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Old 24-04-2020, 05:46   #1
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Battery capacity and dd autopilots

Hey guys,

We are a Pearson 424 - 42', 23,000 lb ketch. I currently have 4 Duracell GC2's, two years old and well maintained as our house bank. I'm calculating these as having about 428ah of capacity at 12v. We have 430w of solar with an excellent charge controller. A 70 amp and a 125 amp alternator on our 58 horse diesel.

Sailing all day in 15-20kt winds and a rolling small swell our Raymarine direct drive autopilot drains the house bank after several hours. I have not timed it exactly as it varies on conditions.

I'm thinking about adding 2-4 more GC2's and adding 50% or 100% more capacity so we don't have to run the motor to charge.

Curious to hear about other people with similarly sized boats running direct drive autopilots for long periods on wet cell batteries like these.

How much battery capacity do you have and what percentage of it do you devote to the autopilot?


Thanks in advance for any input.
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Old 24-04-2020, 05:58   #2
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Re: Battery capacity and dd autopilots

Adding more batteries will not make it so that you don’t have to run the motor to recharge, unless of course you plug in every night, then it certainly could, but for long trips it’s not going to keep you from running the motor or other means to recharge.
Batteries are of course just storage, you are depleting your batteries now in a days sail, so the Solar isn’t enough to break even, much less charge the bank. You will need to either increase charge or decrease consumption.
One reason I have a CPT Autopilot is that it’s average consumption is .4 amps, meaning of course that in a 10 hour sail on average it will use 4 AH, which is minuscule.
Now DDW will increase that substantially, but even if it tripled the consumption, that’s still only 12 AH in 10 hours.

I’m a very similar sized boat, 660AH bank that has degraded to 400 AH
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Old 24-04-2020, 06:00   #3
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Re: Battery capacity and dd autopilots

That seems like an awful lot of power for an autopilot. Do you maybe have the settings a bit on the aggressive side where it's wasting power making tons of tiny, constant rudder corrections when it doesn't really need to?
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Old 24-04-2020, 06:04   #4
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Re: Battery capacity and dd autopilots

We’ve got roughly the same battery capacity as you, and roughly the same solar.

Sailing along, well balanced, we can go for days in nice weather before needing to start the engine to feed the autopilot. In really crappy weather with confused following seas were running the engine for two hours a day to “catch up” with increased consumption.

If you increase the bank size, you’ll need to run the engine for longer, or wait for two or three days for the solar to catch up.

Before adding batteries, ask yourself, how hard is the autopilot working? Could I ease the load on the autopilot?
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Old 24-04-2020, 06:57   #5
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Re: Battery capacity and dd autopilots

Thanks all. Jeez... Duh... Come to think of it, We just replaced the autopilot computer bc the old one crapped out and have never had this issue before.. I haven’t re-adjusted the old autopilot so you’re absolutely right... it could totally be over-correcting.
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Old 24-04-2020, 09:40   #6
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Re: Battery capacity and dd autopilots

let's say your drawing your batteries down near 50% by using 200AH over the course of 24 hours, that's 8.3 amps continuous.
Wouldn't that be quite a lot for an autopilot to draw?
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Old 24-04-2020, 10:11   #7
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Re: Battery capacity and dd autopilots

Yeah. Consumption is up quite possibly up because my settings aren't dialed in right with the new AP computer. However, it could be something else too.



The way I noticed the batts were low was our AIS stopped relaying to my phone. I went down below to check the AIS, looked at the analog voltmeter on my panel and saw that every time the AP drive engaged, the needle dipped way down in voltage - like to 9v or 10v, but then it would spring back up when the drive stopped.


I fired up the motor and all was well after EDIT: a couple of hours or so with the motor running and I charged the batts back up again.


To reply to A64 - I actually do think more batt storage would help as we don't sail under autopilot every day and spend most of our time on moorings or at anchor where the solar will bring my bank back up. Our usage on the hook is minimal as we are an all LED boat.
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Old 24-04-2020, 10:13   #8
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Re: Battery capacity and dd autopilots

Can you be more specific about your AP?

In addition to the suggestions about adjusting the AP's parameters, if you're draining down to anywhere near 50% of your bank capacity in only "several hours," I'd suggest that either your capacity isn't what you think it is, or you've got other power consumption issues.
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Old 24-04-2020, 10:26   #9
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Re: Battery capacity and dd autopilots

The autopilot is:


Raymarine Mechanical Linear Drive (not sure of exact model)

ST6001 Control Head

Raymarine S2G autopilot course computer E12091 Type 150g (newly installed)


EDIT: Also, new Raymarine gyrocompass
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Old 24-04-2020, 10:39   #10
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Re: Battery capacity and dd autopilots

Quote:
Originally Posted by Brewgyver View Post
Can you be more specific about your AP?

In addition to the suggestions about adjusting the AP's parameters, if you're draining down to anywhere near 50% of your bank capacity in only "several hours," I'd suggest that either your capacity isn't what you think it is, or you've got other power consumption issues.



I guess it's possible my batts aren't as good as I think they are. I do maintain them well - checking water levels every couple of months and making sure I don't drain them, but I said I installed them two years ago... just checked and it was actually Dec 2016. Time flies.



Maybe it's time to refresh the house bank and possibly expand it once I dial in the autopilot.
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Old 24-04-2020, 11:31   #11
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Re: Battery capacity and dd autopilots

The spec on the largest Raymarine Type 2 Linear Drive is 4A to 6A current draw for continuous use. Call it 5A at 50% duty cycle and the consumption should be 60Ah in 24 hours. You seems to be experiencing much higher drain than that so it seems that something else is happening.
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Old 24-04-2020, 11:44   #12
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Re: Battery capacity and dd autopilots

Quote:
Originally Posted by Peregrine1983 View Post
The autopilot is:


Raymarine Mechanical Linear Drive (not sure of exact model)

ST6001 Control Head

Raymarine S2G autopilot course computer E12091 Type 150g (newly installed)


EDIT: Also, new Raymarine gyrocompass

Your boat is right on the cusp of max recommended displacement for the Type 1, so you may very well have a Type 2 drive. Raymarine states typical Type 1 consumption is 18-36 watts, Type 2 is hungrier at 48-72 watts. So even a Type 2 shouldn't be draining your bank is such a short time period.

Of course, the drive itself is the power hog, consuming but only while running. The course computer and control head combined, with full illumination on the 6001, only use about 6 watts.

Run the AutoLearn function first, don't forget to save the settings after you get the Pass message. After that you can also manually set the Response Level to 1 to minimize drive activity.

It goes without saying, but I'll throw it in anyway, that keeping the sails well balanced makes a HUGE difference in AP power consumption, course accuracy, and component longevity.
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Old 24-04-2020, 11:56   #13
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Re: Battery capacity and dd autopilots

41' Lord Nelson full keel doesnt use anywhere near that consumption oofshore. suggest for the conditions yoy mention you invest in a windvane and safe yourself a lot of grief.



Quote:
Originally Posted by Peregrine1983 View Post
Hey guys,

We are a Pearson 424 - 42', 23,000 lb ketch. I currently have 4 Duracell GC2's, two years old and well maintained as our house bank. I'm calculating these as having about 428ah of capacity at 12v. We have 430w of solar with an excellent charge controller. A 70 amp and a 125 amp alternator on our 58 horse diesel.

Sailing all day in 15-20kt winds and a rolling small swell our Raymarine direct drive autopilot drains the house bank after several hours. I have not timed it exactly as it varies on conditions.

I'm thinking about adding 2-4 more GC2's and adding 50% or 100% more capacity so we don't have to run the motor to charge.

Curious to hear about other people with similarly sized boats running direct drive autopilots for long periods on wet cell batteries like these.

How much battery capacity do you have and what percentage of it do you devote to the autopilot?


Thanks in advance for any input.
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Old 24-04-2020, 16:38   #14
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Re: Battery capacity and dd autopilots

you should get a battery monitor so you know many ah it's actully consuming.

my guess is your batteries may not be as good. you'd know with a monitor if you draw ~40ah in 2 hours of sailing and the batteries go dead. then they are toast. if you draw 250ah in 2 hours of sailing and they go dead. something is drawing way too much power.


adding 50% more batteries means you need 50% more charging when you recharge them. so your plan doesn't quite add up of not running the motor.
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Old 24-04-2020, 16:52   #15
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Re: Battery capacity and dd autopilots

Not enough information to declare the auto pilot is the root cause of your low battery condition. A simple way to determine power draw is to use a multimeter with a clamp sensor to measure actual draw of any power consumer. It could be something like your refrigerator is the culprit and the auto pilot is just the final straw. It also could be that your batteries are nearing their final usefulness
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