Any 'Sparky' Boffins out there.

[emmitdb]

Greetings,

I've just come home from a fortnight away, during which, half of the time spent on sites was withoutout EHU (through choice and miserlyness!!!)

Whilst pondering the meaning of the universe, I started to think about my tiny inverter that is used (amongst other things) for charging up my shaver and the chief fairy's dustbuster.

It occurred to me that an inverter might be used from the towcar to power the inbuilt battery charger in the 'van. As a matter of course the towcar is used regularly on trips away from the site and any reduction in battery power caused by the inverter could be topped up when on the move via its alternator.

Does anyone out there know how much juice is required to power up the battery charger (and as a consequence, how big an inverter is required)

As a supplimentary question and assuming an answer to the above, how long could an inverter be used on a car battery capable of the above operation.

Any answers to the above conundrum would be appreciated.

 

[rayc]

Del. A quick answer without thinking about it in detail is that you would take as much out of the car battery as you were putting into the van one plus 25% for inefficiency etc. So for every amp/hour you were putting into the van you would be taking 1.25AH out of the car.

{I have not done any maths, the charger itself would not take much current to run it's internal circuits - this is just a gut feeling}.

 

[Paul_374358508]

Del. A quick answer without thinking about it in detail is that you would take as much out of the car battery as you were putting into the van one plus 25% for inefficiency etc. So for every amp/hour you were putting into the van you would be taking 1.25AH out of the car.

{I have not done any maths, the charger itself would not take much current to run it's internal circuits - this is just a gut feeling}.

A (decent Solar Panel) would help to replenish the on board battery, whilst you were on an away day. Paul

 

[RichardJ]

What you are trying for cannot be done, try a small generator, about 600w should be enough, cheap enough on ebay,(seen one for

 

[emmitdb]

What you are trying for cannot be done, try a small generator, about 600w should be enough, cheap enough on ebay,(seen one for

 

[JeremyClarksson]

We have run something similar.

We run the inverter and a charger in the car on a spare battery but only when the car is running on day trips etc, this works fairly well and has meant we can last quite well with a small solar panel as well.

Someone is going to say "why not charge it direct from the car?"

The voltage available via the car 12V system is regulated and not much good for charging a battery to full strength unless you have cables to the unregulated voltage (battery, alternator etc).

Personally I would rather do it this way then the way you are talking about as there is little danger of running the car battery flat.

 

[Woody3]

Eh?

The alternator on the engine charges the battery, and all electrical items come off the battery, either directly or indirectly. Where does this 'regulated' bit come in?

If you have wiring to the 'van for the fridge this will be switched so that it does not provide supply to the 'van unless the engine is running and the car battery being charged. Connect into this cable in the boot and use it to charge the 'van battery that you have remembered to take out of the 'van and put in the boot. Feed the battery connection through a suitable high-current plug and socket and fit a 20A fuse in the positive lead to protect the system. ALWAYS connect the negative last and disconnect it first.

 

[ProfJohnL]

Hello Del,

What you are suggest might work for a while but there are some important factors you need to consider.

Basically the process you are suggesting has several devices all of which have electrical losses. To achieve a 12A charging current into the caravan battery you are likely to the car battery to supply 20A to the inverter to cover the demand and the losses of the system.

Most car batteries are rated at 65Ah (or there about) so assuming the system allowed you to use that much power the battery would only last 3 hours!

In practice other factors will come into play and that figure may be generous.

The majority of domestic 12Vdc to 230Vac inverters have a low battery shut off which if the supply voltage falls below a fixed set limit of about 11V, the inverter shuts down. This is to prevent the inverter from draining the source battery,and in theory should leave enough power to start a car engine, however a battery which only produces 11V has lost a lot of it energy and it may not be enough to start a larger engine or a diesel. The problem is worse if the battery is in poor condition.

To avoid such problems, if the engine is running then the alternator will take most of the load, but this is expensive and wasteful of fuel, and the noise of an engine may annoy others, but the use of the 230V lead will be more effective than just using the towing sockets.

An hour or two of recharging the caravan battery may just be enough for you.

I'm not sure if this information is of any help to you.

 

[RichardJ]

What you are trying for cannot be done, try a small generator, about 600w should be enough, cheap enough on ebay,(seen one for