Measured power draw of various items aboard.

Sunbeam

Having some time to spend at anchor recently, I finished setting up the battery monitor and also measured the power draw of various items I have aboard. I thought the figures might be of interest to others here.

(I had been meaning to do this for awhile, but the immediate reason was that I could see a .19 draw on my Victron battery monitor and I wanted to figure out where it was coming from. After disconnecting everything - luckily the boat is fairly simple - it was still there, and it finally dawned on me that I had not "zero calibrated" the unit after installing it. That was a simple matter once I remembered to do it. After that I reconnected things one at a time and measured the draw. Of course the ones I really pay attention to are things that I may have on for hours (fan or anchor light, for example), not things that are only momentary. Anyway, here is my list. These figures are in amps.)

hardee · Posted: Thu Oct 10, 2013 4:06 pm Post subject:

Sunbeam,

Nice research. Nice device to have on board. Lots more detail than I ever thought about though. I can see it as useful information for long term cruising.

Harvey
SleepyC Moon

Sunbeam · Posted: Thu Oct 10, 2013 4:17 pm Post subject:

Glad you found it interesting. Even for shorter term though, a higher draw device could take the batteries down more than you might think (or, conversely, you might hold off on using said device unnecessarily). For example, sitting here at anchor for a couple of days with Internet access and a laptop, I could draw the house bank down pretty easily (i.e. this could be a weekend, not "long term").

Still though, I hear you, and if motoring a reasonable portion of each day and on a shorter trip, it may not be a "thing."

For me, it is so worth the relatively reasonable price and easy installation. But then I like my data Very Happy

One handy feature of the display is "SOC" or State of Charge. I can glance over and see that the house bank (really just one dedicated battery) is at, say, 87% charge. Then I know how much power I have to spend or save as desired to keep above whatever percentage of charge I want to (and considering how soon I may be motoring again - since for me right now the engine is my source of charging). It also shows the voltage and/or amperage going into the engine while I'm motoring - I found it interesting that the main engine was charging at a fairly high rate even when just idling along in narrow canyons. The alternator on smaller "kicker" sized outboards that I know of don't really put anything out until at a high percentage of throttle). At least this is how I'm understanding it.

Sunbeam

thataway · Posted: Thu Oct 10, 2013 4:58 pm Post subject:

Nice study. We have also mapped out our specific lights (and one of the reasons to go over to LED). For the low draw appliances, we find it more accurate to use a digital volt meter, which does better than the shunt for low draw--in the milliamp category.

Thanks.

Sunbeam · Posted: Thu Oct 10, 2013 5:34 pm Post subject:

Foggy · Posted: Thu Oct 10, 2013 7:54 pm Post subject:

So, what is your average daily use of the listed equipment (amp/hrs) at anchor, not plugged in to shore power and not running you engine(s)?
What do you have for your 'house bank' batteries in amps?
Are you satisfied with what you have or are you running low on amps?

Aye.

Sunbeam · Posted: Thu Oct 10, 2013 8:37 pm Post subject:

Foggy · Posted: Thu Oct 10, 2013 9:19 pm Post subject:

[quote="Sunbeam"]

hardee · Posted: Thu Oct 10, 2013 9:55 pm Post subject:

Hi Sunbeam et al,

Since I am looking at replacing my batteries (2 group 27's) this year it was nice to learn that the G-31 is the same physical size. My batteries are going on 6 years now, and I'm thinking next spring will be the time to make the change.

I have used them pretty much all the time on the "Both" on for all use with no problem. I check the voltage frequently (via a cheap cig plug monitor), and it gives me the trend info I need to keep the batteries up. It is really running on the KISS side of things.

I have thought about solar charging and rarely plug in at the marina, finding that running the boat at least every other day is adequate for my electrical needs, mostly a CPAP at night, and vhf or music during the day if I am not running. I do charge my phone each night.

This has been an enlightening thread because I have not really gotten into how much juice some things use. My last trip, 10 days, was even without a cooler, just to see if I could do it. It wasn't too bad. Had some fresh veggie's, some nuts, dried fruit, some bread stuff and some canned proteins.

Thanks again for sharing,

Harvey
SleepyC Moon

Sunbeam · Posted: Thu Oct 10, 2013 9:55 pm Post subject:

thataway · Posted: Thu Oct 10, 2013 10:26 pm Post subject:

The group 31 can be from 95-135 Amp hours, The group 27 from 85 to 105 amp hours. The battery with the higher capacity will weight more, because of heavier lead plates. We try and get the highest amperage battery we can find.

We found that in AK with 40 amps of the 130 Honda we would run at least 3 to 4 days before visiting a marina--and we usually did that for water and often good hot showers (even though the 25 has a shower). We had a 1000 EU Honda generator and an extra 30 amp battery charger, plus the built in 10 amp charger, but never used it. The usage included a built in refrigerator. This changed at Lake Powell, where ambient temperature was much higher, and we had to run the generator every few days to keep the battery well charged. However we would stay at anchorages often for a number of days.

We like the chest type of refrigerator/freezer such as Dometic/ Waeco. To run this we have a 125 amp, group 31 AGM battery, and run the generator with the 30 amp charger an average of 2 hours a day at Lake Powell--daytime ambient temperature of 80 degrees. The house battery--currently group 27 flooded (will be replaced with group 31 AGM), lasts at least 2 to 3 days without charging. We just only use a few hours of LED lights for reading when at anchor. We will put the boat's 20 amp charger on the house battery every few days to keep it topped off, if we were not running the outboard.

Foggy · Posted: Thu Oct 10, 2013 10:30 pm Post subject:

Running your engine will only partially charge your batteries. To get a full charge, which they need periodically to prevent sulfonation, the batteries should have the proper charge system, via shore power or solar panels, to take them past the 'bulk' charge phase which is the limit of your engine alternator.

So, I'd rethink your idea of "If I want a full battery tomorrow night, but am only going to motor a short time tomorrow,".

Aye. I'm learning too.

Sunbeam · Posted: Thu Oct 10, 2013 10:54 pm Post subject:

NewMoon · Posted: Fri Oct 11, 2013 11:01 am Post subject:

Another bit of analysis to throw into the discussion:

When figuring our boat's electrical needs, and thus the desirable battery banks and alternator, I looked at the documentation (or the case) of each significant current user on board, and plugged their amp draw figures into a spreadsheet, along with conservative (high) estimates of the amount of time the devices would be in use during an overnight at anchor.

This made it easy to calculate the estimated AH usage for each, and the total. And to fiddle with the numbers a bit until I thought I'd got the estimates to a fairly realistic (but a bit high) figure. I also moved the users up and down in the list so as to sort them in order by total projected usage per overnight. The fridge was by far the greatest user, and the anchor light (before I changed it to LED) surprised me by coming in second.

The spreadsheet said we might use as much as 60-70 AH per 18-hour spell at anchor. I haven't yet verified the rates of current draw figures for each device with our Link 2000 AH meter as Sunbeam has, but overall usage is as predicted, ranging from 30 to 70AH per night.

Cruising electrical wisdom suggests that the house bank capacity should be three (or even four) times that AH requirement, since you don't want to draw down below 50%, and pumping back in the last (top) 15% of charge is much slower than going from 50% to 85%. So we chose a house bank of 210 AH, two G31 AGM's from Deka.

Not being limited to the charging system of an outboard, we also chose a nominally 75-amp external alternator and smart regulator to replace the stock one on our diesel engine. The alternator's amp output should be at least 25% (maybe 40% or more with AGM's) of the house bank size in AH. The spreadsheet also calculated how long it would take to recharge in various scenarios.

If anyone is interested in a copy of the AH usage spreadsheet, or of another one in which I collected the stats on a variety of batteries, and compared various possible setups, I'd be happy to email.

Sunbeam · Posted: Fri Oct 11, 2013 11:11 am Post subject:

Good points, and I have worked it that way before. On this boat (my C-Dory 22), I've kind of worked "backwards" for now. That is, I fit in the largest practical house battery (without going to heroics or moving the battery location entirely), in both physical size, weight, and the amount I wanted to be "responsible" for re-charging with my current available methods (outboard's alternator and small smart charger for occasional trailer use). So I'm fitting my electrical draw desires into that (LED's make this so much easier!) instead of figuring out my draws and then designing a system around them. Since things are simple, this works - at least for now.

Once I've used the boat more, I'll decide if I want or need anything more, and then change things as necessary (within the constraints of size and weight presented by the boat).

Wind is down today, so I'm off to do some exploring, which will put some amp hours back into the battery Very Happy

Sunbeam