Test box help

[Chris Yard]

Hi all,
I have been asked by the company to work for to design a test box for the products they sell.

The products I am testing can be run from 230V, 110V, 24V or 12V AC, I must explain this bit each product can only run from one of those AC voltages, but the test box must be able to supply any of those voltages to the product, as if I was to have 4 test boxes (1 for each voltage) I wouldn't be asking this question now.

So far I have the transformers to convert from 230v to the other 3 voltages and I have 4 relays to switch these voltages to the product. What I need to do is now come up with some way that when the product switches the input voltage I can detect it back in the test box.... Confused ???

The product I am testing has it's own relay that will switch it's input voltage (230,110,24,12V AC) I need to test that the relay is working correctly by check that I am getting a voltage back from the product.

So far I have a PIC controlling the 4 first relays and I was sort of thinking that I might have another 4 relay to switch the incoming voltage... would that work ????

Also I need to convert the 4 incoming voltages to 5V DC so that I can fed that into my PIC.... That is going to be hard? right ???

Please some one help me.

Thanks in advance
Chris

 

[Chris Yard]

Please can any one help ??

 

[KMoffett]

Patience my friend...many of us have jobs or are asleep. Or both.

The last one: is the PIC part of the test box? If so, just use an external 230VAC to 5vdc regulated power supply.

Does the "product" have some output that indicates that it has internally switched for the appropriate AC supply voltage?

Ken

 

[Chris Yard]

Ken, Thanks for the reply

Patience my friend...many of us have jobs or are asleep. Or both.

Sorry I am in the UK so I was wake and at work !!!

The last one: is the PIC part of the test box? If so, just use an external 230VAC to 5vdc regulated power supply.

Yes the PIC is part of the test box, I am using this to switch the relays and control a 16x4 LCD display, oh and a keypad. Powering the PIC is not the problem I have that all sorted

Does the "product" have some output that indicates that it has internally switched for the appropriate AC supply voltage?

Sorry I may not of made it clear in my first post, the "product" has a timer on it that switches an internal relay (in side the product) when the internal relay switches, it will switch the supply voltage. So my Test box will switch say 230VAC this will then power the product. When the products timer is activated it will switch it own internal relay, which will be switching the voltage my test box has supplied (so in this case 230VAC) but could be 110, 24 or 12VAC . I need to check that 1) the product has switched it own relay, and 2) it lasts for the correct time (Past 2 is not a problem)

I am having a problem in that 1) My test box can switch 4 different voltages to supply the product, 2) How can I check the the products own relay has switched and is suppling the same as the input voltage.

Thanks again in advance

Chris

 

[KMoffett]

This is getting very confusing as to what controls what.
The "product" is being powered by say, 230VAC from your transformer-bank.
The "product's" timer times out and internally switches a relay that expects a 12VAC input.
You want to detect that, and switch your transformer-bank to output to 12VAC?
Is this a repeat and/or random cycling...230V>12V>110V>24>110V...or just a one shot of the timer...230V>12V....230V>24V...230V>110V?

Ken

 

[Chris Yard]

Ok, Our company makes timers. These can be used on a 230V 110V 24V or 12VAC supply. NOT all at once, so if we send to the UK they would be made to work off a 230VAC supply, send them to the US and we make them 110VAC.

I need a test box that can supply all 4 voltages, via a bank of relays. So the person making it would select 230V 110V...... the correct relay would switch and then send that voltage to the timer that was being built. This part I have working.

Now on the timer the very end user presses a button and it's internal relay switches on for a set amount of time.
The relays contacts are connected to the same supply coming in. So if the timer is made to be 230V when the timers relay switches it will switch a 230VAC voltage. If we build it to 110VAC the timers relay will switch 110VAC.

I need to work out a way that, when testing this timer, I can 'see' via the test box the timers relays have switched. The Problem I am having is what is the best way to detect the the timers relay has switched ???? The test box will be if you like a universal test box where it can supply and detect all 4 voltages (not at the same time).

I hope this is a little clearer. If not then I think I might give up on this idea and design 4 test boxes for each voltage.

Chris

 

[KMoffett]

Do these timers have an output...like the plug-in wall outlet timers? 230VAC in > timed 230VAC out? 12VAC in > timed 12VAC out?

Ken

 

[Chris Yard]

YES, we are bascilly interupting the supply to the 'light bulb' on a timed switch (relay).

I need to some how check that the voltage out from the timer is 230V 110........

But I need to be able to check the 4 voltages in one test box...

 

[JimB]

OK so you have four relays which select one of four supply voltages and connect the selected supply to the input of the Device Under Test (DUT).

What you need now is four relays which connect the output of the DUT to one of four indicator lamps, 240v 110v 24v 12v.

Two possibilities:
Use 4 pole relays, two poles for the supply, two poles for the lamp.
or
For each supply, use two off, two pole relays, wire the coils in parallel so they are both energised at the same time. Use one relay for the supply as you are doing now, and the second relay for the lamp.

JimB

 

[Chris Yard]

Thank you Jim, so I think we are getting some where now, So I can either have 8 relays or 4 relays on my PCB. Neither are a problem as I am still only using Veroboard so can change.

Now my next problem is, the DUT output will be mains voltage (AC) I now need some way to convert to 5VDC so I can feed into my PIC & an LED, as I need a visual indication and I need the PIC to time the output to make sure the DUT is timing correctly.

Is there a simple circuit that could handle all 4 voltages?? or am I going to need to design 1 circuit per DUT output voltage ??? by the way if the first option, would I need any relays from DUT ??? just a thought.

Chris

 

[Chris Yard]

What about if I was to adapt this **broken link removed**, may be make 3 of them as the 12VAC will be an easy one with a rectifier and a 7805. I would also use an opto isolator as well so that I can keep the mains voltage out of my low voltage side.

And yes I have read the warnings on this page as well, I am well aware of the dangers of not having a transformer to split the circuit up.

 

[KMoffett]

Please don't use that supply. It's "intrinsically" unsafe. Since you're in an industrial environment, the government and lawyers will have a field day with you should anyone get injured. Go out and buy a separate transformer-isolated, regulated 5VDC power supply. If you really need to do it cheap...I get 5vdc/1A switch-mode power supplies (cell phone chargers) at Goodwill for $0.99USD.

As for the output detector, I think the attached should do it for you. The "120VAC" input would got to the output of your timer output. The "Load" would go to the relays that select you lamps. It will work for anything above ~3VAC. The taper-off of the "Power-Off" indication can be reduced a little by reducing R2 or C1 a little. But that will increase the ripple on top of the ON signal. Since that time period is constant, I would just have your µC subtract it for the displayed reading. But, that short period may not be significant to your timer's spec's.

Ken

 

[Chris Yard]

Thank you KMoffett,
I have spent the weekend looking at this and I think I might of biten off more than I can chew !!!!

I am going to ask one of our sub contractors to have a look at this project to see if they can design something for me.

Thanks again for all your help, I hope that this post might help someone else at some point.

Again thanks to everyone that has helped me so far.

Chris

 

[KMoffett]

Sorry to hear that Chris. We all get in over our head from time to time, but I do think it stretches our learning for the better. It would be interesting to see the final result, if your willing to share.

Ken

 

[Chris Yard]

I am more than happy to share final results, but it may be a couple of weeks, I now have to fit around the sub contractors. Allthough I have not finished (or started) the project I have some better understanding and may even take up another project involving transformerless power supplys.

 

[KMoffett]

If you're going to play with those, you might want to read this: http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf and this **broken link removed**

But for the life of me, with cheap, tiny, (gut'able) SWMP wall warts, I can't see much use for transformerless ones. And yes, I have built a couple. But did not realize much savings in size or cost.

Ken