DC to AC Converter

[chris66]

I have recently seen a gadget in a shop which is a 12v DC to 240v AC current converter. It had a cigarette lighter plug on one end and 240 v pin socket on the other. I believe it had 50w printed on it. This seems (to a non-techy like myself) too good to be true. I would use it to hook up a laptop, recharge mobile phone/camera battery etc..
Is this system reliable ? Is it likely to drain my batteries real quick ? Is it safe for the electric system to have AC rigged up to the boat electrics?
Thanks for any comments.

Chris

 

[yachtbits]

What you are refering to are commonly called inverters.

Yes they do convert 12vdc to 240volts ac.
Yes you can run laptops etc on them.

for current consumption, look at the wattage of the mains device you want to use, divide this figure by 12. divide the result by 0.9. this will give a very rough indication of the current draw from the batteries.

Always buy one a bit bigger than you think you need.

If you want one for a 14" TV, ignore the wattage on the label as you will probably need upto 600watts to get the thing started!

various brands are available, so it is worth looking at other brands before buying the first you see.

kev
yes we do sell inverters



<A target="_blank" HREF=http://www.yachtbits.co.uk>http://www.yachtbits.co.uk</A>
sales@yachtbits.co.uk
marine electrics & electronics

 

[byron]

<font color=blue>Useful little items but really the 50w is a little bit small. With say 200w you can run a portable TV. They are heavy on your battery and the thing to remember is that even when not in use they are still drawing power from the battery so should be unplugged.
There's always various ones for auction on EBay UK in the Boating section.</font color=blue>

http://www.alexander-advertising.co.uk

 

[alanporter]

Query to Yachtbits: Do the calculations you have given apply equally to the 110 - 115 volt systems we have in Canada ? Many thanks.

Alan Porter

 

[montezuma]

It's perfectly possible to get 12v PSUs for a lot of electronic kit these days, including laptops. Portable tellys will very often take 12v as standard. Mobile phones have car kits, of course, which let them work/recharge on 12v. The cost of a 12v adaptor(s) is very likely to be cheaper than an invertor, you avoid mixing 240v and salt water, and also avoid losing 10% in heat (no invertor is 100% efficient.)

 

[Gunfleet]

Are you implying you know where you can buy a dc inverter for a computer power supply? It would be great it such a thing did exist. I have a laptop with a 20v 3amp power supply, stepped down from 240. It really aggravates me to use an inverter to change the boat power supply to 240 and then another to step down to 20volt. Talk about inefficient!

 

[Guest]

50W is a bit on the low side .....
I use a 150W jobbie connected just as you describe and it works fine.
I run :
Small domestic stereo
Video Charger
GSM Charger
Notebook computer

obviously the larger items NOT as same time. Had it for near 2 years and its fine .....

As to running the batterys down - of course the current demand is high and you don't run it for 'hours and hours' !!



Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[Guest]

I had a Toshiba with 15V charger, and then another with 20V charger ...... both ran OK straight of the baot 12 V ..... but charging didn't happen ... so the LED showed red / orange etc. or even blinked on one - showing that charging was not in pregress and supply low. I do not recc'd next - but to prove it was the 12v powering - I took out the battery pack and then tried again ...... fine it worked !

Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[Guest]

Ohms Law + losses

I am not Yachbits ..... but his calculation is based on OHMS law :

Watts = volts x amps

plus he has allowed approx. 10% losses - which actually is a bit low for an inverter, as they do generate a bit of heat and also have to overcome internal resistances etc. The quality of connections has a bit to do with it as well.

So : 600 W / 110 = 5.45 A + ~10% = 6 amps approx.
(I would add approx. 15% actually after experience of my own ... = 6.3 amps)


Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[Guest]

Forgot to add - ----

When I bought my 150 W jobbie - I was like most only thinking about on the boat !

I now use mine in the car, when I travel etc. etc I have found so many occasions that it's hard to list them now !!

I bet others can add to it !!

Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[alanporter]

Re: Ohms Law + losses

Thanks Nigel. Yachtbits divided the Watts by 12, the DC voltage, whereas you divided by the mains voltage. I don't understand this, can you explain please ?

Regards

Alan Porter

 

[stubate]

go back to basics, they do work as long as you get the right size (see other postings)
a laptop car cigar lighter attachment is about £70 for a HP laptop so a moderate sized invertor is a bargain, (i am biased, i sell them) it is cheaper to buy a 350 watt one off me for £55 and use it in your car to charge your phone, digi cam, or laptop than it is to buy all the cigar lighter convertors and a lot less hassle, you can then use it in your boat to charge all the bits and pieces plus it will just about warm up her indoors's and the rug rats hair straighteners !!
keep them sweet !!

s

 

[Gunfleet]

for current consumption, look at the wattage of the mains device you want to use, divide this figure by 12. divide the result by 0.9. this will give a very rough indication of the current draw from the batteries.>>
I'm not sure I see the logic of this. 0.9 is nearly 1 so either dividing or multiplying by it will give a number very near the one you started out with, if we're in the world of very rough indications. You may as well say just divide by 12.

 

[montezuma]

I got a 12v adapter for a Sony Vaio from RRC Power Solutions Gmbh - it works exactly as the mains adapter, see:

http://www.rrc-ps.com/eng/products/automotive/eng_caradapter.htm

They also have a compatibility table at:

http://www.rrc-ps.com/eng/products/automotive/eng_caradaptercrossref.htm

I think I was put on to them direct by Sony - your manufacturer may also be able to help. I have also used Toshiba and Dell laptops with 12v adapters, but I'm sorry I don't know where they came from. Additionally I have used other laptops with a variety of 240v invertors and invariably the invertor has proved less reliable than the laptop! (Mind you all things are relative...)

I couldn't agree more that going via 240v if a direct alternative exists makes no sense for several reasons - hence my original post.

 

[Strathglass]

John

Let me explain the logic behind Yachtbits power required posting.

1 - The AC wattage is the power the device consumes when it is operating. Assuming no losses the power rating of an inverter and the power drawn from the battery would be precicely the same as the wattage quoted for the device.

2 - If we take the quoted wattage and divide this by the battery voltage (a nominal 12 volts) we get the current that will be drawn from a 12 volt battery when supplying that amount of power. Again assuming no losses.

3 - We do not live in a perfect world as we loose power in most real life energy conversions so we divide the current drawn by 0.9 to allow for a 90% efficiency in the DC to AC converter.

If you were to just divide by 12 you would end up with a loss free system and Yachtbits would have everyone screaming at his post.

The numbers he quoted will give a fairly accurate value of the nominal current an inverter will draw.

Iain

 

[Gunfleet]

The mist clears, however briefly. ;-)

 

[lauradee]

my post was trying to make the point that although wasteful in the conversion it is more convenient to have one source of power at £59 instead of 3 or 4 12v adapters at anything up to £70 each, and as for sony viao spares well !!
as a side issue a customer of mine had a sony viao laptop with a duff cd drive (i own a computer repair shop) sony will not sell spares to the likes of me so he had to send the machine back to sony, bear in mind that it cost him over 3k and was only just out of warranty, over £300 to repair and if you dont want it repairing sir, £180 to have it back!!
s

 

[Guest]

OOP\'s !!!! Sorry about that one !!!!

It should have been divided by the supply voltage !!!!

It's habit - where I do quite a bit of calculations for domestic - I'm sorting out house things !!!!!

So CORRECTED :

600 Watt = 12volt x amps

therefore 600 / 12 = 50 amps

plus 10% for losses = 55 amps supply

That means that the average leisure battery on a boat - 100 amp/hour - theoretically would give you about 2 hours supply, but it doesn't work that way ------ you'd probably get half that as the battery plates suffer !!!

My 150 Watt job calculates out at :

150 / 12 = 12.5 amps + 10% = 13.75 amps

giving me in theory from my 120 a'hr battery - about 8.7 hours ...... in fact I only use it for 2-3 hours maximum unless engine is running ........

NOTE : It is NOT a good idea to start engine while inverter is supplying an appliance. Stop the appliance, unplug the inverter and then start engine, when settled - then restart appliance. I cannot explain fully why .... but that is the advise I have been given by an electrician that I trust !

Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !