Timer delay for DOL 3 phase motor

Thread Starter

Vitessea

Joined Dec 23, 2018
4
Hi, I've been building circuits with my son sometimes using a 555 timer and wondered if this could sort my predicament? The inbuilt timer has failed in the starter for my Dust extractor 380V, no neutral available as is. When the 3Hp motor is switched off a second contractor should switch on to activate a smaller motor for about 30 seconds to shake the dust off the filters. The manufacturer wants about £500 for the timer unit and my electrician says that it can't be done any other way, That doesn't hold with my belief system.
 

jpanhalt

Joined Jan 18, 2008
8,109
Welcome to AAC.

380 VAC may be a problem; my experience is with usual US voltages for smaller motor (<5 HP). Search for time delay switches. Here is my DigiKey search: https://www.digikey.com/products/en/industrial-controls/time-delay-relays/952?k=&pkeyword=&pv110=293&FV=ffe003b8&mnonly=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=500&_ga=2.256097987.959518481.1545597101-1092917399.1518440722&_gac=1.162279048.1545604365.EAIaIQobChMIs6KtzoC33wIVwVuGCh2K1gTIEAAYASAAEgLtffD_BwE By problem, I don't mean not available, but 380V is an industrial voltage and anything for industry has a higher list price.
 

Thread Starter

Vitessea

Joined Dec 23, 2018
4
Welcome to AAC.

380 VAC may be a problem; my experience is with usual US voltages for smaller motor (<5 HP). Search for time delay switches. Here is my DigiKey search: https://www.digikey.com/products/en/industrial-controls/time-delay-relays/952?k=&pkeyword=&pv110=293&FV=ffe003b8&mnonly=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=500&_ga=2.256097987.959518481.1545597101-1092917399.1518440722&_gac=1.162279048.1545604365.EAIaIQobChMIs6KtzoC33wIVwVuGCh2K1gTIEAAYASAAEgLtffD_BwE By problem, I don't mean not available, but 380V is an industrial voltage and anything for industry has a higher list price.
Hi, thanks for that. Those items look useful and I could track them down here in UK. The old device seems to have been a small circuit board going by the noosing which is why I posed the query here, as well as the fun of building it.
 

jpanhalt

Joined Jan 18, 2008
8,109
I had no idea about your level of experience. A 555 timer on a relay will do what you want. A simple 8-pin MCU will also do it. I assumed you wanted to buy something ready made.
 

Thread Starter

Vitessea

Joined Dec 23, 2018
4
I had no idea about your level of experience. A 555 timer on a relay will do what you want. A simple 8-pin MCU will also do it. I assumed you wanted to buy something ready made.
I have some familiarity with components and circuits but don't have the design experience. I worked with my father in his radio shop years ago but it's not my trade.
 

MaxHeadRoom

Joined Jul 18, 2013
19,194
If there is no lower voltage available, usually most electrical suppliers offer 1phase control transformers with in your case, 380v to 24v or 12v, if available, this can be used to feed a low voltage DC by way of a bridge rectifier and a electrolytic cap.
Is there any way the existing unit can be cannibalized for the low voltage supply that it most likely has?
Max.
 

Thread Starter

Vitessea

Joined Dec 23, 2018
4
If there is no lower voltage available, usually most electrical suppliers offer 1phase control transformers with in your case, 380v to 24v or 12v, if available, this can be used to feed a low voltage DC by way of a bridge rectifier and a electrolytic cap.
Is there any way the existing unit can be cannibalized for the low voltage supply that it most likely has?
Max.
Hi, thanks for then reply.
It appears to have been run from the 3 phase supply
Actually I purchased the item with the interior of the switchgear box cannibalised. There are 2 contractors din rail mounted and an area which had a circuit board with a circuit diagram inside the cover of the lid.
I've been making do for several weeks now by manually operating the shaker but will refresh myself on the details today.
 
There are plenty of companies that make delay on break timers. See https://www.functionaldevices.com/about/blog/2018/03/delay-relays-delay-on-make-vs-delay-on-break/

That's going to be a starting point, All of them likely require a steady source of power and a trigger.

In the US with say a 240 system or higher, we would use a control transformer. Here is one that goes from 380 to 24 VAC, https://www.usesi.com/acme-tb81323-1-phase-industrial-control-transformer-208-240-277-380-480-volt-primary-24-volt-secondary-100-va-403835 or pull a neutral. We might use 120 VAC or 24 VAC for controls or even 24 VDC.

Same deal in reverse, you may need a contact closure/open or whatever to detect the loss of a single phase.
A possibly simple way would be to place a relay or transformer stepped down relay to a contact closure on one of the phases.

Another way is to use a phase loss relay such as http://www.ia.omron.com/products/family/3373/specification.html. This one is for 380 V,

So:
Reduce your power supply: control transformer
Select a phase loss transformer for 380V
Select a delay on break time for the lower control voltage.

But....The 3 phase motor probably has a contactor. You can use the coil voltage there. i.e. https://www.newegg.com/Product/Product.aspx?Item=0UW-0015-00CJ3 to get a contact closure or open. Use this in place of the phase loss relay.

If available, you can use an aux contact block on the contactor.

Depending on the replacement cost and down time of the 3-phase motor, the phase-loss relay is an insurance against single phasing.
Like a $5,000.00 USD compressor with lots of down time and expensive refrigerant.
 
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