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Discussion Starter · #1 · (Edited)
Hi Guys


Is there a way beside using a timer to convert a constant 110VDC signal to a 110VDC PULSE signal ?. The pulse time doesn't matter.


What i have is a DOL motor starter that has an remote input that should be a pulse, but the output coming from the control room is an constant signal in other terms (there is always a voltage in the wire as long as the on signal is given) from the control room.

Thanks in advance
 

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The easiest would be to hook an electrolytic in series with the signal. This would give you a pulse while the cap is charging depending on your load and the size of the cap. If it needs to be more precise (less hack) run it to the coil of a relay and let the relay contacts switch the 110 VDC. Also a bleeder resistor to discharge the cap when the signal is gone.

You don't mention how often the switching needs to occur or how long it stays high, so this idea might not work if there is not enough time to discharge the cap. At least it might give you some ideas.
 

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Are you trying to make a 3 wire type control work with a constant "on" signal?
Sounds like that to me too.

If so, you need what is called a "One Shot" timer, they are very common, especially as an option within a multi-function timer. The trickier part is going to be the 110VDC aspect. That;'s a tough voltage level to find on things like timers. Switching DC takes a large air gap, something that small PCB based devices are not designed for.

PS: I guess it wasn't that hard after all...
http://www.ssac.com/product.php?pid=629&catid=73
 

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Discussion Starter · #7 · (Edited)
Sounds like that to me too.

If so, you need what is called a "One Shot" timer, they are very common, especially as an option within a multi-function timer. The trickier part is going to be the 110VDC aspect. That;'s a tough voltage level to find on things like timers. Switching DC takes a large air gap, something that small PCB based devices are not designed for.

PS: I guess it wasn't that hard after all...
http://www.ssac.com/product.php?pid=629&catid=73
The load is just a small contactor coil, the problem is that the engineers maintaining the system there don't want timers to do the job and to me i can't see how this can be done without a timer ?, a PLC was used before but they insisted that they wanted it removed because the technicians working there don't got any experience with PLC's, well i don't know why they don't want timers ether, i think these guys are some how ******* around.


to clear up the picture a bit more, if a constant signal is used at the DOL remote input, the constant signal will not allow the starter to shut off (once the off button is pressed locally on the DOL, it will unlatch the contactor but when the button is released the contactor will latch again because there is still a signal coming from the control room.


My idea is to use two timers, one for the ON and one for the OFF
 

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Discussion Starter · #8 · (Edited)
You don't mention how often the switching needs to occur or how long it stays high, so this idea might not work if there is not enough time to discharge the cap. At least it might give you some ideas.

Switching occurs only when the signal is given (a short pulse for the ON and another for the OFF
 

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A one shot function utilizing a multifunction timer will be the most simple. These can be set to give a high output for most any duration needed. After this time period has elapsed, the one shot output will change back to off and your local stop device will function.

Another possible option could be to install a NC pneumatic timer on the face of the motor contactor. You would set the pneumatic timer to drop out after the coil to the starter pulls in. Your output, from the "control room" would route through the NC contact on the pneumatic timer and then to the coil of the starter. Your starter latch circuit would need to parallel this timer.

On second reading of your post:
Why can you not modify your local control device(s) to standard start-stop buttons. The "control room output" would be the power to the stop button. A start button would be in series after the stop button. Your latch contact would be in parallel with the start button. The stop button would stop the motor at any time, or the loss of the output from the control room would also stop the motor.
 

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Discussion Starter · #10 · (Edited)
On second reading of your post:
Why can you not modify your local control device(s) to standard start-stop buttons. The "control room output" would be the power to the stop button. A start button would be in series after the stop button. Your latch contact would be in parallel with the start button. The stop button would stop the motor at any time, or the loss of the output from the control room would also stop the motor.
I Fully agree with you on this, but the customer don't want any thing changed in there, i know this sounds wired but this is the kind of people i am dealing with at the moment.

I will take some pictures tomorrow and let you guys know how its going. :thumbsup:

PS

Its a real pain in the *** to work with there 30 years old setup that has 30% of the wires unlabeled mummified by the dust that haven't been cleaned for years
 

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I Fully agree with you on this, but the customer don't want any thing changed in there, i know this sounds wired but this is the kind of people i am dealing with at the moment.

I will take some pictures tomorrow and let you guys know how its going. :thumbsup:

PS

Its a real pain in the *** to work with there 30 years old setup that has 30% of the wires unlabeled mummified by the dust that haven't been cleaned for years
Yes, I know how this is. Some equipment, that I work on has no wire marking and no documentation. It can be a little challenging some times. When people ask me what I do, I say that I am a "junk fixer".
 
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