Unknown LEDS

[Hero999]

Uncle Hero: I'd like to ask since this joule looters caught my undivided attention now rather than the LEDs, can we actually connect several joule thieves together to get a larger output current/voltage to feed hungrier devices?

I'm sure it's possible to use a couple of AA batteries in series to power more LEDs wired in series but you might need a larger core.

 

[Tipsy]

I ran the six LED's off the PP3 last night for two hours without noticeable dimming but I realise that's not a good enough test so I pondered on the issue and wondered if I could switch out one or two LED's when the power is too low for all six? Just a thought.

 

[Hero999]

I ran the six LED's off the PP3 last night for two hours without noticeable dimming but I realise that's not a good enough test so I pondered on the issue and wondered if I could switch out one or two LED's when the power is too low for all six? Just a thought.

If you're happy with that then I don't see any need to change.

The number of LEDs wasn't my concern, it was the lack of series resistor that was. The LEDs have a similar voltage to that of the power supply which probably has quite a high internal resistance so it obviously wasn't a problem,.

A better way is to connect the LEDs in three strings of two in series. Each pair of LEDs will need its own resistor, assuming a forward voltage of 3V (for both LEDs) and a current of 17mA, you'll need a 180R series resistor. It's pretty straightforward, I'll post a schematic if you're not sure.

 

[Tipsy]

No, I can't say I would be happy if the battery expires after just a few hours so I'll put my circuit into use as intended and see what the results actually are before deciding.

Out of interest, do resistors "waste" energy by function?

 

[Hero999]

Yes, resistors waste energy but with three LEDs in series they will get really dim when the battery voltage goes below 9V, with two in series and a suitable series resistor the LEDs will stay lit until the battery voltage drops to 6V so more energy will be extracted from the battery.

 

[audioguru]

I think if you use a brand new name-brand 9V alkaline battery then the LEDs in your test that do not have a current-limiting resistor will probably quickly burn out.

 

[kinarfi]

What package size are the?

If they're 5mm and white they'll have a typical forward voltage of 3.5V and a maximum operating current of between 20mA and 30mA.

I'd recommend a Joule thief, which can be made using a single transistor and a transformer or an inductor plus a couple of transistors.
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Made a joule thief and lit up a super bright with .505 from my power supply, neat. Is there a write up on what happening available anywhere.
Thanks

 

[Vizier87]

is the second circuit equivalent to the joule thief?

 

[Hero999]

Yes, the second circuit does the same thing as the top circuit although it has components, it has the advantage of being able to use an off the shelf inductor so if you're getting 1000s cheaply made in China, it's the best solution.

The first circuit requires you to wind a transformer which is more labour intensive so is not an option unless you're either only making a few or are making millions so it's worth getting a machine to do it. You might be able to use a small ready made common mode choke but inductors are probably cheaper.

Made a joule thief and lit up a super bright with .505 from my power supply, neat. Is there a write up on what happening available anywhere.
Thanks

There's lots of information, on the Internet, check Google, YouTube, Wikipedia etc.

 

[acmefixer]

I'm sure it's possible to use a couple of AA batteries in series to power more LEDs wired in series but you might need a larger core.

JT builders can get a lot more power out of a JT by changing the transistor to one that's designed for this purpose. The 2N3904 and BC547 are both poor choices because they're not able to handle currents much over a hundred mA. Change it to a 2N4401 or better a BC337 and you will get more than 50 percent more light.

But you need even more current for a high power LED such as the 1W Luxeon Star or Cree, etc. So use a high current, low Vce(sat) transistor such as the one from the flash unit from a disposable camera. Or buy some 2SD965, KSD5041 from Fairchild, or NTE11, which is ten times more expensive but available from some electronics stores. These transistors will give you enough current to light up 3,4 or 6 LEDs but the drain on the AA cell will be as much as a half amp and it won't last very long.

The nice thing about a JT is you can put a variable resistor or an extra resistor and switch in series with the 1k resistor to reduce the light output and save battery current..

Try this. Put a second transistor in parallel with the original. Connect the emitters and collectors together. Add a second resistor to the base and connect it to the coil, or if the resistor is at the top of the coil, then reduce it to half its value. You should get an improvement in light output. Have fun experimenting..

 

[Tipsy]

Is ENERGIZER a brand-name? I think I've got one unused PP3 left.

Regarding resistors. Is 6V an optimum value to wire for or can I take it even lower - say 3V - and get even more use out of the battery? Would a pot be more useful instead of a fixed resistance?

 

[audioguru]

Energizer is an American/Canadian Battery manufacturer. Them and Duracell used to be owned by competing razor blade companies (remember battery-powered shavers?).
They make alkaline cells in the USA. Their Ni-MH cells are made for them in Japan maybe by Sanyo. Their 9V Ni-MH batteries are made for them in Germany.

The Dollar Store sells old-fashioned cheap Chinese carbon-zinc cells and 9V batteries (called Super Heavy-Duty). Most are dead and are leaking in their packages on the shelf. They also have some cheap Chinese Lithium coin cells that might not have any Lithium inside.

 

[kinarfi]

Originally Posted by kinarfi View Post
Made a joule thief and lit up a super bright with .505 from my power supply, neat. Is there a write up on what happening available anywhere.
Thanks

There's lots of information, on the Internet, check Google, YouTube, Wikipedia etc.

I looked and one nice article got the to the technical part and had " Technical Data Deleted" or similar. So, I'll keep looking, thanks

 

[acmefixer]

Add a Feedback Winding

Yes, the second circuit does the same thing as the top circuit although it has components, it has the advantage of being able to use an off the shelf inductor so if you're getting 1000s cheaply made in China, it's the best solution.

The first circuit requires you to wind a transformer which is more labour intensive so is not an option unless you're either only making a few or are making millions so it's worth getting a machine to do it. You might be able to use a small ready made common mode choke but inductors are probably cheaper.


There's lots of information, on the Internet, check Google, YouTube, Wikipedia etc.

I used an "off the shelf" inductor for the first (conventional) JT circuit. For the feedback winding (B1 - B2) I wound a few feet of 32 AWG wire over the original coil, taped the wire in place, and gave it a coat of liquid tape. I let it dry and connected it into the circuit and powered it up, but no light. So I swapped the feedback winding leads, and bingo, nice bright light.

 

[Hero999]

I used an "off the shelf" inductor for the first (conventional) JT circuit. For the feedback winding (B1 - B2) I wound a few feet of 32 AWG wire over the original coil, taped the wire in place, and gave it a coat of liquid tape. I let it dry and connected it into the circuit and powered it up, but no light. So I swapped the feedback winding leads, and bingo, nice bright light.

Sorry but that's no longer and off the shelf component because you've modified it.

It's still a good method for making a few though.