Why are my LEDs burning out?

[Avo Mk8]

Do you think that there is any chance that the existing bulbs might still be functional and that they would light up again if I fixed some other problem (e.g. replace the Dynaohm or power supply with something different)?

If not, I will try to redesign as you suggest with two strings of six, each with it's own dynaohm (do you think 20maA is the correct size for those?)

Given your bad luck with this, and the work you've put in, I feel it would be worth getting a cheap multimeter (if you don't already have one), get familiar with it, and every time you connect things up, put the meter in circuit on a suitable milliamp range to check the current is what it should be.
Also you would be able to check the resistance values of the lamps you have, to establish if they still might work before you connect them to power.

My concern is that once things have started to go wrong, you can never be sure what might have been damaged. Are the power supply and dynaohm doing what they should? And if a bulb is out, is it because the wires are shorted together, or the bulb is faulty etc. etc.

Your lamps have an absolute max forward current of 30mA, so I would be inclined to run them at 20mA, unless you need the extra brightness. And if you do, I suspect they won't last as long!

If you can get at the wiring to each lamp, you could check each in turn using a working Dynaohm and supply. Be aware that putting the power on the wrong way round, or supplying excessive current because the Dynaohm is faulty, will instantly destroy the lamp (you won't be able to tell by looking at it).

Your power supplies have protection devices in them, but activated at much higher current/ voltage than your lamps will survive. A safer way of proceeding would be to find a constant current 20mA supply that could give up to 48V, and connect all your lamps in series to that. But I confess I haven't found one yet!

I hope the above makes sense. I would be cautious connecting things up now, as I don't really understand why so many bulbs have failed unless your Dynaohm has too, or the power supply is doing something strange.

Regards.

 

[DPG]

I would definitely read Avo's post above. And I agree a multimeter would be very useful for you.

 

[Avo Mk8]

Hi Brouhaha

One thing occurred to me - have you connected the Dynaohm the right way round? There's a little "+" on the positive end, and, as supplied, the leads each end are different lengths to also indicate the polarity (don't remember which way round - sorry)

People call it a resistor, but it is a semiconductor device, and only does its job when wired the right way round.
Putting it the wrong way round could destroy the lamps.

And as far as testing/re-using lamps - is the wiring you've done marked with the polarity of the lamps? ie red and black wires, or a tracer mark on one wire, so within the sculpture you know which is anode and which cathode for each lamp?

 

[Brouhaha]

Hi Brouhaha

One thing occurred to me - have you connected the Dynaohm the right way round? There's a little "+" on the positive end, and, as supplied, the leads each end are different lengths to also indicate the polarity (don't remember which way round - sorry)

People call it a resistor, but it is a semiconductor device, and only does its job when wired the right way round.
Putting it the wrong way round could destroy the lamps.

And as far as testing/re-using lamps - is the wiring you've done marked with the polarity of the lamps? ie red and black wires, or a tracer mark on one wire, so within the sculpture you know which is anode and which cathode for each lamp?

Hi Avo, I have the positive wire coming off of my power supply going to the negative terminal of the Dynaohm--is that correct?

I did color code the wires to the bulbs.

I do have a cheap, old analog multimeter, but I've wondered about it's reliability, so maybe I should get a new one...

 

[DPG]

Hi Avo, I have the positive wire coming off of my power supply going to the negative terminal of the Dynaohm--is that correct?

I did color code the wires to the bulbs.

I do have a cheap, old analog multimeter, but I've wondered about it's reliability, so maybe I should get a new one...

I think this is incorrect. The Dynaohm positive should got to battery positive according to the data sheet.

 

[Brouhaha]

I think this is incorrect. The Dynaohm positive should got to battery positive according to the data sheet.

OH!! That would explain a lot! I am confused however, because I have similarly been wiring the positive power wire to the negative terminal of my LEDs and they do light up when I connect them that way (and not the opposite way). So is there a different convention regarding how the terminals on a resistor are labeled versus those on a bulb?

 

[Avo Mk8]

Hi Avo, I have the positive wire coming off of my power supply going to the negative terminal of the Dynaohm--is that correct?

As DPG replied earlier, no I'm afraid not!

I did color code the wires to the bulbs.

Brilliant - that means you can check (with multimeter) if any are at least still diodes, rather than open or short circuit!

I do have a cheap, old analog multimeter, but I've wondered about it's reliability, so maybe I should get a new one...

nothing wrong with old analogue multimeters. mine's 50+ years old and still good enough to use. If yours does resistance measurements, great! (Might need a new battery?)

 

[Avo Mk8]

I have similarly been wiring the positive power wire to the negative terminal of my LEDs and they do light up when I connect them that way (and not the opposite way).

You are connecting these the correct way.

So is there a different convention regarding how the terminals on a resistor are labeled versus those on a bulb?

The Dynaohm is NOT A RESISTOR . Sorry, not your fault, it's theirs for marketing it like they do, and everyone calling it a resistor! With an ordinary resistor it doesn't matter which way round it's connected, it does the same thing either way.
Whereas the Dynaohm must have some semiconductor devices in it, to alter the voltage across it so that the current through it stays the same.

We should assume the Dynaohm could be damaged, though I think it does have some overload features - I don't know if they save it from reverse connection. If not too costly I would suggest getting another one or two, and putting yours aside for the moment. UPDATE: just looked at the data sheet which says maximum reverse voltage 1V so I suspect it's broke!

 

[DPG]

I'd take Avo's advice. At the minute you have a Dynaohm of unknown condition, and LEDs which may have been damaged. Get a new Dynaohm, and some known good LEDs. Connect them up correctly, maybe in a string of 4, and test them.

Use your multimeter to measure LED current if it will do DC amps. Monitor it at switch on and be ready to switch off if the current is too high.

 

[Brouhaha]

Thank you Avo and DPG for your very helpful replies! It will probably be a few weeks before I can get the replacement Dynaohm and have an opportunity to try testing/rebuilding, but I will come back here either with a success story--or more questions! Thanks so much!

 

[Avo Mk8]

Thank you Avo and DPG for your very helpful replies! It will probably be a few weeks before I can get the replacement Dynaohm and have an opportunity to try testing/rebuilding, but I will come back here either with a success story--or more questions! Thanks so much!

DPG gives good suggestions in his last post.

Just to reiterate, don't wire it up as your original drawing back in post #1. You need 20mA through each string of lamps, so however many you end up with in series, four or six, have a Dynaohm for each string. Perhaps they'll give you a loyalty discount

Best wishes for getting it all working!

 

[Brouhaha]

DPG gives good suggestions in his last post.

Just to reiterate, don't wire it up as your original drawing back in post #1. You need 20mA through each string of lamps, so however many you end up with in series, four or six, have a Dynaohm for each string. Perhaps they'll give you a loyalty discount

Best wishes for getting it all working!

ok, I got new 20mA dynaohms, new LEDs and started over; I made three parallel strings of 4 LEDs and tested each string using a couple of 9v batteries (and a Dynaohm, although it's possible that I might have left out the Dynaohm at some point while testing...) maybe that caused my subsequent problem?). I then wired everything up and tried powering it with my Meanwell power source and found that one of the bulbs in one of the strings is not lighting up--but the other three bulbs in that string are lighting up. I don't even understand how that is possible, I thought if one bulb was bad the whole string would go dark. Any idea how that could happen? And any ideas why the strings were working before I wired up to power source but not afterward?

 

[Avo Mk8]

ok, I got new 20mA dynaohms, new LEDs and started over; I made three parallel strings of 4 LEDs and tested each string using a couple of 9v batteries (and a Dynaohm, although it's possible that I might have left out the Dynaohm at some point while testing...) maybe that caused my subsequent problem?). I then wired everything up and tried powering it with my Meanwell power source and found that one of the bulbs in one of the strings is not lighting up--but the other three bulbs in that string are lighting up. I don't even understand how that is possible, I thought if one bulb was bad the whole string would go dark. Any idea how that could happen? And any ideas why the strings were working before I wired up to power source but not afterward?

Sorry you still have problems.
regarding the LED not lighting up, if a diode fails 'short circuit', the others will carry on working, and the Dynaohm will adjust the current to still be correct for the others.
It could be the diode legs, or the wires to that diode, are shorted together.
It could be that you've inadvertently wired it the wrong way round, and as a result its gone short circuit (but in that case it would never have lit up when you first tried it).
It could be that the diode has just failed short circuit.

Suspect you need to replace that one diode unfortunately, if that is practicable.

 

[Brouhaha]

Sorry you still have problems.
regarding the LED not lighting up, if a diode fails 'short circuit', the others will carry on working, and the Dynaohm will adjust the current to still be correct for the others.
It could be the diode legs, or the wires to that diode, are shorted together.
It could be that you've inadvertently wired it the wrong way round, and as a result its gone short circuit (but in that case it would never have lit up when you first tried it).
It could be that the diode has just failed short circuit.

Suspect you need to replace that one diode unfortunately, if that is practicable.

ah--I hadn't realized that current could still pass through a dead bulb. I will replace that one (again!) and hopefully eventually get back here to report success!

 

[Lucien Nunes]

Yes unlike a traditional filament lamp which fails open-circuit like a fuse, an LED typically fails short-circuit especially if due to overcurrent, as the diode semiconducting junction breaks down and becomes fully conductive. Unless it has been blasted with such a high current that the bond wires have ruptured.