SST-90 acceptable direct drive voltages?

[jamesavery22]

I have a 3D mag that I want to put a SST-90 in. Just no clue how to power it. Was going to wait for a driver but was wondering if I could just direct drive it with 3 D-cells? Primary or maybe NiMH's. Is 4.5v too much?

 

[Magic Matt]

Note - newbie here so please refer to more experienced members for a double check!

4.5V ... Alkalines? I don't think they'd be able to deliver enough current... maybe you'd just damage the cells. :thinking:

I think if you want to drive the SST-90 you need to be thinking of packing some AA's into that 3-D length, as if we were talking 3S3P NiMH AA configuration it would be more likely... perhaps with a 1ohm 15watt resister.
Here's the datasheet http://www.luminus.com/stuff/conten...3_sst_90_w_product_datasheet_illumination.pdf

 

[jamesavery22]

My initial plan was 12 AA with a driver. Just wish there was a driver already out

Would 3 x NiMH D-cell 10000mAh be able to deliver enough current?

 

[Magic Matt]

NiMH kicks butt compared to Alkaline in that area, so yes, I would expect it would. Just that getting hold of NiMH D cells that aren't AA cells in D-size cases is tricky where I am in the UK, and finding good chargers that charge at 0.5C to 1C for such a big battery is even harder... which is why I'm going to build my own battery holders for AAs.

 

[jamesavery22]

Coming to that same conclusion. Only ones I found were these http://www.zbattery.com/NiMH-D-Cell-10000mAh-1-2V-Battery.

Would 12 eneloops in a 4 parrallel of 3 in series configuration do it?
Initial 4.2v be too much fo r a SST-90?

 

[Magic Matt]

The initial 4.2V is above the 3.7V max rating, but I'm lead to believe that the voltage sag at that sort of current may well be enough to ensure that the voltage is pulled down a bit anyway. With such an expensive emitter (plus me being a bit of a coward) I'd pop a resistor in there just to be safe, but I dare say others are usnig it direct drive. I just have a touch of paranoia about expensive emitters and . I'm also of the opinion that the small drop in brightness you'd get looks far bigger on paper (comparing lumens) than it does when you actually see the beam in reality.

Edit - 4 cells in parallel will JUST fit IF you can find a very slim holder, but most NiMH cells are too fat... hence why I'm going to go for 3P on my mod, as that way I don't have to worry about batteries getting stuck.

 

[jamesavery22]

Direct drive causes some drop in brightness?

 

[Magic Matt]

The resistor would cause some small drop in posssible brightness... but would also ensure the peak voltage doesn't fry the emitter. To my mind, a sensible trade-off.

Direct Drive will drop in brightness as the cell voltages drop. Less of an issue with NiMH but a real pain with Alkaline (look at voltage discharge curves posted elsewhere on the forums and you'll see what I'm talking about). This is why I like regulated output - maintains brightness and keeps it steady until the cells can't take it. If you go regulated, you could go for all cells in series, plus have different brightness levels so you can balance the amount of light needed and battery life - keep it low and useful for long life, crank it up when you need it, that sort of thing.

There's nothing wrong with Direct Drive, it's just different, and obviously easier to build!

 

[jamesavery22]

Thanks Matt. Appreciate the replies. I'll wait till there's a driver board out.

 

[jasonck08]

Even driving an SST-50 with 3 fully charged eneloops does not give the LED enough current. I can only manage to get the LED to pull about 2.5A from 3 eneloops. If I use 4AA's then it draws about 6A which is a little too much for the LED. 4AA eneloops might work ok with an SST-90 though, battery life would be very short though.

3 Higher end D Ni-mh cells might be enough. You might want do to some resistance mods to the maglite. The switch is not going to take that kind of current for long, and also the spring has quite a bit of resistance.

A driver would be best, but if/when they come out, there not going to be cheap. $50+ is the quote i hear from people who are working on a driver for the SST-90.

 

[Magic Matt]

2.5A from 3 eneloops.... x3P... that's up to 7.5A - sounds like 3S3P is a good way to go, with a resistor in circuit. Mod it again later when there's a good driver around.

 

[Linger]

there's a ton of ssx-90 mods.
I'm waiting on 3Dnimh for mine.
Techjunkie did one up in a m@g 2D, look to last post re: 8aa's in it.
http://www.candlepowerforums.com/vb/showthread.php?t=256361
Most successes have been with D nimh, 3D's and you'll put a wack load of current through it. Some people have done 4D, anyway you're safe with 3. On the bench I abused a demo -50 quite a bit.
I've pushed 4AAnimh through a -50 while I was testing lenses. The -50 also took a reverse current of 4xnimh (I was talking on phone at the time) with no ill effects. And 2xrcr123's through the -50 (+6vDD), it was a real scorcher. That emitter is now installed and doesn't lag too far behind its top binned brothers so my feeling is that it came through alright. Electrically and thermally the phlatled seems like a very durable package (not like a xre...their bond wires fry pretty easy).
Just do up a little search and you'll find full threads with pics, DMM readings, and the like.

Best,
Linger

 

[The Dane]

NiMH kicks butt compared to Alkaline in that area, so yes, I would expect it would. Just that getting hold of NiMH D cells that aren't AA cells in D-size cases is tricky where I am in the UK, and finding good chargers that charge at 0.5C to 1C for such a big battery is even harder... which is why I'm going to build my own battery holders for AAs.

Help is here:

http://www.component-shop.co.uk/
http://store.modelpower.co.uk/single-cells-41-c.asp
http://www.maplin.co.uk/Search.aspx?menuno=77825

For charger, anything RC related will push 5A

 

[Magic Matt]

I honestly never thought to look for those in the RC section... I just assumed RC was all battery packs!

 

[monkeyboy]

2.5A from 3 eneloops.... x3P... that's up to 7.5A

It doesn't work like that.

The current going through the LED is related to the voltage under load. With 3P, Current will increase a due to lower internal resistance (roughly 1/3) and hence higher voltage under load but it's not that simple a relationship; 3p will certainly not give you 3 x current. (Unless the LED had zero resistance!)

 

[Magic Matt]

Surely if the LED had NO resistance that would be closer to 36A followed by Scottie screaming "She cannae take much more o' this cap'n" and

 

[monkeyboy]

It would be whatever the short circuit current of the battery was. My point is that the LED does have a significant resistance so the current would much less than 3x.

 

[Magic Matt]

I thought the resistance was between 1ohm and 0.4ohm, depending on how much voltage was applied. I'm probably wrong though, lol
Knowing me I've messed the math up somewhere!

 

[monkeyboy]

I think you misunderstood my post, zero resistance LED was just a ludicrous example of the only situation in which 3P would give 3 x current. By "significant resistance" I mean comparable to or greater than the internal resistance of the batteries.

OT:
This is a good place to get chargers in the UK

And this is a good place to get batteries.

 

[jamesavery22]

How would 3S4P AA eneloops do?