Mains failure relay pulling circuit - room for improvements?

Thread Starter

Stajo

Joined May 25, 2019
8
Hi all. I just simmed this circuit that is supposed to pull a DC relay if the mains AC 240 V goes out and switch on 24 V batteries. It was a bit tricky to tune, but in this config it seems to do the job. Do you see room for improvements?
https://ibb.co/Fm1s2Yg
 
Last edited by a moderator:

Thread Starter

Stajo

Joined May 25, 2019
8
Found out how to sim the AC failure. Now AC stops after 20 cycles. Seems like it pulls after around 70-80 milliseconds after outage

 

MaxHeadRoom

Joined Jul 18, 2013
20,729
Why does in need the Opto Isolator?
You still have a relay delay in there.
Why not simply wire a suitable relay across the AC in and switch the DC with the contacts when power fails.?
Max.
 

Thread Starter

Stajo

Joined May 25, 2019
8
Why does in need the Opto Isolator?
You still have a relay delay in there.
Why not simply wire a suitable relay across the AC in and switch the DC with the contacts when power fails.?
Max.
Thats kind of a safety thing, not to mix high voltage high current with small signal circutry. And also for if the ground reference is different between line neutral and battery zero/minus. Well a 240 AC coils that closes high current DC (some 30 amps) would work. But I have never seen such a relay, at least not for small bucks.
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
20,729
The very nature of a relay is that it is an isolating device, there are many choices of AC power relay coil, switching low voltage DC.
Max.
 

Thread Starter

Stajo

Joined May 25, 2019
8
The very nature of a relay is that it is an isolating device, there are many choices of AC power relay coil, switching low voltage DC.
Max.
Everything to the right of the optocoupler is powered by battery DC, not just the relay coil and it doesnt have the same ground reference.
 

BobaMosfet

Joined Jul 1, 2009
1,111
A think a much simpler solution is a BJT power transistor on the DC side, after the opto-coupler. A few other components, but overall, simpler. No inductive spike, no switching spark.
 

Thread Starter

Stajo

Joined May 25, 2019
8
A think a much simpler solution is a BJT power transistor on the DC side, after the opto-coupler. A few other components, but overall, simpler. No inductive spike, no switching spark.
Thanks, yea I had that in mind, or a mosfet and a diode but I dont want to loose to much voltage from the 24 volt batteries that is supposed to hold 24 volt equipment up for a time. How much would you say a such will drop at 20 A ?
 
Top