How to get 12 volts from a Cessna 310?

I have a friend who has a 1978 Cessna 310Q. (At least I think he told
me it was a 1978 model). Here is the question: He wants to plug in
some electrical equipment, a computer and a GPS unit into the cigar
lighter plug. The aircraft has a 24 volt electrical system. He has
been told that the cigar lighter voltage has been dropped to 12 volts
because there is a large resistor in the wire that feeds power to the
cigar lighter. When he checks the voltage at the contacts of the
lighter receptacle, he finds 24 volts. We think that this is because
there is no load on the circuit, and if there was, the voltage would
drop due to the inline resister.
However, he reports that when he tries to run both devices from the
power from the cigar lighter, it does not seem to work.
Any ideas on what to do in his case would be appreciated.

Thanks.


Zenith CH-300 Driver.

Tim Hickey wrote:
I have a friend who has a 1978 Cessna 310Q. (At least I think he told
me it was a 1978 model). Here is the question: He wants to plug in
some electrical equipment, a computer and a GPS unit into the cigar
lighter plug. The aircraft has a 24 volt electrical system. He has
been told that the cigar lighter voltage has been dropped to 12 volts
because there is a large resistor in the wire that feeds power to the
cigar lighter. When he checks the voltage at the contacts of the
lighter receptacle, he finds 24 volts. We think that this is because
there is no load on the circuit, and if there was, the voltage would
drop due to the inline resister.
However, he reports that when he tries to run both devices from the
power from the cigar lighter, it does not seem to work.
Any ideas on what to do in his case would be appreciated.

Thanks.


Zenith CH-300 Driver.

Look at ebay under avionics for a dc-dc converter. I have seen quite
a few 24 VDC - 12 VDC converters.

It would be nice to find one that goes the other way. I have been
looking for one.

Dan, U.S. Air force, retired

Use an LM340T12 (or LM7812C-V) voltage regulator. On the spec sheet you
will find the diode, and 2 capacitor sized need to ensure it's clean.

Something like this (see diagram in Courier font)

diode
------|--------
| |
| XXXXX |
| 7812C |
| XXXXX |
_in_24V_| | |___12V___out_
| | |
0.33uF | 0.1uF
| | |
_|______|_____|___
|
earth


Rgds,
Brett

"Tim Hickey" wrote in message
...
I have a friend who has a 1978 Cessna 310Q. (At least I think he told
me it was a 1978 model). Here is the question: He wants to plug in
some electrical equipment, a computer and a GPS unit into the cigar
lighter plug. The aircraft has a 24 volt electrical system. He has
been told that the cigar lighter voltage has been dropped to 12 volts
because there is a large resistor in the wire that feeds power to the
cigar lighter. When he checks the voltage at the contacts of the
lighter receptacle, he finds 24 volts. We think that this is because
there is no load on the circuit, and if there was, the voltage would
drop due to the inline resister.
However, he reports that when he tries to run both devices from the
power from the cigar lighter, it does not seem to work.
Any ideas on what to do in his case would be appreciated.

Thanks.


Zenith CH-300 Driver.

Bryan Martin wrote:
Here's a better view of the converter at the manufacturers website. It's
smaller than I remembered.

http://www.solarconverters.com/product_frame.html

in article , Bryan Martin at
wrote on 8/21/05 10:21 PM:


http://www.backeastsolar.com/ Click on "Online Store" then "DC to DC
converters".

It's a steel box about 4"w X 6"l X 3"d and about 2 lbs. It's not designed
for aircraft but I have one in mine running a couple of gyros and a comm
radio. Works well. It can step 12V up to 24V or 24V down to 12V.


in article X4aOe.22907$Ie.16982@lakeread03, Dan, U.S. Air Force, retired at
wrote on 8/21/05 9:42 PM:


Look at ebay under avionics for a dc-dc converter. I have seen quite
a few 24 VDC - 12 VDC converters.

It would be nice to find one that goes the other way. I have been
looking for one.

Dan, U.S. Air force, retired


Interesting Item. If one were interested one could repackage it a
lot lighter I assume.

Dan, U.S. Air Force, retired

Bryan Martin writes:

http://www.backeastsolar.com/ Click on "Online Store" then "DC to DC
converters".

http://www.backeastsolar.com/pr_lvco...onverters.html

I went the marine-grade route for the DC-DC converter I use to power a
wheelchair computer.
http://www.jackrabbitmarine.com/prod...pID=682&type=0
My 4A model is in a small aluminum frame. I figure if it can withstand
a marine environment it can take my abuse. The 4 and 10A models are a
little cheaper (and lighter and smaller) than the 20A model from Back
East Solar.

--kyler

Kyler Laird wrote:

My 4A model is in a small aluminum frame. I figure if it can withstand
a marine environment it can take my abuse. The 4 and 10A models are a
little cheaper (and lighter and smaller) than the 20A model from Back
East Solar.

I used the 15amp model found here in our C152:
http://www.powerstream.com/dc1.htm

I can't believe how overpriced the ones y'all have quoted are...

Bryan Martin writes:

These marine units only convert from 24V down to 12V. Dan said he was
looking for one that would go the other way, from 12V up to 24V.

Tim was the original poster. He only indicated that he wants 24V to 12V.

--kyler

Thanks for the input, everybody, and Kyler is mostly right. We want to
end up with a 12 volt power source. We think that the cigar lighter
outlet, even though it is mounted in a machine that has a 24 volt
electrical system, is at 12 volts. But it gets those 12 volts by
running the current through a load dropping resister. This makes a
lot of heat, or so the owner tells me, and we wonder if anyone else
has worked around this.

Thanks again for all input.


On Tue, 23 Aug 2005 13:17:03 GMT, Kyler Laird
wrote:

Bryan Martin writes:

These marine units only convert from 24V down to 12V. Dan said he was
looking for one that would go the other way, from 12V up to 24V.

Tim was the original poster. He only indicated that he wants 24V to 12V.

--kyler

Zenith CH-300 Driver.

Tim Hickey wrote:

Thanks for the input, everybody, and Kyler is mostly right. We want to
end up with a 12 volt power source. We think that the cigar lighter
outlet, even though it is mounted in a machine that has a 24 volt
electrical system, is at 12 volts. But it gets those 12 volts by
running the current through a load dropping resister. This makes a
lot of heat, or so the owner tells me, and we wonder if anyone else
has worked around this.

Thanks again for all input.

I rewired our C152 outlet to the voltage converters output. Even though
the Lowrance Airmap 1000 supports upto 28v input. We didn't have the
dropping resistor, input to the outlet was 24v...

Morgans wrote:

I'm admitting that I'm not the world's best when it comes to those
electrons, all running around helter skelter, but I thought a dropping
resistor only worked with a certain sized (constant) load. If you checked
voltage at the plug with a volt meter, you would come out with 24 volts; if
you checked it with the lighter going, you would come up with 12 volts.
Right?

That being the case, you have to use a converter, or a regulator, or
something. I don't know. Anybody?

You're limiting the current to what the lighter could digest...

Undo the lighter power, wire that to the voltage converter input, wire
the output of the voltage converter to the lighter input. Remove the
dropping resistor from the circuit, whereever its located. The panel
breaker should already be sufficient to supply power for its new role...

If its a certified airframe, get your mechanic to sign it off...