[TG] Autopilot Voltage

[Offshore]

Hi,
Have an Evolution system with P70, an ACU-200, and a type 1 pump.
ACU and Pump are new.
motor sounds weak and choppy.
We connected the pump directly to a fully charged battery and it works fine in both directions, although it sounds different turning to port.
reconnected ACU and pump and same weak sound
we then checked the voltage going into the ACU and it was 12.6 volts.
we then checked the voltage coming out to the pump and it varies between about 2 volts and 6 volts. we did get 12volts out of it once for a second.
we then checked the incoming voltage under load and it stayed steady at 12.6.

not sure what to check next. It is a brand new ACU but it doesn't seem to be putting out the necessary voltage to make the pump work smoothly.

Thank you

[Tom - Raymarine - Moderator]

Hello Offshore,

The ACU 100, 150, 200 and 400 (that is, all models except ACU300) output what's called a pulse-width modulated output (PWM.) They don't drive a straight 12V or 24V, they pulse the output with a high frequency (something like 40kHz from memory) in order to provide a softer start and stop and finer control over the movement. This is very standard in motor control systems. You will almost never measure a straight supply voltage on the output from one of these pilots with a multimeter: to measure the output properly you would need an oscilloscope. This is what an ACU200's drive output looks like on a low-cost PC 'scope:



Secondly: when a boat is not moving, the pilot will not react 'normally' and make strong drive movements. It's looking at speed data (GPS speed-over-ground or paddlewheel speed-through-water) and waiting for the boat to get moving in order to know how much helm to apply for the current speed. Don't be concerned if the pump doesn't appear to be moving correctly when dockside: once you get under way I'm sure it will be fine.

If you have problems with steering performance when underway, however, come back to us of course. Ideally call your nearest Raymarine Support office when you're on the water so we can talk through what's happening.

Regards,
Tom

[Offshore]

Ok, thank you. is it ok that the pump sounds different going one way than the other?

[Tom - Raymarine - Moderator]

That depends on the circumstances. Assuming the pilot is driving symmetrically - and pilots are complex things and will vary their drive output from one moment to the next depending on a number of factors such as current drive position, the difference between heading and locked-heading, rate-of-turn, boatspeed, back-EMF from the motor and so on - and the load on the pump is symmetrical then yes, but there are a number of assumptions and caveats there.

The simplest explanation if you get a different sound when driving each way with a direct 12V supply is that there's different load on the pump in each direction, which sounds like a hydraulic issue. Who installed the pump? I'd get them to check the system.

Regards,
Tom