### Author Topic: Power Supply Lower Volts Higher Amps?  (Read 1084 times)

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#### SydLynx

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##### Power Supply Lower Volts Higher Amps?
« on: March 29, 2023, 09:34:57 am »
Hello, everyone!

I intend to buy a double output bench-top power source.

I decided to go for a linear (safer? more long-lasting? I believe) power supply from Circuit Specialists.

They have 2 options: a linear 0-60V (0-5A), in series, which in parallel provides 0-30V (0-10A), and a linear 0-100V (0-3A), in series, which in parallel provides 0-50V (0-6A).

Which one will I need most of the two? Which one will offer me the best experience as a diy, whilst testing basic stuff etc? Do I need more voltage, or more amps?

And, whilst we're at it, could you please explain to me whether the 0-100V power supply will produce 10Amps at 30V? I know lower voltage leaves room for higher amps, but I still can't wrap my mind around the principle. In this case the 100V PS would be perfect, wouldn't it be?

Thank you!
« Last Edit: March 29, 2023, 10:15:50 am by SydLynx »

#### BeBuLamar

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##### Re: Power supply voltage vs amperage
« Reply #1 on: March 29, 2023, 09:40:04 am »
I don't think one would need more than 30VDC power source that often so I would choose the one with higher current.

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#### SydLynx

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##### Re: Power Supply Lower Volts Higher Amps?
« Reply #2 on: March 29, 2023, 10:26:39 am »

Therefore, judging by your choice, I shall understand that the amps specified at top voltage are the maximum amperage output at all voltages, e.g. even when I will run the PS (say, the series -50-0-+50 VDC one) at -12-0-+12VDC, or -30-0-+30VDC, it will still produce only 6A, right?

#### Eraldo

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##### Re: Power Supply Lower Volts Higher Amps?
« Reply #3 on: March 29, 2023, 10:53:29 am »

Therefore, judging by your choice, I shall understand that the amps specified at top voltage are the maximum amperage output at all voltages, e.g. even when I will run the PS (say, the series -50-0-+50 VDC one) at -12-0-+12VDC, or -30-0-+30VDC, it will still produce only 6A, right?

Yep. That's the max current the supply will be designed to handle.

Another example is a Variac (a variable ac transformer). It has a specified max power and voltage and they can give that power only when you use the maximum voltage. (Eg: 500w variac with a max output voltage of 250v. It can at most output 2A safely. But if you were to set it to 100V the output current would still be 2A since a variac reduces the out voltage by reducing the secondary windings lenth like a potentiometer. The thickness of the wire will not change while reducing the voltage and so the current handling of the transformer will be the same.)

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#### SydLynx

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##### Re: Power Supply Lower Volts Higher Amps?
« Reply #4 on: March 29, 2023, 11:04:13 am »
Thank you! Now I have a much better understanding of how it works, with the wire thickness example.

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##### Re: Power Supply Lower Volts Higher Amps?
« Reply #5 on: March 29, 2023, 11:34:10 am »
Unless you speak about some Hp psu's series, theses ones are a bit tricky

They say Ex: 500watts   say max at  50vdc 10 amps,  but when you go down to 25v it can or will double the output at 20 amps (still 500 watts)  ....  20vdc could be 25 amps, but not ...  like / say 5 vdc at 100amp

They have some chart explaining how they work and what you can get out of them given the voltage selection vs the current selection

some other brand do this too ...

Normally the specs of wattage are given at full power output ...

And all of theses  give 300 watts    It all depends of how you read the serial and or possible parallel values as written or specified, but sometimes we don't read well  loll

0-60V (0-5A), = (2x 30v 5 A / ea) in series,  in parallel provides 0-30V (0-10A)
0-100V (0-3A) = (2x 50v 3A / ea) in series, which in parallel provides 0-50V (0-6A)

But  for any psu in serial, the weakest of them will define the total power available    IE : if you put an 3 amp in serial of an 5 amp,  it will be limited by the lowest value / limit of the two (3amps)

In parallel  if they have the same exact voltage, they will give a total of 8 amp ...

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#### armandine2

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##### Re: Power supply voltage vs amperage
« Reply #6 on: March 29, 2023, 11:35:55 am »
I don't think one would need more than 30VDC power source that often so I would choose the one with higher current.

on the other hand may be you won't need more than 3 amps - then putting 63V across a capacitor might be harder than necessary
« Last Edit: March 29, 2023, 02:26:27 pm by armandine2 »
Funny, the things you have the hardest time parting with are the things you need the least - Bob Dylan

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##### Re: Power Supply Lower Volts Higher Amps?
« Reply #7 on: March 29, 2023, 02:17:03 pm »
They have 2 options: a linear 0-60V (0-5A), in series, which in parallel provides 0-30V (0-10A), and a linear 0-100V (0-3A), in series, which in parallel provides 0-50V (0-6A).

For lab usage purposes 60V / 5A is better than 100V / 3A, because usual requirements for lab PSU is 0-30V and as much current as possible (but higher current PSU also has higher mass and higher price).

Another point is that safe voltage level for people is about 45-60V, for wet skin safe voltage may be even lower. This is why 36 Vrms (50 Vpk) lighting is used for rooms with high humidity (such as bath room or sauna), 220V mains is very unsafe to use in such conditions. So PSU which is able to put 100V on it's output terminal is dangerous for everyday usage. It can make serious damage on heart or even can lead to death.

Also note that PSU which supports very high current (20-40 Amps and higher) also may be unsafe, because it can initiate fire and cause burns due to very high heating at short circuit, so they also needs to be carefully operated.

I recommend to use KORAD KA3005D for everyday use. Also there is a sense to have complete analog linear power supply (without digital controllers) with analog pointer voltmeter/ampermeter and good filtering for use with ultra low noise devices, bipolar output is preferred for such device, because it is often used with circuit that needs bipolar power supply for op-amps.
« Last Edit: March 29, 2023, 02:52:12 pm by radiolistener »

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#### Robert Smith Eco Warrior

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##### Re: Power Supply Lower Volts Higher Amps?
« Reply #8 on: March 29, 2023, 02:38:17 pm »
........... that safe voltage level for people is about 45-60V.......

Good.......currently screwing nuts onto my 48v battery bank

#### pdenisowski

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##### Re: Power Supply Lower Volts Higher Amps?
« Reply #9 on: March 29, 2023, 02:43:36 pm »
They have some chart explaining how they work and what you can get out of them given the voltage selection vs the current selection

I did a short video on this topic:

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#### pdenisowski

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##### Re: Power Supply Lower Volts Higher Amps?
« Reply #10 on: March 29, 2023, 02:44:43 pm »
And I also did one explaining serial and parallel operation

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#### Gyro

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##### Re: Power Supply Lower Volts Higher Amps?
« Reply #11 on: March 29, 2023, 04:13:34 pm »
The only case I can think of for 100V, or rather +50V -50V, is for working on higher power audio amplifier circuits. If that's not on the cards then 30V / 60V is more useful.
Best Regards, Chris

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#### rstofer

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##### Re: Power Supply Lower Volts Higher Amps?
« Reply #12 on: March 29, 2023, 04:17:20 pm »
The latest Raspberry Pi recommends a power supply of 5.1V 3A and that's for a complete computer system - 15.3 W.  You can run a lot of analog circuitry on +-15V 3A so why the high voltages and high currents for a bench supply?  In the age of low voltage CMOS, what would ever need 100V (two 50V outputs in series)?  There are applications for higher voltages and currents but they are edge cases for me.

The Rigol DP832 has two 30V/3A and one 5V/3A (fixed) outputs and that seems typical of bench supplies.  Beyond that, it might be better to construct a dedicated supply - audio or vacuum tube projects come to mind.

I would be far more interested in current limiting and digital readouts than very high voltages and currents.

Don't ask how the supply performs at max volts and max currents, ask how it performs at max current and minimum voltage where the linear supply dissipates maximum heat.  Make sure the supply does a credible job at 1.5V or 2.1V - these are slowly taking over from 3.3V which has just about replaced 5V and op amps are more likely to be single supply on the order of 5V, not +- 15V.

I have the Rigol DP832 and it's a very nice supply.  One day I was bringing up a Z80 project and I had the supply set for 5V and some very low current.  Good thing because I had an address conflict and there was a short on the data bus.  No worries, the voltage dropped to 0V until I resolved the error.  Once things were squared away, I upped the current limit and everything ran properly.  I really like digital control of current limit rather than shorting the output and dialing around for the limit point while watching an analog meter.

The Siglent  SPD3303X-E is a little more flexible in that the fixed output can be switch selected for 2.5, 3.3 or 5.0V.
« Last Edit: March 29, 2023, 04:25:28 pm by rstofer »

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#### donlisms

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##### Re: Power Supply Lower Volts Higher Amps?
« Reply #13 on: March 29, 2023, 06:40:23 pm »
The notes above on power are the bit the untangles it, I think.  If it's a 300 watt supply, you can have 60v at 5A, or 40v at 7.5A, all limited a bit by the particular design.  Ask the folks who made it for the details.

But to me that seems huge. My favorite supply is 20v at 500mA, and my second favorite supply is 20v at 2A. I rarely use them above 10v or 10's of mA.  They are valuable to me because I get voltages I can control down to a small fraction of a millivolt, very accurately. That's my thing.

For audio circuits, +-15v (more or less!) at well under an amp from the Siglent is usually fine.  Power amps probably need their own supply, but basic testing might get by with +-30v at modest current so I don't blow it up again.

IOW, if you're not sure what you're going to be doing, start modest, and eventually you'll know what you need for your second supply.  300W, for example, is beyond modest for most purposes.

If you do know what you're going to be doing, that will answer the question.

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#### pdenisowski

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##### Re: Power Supply Lower Volts Higher Amps?
« Reply #14 on: March 30, 2023, 10:42:26 am »
Why the high voltages and high currents for a bench supply?

We get lots of customers who want higher voltages and higher currents.  In fact, I made the photo below in response to a customer query as to whether one of our power supplies could really source 40 amps (please don't try this at home).

Keep in mind that there are many applications of power supplies outside of electronic design and test.  No matter how high of a voltage / current we support on our power supplies, we still get customer requests for even higher limits

I would be far more interested in current limiting and digital readouts than very high voltages and currents.

These are (or at least should be) pretty much standard on most modern "bench" power supplies.  In fact, I did a video explaining current limiting (constant current mode) and readback as well.  In addition to CC mode, many modern supplies have various protection modes (overvoltage, overcurrent, etc.) that will disable output once a user-defined threshold is exceeded.

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#### pdenisowski

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##### Re: Power Supply Lower Volts Higher Amps?
« Reply #15 on: March 30, 2023, 10:50:16 am »
If it's a 300 watt supply, you can have 60v at 5A, or 40v at 7.5A, all limited a bit by the particular design.  Ask the folks who made it for the details.

You should definitely look at a power supply's derating curve (see video above) before buying one - this can help you avoid the unpleasant situation of buying a power supply that can produce the desired output power, but not at the voltage and current levels that you want.

For many power supplies, the derating curve is a simple mathematical function, but -- especially in the case of switch-mode supplies -- it's still a good idea to check before buying.

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