Small inverter 12v current draw?

[LittleSister]

I'm pondering buying a small inverter for charging/running various low power items from the boat's 12v supply*, but getting a bit confused about the likely current draw.

There are a couple of makes commonly sold as '150w' (which would probably do me) supplied with a cigarette lighter plug on them. IIRC 150w @ 12v = 12.5A. (I'm ignoring losses 12v to 230v.) Surely one wouldn't want to be pulling anything like 12.5A from a cigarette lighter socket?

Am I misunderstanding something?

(*Yes, I know there are DC converters, etc. That's not the issue here.)

 

[pvb]

Should be OK, cigar lighter sockets are generally rated at 15-20A max. A better solution would be to hard-wire it. If you must have a plug and socket, a DIN plug and socket, with positive click-in action, would be preferable.

 

[[164147]]

Simple mathematics, P = IV. Cigarette sockets are typically 15A so fine from that respect. My 1500w inverter draws 200A in peak mode.

 

[Topcat47]

We use one to charge the iPad when the engine is running. It also does phones but doesn't put out enough power for a laptop. We plug it into a standard fag lighter socket although I have recently fitted a unit sourced from a chandlery as the Car one it replaced got too rusty.

 

[PaulRainbow]

I have a universal 12v to laptop charger, about £25. Charges my 20v laptop with little to no loss and has a load of selectable voltages. Tablets and phones charge from fitted USB sockets, again no losses.

 

[LittleSister]

Thanks, folks.:encouragement:

 

[lpdsn]

I'm pondering buying a small inverter for charging/running various low power items from the boat's 12v supply*, but getting a bit confused about the likely current draw.

I've a 150W inverter that I hardly ever use. I don't think it has been out of the bag in the last five years.

Meanwhile I got so fed up with crew members' phones and tablets on the chart table after I fitted a USB charger that the following winter I fitted one in each cabin.

 

[Happy Dayz]

Simple mathematics, P = IV. Cigarette sockets are typically 15A so fine from that respect. My 1500w inverter draws 200A in peak mode.

Do you run your laptop off battery booster cables ?

To derive current drawn using watts as the reference, divide watts by voltage,

Typical room heater
3000W / 230V = 13.4 amps (nominal)


so
150w/12v = 12 amps

Alan

 

[PetiteFleur]

Have you thought about fitting USB sockets? cheaply available on ebay - as long as your charging leads have a USB 'plug' at the input end. Or use a car 12v charging lead. Much better than an inverter if you can use them. I've now fitted USB/cigarette sockets in both cabins. The 150w inverter is only used occasionally now.

 

[nigelmercier]

I can't think of anything below 150W that couldn't be run from a DC source.

 

[Happy Dayz]

USB only supplies 5.1 volts, fine for phones and tablets even some cameras, but laptops and notebooks tend to need 18 volts, even the 12 volt accessory socket can't cope with thst, so likely you will still need a plug in inverter.

Alan

 

[PaulRainbow]

USB only supplies 5.1 volts, fine for phones and tablets even some cameras, but laptops and notebooks tend to need 18 volts, even the 12 volt accessory socket can't cope with thst, so likely you will still need a plug in inverter.

Alan

Nope. As i said earlier, my laptop charges via a fag lighter socket using a convertor with a variety of voltage settings. One of my laptops is 19v and the other is 20v.

 

[Happy Dayz]

Nope. As i said earlier, my laptop charges via a fag lighter socket using a convertor with a variety of voltage settings. One of my laptops is 19v and the other is 20v.

@200 amps? Bet you don't need any rxtra heating on you tub ?.

I said 'you will likely still need an inverter' (which is what you have with variable voltage selection) to get above 12 volts.

Way things were being wrote was as though anything can be run from usb sockets.

Alan

 

[lpdsn]

USB only supplies 5.1 volts, fine for phones and tablets even some cameras, but laptops and notebooks tend to need 18 volts, even the 12 volt accessory socket can't cope with thst, so likely you will still need a plug in inverter.

Alan

You can get variable power supplies that will give you the 19V DC for laptops from the 12V. No need to go via 230/240V AC. I was thinking of fitting one, but as I use a Windows tablet on the boat that runs off 5V it's never really got to the top of the jobs list.

 

[PaulRainbow]

@200 amps? Bet you don't need any rxtra heating on you tub ��.

I said 'you will likely still need an inverter' (which is what you have with variable voltage selection) to get above 12 volts.

Way things were being wrote was as though anything can be run from usb sockets.

Alan

It's a convertor Alan, not an inverter. Mine is a DC to DC convertor with variable settings. Might seem like i'm splitting hairs, but i don't get the losses that you get with an inverter. With an invertor you go from 12v DC to 240v AC, then back to 19v DC and the whole process can be something in the region of 80% efficient. A DC to DC convertor does not suffer those losses, so it's best to use one for any DC equipment that you can.

 

[Happy Dayz]

It's a convertor Alan, not an inverter. Mine is a DC to DC convertor with variable settings. Might seem like i'm splitting hairs, but i don't get the losses that you get with an inverter. With an invertor you go from 12v DC to 240v AC, then back to 19v DC and the whole process can be something in the region of 80% efficient. A DC to DC convertor does not suffer those losses, so it's best to use one for any DC equipment that you can.

I did not say to use your 240 brick into a 12 /240 plug in inverter (which always feels dangerous to me in the confines of a boat or car).

To get above 12 volts, from a 12 volt source wether you stand on your head or tickle its bum you will need some form of an 'inverter'.

I'm sure the packaging will call it a converter (which employs an inverter), as it is an easier term to grasp for the less tech savvy members of the buying public.

To exsplain, early 12v to 240v inverters were basically a transformer wired backwards, a mechanical buzzer was used in series with the normally 'secondary' (output) coil, to cause the Interrupted 12 volt DC, producing a stepped up AC type output from what was normally the 'primary' (input) coil.

My older brother had one in his 'sit up and beg' Ford Popular, he used to run his mains deck to deck tape recorder off it in his car even before cassets or 8 tracks came out, it made a hell of a racket due to the mechanical buzzer, but were we just so 'cool' with the girls back then.

The fun we had playing the James Bond theme, Stones Beatles and Rock & Roll music while driving from London to Southend - The Fonz would have had nothing on us two lol!

Alan

 

[nigelmercier]

To get above 12 volts, from a 12 volt source ... you will need some form of an 'inverter'...

As has been suggested, this is not the case. An inverter is a device that takes a DC input and produces 230V (or 110v etc) on its output for powering an AC appliance. This is rarely the best way of powering electronic devices.

A DC-DC converter may internally use a high frequency AC signal, but to call it an inverter is wrong.

 

[PaulRainbow]

I did not say to use your 240 brick into a 12 /240 plug in inverter (which always feels dangerous to me in the confines of a boat or car).

Erm, post #11 "USB only supplies 5.1 volts, fine for phones and tablets even some cameras, but laptops and notebooks tend to need 18 volts, even the 12 volt accessory socket can't cope with thst, so likely you will still need a plug in inverter."

To get above 12 volts, from a 12 volt source wether you stand on your head or tickle its bum you will need some form of an 'inverter'.

No, as i keep saying, i'm not using an inverter, it's a converter. Two totally different devices. A DC to DC boost converter will output a higher voltage than the input voltage., it does not contain an inverter.

I'm sure the packaging will call it a converter (which employs an inverter), as it is an easier term to grasp for the less tech savvy members of the buying public.

The packaging call it a converter, because that's what it is. Again, it does not employ an inverter.

Perhaps these might explain the difference better than i seem to be doing :

https://en.wikipedia.org/wiki/Boost_converter

https://en.wikipedia.org/wiki/Power_inverter

 

[[164147]]

Both inverters and converters use the same principle of induction through magnetic fields to provide different voltage characteristics.

 

[Hydrozoan]

Does anyone have clear cut data on the relative 12V power consumption of a 12/18V converter versus an inverter? I have always understood the former to be more efficient, but would like to know by how much.