how much current picaxe can handle

[lord55]

i have circuits connected parallel to a 5v dc 1200 mA power supply
two xbee modules , axe033 ,28x1
also buzzer ,switches , relays, LEDs--->power from microcontroller of Xbees and 28x1,
the problem is sometimes LCD fade out specially when output device like an led or buzzer turned on also sometimes xbee modules doesn't work reliable
while when i use batteries ex.. for each circuit a 3 AA batteries the circuits works fine..
is that a problem because of the current

if so.. im planning to buy a power supply that has higher current around 5A
but i dont know if that going to damage something

 

[westaust55]

Can I suggest you first look through:
http://www.picaxeforum.co.uk/showthread.php?t=9272&highlight=95mA
and
http://www.picaxeforum.co.uk/showthread.php?t=9648&highlight=95mA
and
http://www.picaxeforum.co.uk/showthread.php?t=10001&highlight=95mA

If you look in PICAXE manual 1 it indicates which PIC microcontroller is used for each PICAXE so from that looking in the relevant Microchip datasheet will give more information

In general, (someone is sure to give an oposing example), your existing 1.2 Amp power supply should be far more capacity than typical (non-robot) projects will require.

 

[BCJKiwi]

If everything is powered from the same supply (common 5V & common 0V for all), suggest;
1. Put an ammeter (DMM will do) in the 5V line between the supply and the load - see what current is actually being drawn.
2. Change the DMM around and monitor the Voltage and see if it is drooping.
3. Do a simple assessment of the loads to check the total current load is in line with the readings.

The AXE033 manual indicates the LCD really wants a 5 - 6V supply so is Voltage sensitive.

Each load will only draw what it needs from the supply.
However if the load on any PICAXE port exceeds 10mA (20mA max) then the PICAXE will be overloaded and the port (if not the whole PICAXE) will be be permanently damaged. There is also a total combined load limit for the PICAXE and it is quite easy to overload it if you have lots of LEDs.
As per Westy's post, check out the info for all the devices in use - it's all in the manuals/documentation - time to do some homework!

If you install a large PSU (5A) it would be worth considering a separate low current supply for the PICAXE and a higher capacity supply for the rest - common all the 0Vs.

 

[Dippy]

Sage advice.
And DO carry out the measurements as suggested by BCJKiwi.

The suggestion by BCJ of having a 'split' power supply could be very important.
In theory you could power your device happily with a 5V supply capable of 5million amps.
BUT, if you have an 'incident' ... bang!
So, if you are upping the supply capacity it is important you protect the sensitive stuff from accidents.

If yours is the cheapest PSU that Beijing has ever produced and sold via Ebay-Gum then its power claims may be exaggerated.
I would be tempted to do the measurement as BCJ suggested incrementally.
Add a load-at-a-time. This will tell you:-
A) The real capacitiy of the PSU.
B) Whether one of your add ons is taking more than it ought to. (vs Data Sheet values)

I assume you have added up the Data Sheet values for 'current used' for all the devices?
(Data Sheets?) Read Read Read...

One final thing; I would be put capacitors near the PICAXE power pins i.e. +V>>Gnd0. Your circuit sounds like a candidate for interference due to transient spikes and noise from buzzer.

 

[westaust55]

The AXE033 manual indicates the LCD really wants a 5 - 6V supply so is Voltage sensitive.

The AXE033 also has a jumper/link provided so that if you are operating off 4.5V (derived from 3 x AA batteries) you bridge the two terminals for a brighter display at the lower voltage.

I have operated an AXE033 from 5Vdc without the link and the display is still very readable.

 

[lord55]

my pcu is very cheap i bought it around 3 dollars
it has multi voltage output (1.5,3,4.5,6,7.5,9,12)
when i switch the voltage to 4.5 the DMM read more than 7.5 v when i switch it to 3 v DMM reads 5.5 v when i switch it to 12 v DMM reads 22v
those values are confusing me are they alright ?
actually im using 3v becoz DMM reads it 5.5v

anyway i'll do measurements to the current as you suggested

 

[moxhamj]

Yikes!! That is slightly out of spec. Your figures are correct.

Some cheapie power supplies have no regulation at all, and assume there is a load connected. Usually they assume the load is a few hundred milliamps, so when you connect a picaxe that draws a few milliamps there are far too many volts. Hopefully the picaxe is not zapped. It may not be despite what the data sheets say - I got away with 8V briefly a few days back.

You need a voltage regulator. Have a look at a 7805 or 78L05 or 2950. If you are running all those biggish loads, a simple 7805 might be best. Run in at least 7V (stick your pcu on 9 or 12V), and out will come a nice stable 5V up to 1 amp. 7805 regs are really cheap - grab a few while you are at the shop. If you look at a 7805 regulator from the front (at the writing), volts go into the pin on the left, the middle pin goes to ground, and 5V comes out the right hand pin.

 

[Dippy]

I will double-YIKES.
DISCONNECT IT NOW!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I will re-iterate Drac, but more bluntly:- What you have is a cheap UNREGULATED power supply - probably of dubious quality and questionable parentage. Certainly of a known country of Manufacture where 'specification' = 'bull..'

It will be a rubbish quality transformer coupled to a rubbish rectifier.

Try as Drac says with a 5V regulator.

Alternatively, chuck it into a cardboard box.
Then go and buy a PROPER Regulated PSU.
Being 'economical' can be expensive when you start popping chips.
Try and delete Ebay from your mind.....

 

[Michael 2727]

Sounds like your supply is not a regulated supply.
The voltage figures you quoted are well within what you could expect
from a Transformer/Bridge-Doides/Capacitor arrangement.
The voltage will be higher with no load, then closer to the stated
voltage once you load it up with something. A DVM has virtually no load.

The long and the short of it all is to ditch the crappy supply you have
and get a propper Regulated Supply before you do some damage.

5V DC is not always 5V DC. And you get what you pay for in most cases.

 

[westaust55]

Some power supplies and transformers are not well regulated.
They have hight voltage as in this case which drops/droops with load.
The only time they are at the rated voltage is when they are at the rated current/load.

I agree with Michael, get a proper regulated 5Vdc supply.

the problem is sometimes LCD fade out specially when output device like an led or buzzer turned on . . .

the reasons are now obvious - its the poor voltage regulation not the current draw

 

[Michael 2727]

Just because a power supply says ##V DC does not mean a lot in many cases.
DC is not always DC as you can see from the attachment.

Fig- B, C and D are all technically DC, but the only thing they would
much good for is to power Christmas Tree Lights or a Heating Element etc.

Even if you used D (which is is only starting to resemble good DC ) for anything
Audio you would hear an annoying Buzz and it's still nowhere near suitable for a
microcontroller/Picaxe etc.

A Regulator takes voltages similar to D and reduces that input voltage Ripple to
around 1/100th of what it originally was.

Note: you always need some overhead voltage (at all times, even under full load )
on the input side of the regulator to maintain proper regulation, typ- 2V higher than the output side.
Eg: On Fig- E if the load pulls the input voltage down, the ripple above will appear
at the output of the regulator, loss of regulation or even complete dropout/shutdown.

So if you get lumped with a crappy DC supply just add a regulator to the
output and you should end up with a good DC Supply.
Remember the 2V extra rule (read the data sheet on the regulator )
And upgrade the input capacitor if it is only small value, 470µF to 1000µF should
be the minimum for reasonable loads.

 

[manuka]

As most PICAXEs run happily on supplies between ~3 & 5.5V, we've endlessly said that 3 x AA batteries (~4½ V) best suits PICAXE beginners! I STRONGLY hence recommend that you forget mains PSUs until you've got to grips with initial circuitry.

 

[Dippy]

Jeez, there are a lot of echoes on this Forum.
Do you think its an unregulated PSU?