Initial AC current though a coil

Thread Starter

jyjohnhenry

Joined Nov 16, 2014
11
I will try to get the number off the timer, but it is all wired in on a board and maybe not easy to get at. The switch is rated at 3amp 500v DC
 

Thread Starter

jyjohnhenry

Joined Nov 16, 2014
11
I havent had time to get to shed today, so havent got the number of the timer. The reed switch is operated by a perm. magnet fixed to a free swinging expanded polystyrene panel. When the panel is moved by the wind the fan is off ( hopefully). when the panel is stationary the switch conducts, starting the timer which will cause the 3ph contactor to start the fan after say, 10 min. the only purpose of the timer is to delay the start up to avoid the fan hunting, ie switching on and off rapidly if the wind is very variable.
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
If it is working as I suspected the reed switch should not be switching any significant current at all (timer input), so there should be no worry about contacts welding.
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
BTW I knew I had something on file, this from Panasonic Relays.

Quote:
For the AC type, there is an inrush
current during the operation time for the
separated condition of the armature, the
impedance is low and a current greater
than rated current flows;
For the adhered or engaged condition
of the armature, the impedance
is higher and the rated value of current
flows, and because of this, for the case
of several relays being used in parallel
connection, it is necessary to give
consideration to power consumption.
Max.
 

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Thread Starter

jyjohnhenry

Joined Nov 16, 2014
11
Many thanks Max for your help, I am going to try again just connecting it up, if the switch malfunctions again I will have to go to a low DC voltage circuit to the switch with another relay to the AC circuit.
 

Thread Starter

jyjohnhenry

Joined Nov 16, 2014
11
No drawings available - a local firm put a small board in. but the switch operates a timer relay which in turn powers the fan overload and contactor.
I have just had another reed switch destroy itself, but at £10 a pop I am going to take the circuitry from a converter plug from a camera( or something) charger which outputs 700 mA 12Vand run this through a relay (RS no. 800 4441 described as a ' high inrush relay ' rated at 8 amp with max voltage 400 AC switching which should meet the requirements. Will let you know how I get on !
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
but the switch operates a timer relay which in turn powers the fan overload and contactor.
I have just had another reed switch destroy itself, but at £10 a pop !
Normally you would not use a small reed relay to operate a mechanical relay directly, it would trigger the timer relay input which would be low impedance normally.
Another issue if in fact the R.relay is operating a relay directly, is there a reverse diode across the coil?
Max.
 

Thread Starter

jyjohnhenry

Joined Nov 16, 2014
11
What exactly would the reverse diode achieve and across what coil ?
As I am now going for the switch operating a 12v coil in an intermediary relay would I still need a reverse diode ?
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
The BEMF diode prevents large voltage excursions across the coil when the reed switch opens, which could end up destroying the reed switch.
This assuming the Reed switch is operating the coil directly
Max.
 

Thread Starter

jyjohnhenry

Joined Nov 16, 2014
11
It does sound as though I should have had one of these in place all along, may have cured the problem?!
It is along time since I have done anything with electronics and am more than a bit rusty, I have some IN4001 diodes rated at 1 amp with max peak reverse voltage 50v dc which could use . Do you think they would be suitable for my 12v circuit and I would put the cathode at the positive side of the coil, is that correct?
Once again thanks for your input
 
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