?
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there is no fuse on the relay switch so I guess either the PCB or the relay will fail.
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I've seen commercial products with a thermal fuse glued to the switching side of the relay. Maybe that would help some in such situation.
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Whould a 5.1V zener work?
edit: removed the link to the product so that no one would buy it the specs of it is to tight to be used with HLK.
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@m26872 Indeed, mine is 5.08V (with no load). I ordered some 5.1V and 5.6V 1206 SMD diodes from Ali for future use. Plus some 3.6V. And a set of DIP diodes.
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@m26872 Indeed, mine is 5.08V (with no load). I ordered some 5.1V and 5.6V 1206 SMD diodes from Ali for future use. Plus some 3.6V. And a set of DIP diodes.
@bjornhallberg said:
I ordered some 5.1V and 5.6V 1206 SMD diodes
Just to remember, the typical zeners are 1W , which gives a max of 200mA of output capacity, pretty enough for Arduino+radio, but maybe not enough for many relays / Leds etc. And if they burn due overload, they will allow all voltage/current flowing from PSU into arduino.
That explains why we suggested the varistor, in order to short the PSU output and trigger its internal protection. Strange that your varistors didn't survive... Bad lot? Maybe they are not 5.5V as stated?
Home Assistant / Vera Plus UI7
ESP8266 GW + mySensors 2.3.2
Alexa / Google Home -
@bjornhallberg said:
I ordered some 5.1V and 5.6V 1206 SMD diodes
Just to remember, the typical zeners are 1W , which gives a max of 200mA of output capacity, pretty enough for Arduino+radio, but maybe not enough for many relays / Leds etc. And if they burn due overload, they will allow all voltage/current flowing from PSU into arduino.
That explains why we suggested the varistor, in order to short the PSU output and trigger its internal protection. Strange that your varistors didn't survive... Bad lot? Maybe they are not 5.5V as stated?
@rvendrame
No.
The zener will only lead current during over voltage condition and only needs to dissapate enough energy till one of your (multiple?) over current protection trips. Just as your varistor setup is supposed to work. -
@rvendrame
No.
The zener will only lead current during over voltage condition and only needs to dissapate enough energy till one of your (multiple?) over current protection trips. Just as your varistor setup is supposed to work.@m26872 , is it also true in case the PSU itself fail? And what happens if the circuit consumes more current than zener rating? I'm my (poor) knowledge, zeners are more relevant for stabilization, while varistor are effective 'protection' devices...
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I spoke too soon... the unit seems to work well, but I hadn't tested if the relay actually switched or not. The status seems to change fine in the serial monitor, but it doesn't seem to be actually switching. I'll have to do some more troubleshooting.
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@m26872 , is it also true in case the PSU itself fail? And what happens if the circuit consumes more current than zener rating? I'm my (poor) knowledge, zeners are more relevant for stabilization, while varistor are effective 'protection' devices...
@rvendrame
since we're discussing the PSU secondary side (output side), I think we already presume errors with the PSU. A fuse (over current protection) on the secondary is not just there as a back-up if the PSU internal over current protection fails. The fuse will also prevent your over voltage protection (zener, varistor, ...) from overload/burn/start a fire.The current from PSU to load will not pass through the zener and hence the rating is irrelevant from that perspective. In other applications where a zener is used as voltage regulator, the full load current will pass through the zener when in idleing and then the rating is critical.
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@rvendrame
since we're discussing the PSU secondary side (output side), I think we already presume errors with the PSU. A fuse (over current protection) on the secondary is not just there as a back-up if the PSU internal over current protection fails. The fuse will also prevent your over voltage protection (zener, varistor, ...) from overload/burn/start a fire.The current from PSU to load will not pass through the zener and hence the rating is irrelevant from that perspective. In other applications where a zener is used as voltage regulator, the full load current will pass through the zener when in idleing and then the rating is critical.
@m26872 so how do we need to rate the zener? Should the zener be rated so that the fuse will blow before the zener brakes from the current it passes due to an over voltage situation? Or is it OK that the zener brakes to as long as it takes out the fuse first. Then an automatic fuse will no longer work.
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@m26872 so how do we need to rate the zener? Should the zener be rated so that the fuse will blow before the zener brakes from the current it passes due to an over voltage situation? Or is it OK that the zener brakes to as long as it takes out the fuse first. Then an automatic fuse will no longer work.
@korttoma Good questions. As always a trade-off of risk, cost, space, taste, etc. They should already be answered in the varistor case though. Personally I think it's overkill with additional overvoltage protection at the low volt secondary side of a good quality PSU and an inexpensive load - fuse, capacitors and regulators should be more than enough. Focus should be the primary side protections.
Edit: Btw. Found some reading. See p.44
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Just a quick post to confirm I got the relays working as well (with Domoticz). I didn't read the schematic at first and just assumed how the mains and relay external wiring should be done. Still no idea about the smoking varistor.
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Just a quick post to confirm I got the relays working as well (with Domoticz). I didn't read the schematic at first and just assumed how the mains and relay external wiring should be done. Still no idea about the smoking varistor.
I thought all my relays were shot as I was not getting continuity on the load pins when I applied 5V. I checked resistance and there is just over 2K when 5V applied and infinite when none. I am going to put back together assuming the 240V A/C will pass through just fine.
