Here is a question on implementing a relay based soft start and trying to avoid arcs within the relay. I'm switching the AC voltage coming out of the wall, so want to do this correctly. I've got a delay circuit and will implement the soft start as shown on the attached schematic....I think, so I wanted everyone's input.
Here is the schematic:
Its intended to work like this-
1. When the amp is turned on the relay is connected as shown with a resistive soft start element (resistor or thermister or combo of both) in line with one primary of the transformer to prevent a surge.
2. After a time delay, S1 is activated and the 12VDC circuit provides 12VDC to the relay, causing the relay to switch, which connects the primary of the transformer directly to the AC inlet, bypassing the resistive element.
I'd like to prevent arcs within the relay when this switching happens. I heard you all use capacitors for this, which is why I'm thinking of using C2 and C3. C2 would prevent the initial arc, and C3 would prevent an arc when the amp is turned off and the relay returns to its initial state....I think.
D1 is to prevent voltage from relay actuation from interfering with the control circuit. I'm not sure what C1 is for, but I've seen people use a cap here.
3. My question is -- do I have this right? Are D1, C1, C2 and C3 necessary, will this setup prevent relay arcing? Are the C values correct? If not, what will?
Here is the schematic:
An externally hosted image should be here but it was not working when we last tested it.
Its intended to work like this-
1. When the amp is turned on the relay is connected as shown with a resistive soft start element (resistor or thermister or combo of both) in line with one primary of the transformer to prevent a surge.
2. After a time delay, S1 is activated and the 12VDC circuit provides 12VDC to the relay, causing the relay to switch, which connects the primary of the transformer directly to the AC inlet, bypassing the resistive element.
I'd like to prevent arcs within the relay when this switching happens. I heard you all use capacitors for this, which is why I'm thinking of using C2 and C3. C2 would prevent the initial arc, and C3 would prevent an arc when the amp is turned off and the relay returns to its initial state....I think.
D1 is to prevent voltage from relay actuation from interfering with the control circuit. I'm not sure what C1 is for, but I've seen people use a cap here.
3. My question is -- do I have this right? Are D1, C1, C2 and C3 necessary, will this setup prevent relay arcing? Are the C values correct? If not, what will?
If you eliminates C2 and C3, reduce C1 to 100nF and put a NTC ( negative Term. coef. Resistor) in place of C2 have not arcs and works all. 😉
Ciao
Mauro
Ciao
Mauro
C1 is not needed. You need to change your relay switching so that the resistor is shorteD out or not, not two different lines are switched. Youy way you will have a momentary interruption in power as the relay switches, and the consequent arcs.
OK I think i get what you are saying. You are saying that the relay should just short out the resistor or thermister. What about this:
An externally hosted image should be here but it was not working when we last tested it.
The schematic shows the initial condition. After a time delay the switch will flip causing the relay to change states. Thus, when the time delay is over, the relay simply shorts out the resistor or thermister, leaving it in the circuit. Is this design better? Is C1 required or harmful (what value should it be?)
Re: bump
My answer is:
A normal 8 A/250 AVC relay will last more 15 years if you switch on the amp once a day.
You should first ask yourself: Is this a problem?lgreen said:
My answer is:
A normal 8 A/250 AVC relay will last more 15 years if you switch on the amp once a day.
One of the reasons I take the trouble to do DIY is to interact with everyone and try to learn concepts that seem interesting, such as this one. I don't care if it lasts 20 years, I'd still be interested to learn about how to construct a soft start that doesn't arc.
Besides, I can't tell if you are indicating that the 1st or 2nd one would last 15 years, as its not stated.
The circuit is now spot on. Just reduce C1 to a few tens of nF so that you can use a cap better suited to snubbing. It actually wouldn't matter if you left it out as you won't be totally breaking any large currents, but it won't hurt to leave it in.
Re: because
Fortunately, these "obscure" items are carried by Digikey, Mouser, Newark, and similar vendors.
lgreen said:
Fortunately, these "obscure" items are carried by Digikey, Mouser, Newark, and similar vendors.
SY said:
this has been discussed - conclusion was that zero is the worst part of the cycle to turn a toroidal on.
Mauro's idea looks good.
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