24 July 2020 at 16:54 #9498
I recently published the article “Electronic power strip”: the aim was to switch 220v appliances on / off via a web page.
I produced everything you can see in my article after having made tests and counter-tests on the goodness of the connections and in particular the management of the relays and related connections to 220V appliances. All ok until today when I discovered an oddity: if a 220V lamp or led strip is connected to the excited relay, there are no problems but, and herein lies the strangeness, if a PC power supply is connected, this 220V connection does NOT TURN OFF after a certain time. It seems that the related relay remains energized even if it is disconnected: at its ends ZERO voltage: The relays are of the FINDER type and should support 220V voltage as per the datasheet. The strange thing is that after some time (more or less 24 ore) the relay returns to its normal state: in practice it de-energizes without any intervention. That is, the relative contacts return to their initial place. Considering that said relais (to tell the truth elderly) they could have problems I searched the web for other types of relays by choosing the SONGLE 10A / 250V model, an exchange and from the datasheet it also supports 220V 10A. No way: it too has the same problems always in relation to the PC power supply: OK for excitation but when you ask to deactivate it, the contacts remain connected even though they have zero voltage at the relay contacts. Incidentally, by removing the relay from its housing and testing the contact pins, it can be seen that there is a connection between the common pin and the exchange pin..
If anyone has a solution………
PS: any wiring diagrams can be found in the article “Electronic power strip”24 July 2020 at 18:03 #9500AmilcareKeymaster
From the description it appears that the contacts have stuck due to scintillation due to excessive current. You could try with a capacity in parallel to the contacts, it does not need big from 100nF I think it can go with a resistance in series 100 ohm no-load supplies the load with too low a current to allow the equipment to operate. The problem is due to the fact that the Switching, before starting to work, absorbs high peak currents. Always due to arcing and sparking at mains voltage24 July 2020 at 18:31 #9503
Amilcare thanks I'm doing other tests with other relais. I believe that the problem is due to the type of relay. That is between electromagnetic and electromechanical. The former are encapsulated in blocks, the latter are more visible and transparent and have lamella contacts. I have
some of these electromechanical but only go to 12v.
Ciao25 July 2020 at 19:51 #9505Picmicro675Participant
If you have resistive loads then you can rely on nameplate amps. While for inductive loads I would recommend staying at least 3 times lower than the ceilings.26 July 2020 at 11:25 #9512
Mah…. I took out of the drawer very old electromechanical relays with two exchanges with mechanical contacts with blades that close or open anchored to the excitation coil.
These types of relays are energized with both 12V and 5V and after repeated ON / OFF attempts do not give problems. Once excited after some time they can be de-energized normally. I agree with what PICMICRO says but excuse my ignorance but a PC or laptop power supply is an INDUCTIVE or RESISTIVE load ??
And because I connect a printer that has its own internal power supply, the problem in question does not arise ???
Greetings to all27 July 2020 at 3:17 #9517Picmicro675Participant
A switching power supply, like those of today for electronic equipment, inductive loads can be considered, after all, there is always an internal transformer. Although the first load is the smoothing capacitor. For that I would assume a starting peak when the capacitor is completely discharged.6 August 2020 at 13:32 #9526maxmix69Participant
Also in my opinion the problem is that the relay contacts stick to the current peak practically present, one way or another, in all types of cargo. With some loads the peak exceeds the maximum bearable of the relay contacts. Even the little relays are electromechanical, the electronic ones are admittedly. But the small electromechanics are suitable for very small loads.7 August 2020 at 12:29 #9535
I did some tests with coil relays with two switches that both detach and reattach when the relay is energized and de-energized as opposed to those used in the project.
In fact, while in the relays used in the project the contact in which the 220 (pc power supply) l’ other always disconnects regularly.But it does not happen if a printer is connected ( to another relay). The coil ones are quite old in seniority but are still on the market even if with different characteristics. And from evidence it seems that there are no problems. Lately I have suspended the tests taken from other commitments. But I reserve the right to let you know how it will proceed with the old coil relays.
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