Autopilot (ST1000) and battery usage

[sabresailor]

My new (old) yacht has an autopilot (Raymarine ST1000). I'm moving the boat over 2 or 3 days using the inboard (13hp Volvo with 115amp alternator) and sailing with the autopilot on. I want to make absolutely sure the autopilot doesn't flatten the battery as the inboard. There is 1 battery fitted. The spec says it uses 40m amps - this seems hardly anything at all - perhaps this is just the load without much tiller movement.

If the auto pilot is on for say 8 hours how long would the inboard need to run to 'replace' the lost charge? I would imagine I will be using the inboard for at least a couple of hours a day. I do plan to investigate fitting a 2nd battery this winter.

Cheers

Mike

 

[colhel]

I've used ours for 4 hours then started the engine on the same battery with no noticeable power loss. We have 2 85 amp hour batteries with change over switch. It would depend on the size of your battery, sea state and point of sail.

 

[Tranona]

Doubt your alternator is 115A - more likely 45 or 55A. However it is your battery capacity that is important rather than your charging capacity.

The autopilot consumption you quote is on standby - that is not doing anything. The consumption in use will depend entirely on how much work you ask it to do. In calm conditions under motor or with well balanced sails consumption will be low around 2-3AH. In stronger conditions could easily be twice that. If you have a typical 85AH leisure battery , running down from full to half charge might give you around 10 hours (40AH) usage. The battery should be able to take 15A charge from the alternator easily so one hour running would replace more than 4 hours AP usage.

 

[VicS]

Yes 40mA is just the standby current

From the spec in the operating instructions :

Current consumption:
• Standby: 40 mA (90 mA with full lighting)
• Auto: 0.5 A to 1.5 A depending on boat trim,
helm load and sailing conditions​

The most it will use, on a badly balanced boat that is heavy to steer and in difficult conditions, in 8 hours is 12 Ah.

Not a lot if you have a decent sized battery and you should be able to replace that easily in a couple of hours motoring

If you have a 115amp alternator presumably you have pretty large battery to take advantage of it but it would be surprising to find such a big alterator on such a small engine

 

[PabloPicasso]

I have a similar set up auto helm and one 85ah batt. Volvo 2001 single cylinder engine. I've run for 12 hours + on auto helm and no significant voltage drop. I findits other stuff that drains the batt. Especially lights, crew leaving things on unecessarily, plotter, VHF, phone charging and so on. Switch off everything else and you'll be fine. Borrow a spare battery and jump leads if you're worried

Buy a spare batt if you're gonna fit it over the winter so you have it as back up for the trip

 

[onesea]

I have a similar set up auto helm and one 85ah batt. Volvo 2001 single cylinder engine. I've run for 12 hours + on auto helm and no significant voltage drop. I findits other stuff that drains the batt. Especially lights, crew leaving things on unecessarily, plotter, VHF, phone charging and so on. Switch off everything else and you'll be fine. Borrow a spare battery and jump leads if you're worried

Buy a spare batt if you're gonna fit it over the winter so you have it as back up for the trip

Interesting to note, I spent 6 hours hammering to windward not been kind to ST2000 slight voltage drop and the boat started noticeably falling to leeward (she was on wind angle). Then she is heavy on the helm it was wind over tide and I was not being gentle...

My answer is separate starting battery so I just hammer domestic battery at will...