14v or 28v?

[PilotDerek]

Is there a benefit to having either 14v or a 28v? Looking at comms the 28v are cheaper. Is there a benefit to step up to 28v in our older planes. I am looking at upgrading my old Narco radio with a K155 and I can buy an upconverter and 28v radio for the cost of a 14v radio.

[Piloto]

Most aircraft avionics these days can work on either 14V or 28V without the need of an external converter or resistor. For a small aircraft there is no advantage switching to 28V. Besides 28V batteries are more expensive and less tolerant than 14V batteries. Were 28V makes a significant difference is on twins and larger aircraft were the wire run is longer (thus higher resistance). 28V overcomes the requirement for larger gauge wires used on 14V systems (higher currents).

José 

[PilotDerek]

Jose,

I wouldn't be changing the battery, aircraftspuce sells an upconverter that can step up your voltage to 28v just for avionics. The only benefit I can see is that 28v nav/comms are cheaper by around $500. I see that all the garmin radios are capable of both, but I am not planning on putting in garmin. 

Has anyone installed a step up converter?

[takair]

Quote: PilotDerek

Jose,

I wouldn't be changing the battery, aircraftspuce sells an upconverter that can step up your voltage to 28v just for avionics. The only benefit I can see is that 28v nav/comms are cheaper by around $500. I see that all the garmin radios are capable of both, but I am not planning on putting in garmin.

[takair]

Quote: PilotDerek

Jose,

I wouldn't be changing the battery, aircraftspuce sells an upconverter that can step up your voltage to 28v just for avionics. The only benefit I can see is that 28v nav/comms are cheaper by around $500. I see that all the garmin radios are capable of both, but I am not planning on putting in garmin.

Has anyone installed a step up converter?

[jetdriven]

Jets run 115v AC for the same reason.   Smaller wire diameter required.  

[jetdriven]

Quote: PilotDerek

Is there a benefit to having either 14v or a 28v? Looking at comms the 28v are cheaper. Is there a benefit to step up to 28v in our older planes. I am looking at upgrading my old Narco radio with a K155 and I can buy an upconverter and 28v radio for the cost of a 14v radio.

[PilotDerek]

Quote: jetdriven

The principal prOblem is you will have same cost, but more weight, cost to install, and two boxes that can fail instead of one.  

[Vref]

a used KX155 on 14V is way more expensive and rare to find. I discussed a similar problem that only a few 14V KX155 are FM Immune (ICAO annex 10 requirement). It comes to the level that my Nav/Com 2 upgrade, if I would do it, would be cheaper to go for a second GNS430. DC/DC converter is not that expensive the install cost maybe a bit more as you have to remove the side panel if you want to install the converter in the back of the aircraft....

My bird is so full in the front there is no place for an additional DC/DC box...

The SN3500 EHSI I am going to install is 28V only so I need one....anyway. At the same time I will do pre-wiring for a reversionary mode (back-up ATT through the EHSI) that if my old KG102 gives up I can swap to a SG102 and get reversionary mode at the same time (you need an ARINC 429 cable between the SG102 and the SN3500...)

 

rgds

Luc

[N601RX]

I looked at this seriously a while back before I started swapping out stuff in my radio stack and panel.  There is a ton of used 28 V stuff on Ebay compared to the 14 volt stuff and the price is considerably cheaper. KY 96 vs 97, Ky 196 vs 96 and the KX 155's and 165's as well as gps annunciators. The 14 volt stuff sells pretty well, however there doesn't seem to be much interest in the 28 volt stuff.  I recently sold a KLN 89b gps annunciator that was 14 volts for almost $500.  I've saw the same 28 volt unit sell for less than $50 and it took several weeks to sell. However if you are only talking about a single com by the time you add the inverter the savings is pretty much gone.  If your talking about a complete stack there would be some savings to doing this.  If your concerned about reliablily you could use 2 step up converters wired in parallel through 2 diodes.  However if the 28 volt radio says it needs 5 amps to transmitt, then it would actually draw 10 amps from the 14 volt side of the inverter, plus another 10% or so due to converter ineffeciency.

[PTK]

Quote: PilotDerek

Is there a benefit to having either 14v or a 28v? Looking at comms the 28v are cheaper. Is there a benefit to step up to 28v in our older planes. I am looking at upgrading my old Narco radio with a K155 and I can buy an upconverter and 28v radio for the cost of a 14v radio.

[Vref]

Quote: jetdriven

Jets run 115v AC for the same reason.   Smaller wire diameter required.  

[Piloto]

Besides adding a point of failure when adding a 14V to 28V converter there is also the possibility of noise interference. These converters employ switching circuitry that is prone to generate interference on some of the NAV/COM channels. On some channels it will show as an open squelch. They can also introduce a wine noise on the microphone input, specially when the ground is shared.

José 

[John Pleisse]

Quote: takair

The early Garmin 430s were 28V only units and required an up-converter. I have been using one for probably 10 years now and it works fine. It is not as efficient and adds a little weight, but does the job. I also have a 28v standby horizon running on it with no problem. Just have to match the rating to the load.

[N601RX]

The newer units like the Lone-Star are very compact and lightweight.   2.5" x 4.5" x 2.0 and weigh just a little over 1/2 lbs.  I looked at some of th older ones that were large and heavy.  The newer switching MOSFETS have a higher switching frequency, minimal switching loss and almost no on resistance and don't produce hardly any heat. This does away with the large heatsinks that were required several years ago to keep them cool.

[Vref]

Quote: N601RX

The newer units like the Lone-Star are very compact and lightweight.   2.5" x 4.5" x 2.0 and weigh just a little over 1/2 lbs.  I looked at some of th older ones that were large and heavy.  The newer switching MOSFETS have a higher switching frequency, minimal switching loss and almost no on resistance and don't produce hardly any heat. This does away with the large heatsinks that were required several years ago to keep them cool.

[PilotDerek]

Allsmiles,

PM sent

[M20F-1968]

I have an essentiually new Lone Star 14V to 28V converter.  It is the newer model LS03-05002 (.  It was screwed into place in the aircraft but never wired or installed fully.  I bought it new from Lone Star when I thought I would be installing an Artex Nav interface box which was 28V.  The ME406 came out which was a smaller Artex ELT.  Artex took back the Nav Interface and swapped the ELT leaving me with the Lone Star Converter.  This is the newer version, smaller in size and measures 2 3/8 X 3 3/4 X 2".  If you can use it I am sure we can agree on price.  New it selle for about $380 - I am looking to get about $250.  You can e-mail me at johnabreda@yahoo.com or call me at (617) 877-0025.

Thanks,

John Breda