Lotus Elan

Battery connection accidentally reversed.

PostPost by: fireblade » Thu Feb 18, 2016 4:38 pm

I have just connected a new Exide Excell 12v 44 Amp battery to my 69 Lotus Elan SE DHC replacing a Exide Excell 38 Amp and I think I may have committed a fatal error and accidentally reversed the connections. On connecting the second terminal I noticed a small spark followed by a 'frying noise' from the front of the car. On looking towards the engine compartment a plume of smoke poured from the area of the fuse box.The connection would have been for just a few seconds as panic set in and I reacted very quickly and disconnected the battery. I expected a fire but but luckily I got away with it.
The car was professionally rewired many years ago to incorporate a fuse box with 12 fuses and 4 relays. On stripping off the black insulation on the wiring harness it became clear only one cable had fried and amazingly all the other cables are undamaged. The cable affected is a fairly heavy duty Brown lead which is connected to a 'Buzz Bar' or common connection to one side of all the fuses in the box. This cable I have traced back through the bulkhead/firewall and links up with the hidden under dash cut out switch.
So what I would like to know what other damage I might have done to any components. I imagine the alternator would not have liked this and I have probably killed it off. Bearing in mind I thought I connected the new battery correctly but we all make mistakes and having played about with cars for 50 years this is a first for something like this happening to me so Is all the above symptomatic of a wrongly connected battery.
Also why was there no fuse protection to protect this from happening.
Hopefully I have got away lightly and will replace the frazzled cable but I am terrified to connect the battery up again.
Your valued comments would be greatly appreciated.
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PostPost by: CBUEB1771 » Thu Feb 18, 2016 4:50 pm

I did exactly the same thing many years ago and encountered precisely the symptoms you describe. I recall having to repair one or two connections but otherwise there was no damage. My alternator was not damaged, I think the diode rectifier bridge probably protected it. Most of the electrical devices in your Elan are not sensitive to polarity and most were probably isolated by having their switches in the off position at the time. I doubt that you have created any serious damage but just go though the system carefully, switching things on and off one at a time.
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PostPost by: billwill » Thu Feb 18, 2016 5:30 pm

That brown wire is the main feed (I think) from the battery to ALL of the circuits except the starter motor. It should go to the pickoff point on the starter solenoid, but your circuit is non-standard.


The output of the alternaator is connected directly to that lead, but in the alternator are diodes that normally ensure that current flows only from the alternator to the battery, not vice versa ... UNLESS YOU REVERSE THE BATTERY.

I expect that you have blown the diodes and excess current was flowing from the battery into the Alternator. It is probably toasted.

Sad to say if the ignition switch was in the on position, you may also have wrecked your rev counter. But not much else is polarity sensitive.

Radios often have a diode connected straight accross the 12v supply, normally this does nothing, but if you reverse its supply the diode conducts heavily and blows the radio fuse. Hopefully this prevents damage to the rest of the radio as it is exposed to only a low reverse voltage.
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PostPost by: stugilmour » Thu Feb 18, 2016 6:07 pm

As Russ says, the Elan wiring is simple enough you are hopefully OK. I see Bill posted similar info while I was typing. :D

In the standard wire colour scheme brown is "Hot at All Times, Unfused". Typically it is the main power to the whole loom, and also carries the charging current from the alternator. In the standard Elan wiring scheme it is not protected. When I re-wired my Plus 2, I adopted the modern practice, which places a high wattage fusable link between the main positive terminal on the starter solenoid and the rest of the loom. I think you are better off in the Elan configuration; some variants of Plus 2 run a Brown main on the dash to the ammeter. Anyway, make sure you examine all the Browns for damage; one goes to the ignition switch.

Trying to think through how the short circuit would be completed in the reverse direction. Only thing I can think of is blowing out the alternator diode pack and creating an internal short. Might be prudent to remove the alternator and have it bench tested? If you do opt to start the car without removing and checking the alternator, place a volt meter across the battery. Have an assistant gently rev the engine up and down. If you see fluctuating charging voltage above about 14 volts there is an issue. When the alternator failed in my Esprit it would surge to 18 volts when revved.

Depending on the type of relays used there can be a consequence to reverse connection. Assuming they are OK though if nothing was turned on while connecting the battery. Anyway, modern Bosch style relays often have a diode across the winding to prevent reverse surge. Take a look at the little diagram printed on the relay body to see if the diode is shown. Again, they should be fine if nothing was turned on.

HTH. Let us know how you get on. Jeff may move your thread to the electrical section.

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PostPost by: Hawksfield » Thu Feb 18, 2016 10:36 pm

fireblade

What makes you think you have reversed the polarity ? are the two batteries the same pole orientation or not clearly marked. did you fit the battery around the wrong way.
It sounds very much like you have fried something, but first establish how it was reversed if it has been.

Good luck
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PostPost by: RichardHawkins » Fri Feb 19, 2016 2:15 pm

Fire blade,

I am struggling to find an image of the battery you bought. Most batteries have conical terminals of different diameter positive and negative, making it difficult to connect the wrong way round. Are you sure you got it wrong?

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PostPost by: denicholls2 » Fri Feb 19, 2016 2:49 pm

RichardHawkins wrote:I am struggling to find an image of the battery you bought. Most batteries have conical terminals of different diameter positive and negative, making it difficult to connect the wrong way round. Are you sure you got it wrong?


Richard's input was my first thought. At least in modern batteries, the connections are relatively idiot-proof. And if not, given the odd mix of negative and positive earth configurations that is always associated with British cars, you ought to seriously consider setting your battery connections to the right standard relative to a specific modern battery.

That said, I cast my lot with Russ if your ignition was off, possibly as far as Bill if on. I would not expect alternator damage. The smoked cable was ultimately caused by a connection of positive current to ground. And anything in that path to earth had a potential of 50 or so amps to work with.

My own experience with this was helping a neighbor jump-start his MG. There was a large spark on connection and the cables got much warmer than usual while cranking. Then light dawned and I realized the MG is a British car. :? Once cooled down and configured properly, everything was fine. We were connected for much longer than 4 seconds, but I think the MG had a mechanical tach. Note that the dash regulator does limit the current flow to the tach so it should withstand brief bouts of reverse current.
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PostPost by: billwill » Fri Feb 19, 2016 4:45 pm

On an Elan the dash 10v stabalizer is NOT connected to the rev counter.

Rev counters have their own internal stabalizer a Zener diode. If connected wrong way around the zener might behave just like the protective diode in a radio, but bot necessarily.
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PostPost by: Chancer » Fri Feb 19, 2016 6:34 pm

denicholls2 wrote:
I would not expect alternator damage. The smoked cable was ultimately caused by a connection of positive current to ground. And anything in that path to earth had a potential of 50 or so amps to work with.


I would, for exactly the reason given, one pair of diodes in the bridge rectifier would easily carry the 50 amps when connected backwards.
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PostPost by: billwill » Sat Feb 20, 2016 12:55 am

To burn out the brown wire will take lots more than 50 amps. When an alternator is charging a flat battery, up to 50 amp flow would be quite normal.

Since it did burn it implies that the current that occurred was a lot bigger than 50 amps.
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PostPost by: bob_rich » Sat Feb 20, 2016 11:12 am

Hi Fire blade

Sorry to read about the battery reversal problem despite different connectors it is easily done. If you suspect the alternator, and the wiring is not burnt though, then I would disconnect the alternator lead at the alternator and connect on to the alternator a reasonable power bulb (half of a headlamp main / dip for example I keep half damaged bulbs as suitable loads for this type of test). Leave the alternator control lead that is fed from the ignition warning light in place. Start the car and if the alternator lights the bulb ( and combine with a check on a voltmeter if you have one) then I suspect the alternator would be OK. If you have a DVM then the bulb should see around 13.5 to 14V if the alternator is OK and the regulator module in it has survived.

I think that in most cars, old or new, that the alternator main terminal is connected to the battery live. Reversing the terminals of the battery means the battery will discharge through the diodes and the alternator armature winding in series . I suspect this would probably be less than 120A and for a short duration the diodes may just cope with this.

hope this helps and you get it sorted

regards

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PostPost by: fireblade » Mon Feb 22, 2016 8:18 pm

A very big thank you for all the responses to my battery dilemma and I have taken on board all your valued comments.
The new battery did in fact have the terminals the opposite way round to the old battery and i was very much aware of this when fitting. I decided, as it had been recommended for the Lotus ,to go ahead repositioning the battery leads.......job done. i obviously was not paying enough attention and got it wrong.
The ignition was lucky for me in the off position so the instruments should have escaped any damage.
i have sourced the correct replacement Brown cable and hope to replace this later this week.
Will give you an update later this week.

Kind regards

Roger
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PostPost by: fireblade » Tue Mar 15, 2016 12:19 pm

As promised an update on my problem with an incorrectly connected new battery in my 69 Lotus Elan S4 SE. I am more baffled than ever and seem no closer to sorting out my error.
I duly replaced the 'cooked' brown cable........ to remind you this is the cable that runs from the fuse box and joins the main thick heavy duty cable that runs from the negative terminal on the battery and joins the starter solenoid via the under dash isolation switch and is connected to a terminal on the iso switch (I think this is standard fitting?). On reconnecting the battery I turned on the ignition and the red ignition light came on. After a few seconds I observed wisps of smoke rising up from the Alternator so quickly disconnected the battery and concluded the Alternator had been damaged when I originally incorrectly connected the new battery.
So i replaced the Alternator with an identical new one. Connected up the battery terminals again and within 2-3 seconds there was a pop/spark from the fuse box. I purposely left the fuse box loose in the engine compartment after soldering in the replacement brown cable so I could monitor what was going on. I was amazed to see the new brown lead had detached itself from where I had soldered it in to the connection in the fuse box. The brown lead was quite hot but had not been damaged. i am now paranoid about re connecting the battery again and wonder where I go from here. I have double checked the other cables in the wiring loom alongside where the original brown cable had cooked and luckily they are all intact and not damaged. It occurs to me i must have damaged some other component by the accidental reversal of the battery that is causing a short circuit. Your observations are much appreciated.
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PostPost by: billwill » Tue Mar 15, 2016 1:32 pm

Suggestions.

Get an ammeter & find out how many amps are being drawn from the battery. You can do this by connecting the ammeter in the +12V lead at the battery; you need only connect long enough to see the reading.

Remove all fuses in the fuse box and repeat the measurement. Did it go down, replace fuses one by one to try find which circuit has a short.

If you have a radio its safety diode might have burned out.

The alternator often has its two output wires strapped together in one 'loom' the insulation within might have methed letting the two wires touch each other. This would be a complete short circuit accross the battery.
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PostPost by: Chancer » Tue Mar 15, 2016 3:02 pm

Most multimeters only measure dc current in a 200ma, 10 or 20 amp range, a short circuit that can melt insulation and maybe even a soldered joint is at best going to blow the meters internal fuse if it has one, at worst send the meter up in smoke if connected in series

I would use the resistance/continuity function on the meter to look for the short circuit, disconnect alternator, remove all fuses, test and if open circuit (high/infinite resistance) then reconnect each in turn and check the result.
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