12 V questions

[CousinJack]

I have 2 queries I hope someone can help me with.

I have a TV which works on 12 V, but this must be a "regulated" supply. I know that if I powered it directly from 12 V battery, that woould not be regulated, but is the 12 V supply from the 2 pin plug attached to the aerial socket regulated? It's fed from the PMS box.

I'd like to get a secomnd leisure battery for the van for long weekends off mains. My car has a 12 V cigarette lighter type socket in the back. I think it was put there to power kids toys and dvd players for long journeys. Could I simply buy a battery box, rig up something with a cigarette type plug on one end and 2 crocodile clamps on the other end and charge the battery via that socket?

Thanks.

 

[JTQ]

I can comment on your battery charging question:

The 12 volt connection in your car is not directly suitable to charge your "spare" battery.

It is only rated at 10 Amp max, possibly less. However if that battery is low the cars alternator/regulator could be reaching about 14.4 volts [or more if the vehicle is designed for some modern batteries]. That high voltage will induce a current over the rating of the vehicles wiring to the socket and blow a fuse at least.

I do use it but in a more sophisticated way; I plug in a small inverter [now I use a Maplins 75 Watt micro one], and feed that AC output to my CTEK 3600 charger. This is a much better if slightly slow way to do things as the current draw is only 4 amps and the charger regulates the whole charging process optimising the achieved charge and battery longevity.

Other I know do it via a cable from the "white" socket or that sockets feed. This is a fast and cheap method of charging but one that is far from ideal for a leisure battery.

However you do it make sure you can securely physically retain the "spare" battery.

 

[JTQ]

I can comment on your battery charging question:

The 12 volt connection in your car is not directly suitable to charge your "spare" battery.

It is only rated at 10 Amp max, possibly less. However if that battery is low the cars alternator/regulator could be reaching about 14.4 volts [or more if the vehicle is designed for some modern batteries]. That high voltage will induce a current over the rating of the vehicles wiring to the socket and blow a fuse at least.

I do use it but in a more sophisticated way; I plug in a small inverter [now I use a Maplins 75 Watt micro one], and feed that AC output to my CTEK 3600 charger. This is a much better if slightly slow way to do things as the current draw is only 4 amps and the charger regulates the whole charging process optimising the achieved charge and battery longevity.

Other I know do it via a cable from the "white" socket or that sockets feed. This is a fast and cheap method of charging but one that is far from ideal for a leisure battery.

However you do it make sure you can securely physically retain the "spare" battery.

I would add that I then use exactly the same inverter and CTEK to transfer the charge for the "spare" battery to the caravans battery. The Inverter switches off itself when the battery voltage drops too low, but I usually intervene after a few hours.

This type of technique is best used regularly, a little at a time, as by doing this both batteries are never below say 75% capacity which protects them from premature sulphation; the scourge of lead acid batteries.

 

[J.Lo]

Cousin Jack, I use my van most weekends throughout the year along with a couple of hundred members all using televisions of various makes on 12volt and in the last 15 years have no problems running from the battery. J.Lo.

 

[Dave_374330759]

To answer the questions

The 12v volts from the socket next to the aerial would be regulated in so far as it come from the caravan 12v system. This means that it'll be at about 12.6-12.8v when just a battery is connected and at 13.8v when the mains hook up is connected. Thsi may or may not be ok for the TV. It's a case of "suck it and see" however if the voltage is too high for the TV and it damages it you'll have no redress regarding warranty. We've got a Hitachi 17" LCD TV and the regulated supply is exactly 12.1v so I'm reluctant to stick it across the battery as I don't know what the tolerance is, probably about +/- 0.5v so it would probably be ok direct from the battery with a 5amp fuse in series) but I wouldn't contemplate using it when the mains hook-up was connected.

I'd also be reluctant to try and charge a battery form the car cigarette lighter socket - they are only rated at 10a and are not everso good anyway (our one gets quite hot with just a 4amp cool box connected) so you stand a good chance of blowing the associated fuse or even worse burning the socket and wiring. If you really want to do it, get hold of a grey 12S socket and wire it up (WITH A FUSE IN SERIES with the +ve about 15a should do) to charge your second battery (if you use pin 6 for +ve and pin 7 for earth you'll be using the fridge supply which is only live when the engine is running) . Make sure the battery is connected before statring the engine and ensure that the battery is secure in the boot and can't tip over or move about, ideally in a battery box so that any splillage is contained.