Battery consumption. It's a mystery. - SailNet Community
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post #1 of 64 Old 05-15-2014 Thread Starter
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Battery consumption. It's a mystery.

Well, last summer I used very, very little power. So little that a seven watt solar power was my sole means of charging my battery and it never died.

This year I'm upping things. I'm sitting here organizing and packing, well. I'm done for the night, but I've got a LOT of lithium battery toys to charge. I know a lot of it is small. Camera batteries. A laptop. Ipad, phone. Bluetooth things.

Then I have the boat stuff. I've got a ray marine st2000 autopilot, I think I will use extensively, chart plotter, depthsounders, led nav and spreader lights, led interior lights and assorted boat electronics. Oh and a stereo with two speakers.

Battery consumption is on my to do list to learn, but I'm not there yet. Basically do you think I have enough of a system to work?

I have two gel batteries. I believe 97 amp hours each, a 50 watt solar charger, an alternator on my outboard and maybe a small generator. Let's pretend I don't have a generator because I'm not sure I do. Will my solar panel and alternator be enough, and do I have enough for my battery bank?

My thinking is that the solar will do a lot, and the rest I'll just have to be that guy that idles his engine on days I don't spend extensive time motoring to a new place. Maybe idle an hour a day? Is this a good base plan or do I need to start thinking about a fix?


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post #2 of 64 Old 05-15-2014
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Re: Battery consumption. It's a mystery.

First off, before you do anything else, go buy a Victron BMV-602 Battery Monitor.

Victron BMV 602 Two Bank Battery Monitor

It's the best money you'll ever spend on your boat's electrics and will show you exactly how everything is working and where your power is going.

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Re: Battery consumption. It's a mystery.

I have a blue sea systems 8248 multimeter. This is similar?

http://www.jamestowndistributors.com...ter+with+Alarm


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post #4 of 64 Old 05-15-2014
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Re: Battery consumption. It's a mystery.

Here's a link to an old thread that had some good info about battery monitors and how to calculate your electrical consumption.

https://www.sailnet.com/forums/electr...alculator.html

I made an excel spreadsheet for my boat where I listed each electrical device, an estimate of it's electrical draw when operating, and the estimated number of hours per day that it would be turned on - not sure how to copy it here but PM me and I can e-mail it to you.

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post #5 of 64 Old 05-15-2014
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Re: Battery consumption. It's a mystery.

There maybe some who tell you to calculate everything, but its impossible.

The only way to do it is trial and error.

I bought a $10 multimeter and just shoved it in the cigarette socket 10 times per day. No battery monitor, no charge controller, just solar directly into the batteries.

When the multimeter says you are under 12.24 without load (ie everything is off) or below 12.11 with big things on, then get the engine on. Or turn off things.

You will see how its going to work with you. I think you need a larger solar panel. But the engine is fine in the interim. Mine idles at 800 rpm but I charge at 1200 rpm.

If you need to charge at 2am do it then.

All the stupid phine batteries etc we have now, i charge in the afternoon when my batteries are full.

Its all just trial and error.

BTW the multimeter has a continuity checker. Make sure yours has that feature not for this, but other electrical stuff
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Re: Battery consumption. It's a mystery.

Most of your loads are small, with the possible exception of the laptop and the stereo. My gut feeling is you should be OK as long as you are a bit careful with usage. Only issue is that the generators on outboards don't put out the power that an inboard does, so bringing a low battery back is going to take a LONG time. But that 50 watt solar panel should keep up fine. With that size panel and your small battery banks, I hope you have a solar controller.
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post #7 of 64 Old 05-15-2014
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Re: Battery consumption. It's a mystery.

Quote:
Originally Posted by MarkofSeaLife View Post
There maybe some who tell you to calculate everything, but its impossible.
Trying to precisely determine your exact energy usage every day is impossible. No doubt about that. But doing a few calculations, to get you into the general neighborhood, is definitely not impossible. I think it's also very worthwhile.

You at least need to look around and ask yourself what are going to be the big energy hogs, and roughly how much are they going to use. Otherwise you end up like the people we've seen posting here in the past, who can't understand why their battery keeps going dead. Then, when pressed, we find that they are trying to run an air conditioner all night on a single Group 27 battery with a 40 watt solar panel to charge it!

Getting obsessive about trying to nail down your usage to the nearest electron is a waste of time. Doing a few calculations to get a rough idea of how much you will use, and therefore what sort of battery bank and charging capacity you need, is a very worthwhile use of your time.

Oh, and to the OPs question... No, a multimeter is not the same as a battery monitor. Completely different thing.
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post #8 of 64 Old 05-15-2014
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Re: Battery consumption. It's a mystery.

Sounds like this would be a worthwhile investment for you...


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post #9 of 64 Old 05-15-2014
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Re: Battery consumption. It's a mystery.

What model of laptop do you have? Newer ones use very little power, most older ones can use quite a lot.

The battery monitor recommended is the best way to learn how much each of your devices is consuming.

I found a 20 watt panel and the tiny outboard alternator provided more than enough power on my Catalina 25 to keep a cell phone, iPad, and lower-power Macbook Air charged and allowed us to use the LED cabin lights, VHF radio, and ST2000 autopilot. However we were cruising in the middle of Seattle's summer when it was always sunny. We had no battery monitor, just a voltage meter.

On my much longer cruise last summer I had a 40 watt panel and much higher output alternator on my Pearson 28-2 along with a good battery monitor. We've added more electronics (plotter, wind/depth/speed instruments, more advanced autopilot), a second tablet, and electric water pumps. Our batteries never fell below about 90% charge.

On both boats I had 2 group 24 batteries as our house bank. We never plugged into shore power on either trip.

I think you'll be okay, but measuring is the best way to really know. It also depends heavily on your laptop, some consume up to 40 or 50 watts per hour while in use, others consume under 5.
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post #10 of 64 Old 05-15-2014
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Re: Battery consumption. It's a mystery.

A slight deviation here. I'm in the market for a battery monitor. I've looked at the Xantrex Pro and the Victron, and Clipper. In all the reading it was never mentioned that sensing the alternator charging required a shunt shifter as it is mentioned in the blurb on the Blue Sea Sytems DC panel meter in the Jamestown web site.
"Standard meter operates in negative side of circuit only. Shunt Shifter required for positive side installation such as alternators"

Is this requirement standard for all monitors or just for the Blue Sea?
And just how important is temperature sensing in calculating remaining battery power?

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