Today I found out how to test a car alternator. Equipment needed: multi-meter. If the alternator is working well, your multi-meter should read somewhere in the vicinity of 14 volts typically If it is reading excessively higher than 14 volts greater than 15 volts it is possible that the voltage regulator on your alternator is faulty or going bad.
If it is reading lower than volts, there are a number of possibilities as to the reason. Try revving up the engine to RPM or higher and take a reading. If the voltage is still too low, check to be sure all the connectors on your alternator are tight and that the alternator belt is not slipping and is spinning on the pulley correctly. A car alternator needs to be putting out at least volts ideally between When a battery is near fully charged the alternator will cease to put out sufficient voltage to charge the battery and the reading you will get from the battery probing method will simply be the voltage coming from the battery itself.
In this case, you can simply leave your lights on with the car off for ten or fifteen minutes to drain your battery a little bit.
The Most Important Facts (And Myths) About Your Car Battery
It can also be helpful to test at the battery terminals with the engine off and then turn the car on and test again at the terminals. If your battery is more or less fully charged, it should read at around volts with the car off. Corey Davis: Sorry, but with a magnetic screw driver, on any metal part will stick. That test is to be done as follows: With a non magnetic tip screwdriver, or any piece of metal, with the car running, touch the back of the alternator, and there should be magnetism.
The test of removing the battery cable to test the alternator was used for vehicles made before ! Do not do this, as it can cause a major electrical system malfunction. You can also fry electronic parts of your car like that. Costing more in damage than an electrical tester wound cost. While this may work for you, it never a good Idea to disconnect the battery when the engine is running.
Pulling the positive lead with the car running will win you a Darwin Award. Daven needs more electrical engineering classes because putting the other lead on the alternator housing will not ground it out.
What should my car battery voltage be while driving?
The housing is grounded to the engine which is grounded to the frame, therefor no differant than touching the lead to the grounded frame.
Also potential energy does not get passed through one lead of the meter to the other.Unlike outdated electrical systems that used generators and could function without a battery, modern automotive electrical systems need a battery in order to function properly.
There are two ways to charge a car battery: with the alternator, or with an external charger. Under normal circumstances, the alternator charges the battery whenever the engine is running. When a battery dies, then an external charger is the best way to charge it back up. This is why most normal battery usage, like running the radio or dome lights while the engine if off, is replenished naturally the next time you start your car. The flip side of this is that, in some cases, your alternator may not be able to supply enough power to run all of your accessories.
Subscribe to RSS
When this happens, power stored in the battery will pick up the slack. When properly charged, and in good working order, a car battery will typically read at about After subjecting a battery to a load like that for that amount of time, the voltage will have dropped below While individual batteries are rated to show how long they can provide power to a specific load before dropping below a critical voltage, it's a good idea to avoid actually subjecting a regular automotive battery to this type of use.
If you drain a car battery too far, you can actually damage its ability to hold a charge in the future. Extreme temperatures, and wear incurred through the normal cycle of charging and discharging, can reduce the reserve capacity, which is why you may come back to a dead battery after leaving your headlights on while running a short errand, while in another situation, you may be able to leave them on all day and still start the engine just fine.
Car battery chargers run off AC power and provide 12V DC at relatively low voltages, which is the best way to charge a completely dead battery. Charging a dead battery with an excessively high voltage can increase the off-gassing of hydrogen, which can, in turn, result in a hazardous situation where the battery might explode.
If you connect the negative cable to the negative terminal on your battery, be very careful to avoid touching, moving, or removing the cable while the battery is charging. After hooking up jumper cables from a donor vehicle to the battery and engine or frame of a vehicle with a dead battery, starting and running the donor vehicle for a while will allow its alternator to charge the dead battery.
During this process, all of the accessories in the donor vehicle should be turned off, or the alternator may not have enough juice left over to charge the dead battery. Depending on how dead the dead battery is, a few minutes will typically provide enough of a surface charge to get things rolling. Aside from making sure the battery maintains a good level of charge, primarily by not leaving the headlights on overnight, most automotive batteries require regular maintenance in the form of checking the electrolyte level and specific gravity.
The electrolyte, which is a solution of sulfuric acid and water, should always cover the lead plates in each cell, since exposing the plates to the air can cause issues over time. If the specific gravity is low across all the cells, the battery is typically in need of a charge. If the specific gravity remains low after charging the battery, that's usually a good indicator that the battery should be replaced.
If the specific gravity is only low in one cell, that indicates an internal fault, in which case charging the battery may actually be dangerous. Tweet Share Email. Hooking up a car battery charger is a lot like jump-starting a car:. Check to make sure your battery charger is off. When in doubt, unplug it.Our Address. Kings Mills, OH Load up the alternator with everything except the radio removed, as it was dead, all wires capped properly.
Voltage drops to about Not a lot out there about this type of issue specifically, or maybe my Google-Fu has just failed me.
I would have it professionally tested to be sure. Agree with the sound of a bad alternator, but never neglect resistance. Throw an ohm meter on it and see what you got. The only way to tell for sure is to put an amp meter between the battery and the car. Not in the thick cable going to the starter, the thinner one that powers everything else.
If the alternator and voltage regulator are working properly, the ammeter should show anything from zero to an amp or three of charge, with the engine idling and you turning the headlights on and off. During the course of troubleshooting this car I did a parasitic drain test, but after the ECU goes to sleep 30 sec or sodrain is only 0. Volt drop on neg terminal to alt casing was about 0. Volt drop on pos terminal to alt output was about 0. At what point in ohms would you replace a cable? Cut that in half and its what a 96 Jeep would probably tolerate.
From past research it is apparent that jeeps in general are notoriously picky about parts and electrical, and mine has been no exception.
Sounds like just cleaning the battery terminals would help. It would bring the voltage drop down. More information on testing for problems like this can be found here.
This is the normal operation of the charging system. By nature, it will fluctuate. If it falls below It is a 12v system after all.I drive a Sable. Last night I replaced the original battery and took the car for a good drive to make sure the new one was charged.
The car seemed to run a lot more smoothly and maybe even more quietly. Was that psychosomatic or does the battery really affect how an engine runs? Was the old battery dead? Did you check to make sure the alternator is working fine? When you disconnected the old battery you probably reset the engine computer.
That could change the way the engine performs. Have the charging system checked IN the vehicle as there may be something other than the alternator possibly at fault. With my old Civic, I had a battery die. I tried jump starting the car, but as soon as I took the jumper cables off, it died.
I did it again and gave it some time to charge before I unhooked the jumper cables. After I installed the battery, it ran fine. When the battery was fully charged My guess is that the VCM computer needs a minimum input voltage or it gets a little flakely. A poor battery or dirty battery cables can absolutely cause a car to run poorly, sometimes in very odd ways. Some cars are much more sensitive than others.
Auto computers collect most of their information based on resistance readings. They read resistance by sending a low voltage signal to the sensor, and counting how long it takes for the signal to charge a capacitor in the computer up to some threshold voltage.
If the supply voltage is doing odd things as the computer is scanning its inputs, the inputs appear to be changing in irratic ways, and how the computer will respond is anyones guess. Since transmissions started to be computer controlled, more than one transmission problem has been solved by battery replacement. I agree with Manolito completely that a weak battery or cable end can cause poor engine performance. I chalked this up to poor conections and a high current draw dropping the voltage down too much.
When the voltage drops everything in the system is going to be affected. Every single time when the cable ends were loosened a faint scale was present on the mating surfaces and when cleaned with a terminal cleaner the stumble would go away.
CanadianGuy July 4,pm 1. Roadrunner July 5,pm 5. Add some dielectric grease after to keep moisture out. Whitey July 5,pm 6. I have seen a bad battery affect how a car runs, especially on smaller cars. If your original battery lasted nine years, I would stick with the same brand. MikeInNH July 5,pm 8. Thanks, I never thought of it that way.
Manolito July 5,pm Even if you're driving a gas guzzling SUV, electricity remains crucial to driving a car. Thanks to modern-day electric batteries, drivers no longer have to turn an engine over by hand. It now all happens with the turn of a key or a press of a button. But beyond that initial ignition, the battery continues playing a vital role in all of your vehicle's electric systems, but some myths have circulated about this electric heart pulsating in all our autos.
Here's a thorough examination of those myths and some some cold, hard facts to replace them. A car battery should last about six yearsbut like most car parts, that all depends on how you treat it. Of course, a battery can maintain a charge while the engine is on, but once it's off electronics draw directly from the battery.
To avoid this recurring auto nightmare, always turn the headlights and interior lights off when you're done driving. Remember that leaving electronics like GPS or cell phones plugged into a car charger can drain the battery, too. No matter how well you take care of it, eventually your battery will die and you'll need a replacement. Failing batteries usually display obvious symptoms that let you know it's on its way out.
Slow cranking on startup indicates that the battery may not be able to provide enough power to fire up the engine, and an illuminated Battery Warning Light on the dashboard is clear indicator it needs attention.
If vehicle electronics like remote locks or interior lights randomly stop working, a dying or dead battery could be why. Also, batteries—alive or dead—are full of chemicals, so do nature a favor and dispose of dead ones properly.
Don't just toss it in the trash because chances are your local mobile mechanic or auto supply store can recycle it for you. Ambient temperature has a significant impact on battery life and performance. Most car batteries use a liquid electrolyte solution to hold a charge, which is affected by hot or cold weather.
While it takes extremely low temperatures to freeze a batterycold reduces the solution's ability to transfer full power which is why it can be hard to start a car in winter. There's a misconception that buying a battery with a higher CCA cold cranking amp rating will remedy this, but since vehicle computers regulate the amperage required for startup, it actually won't make any difference.
Use a battery heater instead — it's like a toasty jacket that will keep your battery warm and reliable all winter. On the flip side, hot weather can cause the battery solution to evaporatelimiting its ability to hold a charge.
You may notice a rotten egg smell from the sulfur in the solution if this happens. A common myth is that you can simply refill it with tap water to make up for evaporation, but tap water contains minerals and impurities that can damage battery cells.
Use deionized or demineralized water instead, but if you have to do this it's probably a sign that you need a replacement soon. Keeping your car garaged helps the battery cope with temperature extremes so it lasts longer and works more reliably. Almost every driver has to deal with a dead battery, and jumpstarting is usually the easiest way to get it recharged. It's a relatively straightforward process, but it's still important to follow these steps exactly.
Before jumpstarting your car, read the owner's manual.I have an 85 VW Cabriolet, It has a volt meter gauge in the car. When the car is running it states that it only has a charge of about Whenever the signal or anything is on, the volt meter goes up and down in sync with the blinker. I'm pretty sure the alternator is supposed to charge a battery greater than 12V am I right? So why does the battery only hold a charge of 10V on the gauge.
The alternator and the battery are both relatively new, within a year and a half. Possibly defective battery? Defective alternator? Electrical short some where? The battery, fully charged, should read With the engine running, the voltage across the battery posts should read around 16VDC. If the voltage is lower with engine running than with engine not running, something's wrong with your charging system.
If the alternator is fairly new and properly installed and connected, I'd check the cleanliness of battery cables first, then the voltage regulator.
Car Battery Charging and Maintenance
Bad alternator. To charge a battery the alternator has to put out at least. Those older VW's put out around battery voltage at idle and don't really start going over 13 volts till about rpm. Maybe your guage is faulty. Your battery should have about Also, this isn't a bad time to ask for a load test on your battery as well, just to check the condition. A previous due type GM product the alternator can fail in a single of those style that it will bypass all attempting out, regardless of the undeniable fact that it is going to drain the battery in a single day.
With the engine not running the battery voltage should read Sounds like the alternator is bad on your car. Any ideas? Answer Save. Pete M Lv 7. Go to the nearest auto part store and ask them for a charging system check. This will tell you if your alternator is functioning properly.Q&A: How to check your battery charge level and troubleshoot issues?
How do you think about the answers? You can sign in to vote the answer.What should voltage be when car is running? Less than If you measure battery voltage and it is anywhere over See Full Answer. Can you test a car battery? Fully charged automotive batteries should measure at When the engine is running, this measurement should be If you don't have a multimeter to tell you the voltage of your batteryyou can do a test of your electrical system by starting the car and turning on the headlights.
The best way to check battery charge is with a digital voltmeter. A fully charged battery should read A reading of Anything less means the battery is low and needs to be recharged. Take your battery to AutoZone. We have a Duralast Fast Charger that can charge your battery for free while you wait. The fast charger charges volt batteries in about 30 minutes. AutoZone also offers overnight battery charging for 6 or volt lawn and garden, motorcycle and marine batteries.
A car alternator needs to be putting out at least volts ideally between How many volts is a 12 volt battery fully charged?
For instance, a 6 volt battery will have 3 cells 3 x2. That 2. Float voltage is the voltage at which a battery is maintained after being fully charged to maintain that capacity by compensating for self-discharge of the battery. The actual resting voltage, or the voltage a battery will settle at hours after being removed from the charger, is closer to 2.
Resting fully charged 12 volt batteries are around How do you know if your battery or alternator is bad? If jump starting gets your engine started and running, but the car will not start again once you turn it off, the battery is probably the problem. In this case, the alternator is doing its job of keeping the battery going once it has been jumped, but the battery can't hold a charge when the alternator is shuts off. What should your car battery voltage be when driving? With car running alternator charging voltage is between 13 and What are the symptoms of a bad alternator?
The indicator light.