Off Grid and blown air heating systems.

[Anseo]

I intend to spend more and more time off EHU.

The heating system is a whale blown air system.

Blown air requires a fan and when on 12v only I wonder what the effect on battery power duration will be.

Anyone have experience of what to expect under said circumstances?

 

[otherclive]

I intend to spend more and more time off EHU.

The heating system is a whale blown air system.

Blown air requires a fan and when on 12v only I wonder what the effect on battery power duration will be.

Anyone have experience of what to expect under said circumstances?

The system handbook should give fan power in watts so if you can determine that using dear old Power = Volts x Amps you can determine Ampere hours for however long you plan to run the fan.

 

[ProfJohnL]

In essence as battery is like a big bucket of electrical current and its capacity is rated in Amp Hours or Ah. A typical large caravan battery is rated at 110Ah and in theory if you were to draw a current of 1A continually the battery will give 1A for 110 Hours, or 220H at 0.5A etc. Its not quite that perfect but its close enough for what your trying to work out.

To work out how long your battery might last , you need to find the current draw for each appliance that will be used (most 12V appliance will quote their current rating on their data plates) estimate how long (in hours) each appliance will be used in each day, multiply the two figures to get the Ah per day rating for teh appliance. Do teh same for each appliance and add the all together. That will give you your Daily Current usage. The divide your battery capacity by the Daily Current usage, to get the estimate of the number of days the battery will last.

Its easy to think that items with big current values (Movers and water pumps) will deplete the battery most, but becasue their usage is usually intermittent they often use far less battery capacity than the caravans lighting or fans.

The key to off grid power usage is to be frugal, and especially to turn off things when they are not needed.

 

[Guzzilazz]

Most devices display wattage (power consumption) rather than current, however the conversion is simple. Divide the wattage by 12 for an idea of current consumption and add that up.

Also "safe" discharge limit on a traditional lead acid battery is 50%, so only take 55A out of a 110AH battery. Taking more will reduce the life of the battery, and may stop the battery being able to be recharged.

 

[Boff]

I haven’t got the whale heating system. We have got Alde so it requires 12v But my general observations about people going off grid for the first time are. Firstly it find out if your battery is dodgy. What is fine for ehu might only work for 30 minutes off ehu. So make sure your battery is working. Secondly you will use more gas than you can imagine We can go through 6kg in 3 nights in the depths of winter. Obviously much less in the summer. This is not meant to put you off just be aware. Once you have done it a couple of times it becomes a non issue. We are going offgrid for 10 nights day after rtomorrow I don’t anticipate any problems and it is a lot less than £20+ per night.

 

[RayS]

I have Truma combi 6 heating which also depends on the 12v supply even when heating fuel is gas. The fan has Eco and High speed settings and takes more current on high. However, if there is a big difference between the actual temperature and the temperature you set on the control, the fan may run at high speed regardless of which speed you have set until the 'actual' gets fairly close to the 'desired'.
This means the system can trip showing a fault of insufficient voltage. This is particularly true if the battery is already somewhat below optimum charge.
The way round this is to increase the warmth gradually by setting only small temperature difference, waiting until this is achieved and then increasing the setting again.
I am not very happy with the time you can run in this manner off grid, particularly for night use en route to Spain around New Year when outside tempeerature can be pretty low..

 

[waffler]

Had truma blown air 2 vans ago and we did a lot off grid including in winter. We had a 80 watt solar panel on the roof and generally had no problems. In darkest winter the battery got to 11.7 volts after 5 nights.

 

[bertieboy1]

Hi Guzzilazz,
Where are you getting this "safe" info from,I can't belief that if you need 50Ah you need a 100Ah battery

 

[Guzzilazz]

Hi Guzzilazz,
Where are you getting this "safe" info from,I can't belief that if you need 50Ah you need a 100Ah battery

The info is from experience shared in boating world... A quick Google search confirms

e.g.

Link

 

[ProfJohnL]

I think some good sense needs to be employed here.

The website Guzzilazz points to I have no doubt is an honest piece of work, and it probably does describe the way a battery will react to the discharge and recharge cycles. Let me be clear, I am sure that treating a battery in the way they suggest will probably maximise its effective working life.

But unlike boats,caravans and their occupants even those being used off grid, are rarely placed in jeopardy if the 12V power fails, so redundancy and vast over capacity is not warranted nor wanted becasue of the effects of the weight of carrying extra batteries.

I am not advocating total disregard for the care and management of batteries in caravans, and there is nothing wrong with applying all the care Guzzilazz's web page is suggesting, but from a practical perspective caravan owners do expect their batteries to wear out over time. But It is very difficult to establish what the life expectancy of a caravan battery should be.

We have heard of batteries that have lasted many years beyond what might be reasonably expected, but we have also heard of some that have failed well before teh warranty period is up, but that is usually due to a faulty charger.

Caravanners are expected to use "leisure batteries" which are a derivative of Traction batteries. These are designed for long relatively slow discharges as would be experienced by an electric Milk Float (If you are old enough to remember them). These were charged over night, and expected to provide continual discharge to move the float around teh delivery route. They would return to the depot significantly charge depleted.

I would expect to be able to use virtually all the charge capacity of a caravan battery as I describe in an earlier answer. It might shorten the lie of a battery, but if it enables of grid caravanning in the manner you desire, Then go for it.

 

[Gafferbill]

........practice rather than theory soon teaches an off grid caravanner that it is not a good idea to take a battery much past a 50% charge.
Even with that said the battery has to be in top condition since performance of 12 volt appliances drops markedly when past this point.
If the battery is not in top working condition this point can be reached remarkedly quickly!

 

[otherclive]

........practice rather than theory soon teaches an off grid caravanner that it is not a good idea to take a battery much past a 50% charge.
Even with that said the battery has to be in top condition since performance of 12 volt appliances drops markedly when past this point.
If the battery is not in top working condition this point can be reached remarkedly quickly!

My mover let me know when the lead acid battery had gone too low. At 50% charge the battery should read 12.2 volts, at 12 volts my mover trip cuts in to protect the battery from going too low. As my previous battery had been left in the caravan with something draining it (radio?) and it had run down, even my CTEK charger couldn't recover it. But the event re-honed my outfit manoeuvring skills in getting it back into its plot.I am now the proud owner of a new Banner battery which is removed from the van when it goes into store.