Unkown eletrical issue - could use some vetaran help

2611 Views 12 Replies 9 Participants Last post by BillWilliam, Oct 24, 2010

jx_waine

Discussion Starter · Oct 22, 2010

Hello all,
So I have spent the summer attempting to convert my first car. To say it was an up and down battle would be an understatement. That being said, I thought I finally had everything working and had the vehicle towed to a shop for certification. The vehicle started fine this morning and I drove it the length of my drive-way to the tow truck (I have been able to drive it around my property for a few weeks now). After arriving at the shop (10 minutes later), the car was dead. After doing a bit of inspecting I realized that the auxiliary battery was low. I borrowed a voltmeter form the shop and it read 2.6V. I had it charged and then everything seemed to work fine. After a few minutes though I began to smell burning. The emergency break cable was melting under the car. I dis-connected the 12V and it stopped. Has something like this ever happened to anybody? Does anyone have any ideas?. The e-break cable got so hot that one of the two cables going to the rear tires won't release anymore. Again, I haven't had this issue before. I strongly suspect that on the way there (it was a bumpy ride) something touched or created a short for the 12V battery. That being said, I don't even know where to start looking. I am gonna take the panel out from under the steering wheel and start there. I was just hoping somebody could shed some light on this or if anybody has some ideas? Thanks in Advance.

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dimitri

· #2 · Oct 22, 2010

You are talking about a hand brake cable that is pulled via the handle and it links mechanically to calipers on the rear wheels, right?

If so, what does it have to do with electrical systems at all? How can you possibly have electric current flowing thru this cable to a point of burning?

If this is in fact draining 12V battery, it would need a direct electrical contact from the battery positive, bypassing any fuses, to touch the brake cable at some point. I can't even imagine how such thing can be possible.

BTW, if you battery got drained to 2V it probably won't live much longer, so once you resolve this issue, you might want to get a new 12V battery so you don't get stranded on the road.

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jx_waine

Discussion Starter · #3 · Oct 22, 2010

It is in fact a manual cable and has nothing to do with anything electrical or any part of the conversion. That is why it is so confusing. The only thing I can imagine at this point is that the starter wires that used to start the starter motor may have touched something that eventually led to that cable via the frame or something? I have them tapped off but I can't think of anything else.

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GerhardRP

· #4 · Oct 22, 2010

jx_waine said:
It is in fact a manual cable and has nothing to do with anything electrical or any part of the conversion. That is why it is so confusing. The only thing I can imagine at this point is that the starter wires that used to start the starter motor may have touched something that eventually led to that cable via the frame or something? I have them tapped off but I can't think of anything else.

Put a resistor in line with the battery and then search for downstream voltages and ways to change it by moving various items.
Gerhatd

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DIYguy

· #5 · Oct 23, 2010

crawl under the car... follow the brake cable from one end to the other and find out where it is contacting a 12 volt positive conductor.... it can't be more than that.

Then find someone to kick you for messing up! lol

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EVfun

· #6 · Oct 23, 2010

One possibility is that the cable is providing a missing ground. This sometimes used to happen starting a car with a missing engine ground strap. You could try and determine what part of the cable got hot. The heat will only extend a short distance past the section that has been carrying current.

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dezellis

· #7 · Oct 23, 2010

EVfun said:
One possibility is that the cable is providing a missing ground. This sometimes used to happen starting a car with a missing engine ground strap. You could try and determine what part of the cable got hot. The heat will only extend a short distance past the section that has been carrying current.

Hi,
I second what EFfun has suggested. This is definitely the problem, he beat me to posting the solution.

Similar symptoms with normal ICE vehicles, starter motor very slow and mechanical cables getting very hot = earth lead to engine loose or missing.

Headlights very dim but starter motor strong would be loose or missing earth lead to vehicle body.

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poprock

· #8 · Oct 23, 2010

Hi; Have experienced this in an ice engine change when forgetting to re-connect battery to engine to chassis. Ditto the previous answers.

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dimitri

· #9 · Oct 23, 2010

I still don't understand how brake cable completes the circuit, even if it becomes the missing ground connection. Obviously one end of the cable is connected to a caliper and that is how it grounds to the chassis, but how the heck does the other end of the cable gets into the circuit?

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EVfun

· #10 · Oct 23, 2010

Generally the engine (motor) and transmission are not grounded very well on their own because of the rubber motor and transmission mounts. The e-brake cable may be riding the bell housing or sometimes the cables are supported with loops on the transmission crossmember. They are steel, so not a great conductor. It doesn't take all the much current to make them hot.

With a ICE car this raises hell with the starter motor and alternator that are grounded to the engine. With an EV I'm am at a bit of a loss as to what would be trying to use the motor or transmission as a ground for more than milliamps. Still, I thought this should be thrown out there, after all, some EVs do retain the ICEs alternator.

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dezellis

· #11 · Oct 24, 2010

dimitri said:
I still don't understand how brake cable completes the circuit, even if it becomes the missing ground connection. Obviously one end of the cable is connected to a caliper and that is how it grounds to the chassis, but how the heck does the other end of the cable gets into the circuit?

Hi,
You mentioned the auxilliary battery; this I assume is supplying headlights etc all of which use ground or earth as the return to the battery. One side of the battery; normally negative is earthed or connected to the car body. Somewhere in your auxilliary circuits the return path to the battery for one or more of the auxilliary circuits is a lower resistance via the brake cable than via the path it should take which is normally through the car body.
The usual culprit in a normal ice car is a loose or mising ground or earth connection to the engine or to the car body.

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Salty9

· #12 · Oct 24, 2010

I fried 2 throttle cables on an old jeep I had before I realized that the ground strap to the engine was broken.

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BillWilliam

· #13 · Oct 24, 2010

Hi xj waine,
As others have pointed out the e brake cable is providing a circuit it should not. The solution may be easy or not. Go through each wire through out the car and look for contact with some metal part of the car. Correct any problems. Then look at the common electrical conductors aka "grounds" and check each system for proper connection with a multimeter. If the circuit is active, pulling power, set the multimeter to DC Volts and place one probe on one side of the connection and the other on the other conductor. Paint, corrosion and holding the probes wrong can all cause false readings, check several times until you get a consistent reading. This should be a small fraction of a volt, or a few volts on high current connections. Do not use the ohm setting on any connection that may have power on it or go buy another multimeter.

Make sure all power systems use the same, positive or negative common or ground. For the high current, motor power wiring use separate ground wires of the same size as the positive wires. Using the steel chassis may result in more problems. Be patient, check twice or until you are sure you have found the problem. Have someone watch you. Even if they are not an expert you can explain what you are doing and why and this interaction will help you find new tests and solutions to your problem. Some times called "brainstorming", this is different from BS sessions often conducted with some fermented beverage. This is what you do after it is fixed.

If you have more details just ask. I'm old, retired, bored and helping others makes me happy.

I also have 35 years as a mechanic on everything from autos to the most advanced helicopters, to the oil field. Then I got an engineering degree to get out of the oil field.

That did not work. Then I worked for an oil well service co. looking at the formation while drilling, off shore. Think Deep-water Horizon only 15 years ago.
Good luck i will be starting my PHEV in a few months. I have a 1990 Miata in the drive just waiting...

Bill

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