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relay that born at max rating

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DNA2683

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Hi all,

I'm using a NO/NC relay to switch 30V/10A. when i tested the relay i noticed a strange issue. when I close the relay and switched 10 A all work ok but when i open the relay when 10A is passes through the relay , the relay burns and stop working. what can be the reason to this ? (the really spec is 30V/10A)
 

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  • 1645344925138.png
    1645344925138.png
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cheap chinese relay ? ali express ? not enough pcb pad on the pins for cooling ? too many volts on the coil - the reasons fro this predicament are almost endless ....
 

Hi,

You need to provide a lot more informations.
* what exactly is connected to the coil?
* what exactly is connected to the contacts? (Capacitive load, inductive load, motor ....what's the power supply
* what does "the relay burns" exactly mean? Does the contact burn or the coil?
* what's the relay manufacturer and exact type? Link to datasheet..

Upload photos (100kBytes should be sufficient) and a sketch about wiring..

Klaus
 

Is it resistive or inductive load? Has the relay a switching power spec for the respective load condition?
 

Hi,

You need to provide a lot more informations.
* what exactly is connected to the coil?
* what exactly is connected to the contacts? (Capacitive load, inductive load, motor ....what's the power supply
* what does "the relay burns" exactly mean? Does the contact burn or the coil?
* what's the relay manufacturer and exact type? Link to datasheet..

Upload photos (100kBytes should be sufficient) and a sketch about wiring..

Klaus
hi thank you for your quick response this is the circuit
1645347104792.png

to the contacts on one side i connected power supple of 30V and on the load side i connected a dynamic load that takes 10A
1645347240178.png
( i don't know of it's pure resistive load).

when i close the relay all working ok and a 10 A going through the relay . but when i switch back to the NC contact ( = open the relay to stop cuurent flow) the relay stop working and Then the relay is shortened between the coil leg and its outlets
1645347558808.png

this is the mfg. number W11-1C2STLE-DC12V (https://www.fanhar-relay.com/product/w11/)
 

Hi,

Your coil side circuit is rather complex, 8 parts in total. I wonder why. (Some devices/values make no sense to me)
But that should not be the problem.

I don't know what "dynamic load" means. "Dynamic" in my understanding means "variable from low to high" either selectable or automatically.
In either case the relay has a switching current of 10A max... purely resistive. No current peaks, no voltage peaks.
This is where I see the problem.
Possibly the supply causes problems (overshot / ringing) at fast changes of load (relay switching) or the "dynamic load" causes these problems.
Neither a power supply nor electronic loads may be very good for extremely fast changes (relay switching). There may be capacitors involved, there may be a slow regulation loop or ringing regulation loop inside power supply or dynamic load.

Straight forward: I strongly recommend to measure voltage across contact and current through contact with a scope while switching the relay. Then you see the true conditions for the relay contact. Focus on timing in the microseconds to milliseconds range.

Show us the scope pictures.

Klaus
 

The electronic load should be almost resistive. The datasheet performance curve howver specifies only 5A switching capacity for 30V DC.

1645358484854.png
 

The electronic load should be almost resistive. The datasheet performance curve howver specifies only 5A switching capacity for 30V DC.

View attachment 174518
Hi thanks for your replay

so way the mgf. wrote in the main table that he stand 10A (in the table it says 10A in the graph 5A )
1645370088522.png
 

in post #5 you said there is a 30V power supply and the load is set to 10A,
with the relay in between to disconnect power from the load

If the source is inductive, current will continue.
Opening the relay contacts will induce a large voltage across them,
sufficient to keep current flowing, until the associated time constant
drops the current to zero. The induced voltage is likely large enough to arc,
and thereby burning the contacts. The same will happen if the load is inductive.

since the relay is rated at 30V and 10A, the arc that occurs when
you try to open the circuit is the likely culprit, as the arc voltage can be huge.

note also that the graph is about switching, while the table seems to be about
on/off duty cycles
 

Hi,

If the source is inductive, current will continue.

source and load inductance is a main issue while breaking large currents, as the voltage building up is a function of the inductance and the time it takes to open the relay (v(t) = L • di/dt).

Maybe you can share a picture of your satup including the cabling. Or just tell us how the source and the load are connected with the load.

BR
 

How's the exact test sequence? Relay closed with load activated in CC mode or load activated after closing the contact? What's the power supply?

Although the electronic load is unlikely to generate output inductance, there's still some wiring inductance. For clarification, you may want to record the relay contact voltage waveform or even better voltage and current together.

I agree that the datasheet graph and table values are contradictory. I take it as a hint that you shouldn't be sure about 10 A DC switching capability.
 

We still don't know the peak current in the relay contacts at close - for a psu with lots of Cout, and some unspecified "dynamic" load - the peak closing current could easily be > 150A ...
 

Hi,

when I close the relay and switched 10 A all work ok
was the power supply already turned on, when closing the contatctor, or was it turned on after the contacts have been closed? When talking about capacitors which have to be charged, an inductance (of the wiring) actually helps, as it represents a high impedance when closing the realy (fast transient).

BR
 

Make it simple as posible.
Use paper knife then open plastic case of relay. Watch what happen with contact, coil, frame, ..
 

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