Help with decreasing current

[Technician Tonny]

Hello....
I have a portable DVD player
It uses 12vdc 1000 ma
I want to use it on a car battery which seems to be with high current
Any simple circuit to decrease the current of the' battery!
regards Tonny

 

[Martaine2005]

Hi Tonny,
The DVD player will only draw the current that it requires.
There is no need to limit the current.

The 1000mA adaptor supplied for it is already more current than it requires.
It has a headroom on it to stop it working at it's maximum, getting hot and shortening the adaptors life.

Martin

 

[Technician Tonny]

Thanks Martin

 

[cjdelphi]

One thing you should be aware of , the alternator could output up to 14v or higher putting extra stress on the components...

I suggest a simple switching regulator to provide a constant 12v

 

[Technician Tonny]

Hi Cjdelphi
which suitable regulator to use
7812 or !

 

[Martaine2005]

Tonny,
Most AC/DC adaptors are unregulated for these kinds of units.
Cjdelphi had a good point, but generally unfounded in this situation.
An unregulated 12v supply can output 17v or more, so without knowing the original psu specs it's difficult to say.
I would guess that the DVD player already has a regulator if it's needed...

Martin

 

[Technician Tonny]

Sir Martin my portable player have surface mount components when I connect a car battery directly to it, they get too hot
I hope as they are very small they can't handle too much current,

 

[Martaine2005]

Sir Tonny,
What is the DVD player you are trying to connect?
If it's portable and batteries only, it might well be regulating itself via the batteries.
If it has an AC/DC power supply, what does that say on the label?
As Cjdelphi explained, it may need a regulator. A LM7812 would be perfect.
But a regulated 12v DC supply from Ebay might be a better option if you are not sure..

Martin

 

[Technician Tonny]

Sir Martin It's a portable player, It has an Ac/DC power supply model : JD12C-120100E
INPUT:/100-240V ~ 50/60Hz 0.5A
OUTPUT: 12Vdc=1000mA
But I want it to work on a car battery 12Vdc n70

 

[Martaine2005]

Ok, nice info there.
Have you touched the components while using the AC/DC adaptor? Do they get hot too?
The current has nothing to do with this at all!!
Current driven items are for things like LEDs. Not DVD players.
If the 12v car battery is static, the unit should be good as gold...
If it's in a vehicle being charged, it wont go above 13.8v - 14v.
I cannot see a problem here...
Maybe the unit gets hot with the adaptor too?

Martin

 

[Technician Tonny]

When I use its adaptor it gets hot (normal temperature)
but not too hot as on battery

 

[Martaine2005]

OK, I would consider running the DVD player on 9v and trying that first.
It sounds like it is "timed" to self destruct in a very short time...
It should not be getting too hot at all.. Full stop....
Try it on 9v adaptor and see if it plays ok...My guess is it will...And stay a lot cooler too..

Martin

 

[(*steve*)]

0) I agree with Martin.

but also:

1) Measure the voltage that you're getting from the car. (Also measure the voltage from the adapter -- is it really 12V?)

2) does the DVD player operate when connected to the car (albeit while getting hot)? I'm only interested in whether a power light comes on, not whether a DVD plays.

One reason for it getting hot is that the power is connected backwards! The other major one is excess voltage.

 

[Technician Tonny]

Sir Martin I don't have a 9v adaptor
what if I connect lm7809 regulator to my 12v adaptor!

Sir Steve the voltage is 12.47 Vdc from the adaptor and 12.60 Vdc from the battery
It operates well and I connected it the right way following the polarity

 

[Martaine2005]

sorry, just eating my late dinner....

 

[cjdelphi]

I'd really not use a 7812 or 7809 for 2 reasons...

1... unless you have a low drop out version, you'll struggle to get 12v out

2... if you require 9v, that's going to heat up the regulator fast

A simple switcher (lm2596 for example) will give you 1.5v to 12v from the car, feed 9v into your cdplayer and work up)

 

[CDRIVE]

One does not feed a 7812 regulator with 12V. They need overhead. Personally I don't think you need to do anything more than maybe including some spike protection but if you insist on reducing the battery voltage a bit you can use 1 or 2 1N4002 or higher Diodes in series.

Chris