Measured power draw of various items aboard.

[thataway]

Both Foggy and Richard have brought up the charging of the last 15% to 20%, and this is important. This is the reason we try and hit a marina with shore power or run the little generator every few days--to be sure that battery is topped off regularly. There are other ways to help prevent sulfation--and that involves the pulse chargers--some of which actually run on 12 volts--but again you have to be able to keep those batteries topped off with a shore charger.

On our larger boats--where we had very large electrical demands--such as an auto pilot, 10 hours of navigation lights, etc we had not only 200 amp alternators on the engine--and in one boat on the gen set--plus 130 amp chargers on the inverters--which battery banks which were over 1200 amp hours. But this type of technology is not either practical or necessary in a C Dory.

For a 25 or Tom Cat, about the max is 2 engine start (dual engines) one or two in a house bank--and then a separate inverter or refer bank. It is fairly easy to do the 2 group 31's, in the larger banks, some have gone with an 8D battery or a couple of golf carts in series. However, doing this makes any of the boats considerably heavier, and will affect performance.

[Sunbeam]

Just as a random data point, since it has come up in the thread: Yesterday morning when we left our anchorage, the battery SOC was at 64.7% (after two days and two nights at anchor, mostly aboard, weathering a front/wind - and nearly all of that draw down was my laptop/Internet, so nothing "essential).

We cruised for 3.5 clock hours (3 engine hours), all between idle-forward and hull speed (say around 800rpm to 1400 rpm). We covered 14 miles (and incidentally used around 2 gallons of fuel, give or take (hard to measure that little). When we put our anchor down again at the end of that time, the SOC was at 92.6%

Yesterday afternoon, last night, and this morning were more typical of what we have seen (no Internet). While at anchor (a bit under 24 hours) we didn't use any power to speak of (charged a camera battery and a phone slightly). Then this morning we puttered around 30 minutes (1200 rpm or so). We wanted to get back to "Internet land" to see about the park closure and look up weather so we could make plans. Now the SOC is at 93.8% (all as measured on the battery monitor).

I will have to keep an eye out to see what it takes to put that last 5-6% in. We've only been below 90% a couple of times, so I don't have a solid feel for it yet since this is the first cruise with the boat. I could probably kill a battery in short order with easy Internet access and no additional charging methods (but I will exercise some self control!).

Sunbeam

PS: I mentioned this before, but my biggest (happy) surprise is that the engine puts a fair number of amps in to the battery at idle/hull speeds (10-12 amps). With smaller outboards like you'd have on a smaller sailboat (at least in my experience, which granted is not with all motors), the engines don't really put out much until you are closer to WOT (or rather "full normal running speed). I have never run a "large" outboard before so did not know what to expect. My Yamaha is listed as having a 20 amp alternator, but (unlike some other brands, and I have not researched further) not listed is whether this is "available" total or just the total (some of which would go to running the engine). I suppose since it is carbureted, less goes into the engine than would with a newer engine). Also, I haven't yet noted how many amps are going in at higher speeds (maybe it's the same). Also will have to see if that number drops as I get over 95% SOC.

[srbaum]

Sunbeam,
Why do you use an inverter to run/charge your computer, vice powering it from the 12 VDC (cigarette lighter socket)?

[Sunbeam]

[willronco]

Sunbeam (and maybe others who have faced this Mac annoyance),

There is a company called HyperShop that makes a variety of external batteries, connecting cables, etc. to help charge Apple laptops more conveniently:

http://www.hypershop.com/

I haven't used that particular one, but I have used a similar kind of product with a magsafe plug on one end and a 12v adapter on the other which worked OK. If I get a chance to try out the hypershop device, I will report my findings.

A thousand thanks for all the current draw information, it is incredibly helpful!

[Sunbeam]

Thanks for the link, willronco - I'll take a look at it. I'm guilty in that I haven't even shopped for one for a year or so. It just so happened that I was off boats (yeah, it happens) for the most part and living such that I had pretty easy access to 110, and so I got in the habit of the inverter. Not that I didn't think about how dumb it was each time I had to deal with plugging it in!

I think it was "MikeGyver" who was making them back then (and maybe still). One thing I found out in my shopping was that some of the 12 volt chargers (one chooses a "branded" one to splice into the MagSafe end) will shut themselves down "helpfully" if your 12volt source goes below a certain charge level. Problem is, it's a really high level, and one that an informed boater (or RV-er) with a battery management plan might often be below (with no real problem). However there were other brands that did not do this. Somewhere I have the notes stashed on which were which. This thread has jogged me to make it a priority to review the current info and get a 12 volt adapter, finally.

Glad the draw info has been useful - now the thread is helping me to get a move on with the adapter I like how the threads/community here work that way.