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2 Rkcstr drivers in Parallel Huge 445nm Build + Blackjack?

Mrcrouse

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Incase anyone wanted to make a build that used more than one battery in series, but didn't have a driver that would put out enough current, multiple Rkcstr drivers in parallel will do the trick! In this one I have 1 driver at 430ma and the other at 370ma,with a total of 800ma.

This monster runs off of 2 18650 batteries and has a massive 2" diameter heatsink. The focus knob was actually made accidentally, because I accidentally slipped on the lathe and made it a bit too small to make a second heatsink, so it turned into a focus knob. I figured with this kind of power, you don't want your fingers in front of the beam. I also put 2 Rkcstr drivers in parallel to achieve 800ma output with a 2 hour runtime!





Will have a beam shot up soon!
 
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lasersbee

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Re: 2 Rkcstr drivers in series Huge 445nm Build + Blackjack?

Incase anyone wanted to make a build that used more than one battery in series, but didn't have a driver that would put out enough current, multiple Rkcstr drivers in parallel will do the trick! In this one I have 1 driver at 430ma and the other at 370ma,with a total of 800ma.

This monster runs off of 2 18650 batteries and has a massive 2" diameter heatsink. The focus knob was actually made accidentally, because I accidentally slipped on the lathe and made it a bit too small to make a second heatsink, so it turned into a focus knob. I figured with this kind of power, you don't want your fingers in front of the beam. I also put 2 Rkcstr drivers in parallel to achieve 800ma output with a 3 hour runtime!





Will have a beam shot up soon!
Now I'm confused...
In your Title you say 2 Rkcstr Drivers in Series
and in your 1st Post you say 2 Rkcstr Drivers in Parallel

So.... which is it that you did...:thinking:

Jerry
 

Gryphon

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Re: 2 Rkcstr drivers in series Huge 445nm Build + Blackjack?

I pretty sure they would have to be in parallel, otherwise the voltage would be doubled and kill the diode.
 

Mrcrouse

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Re: 2 Rkcstr drivers in series Huge 445nm Build + Blackjack?

Now I'm confused...
In your Title you say 2 Rkcstr Drivers in Series
and in your 1st Post you say 2 Rkcstr Drivers in Parallel

So.... which is it that you did...:thinking:

Jerry
Oops ya, thanks for catching that! They are in parallel.

I pretty sure they would have to be in parallel, otherwise the voltage would be doubled and kill the diode.
I don't think the voltage would be able to be double, if anything the voltage would be less than what the diode would draw wouldn't it? The rkcstr need the diode voltage + 2.25v, so would it be losing 4.5v then? Since its not boost it can't go beyond the 7.4v of the batteries.

I might be wrong with that, but I think that is how it would work?
 

Gryphon

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^ good point, then i don't know what would happen
 

Pontiacg5

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Two in series would probably split the diode foward voltage between the two of them but still limit the output current to 500mA. 2 in parallel is definatly the way to go.

What kind of current draw are you getting off of the batteries?
 

Mrcrouse

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I'm reading about 860ma, but the Laser isn't lasing when I am taking my reading. Is that normal? It works fine when I put the tailcap back on.
 

Xplorer877

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Hmmm well I suppose since it works.... If it's not broken don't fix it.

However, Linear divers adjust the voltage supplied to the load. So if you set the two drivers to supply different currents the by Ohms Law they must be supplying different voltages. Normally it's not a good idea to put two different voltage sources in parallel.

You wouldn't put a 3v battery in parallel with a 9v battery. But I suppose since the voltages are very similar it wont be an issue. But why not set them both to 400mA to begin with? That way they'd be sharing the load and be dissipating the same wattage.

-Tony
 

Pontiacg5

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If the two drivers are on different batteries you need to change that, Xplorer has a good point.

However I think you have them in parallel on one battery which should be fine. If they were on separate batteries though one would drain before the other and the "fuller" battery would try to charge the other one which usually is not very good.
 

chipdouglas

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yes it is normal for the laser to stop lasing when you read the current.

michael
 

Mrcrouse

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No, they are on the same batteries, and I don't think they would be supplying different voltages in the diode. Because of ohms law, they are supplying the same voltage, but different current and there is different resistance in the driver itself.
 

Xplorer877

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It's not the resistance of the driver it's the resistance of the load (the diode) that mtters. The driver doesn't have a constant resistance. It's will draw differing amounts of current from the battery depending on how what current it's set to.

If the same load is being supplied different currents they the voltages must be different as well. The diode has the same voltage drop for both drivers so if the drivers are set to deliver different currents it can only mean that they are supplying different voltages to the diode.

But like I said, it's probably not a problem, but in the future any parallel linear drivers should always provide the same voltage so they share the load evenly. If the difference was significant one driver might push current back into the other (lower voltage) driver. Current always flows from higher voltages to lower voltages.

-Tony
 

charliebruce

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But like I said, it's probably not a problem, but in the future any parallel linear drivers should always provide the same voltage so they share the load evenly. If the difference was significant one driver might push current back into the other (lower voltage) driver. Current always flows from higher voltages to lower voltages.

-Tony
That's not quite how it works - because it's actually a current source. The only "active" part of the circuit is simply putting a constant voltage across a reference resistor (to the greatest extent it can with the input voltage - since the input is the same, not much happens), and that cannot be affected by another current source, because the diode is by far the path of least resistance. I don't think that much would happen, even if you were to disconnect the diode (but in that situation I'm not sure, the regulator might work like a blocking diode, or it might just have a small reverse current. If anyone has a couple of spare LM317s I'd be interested to know what happens ;) ). I certainly wouldn't try this with a boost converter though!

One will waste more energy than the other, but there is practically no risk of damaging either driver or the diode, as long as the input is the same and the output stays connected.
 

Flaminpyro

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Very nice build, I did the same type of double 18650 build about a year ago with a LPC-815 but just took that diode out and replaced it with a 445 diiode.
I only have a single DDL style PYRO driver in my "club Laser" and it seems to be doing just fine, it can go to 1500ma as the regulator is mounted on the back of the masive heatsink so it can handel it's full rated load :) heres a picture.
do it like this and you won't need two drivers ;)

and heres the club :)
 

LarryDFW

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Mrcrouse;

Very nice work on the large heatsink.

The drivers must dissipate ~3.2 watts of heat with a drive voltage of ~8 volts.

The diode also has about 3 watts to dissipate.

I have also done a build with a similar host, using 3 BR diodes for a continuous-duty UV light.



LarryDFW
 




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