Contactor switching in residential lighting

[Jerramundi]

Not necessarily is the arc automatically maintained when switching DC current, the deal is that the arc is easier to extinguish when switching an AC circuit because voltage crosses zero every half cycle. DC the voltage remains constant and contines to feed the arc until the gap between contacts becomes large enough the voltage can no longer maintain that arc. The higher the DC voltage the more gap is needed to extinguish the arc.

I thought DC wave form looked more like the McDonald's arches than it did a straight line (i.e. constant). That unless you have a device that specifically regulates itself to output a constant voltage. Aside from that one instance, wouldn't that mean DC voltage still has a 0V point in the cycle and thus would be equally as likely to extinguish that arc?

 

[ActionDave]

I thought DC wave form looked more like the McDonald's arches than it did a straight line (i.e. constant).

I believe that what you get when you rectify AC.

That unless you have a device that specifically regulates itself to output a constant voltage.

I've often heard a thing like that called a battery.

Aside from that one instance, wouldn't that mean DC voltage still has a 0V point in the cycle and thus would be equally as likely to extinguish that arc?

DC is harder on contacts but we're not talking about putting out a fire here.

 

[Fred B]

I thought DC wave form looked more like the McDonald's arches than it did a straight line (i.e. constant). That unless you have a device that specifically regulates itself to output a constant voltage. ......

I believe that what you get when you rectify AC.
..........

I believe the McDonald's reference is an accurate representation of the wave form of DC when supplied from an AC inverter. Thus if a truer DC is required rectifiers are added to flatten the wave to eliminate or reduce the zero reference. That is why high voltage DC can be so dangerous compared to equivalent AC voltage, no zero V point to unlatch from if contact is made.
I'm not sure if you can even get an absolute flat line (0Hz) DC when provided via an AC inverter xfer.

 

[ActionDave]

I believe the McDonald's reference is an accurate representation of the wave form of DC when supplied from an AC inverter. Thus if a truer DC is required rectifiers are added to flatten the wave to eliminate or reduce the zero reference. That is why high voltage DC can be so dangerous compared to equivalent AC voltage, no zero V point to unlatch from if contact is made.
I'm not sure if you can even get an absolute flat line (0Hz) DC when provided via an AC inverter xfer.

Rectifiers change AC to DC, capacitors help flatten out the humps

 

[Fred B]

Rectifiers change AC to DC, capacitors help flatten out the humps

Not real familiar, just usually installing a device, but got me interested how it works. So would both be combined in a converter device? Seems that it might be an important factor if troubleshooting. Such as LV DC exterior lighting.

 

[kwired]

Not real familiar, just usually installing a device, but got me interested how it works. So would both be combined in a converter device? Seems that it might be an important factor if troubleshooting. Such as LV DC exterior lighting.

Google half wave, full wave, and full wave bridge rectifiers.

Capacitors are used to store some energy when the AC wave is rising, then release that energy as the AC wave is falling - to make a straighter line that represents the DC output. That capacitor still will cause a ripple in the output if only a simple half wave rectifier compared to if used with a full wave bridge.

Bridge circuits can be made for three phase input/ DC output as well, that is what you have on forklift chargers and other higher power applications, and is what the "front end" of a three phase input VFD basically is.

 

[synchro]

Bridge circuits can be made for three phase input/ DC output as well, that is what you have on forklift chargers and other higher power applications, and is what the "front end" of a three phase input VFD basically is.

Three phase bridge rectifiers are also used at the output of automobile alternators. The DC current in the rotor winding is adjusted by the voltage regulator to maintain the output from the rectifiers at the appropriate value for a 12V battery.