Electro-hydraulic actuator

[wdmagic]

ive done this using a home made MOSFET H-Bridge, using a fairchild FDP8440 It takes 4(H) and 4 diodes but ive handled a DC motor 48V and 80amps using this circuit

[HenrikOlsson]

Yes, although conciderably more complicated and easier to destroy than two SPDT relays a MOSFET bridge IS an option. But it takes a bit more than 4 MOSFETs - you need proper driving circuitry for them and most high side drivers can't keep their output on constantly because they need to refresh their bootstrap capacitor. So you really need to understand the operation of the bridge and design it with the correct driver circuitry if the high side needs to be at 100% dutycycle.

Another option is 4 solid state relays, like this one on EBAY? It's rated for 50A DC and it as simple to use as driving a LED. You need to be very careful not to turn on both relays in the same leg at the same time though and you probably need to introdce some deadtime to prevent shoot-thru. That's why two SPDT relays are so handy for this - they can not short out the supply. If all you need is to drive the actuator forward and reverse I really think two 50A SPDT automotive type relays and 4 diodes is your best and cheapest bet.

/Henrik.