Make relays hold position during UPS Switch-over.
Make relays hold position during UPS Switch-over.
(OP)
I have a UPS providing 120Vac to a transformer which converts it to 24VAC. This 24Vac circuit powers several Idec relays (50-80mA coil current each).
I expected them to stay in position when power goes out since it's on UPS, but I failed to recognize that the UPS I am using has a .004 second switchover time.
Is there a simple circuit method of holding this 24V AC voltage for a fraction of a second, so it will ride through a minor power interruption while the UPS switches?
I do HVAC PLC work primarily, and my electronics knowledge level is low.
I would really like to find an inexpensive solution that doesn't require me to purchase (7) new dual conversion UPS's @ $550 each... Can you help?
Thank in advance!
John
I expected them to stay in position when power goes out since it's on UPS, but I failed to recognize that the UPS I am using has a .004 second switchover time.
Is there a simple circuit method of holding this 24V AC voltage for a fraction of a second, so it will ride through a minor power interruption while the UPS switches?
I do HVAC PLC work primarily, and my electronics knowledge level is low.
I would really like to find an inexpensive solution that doesn't require me to purchase (7) new dual conversion UPS's @ $550 each... Can you help?
Thank in advance!
John





RE: Make relays hold position during UPS Switch-over.
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RE: Make relays hold position during UPS Switch-over.
RE: Make relays hold position during UPS Switch-over.
MikeL.
RE: Make relays hold position during UPS Switch-over.
Another alternative is to use a constant voltage transformer, if you can find one for the voltages you require. It should keep the AC voltage up for a brief period while your UPS switches.
xnuke
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RE: Make relays hold position during UPS Switch-over.
CV Transformers seem to be around the same cost as a double conversion UPS.
RE: Make relays hold position during UPS Switch-over.
Some possible choices:
1> Change out the UPS. A true UPS charges a battery and inverts off the battery all the time. In the event of a supply failure the battery simply stops charging. There is no changeover or changeover time and no need for a delay to determine that incoming power has been lost.
2> Change out the relays for relays that will ride through a 4 milli second interruption.
3> Put in a DC power supply, change out the relays for DC relays and hang some capacitors on the power supply.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Make relays hold position during UPS Switch-over.
Or change out the relays to ones that have a small dropout time delay.
RE: Make relays hold position during UPS Switch-over.
I found a simpler way to swap 4 of the 5 relays to DC, install a DC power supply feeding the two circuits that operate these relays. The 5th relay can cycle without causing issues to controlled equipment.
The DC Power supply has a fat little capacitor on it that may solve my issue directly, if not I can add another one on the terminal strip.
Parts are on order, I will prove the concept in a few days.
Thanks everyone!
RE: Make relays hold position during UPS Switch-over.
http://www.apcmedia.com/salestools/SADE-5TNM3Y/SAD...
http://www.apcmedia.com/salestools/JSII-5YQSBR/JSI...
The second paper briefly discusses the myth of needing zero switchover time.
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RE: Make relays hold position during UPS Switch-over.
I think I've found a way to modify the safety circuits to use DC relays and add capacitance at the same time. Will be able to test it in a few days.
RE: Make relays hold position during UPS Switch-over.
Quoting myself from several years ago: "They're like having an unreliable guard dog that is high-maintenance, sleeps through a fraction of the burglaries, makes a huge mess once in a while, and every once in a long while eats one of the children."
It may seem counter-intuitive, but one should be extremely cautious about having a UPS included in any system where reliability is important.
RE: Make relays hold position during UPS Switch-over.
Good luck,
Dave
RE: Make relays hold position during UPS Switch-over.
@VE1BLL - I've never had a UPS eat one of the kids... You should consider procuring a better quality UPS, and changing the batteries more frequently.
RE: Make relays hold position during UPS Switch-over.
If the guard dog isn't fed properly and is so hungry that it starts eating kids, it will be very easy to pacify it with a sausage or two. So, take care to feed the dog properly.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Make relays hold position during UPS Switch-over.
Excellent advice.
(Sorry, you kinda lobbed it in there...)
Anyway, it's clear that the DC relay approach is the best given the circumstances. Good luck.
RE: Make relays hold position during UPS Switch-over.
1-Add to each relay a: diode bridge AC/DC 1A-100V to the control coil, now each of the AC relay will act as an DC relay
2-Add to the output of each bridge a capacitor that its energy will hold the relay to the time needed,
Do you know to calculate the capacitors value?
Any question contact : daveross100@gmail.com
RE: Make relays hold position during UPS Switch-over.
An AC coils needs the low impedance when core is open (to produce enough current to pull in). The impedance then increases so current is reduced. That prevents the coil from overheating.
With a rectifier and an AC coil, you wont get that. And if you add a resistor to reduce current, it won't pull in.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Make relays hold position during UPS Switch-over.
RE: Make relays hold position during UPS Switch-over.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Make relays hold position during UPS Switch-over.
The problem has been addressed more than seventy years ago. It then involved a diode, a capacitor, a resistor and an NC auxiliary contact with late breaking.
The NC Contact allowed enough current for the coil to pull in the core. When the NC contact opened, the resistor was connected in series with the coil to prevent it to overheat and at the same time provide enough current to seal the core in.
I think that the arrangement was Siemens K915 with a special suffix.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Make relays hold position during UPS Switch-over.
I have had issues with a switching UPS like the OP is using causing chatter on a 600A vacuum contactor. The contactor uses rectified AC to power the DC coils and is supposed to have a 90mS average opening time.
I always insist on a UPS that has seamless transfer for AC control circuit backup.
RE: Make relays hold position during UPS Switch-over.