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Help with using a relay module

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floppy32

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I need to use this relay module to switch ON/OFF this SMPS either from at AC input or its DC output.
The SMPS is rated as 12VDC 10A and in my case it will source 5A to 6A to a module.

As you see the relay module uses this relay. An has already flyback diodes and also has something looks like MOVs.

The thing is I was planning to use the relay module for AC side(line) of the SMPS, but I noticed that the SMPS datasheet shows the following:
INRUSH CURRENT: 60A

And the relay I guess cannot handle this inrush current(?). And the relay contacts might weld(?)

So then I thought to use the relay module for the DC side of the SMPS. In this case it is rated as 5A at 30VDC.
In my case it needs to handle a current between 5A to 6A at 12VDC.

So I am stuck at this point and for some reason difficult to buy another relay.

Which option is safer or what could be done to remedy either AC or DC cases?

For the AC case: I heard about NTC series but I don't know how to size it or would that work.

For the DC case: I might exceed 5A a bit but at 12VDC. So I'm not sure would that be fine or require any heatsink ect.

I would be very glad with any suggestions/workarounds.

Thank you
 

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Hi,

eventually a relay module that makes sense. (from the schematic)
* Power supply capacitor, drive transistor (instead of useless optocouplers), control LEDs, protection diode across coil, Overvoltage protection across contacts.

This all makes sense..
sadly it has not sufficient "switch current" rating for your application.
--> Choose a relay with higher switching current specification.

Klaus
 

Upvote 0 Downvote
KlausST said:
Hi,

eventually a relay module that makes sense. (from the schematic)
* Power supply capacitor, drive transistor (instead of useless optocouplers), control LEDs, protection diode across coil, Overvoltage protection across contacts.

This all makes sense..
sadly it has not sufficient "switch current" rating for your application.
--> Choose a relay with higher switching current specification.

Klaus
Click to expand...
How about using a current limiter like here https://sedtronic.eu/img/cms/pics/NTC/ntc.png?
--- Updated ---

KlausST said:
Hi,

eventually a relay module that makes sense. (from the schematic)
* Power supply capacitor, drive transistor (instead of useless optocouplers), control LEDs, protection diode across coil, Overvoltage protection across contacts.

This all makes sense..
sadly it has not sufficient "switch current" rating for your application.
--> Choose a relay with higher switching current specification.

Klaus
Click to expand...
I also asked about using it at DC side. In my case 12VDC 5A(or a bit more).
 

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Hi,

A current limiter seems to be a good idea.

floppy32 said:
I also asked about using it at DC side. In my case 12VDC 5A(or a bit more).
Click to expand...
I think it´s the same problem as with AC side: The nominal current is not the problem...but the inrush current. And switching a capacitor at 12V DC means a huge current peak.

Klaus
 

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The relay is speced at a max of 5A @ 30 VDC. I would switch the DC side
if you don't mind leaving the SMPS on all the time, which would be a sad
waste of energy.

If you do the DC side, I would assume the SMPS caps all charged, so only
transient current you need to tackle would be load caps, and their respective
sizes.

When you choose a component generally speaking always crank in some margin.
So a 10A relay module might be a better choice, in general, reliability, safety.....

Note you could always use a dual relay, and switch in and out a current limiter
if doing AC side. But not all supplies startup without a "stiff" source, eg. one without
series R. So you should contact supply manufacturer support engineering and explain
your issue to see if their supply would behave.

Regards, Dana.
 

Upvote 0 Downvote
KlausST said:
Hi,

A current limiter seems to be a good idea.


I think it´s the same problem as with AC side: The nominal current is not the problem...but the inrush current. And switching a capacitor at 12V DC means a huge current peak.

Klaus
Click to expand...
Thank you can you recommend a current limiter fir AC or DC side? I would be very glad since I dont know how to size it or what component to use.
--- Updated ---

KlausST said:
Hi,

A current limiter seems to be a good idea.


I think it´s the same problem as with AC side: The nominal current is not the problem...but the inrush current. And switching a capacitor at 12V DC means a huge current peak.

Klaus
Click to expand...
Thank you can you recommend a current limiter for AC or DC side? I would be very glad since I dont know how to size it or what component to use.
--- Updated ---

danadakk said:
The relay is speced at a max of 5A @ 30 VDC. I would switch the DC side
if you don't mind leaving the SMPS on all the time, which would be a sad
waste of energy.

If you do the DC side, I would assume the SMPS caps all charged, so only
transient current you need to tackle would be load caps, and their respective
sizes.

When you choose a component generally speaking always crank in some margin.
So a 10A relay module might be a better choice, in general, reliability, safety.....

Note you could always use a dual relay, and switch in and out a current limiter
if doing AC side. But not all supplies startup without a "stiff" source, eg. one without
series R. So you should contact supply manufacturer support engineering and explain
your issue to see if their supply would behave.

Regards, Dana.
Click to expand...
Datasheet I provided already states inrush current of 60A. Why to contact them. But can you recommend a current limiter for AC or DC side? I would be very glad since I dont know how to size it or what component to use.
 

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Hi,
floppy32 said:
Thank you can you recommend a current limiter fir AC or DC side? I would be very glad since I dont know how to size it or what component to use.
Click to expand...
I´d use the application notes provided by the limiter manufacturers

Klaus
 

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I'd be a little careful using a current limiter. The PS might need that big surge to 'get going'.

Cautionary tale: A coworker was testing a board with a switching regulator on it. He didn't want to supply full input voltage initially, so he slowly ramped it up. He kept blowing fuses because at low input voltage it draws more current...
 

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floppy32 said:
Thank you can you recommend a current limiter fir AC or DC side? I would be very glad since I dont know how to size it or what component to use.
--- Updated ---


Thank you can you recommend a current limiter for AC or DC side? I would be very glad since I dont know how to size it or what component to use.
--- Updated ---


Datasheet I provided already states inrush current of 60A. Why to contact them. But can you recommend a current limiter for AC or DC side? I would be very glad since I dont know how to size it or what component to use.
Click to expand...

If you are going to do the ac side use two relays as follows

1654044121768.png


The first relay turns on when power on and charges SMPS thru R1 which limits initial
current. The second relay, after a delay, turns on and shorts out the current limit R1
so SMPS sees full line voltage into SMPS.

Size of R1 from talking to SMPS manufacturer about constraints of not applying full
line V to SMPS and the impact on it.


Regards, Dana.
 

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barry said:
I'd be a little careful using a current limiter. The PS might need that big surge to 'get going'.

Cautionary tale: A coworker was testing a board with a switching regulator on it. He didn't want to supply full input voltage initially, so he slowly ramped it up. He kept blowing fuses because at low input voltage it draws more current...
Click to expand...
In my case what can be an issue? It will be at line side of the SMPS.
 

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You have to contact the manufacturer of the SMPS and ask if there are are
any limitations/minimums of input current, ramp rate of input V, for it to start
up properly. If that info is not in their spec sheet/manual.


Regards, Dana.
 

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Hi,
barry said:
I'd be a little careful using a current limiter. The PS might need that big surge to 'get going'.
Click to expand...
It´s true that an SMPS draws more ccurrent on lower input voltage. This may become problematic with fuses, polyfuses or PTCs.
But an inrush current limiter is an NTC. It gets more low ohmic with higher temperature.

Klaus
 

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KlausST said:
Hi,

It´s true that an SMPS draws more ccurrent on lower input voltage. This may become problematic with fuses, polyfuses or PTCs.
But an inrush current limiter is an NTC. It gets more low ohmic with higher temperature.

Klaus
Click to expand...
All true, but my point was that limiting the inrush current might cause the PS to misbehave. I would think that the mfr. would have limited the inrush if they thought it was ok...
 

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Lets make 50+ posts of this until OP gets it (already posted before)

You have to contact the manufacturer of the SMPS and ask if there are are
any limitations/minimums of input current, ramp rate of input V, for it to start
up properly. If that info is not in their spec sheet/manual.


Regards, Dana.
Click to expand...


Regards, Dana.
 

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