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Does an LED driver rated @ 6v -12v hold/keep a source voltage of 8.4v to 6v or just maintain it between 6v - 12v Answered

I should preface my inquiry with an admission of possessing very limited electronics knowledge. but I am somewhat familiar with battery voltages & amps.

I have several Luminus SST-50 & SST-90 LED emitters. I have found that to achieve the full lumen potential these emitters must be driven beyond Luninus's stated typical vf of 3.2 volts. I do not exceed 6vf. I am aware that current is a major factor in the performance of these lights, but when using 5-6amps or the max of 9amps (SST-90)I notice little difference in the brilliance of the light. However, when altering the vf from 3.2v or 4.5v to 6v the difference is amazing.

When using 5 X NIMH batteries (= 6volts/4.5amps) with an SST-90 the lumens are high. When I use 4 X NIMH bat @ 4.8 volts/4.5amps, there is about a 25% reduction in light production. With my limited electronics info.I assumed the voltage was the key force here. Or is there something about the volt/current relationships that I need to know?

My ? actually concerns the drivers that I have. They are rated @ 6v - 12 v. Do you know if a driver, with these specs, regulates/holds the vf @ 6 volts when the source voltage is greater than 6 volts or does it just maintain the voltage within the range of 6v - 12v.

Using 2 X 4.2v LIon batteries, connected to the driver, gives an 8,4v the volt meter reading. Such a voltage will destroy the emitters. I expected a reading of 6vf (@ the driver leads).

If you are able to answer my question, one I would be profoundly grateful, 2 please be as detailed/specific/simple as possible.

Thank you very much cgc210



5 years ago

I'm concerned you are measuring the correct information

Please let us know ?



I aploogize for the delay in my response. I am unable to supply the V & A, now. When I applied the 2 X Lion Bats (8.4v) the SST-50 survived for about 1 second, if that long. This is the reason why I made the original post re: a 6v limit. I will put another light together & test the V/A you asked me for. If I could discuss the results with for a little bit I'd appreciate it

Prior to trying the 2 Lion bats (to make sure the light assembly was correct) I tried it using 4 X 1.5v, approx. 1000 mAh alkaline Enercell bats. It turned on great, but very low lumens. Which is also why I step up the voltage. @ the advertised specs these lights just don't produce and also part of the point of the original post re: drivers. I don't put a lot trust in the function of mass produced products so I expect a certain failure rate, but every driver/emitter i use gets toasted. Based on what I've relayed to you can you see what I'm doing wrong. I use plenty of heat sink, all of the connections were fine. Is there something about the driver that I'm missing. Regardless of my insufficient knowledge, I thought the driver's purpose was to regulate incoming V/A in doing so protect the system and prevent what happened.

The 2 Lion bats I used were Samsung 2.4 amps, the driver was Kaidomain.com: SST-50 5v -12v, 5 amp, with a Luminus SST-50 emitter.

The emitter went so fast it appeared as though the 8.4v was DD to the diode. If you have any ideas, thoughts. comments as to what might be going on here I'm open

Thanks a bunch, cgc210


The the visual of where & how to measure V & A is very nice. I'm short on electronics knowledge (very much aware of it). I'm familiar with using the DVM I appreciate it very much along with the considerable input from you & Steveastrouk. All I'm trying to do here is find a way to limit the voltage (& whatever the accompanying amperage is) to 6.

So far the only way I've accomplished this is with the 5 X 1.2v NiMH and that has been directly driving the emitters. I have drivers (many of them) but I've gotten so much better results without using them it is tempting to continue DD. I've read, however, so much about how ungood this for the emitters I'm no longer comfortable DD them.

I will provide the voltage/amp results after I put an SST-50 together (their cheaper) than the -90's. Send results later.

Thank you very much cgc210

Exactly my concern too, as oft expressed in this thread.

leds need to use a driver which provides a constant current, not a constant voltage. can you post a link to good drivers? The input volts range looks like 6.q we volts to me, if its a proper led driver, it will take care of the output current itself..


Thank you getting back to me. I'm a bit confused

I attempted to go to "good drivers: and did not see anything relevant to the subject here. Could you please be more specific re: where you'd like me to " post a link.

The volts range is definitely min 6v. I need to keep it there

There is s typo. It should say 'post a link to your drivers'.

I've looked at your device and i too don't see how you can ever see 6volts across it

Here is the link: http://kaidomain.com/product/details.S020079. I should've realize the typo.

I was so disappointed when I initially purchased the Luminus SST-50 & SST-90 I began fiddling around. When I didn't get any indication of damage (bluing) when increasing the voltage I was able to finally satisfy my desire for increased lumen output @ 6 volts.

Once in a while an SST-50 will show signs of being over driven. I've pushed some of these lights @ 6 volts for a year almost daily and see no indication of problems. The SST-90's seem to be much robust than the 50's and certainly more than the Cree XMl-T6's. I've blown a few of those @ 4.3 volts, but @ 4.2 volts they perform very well and are a great emitter.

My goal is to find a driver that will give no more than Vf 6. Got any suggestions


You don't quite see what we're saying here . The led develops a certain vf,given by the data sheet, for a given current. What Iceng and i are saying is that, when you have 9 amps flowing, which is the stated maximum current you CANNOT HAVE more than 3.7 volts or so acRoss the led .


I get that increasing the voltage changes/increases the amps. I saw the graph that Iceng provided. I don't know what the amps increase to . My concern is that an increase in voltage above 6 (and whatever the amps are at that voltage) destroys the emitter so I need a way to hold the voltage @ 6.

I was hoping to find a driver that will allow this.


measure what your existing driver does.,on the led. You can't ever get 6v on this led except at something like 1000 amps

Measure Vf AND forward current Of The led, @the led, and let me have the numbers to compare with the data sheet .


5 years ago

6 -TO- 12VDC sounds like the driver can operate in that range of
source voltage.

The driver then applies the correct current to the LED in question and
the LED will work at it's designed forward voltage VF...


Thank you for the response. I appreciate it when those with more assist those with less.

My SST-90's can be driven @ 9amps. I've done that and I don't see much of an increase over running them @ 4-6amps. When I up the VF from 3.2v (manufct spec) to 6v they really shine, the difference is incomparable.

(as I mentioned) when I use 2 X Lion bats the reading @ the driver leads to the LED is 8.4v, certain doom.

Do you know of a simple way to restrict the Vf to just 6v.

I have no information on your driver.

BTW don't push 9 amps through your LED for long without a
very good cooling heatsink..

It sounds like you may have damaged your device already.

The plot clearly shows the Vf @ 9 amps is 3.7 V  ERGO your desire
to raise the forward voltage to 6v is not in the realm of proper working

And I still have no information on your driver.


The driver was obtained from Kaidomain.com

" -15V, 9A Circuit Driver for Bike Light Features:
- Input voltage :6-15V
- Output current:9A
- Single Mode only "

If you are referring to the driver in your mention of a damaged device, I thought this also. so I tested all 5 (that I have ). Each one gave a MM read of 8.4v @ the LED leads (same as source voltage)
I was puzzled & disappointed by some of the results I've gotten when varying the amperage. Particularly when paralleling the batteries to obtain the increased amps and what I thought would result in max lumens. I got better performance when I went to 6 X NiMH bats @ 4.5 amps. I get these results regardless of the emitter, SST-90 or 50