Topic: Reversed the polarity by accident. What might have been damaged?

[leogriss]

I feel super stupid. What did I do today....
As soon as I connected my car battery, I saw white smoke coming out from the left sidecover.

I know for sure that my rectifier is burned since I'm not getting any Ohms as the manual stated.
My question is what else do you guys think that might have been damaged?
Should I check the regulator, too?
Need experts help!

Thank you

[Gordon]

See this thread:

http://forums.sohc4.net/index.php?topic=64028.0

[ekpent]

I think this may be bad----Jumping from a car is bad

[Gordon]

Jumping from a car is bad

No, it is not.  Please explain why you think it is.

[ekpent]

When the cables are hooked up wrong bad thing happen.    Happens too often but makes for a good thread

[Gordon]

When the cables are hooked up wrong bad thing happen.    Happens to often

Same thing happens when you hook up a motorcycle battery backwards, too.  The type of battery isn't the problem here, it's the polarity that's the issue. 

[ekpent]

It can be a noobie thing-or the old I bought a bike with fried wires thing-makes them cheaper

[Fritz]

Jumping from a car is bad

I think that jumping on a car is bad. Depends on if the owner runs faster than you, maybe

[ekpent]

Hey Fritz do you have snow right now in Germany and Hello what do you ride??

[Kframe]

Jumping from a running car = bad.
Jumping from a 12v car battery is fine.

-K

[Fritz]

Hey ekpent!

Yes indeed, lots of snow here and freezing since weeks. Quite unusual for the north of Germany. Too cold to work on my 550 F. It's my first bike since 20+ years and I'm really looking forward to head north to Sweden on the Autobahn in spring.

http://www.flickr.com/photos/39364615@N03/3663673950/in/photostream/

Cheers

[Fritz]

I know for sure that my rectifier is burned since I'm not getting any Ohms as the manual stated.

Hi leogriss,

I'm not sure about the ohmmeter readings. Mine did not show anything when I checked my rectifier but I know it's fine. I think it depends on the voltage that the meter uses to measure resistance. But most multimeters have a diode switch that should show the correct values.

Last year a friend reversed the mc battery on his Bol D'Or. A ground wire fried all along the wire harness. I replaced it and everything was fine. No damage done to the rectifier.

Cheers
Carsten

[ekpent]

Fritz-you have a wonderful area to ride and be safe .

[TwoTired]

Jumping from a running car = bad.

Any electrical theory or data to back that claim?

I have not found the claim to be factual.  But, as an urban myth, quite prolific.

In fact, I have jumped my CB550 from a running car/truck several times with no damage.  I was very careful with polarity connection.

[campbmic]

This is actually something I have some expertise in after making my "Batman Switch" on my Yamaha FZR. I've researched the topic quite a bit and my knowledge comes mostly from what others have said and not technical data.

Apparently car batteries can give out a constant 12V. However when the car is revving or even running the voltage increases slightly.

I've jumped bikes off running cars and none run cars. I would suggest you not turn the car on when jumping a bike.

The main thing that might be damaged from this is your pride. I'm sure you can pick up a rectifier cheap from ebay or a salvage yard. 

[Gordon]

Apparently car batteries can give out a constant 12V. However when the car is revving or even running the voltage increases slightly.

It's the same with motorcycle charging systems. 

The problem is NOT with the type of battery, or with the type of vehicle it it happens to be currently connected to, as long as it's the same DC voltage.  The problem is with hooking up the polarities incorrectly. 

[TwoTired]

Apparently car batteries can give out a constant 12V. However when the car is revving or even running the voltage increases slightly.

Sure, in order to charge the battery you have to provide the battery with a higher potential than it presently has.  Cars have charging systems and Voltage regulators which limit the voltage to 14.5 V.

But, guess what?  The Motorcycle charging systems uses the same voltage limits as the car charging systems do.  The car can't supply any voltages that the Honda electrical system doesn't routinely handle.

However, in support of Gordon's point, connection polarity errors can create problems at nearly the speed of light.  The result is that the smoke is released, and only the manufacturer knows how to put the smoke inside these parts.

[Fritz]

The problem is NOT with the type of battery, or with the type of vehicle it it happens to be currently connected to

That's right. You could jump your bike with a nuclear power station if it had a 12V DC outlet

But back to the initial question: What might have been damaged?

First let's look at how a diode works (first pic). It will forward current if its cathode (the end the triangle is pointing to) sees a smaller potential than the anode. On the other hand, if the voltage at the anode end drops below the voltage at the cathode end, it will block current.

The second pic is showing the alternator/rectifier circuit. Actually there are three alternator windings and six diodes but for simplicity, I'm just showing a third of it.
If hooked up correctly, current will flow from the alternator winding through the diode to the battery if its voltage is above the battery voltage. If the alternator voltage is below ground potential, the diode on the ground side will become conductive. Since the alternator winding is delivering AC, its voltage will change from, let's say +15V to -15V to +15V and so on.

If the polarity of the battery is reversed, the ground potential will see +12V. Both diodes will see a positive potential at their anode ends and 0V at their cathode ends. So they will both become conductive and short out. Consequently a lot of current will flow through the diodes and the wires that connect them to the battery. The diodes can handle huge amounts of current but eventually they will pass out. The wire with the largest resistance will start glowing before the diodes go up in smoke.

So if you are lucky and the battery was connected for just a very short time, the rectifier should be ok, but you will have to check the wire harness and connectors.

[bryanj]

If you want to run two or more generators in parallel you need to balance the load or nasty things happen when one may try to act like a motor, hence its ok to jump start from a running engine slave as long as you remove a lead as soon as the daed one fires/runs.

This was told me by a teacher wot wrote the books to teach marine engineers electrotechnology theory so i took his word for it

[Fritz]

If you want to run two or more generators in parallel you need to balance the load or nasty things happen when one may try to act like a motor

That's right. But I think that we parallel DC voltage here. Aren't the rectifiers preventing the generators from fighting each other?

[TwoTired]

If you want to run two or more generators in parallel you need to balance the load or nasty things happen when one may try to act like a motor, hence its ok to jump start from a running engine slave as long as you remove a lead as soon as the daed one fires/runs.

This was told me by a teacher wot wrote the books to teach marine engineers electrotechnology theory so i took his word for it

DC generators are different from AC alternators.  DC generators can indeed be powered to cause armature rotation.
AC alternators in our bikes have a rectifier that blocks current going to the alternator (most cars these days have alternators, too).  There is also the mater of powering up the Field coil (electromagnet).  In theory, you could make one alternator drive another by interconnecting all the yellow stator wires directly and energizing the field coils of both with a DC power source. It would be hard to imagine doing this sort of rewiring accidentally, and with a single pair of jumper leads.

You just trying to cause trouble Bryan?   

[bryanj]

Who me? never, I was too young, uninterested and drinking to go into the details of why, how and whatever ( Its not true you get marks for putting your name on an exam answer paper by the way----I manages to score 0!!!) But I respected the man for what he knew and how he taught so i took his word for it

Practically tho he did call me names in the workshop one day:-

We had a diesel 220DC genny that we used to run up a DC motor coupled to a 3 phase slip ring 440v generator to get it up to speed to parralel with the mains then we could use the 3ph as a motor to power the dc end as a genny and drag high amps

Speed control to parrallel was via a resistor box to weaken the field of the DC end but the ideal point was, as usual, half way between two resistor buttons Soooo me being a smartass sent my mate to pretend he was altering the field whilst i lowered the diesel genny voltage to about 190 as i remember which made the paralleling a real piece of cake

Unfortunately this lecturer noticed and called my parentage into question! Although later, privatley, he did praise me for ingenuity as aparently somebody only thought of it every other year on average. Told me that even though i didnt have a hope in hell of passing the exams i would be a good "Hands on" engineer and i have worked most of my life on infernal combustion (and exfernal) enginesso he must had had something right.

Silly story but something different

[camelman]

Bryan,
 
We just threw the breaker and connected to the grid when I worked on Gas Turbines at GE.  Nothing like hearing 200 tons of steel rotating at 3600 RPMs slam into matched phasing with the electrical grid.  If you are dealing with two generators in AC operation, then they do need to be phased immediately.  This is not the case with alternators in most vehicles though, as they output DC.

With regards to charging vehicles from other vehicles, there are only two things to worry about.  The first is voltage and the second is amperage.  You don't want to mix voltages, but anything running on 12V (up to 14.4V) is safe to jump from another vehicle outputting 12 V (14.4V).  For instance, if you really needed to, then you could jump start your 50cc Razz scooter from a tractor trailer... as long as they were both 12V.  Here's another way to think of it.  The starter motor is just a load, much like your windshield wiper motor, cigarette lighter, radio, etc.  As long as it is provided a voltage somewhere near to its design voltage it will be okay. 

Amperage can be an issue if your charging system is not capable of cooling itself during long power supply periods.  I don't think we can hurt our alternators by overloading the system with lights/vests/heated grips/jump-starting a tractor trailer/etc., but some systems are not designed for continuous output at max load.  They are designed to peak temporarily, then back off to keep from overheating.

Camelman

[TwoTired]

Amperage can be an issue if your charging system is not capable of cooling itself during long power supply periods.  I don't think we can hurt our alternators by overloading the system with lights/vests/heated grips/jump-starting a tractor trailer/etc., but some systems are not designed for continuous output at max load.  They are designed to peak temporarily, then back off to keep from overheating.

I think our AC alternators are self limiting in power output.  They have a rated power they will deliver at optimum RPM.  If you exceed their current capability with a too-large load, the AC voltage droops limiting the power output.
Basically, the windings drain off electron collection from the magnetic flux lines faster than they can build to peak AC voltage.  This also shortens the conduction duration through the rectifier as the sinusoidal waveform peak flattens.
The summary is that the alternator simply won't deliver enough power to overload/overheat its stator windings.  In practice, overload the alternator and the battery drains until the ignition spark goes away.
I expect this is the likely reason why it is so rare that stator coils fail on the SOHC4 alternator.  They are far more likely to fail from mechanical/physical abuse than electrical.

[MötleyRöx]

The North Pole is now the South Pole.
The Equator is still in the middle, but now upside down.
Gravity, well?  Who knows?  We're all still here.
But, Santa's GPS took him to the wrong place!
At least he lives on an actual continent now.