I'm looking for the wall wart for an exercise bike in my bin of such things. It needs 9v 0.5A and i've found one that's 9.6v 0.6A which (accepting there's no danger of ever finding the original) is closer than I expected to get. But I have a 12v 1A with a longer cable, past experience tells me there will be no bother using that but is it a problem? And if not when is it likely to become one?
And why do similar rated ones differ so much in bulk? Is this just a build quality issue?
Depends on whether the bike has any regulation on its input. It probably does (assuming this is just an electronic readout of speed / distance etc). The 9.6V one would be the better bet.
The main difference will usually be a light weight switch mode design vs a older style linear supply. The older ones will have much heavier transformers.
Older ones will have a transformer. Newer ones a SMPS - smaller and lighter.
Just before the smoke.
Open it up. If the PCB copper traces wind up *only* at a 7805 regulator than it shouldn't be a real problem, except probably a little more heat
- perhaps arrange ventilation or a bigger regulator heatsink. If they go elsewhere, than bets are off - it may be running analogue circuitry, I guess amplifiers / comparators and the like for this kind of application.
Some "linear" use large transformers run at 50Hz, some "SMPS" use smaller transformers run at 20kHz upwards with more electronics to go bang.
John Rumm brought next idea :
There has been no mention of ac or dc output/input?
If you want to lose 0.6 - 0.7V put a diode in series on the positive output.
Richard
I'm assuming all of these are analogue ones, ie Heavy to pick up. If so then probably the 12v one is using a better specified transformer. Be careful though, as unless you are sure the device is able to accept raw DC you might have issues with ripple. Also I had two here for an old dab radio, one gets so hot it has partly melted the case the other runs cool. The only reason for the difference as far as I can see is that the transformer in the hot one is crap.
Brian
All wallwarts use a transformer. SMPSes just use a smaller one.
NT
Sounds a bit like my Bremshey. It came with a 9V unregulated DC wall wart with a heavy 50Hz transformer which ran quite hot (it's plugged in all the time). It was nearer 12V off-load anyway.
I replaced it with a 9V switched mode one - I needed one with a longer lead anyway. It runs stone-cold all the time.
Nowadays, they can no longer be supplied with 50Hz transformers, as these can't easily meet the efficiency ratings required, so any new one will be a high efficiecy switch mode PSU.
Providing your 9.6V is a light weight regulated switched mode PSU, it should be fine.
Difference is likely to be 50Hz transformer nd unregulated output, versus switched mode regulated PSU. You won't find the former supplied with anything nowadays.
It is a Bremshey. :)
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