Power requirement calculation.

Anthony_G

New Member
Hi folks, I am in the planning stages of a 7.5ton MAN TGL LWB conversion. If I proceed I will be in it six months of the year. For this reason I am posting here and not in camping type forums, where the usage type and consequent design parameters are very different.

I wanted to gather opinion on whether the list of items is missing anything obvious? (obvious one, she doesn't use a hairdryer.) I am not planning for hook up. I am planning on 400% battery capacity and around 1kw solar array. Also plan to carry a generator if the sun doesn't, for many days.

Thanks in advance.

24v list
Item V A W Hrs Watt Hrs
Fridge 24 5 120 1.5 180
Freezer CFX-35 24 5 120 1.5 180
Water Pump 24 4 96 0.25 24
Heater 24 1.40 33.6 1 33.6
Laptop 24 2.50 60 3 180
USB Charger 24 0.42 11 8 88
Lights 24 0.09 2.2 60 132 - this 60 figure is for a multiplication factor for 10 lights @ 6 hours.
Fan 24 1.5 36 5 180
Invertor 24 17 408 0.5 204
Total 35.41 1201

1201 / 24 = 50 watts per day. So a battery bank of around 400w @ 24v will give 4 days off grid with no charge @50% discharge.

Router = USB
Ceiling Fan = 12v step down transformer.
Water Heater = Battery ignition.

240v list

AA + AAA Battery Charger 240 0.5 120 0.357 42.84
Shaver 240 0.0375 9 0.00396 0.03564
Camera Batteries 240 0.116 27.84 0.01 0.2784
Vacuum 240 0.3 72 0.5 36
Total 228.84 79.15
 

vwalan

Well-Known Member
many dont use 24v things . use a durite 24v to 12v battery charger .
its easier with 12 v as solar is easier ,inverters easier. plus every m,caravan or caravan place ,stockist is catering for 12v .
plus some times its far cheaper .
mind fridge 240v is far cheaper .
think hard .
i use 6x80wt solars through 600amp batteries . did use a 2kw inverter but it failed after ten years and i now use a 1kw mod sine wave and a 1kw pure sine wave inverter . i found new 240 v fridges arent happy on the mod sine wave .
end sept oct can be awkward in uk but nov in spain and all winter is usually all ok.
yes get a week of rain and dark clouds have to be careful.
i bought my panels second hand ,well the first three . but these days at the price they are now i would use 100wt panels . prices are very cheap today compared to years ago.
 

Anthony_G

New Member
Wot !No George Melly ? My kind of guy! But I havent a clue what all your figures mean ?
The forum server strips all the spaces which made the numbers much easier to decipher.
These are the columns: Five columns. They are essentially adding up the power use of each item in the list, based on how long I think it will be in use for each day. Then a total is derived.
Volts Amps Watts Hrs 'Watt Hrs'
 

vwalan

Well-Known Member
when fitting the solar remember dont go too big with each panel . one gets broken you lose alot if large . stones dropped off bridges by kids breaks many.
but also shade one small shaded not too much worry . but shade part of a big one its lost.
ideal is gas heating , gas water heating .
i use gas lighting . gives light and some heat.
of course all depends where you will be at times of the year.
 

coolasluck

Well-Known Member
I have 720 watts and 675 amps of batteries and it works brilliantly for us. We have been off the grid for 2 years and now in our 3rd year with no need for a generator or hook up. Mind winters in Spain and Portugal help. Be kind to your batteries with regards to an inverter.I opted for a 1000 watt pure sine wave and a 12 volt house system. We also find that we use appliances the same as we used in our house so miss out in nothing.
If your going down the route of 24 volt I have a 24 volt pure sine inverter and 24 volt diesel eberspacher d4 heater I can sell you.
 

coolasluck

Well-Known Member
Make sure you have a good payload as well.It is also good to have a number of ways to do things. For example we can use our inverter to heat water as well as l.p.g and diesel.
 

chrisjones18

Well-Known Member
if me I would keep the 24 volt truck system and add a 12 volt habitation system as 24 volt "stuff" costs a fortune,
as much "led" as you can get, better if all.
use " mppt controllers" for the solar as they only need daylight not sunshine to work.
I only have gas for water heater and diesel for heating.
 

chrisjones18

Well-Known Member
why am I thinking a laptop runs at 17 to 18 volts not 24volts. and a usb at 13..
its the numbers------arggggggg:banghead: I see it then I don't, pass the Gin please:party:
 

Pops

New Member
I'll add my voice to the 12v system for the habitation.
Have a look at Shoreline 12v fridges and fridge freezers. We fitted a fridge freezer that wouldn't be out of place in a B&M home kitchen which uses around 2.1a/h. Our 600W of solar feeding 400Ah of battery supports it easily.
 

vwalan

Well-Known Member
when i got into solar it was very expensive . 400 quid for 80wt panels . now 100wt costs less than 100quid . but i worked it out that 12v fridges were very expensive also. . 240 v fridges allow extra panel ,an inverter and an extra battery these days . and you can use the inverter for lots other things .
mind i do know several that have fitted 12v fridges and are pleased with them .
but becareful as there are tropical and non tropical 12v fridges . think about where you might be visiting as to what might suit .
i shall stick with 240v .
never use ehu, or campsites or aires .
 

coolasluck

Well-Known Member
Go 12/24 volt fridge rather than 240 volt fridge. Our fridge works well and is great whatever the weather.Not only do you have to keep your inverter on all the time with 240 volt fridge but some feel the need to switch the fridge off at nights to save on power don't they Alan......
 

vwalan

Well-Known Member
yes if its very dark in the day. but even 12v might need it if its dark in the day.
its called compromise.
249 fridges are cheap.
really i should be changing my batteries , last year was really time . but in truth i dont need the fridge at all. its handy. can make lolly pops in the little freezer if its sunny . but bacon ,margarine etc doesnt need a fridge . hardly use milk .
but the solar and inverter are definately usefull for the washing machine . but again dont do washing unless its sunny.
 

sundowners

Well-Known Member
I reckon that you should fit as much solar as you can get on!!!!! And a lot of battery--------I have found that with a big inverter (ours is 3kw) it gives you more flexibility to use the battery power that you have available at any time, eg. When we are charging at 20a we have loads of power to use, if it is cloudy or just very short days in winter we are more restricted.
Remember that if your solar panels can give a max. of, say 20a you will get nothing like that in UK or cloudy weather in winter.
Also Good batteries are a good investment!!!!
I believe that 3 way fridges also come in tropical------ all the 'American' fridges that we have run seem better than European ones, even though they are mostly dometic.
If you fit a gas fridge, put the vent through the roof like all RVs do, it is much more efficient.
Nigel
 
Last edited:

sundowners

Well-Known Member
Personally, I would split the electrics in two systems, 24 for the chassis and 12v for everything else as 12 volt stuff is, I believe easier and cheaper to get hold of, maybe the exception is the diesel heater as these are used on just about every truck with a sleeper cab in the world?????-------- maybe the heater with water heater included is different???
 

sundowners

Well-Known Member
Wherever you fit power sockets fit USB with them (I also fitted extra 12v sockets)--------it gives you the option of running/charging stuff without having leads trailing around. All our phones/tablets/TV/sat Decoder/mi-fi etc run from these
 

coolasluck

Well-Known Member
Despite having 12 volt sockets I find we don't use them as they are not needed.Our inverter does it all.Never needed to turn our fridge off even when we have had dark days Alan.;););)
 

vwalan

Well-Known Member
great i,m always
Despite having 12 volt sockets I find we don't use them as they are not needed.Our inverter does it all.Never needed to turn our fridge off even when we have had dark days Alan.;););)
willing to learn new things .
what i would really like is a eazicool had them in my vw,s you pour a cup of water over it each day hotter it gets outside the cooler inside the box .
not a fridge exactly and never freezes but worked for keeping food .
but what ever suits , i know i,m not keen on 3 way fridges .
 

Adverts

Top