Author Topic: OT: Power supply procedure??  (Read 520 times)

Offline 10KPete

  • Full Member
  • ****
  • Posts: 1564
  • Nordland, WA, USA
OT: Power supply procedure??
« on: January 10, 2019, 12:54:05 AM »
I have a linear DC power supply, 0-30 vdc , 0-5 A that came with some strange instructions. It's made in China, bought from a USA seller on Amazon. It's a nice looking unit that will work in CV or CC mode.

The instructions are sort of Chinglish but not too bad. The instructions say that the load must not be connected to the supply until after the supply is turned on..??? It says that to connect the load to the supply and then turn on the supply will damage the supply..???? Instructions warn specifically against inductive loads like motors being hooked up before turning on the supply.
Does all this mean that I need a separate switch between the power supply and the load?

I'm no electronics wiz but that doesn't seem right. Decades ago I seem to recall that such a procedure was unheard of. We connected the load then turned on the supply. Now, those were the "pre-transistor" supplies. This one is all modern electronics.

Can anyone shed some light on this question? I bought the supply to use for electro-plating experiments.

I have a modern "transistor" linear DC supply that works with the "old" method of hooking up the load then turning on the supply but it's just too light for what I want.

If this "procedure" is necessary then I need to return the supply. Then there's the problem of finding one without this limitation in operation. But how? What words should I be looking for?

Thanks,
Pete
Craftsman, Tinkerer, Curious Person.
Retired, finally!
SB 10K lathe, Benchmaster mill. And stuff.

Online crueby

  • Full Member
  • *****
  • Posts: 9014
  • Rochester NY
Re: OT: Power supply procedure??
« Reply #1 on: January 10, 2019, 01:05:05 AM »
Sounds like the supply on the grizzley mini mill, can only turn on the power if the speed dial is all the way down to stop, or it pops the fuse, even with no liad on the tool. Means no way to keep same speed between runs. The Sherline lets you flip the power switch on with the speed dial at any position, very handy.


I cannot shed sny light on the internal circuit, just that it is a cheap way to do it. I have a good quality variable supply from my old job that can handle any startup combination, but that one was expensive.

Offline AOG

  • Full Member
  • ****
  • Posts: 672
Re: OT: Power supply procedure??
« Reply #2 on: January 10, 2019, 03:06:37 AM »
It sounds like theyíre using a switching power supply. They are sensitive to large inrush currents especially before they have stabilized. Most good supplies of that type have separate switch (and internal relay) for controlling the output. That allows you to turn it on and it to stabilize before the load switch is allowed to connect the load. Are your sure that your supply doesnít have a load switch?

Tony

Offline 10KPete

  • Full Member
  • ****
  • Posts: 1564
  • Nordland, WA, USA
Re: OT: Power supply procedure??
« Reply #3 on: January 10, 2019, 03:30:02 AM »
No load switch. Just the power on switch.

Read the 'book' twice more before I found the words ".....is a kind of switching power supply with LED display."

That's the only mention of 'switching' anywhere. Nothing on the unit, in the description, nuttin about switching.

Sooo, I'll contact the seller and straighten it out.

Thanks guys, if it was simple everyone would do it...

Pete
Craftsman, Tinkerer, Curious Person.
Retired, finally!
SB 10K lathe, Benchmaster mill. And stuff.

Offline AOG

  • Full Member
  • ****
  • Posts: 672
Re: OT: Power supply procedure??
« Reply #4 on: January 10, 2019, 03:45:32 AM »
Just for your information a switch mode power supply uses a form of pulse width modulation to control the voltage. To do that they have a series of FETs switching on and off (hence the name). They dump that output across some filtering and there is your DC. Itís those FETs that are extremely sensitive to current spikes in parts of their opeating range. It takes the control circuits a while to stabilize the circuit inside the range that they can handle the load. Thatís why they want everything stabilized before you apply a load.

Tony

Offline 10KPete

  • Full Member
  • ****
  • Posts: 1564
  • Nordland, WA, USA
Re: OT: Power supply procedure??
« Reply #5 on: January 10, 2019, 04:38:37 AM »
Thanks Tony! Somewhere in the deep recesses of my mind there's a memory of that sort of thing but it's been 30 years.... :o

I've contacted the seller; I'll return the unit.

Now to find what I want/need.....

Pete
Craftsman, Tinkerer, Curious Person.
Retired, finally!
SB 10K lathe, Benchmaster mill. And stuff.

Offline Don1966

  • Full Member
  • *****
  • Posts: 5998
  • Morgan City, LA (Along the Gulf Coast)
Re: OT: Power supply procedure??
« Reply #6 on: January 10, 2019, 03:30:46 PM »
Pete I would return the supply and Tony is right itís probably a switching power supply and not a linear one. A linear supply would be big and bulky because of the transformer size. The CC And CV modes are constant current and constant voltage mode of control. In my experience with switching power supplies you should not have to do what they are saying. Because a well designed supply will produce what itís designed for and be durable enough to withstand its rating. You have bought a cheap chinese made supply so donít expect much.

Regards Don

Offline gerritv

  • Full Member
  • ****
  • Posts: 551
  • St Catharines, ON
    • Gerrit's Hobbies
Re: OT: Power supply procedure??
« Reply #7 on: January 10, 2019, 03:45:30 PM »
A friend of mine has gone through 4 power supplies in a year, mostly his fault. (Hooking up the load before turning on in fact). One had a transformer inside, it was resurrected. The others resisted.

But:
the last one he bought is a switching type, very light and with weird interface use of the same knobs as on previous supplies. It blew as well due to hooking the load up first.

My suggestion is to buy one based on weight, if it is heavy then there will be transformer inside. :-) From the front they all look the same, weight is the differentiator. e.g. this one is 10 lbs https://www.ebay.com/itm/Velleman-PS3003U-0-30V-0-3A-Bench-Supply/160834812530

Gerrit
Don't confuse activity with progress