Ground Power Unit (commercial or DIY)

OK. Anybody with experiences with other GPU variants on the market?

A GPU is used to start a turbine.

What you need is an external power supply. I have this one:

http://startpac.com/products/aviation/model-53025-24v/

I trust they have a good money-back policy

I built two of these – one example is earlier in this thread. Also here

I wonder why your avionics should not work on two 12 V batteries ?? With an engine out or dead alternator in the air your instruments would certainly work on the batteries, wouldn´t they ? A charged 12 V battery is definitely more than 12 V in reality, so avionics should be OK with two of them. Plus get yourself a common charger connected to the battery pack to extend your ground tests , you would not use max amps all the time while testing ?? Vic

Start Pac was founded and is owned by a guy I know, Jim Wurth, and is a good company. How many companies put the bosses cell phone number on their website?

http://startpac.com/customer-support/contact-us/

They supply GPUs too, Peter. But this is just a power supply to save battery power.

I wonder why your avionics should not work on two 12 V batteries

It does, and a lot of the “28V” “starter packs” are just two car batteries on a trolley, with a charger. These give out 24V.

To start an engine you need a car-type battery, or a big lithium battery. One could make a switch-mode power supply which delivers the required 400A or so (the max for some Skytec high speed starters) but you would end up drawing some 50A from the mains which makes it unmarketable.

I recently built another ground power unit, 40A, switchable 14/28V:

It was made to be continuously rain-proof (everything is IP67 sealed). For obvious reasons the output voltage selection was not made to be too easy

and there is an interlock on that little box so if you open it, it shuts down the power supply.

vic wrote:

I wonder why your avionics should not work on two 12 V batteries

They should. The question is, however, for how long as the voltage will drop. I would say radios (of any kind, not just VHF comms) tend to be demanding in this respect, especially older ones. But I would second the charger suggestion.