# How to step 120V DC down to 5V?

Hi,
I'm currently making a motor controller and I'd need to step the DC battery voltage of around 120V down to 5V for my microcontroller. I'm having a hard time finding any regulators or buck converter chips that work with such a high potential. So what's the best way to step this voltage down for my application?
Thanks.

haasiaka:
Hi,
I'm currently making a motor controller and I'd need to step the DC battery voltage of around 120V down to 5V for my microcontroller. I'm having a hard time finding any regulators or buck converter chips that work with such a high potential. So what's the best way to step this voltage down for my application?
Thanks.

The very first step is to actually measure the battery voltage and determine it's real voltage and determine if it varies from that number. Second thing is to determine how much current the battery can supply. Then you have some actual parameters to use in searching for a buck converter.
Paul

Have you considered two stages of buck conversion, the first 120 down to something in the 12 to 24V range, then down to 5V. This can be accomplished for less then \$20 for a load of maybe 2 amps or less. I used two search terms: "buck converter 120VDC input" and "buck converter 120VDC input -site:amazon" the second search gave me several that output 5V.

Or use a cell phone charger to get 120VAC down to 5VDC.

Or use a cell phone charger to get 120VAC down to 5VDC.

What AC?

haasiaka:
Hi,
I’m currently making a motor controller and I’d need to step the DC battery voltage of around 120V down to 5V for my microcontroller. I’m having a hard time finding any regulators or buck converter chips that work with such a high potential. So what’s the best way to step this voltage down for my application?
Thanks.

Standard mains switch-mode supplies generally work fine from DC, as the input is a bridge rectifier.
However they may need derating for current (only half the diodes in the rectifier are used), and the voltage
required may be more than 120V (110Vac has a peak voltage of 155V)

I’m not sure how to be sure that a particular supply would be suitable, but such supplies, if of reputable
manufacture have protection circuitry for undervoltage.

Some brands may even have specifications for use from DC.

So what's the best way to step this voltage down for my application?

A buck converter, it’s the only practical way. Which is exact what the usual plug-into-wall power supplies, a.k.a a wall wort are, they just add a bridge rectifier to the front end. Note That it has to be a modern switch mode unit that is rated for 85-240 vac 50/60 Hz. It will be small and lightweight.

A 5v 1 amp unit will have more than enough capacity to power any Arduino. I buy surplus phone chargers at my local thrift shop. They are typically well known name brand high quality units. If required, you can crack the case open, remove the module and plug and then hard wire them into your unit.

Avoid the no name \$1 Chinese chargers. They’re downright dangerous.

I use a new utility knife blade and hammer to crack them open, blade in the case seam. Tap tap. tap. Flip over, repeat. It’s actually quite easy but incredibly dangerous if you’re not so inclined. Safety glasses are an absolute must. Use a fine tooth hacksaw or jewelers saw if you’re an all thumbs kind of person.

If you want the real deal, they are made, just expensive.

https://www.digikey.com/en/products/detail/cui-inc/PSK-S3-5-T/9838247

The battery will be made up of individual smaller batteries /cells.
You could tap off one of those to give say 12v.

Depending on your setup and how much power the Arduino bit uses , it may affect battery charging balance ( depending on whether the charger balances each sub battery)

Be careful too -120v can give a nasty electric shock , so I assume you know what you are doing

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