Battery Bank Sizing and Type

[plb210]

Hi all. 

Just a quick topic first of many.

We completed the boat fit out on my mum and dads ex hire boat last year but never did anything with batteries.

 

Now we're thinking of putting around a 1000ah 12v battery bank in to run our 3000w pure sine wave inverter/(charger)(powerstar lw) due to short lived run time at nominal loads.

 

I have calculated and clamp metered the cables at 36amps inverter pull lasts 2.5hrs. So we think the current batteries are nackered.

 

Also have 3x 255w solar panels wired in series to give 765w of Solar connected to a 100a MPPT.

We currently have just 4 of these at 110ah each total 440ah and only charge from the MPPT.

http://www.ebay.co.uk/itm/19216714361

 

Should we go 10 x 6v (250ah C100) 225ah C20 wet cell traction giving 12v 1125ah

http://www.ebay.co.uk/itm/160821515076

Or

Should we go for the cheaper 12v flooded leisure batteries

http://www.ebay.co.uk/itm/201462508123 

Or

10 x 12v 100ah C20 AGM Batteries to give 12v 1100ah

http://www.ebay.co.uk/itm/182425047217

 

What are your thoughts.

 

Thanks in advance

[Neil Smith]

Why not go the whole hog and get 6 x 2v traction batteries, they can be run nearly flat without worrying about them, it's ok going for 1000ah if you can recharge them in winter and not rely on solar so what other methods have you got.

Neil

[Robbo]

7 hours ago, plb210 said:

I have calculated and clamp metered the cables at 36amps inverter pull lasts 2.5hrs. So we think the current batteries are nackered.

This sentence makes no sense.

 

I would read this book linked below and do a power usage survey before deciding on battery capacity and type of battery's.

https://www.victronenergy.com/upload/documents/Book-Energy-Unlimited-EN.pdf

[plb210]

20 minutes ago, Robbo said:

This sentence makes no sense.

 

I would read this book linked below and do a power usage survey before deciding on battery capacity and type of battery's.

https://www.victronenergy.com/upload/documents/Book-Energy-Unlimited-EN.pdf

I have worked out the amp draw of the minimum appliances and also used a dc clamp meter to check my calculations this is check on the inverter cables.

[Alan de Enfield]

26 minutes ago, Robbo said:

This sentence makes no sense.

I think you are reading just 1 line in isolation.

My reading of his statement is that they will only LAST 2.5 hours at 36 amps discharge (90Ah) so therefore his batteries are either 'flat' or have insufficient voltage to power the inverter (eg dropped to 10.5v)

The 440Ah battery bank is now (maybe) just 100Ah = Knackered.

[plb210]

1 minute ago, Alan de Enfield said:

I think you are reading just 1 line in isolation.

My reading of his statement is that they will only LAST 2.5 hours at 36 amps discharge (90Ah) so therefore his batteries are either 'flat' or have insufficient voltage to power the inverter (eg dropped to 10.5v)

The 440Ah battery bank is now (maybe) just 100Ah = Knackered.

Correct 

[Alan de Enfield]

8 hours ago, plb210 said:

Now we're thinking of putting around a 1000ah 12v battery bank in to run our 3000w pure sine wave inverter/(charger)(powerstar lw) due to short lived run time at nominal loads.

The point has been made - and it is very important to repeat this :

Whatever you 'take out must be put back in' (plus a bit extra for losses)

Lets take your 1000Ah battery bank, which you wish ever to let drop below 50% SoC.

 

You could have 5 days usage at 100Ah per day, or 1 day usage at 500Ah per day - you will still need to replace 500Ah + losses (maybe another 50Ah)

 

Your 700w of solar will produce a theoretical output of 560Ah per 10 hour day in the Summer, but in practice will probably only produce around 50% (300Ah) due to clouds cover, showers, trees, not being at the correct angle etc etc.

So - during April to October you can 'consume' around 300Ah per day, safely knowing that you SHOULD be getting the batteries fully charged every day.

 

But - what happens October to March when your panels are now only generating 30Ah (yes - THIRTY) per day -

BY WHAT METHOD WILL YOU REPLACE YOUR MISSING 70Ah PER DAY (taking the 100Ah per day consumption)

 

It has been identified that battery manufacturers are suggesting that whatever you use, should be replaced 'immediately' and that waiting for 5 days before recharging will kill the batteries (ala MtB and his Trojans). You need a daily 'top-up' either via the engine, generator, or shoreline to maintain your batteries in the best possible condition.

 

I'd suggest that you buy 'cheap' flooded lead acid batteries until you can prove to yourself that you can handle and maintain your batteries - you will kill expensive batteries just as quickly as cheap ones.

 

In summary - It is pointless having a 1000Ah battery bank if you are only using 100Ah per day, you will still have to replace that 100Ah every day, so a more realistic bank would be (say) 400 / 500 Ah, all you will gain by buying a 1000h bank I that you will be discharging to a 90% SoC rather than a 80% SoC.

 

You can only work out your battery bank by doing a FULL electrical audit of your usage.

 

Just as an aside - I have 6x 230Ah FLA batteries and 170w of solar.

Edited April 29, 2017 by Alan de Enfield

[Robbo]

28 minutes ago, plb210 said:

Correct 

I would look to see what is using the power then, an average of 36amps is very very very high.   With those figures your using around 8-9 times more than the average narrowboat!

   How are you charging your batteries?  A clamp meter only grabs the usage at the time used, it doesn't show an average throughout the day which is what you really need.   Fridges are typically either on or off, but how often it's on is what you need and a clampmeter wont show this.

Edited April 29, 2017 by Robbo

[plb210]

Currently getting 242w a day no sun at the moment.

[plb210]

We have the 70amp alternator and the 70amp charger built into inverter.

Moored in marina mostly but want to be able to use what we currently use in the marina out on the cut.

[Robbo]

3 minutes ago, plb210 said:

We have the 70amp alternator and the 70amp charger built into inverter.

Moored in marina mostly but want to be able to use what we currently use in the marina out on the cut.

On average how many ah's do you use per day?

[Alan de Enfield]

8 minutes ago, plb210 said:

Currently getting 242w a day no sun at the moment.

 

Please be very careful about the units you are using - you are getting 242w (17.4a) for the instant that the picture was taken.

If your "242 watts per day" was to be taken as you wrote it that would suggest that you are only achieving 20Ah (per day)

 

If that 17.4A was to continue all day (10 hours of daylight) you would have replaced 174Ah however, as your battery charges and moves towards 'full' it will probably only be charging at around 2 amps irrespective of how much the solar panels are outputting - this is why you need to BALANCE your :

1) Your daily consumption &

2) Your Battery bank &

 3) Your solar panel size.

 

It all needs to work in 'harmony'

 

Edited April 29, 2017 by Alan de Enfield

[Robbo]

3 minutes ago, Alan de Enfield said:

Please be very careful about the units you are using - you are getting 242w (7.4a) for the instant that the picture was taken.

If your "242 watts per day" was to be taken as you wrote it that would suggest that you are only achieving 20Ah (per day)

 

You missed out the 1 - 242w is 17.4amp not 7.4

[plb210]

4 minutes ago, Robbo said:

On average how many ah's do you use per day?

Want to be able be to use 500w at 240 overnight. 

Have 4.5kva generator for day use when not in marina or cruising.

[Robbo]

Just now, plb210 said:

Want to be able be to use 500w at 240 overnight. 

Have 4.5kva generator for day use when not in marina or cruising.

I would question what that 500w is and for how long you need it for.

[Alan de Enfield]

5 minutes ago, Robbo said:

You missed out the 1 - 242w is 17.4amp not 7.4

I was amending the digit failure as you posted.

4 minutes ago, plb210 said:

Want to be able be to use 500w at 240 overnight. 

Have 4.5kva generator for day use when not in marina or cruising.

Are you sure your 'units' are correct ?

So that's 50a for 12 hours = 600Ah from the batteries.

That is not a sustainable usage.

 

Add in 'normal' daily usage of 50-100Ah (fridge, lights, TV, computer, phone charger, pumps, etc) and you need a portable power station.

IF you are using 600-700Ah per day then you should have a battery bank nearer to 2000Ah rather than 1000h.

 

I'm not sure that you are ready for life on a boat.

Edited April 29, 2017 by Alan de Enfield

[plb210]

So we have a 240v 70w pump for our back boiler that we run 24.7.365 also heats hot water + 6 radiators

 

Want to be able run that plus freezer plus tv as and when

[Robbo]

14 minutes ago, plb210 said:

So we have a 240v 70w pump for our back boiler that we run 24.7.365 also heats hot water + 6 radiators

 

Want to be able run that plus freezer plus tv as and when

Even tho it says 70w on the case, it may not actually be using 70watt.  Plus 70w is hell of a lot for a pump!   I would replace with something a lot more efficient, preferably 12v.

 

you need to find out accurately how much your using per day, you can only really do this with some kind of monitor.   You need this, and not figures pulled from the back of devices.   You can get plug in AC monitors for next to nothing, but I would recommend using a battery monitor like Victron BMV and run everything from batteries for a long as period as possible and see what ah's is used in that time period.  Find out the what uses the power and see if this can be replaced for a more efficient model.   

Edited April 29, 2017 by Robbo

[Alan de Enfield]

6 minutes ago, plb210 said:

So we have a 240v 70w pump for our back boiler that we run 24.7.365 also heats hot water + 6 radiators

 

Want to be able run that plus freezer plus tv as and when

Where did you get 500w from ?

 

Can you please list what you need to run, how many watts are each and every item, what voltage do they run at and for how many hours each item will run.

This will allow you to do an energy audit.

Example

70w at 220v water pump runs 24 hours per day.

The inverter will be using some amount of power just to work - lets say 2 amps.

The inverter will take 48Ah per day, and the water pump will take about 70Ah per day.

Therefore the inverter and water pump will between them consume 118Ah per day.

I am a little concerned that the water pump also heats the hot water - comment ?

Do you have an immersion heater running 24/7 to provide the hot water ?

An immersion heater will use some huge amount - probably 100Ah when it is heating so if it is heating 25% of the time than it will use 600Ah per day (from the batteries)

Electrical heating of water is a very inefficient and expensive way of doing it and 'frowned upon' on a boat.

[MtB]

On 29/04/2017 at 10:02, plb210 said:

So we have a 240v 70w pump for our back boiler that we run 24.7.365 also heats hot water + 6 radiators

 

Want to be able run that plus freezer plus tv as and when

This is like pulling teeth!

What power are the freezer and the TV?

[plb210]

10 minutes ago, Alan de Enfield said:

Where did you get 500w from ?

 

Can you please list what you need to run, how many watts are each and every item, what voltage do they run at and for how many hours each item will run.

This will allow you to do an energy audit.

Example

70w at 220v water pump runs 24 hours per day.

The inverter will be using some amount of power just to work - lets say 2 amps.

The inverter will take 48Ah per day, and the water pump will take about 70Ah per day.

Therefore the inverter and water pump will between them consume 118Ah per day.

I am a little concerned that the water pump also heats the hot water - comment ?

Do you have an immersion heater running 24/7 to provide the hot water ?

An immersion heater will use some huge amount - probably 100Ah when it is heating so if it is heating 25% of the time than it will use 600Ah per day (from the batteries)

Electrical heating of water is a very inefficient and expensive way of doing it and 'frowned upon' on a boat.

Immersion can only be ran from shore or generator.

We have a large back boiler that heats the rads and calorifier but has to have pump on.

 

Reading are comming from plug in energy monitor.

 

Currently doing a 240 power audit.

[Alan de Enfield]

2 minutes ago, plb210 said:

Reading are comming from plug in energy monitor.

 

Currently doing a 240 power audit.

That's a good start.

 

Take the readings daily for 7 days and then take the average.

You can then work out what the equivalent would have been if you had used the batteries to supply the power :

 

Say your daily usage is 2KwH (2000w hours)

Divide this by 10 to get the approximate Ah that would have been needed to be taken from the batteries - in this example you are using 200Ah per day.

 

HOWEVER - do not forget to also take into account the usage of all your 12v appliances, which could also add another 50-100Ah per day.

 

Are you running your central heating pump now it is summer time ? If not your consumption figures will be understated.

Do the tests under the 'worst/ normal' conditions. It is no use designing a system for Summer time usage then expecting it to work flawlessly in the Winter

 

 

[plb210]

Running a benchmark for worst case scenario first. 

Also testing each item individually so can make a spreadsheet.

 

Pump is 70w 24hrs

TV is 280w 4hrs

Fridge when compressor on 70w 24hrs

[Robbo]

2 minutes ago, plb210 said:

Running a benchmark for worst case scenario first. 

Also testing each item individually so can make a spreadsheet.

 

Pump is 70w 24hrs

TV is 280w 4hrs

Fridge when compressor on 70w 24hrs

280w for a TV!!!!    I think it's time for a replacement!   Large ones these days around around 40-70watt!

[MtB]

As an aside, an ordinary mains central heating pump rated at 70w only draws 70w when set to max speed. They usually have three user-selectable speeds. In my experience the lowest speed (typically about 25w) will run six smallish radiators perfectly happily.

These newfangled 'high efficiency' central heating pumps which self-modulate can be a PITA though. I've heard they don't like being run/refuse to run from certain makes/models of inverter.