[CA] [CA11] Type 2 Rotary Drive Current/Amps

[skibum]

The only specs I can find on the current draw for the rotary drives show that the Type 2 uses between 60 and 84 watts.

A quick calculation shows that at 12 volts, the drive unit will draw 5-7 Amps.

But, and this is where my confusion comes in, the chart shows that you need the ACU-400 for the Type 2 rotary drive.

Why?

Specifically, why the ACU-400 instead of the ACU-200?

The ACU-200 specs say that it can power a drive unit up to 15 Amps continuous, which, if the specs on the Type 2 Rotary Drive are to be believed, is more than double the amount of current that the drive unit will draw.

The ACU-400, with a 30 Amps continuous rating seems like absolute overkill for a drive unit that supposedly only draws a maximum of 7 amps.

Can someone tell me what I'm missing here?

[Chuck - Raymarine - Moderator]

Welcome to the Raymarine Forum skibum,

Unfortunately, the drive unit's rated power consumption is only one of the factors taken into consideration in specifying an ACU. When the drive unit is switching polarities, which it does constantly when the autopilot is operating in Auto or Track mode, it will create a current spike which can be 5-6 times that of 7 amps which you have stated. Over time these current spikes would cause damage to the drive FETs of an undersized ACU. ACU failures resulting from use of a drive unit requiring a larger ACU would void the ACU's warranty. Additionally, the inability of an undersized ACU to accommodate may cause voltage drops within the autopilot, causing it to drop to Standby from Auto or Track modes without triggering any error alarms.