For what it's worth...
12 to 24 volt boosters.
I have actual experience with this unit and it is surprisingly efficient, durable, and long-lived. The aluminum shell is SEALED. Submersible and a great heat sink.
Ripple is .06 vdc at 50 watts output.
http://www.ebay.com/itm/New-Voltage-Booster-DC-Power-Converter-Adapter-Step-Up-Regulator-12V-to-24V-72W-/292064645952?hash=item440068d340:g:DsEAAOSwN6JY-Eyg
Description:
100% Brand New and High Quality
Industry grade DC 12V to 24V step-up converter
More than 90% power conversion efficiency
Built-in over/under voltage input, overload, overhead, and short circuit full protection
Application for vehicles, security systems, telecommunications, medical equipments, instruments, etc
Waterproof, anti-shock protection, stable performance
Ultra compact size, light weight
Auto-recovery when device is back to normal operating
Stable and reliable performance
Simple to install
Input voltage:DC 12V(10-20V)
Output voltage:DC 24V
Output current:3A (rated working current in a long period)
Output power:72W
Case material:Die-cast aluminum
Potting material:Epoxy sealed
Size:74*74*31mm (L*W*H)
Wire length:Approx 12cm
US $15.99
And please remember amperage at given wattage is HALF that of 12 volts.