multi DC out put 12V in transformer wanted

[AstonHill]

That makes some sense, but has absolutely nothing to do with your problem, of running a 19v laptop from a 12v battery.

But the point is i can use my invertor to run laptop off of the battery, but wastes to much power even still when in use

 

[AstonHill]

More efficient, is a compressor fridge, but they normally only work on mains power - via an inverter. The problem is, they still need a relatively large amount of current, so cannot be kept running for long, on a 12v battery, unless the engine is running, so the motorhome, must be quickly plugged into the mains, on arrival on site.

Did'int eric-an-doar say somewhere ells that house hold fridges (the ones you are refering to) have a DC motor and an iverter inside of them?

 

[AstonHill]

That makes some sense, but has absolutely nothing to do with your problem, of running a 19v laptop from a 12v battery.

The usual 12v fridge for a caravan or motorhome, is what is called an 'absorption fridge', they work on gas, mains, or 12v. They are not very efficient, but it is the only sensible way to run from three different sources. They are so inefficient, that when on 12v, they do not even need a thermostat - they draw current all the time. On mains, or gas they do use a stat.

More efficient, is a compressor fridge, but they normally only work on mains power - via an inverter. The problem is, they still need a relatively large amount of current, so cannot be kept running for long, on a 12v battery, unless the engine is running, so the motorhome, must be quickly plugged into the mains, on arrival on site.

The guy at the end of the street, must use a fairly substantial relay, to switch the dc high current supply to the inverter on and off.

Do you think a typical 12v 4 pin car relay will do the job?

 

[AstonHill]

Particularly if it's fairly small, it must therefore get pretty hot when it is 'doing nothing'? Does it have a fan?

Kind Regards, John

yes it has a fan

 

[JohnW2]

#edit# since my last topic was close for further disscusion about thermocouplers ... ... will this now be closed because i mention the word thermostat?

No - your previous attempt at a topic was 'closed' because DIYnot does not permit discussion about work on gas appliances or gas installations, other than ('in private') between Gas Safe registered folk.

This discussion is all about electricity, not gas, so is perfectly acceptable - (even if rather confused/confusing at times!).

Kind Regards, John

 

[Harry Bloomfield]

Do you think a typical 12v 4 pin car relay will do the job?

To supply a laptop inverter - yes. To supply a fridge inverter - no.

 

[AstonHill]

To supply a laptop inverter - yes. To supply a fridge inverter - no.

Same principle but I would need a heavy amp relay right?

 

[AstonHill]

No - your previous attempt at a topic was 'closed' because DIYnot does not permit discussion about work on gas appliances or gas installations, other than ('in private') between Gas Safe registered folk.

This discussion is all about electricity, not gas, so is perfectly acceptable - (even if rather confused/confusing at times!).

Kind Regards, John

i wonder if the screw fix forums allow talk on gas then?

 

[JohnW2]

i wonder if the screw fix forums allow talk on gas then?

You'd have to ask them -or someone who knows.

 

[SUNRAY]

...
More efficient, is a compressor fridge, but they normally only work on mains power - via an inverter. The problem is, they still need a relatively large amount of current, so cannot be kept running for long, on a 12v battery, unless the engine is running, so the motorhome, must be quickly plugged into the mains, on arrival on site.

Very good point, I assume there are no hybrid versions available?

...
The guy at the end of the street, must use a fairly substantial relay, to switch the dc high current supply to the inverter on and off.

It should be quite doable, I have fitted an inverter with a control input which required only a tiny current via a float operated proximity switch for a sump pump where only 50V DC was available. I'd be surprised if a similar unit for 12V were not available.