C
Claudio Bonavolta
Guest
Dear All,
I want to feed the lamp (halogen 12V/75W) of a photographic enlarger
with stabilized DC (voltage variations give exposure/color
variations).
I bought for this a 12V/100W switching supply.
The problem is the cold filament has a much lower resistance than when
hot, this forces the supply to furnish a much higher current than it
is intended and the protection switches the output off and on,
cyclically.
I may, of course, replace the supply by a much oversized model, but
I'd prefer to find a better solution ...
I've tried to put electrolytic capacitors up to 100'000uF but it is
still not sufficient. I may try super capacitors in serial/parallel
configuration but they are not really cheap.
My second option is to put a battery after a diode (to avoid the
discharge through the supply) but I'm not sure it is very good for
battery's life to be connected in such a way.
Another option was to insert serially a choke but their DC resistance
is to high (resulting in heat and voltage drop) and for such currents,
they are pretty heavy and expensive.
Is there a current limiter I can set to, say 8A, with a very low
resistance when not limiting current ?
Any other idea ?
Thanks,
Claudio Bonavolta
http://www.bonavolta.ch
I want to feed the lamp (halogen 12V/75W) of a photographic enlarger
with stabilized DC (voltage variations give exposure/color
variations).
I bought for this a 12V/100W switching supply.
The problem is the cold filament has a much lower resistance than when
hot, this forces the supply to furnish a much higher current than it
is intended and the protection switches the output off and on,
cyclically.
I may, of course, replace the supply by a much oversized model, but
I'd prefer to find a better solution ...
I've tried to put electrolytic capacitors up to 100'000uF but it is
still not sufficient. I may try super capacitors in serial/parallel
configuration but they are not really cheap.
My second option is to put a battery after a diode (to avoid the
discharge through the supply) but I'm not sure it is very good for
battery's life to be connected in such a way.
Another option was to insert serially a choke but their DC resistance
is to high (resulting in heat and voltage drop) and for such currents,
they are pretty heavy and expensive.
Is there a current limiter I can set to, say 8A, with a very low
resistance when not limiting current ?
Any other idea ?
Thanks,
Claudio Bonavolta
http://www.bonavolta.ch