Affordable wall wart that provides more than 3A?

Greetings,

I’ve currently made an arduino project that powers 4 servos (this will expand to 6 servos and include a display modeule however in the future) that works off of 1x 9V battery (powers AtMega328) and 4x AA batteries (powers the servos). This all works fine, however I wanted to make changes so that I can power the servos off the mains electricity so I don’t have to maintain the AA batteries (as it means I need 4x AA alkaline batteries or 6x AA NiMH batteries to power this many servos with adequate current).

(I’ve attached what I believe my circuit should resemble at the end of getting the circuit changed for using with a wall wart. Please note, I’ve moved the AtMega328 chip from the Uno board to the breadboard as in theory I’ll be doing this at the end of the project).

So I begun looking into how to do this and I figured I could get a wallwart that could provide 5A-6A of current (this is because the servos can draw up to 1A each depending on the load; unlikely to need that much but of course you should try to budget for this eventuality) and 6V.

I also looked into DC-DC switch converters to step down the voltage if need be from the wall wart (link below to one of those I found). Introducing a DC-DC converter seems to add a bottleneck where I can only draw 2A at most without a heatsink, so this raises an issue I’ll probably put in another post.

http://www.ebay.co.uk/itm/DC-DC-Buck-Converter-Adjustable-Step-Down-Module-LM2596-Power-Supply-1-5v-35v-/310499267197?_trksid=p2047675.m1850&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D11%26meid%3D3361929549708454418%26pid%3D100011%26prg%3D1005%26rk%3D2%26sd%3D120995611839%26

Unfortunatly, I’ve not had uch luck in finding a wall wart that can supply adequate current, the closest I could find was a laptop charger but that was more money than what I wanted to spend and also seemed a bit overkill.

That’s the background spiel, finally, on to the questions!

  • Can anyone reccomend a wall wart that would provide at least 3A (the closer to 6A the better), at least 6V and is also not too pricey or bulky?

  • I havent got any available wall warts around the house, but I have been looking at ones being used and am left slightly confused. Most of my wall warts only have an output of 2A at the very most (the majority are actually 1A or 1.5A) and they power things I would consider quite power intensive. Am I just completely overestimating the max current on the servos or is there a trick I’m missing to boost the current in the circuit without having the power supply provide the current?
    I did check the current on the multimeter when each micro servo was under a heavy load (standard servos wil lbe added once they arrive in the mail) and it came to around 800 mA.

  • If you have multiple power supplies in a circuit you need to connect the grounds, if I do this with a battery and the mains power, will this cause issues (i.e. cause the battery to explode!)?

Thanks as always, I really appreciate any help anyone can provide this newbie :slight_smile:

A servo only uses power when it moves or is holding it's position against a load. Depending on how you plan to use these servos would help you plan the minimum power requirement.

I would try with a 1.5A or 2A power supply if you have one available. If it doesn't work, you can upgrade later.

And the grounds must be connected. Nothing will explode. I would also consider not using the 9V battery. Those things don't last very long and half the power is wasted in the voltage regulator.

Any atx power supply will provide many more than 3a, at a variety of voltages. And they typically come free, if you have a computer laying around your house.

or a laptop power lump. Usually capable of around 5A at 17 volts or so

Finding a 6 volt power supply at that amperage is going to be next to impossible; that isn't a very common power supply voltage. Better would be to go for a 5 volt supply, as there are many of those available in the amperage range you want. As noted, a PC power supply could be used, but most need a certain amount of load on the 5V rail to regulate properly, so keep that in mind (I doubt that the servos will be enough, unless they were all on and moving constantly with loads). You can also find standalone or open-frame 5VDC power supplies fairly cheaply through various surplus sources. Other than that, your only other possible option would be an adjustable bench power supply of the proper amperage capability; but those don't typically come cheap, either (especially once you go beyond 2-3 amps - if it is fully adjustable in voltage and current).

If you can't find one that's good enough, use two that can do 1/2 the job each.

http://www.mpja.com/5VDC-4A-Regulated-Plug-Supply-Openpeak/productinfo/18520+PS/ I'm using this one now for my big scoring machines & 2 remoted display indicators. I use 5V to 12V boost convertor from Pololu to make 12V for LED strings, and to power the remote indicators.

You will get better servo performance at ~6v than at 5v. You might look for a higher voltage power supply and use a UBEC voltage regulator to get the desired voltage for the servos.

Thanks everyone for your suggestions and responses, I appreciate you all taking the time to respond.

The responses certainly clear up why I haven’t been having much luck finding a 6v wall wart with this ampage; they simply don’t really make these at these voltage and current levels :slight_smile:

ATX power supplies are pretty much a no-go for me as that’s far too bulky for my liking on this particular project. I appreciate the suggestion none the less.

Ideally the wall wart or mains supply I use will have a voltage of 6V or higher, for the reason zoomkat raised; that I would get better performance out of the servos. I have no problem adding a DC-DC regulator to bring the voltage down if need be as these modules look fairly cheap on ebay (for instance a 12v wall wart with a high current rating is fine as I can use a DC-DC regulator with that).

I would prefer keeping it as 1 power supply if possible, but thanks for the suggestion Runaway pancake. It’s a suggestion that I could use in a future project possibly as it’s something I’ve never really considered using in this way before.

The closest match I guess is the laptop power supply; 17v at 5A. Though I was hoping there was a way I could use something smaller, but you can’t have everything!

Even if I go with a laptop power supply and have the voltage/current I need from there, when I use a buck converter to step down the voltage, it bottlenecks the current down to 2A or 3A. I may have to just bite the bullet on this one and have to live with the current bottleneck.

Question Time!

  • I’ll certainly look into a UBEC’s, but from what I’ve briefly read on this, it sounds just like a DC-DC regulator or buck converter (example to one is in the original post). Is that the case or is there a difference between the 2?

  • I’m also glad to hear the battery won’t explode! If I wanted to remove the 9V battery also and have the mains also power the atmega328 chip, would it be safer to use a completely discreet DC-DC regulator coming from the mains supply to step down the voltage to 5v (so there would be 2 DC-DC converters in the circuit at this point; 1 providing 6V to the servos and 1 providing 5V to the atmega328), or do you think having the voltage stepped down to 6V (which is then run off to the servos) and then using a resistor to drop the voltage further run off to the chip (a linear regulator wouldn’t work here as it’s voltage drop is 2V, so it would go to 4V if I put one here)?
    My assumption is a discreet DC-DC converter may be better as the current draw may change depending on what the chip is doing, which would fluctuate the voltage and potentially cause damage to it.

As always, thanks again for taking the time to read this. Any responses is always greatly appreciated!