WTB: Variable Power Supply

[diachi]

Switching power supplies are great for lots of power in a small package and I use them myself, but sometimes they put out spikes or transcients which can cause a problem for our laser diodes, if directly driving them off of it. I see the specs though, noise isn't very bad, maybe it will be OK. Better to buy a linear power supply, I think, but they are heavy and won't have the features this unit has at the same current capability unless expensive. It might be OK, I've used switching power supplies to drive diodes when testing etc., but one thing to be care of and tht is turning the unit on with the diode hooked up, or even a diode with a driver between it and the power supply, I killed a diode that way. These power supplies usually put out a big spike of over voltage when first turned on, regardless of the last setting. Be aware of that and you will probably be fine.

I've seen 30V spikes out of variable switching supplies before when turning them on, even with the voltage turned all the way down. 30V was the maximum output of the supply under regular conditions. Adding some 470uF 50V capacitors on the output helped smooth it out.

 

[Alaskan]

I didn't know that myself, when first using mine. Fortunately, only killed an M140 instead of a more expensive laser diode. Between your posting I edited the following into my last post:

I found this statement in the review:

Notes

When using it for constant current remember never to turn it on before the led is connected

That is counter that what I was saying to never to turn it on with the laser diode connected. OK, I don't know what to say now, if you buy this check what happens when you first turn it on and see if there is a voltage spike, but you might need an oscilloscope to catch it.

 

[dubious speculation]

Yep everything you mentioned was brought to my attention when I first started looking for a PS A big old second-hand linear power supply really would be ideal, but being so heavy makes shipping expensive and name brand 2nd-hand quality units are extremely scarce (basically non-existent) in Australia.

Would be nice to make sense or shed light on the conflicting information regarding the correct time to hook up a load :thinking: Just bought the unit in question, regardless of its suitability for laser diodes its a helluva deal and it will be useful for powering many other things anyway! I guess I'll be purchasing an oscilloscope as well and will post my findings when it arrives :beer:

I've seen 30V spikes out of variable switching supplies before when turning them on, even with the voltage turned all the way down. 30V was the maximum output of the supply under regular conditions. Adding some 470uF 50V capacitors on the output helped smooth it out.

Hmm, that's definitely something I should keep in mind! I've also purchased a UNI-T UT61E multimeter so hopefully I can test for voltage spikes when I receive the unit (apparently not see below)

 

[Alaskan]

I like that little power supply, I might order one too.

 

[Cyparagon]

When you make the size (and price) smaller, the noise goes up and the stability goes down. The testing shows that pretty clearly.

potentially one could have a 50V 15A variable power supply for $78 US (cost includes a sufficient DC power supply to power the buck converter.)

I'm seeing these on ebay for $38. Where are you seeing the remaining required 60V 20A DC power supply for $40?

Noise at 12V 5A (Vin 40V) is 14mV rms and 148mVpp

And a 148mV change in voltage is a very large change in current, when it comes to the steep IV curve of a diode. If 148mV is the best it has to offer at a modest load in constant voltage, constant current will inevitably be far worse.

I've used switching power supplies to drive diodes when testing

I would personally recommend against using ANY unknown source to drive a laser diode. If you don't verify the lack of transients and noise with an oscilloscope, "Didn't kill the diode" is the best measurement you can hope to achieve.

"Didn't kill the diode" might very well also mean "damaged the diode to the point it has 10 hours life remaining"

Would be nice to make sense or shed light on the conflicting information regarding the correct time to hook up a load :thinking:

That depends on how shitty the power supply is. The safest method would be turn on the power supply, set everything to zero, verify the output voltage is indeed zero (or short it), then connect the load.

Adding some 470uF 50V capacitors on the output helped smooth it out.

Adding output capacitance might help stabilize constant voltage, but it will destabilize constant current. It may also destabilize constant voltage in some designs. Beware.

I've also purchased a UNI-T UT61E multimeter so hopefully I can test for voltage spikes when I receive the unit.

No. Multimeters will not catch voltage spikes, as they are too slow. You need an oscilloscope.

regardless of its suitability for laser diodes its a helluva deal and it will be useful for powering many other things anyway!

Well, IF you can find a suitable power supply for the power supply. That's a subject being overlooked by most people here. If I were to get this (and I might), I would power it with a DIY lithium battery and have it be portable. For a mains powered unit, there are far better options (in the US anyway).

 

[diachi]

Adding output capacitance might help stabilize constant voltage, but it will destabilize constant current. It may also destabilize constant voltage in some designs. Beware.

Yes, I should have mentioned that. Plus the amount of current that can be sourced over a short time will be much higher.

 

[dubious speculation]

I'm seeing these on ebay for $38. Where are you seeing the remaining required 60V 20A DC power supply for $40?

I should have been clearer about the power supply I would use. True there are no 60V 20A DC power supplies for $40 anywhere that I know of. My current plan is to use a 48V 10A power supply which are readily available for roughly $42 US. This obviously means that you won't be able to utilise the full current and voltage capabilities that the unit has, but that doesn't worry me.

And a 148mV change in voltage is a very large change in current... constant current will inevitably be far worse.

True. However that 148mV peak to peak change in voltage is at 12V 5A. None of the LD's that I would be looking to test will ever need that kind of power requirements. The mV ripple at 12W load is less than half that of the values at 60W load.

I may be feeling optimistic at this point but I will be using an oscilloscope to measure mA and mV ripple at different voltages and current outputs when I receive the unit. What would be an acceptable ripple current peak to peak at 4.8V 3.5A? (typical voltage and operating current for the NUBM07E).

The safest method would be turn on the power supply, set everything to zero, verify the output voltage is indeed zero (or short it), then connect the load.

I will keep that in mind.

No. Multimeters will not catch voltage spikes, as they are too slow. You need an oscilloscope.

I stand corrected. I wasn't 100% sure about my statement relating to that beforehand so thanks for clearing that up.

Well, IF you can find a suitable power supply for the power supply. That's a subject being overlooked by most people here. If I were to get this (and I might), I would power it with a DIY lithium battery and have it be portable. For a mains powered unit, there are far better options (in the US anyway).

A portable PS would be cool but for my uses would merely be a novelty (you obviously have a different use case in mind ). Depending on what cells you use that could end up being quite expensive.

 

[Alaskan]

I still like that power supply you found, I have my reservations for use with laser diodes, but for a general purpose power supply I think it might be OK, worth trying. I have lots of other things I could use it for if it didn't work out for laser diodes, as you mentioned too.

 

[Cyparagon]

My current plan is to use a 48V 10A power supply which are readily available for roughly $42 US. This obviously means that you won't be able to utilise the full current and voltage capabilities that the unit has, but that doesn't worry me.

I would be wary of running a junk chinese PSU much over 60% rated capacity. Dropping 10% for losses, that still gives you over 250W to play with. The full 15A would be available up to 17V or so.

Also, "garbage in, garbage out". Some of the noise from a junk PSU will carry through the DCDC converter.

Depending on what cells you use that could end up being quite expensive.

I'm an unusual case. I find laptop batteries (most under 4 years old) in the scrap bin at work all the time. I have well over 300 good 18650s to put to use.

that 148mV peak to peak change in voltage is at 12V 5A. None of the LD's that I would be looking to test will ever need that kind of power requirements.

Noise scales with output current. Not so much with output voltage. Noise at 4V 5A will be similar to the noise at 30V 5A. Higher input voltage also means higher noise, according to the graphs provided.

 

[dubious speculation]

I would be wary of running a junk chinese PSU much over 60% rated capacity. Dropping 10% for losses, that still gives you over 250W to play with. The full 15A would be available up to 17V or so.

Also, "garbage in, garbage out". Some of the noise from a junk PSU will carry through the DCDC converter.

Noise scales with output current. Not so much with output voltage. Noise at 4V 5A will be similar to the noise at 30V 5A. Higher input voltage also means higher noise, according to the graphs provided.

Well at this point it's looking abundantly clear I won't be using this for any sensitive electronics. The one hobby that I've seen this unit adopted as relatively widespread is on the flashlight forums. Using them to drive at a max load of 100W or so most members typically opt for the cheaper variant and of course LED's are much more forgiving.

I'm an unusual case. I find laptop batteries (most under 4 years old) in the scrap bin at work all the time. I have well over 300 good 18650s to put to use.

Good luck soldering 1000's of welds onto nickel strips You're no doubt already aware of that. Or perhaps you already have a better idea

 

[dubious speculation]

Well I've had this unit for some time now and from my limited use its proven to be very versatile. I haven't measured the output ripple with an oscilloscope but I couldn't resist powering up a PL450B It worked flawlessly when powering the PL450B although I guess the only claim I can make is that it "didn't kill it". Regardless I won't be using it for sensitive electronics, its main use will be to charge my electric skateboard which requires a 42V 6A input, obviously being a variable PS it's handy to have an adjustable end cut-off voltage.