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Topic: how to switch contactors? (Read 1 time) previous topic - next topic

jonisonvespaa

hi,
my electronic/electrical skills are limited, i would like to switch a few contractors on, 24v coils or maby 240v coils but not sure what to use to turn them on would a Mosfet N the one im looking at is rated at 2.7a max be ok for the 24v contactor, but really unsure how to approach the 240v one?
thanks

Grumpy_Mike

Quote
i would like to switch a few contractors on

Go with permanent staff, contractors do not have the commitment.

If it is contacts you want to change then a relay with a 5V coil is easy, just use a transistor and resistor to turn on the relay.

dc42

#2
May 06, 2012, 03:55 pm Last Edit: May 06, 2012, 04:06 pm by dc42 Reason: 1
You need to know whether the contactor coils are intended for AC or DC. The 240V one is almost certainly AC, the 24V one could be either.

To switch a contactor with a 240VAC coil, use a small SSR (make sure it is suitable for inductive loads), or an opto triac (such as http://uk.farnell.com/vishay/vo2223a-x001/phototriac-power-dip-6-0-9a/dp/1870799) + snubber network.

To switch a contactor with a 24VDC coil, I would use a transistor if the coil current is 500mA or less, and a mosfet if it is more.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

Grumpy_Mike

Quote
I would use a transistor if the coil current is 500mA


Schematic of that here:-
http://www.thebox.myzen.co.uk/Workshop/Motors_1.html

jonisonvespaa


pekkaa


hi,
my electronic/electrical skills are limited, i would like to switch a few contractors on, 24v coils or maby 240v coils but not sure what to use to turn them on would a Mosfet N the one im looking at is rated at 2.7a max be ok for the 24v contactor, but really unsure how to approach the 240v one?
thanks


If your  electronic/electrical skills are limited, don't approach 240v relays at all, and be careful even with 24v relays. What kind of load the contactors are switching?

jonisonvespaa

well i soppose my skills arnt that limited, for my second project i want to monitor the temp of a room and when temp rises turn on two frequenct drives / fans anything up to 20a 3 phase,  so it has to be a contractor really.

i suppose my simplest option would be mosfet and 5v relay but a bit worried about the noise of the relay, really kicking myself as ive been inside and repaired a million control panels (lift industry) and never really had to know what was switching on relays/contactors but since ive got interested in processors would have been nice to know what different manufactures were using.

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