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!
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
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
RE: LED indicator on Solenoid
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RE: LED indicator on Solenoid
RE: LED indicator on Solenoid
Mike Halloran
Pembroke Pines, FL, USA
RE: LED indicator on Solenoid
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
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If we learn from our mistakes I'm getting a great education!
RE: LED indicator on Solenoid
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
RE: LED indicator on Solenoid
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
RE: LED indicator on Solenoid
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
Dan - Owner

http://www.Hi-TecDesigns.com
RE: LED indicator on Solenoid
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
RE: LED indicator on Solenoid
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RE: LED indicator on Solenoid
thanx VE1BLL. have it correct in the circuit, but not the diagram! until now.
RE: LED indicator on Solenoid
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RE: LED indicator on Solenoid
Should the -24vdc just be labeled as ground?
It's only a 24 vdc power supply.
RE: LED indicator on Solenoid
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
From your reaction, this is not typically even without some form of solenoid driver in place??
RE: LED indicator on Solenoid
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
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
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RE: LED indicator on Solenoid
It'd be interesting to see what that driver will do for you.
RE: LED indicator on Solenoid
Here's a little vid demonstration:
http://www.youtube.com/watch?v=XF-xmFFJ6vg
RE: LED indicator on Solenoid
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
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
RE: LED indicator on Solenoid
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
Double check your "1/2 watt". Maybe remove the fraction bar.
RE: LED indicator on Solenoid
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
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
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
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'.