For the technical folks.

[Aztec Driver]

How comfortable would you feel running your brand new Aspen avionics primary flight display on generators?

I know it has battery backup, and would switch back and forth when the bus voltage drops, but would it be good to have it do that on a regular basis? I assume that it wouldn't recycle and have to restart.

My battery, (which was brand new when I bought it in 2006, and has been the same since day 1) will not supply enough power for even the standard coms and nav equipment (only beacon for light) on a longer taxi route. (more than a few minutes) Heaven forbid if it is at night and I need to use the landing lights. At night, I have only a few minutes at taxi power before things start to wink off. My coms will stop transmitting unless I add 1700 rpm of power to get the generators up. That was real fun at JFK the other day. Occasionally, my GPS will recycle. When shutting down, I have to run at high power for a few seconds to replenish the battery. That's real unnerving for the line folks.

There is an STC available for alternators, so I might do that, but I wondered what the thoughts were with the current situation.

 

[Steve]

When Aspen units first came out they had the internal battery switchover threshold set pretty high. As explained to me the company wanted the unit to respond immediately to an alternator failure so you would have maximum airframe battery power available to operate your other avionics/gear/etc. After a few months of in service experience a software revision came out that lowered the threshold to accomodate nominal drops in bus voltage that occurred when the charging system was not providing full rated voltage. I was having problems with the unit switching to battery during rollout on landing. Once it switched to internal battery the only way to turn it off was to disconnect the battery leads or let the battery completely run down. The "reversion" button had no effect.

I may be an outlier in the Aspen population, but I'm on my fourth unit (all provided by Aspen under warranty) which has v2.1 software and this latest unit reliably boots up and operates nominally during taxi and cruise. I was having a problem with the previous unit locking up during initialization and the only way to restart it was by disabling the internal battery or letting it run down completely. That seems to be corrected now.

In my opinion you can expect the unit to switch over to internal battery if the bus voltage drops below 26v (on a 28v system, have no experience on a 14v system). Whether that hurts the circuitry my intuition tells me any voltage surge/fluctuation is not good for solid state devices. I know it will not automatically switch back to bus power if the bus voltage recovers above the setpoint while internal battery power is still available. I installed a separate external power switch on the avionics bus just for the unit so I can isolate it and still run the radios. I've considered installing a remote disconnect for the internal battery to ensure the ability to cold boot the unit under any circumstances but I'm waiting to see if the newest unit exhibits any anomalies before doing so.

 

[Aztec Driver]

When Aspen units first came out they had the internal battery switchover threshold set pretty high. As explained to me the company wanted the unit to respond immediately to an alternator failure so you would have maximum airframe battery power available to operate your other avionics/gear/etc. After a few months of in service experience a software revision came out that lowered the threshold to accomodate nominal drops in bus voltage that occurred when the charging system was not providing full rated voltage. I was having problems with the unit switching to battery during rollout on landing. Once it switched to internal battery the only way to turn it off was to disconnect the battery leads or let the battery completely run down. The "reversion" button had no effect.

I may be an outlier in the Aspen population, but I'm on my fourth unit (all provided by Aspen under warranty) which has v2.1 software and this latest unit reliably boots up and operates nominally during taxi and cruise. I was having a problem with the previous unit locking up during initialization and the only way to restart it was by disabling the internal battery or letting it run down completely. That seems to be corrected now.

In my opinion you can expect the unit to switch over to internal battery if the bus voltage drops below 26v (on a 28v system, have no experience on a 14v system). Whether that hurts the circuitry my intuition tells me any voltage surge/fluctuation is not good for solid state devices.

That's interesting. My voltage will actually drop to 9 or 10 volts when at low power. That's low enough to cause everything to shut down.

 

[Steve]

What brand aircraft battery are you using?

Unless you're using a de-sulphating charger I would be suprised to see an aircraft battery hold full charge after 3 years.

 

[gismo]

That's interesting. My voltage will actually drop to 9 or 10 volts when at low power. That's low enough to cause everything to shut down.

Bryon, 10 volts is way low for a good battery under "normal" load (i.e. less than about 35 amps). First thing to do is check the voltage right at the battery terminals with a fully charged battery and 10-20 amps of load. If it's much below 12 volts, the battery is shot (might be recoverable with a desulphator but I doubt it).

As to your original question, I don't see any reason an Aspen couldn't be used on a plane with (a) generator(s) although this might necessitate more frequent replacement of the standby battery in the Aspen. OTOH, an alternator STC probably wouldn't add a lot to the cost of an Aspen installation and would have lots of benefits.