Power Consumption Question.

[Bad Obsession]

I am thinking about making an overnight sail from Colonial Beach to Hampton. I have gotten use to staying up all night (got promoted but the promotion put me on a midnight shift). I would really prefer to sail the whole time because I feel like there is much less of a chance of hanging a crabpot if you stay towards the deeper water and you don't have the shaft spinning. I don't care if I am making 2 knots of progress, I have plenty of time to get to where I am going.In saying all of this I am curious to see how my battery consumption is. How long do you think my power will last if I am just running nav lights, a handheld GPS that is plugged into power, and my autohelm? How long would you go before you started the engine to charge the system?For some reason I have this fear of getting my batter power down too low and having a problem starting the engine. I have a newer battery for the house battery (bought a new Group 27 marine battery last year) and I will probably replace the starting battery this spring. I am almost tempted to buy a jumpstart box just as a backup plan, especially if I decide to try to go overnight.I really don't know how to increase the size of my batteries or add a new battery into the system because the room in my battery compartment of my Catalina 30 is very limited (only will fit 2 group 27 batteries which is one house battery and one starting battery).Any comments would greatly be appreciated.

 

[sailaway78]

Power consumption

First off, if you run with one battery as the house bank, and one as the starting bank, then you should not have a problem with running down the start battery unless you run with the battery switch on both. Then when one goes they both go. I never ever keep the battery switch on both for this reason. You nav lights and GPS should not run down a decent house bank. The auto pilot could, or might, but you have given us no indication of how much it draws or how much you plan on using it. I think my ST 3000 draws 3.5 amps in use, and under .5 in standby, but don't remember for sure. Total the wattage of all the items running constantly, divide by 12 and this will give you the total amp draw. If you are using, say 5 amps, this should give you an easy 10 hours on a 100 amp hour battery that is fully charged.

 

[LANCE ON CLOUD NINE]

stall power consumption with a small soiar cell

On my small sailboat, I have a one foot square solar panel that lays loose on bench in cockpit. It is hooked to automotive group 27 battery. Ican leave the dock in the morning and play car stereo,fish finder/depth meter,and charge cellphone all day and when I come back to the dock, I sometimes have more volts than when I left. You could get one of these cheap wonders and enter the twilite hours of your trip with an almost full house battery. Also when I sail at night, I turn off my rear nav light and clamp on a solar light from the garden. I also use a couple of these to anchor out. People laugh, but they work PERFECT. Have a good trip.

 

[Calif. Ted]

I've gone for a couple days on a good Group 27

AGM running Wheelpilot, nav. lights, cabin lights, radios, small GPS, freshwater pump and helm gauges (knotmeter, depth). All this stuff is a relatively low draw and shouldn't present a problem at all for an overnight. Add Radar, refrigeration or a 12 volt hot tub and you might need to recharge.

 

[Ross]

Monitor your battery voltage and just run the engine at a

fast idle when it drops below 11.5 volts. Half an hour every 6-8 hours should take any worry out.

 

[Bad Obsession]

Follow-up

I am running a Raymarine S1 wheel pilot. I tend to use the autohelm a lot when I am singlehanding the boat. I really won't run cabin lights much and I do have some solar lights for when I ancor at night. At night I have a battery powered lantern for the cabin that puts out enough light but no too much to mess with a person's night vision (that is when the lantern is on low). I have two solar lights that are LED lights that I put in the cockpit of the boat (they hang from my rodholders) and they would keep the cockpit lit just enough.It would be cool to be able to replace the nav light light bulbs with LED light bulbs that draw even less power. I really think that LED is the future for boats because of the low power consumption.I do run a depth finder at all times but I tend to not use the VHF as much. I do use a car stereo sometimes on the boat. I think that there is a battery monitor on the fuse panel of my Catalina 30 but I am not sure. It isn't digital and it is a meter type. Is there a good and cheap replacement to get to monitor battery usage?As far as the way that I run batteries, #1 is my starting battery and the only time that is on is when I turn the engine to both to start the engine. I keep it on both so I charge both while the engine is running. I always switch to #2, my house battery, for when I am on the hook or I am sailing so I don't use the starting battery.

 

[Ross]

You can get a digital volt ohm milliamp meter for less than 25 bucks. you can ge

a very good one for fifty.

 

[LANCE ON CLOUD NINE]

Voltmeter

You can get a digital voltmeter that plugs into cig lighter socket. I got mine at Wallmart for 15 bucks. It has been trouble free for 2 years and always agrees with my built in volt meter on fish finder. Ross is right,the short term solution is to just idle the engine. The long term solution is solar. solar biminis are just around the corner! I'm not really a greenie and I used to think solar was a trinket. But now that I have tried it, I dont belive I would hava a generator.

 

[Ross]

I keep three kerosene lanterns on board .They provide walking around light in th

serve as an anchor light and in a pinch would serve as a stern light. They meet the requirements for night lights on a dink and will burn all night (12 hours) on a half pint of fuel.

 

[LANCE ON CLOUD NINE]

oil lamps are definately an elegant solution

and I have used them before, hanging on the end of boom. But I always worried about the gas from my outboard. Ross, do you think they would be safe if I closed vent on portable fuel tank? My bad,Bad,getting off topic.

 

[sailaway78]

A point to consider

If you run your battery switch on both, when the engine is running to charge both banks, this will work pretty good, unless one battery is weak. If one of the batteries is weak, then the good one will not get a full charge. It will only charge up to the capacity of the weak battery. Better to run it on #1 after starting, till the start battery is charged back up, which doesn't take long. I usually run mine for 15 to 20 minutes on #1. Then switch to #2, and charge the house bank. I avoid using the both position when at all possible for just this reason. A bad battery in one bank will effectively ruin the other bank.

 

[Bob V]

Agree with those recommending solar

Another thing you may think of is to join both of your batteries in parallel ande adding an Optima AGM on one of your switch legs for a starter battery. The reason I recommend Optima is that it can be mounted in any position and is relatively small. Also since it is AGM and therefore leak-proof you do not need to put it in a battery box.Make sure you get the starting battery not the deep cycle. Make certain that you use heavy wire for the connection both between bats and to the starting bat.One caution if your existing batteries are not in equal condition, the bad one will drain the good one. It's best to start with new bats and keep them parallel for life.Two batteries joined in parallel will give you slightly more capacity than using them seperately.

 

[Stu Jackson]

Energy consumption

is based on how much you use each day. How long your batteries will last is based on that and how big your bank(s) is/are.First thing, do an energy budget. WM has a form online.Some boats NEED to start the engine on BOTH because the alternator output goes to the C post of the switch and there'd be no other way to charge both banks unless you start the engine in BOTH to avoid damaging the alternator when moving the switch.Bad, you've been around here for a long time, I'm sure you've read so many of these mind-boggling electrical discussions that your eyes are already glazing over.Do an energy budget, figure out what you need compared to what you have and go from there. Even without doing the math, I can tell you that if you're planning on what you say, your single house battery is going to let you down big time real soon, even if you go to LEDs. Please, do the math.

 

[Ross]

Lance, you must confine the gasoline vapors a little

for a lantern in the open to be a problem. If there is any breeze you will have good ventilation.. There is a known range of combustability for gasoline. I don't recall what it is but your nose would find it unpleasant.

 

[Bad Obsession]

I don't have a refridgerator unit

I don't have a refridgerator unit in my boat, just an icebox. This does help because there is far less power consumption on a boat without a refridgerator.Last time I really looked into it I believe that I was good running the systems that I mentioned for 8 hours and I didn't kill the house battery. I really don't know what the power consumption of the autohelm is when it was running.I would love to have the space to put a bigger house battery into the boat but I really don't know about moving the existing batteries around and rewiring everything for it.For the now I think that I will try to do a work-up on my power consumption and then use the engine to charge my batteries. Oh, btw, I believe that I have to start and run my boat on both in order to charge the batteries without killing the alterinator.Does anyone know where the power consumption worksheet is located at the Westmarine Website? I just checked there and didn't find it. If there isn't one there does anyone know where one can be found?

 

[Benny]

Check the energy consumption per hour

of the combined componentes you intend to operate. A regular group 27 battery should have a capacity of 90 amps. Under duress lets strech the 50% rule and say you have 50 usable amps before inflicting serious wear on the battery life cycle. Navigation lights bow and stern should consume 1.6 amps per hour. The power usage of the Auto Pilot will depend on the condition of the seas but lets say it will use 3-4 amps per hour. The GPS will use .25 amps. If you use the navigation lights for 12 hours you would be looking at 19.2 amps. The GPS for 24 hours would use 6 amps for a total so far of 25 amps which would leave enough power to use the auto pilot for 6-8 hours before consuming the 50 amps available from one battery. This would leave the starting battery to start the engine. A 40 amp alternator would replace 25 of those amps in about 1 1/2 hours. To attempt a 100% charge would probably require you run the engine for around 8 hours. I would try to do with what one battery gives me saving the starter battery for the engine. This means providing power for the necessities and using the auto pilot sparingly. You may be using a radio for music and a VHF on standby and some cabin light so I would limit the use of the autopilot to runs to the head or while cooking food. This example is a mere illustration of the exercise you need to conduct and I suggest you determine the actual consumption of your components which I hope is less than the figures I have used. A battery booster box is not a bad addition as a backup.

 

[sailaway78]

Battery switches

Most battery switches will not break the circuit when switching between 1, 2 or both. I would certainly check on this, and would change the damn thing if it broke the circuit when switching. This would mean that whether you start on 1 or 2 or both, you have to leave the switch there, unless you turn off the engine and then switch the battery switch, and then restart the engine.

 

[Stu Jackson]

Energy budget worksheet

here: http://www.westmarine.com/pdf/Elecbugt.pdf

 

[ruedi ross]

A battery monitor

such as the link series is a very good tool to have. It will tell you how manyamp/hours you have used, how much is left, rate of consumption, etc. It's worth the money IMHO.

 

[Rob Hessenius]

Question Here

You guys seem to know your stuff about 12v. Last spring, I rewired my boat completely, actually a friend did most all of it. I had him put in to 12v power points. I had him wire one to battery #1 and the second to battery #2. My thought was that I could check the state of charge through my GPS. I only care about the state, not my usage.***My question is how reliable is the voltage feature is on a GPS?***Thanks in Advance,Rob Hessenius