Adding 2nd R2 drop-in?

I currently have a DIY head light with a single R2 drop in running from a 13.2V nimh battery.

a. Can I add a second drop in by running + & - wires from one to the other?

b. Will this drop the wattage running to a single one to half and therefore reduce heat build-up but keep the brightness and runtime?

I have the <18v R2 at the moment.

Thanks in advance.

You mean like my Double barrel CREE R2?

You will get twice the power, whether you place them 'in series' or 'in parallel' as the current through each LED is controlled by the electronics on each module and remains approximately constant over the voltage range specified by the manufacturer.

In general, buck drivers (the electronics inside the LED module) become more efficient (meaning less heat is dissipated) with the input voltage closer to the output voltage (3.7V). So there may be a little less heat generated with a ~7V4 battery. Placing the two modules in series on your 13V2 would also do that, but the voltage on each of the modules will probably not be equal, unless the input current for both modules matches exactly.

Thanks for that reply, it will be similar to that yes, but in Nightpro housings. I know that these r2's run at full power with around 6v and at the moment the remaining voltage is turned into heat.

My question is:

If I run 2 leds that take 6v of power from a 12v battery do they take 6v each and therefore reduce the heat build up and prolong the life of the led or do they both run at 12v and still get as hot?

I think that makes sense?

andyeez said:

If I run 2 leds that take 6v of power from a 12v battery do they take 6v each and therefore reduce the heat build up and prolong the life of the led or do they both run at 12v and still get as hot?

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Normally, the driver does not dissipate all 'excess voltage', unless you have a direct drive LED.

The current source in a modern LED module acts more like a switching power supply like installed in your PC. It is more efficient than the old linear power supplies (that did turn all excess voltage into heat).

The problem with placing two modules in series, is that the voltage probably won't divide equally between the two modules. But that may not be a major problem - have never tried it myself. The two modules in my light are placed in parallel on a 2 cell LiIon battery.

For some more information on LED drivers, have a look at the description of the LT3474/LT3474-1 Step-Down 1A LED driver at linear Technologys'

Again, thanks for the response. Nice set of lights you have made there. Have you created a heatsink between the bulb and the outer casing?

Bit of a numpty question but would it make any difference wiring parallel or series and if so which is which. My current idea is to wire pos to pos and neg to neg.

andyeez said:

...Nice set of lights you have made there...

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:)

andyeez said:

Have you created a heatsink between the bulb and the outer casing?

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The outer casing is a tight fit around the module. I Did need to add some aluminium tape around the smallest brass part of the module to make it as thick as the reflector.

andyeez said:

...would it make any difference wiring parallel or series and if so which is which. My current idea is to wire pos to pos and neg to neg.

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Pos to pos and neg to neg equals wiring in parallel. Both lights will get the full 13V2 voltage from the battery.

Wiring in series would supply approximately half of the 13V3 to each light, possibly leading to less heat dissipated by the drivers, but both lights would be equally bright as in the first scenario.

Ok, makes sense so far, Series sounds like what i am after. What do I connect to where to wire in series?

As you may have realised I am no electronics engineer :o

I did guess ;-)

Connect one of the positive leads to the negative lead of the other light. The two wires that are now free one positive, one negative) can be connected to the battery.

Beware; the two lights now both have a different potential on the housing. You cannot connect the electrically to the same heatsink - you will short out one light if you do that :laughing:

Ok, still not clear, sorry!

At the moment I have two leads from the switch. Pos to pos on the bulb and neg to neg on the bulb to create a light that works. I am going to add a second in a separate housing on the same mount. Is there an easy way to connect to it without breaking my current circuit?

I know, you are probably thinking "should this guy be messing with wires"!!! Once I get my head around it I will be ok it just takes a bit of explaining. :ohgeez:

Andyeez
You've done great so far. Please stop and read up some more. (edit - ...)
Sorry for the brief PM, I wanted to catch you while you were online.

Cheers Linger but all that is a little over my head.

What i have is very similar to pe2er's setup but I have used nightpro housings rather than pipe. The only drivers etc. are in the drop in r2 which is rated at input upto 18v. The single one works fine, all I want to do is add another in series.

You bought an R2 drop-in which includes reflector, emitter, driver, etc. The drop-in is rated up to 18v. Excellent plan, I amplify my earlier comment, you've done well.
pics when you're done will be great.

:welcome:

We've joined about the same time. I read the forums for months.

There's a critique/review of this 5v? -18 volt DX driver in these modules in one of the CPF forums. Use Google. It might have been in the Keenan? (right name?) discussion, I'm not sure. :thinking:

Anyway, IF (big if) I remember correctly, this driver is a bit odd in that it apparently is neither completely linear nor completely a sampling driver. It is linear for higher voltages of 8.4?-18 (I think that is the range) and sampling below that. Bummed me out some. This means it is functions like a passive resistor until it drops the Vin closer to the Vf of the LED and dissipates a lot of the excess energy as heat. This affects battery run time (somewhat critical to me) and lumens per watt, but not light output. Someone reportedly fried one at around 17 Vin, so heat management is an issue at higher voltages. Maybe it was a bad driver because someone else used three of these with an 18V three head utility light in parrallel (DeWalt, If I remember right) and the heat output was impressive. :devil:

Soon after? (I think) the DX R2 module came out there was a thread discussing it and someone wondered if they could be cascaded in series in a double barrled bike light like Pe2er's (I agree, nice, BTW) to reduce the voltage across each of a pair or more of them, but I saw no follow-up report (it may have been a review on the DX page). The reason I remember it, is I had a 12 volt battery and the optimal voltage (highest efficiency) for the modules is around 6 Vin, so two in series looked like a viable option to me.

I know from these forums that you can use buckpucks to make a half and full power mode light if you use one buck puck for low and switch in another parrallel to double the current. BUT they need to be wired in a particular way or :poof:

I am no electronics expert. If they were simple resistors, then connecting them in series is just fine, BUT they are active circuits adjusting the current and voltage even it they act like resistors above 8.4 volts. So the thought occurred to me that each module is trying to independently maintain the currrent output to the LED it controls, and the resistance through each driver will vary. If two are in series they are affecting each other's Vin. I can envision that this could dampen out or cause a feedback. I suspect, that if I understood the circuit, I would know which to expect . (I should live so long.) My only option was to try and see. So I was hoping someone had tried it and reported if it worked or failed because I didn't want to spend $20, wait 3-6 weeks for free delivery, wire them up in a test run, and: :poof: I suppose I could have bought a couple of drivers in the same order, to allow for Murphy's Law, but as someone of Scottish ancestry , what was I going to do with the extra drivers if the scheme worked? :broke: :)

I am going a different route now, but I am still curious. Will these drivers play nice and act mostly like resistors when run in series with a battery of 12-14 volts for a pair, 18-20 for three, 24-28 for four? I suspect there will be a similar XP-G module using this driver one of these days, that might be a nice backup light.
Sometimes, I think this is my sign: :stupid: . So if you know :help: Andyeez and me.

BrianMc said:

There's a critique/review of this 5v? -18 volt DX driver in these modules in one of the CPF forums. Use Google. It might have been in the Keenan? (right name?) discussion, I'm not sure.

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I Think you mean http://www.candlepowerforums.com/vb/showthread.php?t=236337]this thread[/url]: http://www.candlepowerforums.com/vb/showthread.php?t=236337
It is interesting; I had not read it before. Thanks :)

BrianMc said:

…like Pe2er's (I agree, nice, BTW)

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:)

BrianMc said:

I am no electronics expert. If they were simple resistors, then connecting them in series is just fine, BUT they are active circuits adjusting the current and voltage even it they act like resistors above 8.4 volts. So the thought occurred to me that each module is trying to independently maintain the current output to the LED it controls, and the resistance through each driver will vary. If two are in series they are affecting each other's Vin. I can envision that this could dampen out or cause a feedback. I suspect, that if I understood the circuit, I would know which to expect. (I should live so long.) My only option was to try and see. So I was hoping someone had tried it and reported if it worked or failed because I didn't want to spend $20, wait 3-6 weeks for free delivery, wire them up in a test run, and: :poof:

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Worst case could be that they start to flicker or don’t light up at all, so I would not be afraid to try. Series connection would look like this:

As you can see, I drew two extra components: C1 and C2. These are optional and are meant to dampen the current drawn by each of the modules in case you experience flickering or other unwanted behaviour. The values are a best guess (if I would do a test, I would start out with these values). Each capacitor should be able to handle full battery voltage – just in case.

But something similar must have been done before. You just need to find it in the vast space of this Furum :D

BrianMc said:

:welcome:

We've joined about the same time. I read the forums for months.

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:oops:Just noticed that I have turned "Flashaholic". That is not a good sign I suppose :devil:

After reading the thread you referred to, I became curious about the efficiency of my own light. Power consumption of my 'Double Barrel' is 1.6Amps @ 7.4Volt if I remember correctly. That amounts to almost 12 Watt power consumed, for probably 2x3W power to the LEDs. That is 50% efficient (and a lot lower than I was hoping for :( )

Looking at one of the graphs in this thread:

It seems to me, that placing 2 drop-ins in series will make things WORSE in your case – assuming that you use the exact same SKU 11836 drop-in that I do. So don’t do it. Place the second module in parallel, as discussed earlier :)

The green line is where you are right now. Power input to the drop-in is a bit over 5 Watt.

The red line is where I am with my Double Barrel CREE R2. Power input to each one of the drop-in is a bit over 8 Watt (I measured 6 Watt). So my drop-ins need to dissipate 3 Watts more than yours. Obviously, I am in shock right now ;)

Note that you can get funny* things happening when you put drivers in series because they don't have a constant load, rather its pulsed.

* Funny as is bad, not haha.

pe2er said:

After reading the thread you referred to, I became curious about the efficiency of my own light. Power consumption of my 'Double Barrel' is 1.6Amps @ 7.4Volt if I remember correctly. That amounts to almost 12 Watt power consumed, for probably 2x3W power to the LEDs. That is 50% efficient (and a lot lower than I was hoping for :( )

Looking at one of the graphs in this thread:

It seems to me, that placing 2 drop-ins in series will make things WORSE in your case – assuming that you use the exact same SKU 11836 drop-in that I do. So don’t do it. Place the second module in parallel, as discussed earlier :)

Click to expand...

Thanks. I obviously read that when I was still early in the learning curve and did not understand the implications. Shows the value of revisiting the treasure trove in this forum. :ohgeez:

znomit said:

Note that you can get funny* things happening when you put drivers in series because they don't have a constant load, rather its pulsed.

* Funny as is bad, not haha.

Click to expand...

Yeah, suspected as much when they couldn't be wired as if they were simple circuit elements, AND that's if you don't do funny* things with your soldering! :poof: :o

This is the Power/ Voltage curve of my Double barrel.

Looks like I can increase runtime by increasing the battery voltage to a value above 9 Volt.

More on my own thread on the Double barrel CREE R2.