Asked — Edited

Power Supply Reference Thread

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I'm making this thread to gather all the power supply references from other threads into one, neat and tidy thread.

Power supplies:

12v car PC power supply:

This gives you 12V, 5v, and 3v at high amperages, which will power sensors, servos, and lots of lights.

Standard PC Power Supply:

Can be found everywhere! And if you want cheap, go to eWaste and pick out one for free-$20! Just get a high Wattage supply.

Courtesy @Steve_G from @fxrtst's Power supply thread:

"I had a bit of a search for you, and came up with the following fixed voltage supplies which was all from one website called TCR Electronics and are all under 100 bucks. Searching other sites pretty much came up with the same makes and models. The ones I've linked to are the best of the bunch that I think meet some of your requirements. I threw a couple of 20 amp supplies in as well in case anyone else is looking...

7.5v 40 amp 345 watts 215x115x50 $44.80 for 1 to 9 units (cheaper after that).

7.5v 40 amp 300 watts 199x105x41 $76.50

7.5v 20 amp 150 watts 199x99x50 $43.90

7.5v 20 amp 150 watts 199x99x30 $36.90

7.5v 32 amp 240 watts 190x93x50 $50.90

And the smallest I found at a reasonable price, but at 20 amps...

7.5v 20 amp 150 watts 159x97x38 $47.70

Anything smaller in the way of form factor, and you're looking to pay out at three digit figures. The one other plus about this website is that they do bulk buy discounts too."

Courtesy @Steve_G from @Askwpccoach's "How Can I Provide Continuous Power To Jd From An Ac Outlet Or Battery That Will" Thread

"So a 7.4 volt, 20 amp power supply is what you will need to have JD working at his best along with a female mini deans socket. This switching power supply is a good example of what you would need, although if you look around, you can find cheaper power supplies. "

Courtesy @Mathprof from his "Usb or Ac-Dc Conversion as a Lipo battery replacement" Thread

"Ok, so a 20 amp supply is a good target. Just looking around a little, I found this:

P/N: RSP-150-7.5 7.5vdc Power Supply Approx Power: 150 Watts Max Current: 20 Amps Enclosed 1U low profile 30mm, built-in active PFC function, built in constant current limiting, LED indicator for power on, adjustable output voltage, and universal AC input range: 85~264vac. Dimensions: 199x99x30mm More Info, Quotes, Purchase $36.90 ea."

As for Tips, Give out your own! Post them below! More power supply references? Add them below following the numbering sequence.(Ended at 5)

Now you can reference one thread to give an answer instead of multiple ones with many posts to sort through.


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Nice combo thread, and a great idea having this kind of info all in one place. Also, thanks for the acknowledgement.

6. Something that I think is relevant to EZ-B power is the following that was posted by Jeremie at EZ-Robot...


I know it has floated around the forum that the digital power pins can handle 5 amp per digital pin, but that's not the case. It's max of 2 amps per pin and a combined constant amperage of 5A for all the digital power pins. While you can have a spiked (pulsed) current up to 20A, the ez-bv4 is only rated for 5A of constant current.

If you find you are drawing much more than this we would recommend externally powering your motors directly from the battery power supply to the motor drive electronics (it's good idea to add a fuse in between them).

Servo power is best to come from a 7.4V LiPo battery (with protection) but you'll need servos that are rated for 7.4V, if you don't have servos that can handle this high of a voltage you'll need a voltage regulator.

The thing to watch out for with regulators is how much current draw they can handle, like most motors, servo motors can draw huge spikes of current when first initialized so you'll likely want to double or triple the current rating of your voltage regulator compared to the operating current of the servo so you don't experience a brown out. Brown outs result in the voltage dropping below a certain level and will either effect the operation of the servo or the electronics controlling them.

EZ-B v4 Data Sheet


Nice Tech! Thanks for getting this together. Switching power supplies are far better than linear converters. However, it's important to know there are many different switching power supplies that will deliver both the input and output voltages you'll be needing. The amount of amps the PS will supply is also AS important. If your PS is being asked by your motors to deliver more amps than it can supply the PS will shut down. Case in point; I have a 120vac to 12vdc switching power supply that is rated at 12 amps. I tried to pull 30 amps through it from a car windshield wiper motor and it quickly turned itself off. No harm done thankfully because it had a protection circuit. A simple power cycle got it running again.

So, if you're shopping for a switching power supply please do your homework. Find out what your max amp draw will from the motors you're using, what voltage (3.3v, 5v, 12, exc) and voltage type (AC or DC) they need and what voltage and type your plugging the PS into. This is the only way to choose the proper PS you need.

Finding one to buy after you know your numbers is another issue. I like to use Mean Well power supplies. Very well built and they offer a wide selection. Here is the master list of Mean Well AC-DC converters:

One more thing; @Steve mentions above and others have echoed that Lipo batteries are best for servos. I'm still not a believer in that theory. I don't have a single battery on my full size B9 Robot and have many High Power, regular and micro servos and a number of big DC motors. I have never had an issue with brownouts when any of them have started up or while they run. The trick is to get a PS and wiring that will handle the MAX power draw. Also as Steve mentioned correctly above, when supplying power to a big motor or servo that it's important to bypass the EZB and power the motor directly from the PS, Do not use the EZB as a power conduit.

Have Fun!:)

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Hey Dave.

I just wanted to say, although LiPos are great for powering servos, I don't actually use them much now, and use NiMH packs as you can charge them while still operating a device (depending on amperage) which are great for low power "monitoring" modes such as security. As are bench supplies which I'm all for as well, as there are lots around that deliver good amperage for a great price. Great for static robots such as your B9 and for bench testing.

I haven't got around to it yet, but after helping Will out looking for a supply for his Alan head project that you may remember, I discovered very reasonabley priced mains power supplies delivering 20, 30, 40 amps and plan to get one myself for testing.

You also make very good valid points about switching supplies too. Very useful Information to know.:)


Sounds great @Steve. I guess it really depends on your application and how you want to be using your robot.

Another thing I've learned about these power supplies is that as you choose units (within a curtain model number) with higher output voltages your available amps goes down. So you will have one unit that delivers 7.5 vdc and provides 40 amps and another that will deliver 12 vdc and only be able to supply 27 amps. You would have to go to a different model to get the higher amp capacity and it would probably be physically larger and more expensive. Like everything else in life. :P



I have two of the Mean-Well power supplies arriving today...let you know how it goes.


Often desk top robots are built and the need of a battery to power it seems un-needed, and a power supply would work best. Almost everyone has an old pc around. Most pc power supplies can supply 12vdc @ about 20 amps. I want to know how to get this supply to run an EZB v4 and EZ robot servos and not burn them out. If a regulator is needed, could one of you electronic guru's advise us what to use or how to make one.

Ron R

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A 12v 20 amp supply would run an EZ-B no problem, but the EZ-Robot 7.4v servos connected to that 12v EZ-B wouldn't like it very much. You could power each servos through a drop down buck converter or linier regulator with an output voltage that matches the servos, but more importantly, the amp output would have to match too, to handle the servo inrush current and maximum holding torque. Supplying 20 amps to a servo is not a problem, as the servos will only take what current they need.

When using a step down converter or regulators, as well as output voltage, is the amp output too. You could be supplying 12 volts and 20 amp input supply through a 6 volt regulator for example, but if that regulator is rated for 3 amps output, that's all your servos will get... 3 amps which may not be enough for a servo. So you would need a buck converter or regulator that matches you voltage needs, but with a much higher current output.

In the first post in point 3, there are some links to some good 7.5v power supplies with high amp outputs.

One think to keep in mind, is when using a power supply, a linear power supply can stubble to supply their specified amperage which is a limitation to how these supplies are designed. Digital switching power supplies like the one I linked to below, and like the ones some computers use, are far better.

Or for a high amp regulator..,


Another thread probably could have been made for this, but to answer your question, a pic outputs 12v, 5v, and 3v. Any servo usually uses 5v or 7.4v. ez-robot servos use 7.4v. So, you will need to step down the 12v rail. Use a buck step down converter, but MAKE SURE IT SUPPLIES ENOUGH AMPS. A servo will use a around 1 amp max, so make sure if it's a 3 amp converter, you have a max of 3 servos on it. You can connect multiple buck converters to the 12v rail, just don't exceed the 20amps or so it can provide, or the power supply will cut out, or burn up.

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1 amp may be enough for the micro servos sold in the shop, but I believe the EZ-Robot HD servos can draw 3 amps and possibly even more, due to the inrush.


With all due respect to you guys, you really need to be careful when giving advice on power consumption and recommendations. Steve is closer to the truth but some HD servos can draw more than 3 amps. The best advice is to look at the specs of the serov(s) you are going to be using and get a power supply or power converter that will deliver at least 1/4 more amps than the max amps your motors need, whether they are simple DC motors or servos. If your power supply or converter will be powering more than one motor then simply add up the total max amp draw that the specs state of all motors and get a power supply that will supply at least 1/4 more the that.

As far as voltage; a computer power supplies will usually supply both 12 & 5 vdc and sometimes 3vdc. They are usually rated in Watts and you need to use Ohm's law to do the conversion to find out what they will be able to supply in amps. There is lots of info and youtube vids on the internet on how to both use Ohm's law and to use a computer PS as a power supply. Simply do a Google search on each subject and there will be a ton of links available to study and educate yourself. One thing to be aware of is how quickly a computer PS will be able to supply an inrush of a voltage demand. I've read that computer power supplies are slow to supply the demand of a DC or servo motor and you may have trouble with brownouts or even see the PS shutdown. I've not personally seen this issue but it's something to keep in mind when you're designing your power circuit.

Good luck and have fun! ;)


My next Project has a mix of voltages needed to run servos, sensors, etc. (3 vdc, 5 vdc, 12 vdc and 7.2 vdc.). I understand the 7.2 vdc for the servos is the odd one for the supply I mentioned. I assume I will get a regulator for the servos to fix that issue. Has anyone heard from @ Jsterne ? Wasn't he building regulators at one time?

Thanks to all for the info and feedback. I will dig deeper to meet my power needs.

Ron R


Wasn't sure whether it was best to start a new thread for this or not -- Please let me know if that would be more appropriate... (But i think this {kudos to Cardboard Hacker and all those referenced} is a good place for the pictures and information i'm posting below as well as any feedback it may garner) I attempted to follow the advice provided here (and in "Amps, Volts, Power Converters and Power Supplies" and other threads etc.)

I needed a power supply for a robot with 10 EZ-Robot servos, so i bought the Mean-Well RSP-150-7.5 7.5v 20 amp 150 watts 199x99x30 $36.90

I wired it as shown below:

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For the AC power cord i snipped off the end of a computer power cord (Note: altho i read somewhere that the 'brown wire should be hot and the blue neutral, my multimeter said otherwise and i believed it).

I connected the barrel jack to the white and black via solid-core copper wire (taken from Romex 14/2 cable) as shown below:

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(Note: i had a 12 gauge Romex wire but it was too big for the barrel jack)

And when plugged in, the barrel jack shows 7.4V as shown below:

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The EZB is working, it connects to wifi and I'm able to move the servos and use them in scripts.

Still, I would like to get feedback from any veterans who have time to comment about this setup. I'm not a hardware guy, so i expect that there is room for improvement, ha.

Thanks -Richard 'twitch' R.


may i ask ,does the power supply have an on/off swiths?

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One thing I wanted to point out for you which is something I touched on in step 7 Multimeters in my tutorial you linked to,. You quoted...


For the AC power cord i snipped off the end of a computer power cord (Note: altho i read somewhere that the 'brown wire should be hot and the blue neutral, my multimeter said otherwise and i believed it).

Brown wires in AC are indeed Live or Hot and blue is Neutral (and if present, green/yellow is Earth). But here’s the thing. AC, by definition, is alternating current, so it is not polarised and current flows in both directions. Basically this means that you can actually swap the wires around and most of your AC devices would still work with no damage. This is why your meter said the opersite to what you read about wire colours. But with that said, not only is it good practice to use brown as Live and blue as Neutral, but there is a safety aspect too.

For an example, I’ll use a table lamp with an in-line switch. Some AC appliances, like lamps, have a switch on just one of the two wires, usually the Live wire. The outlet has a Live and a Neutral wire - the Neutral wire is connected to ground somewhere, either at the local sub-station or on the street outside your house. The Live wire is at 120V US or 240V UK, compared to Neutral.

In the lamp itself, the Live wire of the light bulb socket is at the bottom, and the Neutral lead is on the sides. Sticking your finger in a Live socket (not recommended) with the correct polarity it is much more difficult for someone to accidentally touch the Live wire or terminal.

So when using a correctly wired and polarised table lamp, switch and plug, there is a guarantee that the switch will disconnect the supply voltage on the Live side of the lamp. If the polarity is reversed, then the entire appliance is still live and energised even when it is off, and could be dangerous if you were changing the bulb and happened to touch the metal side of the bulb... as you will get seriously zapped.

DC (direct current) has to be connected the CORRECT way only.

So just for good practice, I’d suggest swapping your blue and brown wires to where they should be on your power supply (as long as the mains plug is wired correctly too).

Hope that helps.:)


Hi Steve G. Thank you for the explanation -- yes that is very helpful and I did not fully understand that set of issues, so I have a better handle on it now -- much appreciated! However, my conclusion is still that the cable itself was mis-wired in terms of the blue and brown cable-color, and I had a bunch of measurement photos to show you in order to try to prove it, then I remembered, hey I still have the severed plug -- here it is:

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Blue=LiveHot -- What do you think?

And Hi to Nomad 6R too -- this power supply does not have a switch (prolly you were thinking along these same lines as Steve G?).

Thanks for your feedback and any other comments are welcome!

Richard 'twitch' R.


this is a great topic.learn alot thanks rregister and steve G

here is a link for all kinds of switshes wires cables.these are up to 12 volt.

on/off swiths

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Hey there Nomad 6R Looks like this inline toggle switch supports 0-2A current and i believe the servos will draw much more than that for short periods during inrush. I have put a simple plug strip with on/off switch on the AC side for the power supply and that seems to be working so far. best regards -Twitch


An update about using this Mean-Well RSP-150-7.5 supply -- It works reliably on my 10-servo robot, but using the power supply on my JD i was experiencing a brown-out once and a while (approximately once or twice a day), and this typically resulted in JD disconnecting from my wifi network. I tried the solution posted by Jeremie and DJ (in post #15 of using two 1Farad 2.5V Aerogel caps in series and that seems to have solved the problem: i haven't seen a brown-out since. - Thanks for that thread and i hope others find this helpful. -Richard 'Twitch' R. Here are some photos:

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