Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Benchtop DC Variable Regulated power supply advice sought

Status
Not open for further replies.

BVH

New Member
New guy here. I've now fried a couple of relatively lower cost, Chinese-manufactured switch mode Mastech 30V, 50A regulated variable DC bench supplies. The first one when I was making some connections by just touching wires together and probably caused a spike? On the advice of a friend, on the second one, installed a Schottky diode in the + output cable. I was recently testing a defective 15 Watt ballast which flickered heavily and before I could disconnect it, poof went my PS. In both cases the displays died and in the latest case, it still produces Voltage that is variable but won't sustain a load. I use the supply mainly for powering 28 Volt military spotlights and searchlights which are of the HID/Short arc type utilizing a high voltage ballast to power the gas discharge bulb.

I've been told by some that a switch mode DC PS is not really the best PS to use for running HID ballasts - which is my primary use. I don't remember what they're called but it was suggested that something like an "SDR"? the older, bigger, heavier supply would be better. I don't think "Linear" was the word they used. I want something in the neighborhood of 30V & 50-60 Amps, which, I know will require 240V input which is not an issue and I know it will probably be over $700. It needs to be variable and to be able to run in both constant voltage and constant current modes. It doesn't matter if its somewhat big and heavy as I can sit it on the floor. I found a U.S. made Lambda 40V-60A switch mode for $1200 but I'm gun-shy to get another one and end up frying it, too without knowing more about what I should be using.

Lastly, I was told that there needs to be two "diodes" used to protect against reverse power flow and "something else" (again, I was not fast enough to absorb everything said). I heard the term "blocking diode" but it looks like something that is used in solar power systems?

So I'm seeking advice on:

1. What type (and brand, if important) of Variable Regulated PS to buy

2. How to protect it.
 
Why are you testings ballasts in constant current mode? Ballasts are supposed to be fed a fixed voltage, the ballast itself is what produces the constant current. Which again begs the question why you need a variable power supply unless the input requirements of these various ballasts is variable?

Those supplies are short circuit protected so brushing the wires against each other shouldn't have killed it. The diode will protect against simple voltage reversal but that shouldn't occur, but they generally will not protect from a high voltage reverse spike which a magnetic ballast could easily generate if the output was flickering unless they're properly rated for it.

What is the PIR voltage rating of the diode you're using? If you are getting an inductive kickback from the ballasts then you definitely have to address that issue as that's likely what's killing the supplies and you'll just keep frying one after another unless you buy one that's specifically designed to deal with high energy reverse discharges from the load. The diode has to have a reverse recovery sufficient to stop the fast rise of the pulse as well as have a sufficient blocking voltage.

Describing the ballasts you're driving a little better might help.
 
Last edited:
Some of what you described is admittedly over my head but here goes. I am not using CC to test and run ballasts and my lights. I vary their input Voltages based on the input Voltage or input Voltage range of the ballast and lights. Some customers want me to test prototype ballasts at higher than spec Voltages to see how much they will take. Besides the 28V military lights I run, I test commercially available automotive headlight HID ballasts that typically have a 9V to 32VDC input range and output a max of about 125 Watts. Some are AC, some DC output. (I test them for output) I have never used the CC function of any of my supplies. I just see most of them advertised as CC/CV so included it in my post. It's a case of "wanting" and needing a variable supply. I like being able to dial in specific voltages for testing purposes. Do I really "need" it, probably no, but I want one. Who knows what else I might use the supply for in the future. I know I'm going to sound naive here but I am not sure what "PIR" Voltage rating means. I was advised to get one that would handle 50V and 60 Amps so that's what I installed. I think I have another one somewhere. I'll look for it and snap a pic.

Here's a few pics of ballasts:

175 Watt Short arc military searchlight

**broken link removed**

1960's vintage 150 watt short arc light

**broken link removed**
Ignitor for above
**broken link removed**

Marine searchlight
**broken link removed**

Typical automotive headlight ballast
**broken link removed**
 
What's the practical power range you typically work with? 30V at 60amps is 3,600 watts, that's massive yet the image's you linked are for a couple hundred watt units.

I'm not sure what you mean by SDR, there really are only two basic types of power supplies and that's linear and switch mode, at least for regulated units. I'm still scratching my head trying to figure out how you blew those two Mastech supplies.
 
I have two 28VDC, 16A helicopter lights I'd like to run at the same time. That's 32 amps total but I need headroom for startup, especially of the 2nd light when the first one is running. I could not do this with the Mastech 30/50. Since I'm buying another supply, I want to size it for this although my typical uses will be a much lower power levels. Startup amps for these lights for a few moments is somewhere btw 2 and 3 times normal draw during ignition and boost phases.

The "SDR". I am not sure I heard correct as the person I was talking to was on a bad wireless phone. He said they worked similar to the switch mode but were larger and heavier?

I wish I had a clue on what killed the Mastecs!!
 
Last edited:
Could the person have said DCR? Sorensen makes some big power supplies and one of their series is DCR. (also DCS) These are switchmode supplies.

Here is one that might be what you need. For other models, search ebay for "Sorensen power"

**broken link removed**
 
How about a lead acid battery bank connected to a float charger that can source a decent amount of current as well? A couple of automotive cells in series will provide hundreds of amps of starting current at those voltages.

Your inability to clarify and understand your own needs is going to kill your pocket book in the end.

What you NEED is to properly define 'common use' and the various ranges you might possible need for secondary testing.

The more money you spend the more multipurpose your tools will be, at great cost.. This is why there isn't just one tool on a swiss army knife, there are different tools for different jobs.

Could it have been a bad ballast on a 125W unit that fried the Mastechs? Doesn't matter if it can power a 3kw load.

Within the range of a few hundred watts I'd recommend PC power supplies or other such fixed voltage sources.

The bench supplies you fried are designed for electronics engineers not for throw it away use, they're powerful-but delicate and you need to know what you're doing to utilize them.

It's like a swiss army knife. There is no one tool that is perfect, so you have to use the right blend of tools.
 
This is the Schottky I was advised to use. I cut off the center of the three legs.

**broken link removed**
 
Last edited:
I don't remember what they're called but it was suggested that something like an "SDR"? the older, bigger, heavier supply would be better.
They meant an "SCR" supply which is 30 year old technology using an SCR adjusting the voltage in 60 Hz transformer. Because the magnetics are 60 Hz they are huge, so you need a fork lift to move one. They were made by Electronic Measurements Inc, and there may be some used ones around.

I am not sure they are inherently more robust, I just assume that cheap Chinese supplies probably have inadequate protection circuitry.
 
Last edited:
That diode is actually a pair, with the center pin cut off will do... absolutely nothing... literally, if you put that in line with the output or input of your supply it simply will cease to function as the diodes are in series and directly opposing no current can flow in either direction.

The PIV (the maximum reverse voltage the diode can sustain before it conducts which it's not supposed to) is only 120 volts. Meaning it will do absolutely nothing to prevent transient spikes. Either you misunderstood something or your friend does't know what he's talking about.

Being you don't even really know how you killed the previous two supplies it's very difficult to recommend anything right now.

Have you had the fried Mastech's taken a look at to see if they're repairable by someone that knows what they're looking at? I sure hope you didn't toss them, even if it's dead I'd considering buying one of those for the cost of shipping (possibly) just for parts. Even if you fried something there are still going to be a great deal of useful components from those supplies.
 
Last edited:
That diode is actually a pair, with the center pin cut off will do... absolutely nothing... literally, if you put that in line with the output or input of your supply it simply will cease to function as the diodes are in series and directly opposing no current can flow in either direction.

I don't know about that specific part, but all of the dual CC diodes in TO-220 packages I have worked with have had the center pin common with the tab. So you can cut off the center pin and use the tab as the cathode connection.
 
A nightmare unfolding . . It's pretty likely the PSUs were destroyed by a massive spike from whatever the OP has connected. Next time try a few light-bulbs (these represnt about 10x overload from the calculated operating current - such abuse should not fail the PSU - although it might shut down and need a reset.)

The suggestion of a 28v lead-acid battery is good...nothing like simulating with the real thing - but fit plenty of fuses and a HD current meter, so you can see any overload. as the pointer gets wrapped round the post.

You should be able to use NiCads too and these could be made into a fairly HD supply - but even D-cells may be a trifle too small . . . but essentially blow-up proof. The charger will need to be protected, otherwise that may go phut.
If using lead-acid batteries you may be able to "tap" the OP (ie losing one cell) this should give you 30v (6v x5) - 2 = 28 but that 28v is probably really 24v - it's just that they are rated at 28v because the charger pushes up the rails. Car batteries are cheap.

Hope that helps.
 
Last edited:
I may not have describe my hookup correctly. The PS + output cable hooks to both of the outer legs. The remainder of the + output cable hooks to the mounting eyelet. It functioned by consuming .5V from the PS output. It is still fine as it tests out fine as compared to a new one I compared it to.

EDIT Add: Just as ChrisP58 says, that is what I did.
 
Last edited:
Again BCH, that will only protect from basic reverse voltage, which honestly in your setup can't occur because the ballasts can't possible generate power. It will NOT protect from high voltage spike's like the inductive kickback from a malfunctioning driver or bulb flicker causing feedback if it's high enough, kickback voltages easily can hit a couple thousand volts, not much power but definitly enough to fry the PSU's control electronics. I've screwed up two multimeters messing around with high voltages.
 
Surely a reverse voltage spike is exactly what a balast can produce, particulalry if it's incorrectly connected, or removed during an overload . . .

The issue IMHO is that these balasts should be tested using a battery-supply . . .either a eal one or a "simulated one" . . . Where I don't get this set-up is this:_ If these are beinf tested as part of a MIl-Spect testing, the "Test Gear and Method" is almost certain to be specified in the Contract. This will usually specify a maker of the necessaary Power units, meters, etc. and if you're lucky the Method of Test will be specified.

So I'm not understanding where OP is gettng these Balasts from . . etc.

Maybe these are "Surplus" and what he's doing is checking they work, before selling-on.

Unfortunately OP has not really provided the full story - and clearly doesn't want a simple battery-supply (fused), which would be far more robust/cheaper than these SMPS.

The trouble with so-called Protection diodes as others here will Testify, . . . there is a good chance the diode won't react fast enough to protect the SMPS.

There, that's my take, FWIW.
 
I'm simply a high powered flashlight/searchlight enthusiast having fun in my garage testing automotive-type headlight ballasts which are then installed in said flashlights/searchlights. The ballasts are available all over the net incl. Ebay. Sellers and mfg's typically overrate their output so I like to bench test them to know how much power is actually getting to the bulb versus the claim.

I also directly run some 28V military lights just for fun using the supply.

But there are other uses I find for the variable PS. My hobby battery charger is capable of outputting up to 1350 Watts but it needs a minimum input of 28VDC and 45 Amps +- to reach it's maximum rate of charge. In the past 6 years, I frequently find myself running small electric motors of widely varying Voltages, powering flashlights with varying Voltages - 3.7, 7.4, 11.1, 14.8, 18.5 and 22.2. There are other uses I'm sure I'm not remembering now. It's just handy to be able to switch on the PS and set what I need and go to it.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top