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Old 07-06-2019, 11:40 PM   #1
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Default Reverse bias diode usage

I have an application where I have 7 valves all supplied by the same pump, but each valve is controlled separately by a set of dry contacts. Normally they control the pump with an 8th set of contacts, and just dead head it in between valves. The cold water pump does ok with this but the hot water pump struggles. The customer doesn't want to add any additional automation, current switches, relays etc, so I was thinking about adding a reverse bias diode to each valve switch leg then continuing to pump relay. Basically all the valve switch legs would be tied together after each diode at the pump relay, but can't back feed through the relay terminals to the other valves. Make sense?
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Old 07-06-2019, 11:49 PM   #2
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Wait, what? You're not talking about a flyback diode. Sketch a pic of what you have in mind. Maybe I'm just tired.
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Old 07-07-2019, 12:15 AM   #3
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Wait, what? You're not talking about a flyback diode. Sketch a pic of what you have in mind. Maybe I'm just tired.
here you go
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Reverse bias diode usage-3af50489-e2b0-43ff-9e1d-7203624d4609_1562472896458.jpg  

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Old 07-07-2019, 12:29 AM   #4
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So basically you want any solenoid to start the pump via a relay. I dont see a problem with that.
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Old 07-07-2019, 12:29 AM   #5
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Looks like it'd work out just fine, provided it's DC of course.......lol.

A lot of scissor lift controls use a scheme similar to this.

Basic blocking diodes, very simple.
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Old 07-07-2019, 12:51 AM   #6
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As long as the diodes can handle the coil current, look good.
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Old 07-07-2019, 12:51 AM   #7
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It's essentially an OR gate, I like it.
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Old 07-07-2019, 02:56 AM   #8
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Before I say anything else, it is cheap and looks like it would work. That being said:


I wouldn't hack that in. Designing a contained control system would be one thing, but if the customer doesn't want to pay for DPST relays, I wouldn't be able to offer much in the way of a solution. Parallel one set of relay contacts to the pump and the other just starts the valve like normal. Either way you are breaking into the wiring of the system.

More importantly, they could also just have a pressure relief valve between their pressure and return on the hot water system, which it seems like they don't have if they are having issues, or that valve has gone bad. Not sure of the exact setup here, but this seems more like a mechanical problem.
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Old 07-07-2019, 07:31 AM   #9
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I think I follow what you're doing, although I don't think I follow what the problem is or why it would cause one pump to struggle. Using the diode between each relay and the pump would work as far as I can see.

I know you said they don't want any more relays, but it seems like an interposing relay between the relay and the pump would accomplish the exact same thing cheaper and maybe better.

I don't know why the customer would care about seven additional relays on their DIN rail but wouldn't care about seven additional diodes on their DIN rail ... but if your customers are like mine, it doesn't surprise me either.

BTW either I am drunk or the wire numbers on your diagram are jacked up.
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Old 07-07-2019, 08:37 AM   #10
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Quote:
Originally Posted by gpop View Post
So basically you want any solenoid to start the pump via a relay. I dont see a problem with that.
correct but I don't want any back feed from solenoid to solenoid.
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Originally Posted by sparkiez View Post
Before I say anything else, it is cheap and looks like it would work. That being said:


I wouldn't hack that in. Designing a contained control system would be one thing, but if the customer doesn't want to pay for DPST relays, I wouldn't be able to offer much in the way of a solution. Parallel one set of relay contacts to the pump and the other just starts the valve like normal. Either way you are breaking into the wiring of the system.

More importantly, they could also just have a pressure relief valve between their pressure and return on the hot water system, which it seems like they don't have if they are having issues, or that valve has gone bad. Not sure of the exact setup here, but this seems more like a mechanical problem.
This a PC based relay logic controller, operating the valves and pump. It doesnt have the capacity to turn a input on multiple times during a program cycle hence the pump deadheading in-between valves. Sometimes the program cycle will only need valves 1 and 7, sometimes only 1 and 3, so the pumps will be dead headed if no call for valves. The pump is on a VFD with a pressure transducer running PID loop based off of psi. This operates from 7am till 9pm 365 so plenty a deadhead time.

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I think I follow what you're doing, although I don't think I follow what the problem is or why it would cause one pump to struggle. Using the diode between each relay and the pump would work as far as I can see.

I know you said they don't want any more relays, but it seems like an interposing relay between the relay and the pump would accomplish the exact same thing cheaper and maybe better.

I don't know why the customer would care about seven additional relays on their DIN rail but wouldn't care about seven additional diodes on their DIN rail ... but if your customers are like mine, it doesn't surprise me either.

BTW either I am drunk or the wire numbers on your diagram are jacked up.
No room in the enclosure on this one for more relays. I bet the numbers are all jacked up, I made the drawing on my phone via remote connection to my desktop. The drawing program isn't very touch pad/screen friendly.
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Old 07-07-2019, 01:59 PM   #11
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Tates,

Just couple quick simple question .,,

what size control transformer you did see it there?

second thing if you set up this in DC I dont see much issue with it as long you using the interpole relay that I do know it work for a fraction of the cost beside the set of other relay .

is this pump set up is for large building ? I am try to get the picture of your layout cuz I have pretty simuair set up I have see at one of my larger local motel have that. ( not super common item in this island )

I know you mention VSD there is the pump running in low speed mode when all the valves are closed ?
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Old 07-07-2019, 02:29 PM   #12
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Here are a few things I want to touch on. First:

Is it possible to just modify the program to perform this task? Ultimately, this would be the absolute BEST way to handle this scenario.


Second, I realize they don't want to add anything, but those relays controlled by the PC could easily toggle an interposing relay as mentioned before. I see this as the second-best solution. You can parallel all of the relays to give a run-enable to the VFD.


Is this pumping system for fill (IE getting a specific water temperature) or is it circulation for heat-transfer?
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Old 07-07-2019, 03:05 PM   #13
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Quote:
Originally Posted by tates1882 View Post
No room in the enclosure on this one for more relays. I bet the numbers are all jacked up, I made the drawing on my phone via remote connection to my desktop. The drawing program isn't very touch pad/screen friendly.
So what are you going to use for the diodes? I have some linked in this thread

https://www.electriciantalk.com/f28/...-diode-271096/

There were DIN rail sized that take up as much space as relays. I found one that's marketed for use with solar products that looks like a fuseholder, but it was limited to a pretty small load.
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Old 07-07-2019, 09:37 PM   #14
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Quote:
Originally Posted by frenchelectrican View Post
Tates,

Just couple quick simple question .,,

what size control transformer you did see it there?
I haven't been there yet to see
second thing if you set up this in DC I dont see much issue with it as long you using the interpole relay that I do know it work for a fraction of the cost beside the set of other relay .
Correct the "Switch legs will all close a relay to start the VFD
is this pump set up is for large building ? I am try to get the picture of your layout cuz I have pretty simuair set up I have see at one of my larger local motel have that. ( not super common item in this island )
Chemical applications on a conveyor
I know you mention VSD there is the pump running in low speed mode when all the valves are closed ?
Off after Valve 7 footage has been reached.

Quote:
Originally Posted by sparkiez View Post
Here are a few things I want to touch on. First:

Is it possible to just modify the program to perform this task? Ultimately, this would be the absolute BEST way to handle this scenario.
WOuld love to but I only have operator access and the program was written by a large company that won't modify it. Also I don't write in C or C+.

Second, I realize they don't want to add anything, but those relays controlled by the PC could easily toggle an interposing relay as mentioned before. I see this as the second-best solution. You can parallel all of the relays to give a run-enable to the VFD.
Each PC relay can only be active once per cycle, without either a 2p relay or diode, the valves back feed each other via the VFD relay. make sense

Is this pumping system for fill (IE getting a specific water temperature) or is it circulation for heat-transfer?
Chemical injection distribution boards, one cold at around 50f and one hot at 150f
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So what are you going to use for the diodes? I have some linked in this thread
https://www.automationdirect.com/adc...dn-q12-1-2dr-a
These are what a stumbled across that sorta triggered the idea

https://www.electriciantalk.com/f28/...-diode-271096/

There were DIN rail sized that take up as much space as relays. I found one that's marketed for use with solar products that looks like a fuseholder, but it was limited to a pretty small load.

Last edited by tates1882; 07-07-2019 at 11:08 PM.
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Old 07-08-2019, 06:15 AM   #15
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Quote:
Originally Posted by tates1882 View Post
These are what a stumbled across that sorta triggered the idea
https://www.electriciantalk.com/f28/...-diode-271096/
At first I thought I really overpaid, the automation direct page says they are rated for 20A, but I looked at the spec sheet and the diode is only rated for 1A

https://cdn.automationdirect.com/sta...wlessdin12.pdf

I found similar DIN rail terminal block style diodes with similar limited ampacity, but at $23 for a 10-pack, these are the best deal. But I needed something heavier.
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