DC-DC converter help

Discussion in 'The Projects Forum' started by Element1, Mar 18, 2010.

  1. Element1

    Thread Starter New Member

    Feb 6, 2010
    I am using a 36-70v input 24vDC output DC-DC converter to power an electric motor from a hydorgen fuel cell. The problem is the converter turns off, goes in to over load protection, when any load iss applied. The converter is rated at 9 amps in 14 amps out and the load I've been trying is 5.3A. I have tried calling the manufacturer but I tried their suggestions to no avail. Any suggestions?
  2. SgtWookie


    Jul 17, 2007
    The motor's stall current is too high for the converter.
    While the motor may draw 5.3A when it's running, it draws several times more than that when starting from zero RPM under load.

    Try placing a 1.7 Ohm 50 Watt resistor in series with the motor when it's starting, and after the motor is partially up to speed, short across the resistor. This could be a relay or a power MOSFET.
  3. Wendy


    Mar 24, 2008
    I've never tried this, but I wonder if a really large capacitor would help the motor start?
  4. SgtWookie


    Jul 17, 2007
    You'd have to limit the charge current for the cap, or it would also look like a dead short to the inverter when it was discharged. Besides, it would take a LARGE capacitor to provide the energy to start the motor.

    Either way, with just the motor, or the motor and cap, you'd have to limit the current at power-up.

    Another option might be to PWM the current on initial start. However, a high-wattage resistor and a big switch or high-current relay would not be much of a technical challenge for a newbie, and would get them up and running very quickly at a pretty low cost.

    The idea is to stay under the maximum current rating of the supply so that it doesn't shut down. 24V/14A = 1.7143 Ohms, rounded up. I figured the motor and wiring will have at least 15m resistance. Sure, it's a low-tech solution, but it should work OK.