Actual power budget of cruising monohull?

[Pelagic]

Originally Posted by MarkJ

I don't see how any real cruiser 'out there' could use one of those 'energy budget' spreadsheets. I have never spoken to someone who uses one.

It's a fudge, a guess, a stab in the dark and then you adjust what goes out by what you have (or can bare) going in.

Fill the boat with solar. You can't ever have too much solar. Many boats refuse as they think it unattractive. So that's a good time for me to stop advice to them. If you regard prettiness above a freezer and cold beer you are not going near my comfort zone.

Fill with batteries. 600amp hours is good if you can fit 500 watts solar. And a wind generator is great. But can be noisy. Using the main engine or generator can be WORSE as its loud and heats up the boat, tgats not a good thing in the tropics. A small Honda generator on deck will piss off the anchorage.

The electrical plan can never work as most things in a boat are intermitantky used: bilge pump once per month 15 seconds.
Anchor winlass 1 minute every 2 weeks.
Water pump 1 minute per day except if your have engine grease ... etc etc. Its all baloney to try to calculate it.

The big draws are freezer and refrigeration, but these are totally variable too: in the tropics getting a freezer down to zero F -18C is utterly impossible. The compressor just stays on chugging away, but set at 10F or -8C you only use 40% of elec consumed colder.

So I don't think a spreadsheet works. What does is filling the boat with solar and batteries.

Well said Mark.
The most contentious part of a builder's contract for a new yacht is a Load Analysis.

The experienced yards refuse to do it!....They just don't want the responsibility of underestimating,

so best advice for a small yacht is to fit as big as you can....you will use it if it's there!

[admiralslater]

Originally Posted by StuM

ROTDLMAO This is why I keep asking people to use correct units.

No such thing as "amps per hour" in any realistic scenario. Amps is a rate. 20 Amps is 20 Amps regardless of how long you are putting it in. Do you mean that you are putting 20 Amps back into the batteries or do you mean you have put 20 Amp hours back into the batteries. Its impossible to tell from your statement.



Depends where your link is connected.

And again, are you talking about Amps of Amp hours here? You have mixed the two, so I don't know whether you are talking about the total energy put back into the battery since charging started (20 Amp hours) or the rate at which you are putting energy into the battery (20 Amps).

The Link should be wired so that it tells you what is going into the battery, not what is coming out of the panels. It should tell you both Amp hours that have gone into the battery since charging started and Amps currently going into the battery.

Sorry for So bear with me , I do have a basic knowledge of this stuff And to your point getting the wording accurate is obviously important.

The link was telling me that the power was going in at a rate of 20 amps
I assume that if it goes in at that rate for 1 hour then I have added 20 amp hours of capacity to the bank . If that is true then if the bank is down 40 amp hours (which the link counts ) that it will take roughly 2 hours to bring them back up to 100 % .
I did some experiments with load and the link is only showing the net gain to the banks .
Mine is an older model and amp hours shows only how far you are to 100 % ,I will take a look at the manual to see if that can be changed.
The Outremer is a much more complex boat than the PDQ and the forum has been very helpful in learning about the systems

[StuM]

Originally Posted by admiralslater

The link was telling me that the power was going in at a rate of 20 amps
I assume that if it goes in at that rate for 1 hour then I have added 20 amp hours of capacity to the bank . If that is true then if the bank is down 40 amp hours (which the link counts ) that it will take roughly 2 hours to bring them back up to 100 % .

Even with your Firefly Carbon batteries, because of the Peukert effect pushing 20A at your batteries for 1 hour will not put a full 20Ah back into the battery.

Also, you will not be able to keep pushing 20A into your batteries until they reach 100%, the Amps they can accept will decrease as you get closer to 100% so it will take a lot longer that 2 hours to put the last 40Ah back in to your batteries.

[LoudMusic]

Originally Posted by SV THIRD DAY

Honestly....cruisers that really want to stay on top of and understand their power balance will have an amp hour counter on the output of their Solar panels at minimum to an Amp hour counter on their battery output. Me being an scientist data type have the a dedicated Amp Hour counter on each of my two strings of solar panels, one on my wind generator, one on the alternator and one on the battery charger. So I know exactly where my power is coming from and in what percentage on a daily, monthly, and yearly basis. Then well you gotta know where it's going. So I have one on the total bank outlet plus one for my freezer and one for the refrigerator.

Sure that is overboard but I find all the time in talking to cruisers that they have no idea or understanding of their power balance.

I'm glad to see there are other people as neurotic about this as I anticipate I will be ...

So your monitoring devices, do they each store their data internally which you check manually or do you have a way of that information automagically ending up in a PC? I've found this neat project to adapt a kill-a-watt into a transmitter so the data can be sent elsewhere, which sounds FABULOUS, but wouldn't it be spiffy if it were a bundled product?

[sailinglegend]

Lets get back to the important issue of 100% fully charged - and why it is so important.

Originally Posted by noelex 77

Maine Sail is right in my view. ...but if you want to get a lead lead battery to reach a true 100% charge it is going to take a positive charge rate for something like 12 -24 Hrs, some would say longer.

…Many people define 100% charged as when the regulation drops down to float. This is sometimes called the "Cruisers 100%”……but it will take many hours to reach a true 100% charge….

This is the key to the problem…

Originally Posted by Paul L

Isn't dropping to Float a good indication if the transition is based on the battery accepting in the order of .5% amps of the batt capacity at acceptance voltage? It might not be exactly 100%, but it is close enough for full-time liveaboards….

And this is the key misunderstanding. Charge controller(Except some Outbacks) don’t measure the charge actually going into the battery, so they drop down to a Float voltage early because they are designed to “charge” batteries not “over-charge” them. At a lower Float voltage on my AGMs the current going in to the batteries is 4-5 times lower than at the absorption voltage, so it takes a very long time to finish off the charging in Float mode.

Originally Posted by tomfl

...While it is probably correct to say flooded batteries never, or almost never, get to 100% this is really meaningless. Once you get above 95% or higher you really don't need to worry on a daily basis....

You do need to worry because the last 5% or less leads to temporary sulfation of the plates - this is a build up of Lead Sulfate which occurs as part of the chemical formula of discharging. Recharging converts the Lead Sufate back to Lead Oxide and Sulfuric Acid. If the batteries aren’t recharged fully at least every three weeks the Lead Sulfate crystals harden and may not be able to be removed, even by heavy equalisation. This permanent sulfation reduces the Ah capacity of the battery is the main killer of batteries. So after 1 month of charging only to 95% the battery capacity will have been reduced to 95% of its original. The next month with the same treatment the capacity may have gone down by another 95%.

Getting all types of Lead Acid batteries to 100% as often as possible will reduce this problem and lengthen their life dramatically.

[conachair]

Originally Posted by sailinglegend

Lets get back to the important issue of 100% fully charged - and why it is so important.



This is the key to the problem…

So keep out of float.

Not that difficult depending on what regulator you have.

[Stu Jackson]

Originally Posted by admiralslater

Sorry for So bear with me , I do have a basic knowledge of this stuff And to your point getting the wording accurate is obviously important.

The link was telling me that the power was going in at a rate of 20 amps
1.......I assume that if it goes in at that rate for 1 hour then I have added 20 amp hours of capacity to the bank . If that is true then if the bank is down 40 amp hours (which the link counts ) that it will take roughly 2 hours to bring them back up to 100 % .
2..............I did some experiments with load and the link is only showing the net gain to the banks .
3....................Mine is an older model and amp hours shows only how far you are to 100 % ,I will take a look at the manual to see if that can be changed.

1. Simplistically, yes. Reality - nope. You must take into account battery acceptance. As a bank gets fuller, it can take less and less. Battery Acceptance by Stu Battery Acceptance

2. Experiments weren't needed, but now you know. You need to understand how the boat is wired and how shunts work. Ammeters & Shunts 101: Ammeters & Shunts 101

3. Good idea to RTFM.

Good luck.

[sailinglegend]

Originally Posted by conachair

So keep out of float.

Not that difficult depending on what regulator you have.

You can't set regulators - except some Outbacks - to measure "return amps" to the battery and switch to Float only when the current into the batteries is 0.5% of the Ah capacity.

Some solar regulators do have a customised setting where you can switch Float off if you know there are not enough hours in the day to fully charge your batteries with your size of solar array - but don't do this if there's a chance they will get to 100% and stay there at Absorption voltage for a long time. This causes excessive gassing which is not good for sealed batteries.

[chala]

Originally Posted by StuM

And that would be 100 Amp hours.

Not really.

Originally Posted by admiralslater

hundred amps in the non solar periods

It all depend how many hours are in a “non solar periods.”

Originally Posted by chala

The terms power and energy are frequently confused.

Well, nobody's perfect.

[conachair]

Originally Posted by sailinglegend

You can't set regulators - except some Outbacks - to measure "return amps" to the battery and switch to Float only when the current into the batteries is 0.5% of the Ah capacity.

Some solar regulators do have a customised setting where you can switch Float off if you know there are not enough hours in the day to fully charge your batteries with your size of solar array - but don't do this if there's a chance they will get to 100% and stay there at Absorption voltage for a long time. This causes excessive gassing which is not good for sealed batteries.

Not all regulators even have a float setting.
All you really need is some test meters and a positive outlook. Bypass the reg, get a cheap fixed voltage regulator til the amps are down. Not too hard for an average cruiser to figure out.

Or listen to some negative comments on the web saying it can't be done and give up.

[KISS]

There's a gigantic amount of (frequently contradictory) information on this subject on this forum and elsewhere online. I've spent an inordinate amount of time digging through it, so let me try to save you some time and tell you my conclusions.

1. Create an energy budget, or rather budgets, as you will use different amounts of power in different situations (e.g. you probably will use a lot more anchored than underway).

2. Take the highest of the budgets and multiply by 5. That's what your battery bank should be in amp-hours, and what your solar array should be in watts (nominal).

e.g. You calculate that you'll consume 50 AH per day at anchor, 40AH while underway. 50AH x 5 = 250. So you need 250AH battery bank and 250W of solar (nominal).

This is a conservative set-up (i.e. very unlikely you'll run out of power), but you can always beef it up if you want. However, if you go much above a 4:1 ratio of watts:amp-hours, you're going to end up creating more power than your batteries can accept (assuming they're lead-acid).

*Note that all of this assumes that you're in the tropics.

[a64pilot]

Originally Posted by Paul L

A64

Maybe you need to start turning things off when you aren't using them A continuous 15 ah usage on a boat your sized is way over the top while cruising. You will be a slave to generating power with this usage. It will be a lot easier to save 30-40% of that usage than to generate it over the years.

I will, just now I have a worst case scenario to plan for.
It's just like a money budget of course, you can only spend more than you have for only a short time.
There are several scenarios including shutting down the fridge at night etc.

[Paul L]

Originally Posted by a64pilot

I will, just now I have a worst case scenario to plan for.
It's just like a money budget of course, you can only spend more than you have for only a short time.
There are several scenarios including shutting down the fridge at night etc.

Power systems on a cruising boat really shouldn't be based on worse cases. Worse case you run the genset or the engine alt and charge when you would prefer not to. It is the normal, everyday case that should be optimised.
Our setup with 550watts solar is fine for full-time live abroad. When the weather turns to crap for days on end, it's time to add in some genset. When we are on passage, the increased consumption requires some genset runs.

I wouldn't want to be manually turning off the frig at night on a regular basis - could even be counterproductive.

[sailorboy1]

I skipped the middle pages, but I'm using 150-200 ah/day

[botanybay]

I think this assumes a 12v system, I would have to double the solar watts. Since AH are not power (watts) without an assumed voltage.

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