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Author Topic:   Reversed Battery Cables
bkovak posted 12-08-2004 09:50 PM ET (US)   Profile for bkovak   Send Email to bkovak  
Well, I finally did the inevitable act of stupidity. I accidently connected the battery cables to the wrong terminals! It was getting dark and starting to rain and I was working on my 25 Johnson. I connected the negative cable to the positive terminal and the positive cable to the negative terminal. It sparked a bit and in less than a minute there was a loud hiss and a few white puffs of smoke came off of the coils or rectifier. I assume that I fried the rectifier, coils, or possibly the stator. Is this an accurate assumption and what is the best way to check this out and figure out what parts to replace without taking it to the dealer for an expensive repair service? I did not attempt to start it, just disconnected the crossed cables and stared in disbelief... Ideas anyone? Thanks, Brian
outrage freak posted 12-08-2004 10:11 PM ET (US)     Profile for outrage freak  Send Email to outrage freak     
Maybe not the starter. I think that when you do this the starter runs the oposite way. But you should be ok if you didn't try to start it. Now the coils are probably ruined.
wwknapp posted 12-08-2004 11:43 PM ET (US)     Profile for wwknapp  Send Email to wwknapp     
Start by tracking the smell of burned electonics. You got smoke, so something will smell. Though it may not be all that's fried.

Get your hands on the service tests for the components. That's really the only way to be sure. They are generally in the service manual.

On my motors there is a fuse that protects everything from this. It would blow. Check the circuit diagram.

Walt

Chuck Tribolet posted 12-09-2004 12:08 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Probably fried the rectifier, not the coil.


Chuck

jflots posted 12-09-2004 10:40 AM ET (US)     Profile for jflots  Send Email to jflots     
Dumb-*ss!

Just kidding Brian. That's in my long list of screw-ups.

kingfish posted 12-09-2004 10:52 AM ET (US)     Profile for kingfish  Send Email to kingfish     
That kind of smoke is normally kept under pretty high pressure, and it is usually pretty hard to get it to back in where it came from...
bkovak posted 12-09-2004 03:55 PM ET (US)     Profile for bkovak  Send Email to bkovak     
Thanks for the comments everyone. I'll start with replacing the rectifier and see if that takes care of it. Hopefully an easy fix and lesson learned... Brian
Chuck Tribolet posted 12-09-2004 05:35 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
You should be able to test the rectifier before you replace
it. Get a multimeter. Rectifiers conduct in one direction
but not the other. I don't know the pinout of this one,
but I'll bet someone does.

Kingfish: the hard part about getting the magic smoke back in
is finding a pair of really sharp tweezers to grab the
particles with before they all blow away. ;-)


Chuck

jimh posted 12-09-2004 08:52 PM ET (US)     Profile for jimh  Send Email to jimh     
Reversing the battery polarity is certain death for the rectifier. If the rectifier went to an open circuit it may have saved the stator. If the rectifier went to a short circuit, then the current was passed to the stator coils. They may be damaged, too.

If the battery did not blow the rectifier and melt the stator coils, it was not much of a battery. You should have discarded it long ago. On the other hand, it may have saved you an expensive repair.

There is no rectifier made that can withstand the current of a fully-charged 12-volt Group-24 battery into a dead short.

bkovak posted 12-09-2004 09:04 PM ET (US)     Profile for bkovak  Send Email to bkovak     
Thanks Jimh, I was afraid that may be the case as I have a brand new battery with a full charge. Could turn out to be an expensive lesson. Brian
wwknapp posted 12-09-2004 09:40 PM ET (US)     Profile for wwknapp  Send Email to wwknapp     
jimh:

Any diode with sufficient voltage rating could withstand a 12 volt battery, no matter how much charge it contained. The rectifier is just a set of diodes.

Some outboards seem to have a blocking diode just for this problem. I've always fumed that all such circuits were not so protected. Or that the rectifier diodes were not just a slight bit higher voltage rating so they would stop it. It's just poor design wherever it's found. Automakers seem finally to have gotten the word for at least some of their stuff, maybe the outboard manufacturers need a bit of a push to do it right. We are talking diodes that cost pennies to a manufacturer.

On my T9.9 the rectifier when I got it was a dead short, something I knew about. But the stator was unharmed, the dead short kept anything from the battery getting to it, shunting it into ground instead. Only a diode set that shorted across a stator coil rather than to ground would burn the stator. And then the fuse should blow first. At least my T9.9 has a fuse in the line. A 20amp for it's 10 amp charging setup.

I don't know if that applies to this motor. Sounds like it's not protected.

Walt

kingfish posted 12-10-2004 08:32 AM ET (US)     Profile for kingfish  Send Email to kingfish     
Chuck-

That's a roger - and as soon as you turn your back on a particle you've stuffed back in to go get another one, the furshlugginer thing slips back out again...it's nearly an impossible task-

Chuck Tribolet posted 12-10-2004 09:23 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Voltage rating on a diode is how much voltage they can
block in the non-conducting direction. Current rating is how
much current they can handle in the conducting direction.

No reasonable diode could withstand the CURRENT of a 12V
starting battery in the conducting direction. Jim is
right -- a backwards battery is going to pour current through
the stator and rectifier. The little speck of silicon in
the diodes of the rectifier is going to go before the beefy
copper wire in the stator.

I said no REASONABLE diode because there are some heatsunk
monsters that MIGHT. But if IIRC, they are about the size
of an outboard motor.

Putting a blocking diode in would cause a voltage drop of a
volt and a half or so (diodes are not perfectly conducting
in the conducting direction).


Chuck

jimh posted 12-10-2004 01:22 PM ET (US)     Profile for jimh  Send Email to jimh     
When the battery is connected in opposite polarity, the diodes in the rectifier will be forward biased and will lead to very high current flow.

Exactly how the diodes will react to the excessive current flow is hard to predict. Sometimes they blow apart into an open circuit or a very high resistance, sometimes they melt together into a short circuit with a varying amount of resistance but generally quite low.

In the course of working with solid state rectifiers since I was about nine years old, I have seen many different failures as a result of excessive current. I don't think you can predict the results. At least I have not seen pattern. The best result would be to hope for an open circuit, as this will tend to stop the current flow.

Well, really, the open circuit is usually the result, because if the current flow gets really excessive, as happens when the failure initially leads to a short circuit, the current usually generates so much heat that it ultimately burns up the conductor, producing the open circuit.

In any case, good luck with the repairs. If you are lucky it will be just the rectifier. The coils associated with it may have survived, but they may have absorbed some current and gotten warmer than usual in the process.

wwknapp posted 12-10-2004 01:27 PM ET (US)     Profile for wwknapp  Send Email to wwknapp     
Just think what a few cents worth of fuse could have done to those massive currents.

If the charging circuit on your outboard does not have a fuse I'd sure think about putting one. For next time.

Walt

bkovak posted 12-11-2004 08:24 AM ET (US)     Profile for bkovak  Send Email to bkovak     
Thanks Walt. A good idea for the fuse. Motor is a '95 Johnson with low hours. Would hate to screw it up from something so simple to prevent. Brian
wwknapp posted 12-11-2004 09:06 PM ET (US)     Profile for wwknapp  Send Email to wwknapp     
The automakers try to have no section of wire that's not protected by a fusable link, fuse or circuit breaker. And cars are metal. Our boats are much more easily burned, it's a good idea to emulate the automakers.

I don't know the Johnson circuit, on the Yamaha's I deal with a single wire comes out of the charging headed for the battery. That's where they put their fuse, before it joins the high amp starting circuit. It only has to deal with the rated charging ability that way. On my T9.9 they use a 20 amp fuse to protect the 10 amp charging circuit. So they do allow some margin. And they build a spare fuse holder in right next to it.

Be sure and check the full length of the wires going from battery to motor. If it's small in any of that it could have damaged insulation now. If it's a big wire for starting as well it's probably ok.

Walt

jimh posted 12-12-2004 10:38 AM ET (US)     Profile for jimh  Send Email to jimh     
In all outboards that I have seen, the charging circuit output is connected directly to the primary battery positive conductor under the cowling of the engine, without any fuse protection.

I don't think there is a fuse made that could pass the full charging current of 30-amperes or more with no significant voltage drop, and at the same time be able to open fast enough to protect a solid-state rectifier from the current flow that occurs when connected to the wrong polarity of a fully-charged battery.

When you connected that battery backwards, the diode was destroyed in a matter of a few milliseconds. No conventional fuse would be able to open that fast. If the link was fused, the fuse would only open after the diode was destroyed but was still conducting because it was now just a fused mass, not a diode anymore. This prolonged current would then heat the fuse element enough to open the circuit. That is sort of what happens inside the rectifier in an instant.

If you do this same thing in your car you will blow the diodes in your car's alternator, too. The fusible link is there to stop a fire from starting, not to protect the alternator diodes.

wwknapp posted 12-12-2004 08:53 PM ET (US)     Profile for wwknapp  Send Email to wwknapp     
jimh:

Obviously you have not looked inside a Yamaha F50 or T9.9. Both have fast blow fuses in the line between rectifier and starter terminals.

I expect quite a few other Yamaha's have fuses in the same location.

It might not protect the diode, but it would prevent the runaway current flow through the stator that you described. I'm certainly not going to test mine.

Walt

stefan posted 12-21-2004 10:13 AM ET (US)     Profile for stefan  Send Email to stefan     
I did the same thing a few yrs back with the mustang I had, trying to jump it my girl but the cables on one way at her battery, and I did the other way and next thing ya know-smoke!- but you're right-fortunately there was a fuseable link so I was a lucky man, and learned to tripple check....
Mumbo Jumbo posted 12-21-2004 09:55 PM ET (US)     Profile for Mumbo Jumbo  Send Email to Mumbo Jumbo     
I have a 150 two stroke Yahama (1999, I think). i took a battery out to charge it and reversed the cables when I re-installed the battery. When I turned the battery selector swich to "on", the resulting short melted all the battery cables, fried the switch, blew the fuse in the ignition switch, and blew a 30 amp fuse on the engine. After new cables were fabricated and installed correctly, a new battery switch installed, and the blown fuses replaced, the engine cranked instantly and has run for a year with with no problems. Although i am no marine engine expert, I attribute the lack of other problems in this episode to the protection afforded by the fuses placed at what appear to be stategic locations.
Chuck Tribolet posted 12-22-2004 12:12 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Mumbo: do you have TWO batteries?

Chuck

AZdave posted 12-22-2004 12:29 AM ET (US)     Profile for AZdave  Send Email to AZdave     
When I hooked my 30 hp Yamaha up with reversed leads, the fuse blew. I took it in to a repair shop that seems quite qualified. They found no other problems. I don't run it long enough to really see if the battery is being charged, so I'm not making an absolute claim that I got away free. I guess the message is that you should not assume that you have a certain set of blown parts until they are tested. Good luck. Dave
AZdave posted 12-22-2004 12:48 AM ET (US)     Profile for AZdave  Send Email to AZdave     
When I hooked my 30 hp Yamaha up with reversed leads, the fuse blew. I took it in to a repair shop that seems quite qualified. They found no other problems. I don't run it long enough to really see if the battery is being charged, so I'm not making an absolute claim that I got away free. I guess the message is that you should not assume that you have a certain set of blown parts until they are tested. Good luck. Dave
Mumbo Jumbo posted 12-22-2004 07:39 PM ET (US)     Profile for Mumbo Jumbo  Send Email to Mumbo Jumbo     
Chuck- I do have two batteries.
Chuck Tribolet posted 12-22-2004 07:55 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
With two batteries, one reversed, the current flow was taking
the path of least resistance -- through the other battery.
That's one reason why the diodes and alternator coil didn't
fry. The other may be that the 30A fuse was protecting the
25A alternator.

Musta been pretty impressive.


Chuck

Chuck Tribolet posted 12-22-2004 08:02 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
This reminds me of the circuit card for a new disk drive a
a while back. The very first time we powered the very first
card up: BANG. Blew the tops off a couple of ICs. We spent
about three hours chasing the bug, pouring over schematics,
scratching our heads, and were about go have a Coors design
session at the local pub when we (me, a software guy, actually)
figured out that the Y connector we'd hooked it up to the
power supply with has +12 and +5 reversed. I've still got
that cable somewhere, with a big red DO NOT USE tag on it.


Chuck

Mumbo Jumbo posted 12-22-2004 11:43 PM ET (US)     Profile for Mumbo Jumbo  Send Email to Mumbo Jumbo     
It was impressive, and scary. When I turned that battery selector switch from "off" to "Both" after putting in the battery, things began to happen quickly. The batteries immediately began to smoke with the corrosive stench of sulfuric acid, the switch knob and housing melted in an eyeblink, and I watched forlornly (from a distance with the fire extinguisher in my hand) as the insulation melted from the battery cables I had just constructed to aircraft quality standards. All my fine work in mess: battery boxes half melted, cables with the insulation melted off and the copper ashen grey, and the batteries and switches ruined. I just glad the Outrage didn't burn to the waterline. Anyway, I needed new batteries and an expensive reminder to not to do stupid things while in boats. The third set of cables was even better than the second.
Chuck Tribolet posted 12-23-2004 12:36 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
How long did it take the copper in the battery cables to
meltdown?
Mumbo Jumbo posted 12-23-2004 08:03 AM ET (US)     Profile for Mumbo Jumbo  Send Email to Mumbo Jumbo     
The copper didn't melt. It, for the lack of a better description, "fried" The strands were separated, brittle, and were covered with an grey powder. The cables were intact, in a sense, but when I removed them they seemed less heavy than before (even considering the loss of the plastic insulation) -but that may have just been my imaginaion. My guess is that the entire episode took less than 90 seconds.
jimh posted 11-10-2005 09:03 AM ET (US)     Profile for jimh  Send Email to jimh     
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