Calculating Daily Battery Use

Stu Jackson · Sep 12, 2014

Yes, because of battery acceptance. Fuller batteries can take less current.

Battery Acceptance by Stu http://c34.org/bbs/index.php/topic,4787.0.html

Why Going Into FLOAT is NOT Full

http://c34.org/bbs/index.php/topic,8216.0.html

Brian D · Sep 12, 2014

On my boat, I have a 50w panel. I run the following:

Wheel Auto Pilot (active)
GPS on Wheel (active)
VHF DSC (standby)
GPS on VHF DCS (active)

My panel runs those items while I am afloat. The remainder goes back into the battery. So, for the most part, my 50w panel (50w/17vdc = 2.9ah) runs my boat. I am sure that there are extenuating circumstances that I am not aware of, and, someone can shoot holes in my system calculations, however, the proof is that my indicators tells me the battery is in float while I am on the water and those 4 items are operating.

I think the major difference between us is I am not running a plotter, just a GPS. I also have a tablet with charts but that is not in the system.

Charlie Jones s/v Tehani · Sep 12, 2014

At normal sailboat speeds, you're NOT gonna get 6 amps out of the outboard. That output is at wide open throttle, and very few sailboat folks run them WOT. You'll do good to get 1 amp

Also I think your Tiller pilot amperage may be too high. I use only a 32 watt panel, one grp27 battery and have had the tiller pilot going 24 seven for several days (offshore)

And I'd find a more frugal stereo- like an Ipod driving a battery speaker, but NOT Blue tooth-THAT uses some power.

centerline · Sep 12, 2014

Bad Obsession said:
on a good day I may run my outboard with a 6amp alternator for 1 hour (longer on days with no wind).

My power consumption is the tiller pilot (I calculate between use and standby it will consume about 27 amps per day), the Garmin 441s (I calculate 5.76 amps per day), and the stereo (about 20 amps per day). This is running them for 8 hours.

Total power consumption for these devices would be around 52.64 amps per day, according to my calculations.

Does this sound right?

According to my other calculations, I put about 1 amp back for the 5 watt solar panel and 6 amps for the hour of using the outboard. That would be only 7 amps replaced.

If this is the case I am going to need a pretty large solar panel, eventually, to keep the batteries up if I am cruising .

Are my calculations off a bit?

I think your calculations are pretty close... maybe a few amps high, but its better to figure a bit too much than not enough.....

BUT.. the output of outboard is rated at WOT (wide open throttle) and it drops of quickly at anything less than WOT, so at half throttle you will only get about a 2amp output... at idle its almost immeasurable. its called the "output curve of the charging system". at this time we dont know exactly what it may tell us for your motor, but it does have one...
so what you are assuming you are putting back into the batteries, is almost certainly going to be much less than you may think.

more solar is the answer...
and if you start seriously thinking about more, you can put it all together yourself much cheaper. and not only cheaper than you can buy "ready-to-install" kits, but if you plan it out and put it together yourself, you will find that the more watts you build into it, the cheaper it will be per watt... much cheaper

for the amount of power you are consuming, you would probably want no less than 120-140watts of output... with the modern noncrystalline panels, you can expect them to be about 50% efficient... some days a bit more, but most days even less than 50%....

one absolute fact that anyone who has installed enough wattage will tell you is, it a great feeling never having to worry about how much charge the batteries have left.

centerline · Sep 12, 2014

TSBB 2 said:
At normal sailboat speeds, you're NOT gonna get 6 amps out of the outboard. That output is at wide open throttle, and very few sailboat folks run them WOT. You'll do good to get 1 amp

Also I think your Tiller pilot amperage may be too high. I use only a 32 watt panel, one grp27 battery and have had the tiller pilot going 24 seven for several days (offshore)

And I'd find a more frugal stereo- like an Ipod driving a battery speaker, but NOT Blue tooth-THAT uses some power.

I agree...

but as for the stereo, sometime back on this board we have discussed the power consumption of stereos, and someone has tested the actual output, and 1.5 to 3amps is about normal, depending on the sound level, UNLESS there are additional components in the system, such as an amp or more than 4 normal sized speakers that are being used... adding an ipod on a usb will bring it up a few watts for driving and charging the ipod itself.

using the ipod with an independent battery driven speaker is an option, and many people do exactly that. (although you still need to recharge the ipod itself somehow)
but no matter how you get the power to drive the device, whether you carry them on as extra drycell batteries or use the onboard house battery, the device will consume what it needs to do its job. and that power usage will always come at a price.
in my opinion, for the long haul, and for the convenience of having a more power readily available whenever its needed, a more powerful charging system would be a better choice.

and when designing a charging system that is properly sized for the needs of a boat that uses electronic navigation systems, the cost for the amount of extra wattage needed to run the optional stereo system will never even be noticed...

twalker H260 · Sep 12, 2014

Over all your power consumption figures appear a bit high.
Raymarine st4000+ standby power consumption spec - .72w or .06amps
In auto 25% duty cycle -10w or .83amps

You'll have to figure out how you use your autopilot but using auto at the 25% cycle for 8 hours you use 6.64 amps - 100% will get you to 26 amps in 8 hours. In 8 hours of sailing my auto will usually see less than 1 hour of use with the remainder in standby.

Stereo 1-3amps depending on volume, system backlighting etc - make sure to have on a switch to avoid standby power draw.

Your plotter manual indicates 15w or 1.25 amps maximum consumption. If you have a separate sonar unit you will need the consumption of that as well.

Autopilot - 6.64amp/hrs
Stereo- 8-12.5amp/hrs depending on system/ volume etc
Plotter - Max 10 amp/hrs + sonar
Total 24.6-29 amp/hrs total consumption.

Chief RA · Sep 13, 2014

As Centerline has already pointed out: you actually need 120 to 140w of solar. On a Catalina 250 I have 2 ea. 80w panels across the stern and 2 ea. size 24 batterys. This design is excellent for a similiar system to yours. Having a nice summer/fall in beautiful Bodega Bay Ca. on our S/V Compass Rose! Chief

kloudie1 · Sep 13, 2014

since you are carrying outboard fuel, a little generator like this:
http://www.harborfreight.com/900-Pe...zIjoiOTkuOTkiLCJwcm9kdWN0X2lk IjoiOTA1NyJ9
which is "on sale" now for $99, can run your battery charger on the boat. Yes, it is kinda loud but ya don't have to run it long since it will power the same charger that you are using when in a slip. Would let ya have some peace of mind for not much money. When ya get the big panels installed, you can use it less.

walt · Sep 13, 2014

another opinion

First thing.. get the battery monitor. I think you will find you use way less power than your original estimate - unless you need a fridge and then everything changes dramatically. Your two highest numbers in that estimate were the tiller pilot and the stereo. I don’t know about the tiller pilot (two people who have them said the power is way less than the estimate) and I have been using a car stereo with four bookshelf speakers for years, the current is more like 1.25 amps on average, maybe 1.5 when Im playing it somewhat loud. By 2 or 3 amps its distorting and terrible to listen to.

I had to post this because I just really disagree that you will need anything more than 30 or 40 watts of solar for what you described. I have a similar setup - exchange the autopilot for a laptop - I’ve marina lived in the boat for a week with only a 10 watt solar panel and two golf cart batteries. I’ve added a 40 watt panel to the same setup for 50 watts total and can have to really work to end up down 30 amp hours after the week is over. I do have a battery monitor and have been watching this for years.

Also, all the outboard charging systems are not equal. I have a 2010 Nissan 9.8 and if you look at the electrical system, it shows a rectifier/regulator vs. just a rectifier that you will see in the older outboards. This charging system actually does put out near its rated current over a fairly large rpm range. The only issue I have with it is that tie regulator cuts back current at about 13.6 volts so it only is charging deeper into the bulk mode phase. However, I think part of this is caused by my outboard being at the very back of the boat and the batteries being at the very front of the boat and this "tends" to cut back on charging a little too soon.

The best place for solar is at the back of the boat and this may not be important to you (depends on if the RV mode or sailing mode is more important to you) but even though panels doesn’t weigh much, they do have considerable air drag and can even make it harder to tack in high winds. This may not matter at all for the larger sailboats but it can on these smaller ones.

I think get the battery monitor first. If your batteries are fully charged all the time, you probably put too much charging capability on the boat. Some will like that, some wont like the tradeoff of having all that panel on a small boat.

walt · Sep 13, 2014

On the other hand...

The battery monitor is a nice toy as it tells you current, amp hours, voltage. It will also estimate % battery remaining but this is only valid when the battery is new. As the battery ages and loses capacity, the monitor has no way of knowing this. I just never use the % capacity reading because of this, only watch amp hours.

Anyhow, when batteries are new and with some charging capacity, you generally have some margin of excess battery capacity. For example, my batteries are 200 amp hours (when new) but I rarely get them down more than 25 amp hours. So I have 75 amp hours reserve that I normally don’t use.

However, as my batteries age, the amp hour capacity drops (which I can tell with the battery monitor but its not a direct reading, you have to watch patterns). So as the batteries age, my reserve capacity gets smaller and smaller until at some point, I really notice this and figure out that I need new batteries.

However, in the above case, I could now increase my charging capacity and still keep on using the same batteries.

So in effect, having more charging capacity makes the batteries last longer simply because you can tolerate less capacity.

It also may be that the smaller charging cycles afforded by excessive charging capability actually does make the batteries last longer because of shallower discharges..

Tradeoffs..

Charlie Jones s/v Tehani · Sep 13, 2014

Cruised almost 3 years with a single 32 watt panel, mounted on top the bimini.

That included frequent ( day to day) use of the tiller pilot, Hand held GPS hooked to ships power, VHF on standby every day, and recharging laptop and cell phones.

ALL interior lighting is LED

In all that time, I was forced to go to a marina to plug in exactly twice. Once after 5 days of steady rain in SW Florida. I can't IMAGINE what I'd need 200 watts of solar for

But I would like to upgrade to a 50 watt panel- mine is getting old enough to require replacing before I go again.

Delezynski · Sep 13, 2014

See my short Youtube video on battery monitor....

http://youtu.be/JUJ0o3SO1y0?list=PLnA9GMvTHKtYwE2hLyiRCwpj9OcuzlRID

Greg

Delezynski · Sep 13, 2014

Bad,

GOOD ON YA!

Sounds like you are following the correct course, at least as I see it.

To many people focus so much on fixing, and not enough on doing!

Greg

Bad Obsession said:
I had a battery monitor in my last boat. I liked it a lot and it was great peace of mind.

I intend to add one sooner than later. My budget is shot for this season so my upgrades are minimal and cheap right now. I am saving up to do a big job of rewiring stuff, moving a water tank and upgrading to a larger flexible tank, moving the battery, adding a battery, and putting pressurized water into the boat with a cockpit cold shower. As you can tell, this will be a fairly expensive project and I anticipate and early spring start time on working on this. This will be a chunk of next year's budget.

Once that is completed I want to do a solar panel and finally the battery monitor. All things in moderation and in due time.

It is so hard to behave yourself when West Marine is a mile from your house and it is so easy to shop on line too.

Right now I am trying to make do for a fall cruise starting on Tuesday. This will be a good test of the boat and the systems and I will adjust my plans based on what I find.

walt · Sep 13, 2014

See my short Youtube video on battery monitor....

http://youtu.be/JUJ0o3SO1y0?list=PLn...RCwpj9OcuzlRID

"Im not living in a cave. When I want to turn on a light, I want to turn on a light"

Best advice is that you better follow the boss's rules... made me laugh..

Delezynski · Sep 13, 2014

walt said:
"Im not living in a cave. When I want to turn on a light, I want to turn on a light"

Best advice is that you better follow the boss's rules... made me laugh..

TRUE story, I may be slow, but I aim to keep her happy! It's worked so far, we still cruise.

Greg

Bill Roosa · Sep 13, 2014

Your calculations seem very high. A stereo is not going to draw even 1 amp so 56 Ah/day seems way to high. Same, same for the rest. I built and excel spread sheet that calculated the loads and production and show how that interacts with the storage. The storage feature is "rocket science" stuff and is not accurate but gives you an idea of what is going on. email me for a copy. All you need to know to use it is what the unit draws in amps and how long you use it (if at all) each hour of the day.