Solid state relays

[AndyEss]

The one thing to consider when using solid state relays is there is a small voltage drop across them - a little over 1 volt.
I built an H-bridge from four single throw relays to offload my old RM 100 and 300 series autopilot computers. This way even the 100 computer can control more powerful actuators used on bigger/heavier boats

[stormalong]

Originally Posted by AndyEss

The one thing to consider when using solid state relays is there is a small voltage drop across them - a little over 1 volt.
I built an H-bridge from four single throw relays to offload my old RM 100 and 300 series autopilot computers. This way even the 100 computer can control more powerful actuators used on bigger/heavier boats

Better carry spare relays. The motor starting current on mechanical drives can reach 40 amps.

[AndyEss]

Originally Posted by stormalong

Better carry spare relays. The motor starting current on mechanical drives can reach 40 amps.

I carry spares for every mechanical/electrical device. I designed and built industrial systems for my business use for decades before retiring and getting back heavy into boating. Solid state relays are quite inexpensive compared to the outrageous prices marine OEM’s charge the unwary.
I also keep relays from 10A to 40A to be able to cover project needs. My autopilot H-bridges work fine on 20A relays. Inrush currents are quite short and within relay specs. If you look into the innards of either the 100 or 300 RM autopilot computers you can only shake your head at the flimsy mechanical relays that were originally used in those units. There is no wonder that those units failed as often as they did.