UV Lamp (my variant)

kaspiysk113 · Mar 31, 2020

Assembled a lamp for lighting a photoresist of 42 (6x7) UV LEDs.
The LEDs are turned on in parallel, the quenching resistor is set in series to the matrix, 10 Ohms 10 Watts.
Power supply 9V-12V.
It works perfectly, but at 12V. it is better to light for no more than 1 minute, since the resistor is heated.

picbits · Apr 1, 2020

Maybe use two or three LEDs at a time in series with a current limiting resistor per pair . Then parallel these banks together. Using LEDs in parallel is bad practice unless they are perfectly matched and generally on the same heatsink / die.

gophert · Apr 1, 2020

If you'd do it with 14 groups of 3 LEDs, with 14 resistors at 150 ohms, you'd be giving up about 1 watt of heat across the whole board (70 mW per resistor).

your way, I think it will be about 8 watts on one resistor. 9 volt drop across the 10 ohm resistor when using a 12VDC supply.

do it this way (you may want to buy new UV LEDs and start over). Also, you may notice your eyes getting sore. They are "just" LEDs but the light is still UV. Wear appropriate welding goggles (not just UV sunglasses).

kaspiysk113 · Apr 1, 2020

picbits said:
Maybe use two or three LEDs at a time in series with a current limiting resistor per pair . Then parallel these banks together. Using LEDs in parallel is bad practice unless they are perfectly matched and generally on the same heatsink / die.

thanks for the comment, but I'm aware of it
it was just interesting to assemble the matrix exactly like this, with a single resistor
of course, I understand that in the event of failures of the LEDs, the remaining ones will flow even more current, which can lead to the death of the entire matrix

kaspiysk113 · Apr 1, 2020

gophert said:
If you'd do it with 14 groups of 3 LEDs, with 14 resistors at 150 ohms, you'd be giving up about 1 watt of heat across the whole board (70 mW per resistor).

your way, I think it will be about 8 watts on one resistor. 9 volt drop across the 10 ohm resistor when using a 12VDC supply.

do it this way (you may want to buy new UV LEDs and start over). Also, you may notice your eyes getting sore. They are "just" LEDs but the light is still LED. Wear appropriate welding goggles (not just UV sunglasses).

View attachment 123973

thank you for advice

Nigel Goodwin · Apr 2, 2020

picbits said:
Using LEDs in parallel is bad practice unless they are perfectly matched and generally on the same heatsink / die.

While I would agree in general, it's not a problem with 'large' numbers of LED's in series parallel, as they average out - as long as you use the same make and type of LED's.

So basically, parallel is bad, series is good, paralleled series chains is 'ok'.

Considering the overheating resistor though, I'd certainly much prefer to use separate resistors per series chain in this case, as per post #3.

kaspiysk113 · Apr 2, 2020

Nigel Goodwin said:
While I would agree in general, it's not a problem with 'large' numbers of LED's in series parallel, as they average out - as long as you use the same make and type of LED's.

So basically, parallel is bad, series is good, paralleled series chains is 'ok'.

Considering the overheating resistor though, I'd certainly much prefer to use separate resistors per series chain in this case, as per post #3.

thank you, this is very constructive

Pommie · Apr 2, 2020

You're currently supplying ~1A at 12V which is 12W and you're wasting 10W in a resistor (which unsurprisingly, gets hot). If you connect 4 LEDs in series they will have a Vf of ~8.5V. Assuming 20mA per LED then you need a series resistor of (12-8.5)/0.02 = 175Ω - this will waste ~70mW - a 1/8th W resistor will do. Parallel up 11 of these and you have 44 LEDs without the waste (and heat) - that's 2 spare ones!!!

Mike.
P.S. maths done in head after a few wines so not guaranteed to be correct.
Edit, missed post #3 which says basically the same thing.

kaspiysk113 · Apr 2, 2020

Pommie said:
You're currently supplying ~1A at 12V which is 12W and you're wasting 10W in a resistor (which unsurprisingly, gets hot). If you connect 4 LEDs in series they will have a Vf of ~8.5V. Assuming 20mA per LED then you need a series resistor of (12-8.5)/0.02 = 175Ω - this will waste ~70mW - a 1/8th W resistor will do. Parallel up 11 of these and you have 44 LEDs without the waste (and heat) - that's 2 spare ones!!!

Mike.
P.S. maths done in head after a few wines so not guaranteed to be correct.
Edit, missed post #3 which says basically the same thing.

to be precise, it is about 8W. on the resistor, however, your calculation is generally accurate, thank you

gophert · Apr 2, 2020

kaspiysk113 said:
to be precise, it is about 8W. on the resistor, however, your calculation is generally accurate, thank you

Except UV LEDs have about 3v to 3.5Vf instead of two as pomme's math shows. So you get a max of 3 in series for a 12VDC supply with stable current control resistor.

Pommie · Apr 2, 2020

As I said, wine involved so no bets!

Mike.

kaspiysk113 · Apr 3, 2020

Time - 20 sec.

Nigel Goodwin · Apr 4, 2020

Thanks for the pictures, looking pretty good.

kaspiysk113 · Apr 7, 2020

Real exposition time 9-10 seconds.

UV Lamp (my variant)

kaspiysk113

New Member

Attachments

picbits

Well-Known Member

gophert

Well-Known Member

kaspiysk113

New Member

kaspiysk113

New Member

Nigel Goodwin

Super Moderator

kaspiysk113

New Member

Pommie

Well-Known Member

kaspiysk113

New Member

gophert

Well-Known Member

Pommie

Well-Known Member

kaspiysk113

New Member

Attachments

Nigel Goodwin

Super Moderator

kaspiysk113

New Member

Similar threads

UV Lamp (my variant)

New Member

Attachments

Well-Known Member

Well-Known Member

New Member

New Member

Super Moderator

New Member

Well-Known Member

New Member

Well-Known Member

Well-Known Member

New Member

Attachments

Super Moderator

New Member

Similar threads

Privacy & Transparency

Privacy & Transparency