Hi, hoping someone can help me - I have a transceiver that relies on
having a good solid 14-15v voltage supply. I am running it from 12V
7.2A batteries ( its a portable system ). When the batteries are fully
charged and giving out a 13V+ all is fine. However, when it starts
slipping down below or near to 12V, the performance of the radio really
suffers. Whats the best way of maintaining a regular, say, 15V supply?
I guess some kind of 'inverter' would be required, but not sure what,
if anything else, needs to be added. The radio is protected with a 3Amp
fuse, and does draw quite a lot of current - I have had a quick look at
a few voltage regulators from RS, but they all seem to be for 5V Vin,
not 12V.
Thanks in advance for any help, apologies if I'm just being
stupid....electronics is not my strong point.
To clarify, the batteries are 2x motorcycle type 12V 7.2AH - used to
power other apps like gps/PDA etc. - Need to keep a 12V supply. Jez
Hi, J. The obvious solution is to replace your 12V battery and 12V
battery charger with three 6V batteries and a 6V or 18V battery
charger, and then use a 3 amp linear regulator to cut the power supply
voltage down to size. Apart from being the most expensive solution, it
would work pretty well.
If you want to get a steady 13.8VDC out of a 12V battery, you're not
going to be able to do it with a linear regulator -- they can only
reduce the voltage, taking the difference between input voltage and
reduced output voltage times the current you're using, and dissipating
it as heat. You can't use a saw to make a piece of wood bigger.
Another possible solution would be to use an automotive inverter to get
120VAC, and use that to power a small bench 13.8VDC supply.
Altogether, though, that would be less than 50% efficient (you'd be
using more energy to power your apparatus than to power your
transceiver). Probably not the way to go, if you're concerned about
battery life.
Switching voltage regulators can boost the power supply voltage up, and
are pretty efficient (typically 75 to 87% of the input power is
actually used to drive the load). But building a good one requires a
little more technical skill than you admit to having.
One easy solution might be using a commercially available DC-to-DC
boost converter. This has the switching regulator built-in. The
device assures a steady input voltage to devices powered from a car
cigarette lighter. Typically, they'll give you 12.5VDC or 13.8VDC from
an input voltage varying between 10V and 15V. They're also fairly
inexpensive, so they'd be a one part solution to your problem. Here's
an inexpensive one ($30) that will give you a steady 12.5V output, if
your steady-state power requirement is less than 25 watts (2 amps):
http://www.powerstream.com/dc-2171.htm
There is a downside to this -- you'll have to be careful about running
your battery into the ground. Your setup has the advantage of becoming
unuseable before the battery becomes deeply discharged. Lead-acid
motorcycle batteries generally don't react kindly to being
deep-discharged repeatedly. You'll have to watch this, because these
DC-to-DC converters generally don't shut down until your battery
voltage is below 8 volts or so. Unless the battery is made to handle
deep discharge, this might reduce battery life. And the additional
power requirement of the DC-to-DC boost converter will probably
discharge your battery that much faster, meaning you probably won't get
that much more useful time out of the battery.
Your best solution might be to just buy a bigger battery. You also
might want to look for a "marine"-type battery, which is made for deep
discharge service.
Good luck
Chris
