A question about led drivers

[default]

I've no experience with them so any info could be helpful.

My question is that it seems to me that there are often a series of
drivers from a manufacturer with similar prices and they all output
the same current only the output voltage changes and they call them
constant current devices. For example a 1-3 watt may output
12-24V/300 ma, while an 18 watt output 24-36 volts/300 ma.

Well, if they are constant current, wouldn't it make sense to get one
with the highest voltage so it can drive more series leds, for about
the same price as a lower V output one? I figure it would be more
versatile and allow me to add leds if that seems necessary.

I'm toying with the idea of building a tabletop hydroponic "garden."
They get high prices for what amounts to a few LEDs and aquarium
air-pump,timer and container, some of which I already have laying
around collecting dust except for the leds and PS to operate them.

 

[Baron]

default prodded the keyboard with:

I've no experience with them so any info could be helpful.

My question is that it seems to me that there are often a series of
drivers from a manufacturer with similar prices and they all output
the same current only the output voltage changes and they call them
constant current devices. For example a 1-3 watt may output
12-24V/300 ma, while an 18 watt output 24-36 volts/300 ma.

Well, if they are constant current, wouldn't it make sense to get
one with the highest voltage so it can drive more series leds, for
about
the same price as a lower V output one? I figure it would be more
versatile and allow me to add leds if that seems necessary.

I'm toying with the idea of building a tabletop hydroponic "garden."
They get high prices for what amounts to a few LEDs and aquarium
air-pump,timer and container, some of which I already have laying
around collecting dust except for the leds and PS to operate them.

LED's are current operated devices and the devices to drive them are
intended for a specific use with a chain of LED's.

Calculating the voltage and current requirements is relatively easy.
But you need to know what the voltage and current values are for the
LED's you intend to use.

For instance a single LED might have a 3 volt and 10 milliamp rating.
So putting two in series would require 6 volts and 10 milliamps,
three would be 9 volts and 10 milliamps and so on.

If you put two in parallel, you would still use 3 volts but the
current would double.

The normal way you would run a chain of LED's is to put a current
limiting resistor in series. So a single LED run from a 12 volt
supply would require a resistor that would drop 9 volts at 10
milliamps.

The formula is supply voltage minus LED voltage divided by the current
equals the resistor value.

In the last example it would be 900 ohms.





--
Best Regards:
Baron.

 

[whit3rd]

On Sunday, February 17, 2019 at 8:25:33 AM UTC-8, default wrote:

My question is that it seems to me that there are often a series of
drivers from a manufacturer.... For example a 1-3 watt may output
12-24V/300 ma, while an 18 watt output 24-36 volts/300 ma.

Well, if they are constant current, wouldn't it make sense to get one
with the highest voltage so it can drive more series leds

Maybe. But, 'more series LEDs' implies you are chaining ten together,
and that implies that one can fail short (and the compliance of the
voltage output makes the rest of 'em still light), or one can fail open (and
they all go dark). A string of ten has ten times the fault likelihood
as a single LED. It also implies that (to keep the specified regulation)
you MUST purchase ten or so of the 300 mA-capable devices to
power up. Is that really the amount of light you want to pay for?

 

[default]

On Sun, 17 Feb 2019 10:04:52 -0500, default <default@defaulter.net>
wrote:

I've no experience with them so any info could be helpful.

My question is that it seems to me that there are often a series of
drivers from a manufacturer with similar prices and they all output
the same current only the output voltage changes and they call them
constant current devices. For example a 1-3 watt may output
12-24V/300 ma, while an 18 watt output 24-36 volts/300 ma.

Well, if they are constant current, wouldn't it make sense to get one
with the highest voltage so it can drive more series leds, for about
the same price as a lower V output one? I figure it would be more
versatile and allow me to add leds if that seems necessary.

I'm toying with the idea of building a tabletop hydroponic "garden."
They get high prices for what amounts to a few LEDs and aquarium
air-pump,timer and container, some of which I already have laying
around collecting dust except for the leds and PS to operate them.

I think I see the flaw in my reasoning. Namely: heat dissipation.
Taking a driver designed to excite a 18 watt string and using it to
drive only one, one-watt LED would put more of a heat burden on the
driver.

 

[default]

On Sun, 17 Feb 2019 18:16:22 +0000, Baron <baron@linuxmaniac.net>
wrote:

default prodded the keyboard with:

I've no experience with them so any info could be helpful.

My question is that it seems to me that there are often a series of
drivers from a manufacturer with similar prices and they all output
the same current only the output voltage changes and they call them
constant current devices. For example a 1-3 watt may output
12-24V/300 ma, while an 18 watt output 24-36 volts/300 ma.

Well, if they are constant current, wouldn't it make sense to get
one with the highest voltage so it can drive more series leds, for
about
the same price as a lower V output one? I figure it would be more
versatile and allow me to add leds if that seems necessary.

I'm toying with the idea of building a tabletop hydroponic "garden."
They get high prices for what amounts to a few LEDs and aquarium
air-pump,timer and container, some of which I already have laying
around collecting dust except for the leds and PS to operate them.

LED's are current operated devices and the devices to drive them are
intended for a specific use with a chain of LED's.

Calculating the voltage and current requirements is relatively easy.
But you need to know what the voltage and current values are for the
LED's you intend to use.

For instance a single LED might have a 3 volt and 10 milliamp rating.
So putting two in series would require 6 volts and 10 milliamps,
three would be 9 volts and 10 milliamps and so on.

If you put two in parallel, you would still use 3 volts but the
current would double.

The normal way you would run a chain of LED's is to put a current
limiting resistor in series. So a single LED run from a 12 volt
supply would require a resistor that would drop 9 volts at 10
milliamps.

The formula is supply voltage minus LED voltage divided by the current
equals the resistor value.

In the last example it would be 900 ohms.

Yeah I understand all that... I'll be working with high power LEDs;
the idea is to simulate sunlight and grow herbs and vegetables
indoors. So power dissipation and cooling are going to be important
design elements.

Another approach may be to power each led or short led string with a
series of slaved current mirror circuits then refine that a bit with
thermal feedback.

 

>"Yeah I understand all that... I'll be working with high power LEDs; the idea is to simulate sunlight and grow herbs and vegetables indoors."

Herbs, yeah, gotcha...

I believe LEDs cannot replace those big 400 watt bulbs. The LEDs are getting good, with white ones having phosphors now, but I doubt you'll ever get the UV out of them.

Yeah I tried to grow some herbs. I had 1,200 watts of lights and a similar amount of air conditioning to not melt the house down. However all my herbs turned out to be male. So a $400 a month electric bill got me nothing. Later I "used" the herbs myself because nobody else would want them.

 

[Sjouke Burry]

On 17-2-2019 22:48, default wrote:

On Sun, 17 Feb 2019 10:04:52 -0500, default <default@defaulter.net
wrote:

I've no experience with them so any info could be helpful.

My question is that it seems to me that there are often a series of
drivers from a manufacturer with similar prices and they all output
the same current only the output voltage changes and they call them
constant current devices. For example a 1-3 watt may output
12-24V/300 ma, while an 18 watt output 24-36 volts/300 ma.

Well, if they are constant current, wouldn't it make sense to get one
with the highest voltage so it can drive more series leds, for about
the same price as a lower V output one? I figure it would be more
versatile and allow me to add leds if that seems necessary.

I'm toying with the idea of building a tabletop hydroponic "garden."
They get high prices for what amounts to a few LEDs and aquarium
air-pump,timer and container, some of which I already have laying
around collecting dust except for the leds and PS to operate them.

I think I see the flaw in my reasoning. Namely: heat dissipation.
Taking a driver designed to excite a 18 watt string and using it to
drive only one, one-watt LED would put more of a heat burden on the
driver.

No.
The driver adjusts the voltage, to get the specified current.

The voltage spec just tells you how many leds you can put
in series.

 

[default]

On Mon, 18 Feb 2019 01:47:53 +0100, Sjouke Burry
<burrynulnulfour@ppllaanneett.nnll> wrote:

On 17-2-2019 22:48, default wrote:
On Sun, 17 Feb 2019 10:04:52 -0500, default <default@defaulter.net
wrote:

I've no experience with them so any info could be helpful.

My question is that it seems to me that there are often a series of
drivers from a manufacturer with similar prices and they all output
the same current only the output voltage changes and they call them
constant current devices. For example a 1-3 watt may output
12-24V/300 ma, while an 18 watt output 24-36 volts/300 ma.

Well, if they are constant current, wouldn't it make sense to get one
with the highest voltage so it can drive more series leds, for about
the same price as a lower V output one? I figure it would be more
versatile and allow me to add leds if that seems necessary.

I'm toying with the idea of building a tabletop hydroponic "garden."
They get high prices for what amounts to a few LEDs and aquarium
air-pump,timer and container, some of which I already have laying
around collecting dust except for the leds and PS to operate them.

I think I see the flaw in my reasoning. Namely: heat dissipation.
Taking a driver designed to excite a 18 watt string and using it to
drive only one, one-watt LED would put more of a heat burden on the
driver.

No.
The driver adjusts the voltage, to get the specified current.

The voltage spec just tells you how many leds you can put
in series.

I get that.

My questions are more to do with why a 3 watt model and 20 watt
constant current supply can be priced so closely with that disparity
of wattage among the sizes. But if they are inefficient enough it
would explain it - using one led for a source designed for 10 may
result in more power being dissipated in the CC power supply.

Or they are doing something questionable, like driving a linear CC
regulator from a CV supply.... That would result in a lot of heat
dumped in the CC regulator. It only takes one power transistor to
make a CC source, so this could just be a cheap and dirty approach.

 

[Jasen Betts]

On 2019-02-18, default <default@defaulter.net> wrote:

On Mon, 18 Feb 2019 01:47:53 +0100, Sjouke Burry
burrynulnulfour@ppllaanneett.nnll> wrote:

On 17-2-2019 22:48, default wrote:
On Sun, 17 Feb 2019 10:04:52 -0500, default <default@defaulter.net
wrote:

I've no experience with them so any info could be helpful.

My question is that it seems to me that there are often a series of
drivers from a manufacturer with similar prices and they all output
the same current only the output voltage changes and they call them
constant current devices. For example a 1-3 watt may output
12-24V/300 ma, while an 18 watt output 24-36 volts/300 ma.

probably the only difference is the voltage rating on the capacitors

Well, if they are constant current, wouldn't it make sense to get one
with the highest voltage so it can drive more series leds, for about
the same price as a lower V output one? I figure it would be more
versatile and allow me to add leds if that seems necessary.

abasolutely it would

I'm toying with the idea of building a tabletop hydroponic "garden."
They get high prices for what amounts to a few LEDs and aquarium
air-pump,timer and container, some of which I already have laying
around collecting dust except for the leds and PS to operate them.

I think I see the flaw in my reasoning. Namely: heat dissipation.
Taking a driver designed to excite a 18 watt string and using it to
drive only one, one-watt LED would put more of a heat burden on the
driver.

No.
The driver adjusts the voltage, to get the specified current.

The voltage spec just tells you how many leds you can put
in series.

I get that.

actually no it doesn't do that. the driver regulates the current, the
voltage is what ever it takes.

My questions are more to do with why a 3 watt model and 20 watt
constant current supply can be priced so closely with that disparity
of wattage among the sizes. But if they are inefficient enough it
would explain it - using one led for a source designed for 10 may
result in more power being dissipated in the CC power supply.

most of the cost is all the other parts of the device, the parts
responsible for max output voltage are relativley cheap.

Or they are doing something questionable, like driving a linear CC
regulator from a CV supply....

I doubt it, such a design would cost more.

That would result in a lot of heat
dumped in the CC regulator. It only takes one power transistor to
make a CC source, so this could just be a cheap and dirty approach.

It takes one resistor fewer than a CV supply to make a CC supply.

OUT -------->|->|->|->|->|-.
|
|
FB ------+--|<-|<-|<-|<-|<-'
|
[ ] R_sense
|
RETURN --'

--
When I tried casting out nines I made a hash of it.

 

[default]

On Mon, 18 Feb 2019 19:22:10 -0000 (UTC), Jasen Betts
<jasen@xnet.co.nz> wrote:

On 2019-02-18, default <default@defaulter.net> wrote:
On Mon, 18 Feb 2019 01:47:53 +0100, Sjouke Burry
burrynulnulfour@ppllaanneett.nnll> wrote:

On 17-2-2019 22:48, default wrote:
On Sun, 17 Feb 2019 10:04:52 -0500, default <default@defaulter.net
wrote:

I've no experience with them so any info could be helpful.

My question is that it seems to me that there are often a series of
drivers from a manufacturer with similar prices and they all output
the same current only the output voltage changes and they call them
constant current devices. For example a 1-3 watt may output
12-24V/300 ma, while an 18 watt output 24-36 volts/300 ma.

probably the only difference is the voltage rating on the capacitors

Well, if they are constant current, wouldn't it make sense to get one
with the highest voltage so it can drive more series leds, for about
the same price as a lower V output one? I figure it would be more
versatile and allow me to add leds if that seems necessary.

abasolutely it would

I'm toying with the idea of building a tabletop hydroponic "garden."
They get high prices for what amounts to a few LEDs and aquarium
air-pump,timer and container, some of which I already have laying
around collecting dust except for the leds and PS to operate them.

I think I see the flaw in my reasoning. Namely: heat dissipation.
Taking a driver designed to excite a 18 watt string and using it to
drive only one, one-watt LED would put more of a heat burden on the
driver.

No.
The driver adjusts the voltage, to get the specified current.

The voltage spec just tells you how many leds you can put
in series.

I get that.

actually no it doesn't do that. the driver regulates the current, the
voltage is what ever it takes.

If you look upward three or four lines he already says that the driver
adjusts the V and I am agreeing with that. That's what CC is all
about whatever voltage it takes. (within limits)

My questions are more to do with why a 3 watt model and 20 watt
constant current supply can be priced so closely with that disparity
of wattage among the sizes. But if they are inefficient enough it
would explain it - using one led for a source designed for 10 may
result in more power being dissipated in the CC power supply.

most of the cost is all the other parts of the device, the parts
responsible for max output voltage are relativley cheap.

I hope they aren't potted in epoxy, I ordered two different
manufacturer's drivers in the same power range. I'd love to take them
apart...

Or they are doing something questionable, like driving a linear CC
regulator from a CV supply....

I doubt it, such a design would cost more.

I agree, but one never knows when you find it on Ebay...

That would result in a lot of heat
dumped in the CC regulator. It only takes one power transistor to
make a CC source, so this could just be a cheap and dirty approach.

It takes one resistor fewer than a CV supply to make a CC supply.

OUT -------->|->|->|->|->|-.
|
|
FB ------+--|<-|<-|<-|<-|<-'
|
[ ] R_sense
|
RETURN --'