LED indicator on Solenoid

[vinic]

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!

 

[LionelHutz]

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.

 

[VEBill]

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

 

[IRstuff]

Your "schematic" is under-detailed, since I can't tell why you've apparently changed connections to your solenoid, nor can I tell what's actually what.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[VEBill]

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.

 

[MikeHalloran]

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

 

[vinic]

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.

 

[ScottyUK]

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!

 

[vinic]

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.

 

[BrianE22]

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?

 

[VEBill]

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.

 

[LionelHutz]

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.

 

[vinic]

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.

 

[MacGyverS2000]

"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

 

[vinic]

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

 

[VEBill]

The 2 LEDs are backwards.

 

[IRstuff]

That seems to be an insane amount of power to be running through a relay (125W). Are you sure this is a 48V relay?

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[vinic]

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.

 

[IRstuff]

If it's a 24V relay, then why are you running 48V into it?

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[vinic]

Perhaps there is more wrong with my diagram!?

Should the -24vdc just be labeled as ground?

It's only a 24 vdc power supply.