Car Stereos: 12v to 24v, 12 volt batteries, volt electronics

Question
hi sir
i have a radio system that i want to install in a car with normal 12 v battery
this system is 24v and for this i will install 2 (12v) batteries in series
but the problem is how i will charge those two batteries while not effecting the car battery or drain it

i thought about installing another alternator but i found it hard to install in the car
another solution i thought about is to install an inverter (12/24v) for charging the 2 additional batteries and to install a protection that disconect the inverter when main battery voltage drop below 12 v ,but for this solution the two batteries may not charge if the protection disconect the inverter also the protection may be not reliable,also i am not sure if it is ok to charge 24v from 12v battery using inverter

please advice and if ther is better idea

thank you for your time and waiting for your advice

Answer
Hi,

Sorry about the delay in answering your question.

I have to admit I haven't worked with 24-volt electronics, so yours is a problem I haven't had to deal with before.  A lot depends on just how much current is required to run your audio system.

Personally, I don't think I'd use the two 12-volt batteries in series.  It's a simple way to get to 24 volts, except for the problem of charging it.  Unless you need so much current that it becomes impractical, then I'd suggest getting a 12-volt to 24 converter and running your audio component directly from that, rather than from a pair of batteries.  An example would be the PST-SR700-24 sold on this page:

http://www.powerstream.com/12V-backup.htm

This device has a continuous current capacity of 12 amps.  Voltage converters with more current capacity would be more expensive.  

If you need to be able to operate the system with the engine off, without draining the main battery, you can add a second 12-volt battery with an isolator.  This can be set up so that the DC converter can be operated just from the second battery when the engine is off, but the second battery can still be recharged from the vehicle's alternator when the engine is running.

Hope this helps!

Brian