What can you cook if you hook the battery up backwards when boosting?

[davepl]

I gave a friend a jump-start today and on the dead vehicle he hooked the cables up backwards. Fortunately it was completely dead, which is probably better, but there was still some sizzling, but no smoke. Sat that way maybe 4-5 seconds I'd say. I generally prefer people to hook up their own end but that didn't pan out today!

The key was OFF at the time in the problem vehicle.

Afterwards, once connected properly, the car wouldn't start because the electric fuel pump wouldn't run, so that's a sign something went wrong somewhere. Gauges, lights, everything seems to work except the fuel pump.

My car, which was running at the time, appears ok (at first the ALT light was on but there's a wiring issue because it was actually due to the parking brake being on), everything seems to work.

What would have cooked on the car being boosted that was hooked up backwards? Would you roast a fusible link, or would it not cause damage at all?

Thanks
Dave

[truckster]

I had someone do that once when I stopped by the side of the road to help them. A hundred miles later my alternator was toast.

[HO455]

There is no one answer to this as it will depend on make and model of a vehicle, not to mention the condition of its components. I jumped a guy years ago and had him hook up the cables to his Dodge Dart. Within seconds most of the harness on the Dart was smoking. After unhooking and reconnecting correctly his car would not start. My GTO was undamaged. Just lucky or maybe superior GM engineering.

[Gmc.guy]

Someone did that to me once too. It burnt the fusible links at starter and the firewall block. I replaced them and all was good. After that the ammeter pointed straight down and didn't change at all any of the time. I changed the guage after checking the little inline fuses and they were good. Just burnt up the guage.

[davepl]

I hope it is just a fusible link but the fuel pump controller goes right to the battery, even though the trigger wire was OFF, the main connection still runs through the controller. Hopefully there's a fuse or fusible link in there, otherwise he'll be replacing that expensive controller at a minimum.

In my own cars I usually use an auto-reset breaker for those heavy circuits. Wonder how they would respond in that situation? Just pop and save or would they hurt or be hurt?

Moral of the story? Flashlight! At least he didn't blow up the battery inside a storage unit with no eye wash station, could have been much worse...

[raggedjim]

Dead battery, fuel pump not working, which came first??? Maybe his battery was dead because he had a bad fuel pump and kept cranking it until he drained the battery?

I NEVER get a straight answer when I ask questions like this...

[davepl]

Originally Posted by raggedjim

Dead battery, fuel pump not working, which came first??? Maybe his battery was dead because he had a bad fuel pump and kept cranking it until he drained the battery?

I NEVER get a straight answer when I ask questions like this...

Straight answer is the car drove to and parked at that location, then was left for 6 months, so that safe bet is that the dead battery came first.

[raggedjim]

Sorry, I meant to say I never get a straight answer from my wife and son!

He may want to check the wiring back to the fuel pump. My wife's Jeep sits a lot in the winter and when it wouldn't start I found a squirrel had chewed through the fuel pump wires!

Good luck, Rg

[Steeveedee]

If you jumped a truly dead battery, you probably dodged a bullet. If his battery was fully charged, you would probably be looking at popped diodes in your alternator, or a trashed regulator.

[In The Ten Ring]

What can you screw up? Let's see:

Fuses
Alternator
Battery (and by that I mean your face gets some sulfuric acid).
Computer (I suspect)

Positive always goes on first and comes off last and NEVER trust the other guy to have a brain (if he did he'd be the one jumping you).

My Honda Accord manual (1988) recommended red clamp to positive post, black clamp to metal on engine bay.

[davepl]

I'm still not clear (Hello, VetteVet?) on why sending current backwards through a circuit would blow things up that are otherwise OK with forward current. I can see them not working, but...

Why does sending current through a fusible link (or pump controller) backwards wreck it? Seems like it should just be the same amount of heat and resistance in either direction. Do voltage dividers become voltage multipliers or something?

[harpo231]

Because it is direct current to ground>>>>A DEAD SHORT

[HO455]

Originally Posted by davepl

I'm still not clear (Hello, VetteVet?) on why sending current backwards through a circuit would blow things up that are otherwise OK with forward current. I can see them not working, but...

Why does sending current through a fusible link (or pump controller) backwards wreck it? Seems like it should just be the same amount of heat and resistance in either direction. Do voltage dividers become voltage multipliers or something?

Sending current through a fuse backwards is not an issue. (A fuseable link is just a different form of a fuse) The problems come from when electronic components are involved and when they allow a high level of current in an unintended manner which may cause a fuse blow. Voltage regulators and pump controllers generally use some form of diodes or transistors to turn current flow on and off as needed. Without going into a lot of detail these devices work on polarity to control larger currents with small currents. When the polarities are reversed you can have these electronic switches closing when they should be open or vice versa. When this happens high current can flow in paths that were not intended for high current and the device overloads and burns up. Electricity will always flow in the path of least resistance. In addition with two battery sources connected you may have a path of conductivity from one battery to the other even momentarily (electricity flows at the speed of light) that can result in a component failure. In the case of a motor it will want to spin in the reverse direction. This may not be a problem in some cases. But in others the motor may jam and then overheat due to a locked rotor condition. The windings in some motors will not allow the motor to run in reverse without overheating and failing.
I hope this helps you. It is a big subject to explain and I have only touched on the tip of that iceburg.

[davepl]

A DEAD SHORT

No, it's not.

Originally Posted by HO455

The problems come from when electronic components are involved and when they allow a high level of current in an unintended manner which may cause a fuse blow. Voltage regulators and pump controllers generally use some form of diodes or transistors to turn current flow on and off as needed.

That makes a lot of sense, thanks. Even looking at just the alternator with all of its diode packs would be a good example of where going one direction is VERY different than going the other.

Regulators (and in particular rectifier bridges) are also good examples.

I think I've got it now!

[HO455]

You are welcome sir!

[Steeveedee]

Originally Posted by In The Ten Ring

What can you screw up? Let's see:

Fuses
Alternator
Battery (and by that I mean your face gets some sulfuric acid).
Computer (I suspect)

Positive always goes on first and comes off last and NEVER trust the other guy to have a brain (if he did he'd be the one jumping you).

My Honda Accord manual (1988) recommended red clamp to positive post, black clamp to metal on engine bay.

That's the accepted method for avoiding an explosion if the vehicle with the dead battery has been cranked in excess to get the battery to a dead state. It's a good idea in general, to avoid that scenario.

[Overdriven]

Originally Posted by In The Ten Ring

Positive always goes on first and comes off last and NEVER trust the other guy to have a brain (if he did he'd be the one jumping you).

My Honda Accord manual (1988) recommended red clamp to positive post, black clamp to metal on engine bay.

Originally Posted by Steeveedee

That's the accepted method for avoiding an explosion if the vehicle with the dead battery has been cranked in excess to get the battery to a dead state. It's a good idea in general, to avoid that scenario.

I always thought connecting the negative of the jumper cable to ground instead of the negative terminal of the battery being jumped was to get the resulting spark away from the battery. You know because of the possible fumes being vented from the battery possibly being ignited.

Speaking of not trusting others to have a brain. Used my personal truck to jump a work truck. Connect my end of cables and coworker has the other end and touches the clamps together on purpose to "make sure it works". My truck is running you moron and he just shrugs after I explain why he could've damaged my truck. Couple days later I'm driving the dead battery truck (super busy no time for battery swap) and he has to jump it with another work truck. Of course he "tests" it out again and the resulting sparks fry the alternator. Best part, he found that out after it ran the battery dead and stalled out on the highway. Boss was not happy having to pay for a tow and alternator just because he had to spark the cables.

[harpo231]

[QUOTE=davepl;7953302]No, it's not.



yes it is ! a short with no resistance which is continuous and hard to track down

[HO455]

[quote=harpo231;7953682]

Originally Posted by davepl

No, it's not.



yes it is ! a short with no resistance which is continuous and hard to track down

Actually the short you describe is one of the easiest problems to track down. But that aside I believe you misunderstood the original question.

[harpo231]

Oh ok , I may have,, wasnt meaning to mislead,,, generaly running direct current to ground =

[sleepertruck72]

That sucks...
I lost count how many times we got cars towed in with no start after a jump start, battery or alternator replacement. Sometimes the blown fuses are easy to replace, some require opening up fuse box...
Were you able to get it running ?

[davepl]

Guess it's running now, fuel pump controller was dead but ECM is OK, car runs, so that's the main thing!