Please help me with converters...

[MatajumotorS]

1. question - how are converters controlled? is there a special switch, or cotrolling is made by switching the woltage to converter board?

2. theere is GD500 Buck/Boost Converter and Wizard2 520mA + Add a resistor **Lower Price** do they will work at 1000mA ? and what is the diference between them, and what size are they?

And what about BB Nexgen Blank ?

I am going to use converter for driving one led at 1000mA from 18650.

Please give me a light.

 

[Reima]

1. There is no special switch, the converters are controlled by the flashlight switch.

2. Both the GD500 and the Wizard2 are Buck/Boost converters. The diameter is 0.55 inch. The GD500 is sandwich compatible, the Wizard2 is not.
The GD500 puts out 500 mA. When you add the resistor to the Wisard2 you can get up to 937 mA output.

BB Nexgen Blank is a boost converter, you select the desired output by adding the resistors. Not a good choice to use with an 18650 cell if you are powering a Lux I, Lux III, Seoul P4 or a Cree. A Downboy 1000 mA would be a better choice.

I hope this helps you.
RC

 

[Nake]

When you add the resistor to the Wisard2 you can get up to 937 mA output.

More confusion for a newbie. I thought resistors cut power, not increased it.

 

[MatajumotorS]

1. There is no special switch, the converters are controlled by the flashlight switch.

2. Both the GD500 and the Wizard2 are Buck/Boost converters. The diameter is 0.55 inch. The GD500 is sandwich compatible, the Wizard2 is not.
The GD500 puts out 500 mA. When you add the resistor to the Wisard2 you can get up to 937 mA output.

BB Nexgen Blank is a boost converter, you select the desired output by adding the resistors. Not a good choice to use with an 18650 cell if you are powering a Lux I, Lux III, Seoul P4 or a Cree. A Downboy 1000 mA would be a better choice.

I hope this helps you.
RC

Thanks

 

[Reima]

More confusion for a newbie. I thought resistors cut power, not increased it.

These are sense resistors, they are used for adjusting the ouput of the converter.
RC

 

[Nake]

Got it. :thumbsup: Thanks.

 

[Nereus]

More confusion for a newbie. I thought resistors cut power, not increased it.

Constant current converter is basically a constant voltage converter that has a sense resistor in series with the load. The converter wants to maintain constant voltage drop across the sense resistor: if the voltage drop across sense resistor decreases the converter increases current in order to maintain constant voltage drop. And since the sense resistor is in series with the load, the load gets exactly the same current that goes through the sense resistor (according to Kirchoffs law).

Let's take BB nexgen as an example. The converter wants to see 0,05 volt drop across its sense resistor. Now let's assume that there is 0,1 ohm sense resistor. Using Ohm's law (voltage=current*resistance) you can calculate that 0,05 voltage drop across 0,1 ohm resistor takes place when the current is 0,5 amps.

What happens if we change the sense resistor to 0,05 ohms? Again the converter wants to see 0,05 volt voltage drop across it. This time 1 amp current is needed to get that voltage drop. Like this you can get ANY (within practical limits of course) current out of the converter. The higher the sense resistor resistance, the lower the current and vice versa.

To answer your question, there is no confusion here. You have correct idea what resistor does. Indeed, even in constant current converter application they "cut power" in the sense (pun not intended) that some power is wasted in the sense resistor. If you take 1 amp BB nexgen as an example, 50 mW is wasted in its sense resistor (power=voltage*current). Actually that is the reason why you want the constant voltage drop across the sense resistor to be as small as possible, in case of BB nexgen 0,05 volts.

You have it correct, resistors do not increase power. I guess that is just the _role_ of the sense resistor that is new to you.

Hope this helps.

-N

 

[Nake]

Thanks, yes that helps me to understand better.
I have a question. Why do Europeons use a comma for a decimal point instead of a period?

 

[Nereus]

Thanks, yes that helps me to understand better.
I have a question. Why do Europeons use a comma for a decimal point instead of a period?

I do not know... but it would be great to know that! In Finland we call it "decimal comma" (very rude and direct translation from finnish) instead of "decimal point". Should we open a thread about this in cafe forum?

-N

 

[Nereus]

More confusion for a newbie. I thought resistors cut power, not increased it.

Given your question, I have even more confusing example. Lets's take BB nexgen 0,5 amp version as an example. It has 0,1 ohm sense resistor, see my post above.

What happens if you add another 0,1 ohm sense resistor there, in parallel with the original one? This time the two 0,1 ohm resistor act as if they were one 0,05 ohm resistor (to calculte this, you need to combine Kirchoff's and Ohm's law) so you have created BB nexgen 1 amp version.

The end result: you have *added* a resistor to the circuit board and *increased* power that it dumps to the load. But again there is no confusion here, it is just the role of sense resistor that makes this happen. Actually adding second resistor increases losses, since both resistors waste 25 mW of power.

What I described above is a useful trick to adjust the output power of a constant current converter. Just use a switch to add more resistors in parallel with the original one. I have used this technique several times with good success.

Wizard, Downboy, BB NG and GD have the same current determining formula so you can use my examples above to your help with any of those. Shark is a bit different story. There is a max current limiting sense resistor there and the converter wants to see max 0,1 volts voltage drop across it. Standard solution is 0,1 ohm sense resistor which means 1 amp max current. By changing that to e.g. 0,05 ohm you can increase the upper limit to 2 amps.

-N

 

[yellow]

GD-board

I am doing the same mod as You.

BB nexgens have died on me 2 times, dunno why (resistor set to very low output, board drawing 1-2 amps for 1/2 a sec --> dead)
normal BBs work "fine" in the way they dont die, but show some kind of "direct drive"-output.

example: board resistor is 0.21 Ohms.
current (1st: from batt / 2nd: to led) is:
initially 0.56 / 0.54 A
30 mins: 0.51 / 0.5
1 h: 0.43 / 0.42
2 h: 0.36 / 0.35
3 h: 0.33 / 0.30
(with the other 18650 slightly other values)

Have just ordered a GD board as it should be buck/boost for an Li-Ion and holding the current, set by resistor, steady.

Nereus' example is perfect for explaining how to get multiple outputs.
Solder the "largest" resistor onto the board, then add 2 wires at the other resistor's position and feature one (or several) other switches with "smaller" resistors somewhere in the light to change the levels. Thus, when one of these switches is activated, the light gets brighter.

 

[macforsale]

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[kenster]

I do not know... but it would be great to know that! In Finland we call it "decimal comma" (very rude and direct translation from finnish) instead of "decimal point". Should we open a thread about this in cafe forum?

-N

I see why I was confused.:huh2: I thought it was called a comma point??? :laughing:


Seriously, great info here guys!:thumbsup: I didn`t understand how the sense resistors worked at all. Thank you!
And for a guy like me to make sense of this with the high resistance of my brain well... You guys worked a MIRACLE!:twothumbs

Ken

 

[yellow]

just wanna say, I did and still do my mods this way, usually switching output by turning the head (which means small switches in case of the 2AA lights, or the modded SF 6P or 8X. More space within the headlamps).
Lead length cant be very long inside a light. If this really has some effect? Arent those boards current regulated, not pwm?

(testing is done with circuit and led outside, connected to a board where all of Wayne's resistors are soldered on + the larger ones for low output, and the measure instruments and batteries. Working good so far)

 

[macforsale]

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[Nereus]

Short leads and wire gage and switch to handle the drive current in that leg of the circuit are not a problem as you are finding. Just a caution because it is part of the feedback circuit and small changes in the signal from addition to the circuit not taken into account by the original design can have the driver doing things outside of specifications. The sense resistor is only a fraction of an ohm and the voltage seen is directly proportional so the gain in the electronics will be high to effectively process the feedback signal.

My experience with current regulation and PWM is in other areas of power control and as it applies to LEDs I am somewhat in the dark. :candle:

Principles will be the same details may vary greatly. Sometimes theory keeps you from doing something that in practice is OK.

Macforsale definitely has a point here: If you read any popular converter datasheet you can see that there are many pages of guidance how to design a good circuit board. Taking such an essential component as sense resistor even few cm away from the circuit board is "bad design" according to datasheets. To minimise problems I have followed these principles:
- Use short and straight wires to switch, no twisting or loops
- Use adequately thick wire
- Use high quality low resistance switch
- Make good hot solder joints
- Do not make wires go through inductor flux
That is how I have got greatly working variable output current converters - to quote Macforsale, maybe theoretically less than perfect but practically very functional designs.

Yellow, your bb nexgen seem to have gone to direct drive because rechargeable li-ion has greater voltage (up to 4,2v) than led forward voltage (typically 3,5v). GD converter suits much better your needs.

One more comment: these converters produce DC with ripple - it is not completely smooth "battery-like" DC. There are very small (approx 0,1 v) and very fast (some 0,2-1 Mhz) changes (pulses) in DC voltage, so it is fast changing, say, between 3,4-3,6 volts, averaging at the led forward voltage 3,5v. These are far from exact figures, but you get the idea. These 0,1 v changes are the AC component around 3,5v DC component. And this high frequency AC is nasty suff running in wires, it wants to react with other wires inductively. That is why it is "bad design" to take sense resistor away from the circuit board.

Finally guys, great to hear that I could help you! I wish you all the best with your mods! :thumbsup:

-N

 

[Nereus]

Here is the datasheet of LM2621 step-up dc/dc converter that I am familiar with: http://www.national.com/ds/LM/LM2621.pdf . Have a look on page 8, "pc board layout". Those principles listed there apply generally to many switching converters, not only lm2621.

Now you see yourself the design "rules" we are violating when taking sense resistors away from the circuit board... I hope that Wayne is not reading this because he would cry if he knew how we ruin his great circuit board design and abuse his converters

-N

 

[macforsale]

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[Nereus]

Guys, have a look on this excellent thread by Newbie: http://www.candlepowerforums.com/vb/showthread.php?t=152964 You get an idea what does the output of a constant current converter look like (wiz2 as an example in this case). Newbie measures light output in his test, but the results apply directly to electrical output too.

-N

 

[DocPeter]

You seem to know a lot about the GD step up converter. What happens, if there is no sense resistor? What about the current from a battery still connected to the GD board? Could that be used as an on/off switch (i.e.connecting/disconnecting the resistor to the board)?