Auto battery question

So, if he inserts the multimeter in one of the battery leads, and then tries to start the car, he will surely need a new multimeter!

Not that I am disagreeing with you Bob, but rather the idea of putting a meter in one of the battery leads worries me greatly. Even if the starter current is avoided, I have an idea that late model alternaters can put out 80 odd amps or so, and not many multimeters (or their test leads) can handle that

Only safe way to measure the charge current to my mind is a proper meter, or a shunt/voltage arrangement

David

BobG wrote:

It isn't crappy design. The auto electrical system is designed to operate with a BATTERY INSTALLED. If you take the battery out, you've buggered the design. Would you saw a load-bearing member from your home, then blame the architect when the ceiling fell in?

Reckon the hard part is convincing the budgeting department to pay for a bunch of fail-safe circuitry, meant to protect the machinery in the event the user removes critical parts, willy-nilly.

Not a bad assumption.

The regulator hasn't had time to figure in the problem; the regulator doesn't factor until your auto is turning rpms. The regulator regulates alternator output to a set voltage in conjunction with the battery, the battery regulates the whole system in conjunction with the output current of the alternator/regulator.

Could be a dead battery.

This is possible, but unlikely if the starter is not giving any indication at all that it is trying to turn. If it is at least wheezing and groaning, then the most likely culprit is the battery.

If you get nothing, I mean absolutely nothing, then you might have some loose or detached wiring in the starter circuit. If you get loud clicking then the starter relay is bad and must be replaced. Seized engine is a bit unlikely. If you get a whirring sound from the starter but no engine movement, then the starter is bad. In any case, the battery is probably fried from its misuse these past few days and should also be replaced.

He's right, as has been pointed out. The battery is an essential component for the proper operation of the auto electrical system. It functions as both a filter and a regulator, and its size in amp-hours is chosen to fit the requirements of the auto electrical system.

Using your good-Samaritan neighbor's battery alone is a really bad idea for two reasons: first, its functionality will be impaired by being used to run two autos instead of just one. Second, once you start your vehicle, the two autos are now merged like Siamese twins. You take the jumper cable off in this configuration, and watch the fireworks start!

Kindly remember that you said that! ;-) I recommend you pursue some web sites in search of tips for proper care of batteries and starters. Unsaid in your post is any indication of how the battery or the starter may have been misused in the recent and not-so-recent past. Such information is helpful when troubleshooting.

You'd do well to get over that lack of vision.

A couple of three points on your excellent point - yes, modern auto electronics can be destroyed by voltage spikes; voltage spikes can and do appear when placing a charged battery in parallel with a discharged battery; the more deeply the low battery is discharged, the more potentially destructive the voltage spikes.

Don't do this without checking your multimeter ranges. Some of them which aren't made for automotive use tend to do poorly above about half an amp.

Michael

Batteries can go dead for no apparent reason. I check the electrolyte on my battery every few weeks (it's very rare that the level is ever below normal) and I don't leave the starter motor whining away if the car won't start - if it hasn't started within a couple of seconds, it's not going to: let the engine rest for a few moments and try again. And being a diesel it starts first time every time (*) so it's rare to need a burst of more than a second or so on the starter motor.

Even with these sensible precautions, I had a perfectly good battery go bad on me the other year. I'd given my girlfriend a lift to the dentist and sat and waited for ages for her to come out. I didn't have any electrics (radio, blower, lights etc) turned on. The battery had started the car fine that morning - and every previous morning. But when I came to set off again, the battery was absolutely dead: it would barely light the ignition light, let alone turn the engine over. In an older car, I'd have push-started the car (the advantage of having a manual gearbox!) but that's strongly discouraged in cars with fuel injection and/or catalytic converters. What made it even more frustrating was that I was parked right outside a car-spares shop, but She Who Must Be Obeyed told me that I was an idiot to simply replace the battery without first of all calling out the RAC (breakdown recovery). The RAC man took a long time to get there, by which time SWMBO was getting very irate and telling me how late I was going to make her for work. When the RAC man did arrive, he did a few tests and quickly established what I've suspected all along and was prepared to take a chance on - the battery was buggered. Two minutes later I'd bought a new battery, already fully charged, the man had fitted it and I was on my way. I resisted the urge to say "I told you so" - but I'm afraid I did think it!

(*) Except when the fuel pump fails - as it did on Wednesday. Engine turning over at full speed but absolutely nothing from the engine - not a splutter or a cough. £200 that's going to cost me in parts and the technician's time to diagnose the fault. Grrr! Still, it happened only about 200 yards from home so I was close enough to go home to wait for the garage man to arrive. And as luck would have it, all except one of the customers that I was due to visit were within walking or cycling distance of home: not often that things work out that well for me!

Over the last 30 years, I've had 3 batteries go open circuit while still being connnected. Apparently an internal jumper breaks. In all cases, there was not enough power to run more than the dome light, and all were jumped and driven to a battery store. 2 of the 3 had computers running fuel injectors and ignition systems and none of the cars had electronics failures. The one 30 years ago was driven 20 miles to get a new battery. I'm sure I listened to the radio on the way. Are you sure those weren't old mechanical (relays and such) regulators? GG

having a battery in the circuit helps the regulator in the altenator do its job, you're unlikely to damage his altenator. but running your car with no battery is a bad idea.

give the starter motor a good hard whack on the side (prod it vigorously with the jack handle etc... the case is 1/4" steel or thicker - you're unlikely to damage it) then try the starter again, (repeat upto 10 times before giving up) If that works your the cause of the failure may have been worn brushes in the starter - time to rebuild it (or exchange it for a rebuilt one)

Bye. Jasen

The symptoms are also suggestive of a poor connection to one or both of the battery terminals - high resistance connection allows the dashboard stuff to work, but not the starter etc. - could also be a bad connection of the earth or starter cables at either end

Worth checking just in case

David

Kitchen Man wrote:

True. Starters do not operate in the cleanest of environments, it would do to check the connections.

If a battery is low on electrolyte, it can appear to be nearly a dead short. Check the electrolyte FIRST, and top up with distilled water, if needed.

Clean the battery posts and terminals. Both tend to oxidize badly over time and present an unacceptably high resistance in the circuit. (Some multiple battery cables (particularly GM types) may corrode underneath the terminal insulation. They may look good but in reality be defective. These too can be cleaned but it is a bit more of a chore.)

Invest in a cheap 6-8 amp battery charger. You can get one for about $20, and your neighbor won't have to risk his alternator and battery. ( Yes, if you don't really watch what you are doing, you can blow the diodes in an alternator and, in some cases, cause the battery to explode.) Charge your battery overnight and have a go.

If your battery is getting over a couple of years old, it may be bad. Lot of cheap crap in the market. (Lots of expensive crap too.) Other things that can discharge a battery include drive belts (can be burnished with use and may slip) and courtesy lights which are staying on.

:) I've never lost one to over current (burned out a few fuses that way though) I did manage to bend the needle round the stop once by giving it

easiest way is to use a clamp meter. cheapest is to mesaure the voltage drop acrosss a portion of the earth strap. while draweing a known current, and extrapolate forom there.

Bye. Jasen

the freewheeling diode in the regulator means that whebn the regulator senses the over voltage all it can do is stop boosting the current it the altenator's field windings (which behave like a large inductor), it can't kill the current and while the current is decaying the altenator is producing an over voltage.

If the altenator was charging at maximum power when the battery was disconnected nasty things can happen.

if you get jump started had have an open circuited battery the voltage in the system is initially limited by the other car's battery and with the other car's engine running the regulator won't see a low voltage and wont turn the altenator on at full power...

pretty much, the first test is to hook a voltmeter across the battery terminals and rev the engine a little (2000-3000 rpm is enough) if the needle stays below 13V the altenator isn't working if it's stays below

most DIY service manuals (eg Haines, Gregorys, etc) cover this in the chapter dealing with the electrics, check the local library.

the cause could be a loose cable, worn brushes, a dead regulator, a diode failure, or other more catastrophic (ie expensive) altenator failure.

measure the voltage across two points on the earth cable (but not the ends in case the terminals on the cable are loose) do it firrst with some small load turned on (eg dome light) and then with it turned off (the reading shoud be significantly less (all that should be running is the clock, alarm, etc... )