Life without EHU

[lolo]

On the broader subject of life without EHU, I wonder if someone who knows about these things could enlighten me (us ?) about the feasibility of what seems to be a quite simple solution to the series of dark miserable days which have resulted in an inadequate amount of energy being put into the battery by the solar panels, often prompting the appearance of the unpopular and expensive to run (and buy) generators.

Yesteryear, I used to drive cars professionally at the time of the advent of the alternator and the demise of the dynamo. At that time, the cars were fitted with a moving coil ammeter (I mention that because they now seldom are) which was scaled up to 70 or 75 amps. When the car was started, the ammeter showed a massive charge deflection – perhaps 60 to 70 amps – but for only a few seconds because of the small amount of energy consumed in the car-starting process, and by half a mile down the road, was showing an indication of fractionally above zero. All this suggests that the battery did not suffer from the massive charge – or did it ? Would it have been detrimental if, due to a partly (or wholly) discharged battery, the massive charge had been for a longer period ?.

All this leads, of course, to the tow car and caravan situation. In the case of a depleted caravan battery, what is to prevent hooking the car up to the caravan on site and running the car at a fast-enough idle to recharge the battery fully in say – 20 minutes. I can’t really think that it would be detrimental to the battery, as after a reasonable length tow to a site, the battery is bung full of energy whereas it certainly wasn’t when we left !!

 

[WoodlandsCamper]

I can’t really think that it would be detrimental to the battery, as after a reasonable length tow to a site, the battery is bung full of energy whereas it certainly wasn’t when we left !!

It might not be detrimental to the battery, but it may well be detrimental to your neighbours - both the noise and the fumes, 20 minutes is a long time. :evil:

 

[RogerL]

A car alternator's output is roughly proportional to it's speed - so it only develops it's rated power at high rpm - even at fast idle it'll only produce fairly low amps.

To recharge a 110Ah leisure battery from 50% discharged (the recommended minimum level) up to 100% would need 55Ah - the cabling is only designed for 10A so it would need 5+ hours to do it.

 

[Gafferbill]

Hi lolo
The most cost effective and simplest solution is to have another leisure battery to take with you in a fully charged state.
This will double your endurance for around £80.00.

BTW.........Hope I can still caravan and be concerned about such things at your age :cheer:
(if your posted age is correct)

 

[Dustydog]

This subject fascinates me.
I ask myself what 12 v power do I need to survive without EH.
Well forget the TV. .
All our lights are 12v as is the water pump and radio..

Everything else will run on gas ie fridge, water heater, room heater, cooker and so on.
Have I missed something?

 

[WoodlandsCamper]

Have I missed something?

The most obvious in a lot of vans - the electric flushing WC.

Edit - and the electrics for the fridge.

 

[Dustydog]

[qu? ote="Dustydog" post=387749]
Have I missed something?

The most obvious in a lot of vans - the electric flushing WC.

Edit - and the electrics for the fridge.[/QUOTE

OMG. How could a Woosie forget the WC?.

Fridge,t electrics?
Surely only the interior light???

 

[WoodlandsCamper]

Fridge electrics?
Surely only the interior light???

Our fridge has an LCD display showing cooling source, temp and something else, but as the fridge is the domain of the catering supervisor then I don't know what it all means. I believe the fridge won't operate without the panel functioning.

 

[JimD1]

Need 12V for the Alde heating/hot water & the oven/grill both have fans.

Jim

 

[watto7]

We are going to a holiday rally for a week I've got an 80w folding solar panel but as the battery is always discharging within 2 weeks so I am a little concerned the tracker apparently draws 0.2 amps an hour ,I don't know if this is normal it's in the dealers at the moment it's a new Bailey Unicorn .any advice knowledge appreciated .

 

[emmerson]

In the past Herself and I have camped for three weeks on one 110ah battery and no EHU. In fact the van did not have mains at that time.
Of course, then, as now, we use old, luxury caravans, with masses of insulation, so didn't need much gas heating, gas for the fridge (with no electronics), ditto for the cooker, and a hand operated flush for the toilet. And no TV. Lights are three small flourescents, with two smaller ones for reading.
Our current old Royale has mains now of course, but we still have no qualms about non-ehu in the summer, but we do like electric heating in the winter. (Well we are very senior caravanners now!)
A quick story re the insulation: a few years ago we attended a rally at Brickkiln near Thursford, and it snowed, very hard for almost 24 hours. Within a short time, most of the modern vans around us had melted the snow off their roofs. The Royales were still covered two days later.

 

[waffler]

We had a similar problem of the battery discharging in 2 weeks. It turned out to be the radio- even with the front off it was taking power. (We took the radio out and solved the problem.) We had a tracker but no problem after losing radio. Another source of loss can be the fridge. The gas igniter stays live on some. I doubt it is this though.

 

[ProfJohnL]

A car alternator's output is roughly proportional to it's speed - so it only develops it's rated power at high rpm - even at fast idle it'll only produce fairly low amps.

To recharge a 110Ah leisure battery from 50% discharged (the recommended minimum level) up to 100% would need 55Ah - the cabling is only designed for 10A so it would need 5+ hours to do it.

Hello Roger,

A battery in pristine condition will only retain at best about 70% of the energy you give it, and older batteries deteriorate to about 50% , to recharge 55Ah w at 10A will take about between 7.5 to 11 hours!

 

[ProfJohnL]

...................All this leads, of course, to the tow car and caravan situation. In the case of a depleted caravan battery, what is to prevent hooking the car up to the caravan on site and running the car at a fast-enough idle to recharge the battery fully in say – 20 minutes. I can’t really think that it would be detrimental to the battery, as after a reasonable length tow to a site, the battery is bung full of energy whereas it certainly wasn’t when we left !!

Hello Lolo,

You would need to know how depleted the caravan battery was before and how full after your towing to make any real sense of your experience.

But considering the use of a car to recharge your caravan battery on site, you need to be aware of scale of teh issue, and how it compares to the use of the battery in the car.

If you could look at the actual current drain when the starter runs it has two distinct current characteristics. The moment the starter is energised it may draw 500 Amps for a small fraction of a second until the motor starts to turn then the second characteristic is when the starter is turning and the current will drop back to to 60 to 100Amps (the actual amounts will be determined by the car) Now unless you have a very difficult car to start you only run the starter for no more than about 5 to 6 seconds.

When you work out the amount of battery charge it uses you multiply the current by the time its used for.
So 500 x .1 /3600 to give Ah's = 0.013Ah and 100A for 6 seconds = 100 x6 /3600 Ah = 0.16Ah so in total starting a good car is unlikely to use more than 0.2Ah of battery capacity. Quite surprising isn't it. !

So with so little car battery capacity used, it shouldn't take very much driving to replenish the power used.

Now the construction of car batteries and caravan batteries differ they sit at each end of a spectrum of abilities. which suits their designed applications.

Car batteries can deliver very large current demands needed to start a car, Caravan batteries can't.
Car batteries are recharged almost immediately, caravan batteries are designed for long deep cycle discharges
Car batteries can handle large charging currents, caravan batteries need relatively low charging currents over longer periods

With the above in mind, attempting to recharge a 50% depleted caravan battery from the car will not be accomplished in 20Mins it will take between 7 and 11 hours ( see other posts)

 

[Gafferbill]

........I successfully use a 600 watt pure sine wave inverter to transfer a charge from the car battery to the caravan battery via the caravan on board battery charger, which in my caravan is an 18 amp smart charger.
The inverter can quickly be attached to battery under the bonnet of my tow car using crocodile terminals.
I have made up a lead to transmit 240 volts AC from the inverter to the caravan using the normal mains connection socket on the caravan.

This set up is successful because of the following...........
Towing vehicle has a large heavy duty battery.
The towing vehicle battery voltage is monitored so that you can be sure the vehicle engine will start.
Caravan has a smart charger that will charge at 14.4 volts DC.

The set up is only used when you know you will shortly be making a trip with the towing vehicle which will recharge it's battery.
I have run the set up for up to 1 hour without the engine running.

 

[lolo]

Thanks gens. In a few days we are going to park up in daughters paddock where EHU is available. I had it in mind to not use my panels there and run my battery down without EHU, then carry out a series tests of various durations with the car, noting the figures produced after each period of time - both without load on the battery and then with. I do have a voltmeter permanently monitoring the battery so it will be quite simple I think. However, I have so much respect for your opinions that it is already a forlorn hope, I suspect.

 

[ProfJohnL]

Hello Lolo,

Your plan is good, at least you will have some real results on which to base your plans. Keep us posted.

 

[SteveW77]

A car alternator's output is roughly proportional to it's speed - so it only develops it's rated power at high rpm - even at fast idle it'll only produce fairly low amps.


At a fast idle most alternators produce at least 50% of it's rated output

 

[Gafferbill]

......a vehicle alternator has an output that is controlled by the demand placed upon it.
It will have no output at maximum engine revs if there is no demand!
At fast idle if the demand is there, it should be capable of 50% of it's output as SteveW77 says.

Lolo will find in his experiment that his car's alternator will not recognise that his caravan battery needs charging.
This will be due to the limitations of the capacity of the wiring back to the caravan battery and to the fact that the state of charge of the vehicles own battery will take precedence and cause the alternator to reduce it's output to that of a trickle charge.

 

[lolo]

Sorry for the delay – I have at last managed to carry out the threatened tests to see if it is feasible to charge a fitted leisure battery on site by connecting it to the car.

Today, my caravan battery was indicating 11.98V (digital voltmeter fitted in van) with a small load i.e. (Thetford) fridge (on gas), blown air fan, tv standby mode, led lights.

When connected to the car with the engine running, there was an instant indication of a13.5V charge rate with the car engine ticking over (500-600 revs). There was no appreciable increase of charge with any increased revs.

The car was left running at tick-over for 10 minutes and then disconnected and after a 5 minute standing period, the reading (without any load) was 12.55v and with the original load applied a reading of 12.35V was shown.

The noise generated by the engine ticking over was minimal, and as the need to resort to this emergency treatment is more than likely to be on the wide open spaces of a c.l. or c.s.,, neighbour conflict is probably less likely.

Useful to know, isn’t it. Just hope I never have to use it !
I

 

[paws]

Hi Iolo,
You haven't really finished the test yet.....
The figures you have obtained indicate that the battery has received a surface charge, hence the apparantly better figures after the short charging period....

However without further charging you need to check the figures again after a period of rest... (24 hours is usually suggested )

You my be surprised by the figures you get for the battery voltage off charge and offload after 24 hours rest.... they may indicate that actually very little charge has been absorbed by the battery....
Let us know what you find.
Regards
paws

 

[Gozza]

From experience I would add...get (or make) a nice long charging extension lead so that if you're going to do this on site you can choose which direction the car exhaust is pointing! I've only ever had to do this onc, and because I only had a short connector I had to stop because my exhaust fumes were blowing straight into my neighbour's tent.