There don't seem to be many dc-dc converters out there that will handle input voltages higher than 60v. Building one from a "Simple Switcher" chip also limits you to under 60v input.
I had a few switching power supplies that were pulled out from medical equipment in my office, so I tried hooking one up to my bench power supply (actually two bench supplies in series to get enough voltage). At 60vdc input, the thing worked great! It's spec'd to operate from 84 to 240vac input, but since the input goes through a bridge rectifier, dc input works fine. It worked OK on 60v, but crapped out somewhere around 50v, so it won't run off 48v.
The one I tested is
http://www.slpower.com/Upload/Technical/20070205104153748706170_GSM28G.pdf
I've seen a wide variety of similar switching power supplies at
http://www.allelectronics.com/cgi-bin/category/480/Power_Supplies.html
I think most of the models with a wide input range should work for 60v and above. Many of them are under $10. Perfect for running 10-20w headlights.
Another cool feature is the input and output are completely isolated, so you don't have to worry about getting zapped by the output. You could also possibly connect two in series for a higher output voltage. Since the input goes through a bridge rectifier, you don't have to worry about polarity either. Most of them have very good regulation and overcurrent protection.
Each particular model may behave differently at low input voltage, so some testing would be needed to identify the minumum voltage the thing will actuall work on.
I had a few switching power supplies that were pulled out from medical equipment in my office, so I tried hooking one up to my bench power supply (actually two bench supplies in series to get enough voltage). At 60vdc input, the thing worked great! It's spec'd to operate from 84 to 240vac input, but since the input goes through a bridge rectifier, dc input works fine. It worked OK on 60v, but crapped out somewhere around 50v, so it won't run off 48v.
The one I tested is
http://www.slpower.com/Upload/Technical/20070205104153748706170_GSM28G.pdf
I've seen a wide variety of similar switching power supplies at
http://www.allelectronics.com/cgi-bin/category/480/Power_Supplies.html
I think most of the models with a wide input range should work for 60v and above. Many of them are under $10. Perfect for running 10-20w headlights.
Another cool feature is the input and output are completely isolated, so you don't have to worry about getting zapped by the output. You could also possibly connect two in series for a higher output voltage. Since the input goes through a bridge rectifier, you don't have to worry about polarity either. Most of them have very good regulation and overcurrent protection.
Each particular model may behave differently at low input voltage, so some testing would be needed to identify the minumum voltage the thing will actuall work on.