Tri-P4 - Series or Parallel?

[lexina]

I have a bored 1.5D that can take 3 X 17670s.

I am planning to build a direct drive tri-Seoul P4 but wondering which would be the better build:-

1) use 3 X 17670 in a parallel holder and wire the leds in parallel; or
2) use 3 X 17670 in series and wire the leds in series.

I did some calculations and it seems that for either case, the resistor would consume about 2W.

Any thoughts on the pros and cons?

Thanks.

 

[Long John]

Hello lexina🙂

Due to the dropping vf and increasing current over time, I would choose the series connections.
This way, each ermitter will see exact the same current and the risk of a burn out is less.
Also the brightness of each ermitter is the same over the time.
With 3xLiIon I would use a resistor like you mentioned.

Best regards

____
Tom

 

[Long John]

I forgot to mention, don't take the SSC H-bins in view of the vf. Take the I-bins for your setup.

Best regards

____
Tom

 

[kenster]

Well, as long as you are at it, 😗 for a couple more bucks and a little more work you can have a lot more versatile 1.5D Tri-P4. Mod the switch to momantary and add a D2Dim. It will still be direct drive so you will need to add the appropriate resistor for your LED`s total vf but you will have PWM dimming control. A very nice feature to have IMHO. :rock: You can get a lot more run time from your batteries if a lower light level is all that is needed for the task at hand. Also, three P4`s can be blinding bright from reflections if the light is used to illuminate something up close. Just an option.

Here is a link to the D2Dim driver:

http://www.taskled.com/d2dim.html

Hope your Tri-P4 modded light turns out FANTASTIC! 🙂

Ken

 

[PhotonAddict]

Is goldserve's tri-flupic still available? If you want to go with batteries in parallel that might be another alternative - batteries in parallel and each led wired to the tri-flupic. Cmacclel has built a few cut-down tri-maglites like this. Multiple light levels and options as well but a very different user interface to the D2Dim. It has an LDO so no resistor but I believe the input voltage is restricted to a max. of 5V

 

[kenster]

Is goldserve's tri-flupic still available? If you want to go with batteries in parallel that might be another alternative - batteries in parallel and each led wired to the tri-flupic. Cmacclel has built a few cut-down tri-maglites like this. Multiple light levels and options as well but a very different user interface to the D2Dim. It has an LDO so no resistor but I believe the input voltage is restricted to a max. of 5V

Yes, that is another option that makes for a very nice Tri-P4 light that I happen to have as well. I recently recieved two more 3x FluPics from Goldserve. With the 3x FluPic it is even nicer cut down to a 1D size with tail switch for an even shorter little bright light around six inches. :rock:

Ken

 

[modamag]

For a quick and simple solution yeah you can go with 3x17670 (series) and a 3x SSC P4.
Series is because typically if it fails only one LED is dead. There are rare case where all go dead in series, but it's rare.

And definitely go with Long John recommendation, get a high Vf to minimize reliance on resistor.

 

[lexina]

Thanks for all the great suggestions!

Long John, good point about the changing vf.

Kenster and Photon Addict, thanks for the suggestions on the drivers. They look interesting. However, I will prob aim to keep it simple since I don't think I know how to wire a driver or keep it in place. I may add a driver later on when my knowledge improves.

Modamag and Long John - yup, I will be using the I-bins.

I might stick to parallel for the following reasons -

1. for leds in series, if 1 led blows, the light will not work. For parallel connection, the remaining 2 leds should still light up. I am not sure, under such conditions, whether there is a risk of the current to the remaining leds shooting up and overdriving them. To guard against this, I guess it would be better to use a resistor to allow some headway i.e. maybe drive at 800mA instead of 1A.

2. more importantly for me, if I wire in parallel, it would give me more powering options and flexibility. For eg, I could move the light engine to a Mag1C and use a single LiIon (for a shorter run-time) or to a Mag3C/3D and use 3 X NiMh.


If my reasoning above is wrong or if there are other considerations, I would appreciate your comments.

Thanks,
Alex

 

[PeterScowcroft]

Your above reasoning seems to be a bit flawed, but not off by much (then again it's 4:30 in the morning here and I am flued to the roof so i could be wrong to).

If an LED fails it does not necersarily break the circuit as with an incandescent bulb, it is more likely to shortcircuit (well mine do).

a short circuit in series isn't much of a prob, in paralel the other LEDs will go out an unless you turn off the torch pretty quick you will have a race between your batteries and resistor to which burns first.

Drivers are much easier to use than you think. If you goto taskled.com they have some great drivers, the owner of the site is really helpfull too.

When i miss-soldered my first board and broke it, i got sent a new board with wires pre soldered and a few weeks later they sent my old board back repaired and soldered.

you can't beat service like that!

also with Li-ion you want a way of detecting if the voltage is dropping to low or you can activate the kill switch on your pack.

you would want some dimming on tha torch too.
I have just finished a 4 x p4 torch at 500mA. a reflection off a wall 5m away is painful. 100mA would make the torch good for close up (and still brighter than most on the market).

gl with the project.

 

[PeterScowcroft]

Thought I should add. When your cells are fully charged they will run with a much higher voltage, resistors cannot correct for this, drivers can.
It may seem expensive but so far by using resistors I have killed £35 worth of cells and 3 led's!

One other point that I didn't realise till today (which probably is the reason for fatality on a few leds) wire the positive of the battery to the positive of the LED. It seems logical when you think about what a diode does, but if they could warn you on the packet that would be nice. If you wire it up as logic dictates you will just kill your LED.

ok birds are singing outside, back to bed for me

 

[Nocturnicus]

a short circuit in series isn't much of a prob, in paralel the other LEDs will go out an unless you turn off the torch pretty quick you will have a race between your batteries and resistor to which burns first.

If your series connected LED's aren't being driven too near their maximum, having one of them go shorted will simply make the others get suddenly brighter. But watch out if you're driving them them to the max. If you've got three LED's in series across a supply delivering 10.5 volts, there's 3.5 volts across each LED. Now, if one goes shorted, that same 10.5 volts now appears across the remaining two LED's, resulting in 5.25 volts across each; guaranteed to hose them instantly. Since a larger number of series elements results in a smaller percentage of the total voltage being dropped across each, there's some safety in numbers, though. But, a driver with built-in current limiting will insure that the surviving LED's will stay that way.

 

[lexina]

If your series connected LED's aren't being driven too near their maximum, having one of them go shorted will simply make the others get suddenly brighter. But watch out if you're driving them them to the max. If you've got three LED's in series across a supply delivering 10.5 volts, there's 3.5 volts across each LED. Now, if one goes shorted, that same 10.5 volts now appears across the remaining two LED's, resulting in 5.25 volts across each; guaranteed to hose them instantly.

What if the 3 leds are connected in parallel and one of them blows? Will the current to the remaining 2 leds increase as well, putting them at risk?

 

[lexina]

If an LED fails it does not necersarily break the circuit as with an incandescent bulb, it is more likely to shortcircuit (well mine do).

Oh, I didn't know that - thought it would shut down the circuit. Thanks.

 

[modamag]

That's why most of us run them in series. Another reason is the current will be balanced (equal) regardless of the Vf. With parallel, you have to really carefully sort your Vf.

 

[PeterScowcroft]

Another side point of the driver is that if in series and a LED blows the voltage will compensate and protect the two other LEDs.

I should point out that if you have set up the circuit properly it is VERY VERY unlikely that an LED will blow.

It is normal to think that LEDs being new technology will be unreliable. They are much more reliable than incandescent and probably won't ever fail.

If you jump to the thread in this forum titled "finally completed my project" you will see the amount of abuse my torch has taken.

try swinging an incandescant bulb based torch from its cable against a brick wall.

or filling it with water for that matter.

I should add the water wasn't intentional but in the prototype stage I thought I would test the brightness of the torch before watersealing it. I was informed a particular cave was dry and went for it.

Half way climbing up a waterfall my equipment jams and I swing into the main force (dry cave my arse). While doing my best not to drown my torch suddenly jumps from lvl 5 to lvl 2. one self rescue later i look into the head unit and it is half under water.

The water had generated a short circuit. the driver compensated by pumping more juice, it couldn't maintain lvl 5 so dropped to lvl 2.

I dread to think how I would have self rescued with no light as I laybacked up a crack to the side of the fall until I could jam a leg then fixed my gear.

erm getting off track here (still full of flu too)

 

[VidPro]

it is interesting to note, on this same subject, that:
when an led fails slowly, and was only being run out of spec, it fails as a closed curcuit.
When an led fails because you TRIED to get it to fail by nuking it with voltage or current, or it gets severe damage ,it can fail as an open curcuit.

so when a person (like me) tests, they would think that a string of leds would fail as a string, wheras in reality, a string of Leds , one goes out, the rest keep going. then depending on the curcuit, the others start overdriving, or it is current controlled.

 

[PeterScowcroft]

I should also add as you are new to this the 'max' varies greatly on heatsinking.
just beacuse a chip says it can be run upto 1A means nothing.
Depending on the sinking the max can be upto a few amps, but in one of my torches I have restricted it to 500mA.

The hotter it runs the dimmer the torch gets so in some cases just a small jump in current can have a massive hit in efficiency, but in turn if it is sinked well you can have a whole lot of light with less bulbs

 

[Nocturnicus]

What if the 3 leds are connected in parallel and one of them blows? Will the current to the remaining 2 leds increase as well, putting them at risk?

In a direct-drive circuit, the battery voltage would probably increase a bit with the decrease in load; just how much would depend on the internal resistance of the batteries - less for Nimh and Nicad; more for alkalines. But unless your LED's are being driven so hard that they're close to self destruction already, the small increase in voltage shouldn't be a problem. An individual low value resistor in series with each LED would help to keep things stable. If the circuit is regulated, the remaining LED's should see no change at all. PeterScowcroft makes an excellent word-to-the-wise point: good heat sinking is essential! Incan bulbs can get very hot, but they won't destroy themselves with their own heat (although they may destroy their sockets, mounting hardware, or reflectors in a badly designed light), but LED's absolutely must be relieved of their heat, or they die, and any change in voltage or current is massively more dangerous if you let them run hot.

 

[PeterScowcroft]

Made me blush!

 

[lexina]

Well, I just completed my first Mag tri-Seoul - thanks for all the feedback and advice! Had to wire in parallel in the end because I wanted to keep it simple on direct drive and I could only drive it on 1 C-LiIon in a Mag1C (still waiting on the D tri-sink). Wiring in parallel is a pain - there's twice as many connections compared to wiring in series and it's difficult not to cross the wires.

The light is bright..but I think it can be even brighter. Using the resistor calculator and setting the desired current at 1A (for each led), I used a 0.22ohm, 2W resistor as suggested. Instead of getting 3A at the tail-cap, I only measured 1.84A (i.e. average of 613mA to each led). Working backwards, I think my set-up has a built-in resistance of 0.14ohm. Next thing to do would be to change the resistor to a 0.11ohm, 1W. This is fun! 🙂