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LED indicator on Solenoid

LED indicator on Solenoid

LED indicator on Solenoid

(OP)
I'd like to wire LED indicators to a series of solenoids.  They are on a 24vdc circuit.  The attached schematic shows what the original layout was on the left, and what I've tried already, on the right.

Before I fry another power supply, I thought I'd ask some folks that may actually know how to do this.  Any help would be greatly appreciated!

RE: LED indicator on Solenoid

Your schematics appear to be incomplete nonsense. In general, use about 2.4kohms in series with the LED and connect it across the solenoid coil. The LED lead beside the flat spot on the case (or the shorter LED lead) goes to the negative.

Honestly, if you can't figure this out then you to learn how to use Google and read the 100's of pages on how to connect a LED until you get it. If you can never get it then you need real hands-on help because a little text here won't do a better job than all the existing diagrams and info already available on this subject.

 

RE: LED indicator on Solenoid

You added the resistors (R1 and R2) and the two LEDs? What value (ohms and watts) resistors did you use?

 

RE: LED indicator on Solenoid

It's more of a connection diagram than a schematic. I interpreted it as showing that the series resistors+LEDs were connected from the relay terminals at the top to the 24-volt return line.
 

RE: LED indicator on Solenoid

In the USA, the 24V return should probably be connected to the brown wire, not the green one.  But that may be a separate issue.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: LED indicator on Solenoid

(OP)
I actually have the LEDs working fine on their own circuit on a breadboard.  It's when  a solenoid is wired in parallel that the trouble occurs.

I'm sure my diagram is not kosher, but was hoping it to be at least legible. Apparently I failed there too.

 The blue and green icons with polarity are leds. R1 and R2 are are 1.5Kohm 1/2 watt.

"NO C  NC" are relay terminals for "Normally Open", "Common" and "Normally Closed".

The solenoid leads should be pretty straight forward.

Again, I can wire the solenoid directly and it works fine.  I can wire the two LEDs directly and they work fine.  But if I put the solenoid in parallel to the "On" LED, a resistor on the Power Supply blows smoke.

 

RE: LED indicator on Solenoid

Does the solenoid have an internal diode to limit the inductive EMF at switch-off? That would make the solenoid polarity-sensitive.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: LED indicator on Solenoid

(OP)
Scotty, and Mike:  These came to me second hand, already wired to a different controller ( left side of my incomplete nonsense diagram).  I believe that diagram would be complete if the leads from the two green connections actually touched.  That doesn't mean that they had them wired properly originally, but they did work wired in that manner.  

And for the record, the solenoids do work if wired in reverse (24+ to the green and the 24- to the yellow). with or without connecting the brown to ground.  I assume the ground if for safety.

 

RE: LED indicator on Solenoid

The 1.5k ohm resistors mean you're drawing over 30 mA for the LEDs.  Does your power supply have enough capacity to drive both both the solenoid and the LED?  What do you have for back EMF protection when the relay contacts open?

RE: LED indicator on Solenoid

Even if the LEDs were 'fried' by the back-EMF from the solenoids, the current should still be limited by the resistors. So it's not immediately obvious why the PS would fail.

Often, the actual cause in cases like this is something that we can't see over the Internet. Something like a miswire that causes a dead short circuit.
 

RE: LED indicator on Solenoid

What's the current rating of the power supply? It sounds like you are overloading the power supply. If the LED's work alone and the solenoid works alone then there is no reason that they can't be paralleled and work together. Otherwise, you're likely making a connection error.

RE: LED indicator on Solenoid

(OP)
Lionel, that's basically what I was hoping to hear.  

The power supply came with the setup, which is large enough to run at least a 5 solenoid system.  I only yesterday noticed the ps nameplate (removed the unit from the enclosure, and see that it's a 7.2 amp supply.  

I'm using no emf on the setup.  One of the reasons I included the left side of my crude drawing was in wonder if there is something inside the original controls that might limit the amperage that goes thru the solenoids!?  

My time for working with this is limited today, and probably can't get back on the project until Friday.  But next thing I will try is to wire this setup through one of the original controls to see if I get a different amp reading.

And VE1Bill, I very much understand how difficult it can be to diagnose something like this from a distance. This is only setup on a breadboard right now to test, so it's pretty easy to see, but also pretty easy to plug a wire into the wrong hole!  Wouldn't a dead short tend to fry it a lot quicker??  This took several seconds, and several 'tries' to smoke the resistor.

Thanx to everyone who has replied... so far.

RE: LED indicator on Solenoid

"Multiple tries" leads me to believe it's back EMF beating the snot out of it... lots of damage with each cycle, but small enough to get you through a few of them.

Dan - Owner
http://www.Hi-TecDesigns.com

RE: LED indicator on Solenoid

(OP)
A small update on my progress.  Attached is a new diagram with the following details:

R1, R2 = 1.5k ohm
LEDs are 3.6 V
Flywheel Diode = 1N4004
Relay coil has a resistance of 18.4 Ohms, so a calculated current of 1.3 amps.

Power supply likes this and seems to be holding up fine after repairing the fried resistor.  

But now the solenoid relay is getting too hot for my comfort.  

Looking into the previous controls, it appears that they made their own solenoid driver based on an LS812CV.

I'd like to play around with the same idea, keeping it as simple as possible, just to match my skill level and budget.

With a little research, it looks like a  DRV102T-ND from TI would do the trick with just an extra diode and resistor added into the circuit.

Does this sound like a viable solution??  Any suggestions, cautions, or other words of wisdom?

Thanx for all help, both former and future,

-Clyde

RE: LED indicator on Solenoid

The 2 LEDs are backwards.
 

RE: LED indicator on Solenoid

(OP)
IRstuff, I'm quite certain that they are 24V relays.  They are quite hefty but I'm really not that versed with this kind of equipment.  They are closing 1" hydraulic (water) valves.

thanx VE1BLL.  have it correct in the circuit, but not the diagram! until now.

 

RE: LED indicator on Solenoid

I was just about to suggest double-checking that the "-24" is actually just the return for the +24 (that's been my assumption).

It's very unlikely to be 48 volts, but if the solenoids are burning hot then make sure that the voltage is actually 24 volts across the coil.

 

RE: LED indicator on Solenoid

(OP)
I'm only reading 24 volts across the coil.  It does not get hot right away, it's been on for few minutes now and is just now getting fairly warm.  Can hold my hand to it for 30 seconds before it gets uncomfortable.  My guess is that it would continue to build heat??  but have not gone there.  Not really into burning up components, regardless at how it may seem!

From your reaction, this is not typically even without some form of solenoid driver in place??

 

RE: LED indicator on Solenoid

24 volts and 1.3 amps is about 30 watts. So it should be getting hot exactly as this amount of power indicates. Which sounds like what you're describing.

More advanced driver circuits can apply full power to snap the solenoid, and then reduce the current to a much lower holding current. It all depends on the application.

RE: LED indicator on Solenoid

(OP)
Out of curiosity I hooked up the old system to this relay coil, and it acts the same way; gets hot after being energized for a minute or so.  I suppose this is the way it's always been and I just did not notice it.  Most of these valves are located in an area where I don't get near them very often.

I'd still like to try to build a driver for this so just now ordered a handful of DRV102 units to test.  The flag feature might come in handy; the word I get from some others using the same setup is that there's a high chance of failure.

thanx again for your feedback... it's been very helpful.  

RE: LED indicator on Solenoid

Being able to hold your hand to a coil for 30 seconds before having to remove your hand isn't hot by any means.

It'd be interesting to see what that driver will do for you.

 

RE: LED indicator on Solenoid

(OP)
Using a solenoid driver on this seems to do the trick.  Have been able to drop the current from 1.145 amps down to 218 mAmps and still keep the solenoid engaged.  The relay coil maintains it's original temp after quite an extended hold time.

Here's a little vid demonstration:

http://www.youtube.com/watch?v=XF-xmFFJ6vg


 

RE: LED indicator on Solenoid

Just because you can doesn't mean you should.  I wouldn't operate it less than 400ma for reliable operation.  I have designed solenoid drivers and mechanical devices have their good and bad days.

For those who want to go cheap, A resistor of equal resistance to the solenoid can be placed in series with the power.  A very large value cap of 4700uf or more is ten placed across the resistor, positive to the supply positive.  The capacitor supplies the initial high closing current.  As the capacitor charges the current drops to half.  Off periods must be long enough for the capacitor to fully discharge.

RE: LED indicator on Solenoid

(OP)
Thanx for the 400ma tip, OperaHouse.  My intent was to find a happy medium with this, and not take it to and keep it on the edge.  Having a figure in mind helps a lot.

I like the idea of just a cap and resistor.  So the current ends up cut in half with your setup?  I don't think  down time is an issue with my system.  It typically takes 10 to 15 minutes at minimum to change the temperature of a tank (volumes are 500 gallon minimum). I assume that's plenty of time to discharge the cap?

Question:  what type of capacitor would you recommend?? I found a 25V Radial Electrolytic Capacitor for $0.90 in small quantities.

RE: LED indicator on Solenoid

At that price, I would use two.  Lot cheaper than a controller.  That was only a guess at a capacitance to start at. I should warn you not to put the capacitor near the resistor because of heating.  Elevated temperatures of a valve that may be on most of the time could cause the capacitor to fail in just a couple of years.

RE: LED indicator on Solenoid

(OP)
Positioning the cap away from the resistor is duly noted. It looks to me like the easiest way to mount them (for my setup) would be on the opposite side of the pcb.

Would you mind looking over the diagram attached to see if I have the arrangement of these components correct?

The main question is the placement of the cap and R3 in relation to the flywheel diode.

The relay coil is showing 18 ohms, so that's the rating of R3 (1/2 watt).  Cap is the 4700 microF.

Unless I hear differently, I'm about to pull the trigger on this order and throw an entire 15 bucks at it!

RE: LED indicator on Solenoid

Capacitor isn't in the right place. If I understand the suggestion of Mr. House, it was intended to be in parallel with the resistor (to provide an initial "short circuit" around the resistor at start up).

Double check your "1/2 watt". Maybe remove the fraction bar.
 

RE: LED indicator on Solenoid

(OP)
That configuration makes sense to me now.  (see attached update)

Not sure how I came up with 1/2 watt, other than two too many decibels.  Power actually calculates out to 32 watts (strange how it's the same as the relay coil ;).  Does the resistor need to be rated that high?  That'll kill my $15 budget.  Eight of these in the control box will build a bit of heat, though it would be rare, if ever, that they'd all be on at the same time.

RE: LED indicator on Solenoid

"32 watts"

Double check your power calculation.

Hints: 18 ohms in series with 18 ohms is 36 ohms. Steady state current is not as high as your latest calculation. Also, if the initial pulse is very short and not endlessly repeated, then the additional power of the initial pulse can typically be ignored.

PS: The capacitor trick is clever, but an active solution might be cleverer.
 

RE: LED indicator on Solenoid

(OP)
Yep.  Feeling pretty dumb about now.  Your help and patience is greatly appreciated!  So your saying the steady state power for the resistor would only be about 12 watts?

By "active solution" are you referring to a device like the DVR102, because I do like the way that works. It's fairly pricey, but if I can feel comfortable that it would be reliable and long lasting, then it's well worth the $100 (total) investment.

I do have yet another question on the DRV102 setup:

They recommend a Schottky diode for D1, but I'm lost as to how to select the properly rated diode for this. Here is the description from TI:

"A flyback diode is (D1) needed with inductive loads to conduct the load current during the off cycle. The external diode should be selected for low forward voltage. The internal clamp diode provides protection but should not be used to conduct load currents. An additional diode (D2), located in series with Out pin, is required for inductive loads."

Is 'low forward voltage' simply the 24vdc?  Is the RMS voltage of any concern here?


Another thing that is not clear to me, and may or may not be important, is the Input pin (1).  Here is their description:

 "The input is compatible with standard TTL levels. The device output becomes enabled when the input voltage is driven above the typical switching threshold, 1.7V. Below this level, the output is disabled. With no connection to the pin, the input level rises to 3.4V. Input current is 20µA when driven high and 80µA with the input low. The input may be driven to the power supply (VS)
without damage."



The first time I read this, I thought I'd need to apply a voltage greater than 1.7 to this pin for there to be any output.  Simple enough as I had a pack of voltage regulators sitting around from a previous project.  It worked to have that connected, but it also worked with no voltage applied.  Not sure how, or what this pin is used for now!? Again, it's  not terribly important, other than I'm just trying to learn as much about this as I can.  Simply switching the 24vdc on and off seems to be a viable, if not easiest solution for my app.

Thanx again for the assistance ( and education!)
 

RE: LED indicator on Solenoid

"...you're saying ...about 12 watts?"

About 8 watts. So reach for a 10 or 15 watt resistor. I mentioned '12' mostly because it was funny (?) about the fraction bar removal from '1/2'.

 

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