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Raymarine forum - EV-100 / Low battery

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my EV-100 system (sailboat with wheel steering, p70 display) has worked well for a couple of years but now gives me a low battery warning and quits functioning when in Auto mode, even if the battery level is over 13 volts. When I press Auto it takes 10-20 seconds before the warning starts.

I opened the ACU-100 and measured the voltage on the power input connectors (under load in Auto mode) and got the same 13,x volts here, so the wiring seems fine.

Any ideas what to to check next, or do I need to service / replace the ACU-100?
Hello Andreas,

By testing at the ACU under load you're doing the right things, but I would still be questioning whether the cause is a short-term dip below 12V when the drive is drawing peak current. Personally, I have very seldom seen pilot installations where there was a consistent 13+ volts at the ACU when under load. This symptom is exactly what I've seen caused by short-term supply dips many, many times over the years. It's possible that the cause is a supply-voltage drop within the ACU when under load (the alarm doesn't happen in Standby, correct?), but I think this is relatively unlikely.

The only true test for supply voltage is an oscilloscope, but testing to see whether the alarm stops appearing if you remove some or all of the load (disconnecting the wheeldrive cable, running with the clutch disengaged or putting an incandescent lamp on the pilot's drive output in place of the drive) would also give useful clues as to where the problem lies.

Alternatively, your nearest Raymarine service centre would be able to load-test the ACU. The EV pilots have a 2 year warranty as standard, 3 years if registered on our website within 90 days of purchase, so your system could well still be within warranty period.

Hi Tom,

thanks for your reply.

I also find it is strange that there is no voltage drop when under load. But it appears as if the unit is not even trying to move the rudder, I get no rudder movement at all, no sound from the unit trying to move and exactly the same voltage before I press Auto as after and when the alarm goes off. I have new batteries and the same happens both with engine on and enginge stopped.

Unfortunately I’m out of warranty also, according to local dealer (bought the boat recently so I was a bit uncertain when the previous owner installed the kit).

Br, Andreas
Did you mean disconnecting the wire from the ”rudder” port on the ACU? I tried that and it gives the same low battery warning as with the cable attached.

And yes, the warning occurs only in Auto mode = no warning when in Standby. But the unit does no attempt to move the rudder at all in Auto mode, and the alarm goes off in about 10 seconds after pressing Auto.

Hi Andreas,

When you press Auto, the pilot 'locks' the heading that you were on at time, but won't start to make course corrections until there's a difference between the current and locked heading values. It sounds to me as if the delay you're seeing is when the pilot is not making a course correction, but once it does, the current peaks, dips the supply voltage at some point in the system and then you get the alarm.

The thing to disconnect is the wheeldrive, not rudder position sensor. I'd disconnect the two wires at the Motor terminals on the ACU100, to see whether/how that changes the symptom. Of course that's not going to fix the pilot, but if the alarm goes away (and is replaced by a Drive Stopped, Motor Stalled or Off Course alarm instead), then that suggests that the trigger for the Low Battery alarm really is the load drawn by the drive. Leaving the wheeldrive connected to the motor terminals on the ACU100 but leaving the wheeldrive's clutch disengaged would be another, subsequent test I'd do.

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