More Wall-wart woes

Hi,

I found this post as i'm in the exact same situation. I already expected the higher voltage when unloaded, BUT...

I fed it to a 7805 regulating circuit and the 7805 got instantly roasting hot (and i presume shut off as is didnt power my PIC circuit).

Why is this? I thought even if it is spikey it would still only supply the current required by its load?

Is it that it puts out a constant power, and therefore if drawing a small current the voltage will be too high in compensation? <-- if so is that the difference between regulated and unregulated wall-warts?


Also, (this isnt as important but its frustrating me). Im really enjoying following Nigels PIC tutorials. But im having problems with those molex connectors. I manage to crimp/solder the terminals onto the wire, but they dont seem to push into the housings right. Everytime i plug an assembled connector onto a board it pushes the terminals back out. Does anyone have any tips for this? Im using quite thin wire if that means anything.

Nigel Goodwin said:

windozeuser said:

Well, I found an old wall wart rated at 9VDC @ 300mA Output. I cut the end connector off, and replaced it with a 9V battery connector. I'm trying to use it as a replacement for the 9V battery on my BASIC Stamp Board. I plugged the snap connector into the battery prongs of the BASIC stamp board. Then nothing happened! I Measured the output of the wall wart while connected to the BASIC Stamp board, and was reading 15VDC! My BASIC Stamp board still worked after that endeavor just with the 9V battery. I infer that the transformer needs to be loaded down with a resistor?

Click to expand...

No!, you're not right!.

You have a crappy unregulated wallwart, when loaded at 300mA it will output roughly 9V, but with VERY high ripple. What is the power supply on the STAMP?, does it have a 5V regulator?, if so it may be fine as is? - but these unregulated wallwarts are really bad news, for a little more money you can buy far superior regulated ones.

A resistor won't help you much, it will need changing for every slight change in load - which is basically what a regulator does automatically.

Click to expand...

Thanks,
M!C/<

elMickotanko said:

Hi,

I found this post as i'm in the exact same situation. I already expected the higher voltage when unloaded, BUT...

I fed it to a 7805 regulating circuit and the 7805 got instantly roasting hot (and i presume shut off as is didnt power my PIC circuit).

Click to expand...

It sounds like you've connected it wrong somewhere?, so it's unlikely it ever provided 5V to work your PIC circuit.

Also, (this isnt as important but its frustrating me). Im really enjoying following Nigels PIC tutorials. But im having problems with those molex connectors. I manage to crimp/solder the terminals onto the wire, but they dont seem to push into the housings right. Everytime i plug an assembled connector onto a board it pushes the terminals back out. Does anyone have any tips for this? Im using quite thin wire if that means anything.

Click to expand...

Never had a problem with one?, they are retained by little 'tabs' that stick out and locate in the housings, have you perhaps flattened them when you soldered or crimped them? - if you look closely it's pretty obvious what holds them in place.

Thanks for the reply. I'll just keep practising with the connectors

Nigel Goodwin said:

It sounds like you've connected it wrong somewhere?, so it's unlikely it ever provided 5V to work your PIC circuit.

Click to expand...

Ahhhhhhhhhhhhhh! ive just realised! Thanks for pointing that out! total schoolboy error from me.
See if u can spot what I did wrong:
(ignoring the circuit on the breadboard)

lol... nice job with the 9v battery connectors, red to black

no hard feelings, i've made that mistake before.

Just as well theres protection circuitry for people like me!

That conectors realy measd up up! :lol:

I did an oposite polariti mistake yesterday when testing my programer.I swaped the Vdd and Vss beacuse i used the same color wires DOUGH!!! And then i was thinking what went wrong.Luckuly the first thig i checkd was the conections.