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75 Westy FI noob Samba Member
Joined: November 04, 2022 Posts: 433 Location: MidWest
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Posted: Sun Jun 11, 2023 10:49 am Post subject: Electrical fire in Alternator when installing battery |
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When I connect my newly charged battery … sparks fly at the negative terminal and my alternator immediately begins to flambe.
Smoke pours from the front of the alternator, and it’s definitely electrical.
I havent changed any main wires.
Ive only cleaned up the connections on the new brake lights.
I was at the finish line (brake lights was the last thing)
Now im at the starting line.. flippin electrical fire and a lost alternator.
i dont understand how it could happen . |
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alman72 Samba Member
Joined: October 09, 2014 Posts: 2575 Location: MICHIGAN
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Posted: Sun Jun 11, 2023 11:12 am Post subject: Re: Electrical fire in Alternator when installing battery |
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these old vws have funky colors on the cables. confirm what you thought was negative is bolted to the body. i think i had clear and black? and black was positive. |
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Abscate  Samba Member
Joined: October 05, 2014 Posts: 23796 Location: NYC/Upstate/ROW
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Posted: Sun Jun 11, 2023 11:12 am Post subject: Re: Electrical fire in Alternator when installing battery |
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Either positive on the alternator is touching ground ( common) or you reversed polarity. Double check battery connections. Red is not positive. _________________ 🇺🇸 🇺🇸 🇺🇸 🇺🇸 🇺🇸 🇺🇸 🇺🇸 🍊 🍊 🍊 |
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75 Westy FI noob Samba Member
Joined: November 04, 2022 Posts: 433 Location: MidWest
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Posted: Sun Jun 11, 2023 11:15 am Post subject: Re: Electrical fire in Alternator when installing battery |
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Thanks guys… i will double check the polarity.
I was focused on the batt platform, may have gotten them flipped.
Think the alternator is toast? |
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Abscate  Samba Member
Joined: October 05, 2014 Posts: 23796 Location: NYC/Upstate/ROW
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Posted: Sun Jun 11, 2023 11:17 am Post subject: Re: Electrical fire in Alternator when installing battery |
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75 Westy FI noob wrote: |
Thanks guys… i will double check the polarity.
I was focused on the batt platform, may have gotten them flipped.
Think the alternator is toast? |
If polarity got flipped the diodes go but the rest of the alternator is fine _________________ 🇺🇸 🇺🇸 🇺🇸 🇺🇸 🇺🇸 🇺🇸 🇺🇸 🍊 🍊 🍊 |
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75 Westy FI noob Samba Member
Joined: November 04, 2022 Posts: 433 Location: MidWest
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Posted: Sun Jun 11, 2023 11:32 am Post subject: Re: Electrical fire in Alternator when installing battery |
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I double checked my battery… i had the leads right.
Ground was to Negative like it should be etc.
I haven’t messed w the alternator wires. Those are all bundled and in the case. I dont see how it could get grounded. cars been a peach.. starts and runs well. just needed brake lights. Yesterday i removed the battery to charged it. installed the brake lights. Cleaned a ground connection inside engine door on the right. and put the battery back in today. immediate smoke. No key.
Btw, tail/brake lights still dont work. |
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crownline Samba Member

Joined: September 10, 2010 Posts: 609 Location: Northwoods of WI
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Posted: Sun Jun 11, 2023 11:44 am Post subject: Re: Electrical fire in Alternator when installing battery |
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Check the terminal posts for the correct length. Compare to original alternator. If the posts touch the tin=ground _________________ 1972 Bus 1700 cc Single Carb. But not a progressive.
Barelymuvin
Wish I still had the ones I got rid of.
"It"s got some dings and dents and neither of us is going to SEMA."(Update, I went to SEMA in 2019 but the Bus stayed home)
[url=http://www.vw-mplate.com/mplate-8446.png]Click to view image[/URL] |
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75 Westy FI noob Samba Member
Joined: November 04, 2022 Posts: 433 Location: MidWest
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Posted: Sun Jun 11, 2023 11:49 am Post subject: Re: Electrical fire in Alternator when installing battery |
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Abscate wrote: |
75 Westy FI noob wrote: |
Thanks guys… i will double check the polarity.
I was focused on the batt platform, may have gotten them flipped.
Think the alternator is toast? |
If polarity got flipped the diodes go but the rest of the alternator is fine |
I’ve just come out to test the battery to see if it was overcharged or something. But it is 11.7 V. The really interesting thing is that it does seem to be reversed off of what’s marked. So if I put the red on the positive and the black on the negative, I get a negative voltage reading if I put the black on the positive + in the red on the negative terminal I get a positive voltage
Maybe i reverse the cables when i charged it? It was a long Saturday.
Shows -11.7 V now if test red to +. Or 11.7 V if i out the black meter lead on the +. |
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sjbartnik Samba Member
Joined: September 01, 2011 Posts: 6041 Location: Brooklyn
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Posted: Sun Jun 11, 2023 12:45 pm Post subject: Re: Electrical fire in Alternator when installing battery |
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Forget about red and black. Cable color does not matter.
From the factory there is no red main battery cable. The + cable was black, and the negative cable was a woven copper strap.
The positive is the one with the wires that got to the starter and up front to the fuse box.
The negative is the one where the other end is bolted directly to the body next to the battery.
Sounds to me like you connected the battery up backwards. _________________ 1965 Volkswagen 1500 Variant S
2000 Kawasaki W650 |
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Abscate  Samba Member
Joined: October 05, 2014 Posts: 23796 Location: NYC/Upstate/ROW
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Posted: Sun Jun 11, 2023 12:53 pm Post subject: Re: Electrical fire in Alternator when installing battery |
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It’s not only reverse polarity, 11.7 Volts is A dead battery _________________ 🇺🇸 🇺🇸 🇺🇸 🇺🇸 🇺🇸 🇺🇸 🇺🇸 🍊 🍊 🍊 |
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75 Westy FI noob Samba Member
Joined: November 04, 2022 Posts: 433 Location: MidWest
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Posted: Sun Jun 11, 2023 12:54 pm Post subject: Re: Electrical fire in Alternator when installing battery |
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Got that … it was connected correctly.. positive to the +
But, my battery itself seems to be reversed polarity.
I seem to have reversed it when I charged it overnight. |
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Alan Brase Samba Member
Joined: March 28, 2004 Posts: 4570 Location: Cedar Falls, Iowa
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Posted: Sun Jun 11, 2023 1:34 pm Post subject: Re: Electrical fire in Alternator when installing battery |
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You charged the battery backwards. Once it is dead, lead acid doesn't have any memory. Drain it to totally dead. with lights or something. then hook charger up correctly.
You killed the alternator. _________________ Al Brase
Projects: 67 sunroof bug, 67 Porsche 912 Targa, 70 Westy
Dec 1955 Single Cab pickup WANT 15" BUS RIMS dated 8/55, thru 12/55
To New owners: 1969 doublecab, 1971 Dormobile
Vanagons:
80 P27 Westy JUL 1979, 3rd oldest known US
83 1.6TD Vanagon, 87 Wolfie Westy daily driver, swap meet home |
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Wildthings Samba Member

Joined: March 13, 2005 Posts: 52300
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Posted: Sun Jun 11, 2023 4:58 pm Post subject: Re: Electrical fire in Alternator when installing battery |
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Don't really know how much of a life one would get from a battery that had been charged backwards, while you could run it down using a headlight or other moderate load and then recharge it to the correctly polarity, I would tend to spend the money to buy a new one. Hate to be stuck on the side of the road over a few dollars saved, while a battery blowing up could end your Transporter Joy. |
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75 Westy FI noob Samba Member
Joined: November 04, 2022 Posts: 433 Location: MidWest
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Posted: Sun Jun 11, 2023 6:33 pm Post subject: Re: Electrical fire in Alternator when installing battery |
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I got a new one.. put it in. Saw some sparks connecting the - .. and i think the Alt even jumped… but no smoke. And the tail light, tag light, and blinkers now work.
Im hoping the Alt will sill work. Slim chance I guess. |
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Wildthings Samba Member

Joined: March 13, 2005 Posts: 52300
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Posted: Sun Jun 11, 2023 9:08 pm Post subject: Re: Electrical fire in Alternator when installing battery |
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75 Westy FI noob wrote: |
I got a new one.. put it in. Saw some sparks connecting the - .. and i think the Alt even jumped… but no smoke. And the tail light, tag light, and blinkers now work.
Im hoping the Alt will sill work. Slim chance I guess. |
There is a very good chance your new battery will be dead in a day or so. You should keep the battery disconnected until you are 100% sure the alternator isn't draining it to nothing. |
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75 Westy FI noob Samba Member
Joined: November 04, 2022 Posts: 433 Location: MidWest
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Posted: Mon Jun 12, 2023 7:51 am Post subject: Re: Electrical fire in Alternator when installing battery |
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Wildthings wrote: |
75 Westy FI noob wrote: |
I got a new one.. put it in. Saw some sparks connecting the - .. and i think the Alt even jumped… but no smoke. And the tail light, tag light, and blinkers now work.
Im hoping the Alt will sill work. Slim chance I guess. |
There is a very good chance your new battery will be dead in a day or so. You should keep the battery disconnected until you are 100% sure the alternator isn't draining it to nothing. |
so, the damaged alternator will now drain the battery bc it's short circuited.
i guess that would explain the sparks. ha
I just put the flippin tins back on. was ready to roll. now i gotta change the alternator... not so easy to access. any recommendations? will one from autozone work or are these peculiar in size/specs?
think the voltage regulator is toast too ? |
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W1K1 Samba Member

Joined: March 04, 2004 Posts: 5288 Location: Southern AB
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Posted: Mon Jun 12, 2023 8:18 am Post subject: Re: Electrical fire in Alternator when installing battery |
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if you have a local motor rewind shop, you can take it in and have it tested and repaired if you just fried the diode or the internal regulator _________________ http://www.thesamba.com/vw/archives/manuals/jim_martin_engine_build.php
1973 super
1965 squareback 1500E
1971 bay window westy- subi swap |
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Alan Brase Samba Member
Joined: March 28, 2004 Posts: 4570 Location: Cedar Falls, Iowa
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Posted: Mon Jun 12, 2023 8:34 am Post subject: Re: Electrical fire in Alternator when installing battery |
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W1K1 wrote: |
if you have a local motor rewind shop, you can take it in and have it tested and repaired if you just fried the diode or the internal regulator |
this is almost ALWAYS a better idea. If the fields are not burned but they might be.
But mom and pop local shops are becoming rare.
BTW all modern alternators have 6 diodes. (3 phases, one plus and one minus for each, wired in a bridge.)
Modern parts store rebuilts source their cores from all over and the quality varies wildly.
These old ones do not have internal regulators, rather a small box with a 3 wire harness that plugs on. _________________ Al Brase
Projects: 67 sunroof bug, 67 Porsche 912 Targa, 70 Westy
Dec 1955 Single Cab pickup WANT 15" BUS RIMS dated 8/55, thru 12/55
To New owners: 1969 doublecab, 1971 Dormobile
Vanagons:
80 P27 Westy JUL 1979, 3rd oldest known US
83 1.6TD Vanagon, 87 Wolfie Westy daily driver, swap meet home |
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75 Westy FI noob Samba Member
Joined: November 04, 2022 Posts: 433 Location: MidWest
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Posted: Mon Jun 12, 2023 10:14 am Post subject: Re: Electrical fire in Alternator when installing battery |
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Wildthings wrote: |
75 Westy FI noob wrote: |
I got a new one.. put it in. Saw some sparks connecting the - .. and i think the Alt even jumped… but no smoke. And the tail light, tag light, and blinkers now work.
Im hoping the Alt will sill work. Slim chance I guess. |
There is a very good chance your new battery will be dead in a day or so. You should keep the battery disconnected until you are 100% sure the alternator isn't draining it to nothing. |
I just checked my battery.. it’s still 12.6 … and it’s been about 16 hrs since I put it in.
So perhaps Alt didnt melt to such a bad extent?
I havent run the motor yet to see if the Alt is sending a charge. |
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mikedjames Samba Member

Joined: July 02, 2012 Posts: 3305 Location: Hamble, Hampshire, UK
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Posted: Mon Jun 12, 2023 11:35 am Post subject: Re: Electrical fire in Alternator when installing battery |
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Until you run the engine you will not know about the alternator.
However - if you disconnect the positive feed from the battery to the alternator, and disconnect the regulator from the alternator so nothing else is connected.
Then put your meter on diode test and connect the positive lead to ground, and the negative lead to the battery B+ connection of the alternator, it should read about 1 to 1.4 volts drop - being two diodes in series.
This is also true for the warning light D+ connection, it too should read 1 to 1.4 volts drop on diode test.
If both of these show about this voltage drop on diode test, then it is likely that at least two of the six diodes in the main B+ rectifier are good, and the same for the D+ terminal.
If you connect the battery backwards (or a reverse charged battery) and the alternator was smoking then you probably blew the diodes in the alternator.
These are replaceable but there is a reasonable amount of work hours to get at them and replace them.
I blew a Hitachi alternator on my boat engine connecting a battery the wrong way with jump leads -- and was able to replace the diode pack inside . _________________ Ancient vehicles and vessels
1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.
1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy |
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