Specifying my domestic battery bank.

[Balbas]

Issue - I need to know that my current battery bank is up to scratch or specify up one that is.

Requirement - Aside from the normal use of anchor / steaming / nav lights etc, I reckon I probably have the following requirements (I have included wattages where I know them):-

• Freshwater pump - I'd be surprised if we used this for more than 5 minutes a day, but allow say 10 minutes.
• Cabin lighting - Say 6 10W lights on for 4 hours / day.
• fridge - Danfoss 40W, runs constantly (I think), but whether it runs at 40W I don't know
• charging phones / chartplotter etc - there's usually something plugged in!
• instruments - depth sounder & radio - probably on for up to 18 hrs / day
• windlass - almost never used. Only ever when the engine is running.

Timing - there's no hurry for this, but I would like to get it sorted sooner rather than later. If I'm going to get any autumn sailing done, with the longer nights I'm going to be using more electricity (although the cooler ambient temperatures will presumably mean that the fridge uses less).

Background - I'd like to be able to survive for at least 48 hours 'off grid', that is without running the engine, worrying about solar (although I will be adding that) or running out of or rationing electricity. This summer (before I changed the setup to the one listed below), we ran out of electricity after 12 hours. Had to read by torchlight, didn't have a fridge and couldn't charge 'phones etc. Which was actually quite nice in a way, but I'd like that sort of thing to be a choice...

My current domestic setup is 2 x leisure batteries rated at 120AH (C100) linked together in parallel. Currently untested.

Yes I know I should have asked for advice / worked things out before I bought batteries, but I didn't so....

Is my current set up going to cut the mustard, or do I need to get more / bigger batteries?

 

[PaulRainbow]

For 48 hours i'd say you need another battery, so be safe and not to deplete the batteries too much, thus shortening their life.

The fridge will draw around 3 amps when running, but should only fun about 20 mins in an hour, 30 if poorly insulated.

The lights should be changed for LEDs, they will use 5 amps when all on, LEDs will use a fraction of that.

 

[Balbas]

For 48 hours i'd say you need another battery, so be safe and not to deplete the batteries too much, thus shortening their life.

The fridge will draw around 3 amps when running, but should only fun about 20 mins in an hour, 30 if poorly insulated.

The lights should be changed for LEDs, they will use 5 amps when all on, LEDs will use a fraction of that.

Cool, so 1 more of the same battery? I was planning to go through the lights and change to LED anyway, so that's fine. Good news then - I'm nearly there!

 

[PetiteFleur]

Interesting - I'm about to do the same. Had to fit a new domestic battery when in Limehouse a couple of weeks ago, so have decided to get another identical, parallel them and add a separate engine battery. I've fitted a 50W solar panel and will fit another 30W panel over winter. So will have 2 x 90ah batteries for domestics and hopefully this will be OK. I also have room to fit 2 x 20w solar panels in the future if necessary. All my lights are now LED(apart from a small fluorescent in the heads).

 

[PaulRainbow]

Cool, so 1 more of the same battery? I was planning to go through the lights and change to LED anyway, so that's fine. Good news then - I'm nearly there!

Yes, one more of the same. Adding solar will be a good move too.

 

[PaulRainbow]

Interesting - I'm about to do the same. Had to fit a new domestic battery when in Limehouse a couple of weeks ago, so have decided to get another identical, parallel them and add a separate engine battery. I've fitted a 50W solar panel and will fit another 30W panel over winter. So will have 2 x 90ah batteries for domestics and hopefully this will be OK. I also have room to fit 2 x 20w solar panels in the future if necessary. All my lights are now LED(apart from a small fluorescent in the heads).

For anyone with fluorescent lights, or anything else where they don't want to change the fitting, you can take the gubbins out of the fitting and put LED strips in.

 

[lw395]

Chartplotters can be remarkably watty.
No stereo on the list? These are often thirsty.
Fridge is the big user. 40W is 3.5A, possibly more, so that's 168Ah in 48H.
Except when SWMBO says 'we'll stop here two days', that often means arrive evening, stay two full days, leave morning, so that's two days and 3 nights. More like 60 hours. Others might mean twon nights and a day.

I'd start by taking a good look at what the fridge really uses.

 

[PaulRainbow]

Chartplotters can be remarkably watty.

Older, especially big, chart plotters might use a bit, but a modern one is pretty economical. My 9" plotter uses about 1a

No stereo on the list? These are often thirsty.

Yes, they can be. I fitted a soundbar and stream audio from my phone via Bluetooth. Including the phone charge, 0.4a

Fridge is the big user. 40W is 3.5A, possibly more, so that's 168Ah in 48H.

If it uses that much there is a serious problem and it won't last long. It shouldn't be running constantly, 20 mins per hour is typical.

I'd start by taking a good look at what the fridge really uses.

Definitely worth a look if he thinks it runs 24/7, it shouldn't.

 

[Balbas]

Chartplotters can be remarkably watty.
No stereo on the list? These are often thirsty.
Fridge is the big user. 40W is 3.5A, possibly more, so that's 168Ah in 48H.
Except when SWMBO says 'we'll stop here two days', that often means arrive evening, stay two full days, leave morning, so that's two days and 3 nights. More like 60 hours. Others might mean twon nights and a day.

I'd start by taking a good look at what the fridge really uses.

We have a young family, so time on the boat is 'essential technology only' as a way to get away from having the kids (and us!) 'plugged in' all of the time. No stereo, no TV, no laptops or tablets. The chartplotter is a tablet, but its one that is dedicated to navigation use only. My 'phone is used to check tide times, set an anchor alarm, get the weather etc. It is turned off the rest of the time as is my wife's 'phone. Yes I have reversionary ways of getting that info, but its quick and easy on the 'phone.

So actually the extra requirements are minimal. It really is mainly just the fridge.

Point taken about the number of hours though. Perhaps I should bargain on adding 2 additional batteries. Aside from the cost (and weight), I don't see any particular downsides. Although if I needed more than 4 I'd be looking at generators I think!

Older, especially big, chart plotters might use a bit, but a modern one is pretty economical. My 9" plotter uses about 1a



Yes, they can be. I fitted a soundbar and stream audio from my phone via Bluetooth. Including the phone charge, 0.4a



If it uses that much there is a serious problem and it won't last long. It shouldn't be running constantly, 20 mins per hour is typical.



Definitely worth a look if he thinks it runs 24/7, it shouldn't.

My 'chartplotter' is actually a tablet. I shouldn't imagine it uses much at all.
No need for music.
Fridge - I'm unsure what it's useage habits are to be honest. Its one of the snags I've been fixing as it wasn't working properly. But point taken, I'll monitor it and see what sort of cycles it's operating on. I would guess it's pretty heavy draw until it gets down to temperature and then depending how often it's opened and how well insulated it is, it's into a steady state.

 

[lw395]

The point is, 48H on a couple of batteries, that's about 100Ah max, so about 2A average consumption.
So a plotter using 1A is significant. Some tablets are several watts, many charge at 2A from the USB, so maybe up to 1A at 12V.
Even phones have to be taken into account. Particularly if you use an inverter to charge them from 230V.

A Garmin plotter at 1A doen't sound bad, but not so many years ago we made do with a GPS at 1W and a LED light to read the paper chart by.

I wouldn't be talking about a UK cruising boat and 'Autumn sailing' in the same paragraph without the words 'Webasto' or Eberspacher' appearing shortly afterwards....

In my experience of sailing around the South Coast on typical holidays, the problem is often a week into the holiday, your starting point is anything but 100% charged when you pick up that mooring in Salcombe.

Realistically, many of us live quite handily aboard without running the fridge all the time. We start the week with a big bag of ice from Tesco. We run the fridge when motoring and plan our eating around what we can sensibly expect from the fridge. Summer in the Med would be a different equation, solar power and cool beers 24/7.

A lot of older yachts have appalling fridge insulation and will run 100% duty cycle if you let them. My mate's boat has a 'Carribbean spec' fridge, it keeps food frozen and beers cold on less than 10% in the UK.
For a cross channel weekend we just chuck in ice, beer, food and leave it switched off, maybe switch it on when the engine's running.

 

[Balbas]

All valid points. I must admit that I hoped if I added some decent solar - I think I could fit 50W easily, 80W at a push - I would build in some redundancy. But of course I'll probably anchor under trees or only sail on cloudy days or whatever, so probably best to take that out of the equation and treat as a bonus if it keeps me going longer.

The 'fridge' in my case is a built in top opening coolbox with one of those danfoss 'add a fridge' kits installed by the previous owner. It does now seem to work quite well, but how efficient it is I have no idea - probably not very.

Autumn cruising. To be fair that's probably a solo / lads weekend thing. And I've slept in snow holes and the like, so a bit of cold and wet won't kill me - I'll just take my warm kit and do wet and dry routine. I would like to add a diesel heater, but that certainly won't be done in the short term - I'll be adding a calorifier and plumbing in hot water first, probably next year. Again, probably worth thinking about in terms of battery capacity though if we want to run the water heater whilst on the hook/mooring buoy.

 

[RupertW]

All valid points. I must admit that I hoped if I added some decent solar - I think I could fit 50W easily, 80W at a push - I would build in some redundancy. But of course I'll probably anchor under trees or only sail on cloudy days or whatever, so probably best to take that out of the equation and treat as a bonus if it keeps me going longer.

The 'fridge' in my case is a built in top opening coolbox with one of those danfoss 'add a fridge' kits installed by the previous owner. It does now seem to work quite well, but how efficient it is I have no idea - probably not very.

Autumn cruising. To be fair that's probably a solo / lads weekend thing. And I've slept in snow holes and the like, so a bit of cold and wet won't kill me - I'll just take my warm kit and do wet and dry routine. I would like to add a diesel heater, but that certainly won't be done in the short term - I'll be adding a calorifier and plumbing in hot water first, probably next year. Again, probably worth thinking about in terms of battery capacity though if we want to run the water heater whilst on the hook/mooring buoy.

For water heating the engine and calorifier is your friend - with the additional advantages of a hot engine warming the cabin and extra battery charging. Using a water heater from batteries is just draining them dry for little gain.

 

[PaulRainbow]

All valid points. I must admit that I hoped if I added some decent solar - I think I could fit 50W easily, 80W at a push - I would build in some redundancy. But of course I'll probably anchor under trees or only sail on cloudy days or whatever, so probably best to take that out of the equation and treat as a bonus if it keeps me going longer.

Definitely worth adding solar, you'll get something and anything is better than nothing.

The 'fridge' in my case is a built in top opening coolbox with one of those danfoss 'add a fridge' kits installed by the previous owner. It does now seem to work quite well, but how efficient it is I have no idea - probably not very.

My fridge is also a top loader with added Danfoss unit. It is very well insulated and only runs for about 20 mins in the hour. Check yours is insulated well, if not add some. lw395s comments about ice are good, especially if only weekend sailing, a bag of ice in the fridge would likely keep things cold all weekend, if not it would certainly save some power in getting the fridge down to temperature.

Autumn cruising. To be fair that's probably a solo / lads weekend thing. And I've slept in snow holes and the like, so a bit of cold and wet won't kill me - I'll just take my warm kit and do wet and dry routine. I would like to add a diesel heater, but that certainly won't be done in the short term - I'll be adding a calorifier and plumbing in hot water first, probably next year. Again, probably worth thinking about in terms of battery capacity though if we want to run the water heater whilst on the hook/mooring buoy.

The calorifier heats the water from the engine or from shore power, you wouldn't want to try water heating from the batteries.