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Sizing a battery bank


jetzi

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Going back to my last post.

 

Energy saving bulbs...TV etc...

 

A hair dryer...is a short 'hit'...so not a great power discharge.

 

The main use of this immense  battery bank and charging regime seems to be the washing machine ?.

Huge amounts of engine running ( maybe half a gallon ?  ).. solar ..filling the water tank..and discharging plastic particles into our canals.

 

Is this really worth it ?.

 

This is a general question rather than criticism.

 

PS... I get plenty of run time for fridge...lights...and TV out of two 110 amp batteries..and they don't drop below 12.2 volts.

 

Edited by Bobbybass
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11 hours ago, Richard10002 said:

Your figures seem reasonable until we reach the inverter.... What are you using the inverter for that will consume 200AH?

I have a Hotpoint WMTF722H washing machine that has a true "cold wash" button that will use the water at the temperature it comes in at. It's hard to say how much this will use without the heating element, but I picked a pessimistic 1000W for just the motor. Others have suggested just 200W-500W for this.

 

Alice has a 1200W hairdryer that she wants to use for 5 minutes every other day.

 

For around 2 washes and a 5 min hair drying I estimated 2kWh / 200Ah.

 

11 hours ago, Richard10002 said:

OK! Wow! :) 

I haven't run any 240V appliances in over a year, we feel like we've earned ourselves a washing machine!

 

2 hours ago, Bobbybass said:

We had a Travelpower on our last boat...for washing machine..hair dryer etc...plus running the battery charger from it. 

We still gave up on the washing machine on most occasions...and used a laundry.

I looked into this, unfortunately my engine won't take a TravelPower. In the summer at least there should be enough juice from the solar panels to do washing. In the winter we may still have to hit the laundry but I'd like to aim for enough of a system to run the washing machine year-round.

 

1 hour ago, Jen-in-Wellies said:

Would it be worth leaving space for a larger battery bank and installing only a small lead acid one first? Say three or four flooded lead acid batteries. Then you can learn what it takes to keep them charged properly over the first winter or two and if you get it wrong and wreck them, then it isn't too expensive to replace. I destroyed the capacity of my first set of batteries very soon doing pretty much everything wrong. Second set lasted longer doing only some things wrong.

 

I've been running on only one 110Ah LA for a year now, it's now beginning to show signs of age. I have learned quite a bit on how to keep them happy, but you're right that I'm likely to make more mistakes with the larger bank.

 

If I was to get 6x 110Ah batteries (or 3 of @Alan de Enfield's type 625 200Ah batteries) that would leave me with my 300Ah of usable capacity that I calculated I needed to skip charging for 1 day of heavy usage or 3 days for light usage.

If I was to upgrade this after a year, presuming my first set survives living with me for that long, what are the implications of adding fresh batteries to an existing bank? Or would I have to replace the whole bank whether they are showing signs of age or not?

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47 minutes ago, Bobbybass said:

The main use of this immense  battery bank and charging regime seems to be the washing machine ?.

Huge amounts of engine running ( maybe half a gallon ?  ).. solar ..filling the water tank..and discharging plastic particles into our canals.

 

Is this really worth it ?.

I hear what you are saying. We've lived without 240V for a year now, so I feel like we have a pretty good idea of our pain points. For us the main pain point of living aboard is lugging bags of clothes to the laundry.

 

Filling the water tank is another concern, the washing machine is going to necessitate a second water tank and/or a filtration system.

 

We only use natural fibres so no plastic particles.

 

In the summer, with the solar in full swing, I shouldn't need to run the engine at all by my calculations. In the winter I concede that we may need to go to the laundry anyway.

 

So yes, the washing machine is certainly a luxury, but it's one we really want. So when sizing my electrical system, I'm factoring it in. We're hardly trying to mimic a land based life - we've managed with no inverter for a year!

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2 minutes ago, Richard10002 said:

For fear of discussing something that has been discussed elsewhere:

 

A 1000W item, (hairdryer), running for 10 minutes will use about 15Ah.

1200w for 5 minutes every second day is 8Ah every other day.

 

I think it is fair to assume that washing machines are rated on the basis that they will heat water, and I could guess, (but no expert), the heating is what uses most of the power. It could be safe to assume useage of 500w if cold filling, so a 90 minute wash would use 62Ah.

 

In fact, your washing machine is rated at 190kWh per annum. I dont know how they work these things out, but it will include heating water, and wont assume more than 1 wash per day, (are you assuming 1 wash per day, or a wash every other day? So the rating suggests a power useage of half a kWh per day, including heating the water. Could we half this using the cold option? 250kWh a day? 22Ah per day.

 

So your washer and hair dryer will probably use an average of about 26Ah per day. Add this to a normal high users useage, and you get about 150Ah.

 

Thus a 300Ah bank will suffice if you charge daily, 600Ah would allow for missing a days charging, along with the natural loss of capacity over time.

 

And nothing wrong with being conservative and assuming a bit more power useage than the figures might suggest.

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2 minutes ago, Richard10002 said:

In fact, your washing machine is rated at 190kWh per annum. I dont know how they work these things out, but it will include heating water, and wont assume more than 1 wash per day, (are you assuming 1 wash per day, or a wash every other day? So the rating suggests a power useage of half a kWh per day, including heating the water. Could we half this using the cold option? 250kWh a day? 22Ah per day.

Yes unfortunately they don't present the information on energy consumption in a very useful way.

 

I've seen one place note that it 2300W (assuming peak).

Cruising the cut guy says it runs happily on his 1300W inverter with cold wash. So that gives a ceiling on peak draw without heater.

The machine states that it uses 1.05kWh per cycle (but which cycle? 90 degrees with prewash or 30 min eco on cold wash?)
It also says it uses 194kWh per year for an A++ rating, which is quite possibly the most useless metric ever. But from the above two pieces of information, I can infer that they expect 185 cycles a year, or one every other day. Which actually is probably about how much we'll use.

 

I felt that a conservative figure of 1000W for 2 hours a day on my "heavy usage" day was reasonable. The system only has to handle my heaviest day and I'll get the light days for free.

8 minutes ago, Alan de Enfield said:

Having too many Ah 'in stock' is no bad thing and will actually extend the life of your battery bank due to a lower discharge (higher SoC)

 

All you need to do is monitor the Ah used each day, and put back 24Ah for every 20Ah used.

 

Its easy (innit !)

Is it easy to monitor the Ah used?

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12 minutes ago, ivan&alice said:

Is it easy to monitor the Ah used?

Yes - very easy.

 

Something like this (click link) will show you Ah used and AH replaced and nett difference (so you know if you need to put more back in)

Like everything it needs to be understood what it is showing you, but basically it tells you what you need to know. Just don't believe it when it says your batteries are 'full'.

 

The unit continuously monitors voltage, current (charge or discharge), number of amphours (charge or discharge), the batteries state of charge and the time to charge or discharge. This information leads to more efficient use of the battery, which can enhance battery life and reduce the risk of failure.
 

 

Other types and manufacturers available.

 

https://www.ebay.co.uk/itm/NASA-Clipper-BM1-Battery-Monitor-Instrument-12-Volt-/351924739339?_trksid=p2349526.m4383.l4275.c1

Edited by Alan de Enfield
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Apologies for being late to this topic.

 

Our domestic PV setup is 5 off 250W panels on an east facing roof and 5 off 250W panels on a south facing roof. Some output numbers for you:

 

January 1st, 2018: the panels generated from 10:20=>16:50, outputting 0.931kWh

January 2018: the panels output a total of 57.3kWh, best day giving 5.0, worst day 0.1, average of 1.8kWh

July 2018: the panels output a total of 345.8kWh, best day giving 14.5, worst day 3.0, average of 11.2kWh

July 31st, 2018: the panels generated from 06:20=>20:40, outputting 11.931kWh

 

You seemed interested in October performance:

October 15th, 2018: the panels generated from 09:30=>17:20, outputting 0.53kWh

October 1st, 2018: the panels generated from 07:40=>18:40, outputting 9.96kWh

October 2018: the panels output a total of 153.3kWh, best day giving 9.97, worst day 0.33, average of 4.94kWh

 

These numbers are rounded, the January worst day is actually 0.09.

The data collection does not do automatic clock changes so while start and end times might look odd, you can deduce the number of hours of useful daylight.

 

Feel free to interpret, interpolate, manipulate the above however you choose, just remember that it's your decision.

 

Hope this helps.

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19 hours ago, WotEver said:

A lot of folk get this wrong. The size of the bank does not in itself impact the recharge time. It’s how much you’ve taken out of it that matters. 
 

Take 200Ah from a 600Ah bank and it will take more or less exactly the same length of time to recharge as it would if you took 200Ah from a 1000Ah bank. 

Not totally accurate. The 600Ah bank starts charge at 66% so is in in Bulk mode and will rapidly get the first 100Ah in, then slow down for the last 10%, The 1000Ah bank starts at 80% so is into battery limited charging straight away and will charge more slowly for the whole 200Ah.  In all cases the bigger the bank the harder it is to fully charge, someone on here  once proved that using a generator and 90A charger it was not possible to charge a 1200Ah bank to 100% in 24 hours from 50% SoC.

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1 hour ago, Detling said:

Not totally accurate. The 600Ah bank starts charge at 66% so is in in Bulk mode and will rapidly get the first 100Ah in, then slow down for the last 10%, The 1000Ah bank starts at 80% so is into battery limited charging straight away

Totally incorrect. 
 

1/ What size charger are you referring to?

 

2/ How long do you think Bulk takes?

 

200Ah is 200Ah, it doesn’t suddenly become less than 200Ah if the bank size changes. 
 

1 hour ago, Detling said:

In all cases the bigger the bank the harder it is to fully charge

Again, entirely incorrect. Apart from the minuscule extra self-discharge from a larger bank there is no difference. 
 

1 hour ago, Detling said:

someone on here  once proved that using a generator and 90A charger it was not possible to charge a 1200Ah bank to 100% in 24 hours from 50% SoC.

That doesn’t surprise me in the slightest - that’s 600Ah that has to be replaced. 

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23 minutes ago, WotEver said:

Totally incorrect. 
 

1/ What size charger are you referring to?

 

2/ How long do you think Bulk takes?

 

200Ah is 200Ah, it doesn’t suddenly become less than 200Ah if the bank size changes. 
 

Again, entirely incorrect. Apart from the minuscule extra self-discharge from a larger bank there is no difference. 
 

That doesn’t surprise me in the slightest - that’s 600Ah that has to be replaced. 

 

Indeed, any lead acid battery, irrespective of capacity tskes the same time to charge from x% to y% providing the charging source is adequate to meet the demand of the battery.

 

Many moons ago I was responsible for charging various capacity batteries from 100Ah to 15,050Ah and they all took tbe same amount of time.

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1 minute ago, cuthound said:

 

Indeed, any lead acid battery, irrespective of capacity tskes the same time to charge from x% to y% providing the charging source is adequate to meet the demand of the battery.

 

Many moons ago I was responsible for charging various capacity batteries from 100Ah to 15,050Ah and they all took tbe same amount of time.

Yup. 
 

However, taking your first paragraph, we’re talking about a fixed amount of 200Ah (in my example) removed from the battery. Percentages don’t even come into it. Given a 50A charger it’ll be in Bulk until it’s replaced 150Ah. A 100A charger will be in bulk until it’s replaced 100Ah. The size of the bank (and therefore the % SoC) is irrelevant. 

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Let me make a couple of comments on the OP.

 

Firstly 300Ahrs use per day is rather a lot for winter use. If I read it right, this is mostly coming from the washing machine. I agree with Richard above. That is an awful lot. Heating the water in the WM by battery power is not a good idea. Far better to fill for the wash cycle with hot water. Rig up some valves to switch to hot water to fill at the start then switch to cold for the rinse etc. We start our washing machine when we run the engine for 1-2 hrs per day in the winter to get the most out of the alternator. That extra 100Ahr per day (heating the water) will take a few hours more engine each day. I pitty your neighbours. A bit antisocial. Aim for 200Ahrs per day.

 

On the choice of battery type, 2nd hand Li's from an EV should only cost around £1000 for 480Ahrs ....which should be ok for 200Ahrs use per day. Ok, you need a battery management system but that can be done for £200-£500 dependent on how complex you want it. You are looking at cheap LA's but if you dont get them up to 100% regularly and are thrashing the batteries by 200Ahrs of inverter discharge per day then you'll be replacing them every 2 years or less.  Having now had Li's for nearly 6 months (ok not in winter yet), I would defo go the Li route if I was in your position as they are so easy to manage with not having to look to see if they are full and always seeing the full power going in from the solar or alternator rather than the endless 10A to 20A LA tail current charging. If you are using 200Ahr/300Ahr per day then I can see you running your engine many many hours a few times a week just to get back to the magic 100%. Try and make it 200Ahrs!

 

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33 minutes ago, Col_T said:

Could you explain this, please? I'm not doubting you, I just don't understand.

Hi Col, sure.

 

A battery will demand a charging current approximately equal to the amount by which it has been discharged. So a battery which has been discharged by 20Ah will accept a charge current of 20A. A battery which has been discharged by 15Ah will accept a charge of 15A, etc. This is known as the ‘AmpHour Law’ (even though it’s not a law at all, simply an observable phenomenon). 
 

So, a battery (whatever its size) that’s been discharged by 200Ah will demand a charging current of 200A. If the charger is unable to deliver that (how many 200A chargers do folk have?) then the charger will simply output its maximum current until the battery demands less (Bulk Charge). So in the case of a 50A charger it will output a constant 50A with a slowly increasing voltage until it’s put 150Ah into the battery. At that point the battery is only 50Ah discharged and will, as it gets fuller and fuller, demand less and less from the charge source (Absorption). 

 

All of the above is relevant only to Lead Acid batteries of course. 
 

Does that make sense?

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Sorry, @WotEver, I didn't ask the question correctly.

 

Given the example of a battery needing 200Ah replaced, why will a 50A charger be in bulk until 150Ah has been put into the battery, whereas a 100A charger will only be in bulk until 100Ah has been put in or, to put to another way, why will the 100A charger not remain in bulk until the same charge level as the 50A charger e.g. 150Ah?

 

Oh, hang on, the penny may have dropped! Are we saying that bulk charge is the phase during which the charger is outputting the maximum that it can, and that that phase ends at the point that the current demanded, and supplied, is less than the maximum the charger can provide?

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10 hours ago, ivan&alice said:

The machine states that it uses 1.05kWh per cycle (but which cycle? 90 degrees with prewash or 30 min eco on cold wash?)

 

Is it easy to monitor the Ah used?

The tech spec seems to refer to a 60 degree wash when quoting anything.

 

On monitoring: The NASA BM1 reads up to 100A, so your hairdryer will be at its' limit. If you use something more than about 1200W, (vacuum cleaner?), the monitor does not record the useage over 100A. I have a NASA BM2... the extra cost is not a deal breaker.

Edited by Richard10002
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14 minutes ago, Col_T said:

Oh, hang on, the penny may have dropped! Are we saying that bulk charge is the phase during which the charger is outputting the maximum that it can, and that that phase ends at the point that the current demanded, and supplied, is less than the maximum the charger can provide?

Yep :)

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