How to connect SST-90 Buck driver?

Hello folks,

I'd like to make my own dive light, using an SST-90 LED. This is the (relevant) stuff I'll be using(~DealExtreme):

SKU Product or Service Name
50026 12V SST-90 5-Mode Memory Circuit Board for Flashlights
47961 SST-90 2300LM LED Emitter 8000K White Light Bulb (4.2V)
00933 Rechargeable 3.6V 18650 2200mAh Blue

I've connected 1 battery to the LED-star, and the led emits. But when I connect the driver to the battery and LED, I get nothing. I can't find any datasheet for my driver, have searched a lot using Google, but I can't find a solution on my own.

So my question is: How do I connect the driver to battery and LED, so I can use the five functions it has (High 6500mA, Mid 2000mA, Low 800mA, Fast Strobe 5000mA, SOS 6500mA).

Thanks in advance,

Hendrik.

EDIT: Obviously I need some sort of switch, but what kind of switch, and how do i connect it?

Your driver requires a voltage higher than the forward voltage of the LED to operate.

The forward voltage is the minimum voltage required to illuminate the LED, and is higher on SST90s than other LEDs, such as the XML.

The driver sheds this excess in volts as heat. IIRC, that driver has an efficiency of around 75%. That means that 25% of the battery power is wasted as heat.

You will need to put a switch along the negative pathway. Interrupting the current briefly will switch you into the next mode.

I hope this is of some assistance.

Also, welcome to the forum. There are quite a few Belgians here. I grew up in Waterloo.

I would not try running the SST90 with a single 18650. Even rated at 2200ma may overheat the battery and POOF !! That battery better have overcurrent PCB protection in it. Even at that, it will not light up the led for more than a few minutes. That driver is a 12 volt DC buck. you will need at least 13 volts going in in order to function. Only way i see is to either change the driver or to up the volts, using more batteries. You may want to see batteryspace for available li-ion packs that have the necessary voltage. Check out Taskled for quality drivers. You may also want to consider adding a lens/reflector on the led in order to narrow down the beam angle. Carlco, Ledil are good at those. Consider the Cree XM-L or the MT-G's. They will shell out more lumens per watt than the sst-90. Be a member of candle power forums CPF. Those people have leds in their blood.

That driver works with as little as 10.8 volts in my testing of a single SST90

If I had to use the SST90, then a Taskled H6CC driver ( single mode ) with an external variable pot as dimmer along with a medium beam reflector or TIR optic (30 to 50 degrees) would be it. Color temperature in neutral white (4000K ish) and a battery pack of at least 9.6 volt and 4000ma capacity to give it a run time of well over an hour at full blast. Make sure the driver ( or any driver ) is well potted and sinked as it gets mighty warm in the casing.

Thanks a lot all of you!! I'm new to electronics, let alone building my own lights. But I'm getting there, bit by bit. I've got 4 batteries, so overheating the batteries won't be a problem.

All my current questions (pun intended) are answered now. I'll test the mentioned advise tomorrow evening. I'll keep you guys posted!

Waterloo? So napolean is a Bull these days? Lol..

You may need to connect 4 of those 18650 batteries in series to arrive at the voltage necessary for your driver to operate correctly. The batteries will get hot and MAY OVERHEAT. That driver may draw well over 3 amps from the batteries at high mode. DO NOT solder the battery terminals to each other, as the heat will damage the batteries if you never did this. If I had to use the 18650's. I would use 8 of them ( 4series 2 parallel configuration) and make sure they have the protection PCB's in them.This way the will have around 1.5 amp going through each string rather than 3 amps. 8 cells will boost the run time.

If I'd use a 4 times 3.6V in series, I'd get a 14.4V... Wouldn't this destroy my driver, since the specs say it's a 12V?

On checking out that driver, I beleive it is designed for 12 v DC as in. The 18650 batteries when fully charged are in reality 4.2 volts instead of 3.6 as marked as is usually the case.I do not think there will be a voltage in issue if 3 of the batteries are in series configuration for 3 X 4.2 volts = 12.6 volts. Parallel another string of those for extra run time and amperage reduction on the cells. They will also run cooler at full brightness. The driver has been noted to work at 14.4 volts but shuts down at full brightness but is operable at a dimmed level. The speciffications are not clear as it is not mentioned as being a Buck or Boost type driver. I am quite sure it is a Buck type with the 12 volt figure being the upper input DC voltage. If that is the case, then 2 or 3 series 18650 should work as well. I would opt for 3 series and 12.6V.

I soldered (I'm familiar with soldering) 3 batteries in series, giving me 12.xxV. I connected them to the driver and gues what, the SST-90 illuminates and all the modes work as expected!

PROBLEM: The LED + Star get so hot that it starts smoking (Probably the solder flux evaporating), and the the soldered wires "jump" off the LED-star--> no more connection. Is it normal for these LED's to get this hot?

Batteries don't get hot though..

The star needs to be heatsinked to prevent damage to the LED.

I use a chunk of aluminum, with a few screw holes tapped into it. A bit of thermal compound on the back of the star, and it gets screwed down tightly to the aluminum block. The heat passes into the aluminum, away from the LED.

The temperature you are describing is just shy of the level where permanent damage occurs. The LED can de-solder itself from the star as well.

Due to the heat shed from that driver, it is recommended that one heatsink the driver, in addition to the LED.

I was aware of the fact that I had to heatsink the LED, I just thought that the heat, generated by LED and driver, wouldn't be that much. Wrong again.

Do you use a solid peace of Aluminium, or a real heatsink. And what kind of dimensions are we talking about for the heatsink/aluminium block?

Thanks for all the comments by the way.

I just use an aluminum block, picked up for cheap at a metal recycler.

A large computer heatsink with fins would also work, assisted by a fan.

In your dive light, it will be important to pay attention to the thermal pathway - you want that heat to be transferred to the water.

If you have a host already in mind, let me know the dimensions and I'll help you make a heatsink for it.

Ok, Thanks!

It is very important to also have the driver heatsinked as well. Do not use FUJIX as a potting compound, many buy the large tube hoping it is a replacement for the Arctic silver and Arctic Ceramic adhesives that are permanent adhesives. Fujix never gets hard and is kind of like white chalk when it dies up. It is not the best solution for heat transfer. You may need a large heatsink for that sst90. It will get mighty hot very fast at full power. Another future alternative to a good high power led is the Cree MT-G. The new ones to come soon will be available at high CRI indexes. They are 6 volt ones and are bright. there are already reflectors designed for them by Ledil.

I've got a lathe, so I'll probably make my "light body" myself, making a custom heatsink shouldn't be a problem. I've built my own propane oven (1400° C), so melting and pooring aluminium is an option (to make a block for example).

The Cree MT-G sounds like an awesome LED. I'll definately experiment with them in the future. Thanks for the advise.

I have one of these drivers arriving any day now.

Well...I hope so...since it should have been here already. Good info here, thanks.

My emitter has much lower Vf (will run off 2 AA Nimh!), so I'm not sure what to expect, but if I learn anything new from experimenting I'll post it here...

I think the only two hurdles left for my light are where to put a switch and how to pot the driver...

You can pot the output, but why would you want to do that? I had to wait for 3+ weeks for my dealextreme delivery... Just add a switch after batteries, negative side.