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Running small dc electronics of 12 volt battery.

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Posted by chris on December 7, 2005, 6:47 pm
I would like to power some small electronic equipment that have
transformer plugs. I read somewhere that you can save a lot of power
loss that comes along with using an inverter by just using the power
from the battery. Unfortunatly they did not specify how and what is
needed to pull this off. Can someone tell me what I need and how I go
about hooking it up? Thanks.

Posted by BobG on December 7, 2005, 7:48 pm
If your equipment needs 12V, you dont have to do anything. If it needs
9V or 6V, a simple 7805 regulator would work, but get hot. A switcher
would be more efficient.

Posted by Eric Sears on December 7, 2005, 8:23 pm
 Greetings Chris

This certainly can be done, and in some cases is very worthwhile, but
you do need to understand what you are doing.
There are a whole lot of questions that need to be asked before your
question can really be answered, such as -
How many transformer plugs are we talking about? What KIND of power
pack are they (transformer or switched-mode?)
What voltage are they? (6v? 9v? 12v? multivoltage? ac?)
Do you need to leave your inverter on anyway? What type of inverter do
you have? (if it has to be left running then it might make little
What is the power pack doing; running equipment or charging a battery?
(charging Lithium batteries from a homemade circuit could be an
explosive disaster!)
What is your main battery voltage?
How much electronics knowledge do you have? (ie do you understand
regulators, voltage drops through resistors etc)

All of these questions may have a bearing on the specific answers to
your question. Unless you are lucky and just want to power 12v
equipment from a 12 volt source, "hooking it up" could easily result
in "cooking it up"!
Give us as much info as possible and we will try to answer.


On 7 Dec 2005 10:47:26 -0800, chris@chrisbreier.com wrote:

Posted by Merlin-7 KI4ILB on December 7, 2005, 11:36 pm
 first thing
You need to know what voltage the things are that you want to run and how
much power (milli-amps) or amps you need.
 If you look on the transformers it should be written on it some where.
 If they are all different but 12 volt or lower. You can use car adapters
for the items and just add a multi-gang cigarette  type connector to your
 I have a 4 socket one that I use to run my lap top, cell phone charger (the
small inverter) etc. off of.

Posted by phatty mo on December 8, 2005, 8:29 am
 Also,Depending on the appliance,it may already have a regulator built
in. (My modem has a 7805 (+5V) inside,so I can feed it any DC voltage
between say 7V and 25V) I ditched the 9V wall-wart,and connected it
straight to my batteries.No problems for 2-3 years now,and it's been
online nearly 24/7.

Appliances with a 12Vdc input can *usually* be connected straight to
your batteries with no problems,but *some* appliances are kind of
picky,and want a well regulated 12V input. (voltage spikes,etc from
chargers and other things turning on/off can cause issues)

I got rid of..eh,about 5-6 wall-warts, by connecting things straight to
my battery bank. If nothing else it's nice to free up the outlets for
other uses! (those plug-pack/wall-warts take up 2 outlets!)

The 78xx (fixed output voltage) and LM317 (adjustable output voltage)
regulators are great for running small stuff off of 12V.(up to 1.5A
load) They are linear regulators,and aren't the most efficient,but
they'll get the job done easily.
(The LM2576T-ADJ is a simple switching regulator,but it requires even
more electronics knowledge to use.)

Eric Sears wrote:

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