New Industry Products

Absopulse Introduces 250W Convection Cooled DC-DC Converters for Railway Applications

January 05, 2021 by Gary Elinoff

Working from 12 VDC input and offering 24, 48 or 125 VDC output, the units are also suited for industrial and other transportation applications

The LTH 65R-F3-HSA series of power converters are built with an under-surface heatsink assembly block attached to the under-surface of the unit for effective convection cooling.


The LTH 65R-F3-HSA series.
The LTH 65R-F3-HSA series. Image courtesy of Absopulse


What are Float Chargers and Hold-Up Batteries?

Absopulse describes the new units as being designed to float charge hold-up batteries. 

Hold Up Batteries are batteries that are seldom discharged. They are used to maintain stasis within a system when the main power is off, or for emergency and backup purposes

Float chargers are often described as chargers that operate continuously. They operate within a system that automatically tweaks the amount of power delivered to keep a hold up battery at its optimal charge density.


Convection Cooling

Convection cooling is achieved by a finned heatsink assembly that the rest of the charger sits atop of. The natural convection that occurs through the fins of the heatsink achieves extra cooling. 


The F3-HSA heatsink’s fins enable convection cooling.
The F3-HSA heatsink’s fins enable convection cooling. Image courtesy Absopulse


The heatsink assembly also makes it easy to mount the device on thermally non-conductive or uneven surfaces such as plastic wood, or even brick walls. These devices can even be deployed in applications where there is no heat sinking surface available at all. 


The Two Members of the LTH 65R-F3-HSA series 

The LTH 65R-F3-HSA meets the requirements of EN 50155 for electronic equipment used on railway rolling stock. The LTH 65-F3-HSA, is an industrial quality version that is in most respects quite similar to the LTH 65R-F3-HSA


Both the LTH 65R-F3-HSA and the LTH 65-F3-HSA

The output voltages float, with either the positive or negative outputs usable as ground. Both units work with inputs ranging from 10.5 to 16 VDC. The units switch at 55kHz ±3kHz.

Optional built-in redundancy diodes allow for paralleling and N+1 operation or for back-up battery connection. 

Line/Load Regulation: ± 1% combined from zero to full load

Dynamic Response: Max 5% voltage deviation for 10% to 50% load step with recovery in 1 ms or less

Temperature Drift: 0.03%/°C over an operating temperature range 

Output Ripple/Noise: Better than 1% of peak-to-peak output voltage or 0.2% RMS of the output voltage (20MHZ BW)

Overload Protection: 

  • Short-circuit protection 
  • Thermal shutdown in case of insufficient cooling (self-resetting)
  • Shock/Vibration: IEC 61373 Cat 1 A&B 


The LTH 65R-F3-HSA


  • 1500Vdc input to chassis
  • 3000Vdc input to output
  • 1500Vdc output to chassis 


  • EN60950-1
  • EN50155
  • EN45545


Meets criteria as requested in EN50155 and EN50121-3- 2 according to

  • EN61000-4-2 (ESD)
  • EN61000-4-3 (RF Immunity)
  • EN61000-4-4 (Fast Transient)
  • EN50155 (Surge)
  • EN61000-4-6 (Conducted immunity) 
  • EN50155 (Voltage variation)
  • EMI: EN50121-3-2 

Efficiency: 85% (typ) at full load 

Temperature Range: -25 to + 55°C at full spec.


The LTH 65-F3-HSA


  • 500 Vdc input to chassis
  • 1000 Vdc input to output
  • 500 VDC output to chassis

Standards: EN60950-1 and corresponding standards

EMI: EN55032 Class A with margins 

Efficiency: 80% (typ) at full load

Temperature Range: 0 to 50°C at full spec.


Physical and Environmental Conditions Common to both Converters

  • Size: 5.2" x 4" x 12.7 
  • Weight: 6.6 lbs 
  • RoHS compliant