How to check you have sized your Electrical System correctly?

[Fuss]

Originally Posted by valhalla360

That assumes they don't accidently leave the combiner switch on...which is a common mistake for a newbie to make.

I still stand by my statement that at least a brief review makes more sense than finding out a few days in that the batteries are dead and you wind up spending time and effort addressing the issue in a potentially inconvienent location.

I'm not saying you need a detailed analysis with a 50 page report but taking an hour to rough out an estimate of your consumption and capacity makes a lot more sense than going out in an unfamiliar boat and hoping it works out.

I wasn't really directing this at newbie sailors or sailors who would read the post, hop on an unfamiliar boat having no idea or feeling for the systems and also leave the start batteries connected to the house bank.

Sailorboy1 ... nearly 8000 posts on these forums and you still believe batteries must be charged to 100% every day.

[monte]

True a field test is the only way to see if you have done your homework properly. But the basic calculations should have been done beforehand and the idea of not checking the soc for 2 weeks is ridiculous. Batteries should be monitored daily and if getting anywhere near 60% during the day we have a problem Houston. Our daily usage on passage is around 250ah per day. At anchor around 160Ah per day. Big difference. So it will depend on the type of cruising and number of days on passage to size. I do t expect to ever have a low battery when at anchor and even if that happened, turning off equipment is easy at anchor to save power.
We have 1180w of solar and 840Ah of batteries so 250 Ah draw should last almost 2 days without any charging. The only other charging source is the alternators so we do have a backup but ideally we would rather sail without having to run the engines just for charging. Our system will be tested in November when we cross the Atlantic, but until then it is all just theoretical. I will be checking the soc regularly during that passage and taking measures while underway to ensure the batteries stay healthy!

[Fuss]

Originally Posted by monte

True a field test is the only way to see if you have done your homework properly. But the basic calculations should have been done beforehand and the idea of not checking the soc for 2 weeks is ridiculous. Batteries should be monitored daily and if getting anywhere near 60% during the day we have a problem Houston. Our daily usage on passage is around 250ah per day. At anchor around 160Ah per day. Big difference. So it will depend on the type of cruising and number of days on passage to size. I do t expect to ever have a low battery when at anchor and even if that happened, turning off equipment is easy at anchor to save power.
We have 1180w of solar and 840Ah of batteries so 250 Ah draw should last almost 2 days without any charging. The only other charging source is the alternators so we do have a backup but ideally we would rather sail without having to run the engines just for charging. Our system will be tested in November when we cross the Atlantic, but until then it is all just theoretical. I will be checking the soc regularly during that passage and taking measures while underway to ensure the batteries stay healthy!

Interesting calculation you have made.
You have a boat with 1180w of solar and 840Ah of batteries drawing 250 Ah per day and you calculate that it should last almost 2 days on passage without any charging.

That calculation is not at all accurate.

You need to be more in tune with your energy systems.

The post is designed around 2 weeks of sailing and anchoring with 4 days in a row at anchor.

Your boat would pass this test and at the end of it, you would have a far better feeling for your energy systems than you have at the moment.

I suggest you do it.

[monte]

Thanks fuss. Of course I've done the calculations. 250Ah per day. Let's round it down to 10amps per hour average. A bank of 840Ah has around 340Ah of usable amps till it's at 60% soc, so approximately 34 hrs. If I push it to 50% that's 42 hrs. So that's close to 1 1/2 days without charging. So theoretically we could sail through one overcast day with very little charging, but 2 days or 3?
I have however designed the system on the possibility of surviving several overcast days with lower charge rates. Ie. inputting 20amps for 8 hrs would leave us 90 Ah short of our daily budget. We could sail for 3 days till the batteries are at 60%, then
Charge with engines
Turn off refrigeration
Pray for sun
So obviously we have considered the variables. Also inverter loss and peukerts are left out if the above simplified calculations. It's worthwhile making a spreadsheet to calculate power budgets and don't be tempted to cheat because in real world conditions it will soon catch up with you.

[valhalla360]

If it's not for a newbie or new boat, I really don't understand the point of your test.

If you've been cruising for a few years, you should already have it figured out.

[goboatingnow]

I find this thread confusing

IN general expecting a modern boat to last 4 days without any form of recharging is not realistic, short of large banks or exotic chemistry.

after that its a compromise between charging sources and consumption, one that is not static either,

Dave

[Fuss]

Originally Posted by goboatingnow

I find this thread confusing

IN general expecting a modern boat to last 4 days without any form of recharging is not realistic, short of large banks or exotic chemistry.

after that its a compromise between charging sources and consumption, one that is not static either,

Dave

This was never said or expected that there is not additional charging such as solar.
the first post said more solar or more alternator or more wind charging etc
Of course solar will be contributing and at the very least lengthening the time until the batteries are at 50%.

[Fuss]

Originally Posted by valhalla360

If you've been cruising for a few years, you should already have it figured out.

Absolutely, I agree completely.

However as we see from this thread, there are experienced sailors out there who do not understand the concept of balanced energy systems and what is generally a comfortable amount of time they should last before needing some extra charging such as running the engine longer.

In the very post you are replying to, there is an example of an 8000 post member who still believes batteries need to be charged back to 100% every day.

[Ex-Calif]

So let's go back to the first post...

If the state of charge is worse than you guessed then you are using more energy than your expectations. A resize may be needed.
If the state of charge is better than you guessed then you are using less energy than your expectations. No resize required and good for the future.

If the state of charge is below 50% then you need to be more in tune with your energy use and generation before doing tests like this.
If the state of charge is above 50% all is fine.

Maybe we've made a very simple concept too hard.

All you are really saying is that one should be able to live on the hook doing "normal" routine charging (whatever that is) and not use more amps than expected or drop SOC below 50%

So if I normally run my generator for 4 hours a day I just do that during your test and if at the end SOC is what I expected I am fine.

Thanks, Captain Obvious...

Most don't need to guess because they monitor SOC and consumption. I stilll don't understand the point of the test over monitoring the batteries.

[sailorboy1]

Originally Posted by Fuss

In the very post you are replying to, there is an example of an 8000 post member who still believes batteries need to be charged back to 100% every day.

You have a reading problem!!!!!!!!!!!!

I never said need, I said should. And BTW mine normally are 100% charged each day from my solar, but not every day.

Sounds to me your idea of a "balanced" system is 50% SOC. That isn't balanced, that's bottom basement get by with.

But in the end it really doesn't matter to me how you like to maintain your batteries or anything else on your boat.