Electrical Question - LEDs and Line Voltages

[MrH]

Ok, I'm just about done with my new CP and I realized I just exhausted my electronics knowledge. Sorry for the length here but I have to 'splain before I can ask a question.

For a couple of reasons, my CP is fed from two separate circuits: A 30A 240V circuit for my HLT element, and a 20A 120V circuit for my RIMS element and all the other electronics. Both circuits are GFCI protected and are completely isolated in the CP. Each element is cycled by a PID controlled SSR, but I also have a switch for each that energizes a contactor which supplies power to the SSR. The SSR is always switched by the PID, but unless the switch is turned on for that element, the element gets no power.

I also have separate indicators (LED) that I want to turn on when the element is actually heating, which means they are connected to the output of the SSR along with the element. That way, I can tell by a glance if the element is on. Ok, so here's the question: For the 120V element, it's a straightforward connection. I'm using 120V LED indicators from AutomationDirect. What I haven't been able to figure out yet is how to get the indicator to work with the 240V element. If I was feeding 4-wire 50A to the panel I could just use the neutral, but in this case the circuits are separate and I'm concerned that the 5mA that the LED draws will be enough to trip one or both of the GFCI's if I "borrowed" the neutral from the 120V feed just for the LED, not to mention the fact that I want to do it the right way and not cut any corners. I'd rather not have to use a stepdown transformer just to power a stupid indicator. I'd be game to use a CR circuit to reduce the voltage, but while I know what a CR stepdown does, it's been way too many years since my basic electronics classes to remember how to calculate one.

Any electronics geeks out there who can help?

Thanks!
MrH

 

[ndsgr]

I haven't worked with the components you describe and don't know what most of them are, so please excuse the response if it's off base.

2- 25k ohm resistors in series and connect the LED in between? That would give you 120V in between and about 4.8mA of current available. Not sure what the minimum for the LED is. Add some shrink tubing and solder and it would probably cost about a dollar.

 

[CodeRage]

there probably is a resistor built into the panel meter already. Using a multi meter measure the resistance across the led. It's a diode so it will appear open if you measure it backwards, so just swap the leads. Post back the resistance value.

 

[paledragon]

on the 240V side, split the output of the SSR. one will go to the heater and ultimately meet up with the other hot leg. the other will go to the LED then the neutral line on the 240V inlet, effectively giving you 120V power for the LED. this won't trip the GFCI breaker either.

p.d.

 

[MrH]

there probably is a resistor built into the panel meter already. Using a multi meter measure the resistance across the led. It's a diode so it will appear open if you measure it backwards, so just swap the leads. Post back the resistance value.

Thanks for all the replies. Code, I'm not getting a reading either way on my meter. Strange, it acts like it's open when reading both ways. I'm wondering if it's fully rectified, since it accepts AC or DC. I peeked inside the vent slots in the body and it does have two 5.6K 2W resistors in series (one on each leg). The specs say it draws 5mA @ 120V.

MrH

 

[IrregularPulse]

Doesn't PID have an "on" led already on it? What PID did you get. The one I got has an Indicator for when the output is turned on. I understand a larger lamp is easier to quickly reference but just incase you weren't aware that the PID had this.

 

[MrH]

Doesn't PID have an "on" led already on it? What PID did you get. The one I got has an Indicator for when the output is turned on. I understand a larger lamp is easier to quickly reference but just incase you weren't aware that the PID had this.

Yes, absolutely. I just like the really big yellow light, and I didn't find any external indicator output on my PID (TET612). I suppose I should post a pic of my CP. Now I just have to take one then figure out how to insert it.

 

[CodeRage]

Thanks for all the replies. Code, I'm not getting a reading either way on my meter. Strange, it acts like it's open when reading both ways. I'm wondering if it's fully rectified, since it accepts AC or DC. I peeked inside the vent slots in the body and it does have two 5.6K 2W resistors in series (one on each leg). The specs say it draws 5mA @ 120V.

MrH

You got the good ones then, some havemultiple leds in the bulb biased opposite of each other.

So there should be 6k ohms of resistance for 5ma.
I get at 120V you should have 24kohms, so four 5.6ks in series would make sense.
0.005A*R=240V | R=48k. 48k-5.6k*4=25.6kohms.
So add a 20k on one side and a 5.6k on the other and you should be good. It may be slightly dimmer because the 120 draws slightly more current.

May want to double check my math, been hittin the keezer tonight.

 

[oldschool]

on the 240V side, split the output of the SSR. one will go to the heater and ultimately meet up with the other hot leg. the other will go to the LED then the neutral line on the 240V inlet, effectively giving you 120V power for the LED. this won't trip the GFCI breaker either.

p.d.

This would work just fine and, is really simple.

 

[MrH]

You got the good ones then, some havemultiple leds in the bulb biased opposite of each other.

So there should be 6k ohms of resistance for 5ma.
I get at 120V you should have 24kohms, so four 5.6ks in series would make sense.
0.005A*R=240V | R=48k. 48k-5.6k*4=25.6kohms.
So add a 20k on one side and a 5.6k on the other and you should be good. It may be slightly dimmer because the 120 draws slightly more current.

May want to double check my math, been hittin the keezer tonight.

LOL you and me both, brother. The calcs look good to me. The only problem is that it really doesn't look like there are more than two resistors in there, so 11.2K, which adds up to only 56V. Also, after you mentioned multiple LEDs, I removed the lense and indeed, that's what I've got. I fed it some juice (120V) and it's not very bright. Maybe I'll look into replacing them with Neons or something. I mean, as IrregularPulse indirectly pointed out, it doesn't make much sense to have big yellow indicators if they're not bright enough to see easily in daylight

Thanks!
MrH

 

[MrH]

This would work just fine and, is really simple.

on the 240V side, split the output of the SSR. one will go to the heater and ultimately meet up with the other hot leg. the other will go to the LED then the neutral line on the 240V inlet, effectively giving you 120V power for the LED. this won't trip the GFCI breaker either.

p.d.

What I think you guys both missed is that there is no neutral on the 240V feed. There are two separate, isolated circuits inside the CP, and the 240V is a three wire feed. If I use the neutral on the 120V feed, there will be a 5mA variance in both the 120V and 240V GFCIs. Checking the specs for residential GFCI (which is designed for protection from electrocution and not equipment), 5mA may be enough to trip one or the other. Close enough that I don't want to take the chance. I want to build this as glitch free as possible.


MrH

BTW, if I'm wrong about this, please feel free to let me know

 

[CodeRage]

I wired mine up once and thought they looked dim as hell and was a little disappointed. Then I measured the voltage across the pins and I only had 24vac. Don't remember exactly what I did but I put 110 across it and it was happy, so was I.

You have a link where you bought them?

 

[MrH]

Here

I got the Yellow 120V ones.

 

[CodeRage]

those are the same ones. and they should be plenty bright.

Make sure you have 120V between the Line side and Neutral.

You are picking up the 120V at the SSR right?

If anything wire it to a suicide cable and plug it in. That should give you an idea if there is something wrong with it or if you have something wrong with your wiring. Goodluck.

 

[MrH]

I wired mine up once and thought they looked dim as hell and was a little disappointed. Then I measured the voltage across the pins and I only had 24vac. Don't remember exactly what I did but I put 110 across it and it was happy, so was I.

116.7V, which is about the best I can expect for our grid out here in the country. We routinely dip to 100V, which is why everything electronic we own is on a UPS.

I'm thinking these cheap indicators are just dim. It looks like their more expensive metal body indicators use a replaceable single LED bulb. Could be those are brighter and would work better. I may buy a couple to try. I'm not opposed to incandescent if they will work well and be bright, but I like the lower power and cooler operation of LEDs.

MrH

 

[MrH]

If anything wire it to a suicide cable and plug it in. That should give you an idea if there is something wrong with it or if you have something wrong with your wiring. Goodluck.

LOL, I haven't even run it from the SSR yet. I have it on a suicide cable right now. I have some old 80's era indicators on a couple of industrial fire pump controller cabinets I picked up at auction a couple years ago. Those indicators are BRIGHT, and I guess I was just expecting something similar. These aren't even close.

 

[diatonic]

I'm not an electrical guru, but it seems to me, that you should either...

1. Get an indicator that you can power with the same line that powers the SSR
2. Use a transformer to convert your 240 to 120 to power the indicator (added benefit is being able to tell if the SSR stuck on when it's not being told to be on)
3. Get a second small SSR to power the indicator from your 120 circuit

 

[MrH]

Yeah, those are all last resorts, but since I'm not happy with the brightness of these I may look at getting different ones anyway.

 

[oldschool]

I guess I don't really understand exactly what is going on and I don't understand why a GFI would trip for a 5mA increase. You said that there is only two hot legs feeding your element? You don't ground anything? A ground would work just the same.

 

[CodeRage]

MrH, are you sure the bulb is seated in there real good? there is nothing on the bayonet contacts or anything is there? That thing should look like Christmas. If anything write AD tomorrow and tell them the trouble you are having. Because if it isn't bright then there is something wrong with it.

 

[diatonic]

GFCI breakers detect if power is going to ground (which it shouldn't for a properly operating circuit) and trip the breaker.

 

[egurney]

Would this work?
http://www.factorymation.com/s.nl/it.A/id.61010/.f

 

[Sawdustguy]

You got the good ones then, some havemultiple leds in the bulb biased opposite of each other.

So there should be 6k ohms of resistance for 5ma.
I get at 120V you should have 24kohms, so four 5.6ks in series would make sense.
0.005A*R=240V | R=48k. 48k-5.6k*4=25.6kohms.
So add a 20k on one side and a 5.6k on the other and you should be good. It may be slightly dimmer because the 120 draws slightly more current.

May want to double check my math, been hittin the keezer tonight.

Doesn't it say on the data sheet that the indicator at 120 VAC needs 12 mA? If that is correct all you need is a 20K 1.5 watt resistor in series for 240 VAC.

 

[CodeRage]

Doesn't it say on the data sheet that the indicator at 120 VAC needs 12 mA? If that is correct all you need is a 20K 1.5 watt resistor in series for 240 VAC.

Good call on looking at the spec sheet. Yeah, I get 20k total resistance too. with 2 5.6ks in there already he needs to add 8.8k.

 

[oldschool]

IMO this is becoming too complicated. just do as others have suggested without the resistor or get a 120VAC lamp and be done with it. start with the stoning....

 

[Brewmoor]

Maybe I missed it in another post but, Why are you using 120v lamps? You could use an LED and power it from the voltage that leaves the PID and goes to the SSR. That is going to be a few volts DC. Then when it fires you know you are activating the SSR.

This way you are not messing around with line voltage and neutrals to power the light. It would be easier to wire because the location of the lamp will be right next to the PID.

Just a thought. Again I missed why you were using 120v lamps so disregard if I am way off base.

 

[MrH]

Doesn't it say on the data sheet that the indicator at 120 VAC needs 12 mA? If that is correct all you need is a 20K 1.5 watt resistor in series for 240 VAC.

HOLY CR@P! I have no idea how I missed that! Until I looked at it again myself I could have sworn it said 5mA (where's the damn forehead smack imoticon when you need one?)

This makes total sense now! Thanks for pointing out the obvious and reminding us all that it pays to read, read, and reread the specs (much like measure twice, cut once) before spouting off with misinformation

MrH

 

[MrH]

Would this work?
http://www.factorymation.com/s.nl/it.A/id.61010/.f

Wow! Thanks a ton for this link! Obviously my Google-Fu has been off, because I searched and searched for exactly this. I'm going to try adding the additional resistance, but if it ends up dimmer as CodeRage has suggested, I'll look at these next. Price is good, too. Looks like a great alternative to automationdirect (happy with them, but choice is always good)

MrH

 

[MrH]

MrH, are you sure the bulb is seated in there real good? there is nothing on the bayonet contacts or anything is there? That thing should look like Christmas. If anything write AD tomorrow and tell them the trouble you are having. Because if it isn't bright then there is something wrong with it.

Yeah, like I said in an earlier post, I've determined these aren't the better quality ones with a socketed bulb. The LED array is permanently soldered in and non-replaceable. I think that's why it's not as bright as with a single superbright LED. When I remove the lense and diffuser, there are three fairly weak micro LEDs in the array. I might look at replacing them all with socketed superbrights eventually. for now, they'll work.


MrH

 

[MrH]

Maybe I missed it in another post but, Why are you using 120v lamps? You could use an LED and power it from the voltage that leaves the PID and goes to the SSR. That is going to be a few volts DC. Then when it fires you know you are activating the SSR.

This way you are not messing around with line voltage and neutrals to power the light. It would be easier to wire because the location of the lamp will be right next to the PID.

Just a thought. Again I missed why you were using 120v lamps so disregard if I am way off base.

Brew, by running the indicator off the HOT side of the SSR, I'm directly reading the state of the element, not the control. That way, if the SSR fails and fuses the HOT side, I'll know it by the indicator. I'm using industrial control panel mount indicators for a polished look. I'll post pics eventually, but I've been waiting until it's finished so I can avoid the inevitable discussion about how it will never work and I'm about to die.

 

[egurney]

BTW, I wasn't suggesting that those 240 LEDs would work, I was really asking if they would work. I'm still planning my build (trying to figure out how to fund) and really didn't know!

 

[CodeRage]

Yeah, like I said in an earlier post, I've determined these aren't the better quality ones with a socketed bulb. The LED array is permanently soldered in and non-replaceable. I think that's why it's not as bright as with a single superbright LED. When I remove the lense and diffuser, there are three fairly weak micro LEDs in the array. I might look at replacing them all with socketed superbrights eventually. for now, they'll work.


MrH

Most of the panel lights are like that, have a bunch of small leds instead of one big one. I think I have a red one at the house, I'll plug it in and take a picture of the brightness. See if it is what you are experiencing. I don't think it is though.

As for just grabbing a neutral or ground from the other circuit? Come on guys, op has made it clear he wants to do it the right way and not take any shortcuts. He is well aware as to what his options are in the half-assed department.

Mr.H,
Do you have 2 of these panel indicators? and do they both behave the same way on 110?

 

[CodeRage]

Here's a pic of my panel. the indicators aren't lit but the HOA switched have the same luminosity. The flash makes them look dim but they are in fact pretty bright.

 

[Brewmoor]

Brew, by running the indicator off the HOT side of the SSR, I'm directly reading the state of the element, not the control. That way, if the SSR fails and fuses the HOT side, I'll know it by the indicator. I'm using industrial control panel mount indicators for a polished look. I'll post pics eventually, but I've been waiting until it's finished so I can avoid the inevitable discussion about how it will never work and I'm about to die.

Right on! I can see why you might want to do it that way. Can't wait to see pics. Oh by the way. It will never work

 

[lschiavo]

I just used bare leds with mounting collars. Very cheap and easy. Then just bias the led to 20mA at whatever voltage you need. Most in my panel are 24V and one at 120V...just change resistance. I mounted them in my panel and soldered on a piece of perfboard to make the final connections. Like this:

Front:

Anybody ever get parts from here? This is where I usually go for basic electronic components and where I got my led's and mounting collars. They often have great closeout prices on components.

http://www.parts-express.com/electronic-components.cfm

I don't understand the GFI issue. If you are using the 120V circuit to power your led indicator and using the neutral to return to you will not have a problem unless you are leaking current to ground.

 

[MrH]

Parts Express is da bomb. I've been using them for quite a while for speaker building components. They're good guys.

I'll post a pic of my CP in it's current state later today. It should clarify things a bit.