Figuring out DC input

T

TarfHead

Registered User
Messages
1,672
Some time back I bought a FM transmitter from Hong Kong, via ebay. The instructions supplied were the bare minimum.

It uses 2 AAA batteries, and also came supplied a car cigarette lighter adapter for DC input.

When using it at home I would like to use a mains adapter but have no information about what level to use. My fear is that I could damage it if I got it wrong. Is there any way of figuring it out, based on the facts above (AAA batteries, car lighter adapter) ?

There is nothing (on the unit, on the 'documentation', on the car lighter adapter) that answers this question for me.
 
The two factors to consider are voltage and current draw. If it runs on two batteries, current draw won't be a problem.

As for voltage, AAA batteries are 1.5 Volts. But there are two batteries, so the voltage you need depends on how the batteries are connected inside the device.

If the batteries are connected "in series", sum the voltages, i.e. 1.5V + 1.5V = 3 Volts

If the batteries are connected "in parallel", 1.5V is still the voltage.

(I'm assuming the car adapter DC output is equivalent to the batteries.).
 
Polarity may also be an issue if the DC connector is a round one - i.e. you'd need to know whether it's a positive or negative centre and hence a negative or positive outer connector. Probably best to bring it to an electrical shop (e.g. Maplins or Peats or the like) and ask for advice.
 
Can I ask the question from another perspective ?

In addition to the FM transmitter, I also have a portable DVD player with a car lighter adapter and also a mains adapter.

Not having a rashers about electronics, would it be reasonable to assume that the mains adapter for the portable DVD player & the car lighter adapter for the DVD player & the car lighter adapter for the FM transmitter are all compatible ?

In other words, if the power output from the car lighter is standard, then the DVD adapter & the FM transmitter are the 'same'. If this is true, then the mains adapter for the DVD player should work for the FM transmitter ?
 
Nope, afraid not. DC output from a car adapter can be anything from 12V down, and, as ClubMan pointed out, the polarity of the connector varies. A DVD player is very unlikely to run off 3V as it sounds your transmitter does. Trying this is likely to kill the transmitter. You can pick up inexpensive adapters in the likes of Maplin or auto factors that allow you to select the output voltage and polarity.
Leo
 
You must log in or register to reply here.
Back
Top