A friend jnust put a lipo battery in his plane, the battery is speced for airplanes, not a modification. he replaced his lead acid battery (12 VOLT) and now he has bad radio noise on recieve and transmit. A loud static type noise. his alternator is new, and he supposedly checked his wireing. Anyone got any ideas?
Cliff

 

I suspect it is noise from a DC/DC converter. What is the actual voltage of the LiPo battery?

John

 

would there be a dc/dc converter in a battery for starting an engine?

 

I had a small airplane with a 24V system. There was a DC/DC converter for the radios. The engine starters were 24V. It would help to know more about the installation. Many years ago, Lear introduced NiCd's in its jets and there were problems with fires. I suspect putting LiPo's in a certificated airplane wouldn't be simply plug and play. They need to be monitored/controlled for both discharge and charging. Mike probably has more recent information about it. I topped keeping up to date several years ago.

In answer to whether a converter would be used for starting, I think that would be pretty uncommon. I have never seen it, but my experience is only with small GA aircraft with reciprocating engines.

John

 

I suspect there is an electronic box added along with the lipo battery that has some switching electronics causing the interference.

 

this is actually a lifepo battery, 4 cells for 12.8 volts, and no switcher. the plane is a homebuilt with a corvair engine. the plane has been flying for a while and has been inspected by the faa.

 

this is actually a lifepo battery, 4 cells for 12.8 volts, and no switcher. the plane is a homebuilt with a corvair engine. the plane has been flying for a while and has been inspected by the faa.

Totally different than the certified aircraft I fly. The home-builders can (and do) damn near anything they want, while certified aircraft require almost impossible to get Faa field-approval to install new technologies in older aircraft. I am not aware of any LiFePo batteries that are approved for installation in certified aircraft (see item 19 in this FAQ).

My guess is that it is the new alternator installation that is responsible for the increased radio noise. Might be possible that the internal impedance of the new battery is different than the flooded-cell battery that it replaced, bringing an increase in noise.

Chances are that the noise is coming from a ground loop in the airframe where alternator currents flow along the airframe and the audio equipment (radios, intercom, headphone circuits) are connected to the airframe in multiple place, violating the single-point ground principle.