I am pretty new to caravanning and would appreciate any help about the subject.
I want to be free from 240v mains electric so I am not tied to a hook up. However, I still want to watch TV(I have a normal 240v one-portable colour and don't really want to pay for a 12v one which I think take up less power(?) and seem to cost a fortune).
I have been told to get an invertor to plug the 3 pin plug from the TV into. However Ihave also been told that I will be only be able to watch a couple of hours of TV before the battery goes flat.
Could anyone suggest what is the most efficient(and cheapest)way of doing this as I dont want to take 20 batteries away with me or have to charge the leisure battery every day. Lights, water pump and Carver switches for heating and water will also be used.(Ive got a feeling the kettle,fan heater and iron are out the question here!).
Also, any clues on what is the best size leisure battery to use(amphours)and how long it would last and how long it would take to charge up.
Also, what charger should I buy to do an adequate job of charging the battery.
Any good websites to purchase these things?(invertor,charger,battery,powr packs,12v TV)
Last one honest!- I have seen an all in one invertor/battery(I think they are called power packs/stations) - is this the better option as it seems this could rid the need to buy a leisure battery and charger?
As an electrical engineer, I can give you some reasons:
Inverters are by their very nature and design, somewhat inefficient: i.e. power is "wasted" in the process of converting fron 12V DC to 240V AC. Additionally, there is no getting away from the basics of mathematics.
If a 240V TV consumes 1Amp, then applying the maths it consumes 240 Watts.
To run the same TV from an inverter/battery, the Watts remain the same, but the current needed from the battery now becomes 240 divided by 12 i.e 20 Amps!
A good 110Ah leisure battery will therefore theoretically run the tv for about 5 hours.
In practice, however, the inverter will demand more than the 20 Amps to cover the "wastage" I mentioned earlier, and a battery will rarely perform right up to it's rated capacity, so you could expect less time than the theory suggests.
Other disadvantages are that the inverter is bulky and chucks out a lot of heat. Also carrying a 110Ah battery is no joke!
The best solution is to buy a (more expensive) 12V DC tv.
Power "station" type gizmo's usually have NiCd batteries, are of faily limited eendurance an cost quite a bit. You really are better off sticking with a leisure battery of a sensible size/weight and "cutting your cloth" to suit as far as the type of appliances that you buy.
-Lastly, (honest!) any reasonable charger from a reputable source will do to charge your battery - Most good car accessory shops will stock a later-generation charger with an electronically-controlled output. - These are the best (in my opinion), although any simple charger will work.- It's all a case of looking after the battery and keeping the electrolyte topped up. - Don't assume that leisure batteries are "sealed for life" or "maintenance free" - there is no such thing.
14" PORTABLE TV will use aproximately 60W on max volume ie in reality it will consume 40w at normal volumes.
40w at 240v is .16666 of an amp x that by 20 to get 12v ampage is 3.333 allow for invertor inefficiency its would use just under 4 amps an hour.
With a fully charged 110ah battery thats 13.75 hours viewing, no thats not a maths error because you should never really discharge a battery by more than 50% if you want it to last.
This brings us on to charging, split charge from alternator will only charge to about 70% (and thats being generous) a zig type charger will charge to 90 odd percent if left on all week without any loads.
This low charging is the reason people seem to think a tv will only run for a couple of hours via an invertor, if you only have 70% charge less the 55 amps you shouldnt really use that leaves 22 ah which would give about 5 hours veiwing.
To fully charge a battery a good three or four stage charger is required, one that can also act as a power supply when hooked up is the best.
I am using Sterling marine gear on my motorhome, a 10a international charger costs around £129 (less if you join the SBMCC, as you will get a 20% discount at least) a 150w invertor would cost £34 (less disc etc etc)
If you need to travel regularly and will not get near a mains socket an alternator regulator will make the output from the alternator into a good 3-4 stage charger these cost the same as the mains charger mentioned above.
"Ive got a feeling the kettle,fan heater and iron are out the question here!"
These would take far too much power as you have already guessed. I have 10 X 110ah batteries in my motorhome and I would not consider running any of these items by invertor !
Power packs are a waste of time (for what you want to do) as they have a very limited run time.
Really appreciate the quick replies. This site is excellent!!
Quick reply to Karl: there are many reasons why one would not be using an electric hook up, and as Suzzie suggested an obvious one would be rallies(although that it not what I will be taking part in).
PS. I wish I had stuck in at maths/electronics as the above takes a little thinking about to say the least.
Would one of the very small TV's like the 7" screens use a lot less power than a normal colour 14" TV?
Absolutely facinated with this thread..thanks for the electronics revision classes too...forgot stuff like P= IV !
So can anyone add to this...whats the preacticality of charging the aforementioned battery with solar panel/wind power? (As recharge will difficult without hookup!)
Windpower. Too noisey and means parking in exposed spots.
Solar power, will produce power when there is light available, however the output is seriously reduced with any partial shadowing, also you then need to park in the glare of the sun. You will need roughly £2,000 to run a small compressor fridge and a light reliably.
Add a smart regulator to the alternator and this will produce more power in 1 hour than 4 panels produce all day! note in the link below 2 amps x this by say 8 hours of gives 16 amps, a small alternator can put out 40 amps (with a smart reg attached) so in one hours driving / running you will get 2.5 times more power in from the alternator !)
The chap in he link above does Adventure "tours" a lot of driving with only a day or so on any stop, a smart regulator would have given him far more power in the batteries, at a far lower cost. Think how much extra cooling you would need to do parking in direct sunlight ! would probably use a lot of power keeping cool !
Small TV's do use less power. LCD screen types should be checked because the gains in power reduction using LCD can sometimes be offset by the power requirements of the backlighting system. General rule of thumb is that yer gets what yer pays for..
I have tried to steer clear of getting too technical (I hate maths, I'd rather be fixing things) so did not go into great detail in my last post, or this one.
There is a lot to be said for "going back in time" a little, Our first 'van would survive a whole weekend on a rally with a 70Ah battery, BUT.. It had a Gas light, a Gas fridge, a foot pump and NO blown air, kitchen extractor, flush toilet etc. The van I have now with a 110Ah battery would probably survive the weekend with very careful use of the electrical system, by try explaining that to the kids! - As ever there is a price to pay for all the luxury items we now have in caravans, that price is increased energy demand, from whatever source.
A solar panel will, as George has said, contribute little unless it is a) huge and b) in the sun! - I know several folks who have fitted or take solar panels with them and also one or two who have bought those dinky little wind-powered generators. - My opinion? - Very expensive for the benefits gained, and those benefits cannot be relied upon in the British Isles (despite what we may think of the weather).
P=IV rules as a rule (pun intended) and the only way to go is as I said "cut yer cloth to suit" !
A day of all things motorhome and campervan. The show is held both in the main indoor arena and across the grounds. Catering, hot drinks and food options are available. Easy access to the site and free parking included. Win one of five pairs of day tickets
Topic: Invertors/PowerPacks/Batteries?
