Electrical ?s

  • PAOLO MONTANARI
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2 weeks 3 days ago #3023 by PAOLO MONTANARI
Replied by PAOLO MONTANARI on topic Electrical ?s
Steve , I agree with you.Nevertheless what I marked are the words in the POH and they disoriented me

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2 weeks 3 days ago #3022 by STEVE ELLS
Replied by STEVE ELLS on topic Electrical ?s
Hi Paolo,

As I understand this circuit, it supplies power from the ground power plug to the "master switch" side of the battery contactor, so there is power at the "batt" side of the battery contactor.

Without power to the batt side of the master, there would be no way to close the batt contactor when the battery is dead.

An interesting solution for a situation where the airplane is not airworthy. I say it's not airworthy because the battery has to be "healthy" enough to provide 80 percent capacity. Obviously if the battery is dead, there's no capacity.

The Cessna style ground power plugs have three prongs. A large negative, a large positive and a small positive.

The small positive prong is shorter than the two large prongs and only make contact after the two large prongs are connected to the power (+)and ground (-) connections to the airplane.

When the small positive prong makes contact with the airplane receptacle, it supplies power to close the ground power contactor, which connects to the airplane side of the battery contactor.

So the easy answer is yes you can charge your battery using the ground power plug but it will require you to limit the current applied at the ground power plug and jump power to the battery contactor to close it so the power will be on the battery positive terminal.

But that's a lot of trouble.

Steve

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  • PAOLO MONTANARI
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2 weeks 3 days ago #3018 by PAOLO MONTANARI
Replied by PAOLO MONTANARI on topic Electrical ?s
I just discovered a sentence about the battery minder that fully changed my mind.Maybe Steve can be of help....Curious..?
At page 7-38 of my poh at the bottom of the page (it is for T210M but I think is valid in general) is written :
" a special fused circuit in the externalpower system supplies the needed jumper across the contacts so that with a "dead " battery and an external power source applied,turning on the master switch will close the battery contactor"..
Dors it mean that I can charge the battery if the master is on ?????

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3 weeks 3 days ago #3006 by STEVE ELLS
Replied by STEVE ELLS on topic Electrical ?s
Hi Gary,
If the alternator voltage regulator is adjusted correctly, the alternator output should be 28.5 Volts.

Since there will be a voltage drop between the alternator output stud on the alternator, and the main aircraft bus, check the output at the alternator stud.

According to the service manual, Cessna does not recommend adjusting the voltage regulator on the airplane unless the Cessna test harness/box is used. However, earlier VR were field adjustable after a small rubber plug, or a decal was peeled back from the forward face of the unit.


I believe the Cessna VR part number is C611001-0105.
Zeftronics, an after market company has a VR that is approved to replace the Cessna VR. The part number is R25400.

Let me know what you end up doing.

Steve




Steve

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  • Gary Shaffer
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3 weeks 4 days ago #3003 by Gary Shaffer
Replied by Gary Shaffer on topic Electrical ?s
Steve,

It's a 24/28-volt system, so should that be 28 +/- 0.2? The max I've seen is 27.3. The battery definitely has more cranking power after being on the BatteryMinder.

Shame about not being feasible to use the ground power plug for the BatteryMinder. Oh well.

There's a note in the log about previous work to fix a slow battery drain. Guess I need to re-visit that.

Thanks again,
Gary

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3 weeks 4 days ago #2999 by STEVE ELLS
Replied by STEVE ELLS on topic Electrical ?s
Hi Gary,

You should see between 13.9 and 14.2 volts DC on you main electrical buss during cruise flight.
Actually you should see that voltage any time the engine is running if your alternator is good.

You can't charge the battery through the ground power plug on your airplane.
As Paolo mentioned, there is a relay that is closed when the "Cessna" ground power plug is fully seated that provides power to close that relay.

I keep my CONCORDE RG-35AXC battery charged when I'm not flying by using a the appropriate Battery Minder ( www.batteryminders.com ) and connecting it when I'm not flying with the appropriate airframe interface kit.

With the kit installed, all that's required to hook the Battery Minder to the battery when not flying is a simple plug in to the airframe and 120 VAC power source for the Battery Minder.

As long as your battery is in good shape, and there's no current draw when the master switch is off, that battery should stay strong for quite a while. I know that's a nebulous answer but it's the best I can do right now.

One of the tests that battery manufacturers call for at each annual is what's called a battery capacity test. It's a test when an electrical load is applied to a battery, then the remaining battery capacity is checked. To be airworthy, the battery has to still have 80 percent capacity after the test.

Cessna single engine airplanes used to have a fused circuit that drew battery current even when the master switch was off. This was to keep the electric clock powered. It's what's called a "keep alive" circuit.
Today's avionics also have keep alive circuit needs but the current draw is so small compared to the older clock keep alive circuit, the battery stays strong for a long time.
Things that can lessen battery life, are inactivity, high ambient temperatures, and dirty connections.

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