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Hi All

There are several reasons for wanting to avoid using EHU. The first reason is cost. The second is that  some sites have far nicer pitches away from EHU, and finally we like not to have to book, and the EHU pitches are nearly always booked up well in advance during the mid and high season.

Inspired by Wizard’s posts on going non electric, we went away for a week in our caravan and tried to stay off mains EHU for the whole week. The results surprised me.

First I researched the facts about leisure batteries, and came up with a range of conflicting information about how much a battery can be discharged. I really do not believe you should only discharge a battery by 50% before charging, the evidence for this seemed just hearsay. I do know that the caravan charger will not charge it below about 10 volts and you need a good quality charger to recover a battery with a reading below this. In the end I decided to simply measure the voltage accurately each day and use the following scale as a rough guide.

12.7v or higher                  Fully charged

12.5v                                     Three quarters charged

12.4v                                     Half charged

12.2v                                     A quarter charged

12v or lower                       Empty 

We have a new caravan with a new 110ah battery. I ensured the battery was fully charged on the caravan charger before starting. I checked the electricity and gas before setting off, and after a 5 hour journey read the voltage again. Before setting off the voltage was 12.68. On arrival it had risen to 13.24 v due to the higher charging voltage of the car alternator, but dropped rapidly back to 12.6ish. After a week the voltage had dropped to 12.42 volts. Wow, still half charged, or half discharged depending on your frame of mind.

We used the following equipment:

Motor mover:

5 minutes at, say, 10amps  = 1ah – (according to an earlier post, Powertouch say theirs will run for 90min on an 85ah battery).

Water Pump

Ours uses just 1 amp. Total running time during the week estimated at 20min. Usage 0.3ah

Lights

Each light uses just under 1 amp. Estimated 2 lights each on for 1.5 hours a day. 21ah for the week.

TV

Use a laptop as a TV. Uses 4 amps per hour. Hours used 4. 16ah for the week.

Fridge

Ran on gas, no electricity used.

Space Heater

Not used

Water Heater

Ran on gas, but control system uses 0.3 amps. Average time on 8 hours per day. About 16ah for week.

This gives a total of 54ah, exactly half the stated capacity, which matched the final voltage.

During the week we used exactly 2.6kgm of gas. We had a few problems here which came as a surprise. The first was with having a rear kitchen there is not much flat space for washing up etc and having the cooker lid up for the kettle was a nuisance. On the last night we had trouble with the fridge not staying alight. (Yes the van was level.) This was probably due to a strong wind blowing straight into the fridge vents.

Cost wise we saved 7 x £2 for EHU which was £14. For cooking we know we use about 0.5kgm of gas per week, so the extra gas cost us £6.30 at the Calorlight gas prices. This was quite a surprise.

Conclusion

If we want to spend a week during summer without EHU it is easily possible without any extra kit. Sadly though the cost saving of about £1 per day was far less than expected and was outweighed by the inconvenience of using gas. Solar cells, not necessary unless we want to watch a lot more TV. In future we will save weight and only take a 65ah battery instead of the 110ah. Anyone want a 110ah battery?

Martin

Martin,

thanks for an interesting report.

I would add that a lot more sites now have a £3 per night premium for EHU.  That would double your daily saving to £2.

I also agree with LDKO in that there are more sites available if you can go without EHU.  My personal delight is to visit one of the unequipped New Forest sites (water tap and waste disposal only).  Even in the height of the season there is hardly anybody there.  Brilliant.

The big saving as LDKO and Crypto say is that if you don't use EHU you can stay on rallies and non-facility sites which have much cheaper pitch fees and will save much more than the £1 per night you have saved on a proper site.

I find a gas kettle more flexible than an electric one as you don't have to move the lead around as well when you want to use the work surfaces (you let the kettle and hob cool down first, of course).

Re the gas consumption, I suppose it depends on how much cooking and showering you do but we've never used anything like that amount. We only tended to put the water heater on for a shower, not leave it on for hours at a time - it's quicker to boil a kettle for a wash or washing up.

Hi John

Thanks for this, had seen something like this before. However, this assumes that each time you use the battery there will be a deep discharge to the same level and in practice it is likely to vary. I suspect battery life  is also dependent on the rate of discharge. Also, if you go out every weekend for 6 months of the year and fully discharge the battery every time there will be 8 years life in the battery. I suspect that other aging processes will also be taking place during this time, whatever the DoD. What effect will shaking all the gunge up at the bottom of the battery each time the van goes out have on battery life?

Also an 85ah battery is about 2/3 of the weight of a 110ah battery and 2/3 the price, so for the same overall cost you could replace it more often.

Martin

Quote: Originally posted by freeatlast on 11/8/2008

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I really do not believe you should only discharge a battery by 50% before charging, the evidence for this seemed just hearsay.

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Battery manufacturers quote the battery capacity in a fully charged state - i.e. at 2.6 volts per cell.  If the battery has been charged on a caravan power supply or in a car, it will only have been charged to 2.3 volts per cell - 13.8v.  This means that the "fully charged" battery is really only 80% charged, i.e. a potential availability of 88 Ah.

 

When the battery has fallen to about 12v under light load, it still has about 15% of its theoretical capacity available, i.e. about 16.5 Ah.   We can, therefore, only usefully extract 88 -16.5 = 72.5 Ah. which is around 66% of the nominal capacity.

 

The life of lead acid batteries is shortened by deep discharges.  This isn't hearsay.  There are lots of references on the internet that will confirm it.  My bet is that the 50% figure you've heard (and I have too) is someone's idea of a reasonable figure to use for reliable service and reasonable longevity.  I don't think there's a lot wrong with that.

 

As an aside, the battery voltage offload does not give a reliable indication of its state of charge.  I don't think you can assume that a voltage of 12.4v means that the battery is at half charge.  It might only be 25%.  You might find the charge/discharge graphs in this article interesting: http://www.arttec.net/Solar_Mower/4_Electrical/Battery%20Charging.pdf

 

Your post was interesting and quite heartening.  I'm taking the van away in a couple of weeks time for a few days in North Yorkshire.  I will not have a EHU available - for the first time ever!!!  I think your experiences make me a little more confident that I'll be OK.  Thanks for that.

 

Cheers

Andrew

Cheers for the comments everyone. Good link Andrew, thanks.

As regards topping up after charging on van system, it was topped up by the car with over 5 hours driving at the higher voltage that the car alternator produces. Yes the voltage did rise, but within a day it had dropped back to the previous voltage. This would suggest that this topping up does not add as much as 20% but possibly ony 5%.

Interesting point about batteries being shaken up. Would not have expected that.

I take the point John that it is important to charge the battery up fully once home. I am fortunate to keep the van on the drive where I do leave it on charge for a day or two on returning.

I would guess that a common reason for battery failure is not topping up the water in a non sealed battery, or using ordinary water rather than distilled water. In my experience, this is not routinely checked on servicing.

Either way, a week away without EHU appears to have only half discharged the battery.

Martin

Hi Martin

How do u get TV on your laptop?

Terry

Hi Terry

See the following thread:

http://www.ukcampsite.co.uk/chatter/display_topic_threads.asp?ForumID=6&TopicID=159363&PagePosition=1

Martin

 we used to always use non EHU pitches but as we get older we find that we rely on TV as our evening entertainment .

This was fine when the BBC radio 4 had decent programmes IE plays with beginings and ends about interesting people .

Unfortunateley now the PC croud who run the BBC have inflicted on us plays about the underclasess which are so depressing that one is inclined to get out the gidion bible and read a bit of Revelations for some light relief .

We still use non EHU pitches over the weekends when TV is not worth watching and the pub beckons .

However every one to their own thing and so long as its caravanning its fine by me .

Now back to more G&Ts     Col