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In yesterdays episode, Dr. Modulus (played by Scott) asks:



<< 1.) is it possible to use a 24 volt alternator to charge 2 12 volt

batteries

 in series and then just use 2 12 volt and 1 24 volt buses in the plane?

 seems like this could give you the best of both worlds. anyone done this?

 anyone willing to send in the wiring on how it is done?>>



Bad idea. All Pb-H2SO4 (lead acid) battery cells are nominally 2 volts. They

are combined in series to get higher voltages. Placing two 12 volt batteries

is OK to do if they are of the came capacity and type. Tapping off of two

would only work if the loads were matched and you could tolerate a "ground"

floating at 12 volts on one of the busses (potentially very dangerous. PTP).

The problem comes in charging battery cells that have not been evenly

discharged. Sooner than you would think, one of the cells will fail. I know

this because back in the mid 70s I built an electric car and tapped off 12

volts to run the radio, lights etc. I soon found out that one dead battery

meant that all were as good as dead. The tapped batteries soon failed and had

to be replaced.



Another way to look at is that although you are regulating the voltage to the

cell stack, the individual cells form a voltage divider and are unregulated

and therefore must be matched to charge evenly. Putting a load across of them

upsets the balance.



Of course you could put a charge regulator across each battery but by the time

you get done with that you bight as well have put a DC-DC converter to run

your 12 volt aux buss.

 

<<<

 2.)  I went up to see Dick Mitchell's 320 in park city. fantastic work(7000+

 hours!!) and he had put capacitors on all of his solenoids. he could not

 remember the size. has anyone else done this, and do you know the size of

 the capacitor? does it extend the life of the units?

  >>



I don't think they were capacitors. Likely they were varistors (they LOOK like

caps). Varistors turn into short circuits above a specified voltage and they

are needed because of the flyback voltage from the solenoid coil. YST, when a

solenoid is turned off it's magnetic field collapses causing a voltage pulse

at the solenoid terminals of several hundred volts. This pulse can acr across

the opening switch can cause mischief in the electrical system.



TLA Glossary:

Pb-H2SO4 = lead acid

PDP = pardon the pun

TLA = three letter acronym

YST = You see, Timmy



Regards

Brent