Author Topic: Power Supply: Build or Buy?  (Read 11738 times)

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Online tautech

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Re: Power Supply: Build or Buy?
« Reply #75 on: May 11, 2023, 03:39:13 am »

What PSU are you using for that development Mike ?

Have you looked at the SPS5000X range ?
I've been using my 40V 60A unit for charging solar array batteries lately....a remote installation so powered with a genset.

The Korad KWR102, but it's not enough for the higher current pump motors which may need up to 50 amps! We should have more data on the motors soon to help with the decision, and the SPS5000X might be a candidate.

Best,
Mine's a 5042X 40V/60A 780W but they do have a total output rating in W so can't do both those figures at once.  :(
They start getting up in cost and even the 40V/90A 1080W 5043X jobby might not quite meet your needs or the coming 200V 25A 1500W SPS6000X either although that's not due for a bit I believe. I did start a thread for both you can hunt out if required.
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Offline nctnico

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Re: Power Supply: Build or Buy?
« Reply #76 on: May 11, 2023, 09:42:39 am »
It won't be easy, there's usually a big capacitor across the output that will absorb it.

Not in a bench supply, a big capacitor across the output reduces the effectiveness of current limiting in the event of a short circuit.
A reasonably sized capacitor is necessary for control loop stability. But in the end there isn't much energy in it.

About connecting inductive loads: the higher end power supplies from (at least) HP/Agilent/Keysight have an active load circuit inside that sinks current called a 'down programmer'. This is there to make the output voltage lower quickly AND dissipate energy coming into the power supply. You can see this in action when connecting a motor to it and turn the output off. You'll see the current go negative while the motor spins down. This active load circuit is typically engaged for a few seconds at most but it does help.
« Last Edit: May 11, 2023, 09:46:46 am by nctnico »
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Offline David Hess

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Re: Power Supply: Build or Buy?
« Reply #77 on: May 11, 2023, 12:22:51 pm »
It won't be easy, there's usually a big capacitor across the output that will absorb it.

Not in a bench supply, a big capacitor across the output reduces the effectiveness of current limiting in the event of a short circuit.

A reasonably sized capacitor is necessary for control loop stability. But in the end there isn't much energy in it.

About connecting inductive loads: the higher end power supplies from (at least) HP/Agilent/Keysight have an active load circuit inside that sinks current called a 'down programmer'. This is there to make the output voltage lower quickly AND dissipate energy coming into the power supply. You can see this in action when connecting a motor to it and turn the output off. You'll see the current go negative while the motor spins down. This active load circuit is typically engaged for a few seconds at most but it does help.

25 to 100 microfarads per amp is typical however with careful design, less than 0.1 microfarads per amp is possible.  I just noticed that it is the later designs which always seem to include the class-AB output stage or active load.
 

Offline mawyatt

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Re: Power Supply: Build or Buy?
« Reply #78 on: May 11, 2023, 01:33:21 pm »

Mine's a 5042X 40V/60A 780W but they do have a total output rating in W so can't do both those figures at once.  :(
They start getting up in cost and even the 40V/90A 1080W 5043X jobby might not quite meet your needs or the coming 200V 25A 1500W SPS6000X either although that's not due for a bit I believe. I did start a thread for both you can hunt out if required.

We did take a look at the 5000 series, and yes they are kind of expensive!!

Once we get the pump motor profiles for the various pump motors, then we'll have a better idea of what we'll need. The KWR102 isn't going to be enough tho.

The system design is leaning towards separate power supplies, rather than one unified supply. This allows a dedicated supply for the pump motor, and another for the other stuff. With this in mind the heavy load motor supply doesn't need to be accurate or low noise, just have enough to hold up the pump motor and one option is to use a Mean Well Open Frame Supply and design a quick acting current limit, as we don't need a variable voltage range, so this may work out.

It's interesting to see discussions of power supply active sinking capability, IMO this should be a prerequisite in any modern quality Bench Level Supply, but few have this built-in capability. Same goes for output capacitance, this should be as low as possible in a quality Bench Supply. It doesn't take much energy to destroy/damage a modern IC, and even with a low current limit set point the output capacitance energy storage is sufficient to quickly dump into a circuit and take out various chips, as as we know Murphy will direct that energy to the most expensive and elusive chips!! 

Best,
Curiosity killed the cat, also depleted my wallet!
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Offline armandine2

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Re: Power Supply: Build or Buy?
« Reply #79 on: May 11, 2023, 02:22:22 pm »
 :clap: a good time to check my kikusui manual re. sinking current

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Offline mawyatt

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Re: Power Supply: Build or Buy?
« Reply #80 on: May 11, 2023, 02:23:05 pm »
A story related to the power supply output capacitance that some folks might find interesting. Back in 70s and 80s much effort went into nuclear survivability for electronics, and research found the levels of minimum energy in a supply line or power supply that would damage/destroy a chip. Basically a nuclear detonation will turn on all PN junctions of exposed semiconductors, this includes diodes, transistors and junction isolated chips and why for high radiation environments (space for example) insulated substrate chips are preferred.

For survivability the supply line and power supply had a maximum available capacitance and discharge profile which often dictated utilizing a "Crowbar" type Power Supply, where the Crowbar (we used an SCR) would act upon an event leading edge. The available capacitance was a complex assessment of the capacitance that could quickly discharge during an event leading edge from the power supply and PCB distributed decoupling capacitances, and recall this was something on the order of ~90uF for a 10mJ energy level for a 15V supply (vaguely recall this as the maximum available discharge energy to cause chip damage).

Anyway, this is kind of related to the output capacitance of a Power Supply and why one prefers a lower capacitance as an "event" could be a malfunction of the test circuit, device or even operator (scope ground lead dangling and shorting something on the PCB, been there done that) :o

We must remember that the power supply output capacitance, or a portion of such, is generally outside current limit circuitry and the current limit can't help with the instantaneous discharge levels for the output capacitance, so lower is better :-+

Best,

 
« Last Edit: May 11, 2023, 02:25:36 pm by mawyatt »
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Offline David Hess

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Re: Power Supply: Build or Buy?
« Reply #81 on: May 11, 2023, 03:13:23 pm »
It's interesting to see discussions of power supply active sinking capability, IMO this should be a prerequisite in any modern quality Bench Level Supply, but few have this built-in capability. Same goes for output capacitance, this should be as low as possible in a quality Bench Supply. It doesn't take much energy to destroy/damage a modern IC, and even with a low current limit set point the output capacitance energy storage is sufficient to quickly dump into a circuit and take out various chips, as as we know Murphy will direct that energy to the most expensive and elusive chips!!

In a majority of applications, minimum output capacitance and active sinking are not required.  And both have at least the increased potential of creating oscillation with certain loads.  Of course either or both may be indispensable in specific cases.

Active sinking is nice, but so are readouts of current and voltage, and I can get by without the later as long as I have an indicator that the power supply is current limiting.  None of these things are something that I consider indispensable.

For survivability the supply line and power supply had a maximum available capacitance and discharge profile which often dictated utilizing a "Crowbar" type Power Supply, where the Crowbar (we used an SCR) would act upon an event leading edge. The available capacitance was a complex assessment of the capacitance that could quickly discharge during an event leading edge from the power supply and PCB distributed decoupling capacitances, and recall this was something on the order of ~90uF for a 10mJ energy level for a 15V supply (vaguely recall this as the maximum available discharge energy to cause chip damage).

"Intrinsically safe" designs are subject to a similar analysis.  Systems which support hot-plugging, including USB, also have limits on total capacitance to prevent high inrush currents which could cause glitches.
 

Offline rsjsouza

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Re: Power Supply: Build or Buy?
« Reply #82 on: May 12, 2023, 10:58:04 am »
I don't see much point in using 24VDC power supply to power a soldering iron. Get an AC powered soldering iron and save the 24VDC iron for when you want to use it on battery.

I've had the soldering iron for a few years now so purchasing another one would be a waste of money. Having a bench PSU that can do double duty when I feel like it would be more worth it IMO.
So lash up a salvaged transformer, rectifier and filter capacitor (assuming the iron contains electronic temperature regulation) and call it done. If the iron is not a temperature controlled soldering station then IMO it's not really worth having except as a backjup.

Perhaps this was mentioned before but, since you are in the US, there are several relatively cheap sources of 24V power transformers that would only need four diodes, a capacitor plus a few parts to make a voltage regulator to tame the input voltage (LM317 is quite versatile and can even perform current limiting and high output current applications). Look for the typical 40VA transformers for HVAC and house alarm systems. Forget about doorbell transformers, which are probably too weak for a soldering iron.
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Offline br4n_d0nTopic starter

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Re: Power Supply: Build or Buy?
« Reply #83 on: May 16, 2023, 09:47:50 pm »
 :popcorn: Well, I either made a good deal or a very expensive (for me) mistake. I'll see when it arrives.
 

Offline james_s

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Re: Power Supply: Build or Buy?
« Reply #84 on: May 17, 2023, 12:52:54 am »
What did you get?
 

Offline br4n_d0nTopic starter

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Re: Power Supply: Build or Buy?
« Reply #85 on: May 17, 2023, 02:40:55 am »
A beat up BK Precision 9206 with the hope I can get working properly; it' a gamble :scared:
 

Offline james_s

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Re: Power Supply: Build or Buy?
« Reply #86 on: May 17, 2023, 02:47:17 am »
That's a beast of a power supply. The single output and high voltage makes it quite a specialized instrument but I can see it being useful. Hopefully you can find a schematic for it, not surprisingly there isn't one in the manual.
 

Offline br4n_d0nTopic starter

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Re: Power Supply: Build or Buy?
« Reply #87 on: May 17, 2023, 02:57:44 am »
Yeah, it fits my needs perfectly and more @ 150v/10a/600w so I hope it works out.
 

Offline br4n_d0nTopic starter

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Re: Power Supply: Build or Buy?
« Reply #88 on: May 19, 2023, 09:51:00 pm »
F**K YEAH! This thing seems to work fine ;D  this gamble paid off for the price I got this thing.

I tested the voltages from the millivolt range all the way up to 150 volts, tried testing the current which was a little more difficult for me, but seemed to be fairly close on the same amperage range all the way up to 9 amps where I stopped because my meter blows a fuse ~10 amps. The VFD is in mint condition and very bright and scrolled through the menu to test a couple other things. All seems good except for a missing encoder knob, some dings on the metal case, and a little dirty, but I can clean that up. :phew:
 

Offline james_s

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Re: Power Supply: Build or Buy?
« Reply #89 on: May 23, 2023, 11:47:09 pm »
Always nice when that happens. I've bought a surprising number of untested as-is things and even some "not working" stuff that turned out to work just fine.
 

Offline armandine2

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Re: Power Supply: Build or Buy?
« Reply #90 on: May 30, 2023, 11:18:05 am »
Build or Buy ?

Buy , a few - attempt to build  :-DD

https://sound-au.com/articles/bench-supply.htm

I wouldn't want to build one if I didn't have one  :palm:

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