Battery conected + to - ?

[wireweinie]

What happens at the negative terminal while the positive terminal is feeding the bus? Is it like oil going back to the oil pan after being pumped thru the engine.. whats not used goes back? After I get a handle on the correct polarity, I want to try to understand what happened at the pos and neg terminal with it connected backwards. Hopefully I never do this, but just trying to understand battery power and how it moves through the plane.

Imagine a simple circuit with a single light connected to a single battery. Electrons will flow out of one battery terminal, through the light bulb, and back into the battery through the opposite terminal from where it started.

Now take that same circuit. Install a switch in the wire between the battery and the light bulb. Then cut the other wire and connect each cut end to a steel tube. Got that? In this case, the only way the bulb will light up is if the switch is 'closed'. In effect the switch reconnects the wire. So now the electrons will flow from one battery terminal, through the closed switch, and to the bulb. after the electrons exit the bulb they will flow through that wire and into the steel tube. From the steel tube, they will flow back to the opposite battery terminal through the other cut wire.

The path of electrons will not change from the first example to the second. The electrons still exit the battery, go through the bulb, and return to the battery. But in the second example, we've installed a 'common ground'. One battery terminal is connected to the steel tube, and one wire from ALL bulbs installed may be connected to that tube at any point. The opposite wire from battery to bulb now has a switch installed. The switch makes a mechanical connection between the cut ends of a wire. When the switch is 'open' the wire ends are held apart from each other and there is no path for the electrons. But when the switch is closed, the ends of the wire are touching and electrons will now flow through the wire.

In an aircraft the battery from above will have the negative terminal connected to the airframe. This means that when we install an electrically powered item, the negative wire from that item only needs to be connected to any part of the airframe. The positive wire from that item will connect to a switch, which in turn, will be connected to the positive battery terminal. This is simplified but it should shed some light on how the power distribution works.

Web

[frequent_flyer]

I want to try to understand what happened at the pos and neg terminal with it connected backwards. Hopefully I never do this, but just trying to understand battery power and how it moves through the plane.

The current leaving one battery terminal passes through whatever is connected to it and the same magnitude of current arrives back at the other battery terminal. That is true whether the battery is connected the right way round or the wrong way round.

The difference between correct battery connection and reverse polarity connection is that, with reversed connection, the current direction is reversed and will quite likely be a lot larger than for correct polarity (but not for long).

[Supertwotwo]

Thanks Web and FF for the simplified explanations. Regarding reverse polarity though, take your first example, the battery positive wire to light back to battery negative, if the battery was connected backwards than it wouldnt make a diffrrance?

[Supertwotwo]

Here is a link to the post I copied that from, others are posting on it now https://vansairforce.net/community/s...d.php?t=213774

[frequent_flyer]

Thanks Web and FF for the simplified explanations. Regarding reverse polarity though, take your first example, the battery positive wire to light back to battery negative, if the battery was connected backwards than it wouldnt make a diffrrance?

Tungsten filament lamps don't care about the direction of current flow. They are not sensitive to voltage polarity. Some lamps, e.g. simple LED lamps, do require proper polarity but if connected with wrong polarity they are not damaged. They just don't light up. LED lighting is not always simple though. Typical aircraft LED lights include voltage regulator circuits and some may be damaged by incorrect polarity.

Diodes, such as those used for suppression of back EMF on relays and contactors, will almost certainly blow if the battery is connected reverse polarity and the relay or contactor is energized. Linear voltage regulators in electronics equipment will likely be destroyed and the downpath damage may be far more extensive than that.

In an aircraft with an avionics master the damage may be confined to contactor diodes, the alternator, the alternator regulator, and all the associated wiring. Still an expensive mistake to make.

A well designed aircraft battery installation would make it impossible to connect the battery leads the wrong way. There is a reason the battery terminals are offset to the side of the battery and not on the center line.

[Charlie Longley]

https://yourlogicalfallacyis.com/no-true-scotsman

I used your references...

I did a little more research into what the FAA had the A&P school teach me. That’s basically all I know. I agree that the FAA is in the minority on some subjects compared to the rest of the world. But guess who regulates aviation in the US? I am going to put out a separate topic on DC circuits according to the FAA tomorrow.

Charlie

[wireweinie]

Thanks Web and FF for the simplified explanations. Regarding reverse polarity though, take your first example, the battery positive wire to light back to battery negative, if the battery was connected backwards than it wouldnt make a diffrrance?

'Making a difference' depends on what is connected in the circuit. Hang in there for the explanation. For simple items such as incandescent bulbs, polarity doesn't actually matter. I.e., if you take an old school landing light from a Cub and connect it to a battery, it will light up whichever way you connect the positive and negative wires. DC electric heaters are the same. There are even a couple of types of motors that will power up just fine despite the wire order.

BUT . . . . Almost all newer design electrical items are going to be polarity sensitive (i.e. positive wire to positive battery terminal. Negative wire to negative terminal). The newer landing lights are LEDs, meaning that the bajillion little light producing elements inside are Light Emitting Diodes. Diodes that produce light. This means that when you swap out an old school incandescent landing light for an LED landing light, you need to figure out which wire is positive and which is negative, and then connect them correctly. Remember that diodes only allow current flow in one direction and block it in the opposite direction. So if the LED light is connected correctly, it will allow current to flow through it and it produces light. If you connect it wrong, then it will block current flow and no light will be produced. In this way, LED lights are kind of self protecting; connect it wrong and it doesn't get damaged.

The problem comes with other designs that use these semiconductors. These may be designed to block current flow during normal operations. Now if you connect the battery incorrectly, even for a moment, suddenly those diodes and/or transistors that are built to stop current flow in one direction will allow current flow, uncontrollably, in the WRONG direction. By the time you hear the spark 'snap' the damage will be done. When that occurs, the current flow is so extreme that it will burn wires and cause smoke. It also causes so much heat inside the semiconductors that they fail.

Remember that one item I called out to troubleshoot on that aircraft was the spike diode on the start relay? When a spike diode is installed correctly, it will block current flow and the circuit doesn't even 'see' it during normal operation. But when the battery was connected backwards, current was allowed to flow through the diode, uncontrolled. No way a spike diode can withstand that much heat. And, when they get replaced, LOTS of them are installed backwards and fail as soon as the master is turned on.

BTW, a 1N4004 diode makes a great spike diode. And cheap.

Web

[Supertwotwo]

Thanks guys, I tried to transfer from AO to AE but couldn't get in, and glad you cleared the LED backwards polarity up, I thought for sure they would suck the light out of the sky if they were wired backward

[Supertwotwo]

Seriously thanks for the explanations, I am going to read up on battery flow, pos and neg charges. I always thought the flow was like that one way diode and nothing could ever come out the neg terminal, that the pos terminal was the only way out for the volts. But now see its not that way. I have heard of pos ground systems, can you touch on how that differs from neg ground like most USA systems are today? Would the same battery and light bulb work in a pos ground setup just need connected backwards on purpose?

And where do I put the spike diode, not sure where it protects, would you have one in every circuit you want to protect from a spike?

[Skywalker]

The alt breaker only controls field(rotor) current, so even if you leave it off, the heavier wiring of the stator hits the bus as soon as the master is closed. And all six large diodes in the alt are now installed backwards.

[frequent_flyer]

The alt breaker only controls field(rotor) current, so even if you leave it off, the heavier wiring of the stator hits the bus as soon as the master is closed. And all six large diodes in the alt are now installed backwards.

Depends on the installation. I have a 50 A alternator breaker in one of my aircraft and that breaker is most certainly not for field current.

Edit to add - Alternator field in this aircraft is a separate 5 A breaker.

[Cub Builder]

Depends on the installation. I have a 50 A alternator breaker in one of my aircraft and that breaker is most certainly not for field current.

Edit to add - Alternator field in this aircraft is a separate 5 A breaker.

True enough. I use the same in my SC clone since it has an integral regulator that may be subject to an uncontrolled runaway. The 50 amp breaker is between the alternator and the DC bus to protect wiring from overload from a runaway alternator. And that 50Amp Alternator breaker may very well trip, sometime after the alternator diodes go up in smoke following a reverse polarity battery connection. I suspect the diodes may fail at less than 50 amps current when biased on.

For the OP, as Wireweenie has stated a couple of times. Break the circuit down into it's smallest pieces for troubleshooting. As you start connecting things back into the circuit, you'll find the culprit(s) tripping the breaker and then you'll know what needs to be fixed.

FWIW, most of the LED lights being sold for tip lights and landing lights are not polarity sensitive. Obviously the LED itself is, but many have circuitry in them to allow them to be connected to the circuit either way. LED Landing lights on my SC are not polarity sensitive. LED landing lights on my RV are.

Interesting problem recently when replacing the external lights with LEDs on my planes. My SC has a 14V electric system, while my RV has a 28V electric system. Both use the same 10 - 30V LEDs for the external lighting and both use a wedge type bulb in the tail light. Tip and tail lights worked perfectly on the Cub. Tip lights also worked perfectly on the RV. Tail light generated so much EMI/RF noise on the radios to render them unusable. I tried several 10 - 30V LED wedge bulbs in the 28V system (both PMA and cheap Chinese LEDs) with all generating extraordinary amounts of noise. I finally added a 15V Zener diode in line with the tail light LED to drop the voltage down to 13V at the LED. Noise is gone. The zener limits the voltage for the LED and since the LED only uses .09 amps, it limits the current so I don't blow up the zener.

-Cub Builder

[frequent_flyer]

For the OP, as Wireweenie has stated a couple of times. Break the circuit down into it's smallest pieces for troubleshooting. As you start connecting things back into the circuit, you'll find the culprit(s) tripping the breaker and then you'll know what needs to be fixed.

In that situation I would not want the battery in circuit for initial trouble shooting. I'd start with a DVM on a low resistance range and look at how the total circuit resistance seen at the battery terminals changed as components were added to the circuit. Very low risk of adding to the damage with this technique.

Edit to add - A DVM outputs a voltage when on resistance ranges. The positive voltage DVM lead should be connected to the battery positive lead. If the DVM is reversed the results may be misleading if any diodes survived.

[supercub83a]

https://youtu.be/bHIhgxav9LY

This is a great video on how electricity actually works.

There is sometimes a difference between how things actually work and practical ways to think about how they work. For another example look at orbits. Newtonian physics is used to model orbits because its simple and typically works for practical needs, but if you needed to be extremely precise (or model the orbit of mercury) you would have to use the much more complex General Relativity.

Going to a positive ground would work too as long as any polarity sensitive devices are also reversed. Its more a naming convention, an abstract simplified view of what’s actually happening. The convention we have adopted (out of ignorance of what was happening when we adopted the convention) is that current flows from positive to negative. In actuality the electrons are moving from the negative terminal to the positive terminal and they are doing so at a speed slower than your running pace. So if you place a light on the circuit 1/4 mile away you could walk to the light and back before any electron from the battery makes it from the negative terminal to the positive terminal… but the light comes on almost instantaneously… because electric fields (not electrons) move at the speed of light… chew on that!


Sent from my iPhone using SuperCub.Org

[RVBottomly]

https://youtu.be/bHIhgxav9LY

because electric fields (not electrons) move at the speed of light… chew on that!


Sent from my iPhone using SuperCub.Org

I was sitting on my fingers wanting to say just that!

[Supertwotwo]

I was sitting on my fingers wanting to say just that!

I would have to watch that video 3 more times to start to understand that the stuff moving through the extension cable is not what lights the bulb... A lot of dangerous arrows moving around outside that cable

[skywagon8a]

I thought I was confused before reading these two threads .... Now I'm certain.

[mam90]

https://www.industrytap.com/floresce...ic-fields/1763

Heres the best line from the linked article..

In a 1972 book called Power Over People there is a picture of author Louise B. Young holding a shining florescent bulb while standing next to energy transmission wires. In the late 1960s-70s homeless hippies in Siskiyou County, California were arrested for laying out wires on the ground beneath high power lines to run kitchen appliances.

[cubdrvr]

You guys make my head hurt

[wireweinie]

Web

[hotrod180]

From another related thread

This is like a debate about which came first, the chicken or the egg.

[wireweinie]

Web

At least SOMEBODY got that reference.

Web

[hotrod180]

Was that what your cartoon was about?
I like this one:

[mvivion]

https://youtu.be/bHIhgxav9LY

This is a great video on how electricity actually works.

There is sometimes a difference between how things actually work and practical ways to think about how they work. For another example look at orbits. Newtonian physics is used to model orbits because its simple and typically works for practical needs, but if you needed to be extremely precise (or model the orbit of mercury) you would have to use the much more complex General Relativity.

Going to a positive ground would work too as long as any polarity sensitive devices are also reversed. Its more a naming convention, an abstract simplified view of what’s actually happening. The convention we have adopted (out of ignorance of what was happening when we adopted the convention) is that current flows from positive to negative. In actuality the electrons are moving from the negative terminal to the positive terminal and they are doing so at a speed slower than your running pace. So if you place a light on the circuit 1/4 mile away you could walk to the light and back before any electron from the battery makes it from the negative terminal to the positive terminal… but the light comes on almost instantaneously… because electric fields (not electrons) move at the speed of light… chew on that!


Sent from my iPhone using SuperCub.Org

Hooooo, Boy....next we'll get into "Hole Flow Theory".

MTV