Critique my G3X VFR load analysis

[BobTurner]

The thing that caught my eye was the 8 amps from the pitot heat, along with 6 amps for landing lights. (Flaps have already been mentioned). IIRC Cessna put landing lights into the ‘intermittent use’ category (e.g., it was acceptable to let the battery carry that load for the 5 minutes they were in use). And of course, landing lights are not even required, so you could leave them off if you so choose. For pitot heat, I assume you have one of the more modern, temperature regulated units. Unless it’s very cold and you are at high speed (when you won’t require landing lights) the pitot will draw less. The only time you’ll need both pitot heat and landing lights is if there’s visible moisture (and it’s cold) all the way to the ground. In that case just hold off on the lights until you need them, let the battery carry the load for a few minutes.

[emsvitil]

Originally Posted by mfleming

Here's a look at my load analysis spreadsheet. It hasn't been 100% finalized but it will give you another data point.



Open the image in a new tab or window and you'll be able to read it.

Link doesn't show up with IMG code, so.......



http://myplace.frontier.com/~tokosha/rv7/vaf/load.pdf

[Draker]

Thanks to everyone who pointed out that rarely or intermittently used devices' loads can be safely carried by the battery. This is something I did not think of.

I guess one other argument for going with a larger-than-required alternator would be future proofing. If I ever one day decide to put in a big ol current sucking IFR navigator or another comm radio, I'll need the extra juice. But I suppose at that time I could swap out to a bigger alternator.

[mfleming]

Originally Posted by emsvitil

Link doesn't show up with IMG code, so.......



http://myplace.frontier.com/~tokosha/rv7/vaf/load.pdf

Weird...It shows up in my browser??

[I-TERA]

Hallo gent's,
my approach to the load analysis is quite different, I started from an assumption:
I will not take off with battery not enough loaded considering that I will need to land without alternator charging or without battery ( failure ).
So ( FAR ) if my alternator gives up in flight I must have 30' of partial load to land safely. The battery does not have the nominal capacity ( age, temp, efficiency) the alternator suffer from temp and low RPM.... so I calculated how much time is neaded after start ( energy absorbed from starter ) to recharge my battery with a stated load. My spreadsheet is developed in time( so it is easy to avoid to consider to use the flap motor all the time you flight ) and efficiency and not only in load. ( for example remember that you need 14,2V to charge a battery , the current of a resistive load at 14V will not be the same as at nominal 12V, the battery will give you the 80% of the electrons charged at 12V or less ).
Here the link at my simplified spread sheet :https://www.dropbox.com/s/bxdxwe301z...%3A18.xls?dl=0
It is written in Italian but I hope it will be easy to translate the few words.

Claudio