I know that for providing power to my breadboard with a 7805 power regulator, I was directed to use two 10uF capacitors. Is anything like that needed for my servo? Would it be a good idea even if not really required?
I apologize if I sound clueless about this, but I just fried two older servos with a 5V power adapter, and don't want to repeat the mistake.
BBX:
Do I just buy any power adapter that provides 6V and at least 2A?
An important thing to remember is that a regulated power supply will provide the stated voltage regardless of load (within a reasonable tolerance, like ±5% to 10%). In contrast, unregulated power supplies the voltage can, and often will, be significantly higher than the rated voltage until the current drawn is sizable fraction of the maximum current (sometimes half or more). For example, I once measured open circuit voltages of a little over 13 VDC an unregulated 9 VDC wall wart. That's almost one and a half times the rated voltage. So if the 5 VDC power supply that fried your servors was unregulated the voltage being feed to the servo controllers could have been around 7.5 VDC.
While the motors in servos can take some overvoltage, the control circuitry isn't that robust so you want to make sure the voltage supplied to your new servos is never more than about 6.5 VDC. Regulated power supplies are fairly common and inexpensive these days, but you want to verify the supply really is regulated before hooking it up to the servos. The other option is to use an unregulated supply with additional regulation circuitry (similar to 7805 you mentioned).
Far-seeker,
Thank you very much for answering that for me, I really appreciate it!
I can't find a good regulated 6V 2A power supply for anything in my price range, so I want to use a 6V voltage regulator which an unregulated 12V psu. The only one I can find is the 7806, which only supplies 1A.. I also read that it was a bad idea to use them in parallel to double the current.. Then I found this:
I think I'll try for a laptop power supply online (~$25) and step it down to 6V at 2A with the 78xx circuit.
First what you propose isn't the greatest of idea's for several reasons. 1. a 7805 is a 5V device and you would need a 1N4001 and a 1N5818 in series with the ground leg (.4V conduction for the schottky and .6 volts for the junction diode) and second the device is only a 1 A device to begin with and three If you are drawing 2 A from a 6V 2A load (I know you said servo but bear with me for a moment..).
A typical Lap-top charger produces 16 to 20V @ 2 - 3A... so for the moment we will choose the 16 V charger @ 3A. The load is 6V at 2A and P = E X I substituting we have 2 X 6 or 12 Watts of power required by the servo and 48 Watts available from the charger. The Magic of switchers is that they transform power more that specifically amps or volts, that's the feature that makes them so very useful.
That having been said, Lets do some simple math. If we choose a linear regulator we have to calculate how much power is dissipated as supply power and load power as well as power wasted as heat.
Case 1. A 7805 and we'll pretend for now that it can supply 2A (it can't, ever by itself). A linear regulator can be thought of as a voltage controlled resistor and we all know that when current flows through a resistor it causes heating so now we have a voltage controlled heater. With a load of 2 A the supply power is 32 Watts or 2A X 16 Volts while the load power is 12 watts. Subtracting the load power from the supply power leaves 20 watts; (2 x 16 =32W) -( 2 X 6 = 12W) = 20 Watts we have to get rid of from the regulator and it is 12/32 X 100 % efficient or 32% of the total power is used as power to activate the Servo and perhaps we Might be able to use the rest of the power (68%) to keep the coffee warm. Or the room on those nice cold wintry day's.. A couple of month's here at least before it gets cold for Southern California.
Case 2. A Buck mode (step down, Boost is step up and there is a buck-boost topology that can supply power out at or very near it's input voltage as as a step up/down too) We have a 12 W load from the previous example BUT since a switcher efficiently switches power the switcher puts just enough energy (Current stored as a magnetic field) into the coil to keep the output voltage at whatever it is set to and 12 Watts at 16V = .75A.
To prove this we multiply 16 X .75 = 12 Watts of power (P = E X I) the total power is 12 Watts + the Efficiency of the switcher or (assume 80% therefore we have 12 X 80% - 1. = .2 X 12 + 12 = 12 + 2.4 = 14.4 Watts load on the power supply instead of 32 and 2.4 watts of power wasted and .9A (.15A Loss) of load current drawn from the power supply instead of the 2A in the previous example..
The Switching regulators can be purchased here at ElectroDragon for $1.70 Ea... http://www.electrodragon.com/?product=better-than-lm2596-dc-dc-step-down-adjustable-power-supply-module
While I realize that a servo is an intermittent load, several aren't especially if doing repetitive tasks.
This was in part why I choose to use the servo as an example because I wanted to point out that although it isn't a really bad load as such it is a difficult one to supply because of the nature of the load and many aren't as cautious as you in deciding to use a separate PSU for the Servo's and thus have compounded their issues... Un-necessarily So. At least on paper...
Thank you for the very thorough and informative reply. I'd like to mention that I was planning to use a 7806 for the hacked-together 2A circuit.. But I do believe you've offered a much more reliable option. From what I gather on your post and the wikipedia page for buck converters, this device should directly interface between a power source outputting over 8 volts (16 Watts), and my servo's power pins?
StevenBrooks,
Thank you for directing me to the power supplies, I didn't know that pre-made regulators for powering servos off a wall outlet were available!
This is the best SPS I can find right off the bat,
http://www.servocity.com/html/6v__3_5a_power_supply.html
I guess I'll have to spend some time researching these two options, they both seem very well suited.
A 7806 won't work by itself very well if at all as it has a maximum of 1A available output current, they'res a way to "wrap" a PNP around the regulator...but the added 'pass' transistor (it takes one more resistor) WILL fail if you accidentally short the output to ground. For 15+ years I designed controllers that were radio controlled, solar powered and could drive any 2 or 3 wire solenoid of up to 5A load current. I did both 12V and 4V powered devices.
That sounds really neat! I'm a computer engineering freshman, and I hope that I can make cool stuff someday too
Actually, today we're supposed to go over the Power = Current * Voltage notion in my CPE 100 class, which is awesome because I already know about it from looking it up in my textbook for your post yesterday!
I went ahead and ordered the DC-DC step down converter, even if I end up with a pre-made servo power supply, I'm sure I can find a use for it elsewhere.
I'm much obliged for the help, thank you,
-BBX
P.S. Woke up to 41 Degrees this morning, which is NOT supposed to happen in Alabama, I could really use some coffee!
Doc had some excellent suggestions and information on adjustable switchers and buck/boost converters, so perhaps I should have written "Another option" instead of "The other option". Although switching power supplies can honestly be included the category of regulated power supplies. Here's a link to fairly inexpensive one one that I use in my own work shop that has a good 6 VDC output level and has a maximum current of 2 A.
In regards to voltage converters, since you seem to be familar with Polou, you might want to look at the modules they sell. Even though they are a bit more expensive than the one Doc linked to, it would still be an inexpensive option to get a boost or buck converter and use it with the supplies you've mention you already have on hand.
Remember to convert watts back to amps at the new input voltage to the converter/switcher and add the efficiency losses to get the final input current. I've used converters from several sources including the Polou and unless you have requirements to buy a specific device there is no gain in spending the same money for the same circuit and parts and very possibly the same PCB from another higher priced vendor.
A note on Chinese Electronics might be in order. Most of the Chinese electronics things that are used with an Arduino are very similar to the open source concept used with Arduino and are "Reference" designs. These are circuit designs and PCB layouts done by the Parts Mfr to sell parts by demonstrating the device and it's capabilities. There is NO added value here by the Chinese. Rather it is work done here i the United States for the most part and Mfd by the Chinese. The Chinese are really great at copying things and there is a great disconnect between parts cost and value. A Buck converter is a great example. The total parts cost burdened or labor added is about $0.60 So paying a dollar is a decent profit.
Paying a dollar more is not adding to the real value of the part and is NOT going to give you better performance, It might however help the vendor make a payment on his new BMW...
There is a cachet fostered by the vendors themselves that would seem to indicate that paying more is buying better... Within a class of items like what we are discussing everything is essentially the same so paying a dollar more is better.. Only for the vendor. IMNSHO
Docedison:
Paying a dollar more is not adding to the real value of the part and is NOT going to give you better performance, It might however help the vendor make a payment on his new BMW...
I totally agree with your point about paying more not usually making difference in hardware performance. However, a price difference doesn't always go directly into a vendor's bottom line profit. It can also be used to provide additional resources (e.g. example projects, code libraries, etc...) or to hire some extra people for technical support and/or customer service. Of course it's entirely a personal judgement call how much, if any, extra cost is reasonable for the additional service and resources available at any given supplier.
I agree with you BUT the subject was a simple Switcher... Not a fully orchestrated project. In "Shopping" I take the information offered and use it later when it is available. Some don't offer data until you buy the product unfortunately. One of my big issues is learning, You Never know when something might be valuable. IMO
Although switching power supplies can honestly be included the category of regulated power supplies. Here's a