what's the difference between AC and DC contactor - Page 1
Forum section: electronics / beginners

author: erdos
author_rank: Newbie
timestamp: April 17, 2015, 08:14:40 pm
content: helloI've some questions regarding contactors:are the AC or DC referring to the control signals for the Contactors? are these the same thing as internal coil voltage?what are the advantages and disadvantages of one over the other?

author: KeepItSimpleStupid
author_rank: Regular Contributor
timestamp: April 17, 2015, 09:11:31 pm
content: There are actually two specs.1) The coil rating2) The AC and DC contact ratings and/or the HP (horse power) ratingsand lots more. Some contacts on some relays can't be switched under load.Since this relates to switches, simple slide switches that are used for ceiling fan direction should not be switched under load.In some cases, the ratings have to do with arc suppression.All of the ratings have to be adhered too.

author: tautech
author_rank: Super Contributor
timestamp: April 17, 2015, 09:28:34 pm
content: And to expand a little moreCoil:DC or AC with an AC Frequency rating, normally 50, 60 or 440 Hz.ContactsAC rating AND DC rating, that is usually much lower to minimise arcing and therefore meet the MTBF spec.

author: Cherry
author_rank: Contributor
timestamp: April 20, 2015, 06:47:12 am
content: A little understand after reading the above information.

author: Pillager
author_rank: Unknown
timestamp: April 20, 2015, 07:09:51 am
content: In any case, don't hook up an AC-coil-contactor to DC-voltage. Unless you wan't a smoke machine

author: woodchips
author_rank: Frequent Contributor
timestamp: April 20, 2015, 08:02:03 pm
content: I am still unsure as to whether the question refers to the coil or the contacts? Being that this is a contactor, not a relay, then the power being switched could be considerable. AC and DC are not the same in that case.More details?

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 20, 2015, 08:21:42 pm
content: The question is to vague. It doesn't work as a generic question.Are you talking about the ratings of the switch contacts? Or about the rating of the coil?It is not a matter of "advantages" or "disadvantages". You generally cannot use an AC-rated contactor for a DC application and vice-versa.As others have mentioned, there are so many details missing, it is not possible to have any meaningful discussion.

author: max_torque
author_rank: Super Contributor
timestamp: April 20, 2015, 09:24:46 pm
content: If we talk about the main power contacts, then an AC rated contactor can for any given size / type generally be rated to break a much higher current.This is because the voltage across the open contacts goes to zero during the AC cycle, which means any arcing generated as the contacts are separated when carrying a high current is extinguished in a short time.As the voltage across the opened DC contactor remains above zero, the arc that is generated upon opening does not stop (without other deliberately designed in "arc breaking" functionality, such as magnetic,compressed air, internal damping compounds or even explosive arc extinguishing) and hence current can continue to flow and physical damage can be caused to the contacts