Power bricks in series?

[evilkitty]

I do not have a variable bench power supply so i was wondering if i can do this

If i take a DC 12v and a 5v power brick is there any problem putting them in series to get 17v? or using two 12v bricks for 24v

if i can do this how would i calc the amperage i would need from both bricks

[sam_sam_sam]

Re: Power bricks in series?

It going to be difficult to do this however you can put a mr16 20 watt light bulb in series with device and have some current limiting which would be better than none

As far as your other question about putting bricks together for more voltage I have not done it myself so will not comment on how to do it or weather or not it would work or not

Each brick should be at least an amp

[sam_sam_sam]

Re: Power bricks in series?

I do not have a variable bench power supply so i was wondering if i can do this

I would highly recommend you think about buying one and if you decide to buy one I would recommend buying one that has 50 or 60 volt and at a minimum 3 amps with meters for the output this is a nice feature

You could buy one with lower voltages but when I did this I would another one with higher voltage

They start with voltages like. 12 / 15 / 30 / 50 / 60 / 120

This is only an example of the type of power supply I am talking about

https://www.ebay.com/itm/1PC-KPS605D...8AAOSwljFd5HDc

[budm]

Re: Power bricks in series?

Is this related to this thread? https://www.badcaps.net/forum/showth...932#post971932

[budm]

Re: Power bricks in series?

https://www.keysight.com/main/editor...0&lc=eng&cc=US

https://www.acopian.com/acopianPower...lies-in-Series

Also make sure that either one of the output of each one of the power supplies is not connected to safety ground.

[evilkitty]

Re: Power bricks in series?

Is this related to this thread? https://www.badcaps.net/forum/showth...932#post971932

It is, but still a general question
* the mist thing is at my moms place do i do not have it with me to open it today to check the cap rating

[Curious.George]

Re: Power bricks in series?

I do not have a variable bench power supply so i was wondering if i can do this

If i take a DC 12v and a 5v power brick is there any problem putting them in series to get 17v? or using two 12v bricks for 24v

if i can do this how would i calc the amperage i would need from both bricks

The load will determine the current (amperage) that will be drawn from EACH power supply (as the load current flows through one power supply, then the other before getting to the load).

This sort of connection is often possible, but depends on the design of the power supplies and the characteristics of the load (highly reactive loads can be challenging).

I use a pair of 80A 12VDC power supplies rescued from a server, wired in series, as a "battery eliminator" for my electric wheelchair (big batteries are expensive and "die" if left unused for months at a time; power supplies are always waiting for use!).

I had to disassemble each to ensure I could isolate "ground" (0VDC) from "chassis" -- which is also connected to "earth". The 0V connection on power supply #1 is tied to "wheelchair 0V" while the 0V from supply #2 is tied to the 12V output of supply #1. If the chassis/earth/ground connections hadn't been severed, the 0V of supply #2 would be "earthed"... as would the 0V of supply #1. So, the 12V of supply #1 would be connected to "0V/earth" at supply #2 -- which would be the same as earth/0V of supply #1 (a direct short).

Try your setup with a dummy load before you risk it in a "real" use.

Also, note that you can often tweek the voltage feedback on the power supply to get some (small) range of output voltage adjustment. You have to be careful as this can change the thermal characteristics of the circuit.

[Curious.George]

Re: Power bricks in series?

Also make sure that either one of the output of each one of the power supplies is not connected to safety ground.

"Either" should be neither cuz you don't know how the load is wired wrt "earth".

[budm]

Re: Power bricks in series?

"Either" should be neither cuz you don't know how the load is wired wrt "earth".

English is my second language.

[momaka]

Re: Power bricks in series?

Curious George already answered this, but I am posting simply to confirm that I do this all the time as well - typically with small power adapters of various sizes when I need an odd voltage.

The other day, for example, I was dealing with some larger-ish NOS 50V capacitors. Before using them, I wanted to reform them. The highest voltage power adapter/brick I have is 34V from some HP printer. I also have a number of 5V, 12V, and 15V power adapters. Taking a 15V brick and putting it in series with the 34V brick provided very close to 49V, actually - just a smidgit under 50V, which was exactly what I wanted.

As CG mentioned, just watch out if the adapters are grounded. 2-pronged power adapters/bricks are almost always floating/ungrounded, and thus can be connected any which way you like. Adapters with 3-prong plugs are usually grounded (that is, secondary/output ground is tied to primary ground.)

In terms of "un-grounding" a power supply, the easiest way is usually to take a 2-prong "extension" wall adapter plug and plug the power supply into that. However, if you do that, beware that grounded PSU's often have ceramic Y2-class capacitors from Live to Ground and Neutral to Ground (for extra EMI/RFI suppression.) Leaving ground floating can result in an AC voltage equal to half of your line voltage (about 60V AC for 120V line and 120V AC for 230/240V lines) present on the ground. This voltage is limited to very small currents and will quickly drop even with a tiniest of loads to ground (so it's not dangerous to you... though if the Y2 caps are large enough, sometimes you may feel a slight "tinginess" if you touched a grounded object.) But if you are dealing with audio circuits, beware that this can introduce line hum into your device(s). Then again, grounded SMPS adapters can also pretty bad about leaking line frequency hum into audio devices.

That aside you can also usually share ground between power adapters/bricks and then use the difference in potential between the positive outputs on each adapter to get a voltage that you don't have. For example, last week I wanted to quickly test some PC fans @ 7V to see how loud they are. I don't have an adapter that outputs 7V. However, I do have a good number of 5V and 12V adapters (and always keep a few out next to my bench, since I don't have an adjustable PSU either.) Connecting the (-) / ground on the 5V and 12V adapters doesn't change their output voltages. However, I can connect the fan's positive (+) terminal to the 12V adapter's (+) terminal and the fan negative (-) terminal to the 5V adapter's positive (+) terminal. The difference is then 12 - 5 = 7V. As long as I don't overload the max current limit on each power adapter, I can safely use this. The same applies to series power adapters (i.e. don't try to pull more current than each adapter is capable of.) In my case, my 12V adapter was rated for 1 Amp and my 5V adapter for 2.5 Amps. But the fans I was testing are rated for 0.4 Amps at 12V. Thus, @7V, they were pulling even less current and not overloading either adapters.

[eccerr0r]

Re: Power bricks in series?

Incidentally, are we "overloading" or actually "underloading" it? (What current is the 5V supply supplying when hooked up in inverse series with a 12V power supply? Where is the energy going? Is this healthy for the PSU?)

No reply needed, just some food for thought...

[Curious.George]

Re: Power bricks in series?

Incidentally, are we "overloading" or actually "underloading" it? (What current is the 5V supply supplying when hooked up in inverse series with a 12V power supply? Where is the energy going? Is this healthy for the PSU?)

No reply needed, just some food for thought...

That depends on the design of the power supply.

If it is only capable of operating in the first quadrant, it simply won't work (in this configuration).

[momaka]

Re: Power bricks in series?

Incidentally, are we "overloading" or actually "underloading" it? (What current is the 5V supply supplying when hooked up in inverse series with a 12V power supply? Where is the energy going? Is this healthy for the PSU?)

No reply needed, just some food for thought...

Actually, that is a really good question I didn't think about at all, at least when doing it with power bricks/adapters.

With ATX PC PSUs, especially older ones, it's not a problem, because the 5V rail is usually either just a "tap" on the 12V rail winding in the main transformer or the 12V rail is actually a winding for a 7V rail that is super-imposed on the rectified (DC) 5V rail. The former is found in earlier group-regulated ATX PSUs, whereas the latter is considered a more modern approach that brings better group regulation at the expense of small efficiency loss. But in either case, both the 12V and 5V rails come from the same (main) transformer, so there is usually no issue with rail-to-rail connections like that - at least for lighter loads (for heavy loads, the PSU may not be able to regulate properly.)

But with power adapters/bricks, now we have two separate transformers with separate windings... so I can definitely see why you asked "where is the energy going"... or more accurately, how is the 5V brick still able to regulate and not go OV.

So because you brought that question, I'll try a small experiment to morrow and see what happens with the 5V brick's voltage when inversely connected with the 12V adapter again. I'm actually not sure how or why this works like it does with ATX PSUs. And to think I've been doing it all these years.

[eccerr0r]

Re: Power bricks in series?

Warning: not responsible for any magic smoke leakage if anyone tries it

Another hint: Many PSUs are not designed to work properly when going over voltage. And yes, the special case is where windings are coming from the same inductor...

Oh and yet another hint: (electrochemical) Batteries are better "voltage sources" than PSUs but one thing is true: there is no such thing as an ideal voltage or current source.

Gosh. All these people being taught EE 101 and KCL/KVL and they don't teach you this stuff - what happens with "real" devices ... heh.

[evilkitty]

Re: Power bricks in series?

@momaka
i really want to know this, looking forward to the results, i really do not want to kill a pair of perfectly good adapters
@eccerr0r
as if i ever took EE 101...
i was kinda asking that in my 1st post, but you worded it better

[eccerr0r]

Re: Power bricks in series?

Honestly I've never tried hooking up two independent PSUs in inverse series in order to subtract. However after thinking about the design of PSUs, well, I'm pretty sure I know what's going to happen.

I have hooked up something between +5 and +12 on a group reg/single inductor PSU. This was when I first thought of the consequences of doing such, and, well, even these have problems if it's used in the 7V fashion, just like the discrete PSUs!

Oh and well, just to be clear, this is inverse series. If you're using sequence series as the original post seems to imply, this doesn't apply - you can add two power supply voltages with the caveats above which I won't repeat here.

BTW if momaka or someone doesn't post in a few days on how to get it to reliably work inverse series without PSU hacks, a trick shall be revealed then... or anyone else can go ahead and post how to reliably inverse series if they want. I thought the answer is kind of trivial and is the reason why it (apparently) works on an ATX PSU.
The hint is: "where is the energy going?" Solving this is the solution to the puzzle and also explains why it works in a computer

[Curious.George]

Re: Power bricks in series?

The hint is: "where is the energy going?" Solving this is the solution to the puzzle and also explains why it works in a computer

Put a solenoid on a power supply. Drive it with a switch. When you open the switch, there is a "kickback" -- current flows INTO the regulated output. There is a voltage spike on the output. Why doesn't the power supply blow up due to over-voltage? Where is THAT "energy going"? I.e., current is flowing INTO the power supply's output (voltage is positive but current is negative -- instead of voltage AND current being positive!)

[budm]

Re: Power bricks in series?

Here is something to look at, analyze, and think about.
The top left shows hooking up cap that is charged to 12V to he 5V power supply.

[budm]

Re: Power bricks in series?

Hooking up power supply in series do and don't.

[Curious.George]

Re: Power bricks in series?

Here is something to look at, analyze, and think about.
The top left shows hooking up cap that is charged to 12V to he 5V power supply.

The power supply shown is only capable of operating in the first quadrant.

Imagine taking a BATTERY (pick a variety of voltages) and connecting it across the output (i.e., a cap eventually loses its charge into its load; a battery takes considerably longer -- practically forever, in terms of signal response -- to do so, given it's low output impedance!)

Replace switch with a real load. Repeat.