DC-DC Convertor/regulator

[Cynic-al]

i have a device that i want to run off a car bettery, it's rated at 12v & 5A, i don't know what tolerance i have on the voltage so i don't want to plug it straight onto a battery. anyone know any nifty little products to save me searching the net?

 

[Tom]

There are devices out there, will dig out some links but they are in the 50-60 quid range.

 

[Mick]

if the device is rated at 12V then it will work straight off the battery. but at 5A you will run the battery down quite quickly

 

[Tom]

Remember when the engine is on its nearer 14v.

 

[Mick]

yes but at 5A you will drop the extra 2V in the cabling with out a problem and unless its the most sensitive piece of electronic equipment 2V will not hurt it in the slightest!

 

[Tom]

If you drop 2V in the cabling then with the engine off its only getting 10V!

 

[Cynic-al]

it's an LCD tv which i want to run on a boat, there are two batteries for the aux items and one for each engine. I could use an invertor to get it to mains then use the supplied transformer to cut it back down, but that does seem a little pointless when it's already 12v. If it's on the 12v side it also makes it easier for running on shore power or batteries as the boat has a control panel which deals with that.

 

[Craig]

12v is a flat battery

 

[Anonymous]

Maplins do one for a about £20, can't see it on there site, but i know they sell it...

Its one of thier DIY kits.

Daz

 

[Grandad]

Methinks it was made for a car, with secondary use from the mains, but like Mick said it'll drain battery if used without engine running!

 

[Cynic-al]

no, it is one designed for house use, it is not one designed for 12v use.

Battery life is not an issue, it will run off 2 90Ah batteries which can be charged from a mains supply or the 2 volvo 150hp diesels which have their own batteries for starting.

 

[Owen]

Re DC-DC converter/regulator

Hello,

Does the TV have an external AC-DC adapter for normal house use, or can it take 12V from a cigarette lighter socket ?. I would'nt be too worried about it if its designed for car 12V, as most of these items have an internal regulating power supply anyway which would easily cope. if its got an adaptor, then you would need to be more careful, but its probably still got an internal regulator anyway. by the way, 5 amps sounds a lot of current for a small LCD tv, are you sure this is what it draws ?..

Owen.

 

[Cynic-al]

Re: Re DC-DC converter/regulator

it is designed for house use, it has an ac-dc external convertor, i want to jam 12v dc directly into it from a battery but as the transformer is currently external i do not want to risk dumping 14v into it from the battery.

I think the 5a is at 12v not 230v, it is a 15" lcd tv.

 

[Owen]

Re: DC-DC convertor/regulator

Hello again,

so that explains the 5 A current draw then, around 60 watts (still sounds a bit high though). anyway, its not an easy one to get right - the regulator would probably need to be a switching regulator. i dont know of any low voltage drop linear regulators that can supply that current. I would try it on a variable power supply, wind it up slowly from 12 to 15 volts and keep an eye on the current. you could have a look and see what type of power supply it uses - its probably a switch mode anyway (uses a small high frequency transformer), which would cope..

Owen

 

[Tom]

Re: DC-DC convertor/regulator

Its likely the backlight is driven directly from the 12v, most likely a CFL lamp and they usually have unregulated supplies and rely on a fixed input voltage.