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My instruction sheet is at the hangar, but I seem to recall you turn the master on first, before turning on the GPU so that the relay activates when you power it up.  But I’d have to double check that.

Thanks.


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I don’t know the specific instruction, but you need to check bus voltage right away with the GPU connected for ~28V or you won’t be sure your running on GPU power versus battery power; just like when running the engine and alternator is not on.
that’s a seriously discharged battery at only 24V.

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Things that often come up in conversation….

1) There is a relay that allows the GPU socket to be connected to the electrical system…

2) The relay requires sensing proper polarity… the three prong plug with only two wires connected to it…. Works wonders….

3) Some power supplies also require sensing proper polarity of the system

4) The dumb relay can interrupt smart systems from connecting…

5) Example… if you connect a BatteryMinder to the GPU socket…. Nothing happens…

It doesn’t sense any proper voltage and does not engage…

6) In this case people use external plugs from the BatteryMinder directly to the battery with all the proper fuses….. often wired near the GPU plug… or O2 source for convenience…

 

7) next issue for consideration… some people were concerned about the GPU relay’s ability to stay hot for so long… it has the same relay as the master and battery selector circuit… so delivering full power for a long time is in its design…

8) Last issue I have…. The BatteryMinder may be a little bit light for supplying all of the power needed for some avionics exercises…. There are discussions around here for best power supplies for the job… or keep an eye on how much the battery charge decays over time…

9) +1 for knowing where the GPU connects into the system… it is probably locked into battery #1 only…. #1 powers all of the circuits not cut off by the master switch… and is voted most likely to be dead after your kids leave a light on in the cabin…. :)

10) the POH probably details the GPU system use the best…

The Service manual has the electrical diagrams for the tail cone, nicely laid out….   Soooooo many wires it takes a ton of memory to remember them all…

+1 for checking power being delivered early on…

Expect the smart charger and dumb relay to not get along….

:)

PP thoughts only, not an avionics guru…

Best regards,

-a-

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Things that often come up in conversation….
1) There is a relay that allows the GPU socket to be connected to the electrical system…
2) The relay requires sensing proper polarity… the three prong plug with only two wires connected to it…. Works wonders….
3) Some power supplies also require sensing proper polarity of the system
4) The dumb relay can interrupt smart systems from connecting…
5) Example… if you connect a BatteryMinder to the GPU socket…. Nothing happens…
It doesn’t sense any proper voltage and does not engage…
6) In this case people use external plugs from the BatteryMinder directly to the battery with all the proper fuses….. often wired near the GPU plug… or O2 source for convenience…
 
7) next issue for consideration… some people were concerned about the GPU relay’s ability to stay hot for so long… it has the same relay as the master and battery selector circuit… so delivering full power for a long time is in its design…
8) Last issue I have…. The BatteryMinder may be a little bit light for supplying all of the power needed for some avionics exercises…. There are discussions around here for best power supplies for the job… or keep an eye on how much the battery charge decays over time…
9) +1 for knowing where the GPU connects into the system… it is probably locked into battery #1 only…. #1 powers all of the circuits not cut off by the master switch… and is voted most likely to be dead after your kids leave a light on in the cabin…. 
10) the POH probably details the GPU system use the best…
The Service manual has the electrical diagrams for the tail cone, nicely laid out….   Soooooo many wires it takes a ton of memory to remember them all…
+1 for checking power being delivered early on…
Expect the smart charger and dumb relay to not get along….

PP thoughts only, not an avionics guru…
Best regards,
-a-

Thanks. I have the White Lightning System.
82fb00a2e50bf9bdd198cec1223ea6bd.png


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Be on the lookout / listen out for the sound of the GPU relay clunking into operation….

If the GPU relay doesn’t close… use extra caution to make sure the power supply isn’t presenting reversed polarity for some reason…

Try it with the battery access panel open…

If you have a spare 28V battery lying around…. It makes an easy test for the GPU relay…

The GPU relay should give the same clunk that you can here with the master relay….

A simple volt meter will show the voltage of the power supply making it to Battery #1.

PP thoughts only….

Best regards,

-a-

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I use a pair of deep cycle 12 volt batteries wired to deliver  both 12V and 24 Volt.  They have a marine battery charger with a two battery output (super common in the marine world) so the two batteries are charged but have plenty of reserve should my load exceed the charger capacity.  The kit is on a dolly and thus mobile.    We don't have a shop on our field so this way I can swing my gear, check avionics and jump a stranded transient or hanger neighbor.  By purchasing marine gear, the cost was very reasonable and the only aviation item is the special aviation three prong jumper plug.  at west marine the battery charger is less than $200 (sold as a two bank unit and rated for continuous duty).  I've noticed that some of the "airplane" power supplies really struggle to supply clean and consistent power and they give off some pretty horrific electromagnetic field interference.  When I switched to the battery pack system these issues all went away.  good luck. 

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What you describe we used to call a “start cart” often put in a kids little red wagon to make it easy to move around. Works great and unlike a GPU it can supply starting current, usually GPU’s max out amps pretty easily.

A golf cart makes a great start cart too, with jumper cables you can hook up either 12V or 24V and use it as a tug and a run around the airport vehicle, my golf cart easily pulls my Mooney through grass.

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