# High current, low voltage (~10v area) supply from standard 220v/10A outlet

I have a few brushless motors and some ESCs (Electronic speed controllers) which expects a 2 or 3 cell LiPo battery. For testing purposes I would like to have a power supply that can drive the motors - with the ESCs - so that I don't need to charge the batteries all the time.

I need 7.4v (2 cell) or 11.1v (3 cell) and it would be great to have 10A+. I want to keep down price, so can I make one myself?

• What's an ESC? Is it relevant? – Andy aka Mar 25 '13 at 13:23
• Electronic speed controller. Yes I would say it's relevant, since I use brushless motors and have no intentions of creating the control logic myself. (ofc. only relevant as contex information) – user20690 Mar 25 '13 at 13:24
• 9 V is a standard value within your range of 74.4-11.1 V. You should be able to find a 9 V 10 A supply. Are you sure you can't handle 12 V? If so, there will be a much larger selection of supplies available to you. – Olin Lathrop Mar 25 '13 at 14:41
• It is not an intervall, but two possibilities. Actually I don't know if 12V is applicable, but i guess that it could be fine. My plan, based on the answers is, to use whatever powersupply I can get and not make one myself. I'll try a 12V (which I think I have somewhere for an old computer) and hope the components can take it :) – user20690 Mar 25 '13 at 14:46

## 3 Answers

Power supplies would really be better named power converters. It sounds like what you have is a power supply that converts AC to 19V, but you need 12V, and you are thinking that converting from 19V to 12V will be easier, cheaper, or somehow better than converting from AC directly to 12V.

There are devices that will do this. The simplest is a linear regulator, which will convert the excess energy from the excess voltage into heat. This is not practical at your design current: a linear regulator would create $(19V-12V) 10A = 70W$. This is quite a lot of energy to waste, and simply keeping it cool will be hard.

There are DC-DC buck converters that can do this more efficiently, and this would be the solution if you had to power your device from 19V.

However, it sounds like the 19V supply isn't a hard requirement in your case, but rather you are assuming using it will be better. This isn't really the case. It doesn't matter if you are converting from 19VDC or 120VAC, the problem is the same: you need a power supply. However, converting from 120VAC directly to 12VDC will be more efficient, and since 12VDC supplies are so ubiquitous, it will probably be easier and cheaper to find this supply than a DC-DC buck converter that meets your specifications.

I would further advise that you purchase, rather than build the 12VDC supply. You probably won't save much money doing it yourself, and it's much safer to get one that's been designed by an experienced engineer and been put through a safety certification process.

No, in your case you should simply buy one. What you want is called a "power supply". Jameco has a pretty good selection. They probably have a model that produces the current you want at the required voltage. Since you didn't say what either of those are, there is little more that an be suggested.

• Yes I could buy one. I have updated the question to be more specific, what if I have one, but it outputs a little too high voltage? – user20690 Mar 25 '13 at 13:45
• @JacobGrevald a "power supply" could really be called a "power converter". If you have a supply that outputs too high of a voltage, then you could build another supply to convert it, but it's probably cheaper, easier, and more efficient to buy or build a supply with the output you need in the first place. – Phil Frost Mar 25 '13 at 14:19

What you think you need is called regulated power supply. It's main property is that the voltage output is regulated and it's supposed to keep it within range of values close to set output voltage even as the load changes.

Today very large number of power supplies are regulated, so the usual assumption when talking about just "power supply" is that you're actually talking about regulated power supply.

Different types of regulated power supplies will have regulation of different quality. For some purposes, very tight regulation is needed, but to power motors, there's no need to worry about how good power supply regulation is.

For motors, even a power supply with very bad regulation will do, as long as it can supply needed current.

• But I try to work with what I have. This is the reason that I asked how to down-regulate a (e.g. 19v) regulated supply, as I just thought it would be easier than building a new. Also, I'm using the ESC to control the motors, and they expect LiPO batteries. I don't know how they handle too high voltage, but they'll "cut off" on too low voltage. Anyway I would guess it would be best to just emitate the battery voltage and avoid unexpected results. – user20690 Mar 25 '13 at 14:30
• @Jacob Grevald Maybe I misread the question... Did you tell us what you actually have from equipment? If you want to build something, go ahead, but it boils down to a power supply. As for ESC, do tell us exactly what kind of batteries it expects. It will certainly tolerate the upped bound of battery voltage, so we need the number of serially connected cells in the battery. If you do have 19 V at high current (and I can't conclude that from question text), you'll (maybe) need a step-down converter. Step down converters will regulate their output and are available for high currents. – AndrejaKo Mar 25 '13 at 14:52
• It expects Lithium-ion polymer batteries. 2 or 3 cells, hence 7.4 - 11.1. I'll use a 12V powersupply, which should be fine for the purpose, since the ESC must be able to handle that (the batteries could output that when fully charged). I guess my question wasn't clear, but I've found a solution. – user20690 Mar 25 '13 at 15:00
• @Jacob Grevald Looks like it. It would be appropriate if you could edit the question to ask that, post your answer and accept it after two days. 12 V power supply would indeed be appropriate, since fully charged LiPos would be 12.6 V. – AndrejaKo Mar 25 '13 at 15:04