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No liability is accepted by UBeaut or the Wood Working Forum's administrators
or moderators for advice offered by members posting replies
or asking questions regarding electrical work.
We strongly advise contacting a Licensed Tradeperson for all electrical work.
WARNING
Information supplied within posts is not to be considered as detailed formal instructions to complete a task.
Members following such information do so at their own risk
Information supplied within posts is not to be considered as detailed formal instructions to complete a task.
Members following such information do so at their own risk
WARNING: This is a Mains AC project. DO not attempt this unless you are competent and comfortable with Mains AC voltages.
Members have been following my threads on the Dust forum might remember that I advocate running a dust collector (DC) for some time after the last dust making activity.
The additional time to run the dust collection varies depending on factors like,
- how long the dust making activity base been going on for
- type of material being cut
- type of dust making activity
- flow rate of DC
- size of shed
The times will vary from a couple of minutes for a large DC in a small shed to indefinitely for a small DC in a large shed. Typical times for me (medium sized shed 3HP DC) would be anywhere from a few minutes to perhaps 10 minutes.
What I have been after to semi-sutomate this is know as a “Delayed power off” timer. There are simple "off the shelf" electronic kits out there that will do this for low power devices but do not meet the power requirements for a bigger DC. There are also more complicated (and expensive) kits that can be used to trigger relays according to set times. These are overly sophisticated for what I’m after and still require the purchase and wiring up of power relays to perform the actual switching.
I had designed a timer from scratch but while scavenging during a council pickup I found what looked like some sort of 3 Phase air conditioner controller which consisted of several enclosures, a bunch of 3 phase wires, conduit, contactors, relays and a couple of industrial strength timers inside it. I used the 3 Phase wiring harness to wire up my linisher.
Anyway after a bi tot mucking about here is what I came up with as "delayed offf" timer.
My unit can be hard wired to a machine in place of a no-volt switch however, for my ease of use I have attached it to a pair of 15A plugs and sockets so it can be inserted between mains AC and a machine. If the machine has a no-volt switch on it this needs to be removed otherwise the timer will not work correctly. Please be aware that removing a NVS from any machine represents a risk in that someone that does not know about this could then plug a machine straight into the mains.
Here is the semi schematic circuit diagram.
For safety, power is supplied though a no-volt switch (NVS). This then supplies power to a terminal block and continuous power to a 240-16VAC transformer (scavenged from a stove also picked up at council pickup time). The 16VAC is converted to 12V DC via a button bridge rectifier (BR) also from the same stove, and then directed via a switch (SW) to power either relay 1 (R1) OR via the timer to power relay 2. (R2)
R1 and R2 are power relays and can switch 240V /30A - I bought these from Altronics.
When SW provides 12V to R1, R2 is turned off and R2 thus provide full mains power indefinitely direct to the outlet so the machine will continue to run until it is manually turned off. When SW is toggled the other way, R1 switches off while 240VAC is provided to the timer to start the timing sequence which also allows 12V DC to reach R2 so it can close and provide full mains power to the outlet.
The time is controlled by the timer which is an Omron XXX-8A model which I also obtained from the air-conditioning controlle.r. Omron like units are valuable on ebay complete with their respective bases for around $20. The timer I use runs under interval (E) mode but these devices can do some neat things. The time range (deci-sces, secs, mins, hrs, 10s of hrs) over which the timer will run is set manually using a set switch (accessible from the from of the unit). For my DC use I use a range of 0 to 12 minutes. The unit does have a couple of indicator lights (C) on it that tell you whether it is "on" (POWER light) and if it is in the middle of a timing Sequence (OUT) which is handy. As the end of the timing sequence approaches OUT also flashes.
User switchable screws A,B alter the range and scale on the dial while D alters the mode.
Once the timing sequence is started the full mains power will continue to be supplied via R2 until the preset time set on the timer elapses which them tuns R2 off. The unit then remains in a safe mode with both R1 and R2 off until operator intervention.
And here is what the unit looks like inside.
The components are enclosed in a transparent box but it does not need to be, this was just one of the enclosures on the air conditioning controller.
If it looks like spaghetti junction, it is. This makes it difficult to test and part of this is because I wanted to reuse the transparent covered box with the switches attached to the cover which requires longer leads so the cover can be removed.
With some thought the wiring could be tidied up considerably. I used insulated spade connectors which is appropriate for AC power but all the 12V relay control lines could have been soldered.
Outside it looks a bit better.
The modes of operation are thus.
Normal use: set SW to power up R1 and the machine will run until operate intervention.
Delayed off use: After normal use, set the timer to how long you want the machine to keep running and then set SW to the other position and walk way.
Anticipated delayed off use: If you wish to perform a dust making activity for a brief period e.g.: a couple of cuts on a TS, then when you start the machine you can use the delayed off mode but add enough time to incorporate the expected work time, This saves the need to return to the switch to switch it to delayed off.
The time period the unit stays on for after switching is controlled by a rotary knob on the front of the timer. If the unit is already running in timing mode and a changed time is required the unit does need to be reset by switching SW on-off.
The knob on the timer must be set before the reset.
The main costs for me were the power relays ($16), the 15A plug and socket, a terminal block, and few connectors. If you had to pay for all of the components it should still be possible to purchase most of these on ebay for <$100.
Improvements:
I was thinking of adding some LEDs so that I could tell what mode it was running in from the other side of the shed.
Thanks for looking.
PS I need too cut some ventilation holes in the box as the transformer warms up the contents after a couple of hours.
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