Considerations in a bench/lab power supply?

Question

I'm looking at adding a low-cost variable power supply to my electronics hobby bench. After years of cobbling together LM317's and LM7805's, it's about time...

Considerations:

I've found a few options which I am unsure about.

Dave at EEVBlog states in various videos (#8, #30, #166 (@04:16), #168, #272, #314) that you should look for the following:

• Multi-turn knobs for voltage and current adjustment (as opposed to pushbuttons and separate coarse/fine knobs)
• A power supply that can range from 0 volts on the low end instead of 1 or 1.2 volts
• A switch to turn on/off the load
• The supply shouldn't overshoot the target voltage when switched on
• It should have a separate mains earth ground terminal (to allow combining supplies)
• Prefer linear for less ripple and noise (though switching offers smaller size and cost for higher currents)

Of course some factors depend on the intended use, some depend on preference, and some depend on budget.

(My intended usage is primarily microcontroller projects (3.3V-5V, <1A), automation and control projects (solenoid, stepper motor, etc) (12-24V, <5A), and low voltage lighting projects (12-24V, <3A). Budget ideally < $300.)

I asked earlier about the last point, linear vs switching, in a previous question. Olin convinced me that the disadvantages of a switching supply are minor, and certainly for my application, make sense for budget, bench space, and other reasons.

Thoughts:

To touch on the other points:

• Multi-turn pots must be preference. I think they are better than single-turn pots, but I would prefer coarse/fine adjustments (or direct-entry via buttons) over turning a knob multiple times to make a larger adjustments.
• I haven't needed to work on projects below 3.3 volts, but I am mindful of the pico-power AVR micros, which can run at 0.7V. Certainly a supply that can go below 1 volt would be useful for this.
• A load switch is nice, but not a deal-breaker.
• How essential is it to have separate earth ground? I don't think I need to combine power supplies.

Possible Supplies:

I've found a few supplies that I like, but I can't commit because none meet all the criteria.

1. BK Precision 1550, 1-36V 0-3A, $150. Concerns: Doesn't go below 1 volt. Uses up/down buttons for adjustment.
2. Circuit Specialists CSI3005X5, 0-30V, 0-5A, $130. Concerns: Unfamiliar brand and low price. (quality issue?)
3. BK Precision 1671A, 0-30V 0-5A, $220. Concerns: Unknown adjustment turns; no earth ground terminal.

Is there some other supply or brand that meets all of these requirements? What points (if any) above, are truly important?

Answer 1

BK Precision 1550

This is a switching supply.

The up-down adjustments would make this a non-starter for me.

CSI3005X5

A whole bunch of companies re-brand this unit. They're actually fairly decent. The voltage pot is a 10 turn, the current limit is button-driven in 0.03A increments.

The most common resaler of the power-supply is MPJA. It also comes in a bunch of voltage and current ranges: 0-30V 5A, 0-60V 3A, 0-120V 1A.

One thing you can't see in the pictures is that the unit has a set of screw terminals in parallel with the output banana jacks, below the cover plate labeled "EXT OUTPUT". If you need more permanent connections, you can use the screw terminals.

The schematic for the whole supply is available. This makes it enormously more repairable (and hackable) then ANY of the others.

BK Precision 1671A

The funky extra output connections on this make me nervous (speaker terminals? really?).

I would guess that the potentiometers are single-turn, both from the artwork on the case near the knobs, and the fact that it does not mention multi-turn knobs, as that's normally a significant selling point at this price range.

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On the whole, If I had to choose from the supplies listed, I would wholeheartedly recommend the CSI3005X5, more because the alternatives are considerably worse.

Anyways, I would say that even if you don't think you need a floating output power supply (what you really mean when you discuss a separate earth terminal), you almost certainly will find it useful in the future, so I think you shouldn't dismiss it. Just being able to string multiple power supplies in series for higher output voltages is tremendously useful.

Answer 2

Here is the list of the generic china ones that are sold on Amazon under the names Mastech, Elenco, Sinometer and others.

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$185 Mastech TRIPLE LINEAR DC POWER SUPPLY 30V 5A HY3005F-3

• Dual adjustable outputs: 0-30V and 0-5A
• Fixed output: 5V and 3A
• Line regulation: CV <= 0.01% + 2 mV, CC <= 0.2% + 2 mA>
• Load Regulation: CV <= 0.01% + 3mV, CC <= 0.2% + 3 mA
• Display reading accuracy: +/-1% for voltage and +/-2% for current

Having the extra adjustable power outputs are convenient. They can be connected independently or in series or parallel to allow for higher amperage or voltage if needed.

The disadvantage is that the pots are all single turn, so it's hard to get very fine changes. Although you can replace them with 10 turn ones.

Also, the voltage and current displays come in LED (as shown in the picture,) or LCD.

As I mentioned in my other answer I have this one and it is pretty nice and the extra outputs come in handy.

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$130 Sinometer HY3005D Variable Linear Lab Power Supply 0-30V 0-5A

• Adjustable outputs: 0-30V and 0-5A
• Input voltage: 110V AC and 220V AC switchable
• Ripple noise: CV <= 0.5 mV RMS, CC <= 3 mA RMS

Coarse and fine control for both current and voltage outputs.

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$80 Mastech HY1803D variable dc power supply

• Adjustable outputs: 0-18V and 0-3A
• Line regulation: CV <= 0.01% + 1 mV, CC <= 0.2% + 1 mA
• Load Regulation: CV <= 0.01% + 3mV, CC <= 0.2% + 3 mA
• Ripple noise: CV <= 0.5 mV RMS, CC <= 3 mA RMS
• LCD reading accuracy: +/-1% for voltage and +/-2% for current

Just a very cheap adjustable unit that doesn't take up much bench space.

Answer 3

I just order a KORAD KA3005P - Programmable Precision Variable Adjustable 30V, 5A DC Power Supply from Amazon.

I watched Dave's Review/FAIL video of it and then watched the follow up video and a follow up video by Charles Holtom from TrioSmartCal . For ~$100 I thought it was worth giving it a try.

From SRA

Features:

• Compact Design
• Dual 4 Digit LED Displays
• Digital Controls
• Output switch control
• Switchable between 110v and 220v
• 4 sets of parameters can be stored inside for fast recall
• Keyboard Lock to prevent accidental changing of set parameters
• Circuit protection for over load, short circuit and over temperature.
• Automatic switching between mA and A display
• Quiet variable speed fan
• 2 Year Warranty!

Operating Conditions:

• Input voltage:110V +/- 10% switchable to 220V +/- 10%
• Frequency range: 50- 60Hz
• Operating temperature: 32- 104 F (0- 40 ºC)
• Operating humidity: < 80%RH
• Storage temperature: 32- 158 F (0- 70 ºC)
• Storage humidity: < 70%RH

Stable Voltage:

• Output Voltage Range: 0- 30V Continuously adjustable
• Setup Resolution: 10 mV
• Setup Accuracy: <0.05% +20 mV
• Ripple: < 1mVRMS
• Read back Accuracy: 10 mV
• Temp. Coefficient: < 0.1% + 10mV
• Read back Temp. Coefficient: < 100 ppm+10 mV

Stable Current:

• Output Current Range: 0- 5A Continuously adjustable
• Setup Resolution: 1 mA
• Setup Accuracy: <0.1% +3 mA
• Ripple: < 3mARMS
• Read back Accuracy: 1 mA
• Temp. Coefficient: < 0.1% + 5mA
• Read back Temp. Coefficient: < 100 ppm+5 mA

This power supply seems like it should be mentioned when considering a bench power supply.

Answer 4

If you don't mind something old, and affordable, a Tektronix PS503, or two, or three, or four, in a TM50x mainframe fits the bill perfectly. Two channels, 20VDC each, can be put in series, current limiting, no overshoot on turn on, control down to zero, ground available, regulated, ... Everything you asked for. And you can add a DM50x to monitor it with backplane connections to economise on front wiring.