Auxiliary Power Units (APU)
 

I'm looking at purchasing an APU for my Skymaster, but I can't find specific information on the type to buy. For those who have one, can they be used for Avionics only, or can they start the engine if the battery has run down. I'm looking at 24V types with capacities of 20amps, 25amps, and 50amps. Does anyone know the amps needed to turn over an IO-360?

Thanks for any help.

Karl

From the Owner's Manual for a 1971 F model:

"When an external power source is connected, a split bus contactor automatically removes power from the electronic section of the split bus to protect against damage to the transistors in the electronic equipment by transient voltage from the power source. Therefore, the external power source can not be used when checking electronic components."

Thanks Jim,

I am starting to discover the power requirements to start an aircraft piston engine. It's 28V, but it looks like the large APUs that the FBO on my field use have a capacity of 400amp. It seems to start the engine does require about 250 to 300 amp. It looks like none of the APU's I was looking at would work. I can use it to power the avionics for maintenance. I have a 337-A, and I looked at my owners manual. That year does allow connected to a external power source, but I have to use different procedures if I'm using a Generator APU, or series of batteries APU. Thanks for the help,

Karl

Another question: do you think your battery will be run down so often that you need to have your own APU?

I think starting APUs make sense for FBOs - for individual owners, not so much. What am I missing?

If you need an APU to start your Skymaster you probably have a bad battery or somebody left the master on. Once the battery is down beyond starting it will need to be charged before it's going to work properly if at all. Keep a battery conditioner on the battery at all times when it's not in use and the battery will provide good results for the time period expected. I change mine every 3 years even though it will still start the engine. These batteries only have an intended life of 3 to 4 years and that's if it is properly maintained. The maintenance between using is most important. Think about how long the battery is going to last when you loose alternators in IMC. I want the most I can get. Change the battery before it goes dead and maintain the battery between flights.