Alternator or battery?

carl310166

I was driving to work in monday,and the battery light was flickering faintly.When i left work that morning,it continued to flicker.

Last night when i needed to get to work,the car would not start,the battery was flat.

Does anybody know how i can tell if the alternator OR battery has packed up? Is there a test i can do before buying either?

Thanks.

mr_fishbulb

I'm just taking a guess here, but if the light was flickiering when you were driving that would suggest it was the alternator.

But it's just a guess.

wagster_2

Easiest way is to get a meter that reads voltage, connect it acroos the battery terminals and measure the voltage with engine switched off, then start the engine and measure the voltage again, the voltage should be slighty higher due to the alternator charging the battery, if not the aternator is on its way out, if you cant get hold of a meter another way is to connect a 12v DC lamp across the battery and watch the brightness as you rev the engine, if the lamp gets brighter you alternator is ok.

ronnyb_2

Try the fanbelt as well, it may be slipping.

basill

If you dont want to get your hands dirty, quick fit et al have battery testing devices and will usually do it for free.

B

boogiemaster

Just switch your lights on at night and rev up the engine, if the lights get brighter then it’s not your alternator it’s your battery.
Looks like there are a few dead cells in your battery, just buy a new one and problem solved.
Also, don’t buy a cheap battery as it’s not worth it, come winter a cheap battery might not start your car.
Pay a little more and get one with a three to four year warranty as you will need a decent battery with the cold spells we have been having.
I bought a batter for my land rover discovery and its cost me £65 and it has a four year warranty on it, it started my car when we had the minus temperatures the cheap one didn’t.

tonys_3

It may just be as simple as a slipping fanbelt. But if its not, you may have to replace either the battery and/or the alternator now, and at least one of them
within a few months.
To avoid that, it is recommended that whenever you replace an electrical appliance, that you check out the whole electrical system at the same time. This will highlight
other problems should they exist. There could be an underlying problem with your voltage regulator for example and if not attended to, will blow your battery or alternator again.
Given the prolonged cold spell that we are having, the cause of your problem may well be that your voltage regulator has,even in its normal workings, consistently undercharged the battery. And with you driving at night compounds the problem, since you will be using head lights, heater, blower, rear screen heater, and possibly fog lights and windscreen wipers all at the same time, which makes it hard for the alternator to supply sufficient power to them all and recharge the battery at the same time.
Normally better to use your regular garage rather than a "free" testing service which is often a sprat to catch a mackerel -especially in this instance where alternators and
batteries are often quite highly priced.

carl310166

I bought a battery/alternator testing device,it showed the alternator was not charging the battery,so i bought a second hand one from the scrappy yesterday.

I fitted it,and the testing device showed that the aternator was now charging the battery,so i drove to work as normal,but the battery light was still flickering slightly,does this mean the battery is still a bit run down? and will charge over the next few days?

Do you think i should take the battery off the car,and charge it independently?

Thanks in advance.

skiddy2k

id say, take the car for a spin up and down the motorway, this way you know that the battery will have been given a good charge - or, hook it up to a charger and charge the battery till its full. (check the battery water level to make sure its okay)

once you've done this, take it to your local halfords store an hour or so after you've given the battery a good charge. they will test it for you and tell you the amps in the battery after you took it for a drive. make note of the value.

go their the next day, without having driven your car up the motor way and tell them to check it again.

Now, if the battery isnt holding the charge, the amps will be substantially lower than the first measurement you got from them. therefore, the battery is a bit knackered and you'd probly think about replacing it with a new one.

If the battery shows a similar amps rating, you know that the battery is fine and your on your way!

hope it helps,
tell us how it goes,

Skiddy

Wig

If you had been able to bump start the car then it would have been the battery. If not then it is the alternator.

Symptom suggests alternator (flickering battery light). The scrappy one is prolly no good either, you should be able to get your money back. Buy a new one.

Defo remove the batt and give it an overnight charge.

BobToo

Alternators are one of the things I wouldn't buy from the scrapyard, along with tyres, batteries and exhausts unless they are obviously nearly new. The saving on new price just isn't enough. Look up Motor Factors and LSUK in your phone book and phone for a price on a new one. I say "new", what you'll get is a reconditioned unit that's as good as new and they'll want your broken one to send back for reconditioning. It might seem a bit dear but it turns your car back into a useful tool. A car with dodgy electrics is a nightmare.

The battery light means the battery is giving more power than it is receiving, which is why it comes on before you start the engine. That always means the alternator or regulator (and the regulator nearly always lives inside the alternator nowadays) isn't working. It will NOT tell you if your battery is faulty.

Many alternators have a brush/ regulator pack that plugs in easily and effectively replaces just about everything that can go wrong. These cost a little over £10, again from LSUK/ motor factors.

Some alternators (Vauxhall and Saab being two) are rubber mounted and need a separate earth wire to the engine. These can break while seeming to be intact, or they can kill the alternator by having a loose connection that makes and breaks with the vibration of the engine. A good tug will expose any weaknesses here.