Will a old laptop charger power 10x 10watt leds?

vivbar · Nov 1, 2014

Hello i was wondering if it is possible to power 10x 10watt leds?

The leds specs
Emitter Type: large power LED
Total Emitters: 9
Power: 10W
Rate Voltage: 7.5~8 V
Chip working voltage: 7.5~8 W
Input current: 1.3A

Specs laptop charger: Output voltage 16V Output current 6A

idleprocess · Nov 2, 2014

vivbar said:
Hello i was wondering if it is possible to power 10x 10watt leds?

The leds specs
Emitter Type: large power LED
Total Emitters: 9
Power: 10W
Rate Voltage: 7.5~8 V
Chip working voltage: 7.5~8 W
Input current: 1.3A

Specs laptop charger:
Output voltage 16V
Output current 6A

Relevant statistics: LED Vf of 7.5 - 8V, drive current 1.3A; power supply voltage 16V, current limit 6A.

On the simple balance of watts - 104 LED watts (8V x 1.3A x 10) vs 96 power supply watts (16V * 6A) - you cannot drive all 10 LED's at full power.

You can drive 8 at full power in 4 parallel strings of 2 LED's assuming that you have around 1 volt of margin to limit current (7.5V Vf x 2 = 15V). A 750 mOhm resistor will produce slightly more than 1.3A of current while a 1 Ohm resistor will be around 1A (which buys you more current margin to add in another string in parallel). But your LED forward voltage is a wild card and might be closer to 8V per unit, so you might need to experiment. You could also use buck-boost drivers set to your desired current limit, but that will add some expense.

DIWdiver · Nov 3, 2014

A laptop supply may not be designed with anything like a precise current limit. Also, it may very well not be designed to run reliably at current limit.

I would strongly recommend some sort of device to limit the current to a safe level (6A total). Resistors are the simplest, but in your case may not be able to give you full power. If your LEDs are 8V at full power, the math says you need zero resistance and you have no control over the current. A slight change in the system (like Vf drops as the LEDs warm up) will cause an overcurrent condition. On the other hand, as idleprocess shows, you may have plenty of overhead for proper control. You'd have to test the LEDs at power to know for sure.

A buck-boost driver could drive strings of 2 LEDs, or a boost driver could drive strings of 3 or more, or a buck driver could drive them all in parallel.

If you want to investigate the LEDs, just get a couple of 1 ohm, 2 watt resistors, hook them up, and see what happens. 1W is probably enough, but most resistors get REALLY hot at rated power.

idleprocess · Nov 3, 2014

DIWdiver said:
A laptop supply may not be designed with anything like a precise current limit. Also, it may very well not be designed to run reliably at current limit.

I would strongly recommend some sort of device to limit the current to a safe level (6A total). Resistors are the simplest, but in your case may not be able to give you full power. If your LEDs are 8V at full power, the math says you need zero resistance and you have no control over the current. A slight change in the system (like Vf drops as the LEDs warm up) will cause an overcurrent condition. On the other hand, as idleprocess shows, you may have plenty of overhead for proper control. You'd have to test the LEDs at power to know for sure.

A buck-boost driver could drive strings of 2 LEDs, or a boost driver could drive strings of 3 or more, or a buck driver could drive them all in parallel.

If you want to investigate the LEDs, just get a couple of 1 ohm, 2 watt resistors, hook them up, and see what happens. 1W is probably enough, but most resistors get REALLY hot at rated power.

Ah yes, I forgot that laptop power supply max current ratings are often not sustainable ... and that said PSU's might not like running at full power for hours on end. 4-5A probably the most that such a device could comfortably spit out continuously.

My theory on fixed lighting is to drive LED's appreciably below their maximum ratings since they'll ideally last for many tens of thousands of hours of operation, as opposed to the tens of hours of operation that most flashlights see by comparison. So at least an Ohm of resistance on each string of two isn't a bad thing even if you see < 1A of drive current.

Would be helpful if vivbar would give us more information to work with ... such as what the intended application is and how much electronics experience they have.

mattheww50 · Nov 3, 2014

My experience is that most laptop supplies can provide the rated current output for long periods of time, however it is also my experience that voltage regulation on these supplies often isn't very good, and the ratings are nominal. I.E. at lower currents the voltage may be signficantly higher, and at high currents the voltage may be significantly lower. Generally voltage regulation for the laptop and battery charging is inside the laptop. This holds down the cost of the power supply, and in PC's, cost is just about everything. that being said, it is quite likely that you will need to invest in a driver because at full load the laptop supply may be putting out considerably less than 16volts, and at lower currents, will put out significantly more than 16V. YMMV

idleprocess · Nov 3, 2014

mattheww50 said:
My experience is that most laptop supplies can provide the rated current output for long periods of time

I must have cheap ones or a bad sample set because all of the ones I've used lately get alarmingly hot after only an hour or so of operation at high loads (recharging a spent battery and the laptop). Perhaps they can handle the abuse, but I'd rather not take that risk.

FRITZHID · Nov 8, 2014

idleprocess said:
I must have cheap ones or a bad sample set because all of the ones I've used lately get alarmingly hot after only an hour or so of operation at high loads (recharging a spent battery and the laptop). Perhaps they can handle the abuse, but I'd rather not take that risk.

That may just be a brand issue as well, all the HP laptop PSs I've had get almost alarmingly hot when charging & powering the pc.... especially when running the pc hard, . Like in gaming..... the few Dell supplies I've had did not get nearly as hot.... but the pc itself did.

Will a old laptop charger power 10x 10watt leds?

vivbar

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idleprocess

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DIWdiver

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idleprocess

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mattheww50

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idleprocess

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FRITZHID

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