Read this on another forum, what the heck happens when you connect the battery to the system backwards? This guy is still broke, I dont have any more info on the system, but if someone could explain what the power from the battery did when the master was turned on with the battery connected wrong, I would really like to hear it. Would more power go out the pos terminal or would it flow backwards out the negative?
Last edited by Supertwotwo; 01-30-2023 at 11:09 AM.
Context?
New experimental first time powered up, or battery/relay replacement?
Sounds like a first power up of new system... Heck, if it were my wire genius work I would only be doing it on July 4th to ensure I fit with the other flash bang booms.
I don't know where you've been me lad, but I see you won first Prize!DENNY liked this post
Maybe it fried an instrument? There are several things that cannot tolerate reverse polarity - the GTR-200 specifically says damage will occur. Disconnect all electronics, then add them back one at a time.
Conventional current alway flows from positive to negative just as water flows from high pressure to low pressure. Impossible to speculate on what damage was done without a wiring schematic and knowledge that the aircraft was actually wired as shown in the schematic.Originally Posted by Supertwotwo
Many of the modern Garmin avionics LRU have dual redundant power inputs that are diode "OR" connected. Nothing happens to these units is they are connected reverse polarity. Other older units may, or may not, be protected against reverse polarity.
Electronics stuff is powered by internally encapsulated smoke. If the smoke gets out it usually stops working.
I would say he most likely has it wired wrong.To melt a wire like that you pretty much need it shorted or connected to ground. If he connected the P lead shielding to the starter solenoid lead?? I believe some of the early cubs had a positive ground not negative if he is wiring from that it could screw stuff up. Web should be by soon. DENNY
Thanks, thats what I am looking for.. I was wondering how the wire burned on the master switch side (traveling backward neg to pos, without the positive getting hot and burning something up since its connected to the airframe ground and should be making sparks as soon as the master switch closed completing a ground through the bus
DC current actually flows from negative to positive. Don’t want to start an argument but I can quote text if you would like.
Last edited by Charlie Longley; 01-30-2023 at 01:02 PM.
The electron flow is from negative to positive. "Conventional" current is from positive to negative.
https://web.engr.oregonstate.edu/~tr..._vs_conv_I.pdf
Your turn ....
Unless you went through Navy electronics schools, current flows positive to negative. Electron flow is negative to positive. It matters not how you picture it so long as you use the proper equation -E=IR.
reversing the battery would cause pretty good current flow through any wires feeding a diode around a solenoid coil - but not sure it would harm the solenoid.
If the diode around the starter solenoid was backwards, and fused, actuating the start button would blow the fuse, rather than burn the wires.
Charlie is correct. Electrons flow from negative to positive.
IF: the only problem at the moment is the 'instrument breaker popping when turning the key to the 'start' position, then stop throwing parts at it. If that breaker is the only one popping then it has to be a circuit connected to that breaker.
Disconnect all circuits, from that breaker, except the starter circuit and check to see if it pops.
If NO, then one of the disconnected circuits is the problem.
If YES, troubleshoot the starter circuit.
Just opinion here, but I'm going to say that there is a problem with the start circuit. It's easy to troubleshoot. Power wire from the 'instrument breaker to the 'B' terminal on the key switch. Then a wire from the 'S' terminal on the key switch to one of the small terminals on the start relay, with the other small terminal tied to airframe ground. Check for a short on the wire from key switch to start relay. If that's good, replace the diode that was installed backwards on the start relay .
Just from past observations, this isn't the only problem here. Every single item on that bus, that has a diode or chip installed, is going to be suspect. And even if it works now, some of them are going to fail in a short time.
Bad things happen when them 'trons stampede in the wrong direction.
Web
Life's tough . . . wear a cup.
Here is an interesting discussion on current direction -
https://www.quora.com/Does-current-f...her-way-around
Read the post by
Gary Novosielski
But that isn't what he said.
'Conventional flow' has current/current flow/electron flow going from positive to negative.
'Electron flow' has current/current flow/electron flow from negative to positive.
Either concept can be made to work with basic troubleshooting. But, modern items like semi conductors are marked (think of the blocked arrow on a diode) to reflect the actual movement of electrons in the circuit, which is 'electron flow'. That makes electron flow much more useful in troubleshooting.
Web
Life's tough . . . wear a cup.
https://www.faa.gov/documentLibrary/...r/AC_65-9A.pdf
Page 271 and 376. Your turn
Agreed. That's what I said back in post 9.
How many installed aircraft battery ammeters show positive current when engine is not running and the battery is passing current into a load?
How many alternator load ammeters show negative current when the alternator is producing power?
What current direction is shown on a DVM when the positive lead is connected to battery positive and the negative lead is connected to a load the other side of which is connected to battery negative?
I would submit that a DVM, an installed battery ammeter, and an installed alternator load meter, all indicate "conventional" current direction.
The section on current flow is on page 272 of the printed document which is page 278 of the linked PDF. That definition does seem to conflict with anything I have posted.
I had a really good instructor named Dale Dutcher in A&P school for the electrical section. He had considerable real world and theoretical experience. He had some sort of electronics background in the Air Force. He stated that everything he read indicated that DC current flowed negative to positive except for one esoteric paper on theory. All aircraft manuals are written that way. Take an external power schematic with its associated diodes for example. So for real world troubleshooting it makes sense to think of current flow going from negative to positive. Leave theory to theorists.
* Electrons flow from negative to positive.
* "Holes" flow from positive to negative.
* "current" flows from positive to negative.
The most basic electrical differential equations. Anyone who knows anything about electronics knows them:
* V=I*R
* V = L*di/dt
* I = C*dv/dt
If you want to argue that current flows from negative to positive, you are on your own because that is not how the world communicates. You are choosing to speak your own language instead of being reasonable and constructive.
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Bearhawk, RV-4
The FAA is full of idiots and they publish that fact from time to time. Check page 282 (288th page of the PDF). Their diagrams and equations for Ohm's Law are not self consistent. This document was not approved by anyone who knows about this topic.
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Bearhawk, RV-4
This is the first link that comes up for a search of "which direction does current flow in a diode":
https://learn.sparkfun.com/tutorials/diodes/all
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Bearhawk, RV-4
Probably not applicable totally here, but when I installed the battery backwards in my wife’s Volvo many moons ago it killed the alternator and the solid state regulator. Of course this was 1974 when semiconductor circuits were not so robust. I check three times when I but batteries in anything including a flashlight ever since then.
Ahh so we’re going to use random websites off the internet now. Tell you what I half ass trust Wikipedia cause people tend to make sure it’s correct. Here’s the definition of a diode. https://en.m.wikipedia.org/wiki/Diode Pay attention to which side of the symbol the anode is on then look up the definition of an anode. Oh wait here it is- https://en.m.wikipedia.org/wiki/Anode
Last edited by Charlie Longley; 01-30-2023 at 04:34 PM. Reason: Typo
I'm not quite sure how to respond at this point. ...because the links you just provided show conventional current going from positive to negative...???
And to directly quote your 2nd link:
The direction of conventional current (the flow of positive charges) in a circuit is opposite to the direction of electron flow,
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Bearhawk, RV-4
If you can wade through the BS, let us know what you find.
Web
Life's tough . . . wear a cup.
The definition of current flow is the flow of electrons. Seems like it's self evident.
Web
Life's tough . . . wear a cup.
...except that it's not because the convention was set before people understood things like electrons. The definition of current flow is the flow of holes; the flow of positive charges. See the the quote above from the link provided by Mr. Longley. Read both links he provided. That is what the words are defined to mean.
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Bearhawk, RV-4
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Bearhawk, RV-4
Who knew that those arrows on PNP and NPN transistor symbols were so misleadingly depicted. Makes me wonder how I ever manged to diagnose and fix anything electronic. Not to mention that pointy triangle of the diode symbol that I'm now being told does not show the direction of forward biased current flow.
Sigh-
“For example, the end of a household battery marked with a "-" (minus) is the anode.“
Why don’t you read through the article a few more times.
A battery is an energy supply. A diode an energy sink. The electrons will flow out of the anode of the diode and into the cathode of the battery. The holes will flow out of the cathode of the battery and into the anode of the diode. Up to here, I see no disagreement. let me know if I'm wrong about that.
...and none of the above conflicts with this statement from your own link:
..or this: https://en.m.wikipedia.org/wiki/Elec...nt#ConventionsThe direction of conventional current (the flow of positive charges) in a circuit is opposite to the direction of electron flow,
The cool thing about Wikipedia is that most "facts" include references. Follow through for references [10] and [11].
Last edited by kestrel; 01-30-2023 at 05:03 PM. Reason: messed up ordering of anode and cathode
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Bearhawk, RV-4
The beauty of the internet is it puts a lot of information at a person’s fingertips. The not so beautiful thing is just because it’s a professional looking website doesn’t make it true.
Ok. You made me laugh so hard I snorted!
Web
Life's tough . . . wear a cup.
For those that can't be bothered to follow the reference links from links:
Last edited by kestrel; 01-30-2023 at 05:08 PM. Reason: screen shot didn't show?
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Bearhawk, RV-4
You be you.
Last edited by Charlie Longley; 01-30-2023 at 05:07 PM. Reason: Typo
In this case, if you keep looking, you'll find that the FAA is solidly in the minority on their views and out of step with reality. ...who's ever heard anything like that before?!
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Bearhawk, RV-4
Yes, I was just trying to get a picture in my mind of what exactly happened the second they flipped the master on. I appreciate the info on electron and current laws, but I was looking for a simple if there is simple answer. If it was hooked up correct, than flip master on the volts travel upstream to the master than bus and things work. Sorry for sounding stupid but this does not come to me as easy as stick and rudder does. 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. I did accidently connect a battery charger backwards to a battery and luckily it had a reverse polarity protection.
To the OP, and anyone doing troubleshooting on simple DC circuitry found on aircraft and automotive systems; the above argument means NOTHING to you. Yep. Zip, zero, nada. No impact whatsoever.
Specifically for the OP, you are looking for short circuits in your system. That means no resistance between a power wire and the airframe ground. No resistance in the circuit means that current can flow from positive to ground without control, right up until something burns/melts. Think about a bare wire touching ground. It could also be an item such as a diode, that has failed in a shorted condition (very common failure mode). This means it shorted internally and has become a path to ground with no resistance. Since semi conductors (diodes, transistors, and chips that incorporate them) can be found in most modern electronics, this means that anything that was exposed to reverse polarity from the incorrectly connected battery may now have a shorted semiconductor inside it. That's also why I suggested disconnecting everything from the 'instrument' breaker except the start relay wire. It's just a troubleshooting method. You can re install circuits one at a time until you add one that causes the breaker to pop. Then you have identified the circuit with a hard failure.
Web
To the original question:
If the master relay had the diode on it that it should have had, when the master switch was turned on, most of the current would have flowed through the diode instead of the relay coil. This current would be much higher than you would normally see if it were flowing through the coil. The diode is normally reverse biased so that it will not conduct. It is there only to provide a path for current to flow until the magnetic energy in the coil dissipates when the master switch is turned off.
So, the diode that should have been reverse biased was forward biased. It provided a lower resistance current path through the master switched and cooked those wires. If the diode survived, the master relay probably never actuated. If the diode died, it will have opened and then the current would flow through the coil, turn on the master relay, and provide reverse polarity power to all the electronics. Then it is down to the design of each component.
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Bearhawk, RV-4Dave Barras thanked for this post
https://yourlogicalfallacyis.com/no-true-scotsman
I used your references...
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Bearhawk, RV-4
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