powering picaxe projects

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jeff96

New Member
I apologize for such a basic question but what do people use for a power supply for their projects?

I built a relay circuit that switches a furnace fan on and off periodically. The relay draws 380mA (as measured at 4.5V). I got a wall wart transformer that says on the outside that it's rated for 2100mA (though it also said in a different spot 2100mAh) When I connected it to the relay, it started making a funny noise and stopped producing voltage.

Right now I have a 200mA transformer hooked up in parallel to a rechargeable battery pack. It's been working for over a week, so I'm assuming it's adequate to keep the batteries charged but I'd rather not use batteries.

I know pc power supplies can be modified to work as bench power supplies, but I think this would be overkill and I'm looking to keep the device small. Any ideas? Relatively cheap and readily available would be nice too.
 
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moxhamj

New Member
I use a wall wart of about 9V and then a 7805 regulator. Good for up to an amp.

Sometimes I use a 'simple switcher' if I want to conserve power.

If you can get a regulated wall wart 5V regulator that makes things even simpler. These are getting cheaper and are smaller than transformer ones.

PC power supplies are tricky as they need a minimum load just to run. And the minimum load current is quite high. I've used old motherboards as the 'load' but it seems a bit wasteful. PC supplies won't work with no load.

This sort of thing makes things very easy http://www.jaycar.com.au/productView.asp?ID=MP3144&keywords=5V&form=KEYWORD
 
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jeff96

New Member
yep, that's what I'm running right now, only without the batteries it doesn't have the oomph. looks like I'll just have to spend a little more on the next one
 
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Haku

Senior Member
I used to make camera setups that run on & power from Archos AV500's, using a miniature chalk-cube sized camera, unsoldering the cable & replacing it with a longer one plus connection plugs.
The cameras run off 5v and in the removed connection cable is a 7805 with 2 (I'd guess) 0.1uf capacitors and a blocking diode - I have big jar of these removed leads I've been salvaging the power+phono sockets from, and now I have a use for the pre-wired regulator boards, once they're cut out of the plastic block :)
 
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lanternfish

Senior Member
Dr_Acula said:
..... PC power supplies are tricky as they need a minimum load just to run. And the minimum load current is quite high. I've used old motherboards as the 'load' but it seems a bit wasteful. PC supplies won't work with no load. ....
Click to expand...
Hi Dr_Acula.

I do have to contradict you on that.

Old AT supplies are a great cheap source of regulated supply. And they run within spec with only and LED attached. I do recommend that each circuit attched should have a suitably rated fuse in-line as the supplies can delivery a fairly hefty current.

And you can use most of the lower rated ATX supplies in the same manner. The trick is to short a particular wire on the ATX plug to ground. Note to self - locate URL before posting.

I particularly like the ATX supplies as they provide 12V, 5V and 3.3V

Once again, the warning about a suitable fuse is given.
 
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hax

New Member
Just to clear things up, the AT specifications require a load of 1A on the 5V rail only to regulate all rails to the specifications.

There is no mention of a minimum load on the 3.3v and 12v rails.

I have used some pc power supplies that require this load to switch on, and I have used others that don't seem to need it at all, so it all depends on what you have. If in doubt, use a dump load.
 
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Dippy

Moderator
Power Supplies are quite an issue and a BIG subject.

There is little point going into great detail here as this thread will probably be 'lost' in a week's time.

First, you have to determine the voltages and loads required.
Some projects may require several voltages e.g. a 5V for PICAXE and 12V for a motor or relay.

If we mix in to the equation Newbieness and Budget restrictions then we have to be careful. AlWAYS check the power rating. ALWAYS check o/p voltage. Trust nothing - especially if not a well-known brand.

Wallwarts (mains plug-in AC Adaptors).
You can get good or bad.
You can get regulated or unregulated.
You can get linear or switched.

PC PSUs (and other 'liberated' PSUs).
Many tend to be switched-mode and most will easily give out enough oomph to pop an unsuitable circuit. Some need min. load as mentioned. Don't use them in ignorance of spec.

Remember, all the above are usually designed for use with other circuits.
In many cases, with Switched Mode desgins, the final bit of smoothing is probably done on the target PCB.

So, filtering/decoupling/bypassing capacitors will almost certainly be needed on your PCB.

Ooomph!
Most of these PSU will be able to provide plenty of power/current.
Some will have lousy regulation and may be electrically noisy.
(Get an AM radio and put it next to it).
This also means that a cocked-up circuit can easily go POP!
Use a fuse or lose.

Voltage.
Beware.
Always check - regardless of the label. Sometimes there may be a fault.
Or there may be an error in the translation from Chinese.

Making your own.
If you decide to make your own regulator, say from 12V to 5V be aware of heat and power.
If using a LINEAR (normal/ old-fashioned) type then DO the POWER CALCS to see if you need heatsinking.
And READ the F. DATA SHEET to see what capacitors are required for YOUR DEVICE.
Note.
If your supply voltage to your regulator (e.g. 12V) is noisy and spikey a 5V regulator will NOT stop the noise. HF will go through it and into your circuit. So check with 'cope as you may need supplementary filetring LCR.

If using Switched Mode (e.g. Simple Switcher etc.) then READ the DATA SHEET to see the recommended components.
NOTE: With Switchers component choice is crucial for top performance - you may even (I'm SO SORRY) have to get out your calculator to work things out.
ALSO with Switchers your PCB track layout/design can make a huge difference to performance. A breadboarded Switcher will be poor compared to the well-designed on-PCB equivalent.
Top design requires a good ( I mean good) 'scope. Not a £10 USB plug-in.

Again, be prepared to protect your PICAXE circuit with a fuse.
The clever project-builders could build a trip with an Op-amp and transistors.

Home-made switchers.
With MOSFETs and drivers. Newbie.... forget it. Getting something really good (Lab spec.) is way beyond 99.99999% of people. Something good enough for a battery charger is possible but I'm sick to death of MOSFETs.


The BEST?
For prototyping you CANNOT beat a proper bench PSU with Current limiting.
The best Bench PSUs include Thurlby-Thandar (TTi) , METRIX , ELEKTRO AUTOMATIK , HAMEG ('n'chips). AGILENT.
The best ones use opto knob adjustment (no dirty pots) and some have serial control inputs.
None will be cheap, but top quality stuff will usually last longer than the operator.
And Current Limiting is faster than fusing and will save you money ( replacement popped components/PICAXEs inc Postage).
Yes, they empty your Piggy Bank. But as Christmas is coming the above should be able to justify it to Mum and Dad.
Cheaper options are available but I can't vouch for quality or durability.
 
hippy

hippy

Ex-Staff (retired)
Power supply usually depends on what my projct is or what I'm doing.

Benchtop PSU during development, occassionaly 3xAA battery pack.

Serial Port derived power when current draw is low ( haven't tried using USB power yet ).

9V PP3 battery plus 78L05 for handheld units.

Walwart 9V PSU plus 7805 or 5V switched mode supplies direct if needing reasonable current.

For equipment to be permanently installed I normally build the entire PSU within the unit's case. Transformers, even whole PSU boards, are usually taken from junk equipment. I sometimes fit walwart switch mode supplies within the case.

I never use PC PSU's. I've seen what they can do in short-circuit situations and a fuse often won't save a project from that. The switched mode supplies I've picked up from car boot / garage sales have all been very cheap and take up a lot less storage space. Most PSU's for routers etc have a 1A/2A supply capability which is more than I need.

I wouldn't say "don't use a PC PSU", but I wouldn't recommend it as a general purpose supply for development.
 
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Dippy

Moderator
Re: PC PSUs.
I'm with you there me old hipster.

But I know what it's like with people doing things on the cheap, sorry, I mean recycling available devices :)

Any PSU with lot's of oomph or large output capacitance is a potential killer for low power / delicate circuts.
And newbies haven't seen the magic smoke - so out comes the PC PSU, great fat cables connected to breadboard and flick the switch.

All I can say is "You have been warned". So, be careful. Use a suitable fuse, but fuses aren't as good as a good current limited supply.

Anyway, this could go and on so good luck to all. If, after ALL the warnings, your circuit starts smoking then hopefully you may learn.
If you don't learn then carry on with selling ice-creams as it'll be safer.

Project 1. A Current limiter / circuit-breaker. An op-amp or two and some discretes - Bob's yer uncle.
 
hippy

hippy

Ex-Staff (retired)
Iomega PSU's ( ZIP drives etc ) are amongst my favorites. Very compact, regulated 5V, 110V/230V, with either figure-8 mains plug-in connector or flying lead. Easy to solder up to an IEC inlet, switch and fuse within equipment or use as an external PSU. Runs cool and I've not personally run into any noise / ripple problems. Probably similar from other manufacturer's. YMMV.
 
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fritz42_male

Senior Member
I use some PSP power supplies from dealextreme - 110/240v in and regulated 5V out at (supposed to be) 2A. Cost US$4.77 inc free shipping.

http://www.dealextreme.com/details.dx/sku.22383

I used these on my Halloween Picaxe controllers and they worked fine. Some of the Picaxes were driving servos and others were used as timers and random blinking leds controllers.

If you need higher currents, these units seem pretty good as well:

http://www.allelectronics.com/make-a-store/item/PS-575/5VDC-11A-SWITCHING-POWER-SUPPLY/1.html
 
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Dippy

Moderator
For those who:-
A) Have a bigger budget
B) Want Top Quality
C) May wish to speak to a techy in English.

Then check these out:
http://www.tti.co.uk/products-tti/psu/psu-bench.htm

Superb quality.
Opto knobs with coarse and fine control.

One gripe.
The terminal posts are a bit close together for fat fingers.

I can't remember which one I have, but it has RS232 serial control which can be controlled by PC and PIC so I assume PICAXE too.
I chose the one that can go up to 30V so I can develop 24V circuits.

Yes, they are expensive-ish.
But, local service is important to me, so if my knob drops off, I can phone up the service section and get a new one in the post.
Horses for courses.
 
hippy

hippy

Ex-Staff (retired)
Mine's a PL154 ( single channel 15V/4A ), even older than the one in the "older products" photographs ! One thing to bear in mind when disinclined to pay higher prices is that if it 'lasts forever' that becomes a small year-on-year investment.

I have to agree that having a coarse and fine for voltage control really is useful. The later versions have some really nice features. The voltage sense is a minor PITA on my version as it's not something I use, and it's only standard 4mm banana plug sockets not shrouded, but those paddle switches for on / off I really love.

If I had to find a replacement for what I have I'd definitely consider the PL320QMD as very flexible and on the right side of not being ridiculously expensive - Did I mention it's my birthday and Christmas is just around the corner ?
 
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