Voltage critical
 

Power supply brick for Bro Draper's Virgin Broadband Modem has gorn TU,got boxes full of PSU but none at all the 1.2 amp 10 VOLT indicated on the buggad PSU, 9 volt or 12 volt of suitable ampage by the score, will they do any harm?
Lord knows how long it will take for a replacement to turn up,could buy a newun at Maplins but Bro Draper is even more reluctant than me to part wi coin,beside he reckons tiz Virgin Media's duty to replace it.
:confused::rolleyes:

I would give the 9V one a try first, but make sure the plug polarity is right before you try, and it obviously needs to have sufficient current capability, and as you are going to be 1V low, as much headroom on the current capability of the supply may help, if it is going to work at all.

My BT router says it wants 9v so yes try the 9v first but as MacBoero says the available current is the most important thing in those circumstances.

And of course, curly amps V straight amps, but you wouldn't be caught out by that, I'm sure.


You could look at the voltage on load. If it sustains 9, and runs, then the power supply's heat will be the next clue.

Mr D - There is no way I would answer your question over the internet. You haven't told us whether the broken power unit is ac or dc, whether it is regulated or unregulated, if the latter what the max oc voltage is, and whether it contains any filtering to avoid interference with ADSL or modem (router?). And you have not told us how you 'know' the fault is in the supply, not the router. As both items are specialist matching units and I guess owned by your isp, I would advise hands off don't touch. :ok:

both items are provided by the ISP and are known to be damned unreliable.

You also run the risk of Virgin getting a bit peed off if by using a charger that they didn't supply you end up sticking a voltage down their network because the modem shorts

But where's the fun in that? The thrill of the anticipation, the rush of adrenaline, the rollercoaster of emotions as you reach a trembling hand out to the 'on' switch.

That's why I became a controls engineer.

Bro Draper managed to eventually get through the plethora of phone button presses and robot voices and got to speak to a human at Virgin who agreed to supply him a new power supply plus a new cable modem for some reason,so thanks chaps,he can live without the tinternet until tomorrow.
Thanks chaps.

Mr D - Glad to hear it's resolved. The reason for replacing both is that the fault could be in either. Bro will hopefully receive upgraded and less troublesome hardware. :ok:

Will tell bro Draper to try and hang on to the old modem as a spare,tiz identical to mine,it was def the PSU,brought it here plugged it in and stuck me meter on it it was still putting out 14.5 volts off load but it got very hot in seconds and started emitting that burning insulation smell.
:uhoh:

Mr D - Maybe so, maybe not. There is such a thing as consequential failure.

you can expect that the modem is also buggered because of the overvoltage

or the fault in the power unit could be due to a short in the modem.

bin it
holding onto it is just a liability waiting to happen
or maybe a fire waiting to happen

Dunno if it is my digital meter but all power supplies read over the rated voltage when not loaded wi summat apart from the meter, just tried a 12v PSU running a CCTV camera it reads 12 volts dc,disconnected just on the probes it reads 17 volts.
:uhoh:

It depends. Supplies differ in design, some are relatively crude and voltage varies with load. Others are regulated and voltage remains substantially constant. But a regulated supply on absolutely no load at all could read high. It depends what the design engineer (me) has decided to do.

You need to know what you are doing, you need to know what you are testing, and you need to apply appropriate loading to simulate the correct test condition.

Power supplies off their design load can go a long way over nominal voltage.

Years ago I was working on an HF radio in a nice twin-engined aircraft, with the external PSU connected to save running the battery down. The owner was doing something with the Nav kit (all switched on and displaying) when his wife - an energetic and aggressive woman - yelled at us for having the battery master "on" while using external power.

She switched off the battery master. Cue loud sequence of popping sounds as CBs and fuses blew. My test meter showed 70 volts (on a 28 volt system). All the electric instruments in the panel, all the bulbs, and the VHF Nav/Comm radios had to be replaced. He reckoned that switch change cost him over £10k.
They divorced not long after.

On the subject of cheap power supplies...... nicely illustrated with photographs here.....

Heroic Register reader battles EXPLODING COMPUTER ? The Register

Keef

I think you may possibly be confusing the terms PSU and Charger.

Nope, this was labelled "Ground Power Unit 28v".

But many chargers [edit: and power supplies] will put out something around root 2 times the nominal voltage off-load.

Ah, so you were running rectified ac rather than dc. We had one clown at bae who hooked an electronic board onto the 28V line. We got sent a whole lot of boards back from the field with exploded capacitors. The poor little things had been trying to smooth the entire generator output all on their own To give the guy his due he was ex-Concorde so he couldn't really be expected to know. :}

Your pal using the Ground Power Unit was quite right to keep the battery on line. It acts both as a zener (of sorts) and as a large capacitor. Very necessary.

Indeed. It's a simple rule, and an expensive one to ignore. Whenever I build a power supply for my amateur equipment, there's almost always a regulator in there to hold the output close to nominal.

For setting up the HF radio in the aircraft, his GPU was the obvious thing to use...

We did get the HF sorted, some time later. The fuse in that protected it, and no harm was done.