LED drivers

[TheWorkman]

I have just ordered and recieved a SSC P7 which I plan on using for a light mod. I hooked it up to a couple D cell batteries to check it and it looks fine. My question is if you need to have a driver with this LED or can I just direct drive it with batteries running the max voltage of the LED? What are the advantages of using a driver and which one would I need and why?

 

[Hallmac]

You may direct drive.

Drivers are used to extend peak performance. Batteries will only provide the max amperage and voltage for a short time. As the charge burns off the available output decreases.

Drivers allow a consistent amperage output at a given voltage with a wider range of battery voltages.

 

[TheWorkman]

Are there any you suggest?

 

[Hallmac]

If you will tell me your planned use, size of housing you want to use, batteries you want to use I could give you a few suggestions.

Have you search the candle power forums?CandlePowerForums - Powered by vBulletin

 

[bronk]

You have a LED that can tolerate a much higher current drain (3.7A as I recall) than your test batteries can provide. If you hook it up to a substantial battery pack with significant current output capability you will have a flash bulb rather than a flash light.

See my article for a more complete discussion at: http://www.scubaboard.com/forums/4398473-post30.html


http://www.scubaboard.com/forums/4398473-post30.html

 

[Packhorse]

It depends on many things. The Vf of the LED is one of them. Also the type of cells you want to drive it from.
If you plan on driving it off a battery pack in the 3.5- 5 volt range then I'd suggest a amc 7135 based driver. These act like smart resistors that will drop the voltage down to the Vf of the LED as long as the Vin is higher than the Vf of the LED. When the Vin drops to below the Vf it works as direct drive.

On the other hand if you have a battery pack of 6-12volt then you could use the Kai Domain 2.8a P7 driver and have many more features like 3 modes, low battery warning etc.

 

[Packhorse]

You may direct drive.

Drivers are used to extend peak performance. Batteries will only provide the max amperage and voltage for a short time. As the charge burns off the available output decreases.

Drivers allow a consistent amperage output at a given voltage with a wider range of battery voltages.

Yeah, but choose the wrong batteries or Vf LED and *poof*

Why risk a $25 LED for a $3/$12 driver?

 

[TheWorkman]

I haven't chosen any batteries yet and I don't honestly know the difference between the types. I'm a industrial mechanic but have no knowledge in the electrical field. In response to HALLMAC, I want to light to run for 3 hours MAX and I can custom make a housing to any size I need. Maybe you guys could suggest a battery/driver combo to achieve this run time. I really appreciate the help.

 

[cfelliot]

I would use the constant current circuit below with the KD Super Output SSC P7 LED Driver Board mentioned above. http://kaidomain.com/ProductDetails.aspx?ProductId=1866

This will allow you to use a battery voltage of 6, 9 or 12V.

The problem of using a constant voltage source is that you must use a limiting resistor in series with the LED and far more power is wasted driving the resistor than the driver board.

 

[Packhorse]

I haven't chosen any batteries yet and I don't honestly know the difference between the types....

Forget SLA.
NiCd is pretty out dated and offers no advantages over other types unless you have them already (thats why I still use them).

So then its NiMh or Lithium types.

Lithium Ion offers the highest energy density while NiMh may offer a longer life span.

For me the real reasons I choose one over the other is
A. Run time
B. Size/shape
C.Cost

1st decide how long you want your light to run for.

A P7/MCE run at 2.8 amps will consume about 10-12 watt including driver.

So if you want 4 hour burn time you need (12 x 4 =)48watt hours of battery power. Then add in efficiency, rule of thirds, manufactures "specs" etc and aim for say 80 watt hours.
You really should choose a batter pack that matches the VF of your LED and or driver. A P7 Vf is 3.7volt. The above mentioned driver is designed for 7.4volt input ideally. So your choices are...

2 lots of seriesed Li Ion batteries wired in parallel.
EG 8 Li Ion 18650 cells( 3.7v 2500ma each) 2S4P will give you a 7.4v 10000ma pack or 74watt hours. A little short of target so try a 10 cell pack (2S5P) at 7.4v 12500ma or 92.5 watt hours


Or you could try NiMh. If you go with D cells you could get 10000ma 1.2v cells.
10 in series or 10S1P ( Dont wire NiMh in parallel) you get 120 watt hour. Or 7 in series gives you 84 watt hour @ 8.4 volt.


All above options would work. 1st will offer most efficiency and get the most out of the driver ( eg low volt warning at 5.5 volt).

Use a different driver or if you use a different LED then it all changes.
The MC-E LED allows you to wire each of its dies independently. So you could wire all 4 in series (14.8Vf) or parallel(3.7Vf)or 2P2S (7.4Vf).