LED constant-current power supply

[Paul Andrews]

I'm looking at one of these Meanwell power supplies to power a very power-hungry display. It says it is 'constant current'. I assume that that really means it just has a current limiter built in?

[gregebert]

Essentially, yes. But be aware of the open-circuit output voltage; the supply will attempt to pump-out the amount of requested current, and in order to do so, it will increase it's output voltage until the desired current is obtained.

Just make sure that *you* are not the load. For example, if you set the current to 150mA, and touch the terminals, you will probably be killed. I'm not joking. The 1400mA supply will crank out as much as 420V, and 100-200mA is fatal.

I suspect that when the supply is energized, it will rapidly increase the output voltage from 0 volts, up to the maximum no-load output voltage (420V), until the measured current reaches what you set it to. If the load's resistance decreases as the current increases, the output voltage will also decrease; this is typical behavior of a gas discharge as it ionizes.

What are you driving from the supply ?

[Paul Andrews]

A whole bunch of IN-28s. The current won’t be constant, and I don’t want the voltage to fluctuate, so time for plan B it seems. Whatever that might be.

Thanks for the insight, is that on that datasheet somewhere?

On Feb 20, 2020, at 6:48 PM, gregebert <greg...@hotmail.com> wrote:



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[Paul Andrews]

Yes I see it, ‘open circuit voltage’.

Sent from my iPad

On Feb 20, 2020, at 7:37 PM, Paul Andrews <judg...@gmail.com> wrote:

A whole bunch of IN-28s. The current won’t be constant, and I don’t want the voltage to fluctuate, so time for plan B it seems. Whatever that might be.

[gregebert]

You probably just want a HV supply, about 250 VDC, and a fuse instead of a constant-current supply.

I think IN-28's are rated at 13mA, so you could arrange them in groups of 16 with a 1/4 amp fast-blo fuse to protect each group.

If power consumption is a concern, you can get clever and step-up the voltage to 250VDC for a few hundred usec when you know tubes will be turning-on, and throttle-back to around 180V for sustaining.

[Paul Andrews]

I’m having trouble finding a 250V DC power supply that can generate 1/4 amp. Meanwell were the closest I have got so far.

I’m looking for something to drive 4 banks of 26 tubes arranged as a seven segment display. Using a bench supply, it seems that 250V is the smallest voltage that will reliably light them, and one bank I tested drew 237mA when lit.

Then I’ll have to figure out some way to control them.

On Feb 21, 2020, at 12:38 AM, gregebert <greg...@hotmail.com> wrote:



You probably just want a HV supply, about 250 VDC, and a fuse instead of a constant-current supply.

I think IN-28's are rated at 13mA, so you could arrange them in groups of 16 with a 1/4 amp fast-blo fuse to protect each group.

If power consumption is a concern, you can get clever and step-up the voltage to 250VDC for a few hundred usec when you know tubes will be turning-on, and throttle-back to around 180V for sustaining.

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[David Forbes]

This supply is probably the correct one for your application. You will need to use a series resistor on each IN-28 tube to get them to start ionizing, since the lit tubes will run at a lower voltage than the unlit tubes, which will prevent the unlit tubes from striking. 

There is an adjustment for the current ranging from 700 to 1400mA. You will want to turn that down all the way at first, and be sure that your tubes really need as much current as you adjust the power supply to give. 

And, be careful! That supply is lethal.

On Thu, Feb 20, 2020, 4:08 PM Paul Andrews <pa...@nixies.us> wrote:

I'm looking at one of these Meanwell power supplies to power a very power-hungry display. It says it is 'constant current'. I assume that that really means it just has a current limiter built in?

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[gregebert]

I would start with a few ideal scenarios to understand your total power. For example, if you use 180V most of the time, and have a short "boost" when bulbs need to turn on, your power will be minimized.

But with all segments on, that works out to 180*26*4*0.013 = 243 watts to display 8888, and probably 56W to display 111 (I assume this is a clock). So there's quite a bit of heat to deal with, not to mention your electric bill.

If you use a 250V supply and series dropping resistors, your power will only increase, to as much as 338 watts.

[Paul Andrews]

I'm definitely not planning on leaving this on, unless the room needs warming up. These are original soviet modules like the one below. Try not to have a heart attack looking at the collection of crocodile clips - I was careful not to touch anything while the power was turned on! They have an interesting diode arrangement for the IN-28 shared between segments.

It will probably take me a while to get anywhere with this...

[Alex]

Be careful with the Meanwell LED Constant Current supplies, we used a boat load (literally - it was a complete lighting refit on some gigantic yacht) of them driving series strings of various lengths of 350mA bare LED dies in posh housings. They worked fine and would easily put out >300VDC at 350mA but one intermittant connection would kill the entire chain as the voltage would jump to rail and they had a fair bit of output capacitance. Lost quite a few hundred quids worth of posh LED fixtures that way.

Worked well when used properly though, the 0-10v dimming was successful on the ones we were using as well.

[Paul Andrews]

I’m thinking of stacking five 48V constant voltage supplies instead. Some have reverse polarity diodes in them, or I might just add external ones anyway.

On Feb 22, 2020, at 4:34 AM, Alex <ajlg...@gmail.com> wrote:



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