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Author Topic:   Jump starting, sparking, inductive loads, fried diodes, and the real world.
Chuck Tribolet posted 05-14-2007 11:05 PM ET (US)   Profile for Chuck Tribolet   Send Email to Chuck Tribolet  
Having gotten past the immediate problem at work (a raccoon
decided to scale our private power substation and fried himself
and some of the wiring -- raccoon discussions in another
thread, and I'll contribute a good one THERE.), I'll accept
jimh's thrown gauntlet and open a thread on this subject.

JIMH said: Chuck--if you would like to engage in a technical discussion of engine starting with jumper cables that spark like crazy, please start a new thread and I will be glad to explain my thinking on why I do not recommend that procedure.

Here's the relevant past discussion in

jimh: posted 05-08-2007 01:03 AM ET (US) I do not
recommend jump starting. You can cause damage from sparking.

jimh posted 05-08-2007 08:30 AM ET (US) I do not
recommend jump starting. You can cause damage from sparking.

(Yes, he repeated himself).

Chuck Tribolet: posted 05-09-2007 12:26 AM ET (US) How is
the jump starting going to exceed the PIV of the diodes? 12V is 12V is 12V (well, 13.8V is ...).

jimh posted 05-09-2007 01:53 PM ET (US) Inductive loads
can easily generate voltages higher than the source when the
current is interrupted.

Chuck Tribolet posted 05-09-2007 03:41 PM ET (US) But once
the motor starts, the alternator is putting out 13.8V
so there's no interruption of the current through the
inductive loads. And there aren't any huge inductors when
the engine is just sitting there not started.

And the PIV of those diodes better be pretty good.

Ever put a scope on "12V" when a big V8 starts? It goes way
up briefly, but that's the voltage regulator which has
saturated the windings on the alternator trying to pull up
the voltage during cranking. You can make your lights last a
lot longer by turning them off while starting, then back on.
Compared to that spike, I'm not worried about jump starts.

jimh posted 05-10-2007 01:55 AM ET (US) There is no
problem in starting a engine with a second battery in
parallel with the primary battery. The problem arises from
voltage transients which can occur when there is sparking.
Sparking represents a momentary connection and
disconnection. Most jumper cables have poor quality
connectors and are prone to sparking. My personal experience
with jump starting in which there is sparking in the
connections is that it leads to problems in the charging
system, often damaged diodes. Most charging systems warn
that you must not disconnect the battery while the charging
system is operating. Sparking represents a momentary
disconnection of the battery.

Everyone is free to follow their own precepts and
preferences with regard to jump starting. My recommendations
are not binding.

My recommendation to the fellow with the engine that does
not crank with a new battery is still the same. Investigate
the battery first, then check all connections. And monitor
the voltage during cranking.

Chuck--if you would like to engage in a technical discussion
of engine starting with jumper cables that spark like crazy,
please start a new thread and I will be glad to explain my
thinking on why I do not recommend that procedure.

OK, Here's my take: There aren't any inductive loads when
the jumper cables are connected or disconnected. Jim, if
you think there are, WHAT ARE THEY?

Sparking per se does not generate any voltage transients.

I think Jim has confused cause and effect. With my '72 240-Z
there was a correlation between jump starts and blown
diodes, but the blown diodes (every 30K miles) caused the
dead battery that caused the jump start. Not vice vice versa.


jimh posted 05-15-2007 12:02 AM ET (US)     Profile for jimh  Send Email to jimh     
When jump starting, the dead battery has high resistance compared to a normal, fully-charged battery. The inductive load is the starter motor. The source of voltage is the external battery.

Sparking is an indication that the circuit has been interrupted and restored.

When the voltage source (jumper cable) disconnects, the field in the starter motor collapses. This generates an inductive kick-back voltage transient. The transient may be absorbed by the dead battery, but if the impedance of the dead battery is high (and it may be if it is really dead), the transient may not be effectively suppressed.

Another possibility is the boat battery has been damaged internally and is an open circuit. This further increases the possibility that there won't be much load to absorb any transients.

A further possibility is there is a problem with the connections at the battery, and the boat battery is entirely disconnected from the motor. This also increases the possibility that there won't be much load to absorb any transients.

In automotive applications if you blow an alternator diode you can usually get a rebuilt alternator for less than $100. Marine alternators are more expensive. In motors with permanent magnet alternators the rectifier assembly can cost as much as $300. And on some modern engines the rectifier is a part of the engine management module, which has an astronomically high replacement cost.

In 40 years of car ownership I have replaced at least three alternators. In each case there was a dead battery and a jump start associated with the alternator damage. The last few occurrences of a dead battery I have refrained from trying a jump start. Instead I have carefully attached a battery charger and allowed the battery to re-charge slowly. The result was no alternator damage. The only exception to this was a recent problem where I borrowed a battery charger on which someone had bypassed the on-off switch so the unit was always ON. I did not know this, and when I connected the charger there was sparking. I later discovered that the alternator was damaged and had to be replaced.

If the charging system were immune to damage from having the battery connected and disconnected, there would not be warnings about being sure the battery connections are tight, warnings to never disconnect the battery while the engine is running, and warnings not to move the main battery switch to OFF.

Chuck Tribolet posted 05-15-2007 12:16 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
jimj: "When the voltage source (jumper cable) disconnects, the field
in the starter motor collapses. This generates an inductive
kick-back voltage transient."

Except that that when the jumper cable is disconnected, the
starter motor isn't cranking. There are two scenarios here:

1. Connect jumper cable, engine starts, leave jumper cable
connected to help charge the tired battery. By and by,
disconnecct the jumper cable. No problem, we aren't
cranking when the jumper cable is disconnected, NO PROBLEM.

2. Connect jumper cable, engine does NOT start. By and by,
disconnect the jumper cable while not cranking (disconnecting
while cranking is farm animal stupid). No problem, we aren't
cranking when the jumper cable is disconnected, NO PROBLEM.



Chuck Tribolet posted 05-15-2007 12:27 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
In 35 years of car ownership, I've had four dead alternators.
Three were on the 240Z (see above), one was quite recently
on my '87 Corvette (which hadn't had a jumpstart in the last
12, more likely 15, years).

"In 40 years of car ownership I have replaced at least three
alternators. In each case there was a dead battery and a jump
start associated with the alternator damage."

AGAIN. What was cause and what was effect? Dead alternator
causes dead battery causes jump start??? or Dead battery
causes jump start causes dead alternator?


If this were a real problem CSSA, GM, Ford, Chrysler, and even
the imports would be shouting "DO NOT JUMP START!!!"


HAPPYJIM posted 05-15-2007 07:20 AM ET (US)     Profile for HAPPYJIM  Send Email to HAPPYJIM     
I thought Jim explained it pretty good. Sparking causes all Inductive and Capacitive loads(magic stuff inside computer controlled motors)that are in parallel circuits to produce voltages higher than 13 Volts DC, some in the hundreds of volts. Not much current capacity but the voltage is definitely there for nanoseconds. It is possible for this spike voltage to destroy electronics that are protected by fuses because fuses work on current not voltage.

I cringe when I see someone tapping the jump start cable on the battery terminal, several times, to check for spark(hence a good connection) before making a connection.

Chuck Tribolet posted 05-15-2007 07:18 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
There aren't ANY inductive or capacitive loads with the
ignition off, which it should be when you connect the jumper

And remember correct jumper cable procedure:

Start donor car. Recipient ignition off.
Connect cables, positives first, negatives second, recipient
before donor.
Run donor car at fast idle for a couple of minutes.
Start recipient.
Run both cars at fast idle for a couple of minutes.
Disconnect cables in the reverse order of how they were

Arcing at attachment is not a problem, ignition is off on the
recipient. At disconnect, both batteries should be at close
to the same voltage, and there aren't any serious inductive
loads anyway.


jimh posted 05-15-2007 08:14 PM ET (US)     Profile for jimh  Send Email to jimh     
It costs about $275 to replace the rectifier-regulator assembly on my motor, plus the labor to replace it, which is about another $125. If Chuck sends me a check for $400, I will test his theory.
jimh posted 05-15-2007 08:20 PM ET (US)     Profile for jimh  Send Email to jimh     
A small arc when connecting the jumper cables or disconnecting them is not significant. I assumed we are talking about the sparking and arcing which occurs in the process of trying to start the motor when the poor clamp connections on the jumper cables go bad and interrupt a significant current flow in the starter motor.

There is little chance that the simple act of connecting a battery in parallel will be destructive (unless the polarity is wrong). The damage occurs when a lot of current is flowing, the jumper cable clamp-on connector arcs, and the circuit is interrupted, then restored, then interrupted, then restored--all in the matter of a few milliseconds. This is what blows up stuff.

By the way, I decided it was not worth my time to have to take my boat out of service to have the charging system replaced, so I will ask Chuck to let me experiment on his boat. I will open and close the clamp on the jumper cables a number of times to induce sparking and arching while Chuck is cranking his engine over. This way Chuck can take the risk.

Well, heck, I don't need to be the one to do this. Let's just have Chuck videotape himself doing it. If Chuck believes there is no risk, I am certain he will not be shy about doing this to prove his point.

Chuck Tribolet posted 05-15-2007 10:18 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
You didn't make that at all clear. And you also stated that
you borrowed a charger that arced when you connected it
and that blew the alternator.

So use good jumper cables with good clamps that stay clamped
when you clamp 'em. Mine do (one set in the truck, one in the
'vette, one in the boat).

Several more reasons to use good jumper cables:

Heavier gauge wire.
More flexible wire.
More flexible insulation when it's cold.

The difference in price between good jumpers and cheap ones
isn't much.


jimh posted 05-16-2007 12:28 AM ET (US)     Profile for jimh  Send Email to jimh     
If you have to use jumper cables--and there is always that possibility, even for the best prepared among us--I agree with Chuck's recommendation to use jumper cables with good clamp connectors because they will reduce the chance for high-current interruption and sparking.
Tom W Clark posted 05-16-2007 09:36 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

If one finds themselves in a parking lot with a dead battery and the need to get one's vehicle started. What DO you recommend?

jimh posted 05-16-2007 09:43 AM ET (US)     Profile for jimh  Send Email to jimh     
I like those cigarette lighter plug chargers. Let it sit for an hour and charge. Or use really good jumper cables and cross your fingers.
Tom W Clark posted 05-16-2007 10:10 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
So let's say I leave my headlights on while grocery shpping. I am stuck in the middle of the grocery store parking lot.

You recommend I whip out the cigarette lighter plug equipped charger I always carry around with me and then run a couple hundred feet of extension cord (should I store this in my glove box?) to the nearest available wall receptacle, plug it in and then chill out for an hour while my battery is recharging via the small gauge wiring behind my dash?

No thanks. I'll take my chances with the jumper cables.

Honestly, in seven years of following along with ContinuousWave, this is the worst advice I have ever seen offered by you Jim.

jimh posted 05-16-2007 02:48 PM ET (US)     Profile for jimh  Send Email to jimh     
As I mentioned in a previous narrative, the last time I had a car with a dead battery, I just bought a new battery, drove over to the car, and installed the new battery. I figured it was cheaper than getting a new alternator after I jumped started the car. My ratio of new alternator-to-jump-starts is close to 1.0.
jimh posted 05-16-2007 07:44 PM ET (US)     Profile for jimh  Send Email to jimh     
Let me respond to Tom and his judgement about the value of my advice. The recommendation I made has to be judged in the context of the situation in which it was offered. Let me summarize:

--A fellow informs us that when he turns the key to start his engine the starter motor does not crank.

--I recommend he check the battery.

--A third fellow recommends a jump start.

--I recommend against jump starting.

As far as I can tell, we don't have any emergent circumstance here. The boater with the starting problem must be safe ashore, as I presume he's connected to the internet from somewhere else than the boat with the dead battery. So there is no urgent reason to start the motor.

The goal of the inquiry is to diagnose and remedy the problem. The goal IS NOT to get the engine started as fast as possible.

As a diagnostic tool, a set of jumper cables and a second battery are somewhat crude instruments. I would much rather check the battery using methods with a bit more science. To check a battery, I recommend:

--measuring battery voltage with an accurate DC voltmeter. By correlating the voltage with the temperature, you can obtain a very accurate measure of the state of charge of the battery;

--measuring the current delivered by the battery into a resistive load. This will quickly establish the current capacity of the battery; and,

--measuring the internal resistance of the battery. This will help confirm the battery's condition.

Making these measurements requires a varying degree of sophistication in test equipment. In order to perform any sort of electrical trouble shooting and diagnosis, it is reasonable to expect that an accurate voltmeter is available. If it is not, the probability of successful diagnosis is reduced. Measuring actual current delivered to a load requires more specialized test equipment. Most boater will not have this equipment, but most stores that sell batteries will. So it is a simple matter to take the battery to a store to have it tested. This will produce much more information about the battery.

Measuring a battery's internal resistance requires even more sophisticated equipment, but it is my experience that most battery retailers will have a device that can do this. So, again, take the battery to a retailer for testing.

The other reason I did not recommend that a jump start be attempted is the potential for further damage to occur. In the original situation we are trying to diagnose the problem with the engine starting circuit. By jump starting we risk creating more problems.

If the situation is different, say we are taking on water, about to be driven onto a rocky shore, and our only option is to jump start the engine, well then, by all means, try to start the engine by jumping it. However, in the context of the original discussion, I do not think that trying to jump start the motor is the best approach to finding out what the problem actually was.

In Tom's hypothetical situation of a car in a parking lot, I would still recommend avoiding a jump start unless there was some special urgency.

Regarding the suppression of transient voltage spikes in most 12-volt battery systems, the principal device that works to suppress transients is the battery. The battery is shunted across the 12-volt system, and its very very low internal resistance provides a very very effective means of shunting and absorbing any voltage transients which occur. However, if the battery is removed from the system (by a loose or intermittent connection) or if the battery condition is such that it has a high resistance (as might occur if the battery has a bad connection internally), there is not much to shunt or suppress voltage transients in the system. The windings of the starter motor offer an inductive load with a great deal of energy stored in its magnetic field. The transients generated by collapsing fields will be able to reach much higher voltages than usual (because there is no shunt from the battery). Under these conditions, it is possible to cause damage to other devices connected to the 12-volt system.

The rectifiers and regulators contained in outboard motors have two characteristics which distinguish them from automotive equivalents: they are much more expensive to replace and they seem much more fragile and less durable. Most automobiles have alternators which can be replaced for as little as $50, while the rectifier and regulator of an outboard might cost $1,000 or more (if it is part of a sophisticated engine control module). There are numerous accounts of having to replace outboard motor rectifiers, stators, regulators, diodes, etc., just from normal operation, so it seems reasonable to assume that the typical outboard motor charging system is more fragile and less durable than the typical car.

So, on the basis of all this, I do not find that my advice to recommend against jump starting the motor as part of the diagnostic procedure to locate and remedy the problem with the engine starter circuit to be, as Tom described, "the worst advice... ever seen offered."

contender posted 05-16-2007 11:39 PM ET (US)     Profile for contender  Send Email to contender     
Jim I have to ask you a question, If it is true what you stated then tell me what happens if I disconnect the battery to connect a new battery thus creating a spark??? I did not break any diodes and the engine starts. As far as you batteries going out, this was because your alternator broke down first and your car worked of the battery until it died, Then you tried to jump start it, and took it to the garage and they told you you had a bad alternator. So did you assume it was the jump that cause your alternator burn up??? I do have to agree with chuck on this one...good luck
bitwrench posted 05-16-2007 11:49 PM ET (US)     Profile for bitwrench  Send Email to bitwrench     
Just the facts man. No car manufacturer recommends that you ever jump start that vehicle.
Fact. The reason is the possiblilty that you will fry one or more of it's onboard computers which operate at millivolt levels. Even AAA the auto insurer's tow vehicles no longer operate with 'jumper' cables. They pull up, hook up an onboard charger, and sit there with there diesel motors chugging away, charging your dead battery. Fact. You are not guaranteed to fry the computer, you are only taking a risk, albeitt a pricy risk.
The reason auto makers strongly recommend you do not disconnect a battery, leaving NO 12volt battery in the circuit, is that the alternator will 'open circuit' and regardless of its voltage regulator, continue to climb in voltage far exceeding the 13v to 14.5 voltage at which it will normally operate. If left in this state for any length of time damage will occure, if you have a computer controlled vehicle left in this state, your gonna be hurtin.
Old school white trash beer drinkin boys would commonly use a friends battery to start their dead vega/pinto/other white trash car, then once it was running, take out the 'good' battery, and install the dead one so they could get down to the licker sture. My take, it's 'O.K.' to jump start old school vehicles, no way I would do it an a modern computer controlled vehicle unless I was in a real bind.
Tom W Clark posted 05-17-2007 10:09 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

I am trying to figure out if you are pulling my leg or not:

...the last time I had a car with a dead battery, I just bought a new battery, drove over to the car, and installed the new battery. I figured it was cheaper than getting a new alternator after I jumped started the car."

Now even if you discount to obvious inconvenience of finding a new battery to buy when you have no vehicle to drive because the battery it has is dead, the reasoning here is stunningly illogical. My degree is in economics, so let's look at the numbers and see how the costs stack up.

I have been driving for about 30 years. In that time I have had occasion to jump start my own vehicle and help others in need of a jump start. I have not been keeping records, but let's just say that twice a year I have jump started a car, that is only about 60 times in my entire lifetime.

If I were to have followed such advice as you are offering, I would have had to go out and (somehow) buy a new battery each time. How much does a new battery cost? Oh let's just say for the sake of argument a new battery costs $50.

So if I had bought 60 batteries 30 times I would have spent $3000 and incurred the inconvenience of removing and disposing of the old batteries and installing the new batteries.

So now let's examine how many times an alternator has been damaged while I was jump starting a vehicle: Zero. It has never happened. Oh, now I concede something bad may happen the very next time I try it, in fact let's say that it does.

On the 61st time I try to jump start a vehicle, I damage an alternator. Cost to repair/replace? I see figures above ranging from $100 to $400. Let's take the average of that and call it $250.

So there you have it, $3000 worth of new batteries or one $250 repair. Your choice.

towboater posted 05-17-2007 12:35 PM ET (US)     Profile for towboater  Send Email to towboater     
Hehe, Clash of the BW Titans.
Chill, you are both right.

Using the PROPER sequence to attach cables, the dead car's electrical components does not know or care whether the 12v source is coming from its own battery, thru a set of jumper cables or a Cat 12D. There is no difference between...again, properly connected jumpers between batteries or cig plugs. 12v is 12v.
A jump or spike in voltage or reverse polarity in WILL blow a alternator diode. This usually happens if you fiddle around with the jumper cables while the dead batteries ignition switch is ON.

example. Your wife is trying to start the car using a jump, she quits cranking (key still in the run/on position) and you reposition the pos cable. POP. Goodbye diode & who knows what else could fry. Turn the switch all the way off, then reposition the cables.

Grounding out the pos cable on the jump vehicle will also blow diodes. You need to be careful. Cig plug is a safer option.

Ive been attending the Mariners School of Engineering & Economics for over 30 years.
A good set of 4 gauge jumpers (est $60) with strong welder type clamps, properly used & maintained will last a lifetime.
$60 investment over a lifetime. Depending on old you are now, how long you live... If you cant do that math, you shouldnt be messing around with jumpers AAA or a Towtruck.

In $$ terms, faced against todays world of vandals & thieves, I would not hesitate to jump or tow a rig to a safe haven.


Chuck Tribolet posted 05-17-2007 08:49 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
bitwrench: The owner's manual for my '01 Nissan Pathfinder
describes basically the procedure I described, plus a couple
more things that were clearly written by some lawyer that
that interned at the consumer product safety commission.

And there's not a word about jimh's concerns.


contender posted 05-17-2007 09:08 PM ET (US)     Profile for contender  Send Email to contender     
I have rigged my 2003 chevy diesel truck with jumper cables hook up on my rear bumper. (I used welding connections) I have grounded one of the cables to my truck frame and the other to the positive on the battery. I do have a cut out switch on the positive cable going to the battery. I run this rig for two reasons: One, while jumping other vehicles I can back up to it and not have to turn around facing the traffic in the wrong direction. Two, I use it for my starter motor that is connected to my trailer winch for my whaler. I have used this system since 1977 on my first pick up truck, and no problems jumping or starting other vehciles. Here's another trick, ever have a set of jumper cables that do not provide enought juice to the battery. I use to ground the two vehicles together by touching the bumpers (ground), and then use both cables on the positive for the power...good luck
jimh posted 05-17-2007 11:27 PM ET (US)     Profile for jimh  Send Email to jimh     
Re replacing a dead battery in lieu of jump starting:

Most of the time when a flooded cell lead acid starting battery is so flat (discharged) that it won't crank over the engine, you are going to need to replace it. The battery will never recover from the deep discharge, and this is particularly true if the battery is more than a few years old.

As far as I can remember in my experience, the only time I have not immediately replaced the battery--or replaced it very soon afterwards--when it had gone completely flat was on a brand new car. That battery was only a few weeks old when it was deeply discharged. That battery came back and lasted several years.

An older battery that is dead is a throw away battery. You are going to replace it, if not now, then very soon. So my preference is to just replace a dead battery instead of trying to jump start the motor. Why risk damaging other electrical components.

As for being a good samaritan and going around offering jump starts, I do not. I would not offer my vehicle and my battery for a jump start unless there was a real true emergency. There is too much risk.

What has happened here is that the circumstances of the argument have been shifted. For some reason we are off on a discussion of automobile charging systems, batteries, supermarket parking lots, and so on. Let's go over a few things:

--the stuff that might blow up on your car is very likely a lot less expensive than the stuff that blows up on your boat. I can go to the store, buy a quality alternator, and install it in my GMC truck for about $85 and 30 minutes work. If I damage something in the charging system of my outboard motor, the costs are much higher. A new rectifier-regulator is $235, a new stator coil is probably $200 and a great deal of expensive labor to install it. It will be more expensive and more time consuming to repair or replace the boat stuff than the car stuff.

--the guys who designed the stuff on your car figured that you would be jump starting it, so they created components that tolerate it--well maybe not the guys at GM (if my experience with GM alternators is representative). The guys who designed the stuff on your boat may or may not have built the system with enough headroom to tolerate big voltage transients. And in the case of a 10 or 15 year old motor, maybe the stuff is not quite in prime condition anymore. Boats seem to experience more spontaneous failures of components in the charging system than cars, and this make me more cautious about connecting

--a manufacturer of an outboard motor, Evinrude, sternly warns that the connections to the battery must be made with securely tightened fasteners--no wing nuts. It is reasonable to infer from this that they do not want the battery to ever become disconnected momentarily while the engine is operating. Why do you think that is? Because they do not want the electrical system to be stressed by whatever occurs when there is connection and disconnection of the battery.

As far as being a good samaritan when boating, I have on two separate occasions removed a battery from my boat, disconnecting it entirely from my electrical system, and loaned it to another boater, who connected it to his electrical system, so that he could start his motor. On boats where there are two batteries and the usual OFF-1-BOTH-2 battery switch wiring, it is straightforward to wire in a new battery, start the motor, isolated the new battery, disconnect it, and remove it. This avoids having to resort to jumper cables and paralleling two batteries.

To go back to the original situation which began this discussion, where we are trying to diagnose a problem in the starting circuit, it make much more sense to REMOVE the suspicious battery from the circuit, replace it with a known good battery, and then test for starting. This ELIMINATES the original battery from the process. If the engine starts, we know the battery was the problem. If we parallel a second battery, we really don't know what might happen. One possibility is the original battery has a shorted cell, and it may immediately begin discharging the paralleled battery.

In the near future the electrical system on modern vehicles will probably transition to a permanent magnet alternator system built into a flywheel, much like we see on two-stroke outboard motors. The days of the $50 alternator rebuild will be long past. Damage to the vehicle charging electrical system will be very expensive to repair and replace. The days of jump starting cars in the parking lot of the supermarket will be long over, a fond memory of the past.

Tom W Clark posted 05-18-2007 12:22 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Like Chuck, the owner's manual for (my 2005 Toyota Tundra) gives explicit instructions for how to jump start the truck.

About 50 percent of what is written is a series of warnings of what not to do to avoid lighting gasoline on fire or pouring battery acid on yourself. None of it has anything to do with what is being discussed here.

No mention at all of the alternator or any diode, voltage, circuits or computers. No discouragement is given at all.

HAPPYJIM posted 05-18-2007 06:55 AM ET (US)     Profile for HAPPYJIM  Send Email to HAPPYJIM     
Jump starting a motor does not guarantee that you will smoke any electronics but there is a real POSSIBILITY of doing damage if connections are not made properly. The only time that I have jumped a boat to get going for fishing, the motor quit after about a mile of running and we had to paddle back. Not even enough power to call anyone on VHF. I will never jump start a boat unless it is an emergency situation. Find the cause and fix it.

Another real problem is making connections in the boat. The final connection should be made to the frame or common ground to prevent sparking at the battery causing the battery to explode from igniting gases produced by the battery. I have seen this happen. It was not pretty. My best friend was jump starting his truck(very knowledgeable, owned a gas station/garage for 20+ years)and made the final connection at the battery instead of the frame. The entire top of the battery blew off and spewed plastic shards and battery acid in his face. He was lucky that I was there because he was temporarily blinded by it. I rushed him to throw lots of water on his face and clothes and run him to the doctors office. We both learned a lesson that day.

Electricity and electronics involve a lot of theory. Sometimes you just have to believe that damage will be done just from experience of others that have worked in that field. There's no electrical reason for a battery to discharge while sitting on concrete....not many of us will set a battery down for an extended period without putting a board or something under it.

swist posted 05-18-2007 08:39 AM ET (US)     Profile for swist  Send Email to swist     
I can certainly see where even good jumper cables might make intermittent contact - battery terminals frequently have crud on them, and even if contact is made, high current flowing though a loose mechanical connection can actually move the contacting surfaces, possibly breaking the connection.

What I don't understand is - if a current from a collapsing magnetic field is a risk, why aren't the cars/boats protected from such a problem by flyback diodes?

I work with low-voltage DC circuitry in my job - there are a lot of solenoids and relays that can and do produce spikes when turned off. We install "flyback diodes" - a small diode hooked up backward across the inductor producing the spike. Since the spike is the opposite polarity of the supply voltage - the diode, while having no effect during normal operation, harmlessly short-circuits any spikes. As someone mentioned, these phenomena may produce an amaxing amount of voltage (100s of volts in a 12V DC system), but with very little current, so you don't even need a very big diode.

This is even cheaper insurance - how come starter motors don't have them?

jimh posted 05-18-2007 09:49 AM ET (US)     Profile for jimh  Send Email to jimh     
My feelings about jump starting are somewhat like those of football coach Bo Schembechler about the forward pass. I believe Bo once said, "There are only three things that can happen when you make a forward pass, and two of them are bad."
swist posted 05-20-2007 07:17 AM ET (US)     Profile for swist  Send Email to swist     
I've heard that remark myself (although attributed to other college coaches who hated to pass). It strikes me as silly - if you run the ball four things can happen (gain, no-gain, loss, fumble). Three of which are bad.

But I digress - cavalier and incorrect use of jumper cables is rampant - I don't think people realize that is pure luck when they avoid various disasters from blown diodes to exploding batteries.

Mobjack posted 05-21-2007 11:30 AM ET (US)     Profile for Mobjack  Send Email to Mobjack     
I have been following this thread with interest. I have to confess that my knowledge of electrical systems is clearly far inferior, and not adequate to participate fully in this discussion, however I do have a great deal of experience using jumper cables. Maybe it has something to do with the fact that I was taught to use them properly at an early age, but I would venture a guess that I have performed somewhere in the vicinity of 250-300 jump starts, on a range of equipment that includes the following: outboard motors, cars, trucks, large trucks, 4wheelers, inboard marine motors, tractors, and aircraft. Of that number probably 25 incidents have been for other people who were in distress and whom I did not know, so I cannot verify the long term effects of my reckless jump starting on their vehicles, but the remainder of these cases occurred without any incident whatsoever, and without any ill effects to either vehicle involved. So there's my two cents.
BQUICK posted 05-22-2007 02:28 PM ET (US)     Profile for BQUICK  Send Email to BQUICK     
The point I haven't seen mentioned is that if you have a dead battery and you jump it and start it right away and disconnect the jumper cables the alternator goes nut i.e. FULL rated output to try to charge the still dead battery.
Whlie this shouln't hurt an alternator, if it is on the old side it could as it will get REAL hot working at max.

As an example my daughter went to a b-day pary and used her cigarette lighter socket to run a small air compressor to blow up ballons (alot of them!. When she went to leave it wouldn't start, she got a jump then immediately turned on the headlights and AC. So on top of the dead battery the alternator has the additional load of headlights and AC.....not to mention the fact that it was hot outsire adding additional heat to the already overworking alternator. Yes, the alternator was toast......

I've seen this more than a few times as a auto mechanic for 30 yrs.
When we replace an alternator we often ask, "did you jump it recently?". The most common answer is "how did you know"?.

The way around this if you have to jump start is to charge with the other verhicle for at least 5 min. That way the battery will have at least a partial charge that the alternator can handle.

Chuck Tribolet posted 05-23-2007 07:20 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Bquick: well said. Get that tired battery charged up before
you disconnect.


swist posted 05-25-2007 08:12 AM ET (US)     Profile for swist  Send Email to swist     
Aren't auto A/C systems belt-driven off the engine? If so, how do they consume electricity when running, other than the fan motor, which is minimal?
jimh posted 05-25-2007 08:32 AM ET (US)     Profile for jimh  Send Email to jimh     
The fan motor for the air conditioning system can be a significant load. Other than that, the only electrical part of the air conditioner is the solenoid holding in the clutch on the compressor drive belt pulley.
andygere posted 05-25-2007 12:15 PM ET (US)     Profile for andygere  Send Email to andygere     
Many folks here have reported that a new, off the shelf 12 volt wet cell battery needed charging before it had sufficient current to start the outboard motor. So, upon finding the installed battery in your boat at a state of discharge (perhaps the bilge pump ran a long time at the dock), you diligently buy a new battery to avoid the possibility of a voltage transient damaging the alternator during a jump start, but now the new battery can not crank the motor. What now?

Most boats have some type of battery switch that disconnects the battery from the charging/starting system. It seems to me that selecting the "off" position before attaching the cables would protect the alternator from any transients that might occur. If one were particularly cautious, one could leave the cables connected for a few minutes while the weak battery charged, then shut everything down, close the battery switch and then disconnect the cables. Similarly, if using a portable "jump box" (a rechargeable battery pack with integral cables) one could turn the battery pack switch to the off position before making or removing any connections.

It's both dangerous and foolish to attempt to readjust jumper cables on a battery while cranking the dead motor. One is likely to lose a hand in the fan or serpentine belt, or cause an explosion and be sprayed with battery acid. That said, I've never had a problem getting a good connection with decent quality cables. Many newer vehicles have a "jumper terminal" to make it easier to connect jumper cables in cases where the battery is difficult to access.

For what it's worth, I had a brand new battery discharge sufficiently to prevent the engine in my 1999 Grand Cherokee from cranking (my sister inlaw left the interior lights on overnight). I jump started the engine, and with no damage to the alternator or EMM. That battery has been in service for several years since then, in a vehicle with high electrical loads. It would get pretty expensive to replace the battery each and every time someone forgets to turn off the lights!

swist posted 05-26-2007 07:37 AM ET (US)     Profile for swist  Send Email to swist     
Auto batteries (which are pretty much the same as marine starting batteries) will survive a few deep discharge cycles, particularly if they are relatively new and have been properly maintained and charged. But that is not what they are designed for and if you can get 3 or 4 full recharges and still have a good battery, you are doing well.

IMHO, I don't see why starting batteries are used in outboard boats at all. Regular lead-acid deep-cycle or combo deep-cycle/starting batteries can be had for a few bucks more than a pure starting battery, and all have more than enough CCAs to start any outboard. You are so much better protected against killing the battery due to excessive discharging - which is much more likely on a boat than in a car given all the electronics and other gizmos you might use when the boat engine is not running.

jimh posted 05-26-2007 08:20 AM ET (US)     Profile for jimh  Send Email to jimh     
It is the five-year-old cranking battery that has been deeply discharged that, in my opinion, is not worth recharging. The cost of a new battery is modest compared to the expense or impact that a dead battery can create at an inopportune time.

The trio of dead battery, jump start, and failed alternator diodes does seem to travel together, but it is hard to determine exactly in what order they are most likely to occur. If an alternator diode fails spontaneously in normal operation, this will result in a dead battery, and perhaps require a jump start. Or perhaps the sequence will be in a different order: dead battery, jump start, failed diode.

Battery life depends on the initial quality of construction, the service in which the battery is placed, and some random luck in avoiding misfortunes. The replacement interval often depends on how the owner or operator feels about risk.

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