Cosel VAA505 Power Supply

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GDSever

Member
I have built some test circuits using a 28x1, breadboard, and the Cosel VAA505 power supply and have not found any issues with it - Downloads ran fine, the Picaxe performed as expected for a 45 minute test...

http://www.alliedelec.com/Images/Products/Datasheets/BM/COSEL_USA/Cosel-USA_Power-Products_8002800.pdf

My concern is the spec that indicates it is a 5V >>1.0 amp<< supply - I read somewhere that Picaxe chips should only get 200mA max... Is it just blind luck that my 28x1 didn't fry?

If I need to be concerned, some advice on how to knock the input current down would be most appreciated... Choke? Resistor? I went with the VAA505 because it was small, compact, and simple. Hopefully the required adjustment for the current will be equally simple.
 
T

Tom2000

Senior Member
The spec means that the supply can furnish a maximum of one amp.

Ohm's Law: Current equals Voltage divided by Resistance

So, the power supply will only furnish as much current as your project draws, up to a maximum of one amp. It won't try to force one amp through your circuitry.

Don't worry. Be happy. (Hey, that's a catchy phrase. It would make a good song title. :) )

Tom
 
M

moxhamj

New Member
The picaxe only takes what it needs. In this case, probably less than a milliamp. The "required adjustment" will indeed be very simple. You don't need to do anything!
 
G

GDSever

Member
Dr_Acula said:
The picaxe only takes what it needs. In this case, probably less than a milliamp. The "required adjustment" will indeed be very simple. You don't need to do anything!
Click to expand...
I am very relieved to hear both of you say that. I assumed as much, but being a Chemical Engineer by education (and having received only passing marks in my electronics curriculum at the time), this stuff is sometimes black magic to me... I wanted to validate with experienced people.

Thanks!!
 
hippy

hippy

Technical Support
Staff member
There's no such thing as a dumb question; it's far better to ask to be sure than assume and be wrong.

I had an interesting discussion a while ago ( not this forum ) on replacing my UPS batteries with higher Ah versions - may take longer to recharge but will keep things running longer when needed - but it was pointed out that some are designed only to run for as long as the batteries are meant to last, extend the run-time and things start to overheat and it does more damage than good. Something I'd never thought of.
 
D

Dippy

Moderator
Well I'll be.
That was something pointed out to me by an enginer at Galatrek when I was scoffing at the price of their inverters vs a DIY jobby using a UPS and Fat Batt. It hadn't crossed my mind either.

Yes, ask away GD. Better safe than sorry.

Though obv you will be careful if you have a 5V 3000 Amp supply. As it WILL supply 3000 Amps if you accidentally short-circuit something :)
A cheap thing 4 letters long beginning with FU can save the day - or else you may shout a 4 letter word beginning with FU.
 
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Mycroft2152

Senior Member
Dr_Acula said:
The picaxe only takes what it needs. In this case, probably less than a milliamp. The "required adjustment" will indeed be very simple. You don't need to do anything!
Click to expand...
Careful Dr. A,

This is true with one requirement, "a properly designed circuit".

If there are any errors, resulting in short circuits, then the magic smoke will be released, or you will have a spectacular failure.

Keep some marshmallows or a fire extinguisher handy.

This is one good reason for an expensive current limited power supply when prototyping.

Myc
 
G

GDSever

Member
Mycroft2152 said:
Careful Dr. A,

This is true with one requirement, "a properly designed circuit".

If there are any errors, resulting in short circuits, then the magic smoke will be released, or you will have a spectacular failure.

Keep some marshmallows or a fire extinguisher handy.

This is one good reason for an expensive current limited power supply when prototyping.

Myc
Click to expand...
You sure know how to shore up a nervous person's confidence. Thanks for the encouragement :p

Actually the circuit has been both simulated in PICAXE VSM and fully prototyped on a pair of breadboards, so I am relatively confident that short circuits are not an issue.
 
D

Dippy

Moderator
Blimey, you're a bigger 'Old Worrier' than me!

There's another "old Brit colloquialism"; man or mouse :)
 
G

GDSever

Member
eclectic said:
Have you got .....
Insulated box? Fuses? Strain relief cables?
Does your set-up comply with State/National regulations?
And anything else required.
Click to expand...
Yes. The power supply will be mounted on a PCB inside a properly grounded enclosure along with a few SSRs and assorted 120VAC wiring. The PICAXE turns pumps on and off based on float switches. There is a 2A slow-blow fuse (as recommended by the owner's manual) to protect the power supply etc... and I will not be fiddling around in the box while it is energized. Electrical-code compliant? As much as a >>HOBBYIST<< can make it, then some.

I am not a cowboy. I work for a large chemical company that puts safety as its number one priority and I have twin 5 year old children that I want to see grow up. I am not about to put myself in a position where I would jeapordize those things.

I'm not quite sure how this thread has degenerated from a "is this power supply going to destroy my circuit" into a "treat me like an invalid" discussion, but whatever. I do appreciate the constructive comments.
 
E

eclectic

Moderator
Actually Dippy, the FULL facts were not made apparent in the initial posting.

Draft 1

He who checks, if all is clear;
will live to check another year.

But he who is by mains volts slain;
will never live to check again.

With apologies to Macauley.
but NO apologies for checking!
 
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Mycroft2152

Senior Member
GDSever said:
I'm not quite sure how this thread has degenerated from a "is this power supply going to destroy my circuit" into a "treat me like an invalid" discussion, but whatever. I do appreciate the constructive comments.
Click to expand...
G,

It's nothing personal, just some of us old farts are a little concerned with PICAXE users playng with mains voltage. considering the average PICAXE newbie is, well, let's just say, lacking in experience and believing they can live forever...

It sounds like you have all the bases covered. Nicely done.

BTW, is Macauley a relative of Murphy?


Myc
 
D

Dippy

Moderator
GD, like Myc says, it's because many/most posters here are new and 'enthusiastic'. We don't know whether you're experienced or a schoolboy or, even worse, a teacher.

Usually we can spot a teacher by the number of spelling mistakes.

It's almost like a programme in itself.

If Post text Includes "PICAXE" AND "MAINS" OR "CAR" then all the old lags go into Boolean PANIC=TRUE.
Sometimes with some justification it has to be said as it's difficult to type your Project up when your fingers have been blown off.

In your case it is obvious that you have thought these things through and therefore the Old Lags needn't go into Mother Hen mode.

I dare not even mention the Microwave neuron stimulator that I'm designing. I've just stuck my tongue on the Magnetron to check the output. I'm sure thats OK. OW! Yes, I reckon 3.76 GHz @ 400Volts but not sure if it's TEM.
 
G

GDSever

Member
No worries. I am certainly inexperienced compared to many here on the forum... and was hoping to draw upon their experience to validate my own thoughts.

Thanks again for the assistance. Once I get my prototype box built, I'll have to post some pics.
 
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moxhamj

New Member
Re Mycroft2152 "This is one good reason for an expensive current limited power supply when prototyping."

Manuka will say that the best prototype power supply is 3 batteries and there would be a good argument for this.

My personal preference is a 9V rechargeable coupled with a low quiescent 100mA 5V regulator as many of my picaxe circuits need a stable 5V refererence to read analog voltages.

My other preference is a 5V supply (not dissimilar to the one suggested in this post) with a fuse in the 5V line. But I got sick of replacing the blown fuse so I changed it over to my favourite sort of fuse, which is a lightbulb. In this case, a 6V 500mA torch globe.

A lightbulb has some very useful properties. When small amounts of current are passing through it has negligable resistance as it is cold. But when the circuit is shorted, the current rises and it lights up. As it does so, its resistance increases, and in this case a 500mA globe ends up drawing 500mA in the case of a short, which is less than the current rating of the power supply. Of course, you get a visual indication of a short as the bulb lights up. And unlike a fuse which has to be replaced if there is a short, a lightbulb does not need replacing. Finally, a lightbulb can cost less than a fuse and fuseholder.

For a 5V supply, you could use a 4.8V or a 6V torch globe.

But if you have a fuse then use that. Or you could use both.
 
D

Dippy

Moderator
Ah, the old light bulb trick. Good stuff. Very handy. Fuses.. wonderful. Circuit breakers...lovely.

I don't want to ruin anyone's party but the only real safe (i.e. best) way for prototyping is an expensive power supply with current limiting adjustment. Anything else is second-best but, on many occasions, good enough. I'm in a good mood so I won't rabbit on about how good TTi Power Supplies are. Phew!
 
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moxhamj

New Member
Yes agree. Current limiting is the best, especially adjustable. You can set it for adjustable volts. Or you can short the output and set it for adjustable current. Dial up 20mA and you can put a led across the output and not worry about the voltage or a resistor. Or you can dial up something small like 10-20mA and run a picaxe and even if something awful happens in the circuit it won't destroy anything.
 
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Mycroft2152

Senior Member
Dr_Acula said:
Yes agree. Current limiting is the best, especially adjustable. You can set it for adjustable volts. Or you can short the output and set it for adjustable current. Dial up 20mA and you can put a led across the output and not worry about the voltage or a resistor. Or you can dial up something small like 10-20mA and run a picaxe and even if something awful happens in the circuit it won't destroy anything.
Click to expand...
Dr A,

Didn't I say that about 11 posts ago?

Must be some kind of time warp when crossing the equator.

Myc
 
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moxhamj

New Member
Re Mycroft "Didn't I say that about 11 posts ago? Must be some kind of time warp when crossing the equator."

Indeed you did say that! Sorry, in my line of work I find repeating things over and over is the only way to get a message through. Eg "Your chest infections are never going to get better till you quit smoking".

Just a quick check in my trusty Electus catalogue (Jaycar's wholesale division) reveals a 0-30V, 0-3A model with constant current or volts for $127. Well worth the investment for anyone getting into electronics.
 
M

Mycroft2152

Senior Member
Every time I visit my physician he has the same problem, especially after reading my chart for the first time --again.

You had me worried that the laws of phsyics changed, electrons generally move at the speed of light, so 12,000 miles shouldn't take that long.

Myc
 
D

Dippy

Moderator
"electrons generally move at the speed of light"

- Now you've got ME worried that the laws of Physics have changed!!!!!!!
 
M

manuka

Senior Member
You've all reminded me of long past workmate who taught on the "hammer & nail" principle. This essentially involved "The more often and LOUDER you say things, then the further in the material goes". Yes- he was ex army!

For the chemical equiv. of a circuit taking only the current it needs, perhaps just consider a simple reaction of a lot of acid and a few zinc pellets. Even though the acid has abundant mischief potential, only a small amount is actually used to create the zinc salt, with the rest "sitting" idle. How's that for a single coffee early morning comparison? Stan
 
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