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Creating a cheap 400V DC battery which does not give off any mains 'hum'? Answered

I want to create a battery which will be used for powering high voltage circuits such as valve circuits, at 400 Volts DC while also creating as little noise as possible (I want to avoid using the mains due to mains 'hum'). It needs to be a relatively cheap option if it can be helped. Any help/point in the right way would be welcome, Thank you!


Many moons ago portable tube (valve) radios were made using specially designed tubes - this operated at an anode voltage of 90 volts and you could buy a 90 volt HV battery. About the size of half a house brick.

The current available was very low but it worked (with a weight penalty).

However such beasts are long gone now and even antique examples are unlikely to retain a charge.
A standard 9 volt battery (in the UK a PP3) might offer you an alternative - BUT your going to need 45 in series.! it's not a cheap option.

Your far better off with a well regulated and smoothed power supply. It shouldn't hum.

Assuming you have tried something and found it hums at mains frequency you may even be able to add filtering to what you have to reduce any hum.

Most likely cause of hum in an existing power supply is a leaky electrolytic capacitor in the system that is no longer doing it's job.

Right 90VDC was the plate supply for the first portable vacuum tube radios..


Thank you! I can use this to further my research as well as adding it in to my report as an argument towards batteries vs power supplies.

It would be nice to know how much current must be supplied at 400 volts DC.

A 400 volt stack of batteries sounds to me to be kind of crazy and expensive (Although I have to admit it would be quiet , quiet like the dead.)  The rest of this answer discusses only electronic solutions.

The reason it would be nice to know how much current must be supplied, at 400 VDC, is because the cost and complexity of a power supply kind of tend to scale with how much power (I*V) it must supply.

Theory (regarding ripple voltage magnitude)

Load current, I, is a factor in that ol' ripple equation

ΔV = I*T/C

That's the approximate magnitude of the ripple voltage on a capacitor C being fed by half-wave rectified AC with period T (frequency f =1/T) and just from that equation you can see some possibilities for making the ripple, ΔV, smaller. These are:
  • make I, the load current, smaller
  • make C, the capacitor, larger
  • make T smaller ( or equivalently make 1/T = f larger)

And the usual way the professionals do it, is by making T small.  That is by designing an inverter that runs at very high frequency, usually f in the 10s or 100s of kilohertz.

Sorry to bore you with all that theory, but I think the point I was trying to make was that I and T are just as important in that equation for determining the size of ΔV, and it just really helps a lot if your load is one that does not draw a lot of current. If I is small, that usually helps. Small I helps in other ways too, by keeping power levels low, which helps keep components from melting, burning, or otherwise releasing the magic smoke.  Because, you know, when the magic smoke escapes, there's just no way to put it back in.

Guesses for stuff that ?maybe? could be hacked to give you 400 VDC

Building a switching power supply from scratch is probably going to be difficult and/or expensive, even if you're a genius with that sort of thing,  so it would be nice if there were some existing electronic gizmo out there with output voltage close to what you want.   Some easy to obtain circuits  to maybe try experimenting with:
And, you know, be careful where you put your fingers, because circuits like this do not like to be touched, and they can bite.

Unfortunately my lecture has made this project redundant and so I'm having to change it. Thank you all for the fantastic help and information.

To make this little more clearer, this is my final project which I have to design and build. I have to make it as a battery as the theoretical uses could be on a space craft. Thank you for all the comments so far!

So you plan to magnetic sweep, collect and accelerate ionized H2 nuclei for engine reaction through the galaxy using a 400 potential polarity difference ?.

In a spacecraft, typically a 48V DC rail from fuel cells is used. You're really asking for a 48-400V boost converter. Now, specify the permissible ripple voltage and supply current.


4 years ago

You did not specify a current.

Were I to rapidly assemble a 400V battery
I would simply  clip 44 9V batteries and put them
in a series string and put them in a box.


A well designed power supply will be able to give you what you need from a mains power source. But finding a single battery that offers 400VDC or making your own battery bank for 400VDC will not be cheap or even reasonable. Your most afordable option would be to buy a power supply that offers the 400VDC you need.

As I have to use a battery what would you recommend, ignoring the cost factor? I'm thinking of using a DC to DC switch mode converter to increase the voltage if viable.


4 years ago

  • Batteries use chemicals in an electrolyte between two metallic poles.
  • A single battery cell is only a fractional voltage never more then a few volts.
  • These cells must be combined in series with many others to provide a usable voltage.
  • Rechargeable batteries are far less efficient then a power supply costing more money.
  • A common lead acid car battery only returns half of the energy used to charge it.
  • Charging a series of cells is problematic if some charge faster then their companions.
  • Overcharging a battery cell can damage it and reducing it's storage capacity.
  • Batteries can vent corrosive and poisonous fumes
  • Compared to a power supply batteries have a short 2 to 3 year useful lifespan.
  • Finally batteries can crack and spill acid.

  • Properly designed well built power supplies are hum free.
  • Power supplies have a minimum 25 to 50 year life span.
  • Power supplies can adjust output voltage and current as needed.
  • Power supplies are solid state and have no chemicals to be concerned about.
  • Lightning traveling on mains power lines can damage or destroy even fuse protected power supplies.
  • A 400 VDC power supplies are as deadly as 400 VDC batteries.


Thanks! I can add this in to my report as an argument towards batteries vs power supplies.

If your supply hums, you're doing it wrong.