A way To Save Charging Time

[Kenomac]

Originally Posted by mrm

So, given your bank size (377Ah), the bulk/absorption transition point is
37.7A at 14.7V (maybe 14.5V? check your battery spec). The absorption to full is holding voltage (14.7V) till current drops to 0.5% of C20 (<2A).

Modeling this as a linear current drop over time and estimating the whole process to take 5 hours, the energy requirement is:

14.7V * (37.7 + 2)/2 A * 5h =~ 1460 Wh

without accounting for charger inefficiencies. Seems way above your net energy budget, but likely the linear current drop model is wrong. MaineSail? Help?

Say wut?

[mrm]

Originally Posted by Kenomac

Say wut?

Yeah, me too.

As I wrote, the linear model is likely wrong, it is probably logarithmic or similar. No time to research it right now.

[a64pilot]

Originally Posted by mrm

but likely the linear current drop model is wrong. MaineSail? Help?

I think his consumption estimate is, however he did state probably very correctly that in the hot months it will increase quite a bit.
If he spends his days in town and not on the boat mostly coming back to just sleep, then his consumption may well be minuscule.
However I'm sure that even 450W will not cover his needs, much less 250W.
The afternoon generator runs will from a battery charging perspective be pretty much wasted, but necessary to cook.
With two generator runs a day, why not just extend your run times by say a half hour each and see what that gives you? Its not enough fuel to worry about, and your running the thing anyway

[Kenomac]

Originally Posted by a64pilot

I think his consumption estimate is, however he did state probably very correctly that in the hot months it will increase quite a bit.
If he spends his days in town and not on the boat mostly coming back to just sleep, then his consumption may well be minuscule.
However I'm sure that even 450W will not cover his needs, much less 250W.
The afternoon generator runs will from a battery charging perspective be pretty much wasted, but necessary to cook.
With two generator runs a day, why not just extend your run times by say a half hour each and see what that gives you? Its not enough fuel to worry about, and your running the thing anyway

I plan to do this experiment over the next two or three days. Right now I'm unplugged from shore power to see what happens with the new charging arrangement.

[Sailmonkey]

Originally Posted by Kenomac

Some of these mysteries now have numbers.

During the day with only the stereo turned on the drain is 1.5Ah, when the freezer compressors turn on with the associated water pump, the drain increases to a total of 11Ah on the meter for 10 minutes, then drops back to 7Ah. The fridge draws 3Ah on start up, then drops back to 2Ah. When both units are running at the same time, the total draw is 9Ah continuous after they settle in when combined with the stereo.

The fridge runs 5-6 hours per day (24hrs) and the freezer 4-5 hours per day. Each runs at least 3-4 hours during the daylight hours, less at night.

It's beginning to look like our boat is more energy efficient that I thought, although the energy consumption will certainly increase by 50% during the hot summer months.

Another Solbian factory direct quote just arrived in at €2500 for 450w excluding installation, which I think we can handle ourselves.

Do you have an AH counter, or just an Ammeter? If the former, just let us know how many AH you expended at the end of your drawdown. The numbers you posted are amps, not amphours......there is a huge difference.

[a64pilot]

You may also want to either find out how to calibrate your existing battery monitor or invest in a Smart Gauge, I have no idea how the thing works, but it seems to remain accurate.
I assume this battery monitor you have is how you determined your usable AH capacity?
If so I have a gut feeling your bank may be in better shape than you think

[senormechanico]

Originally Posted by a64pilot

Your way North, but I think also during the Summer, you have some really long days to make up for it.
Your Winter numbers I bet are bad though

You've got that exactly right.
This last winter was SO BAD, I barely had enough solar to run my UltraSoniTec which only draws 0.75 amps 24/7

[sailorboy1]

Originally Posted by Kenomac

Can you please remind me where your solar panels are mounted? My only choice is the top of the bimini.

on top of the bimini

[Sailmonkey]

Originally Posted by sailorboy1

on top of the bimini

this is one of those times I've got bimini envy

[Kenomac]

Today's amp burn was 70 amps over a nine hour period. Fridge, freezer, iPad and stereo.

Now I'm going to run the generator for an hour while I cook dinner and see where I'm at.

[Kenomac]

Originally Posted by sailorboy1

on top of the bimini

That information helps.

Thanks

[Sailmonkey]

Originally Posted by Kenomac

Today's amp burn was 70 amps over a nine hour period. Fridge, freezer, iPad and stereo.

Now I'm going to run the generator for an hour while I cook dinner and see where I'm at.

That means that solar will create a scenario where your generator will only need to bulk up overnight losses (easy while you're cooking) and can then merrily overcome your daily consumption an slowly put the last 10% into the batteries.

Go with the 450 watts and you can stop worrying about shortening your anchorage stays.

[mrm]

Originally Posted by mrm

Yeah, me too.

As I wrote, the linear model is likely wrong, it is probably logarithmic or similar. No time to research it right now.

Did some further research and it appears that while the linear current taper approximation was indeed too crude, I wasn't too far off in my estimates. Using current taper curve from Fig. 1. here: Charging Information For Lead Acid Batteries – Battery University I did some quick spreadsheet math. Results are attached. My conclusion is that if you extend generator run time to cover the first hour of acceptance phase, solar will cope with the rest. The values in 'Ah' column were calculated using trapeze integration method. If you want to have even better precision you can integrate the included fit function. I didn't see a need for that.

[Kenomac]

It took an hour to get back to 97%, then another hour to get to 99%. So I'm now thinking the idiot electrician/technician who programmed by monitoring system and tested my batteries four years ago in Mallorca screwed things up. Which was also semi confirmed last September when two Italian technicians here in San Giorgio said there was nothing wrong with my batteries after running a test.

So now, me and the admiral will need to decide if it's going to be 225w, 297w, 375w or 450w of solar added on to the bimini.

Solbian is offering very cheap factory direct prices to Italian buyers at this time. 'Just found out earlier today, much cheaper than my earlier quotes.

Thanks everyone for all your help.

Ken

[daletournier]

Originally Posted by Sailmonkey

That means that solar will create a scenario where your generator will only need to bulk up overnight losses (easy while you're cooking) and can then merrily overcome your daily consumption an slowly put the last 10% into the batteries.

Go with the 450 watts and you can stop worrying about shortening your anchorage stays.

Bingo:-)