Battery or alternator?

[dave c59]

Battery keeps letting me down. Starter motor starts sluggishly and then speeds up before the engine catches, or it just dies and needs a jump start or battery charger.
I've changed the brush pack in the starter motor to no avail.
battery voltage when charged is 12.6v.., engine running at 1500rpm then voltage is 13.6v.
Anyone have a clue what I should start with (no pun intended!).

2005 S60 D5.

[davebb]

Hi you need to do a load test on the battery,
also is the engine earth cable good,
Dave

[wynnj]

Originally Posted by dave c59

Battery keeps letting me down. Starter motor starts sluggishly and then speeds up before the engine catches, or it just dies and needs a jump start or battery charger.
I've changed the brush pack in the starter motor to no avail.
battery voltage when charged is 12.6v.., engine running at 1500rpm then voltage is 13.6v.
Anyone have a clue what I should start with (no pun intended!).

2005 S60 D5.

If it's your starter that's sluggish, change it, as they can chew up the teeth on the starter ring if they don't engage cleanly. £150 for a recon starter is a lot less than removing the gearbox to change the starter ring when the starter will no longer engage with it. I learnt this the hard way!

[dave c59]

Originally Posted by davebb

Hi you need to do a load test on the battery,
also is the engine earth cable good,
Dave

Thanks Dave, what's a load test? Is it something I can do with a multimeter?

Good point about the engine earth cable, any idea whereabouts it is?

[reggit]

Mine was giving similar symptoms. In my case the earth strap had failed. Only found out when it let me down.

It attaches on a lug near the starter motor down the front of the engine and runs to the near side inner wing. Mine failed inside the strain relief moulding at the starter end so wasn’t obvious.

[Brendan W]

What reggit said. Mine failed last year just at the lug below the starter.
You could check for pos and neg drops.
Check the voltage between the alternator post and the big post at the fusebox and check between the alternator case and a good body earth. Ideally less than 0.1 Volt.

[Georgeandkira]

A load tester is recognizable by the fact that it's a box with holes (for ventilation) about 6" X 5" X 12" long with short clamp cables and a meter.

Other units are hinged without clamps so you can spread the contacts to touch your battery's terminals. The construction uses a brush-on-coil so the amount of resistance is set by the angle of the tool.

Either holds a resistance coil of wire through which the battery's juice is sent. It will warm up hence the ventilation.

They leave it connected for 10 seconds or so to see how strong your battery is. It's been called "the only real way" to test a battery.

[old onions]

Originally Posted by dave c59

battery voltage when charged is 12.6v.., engine running at 1500rpm then voltage is 13.6v.

In my opinion 12.6 volts is low for a charged battery with no load. I think it should be 13.2 V (1.2 volts per cell)

Although an actual measurement is much more accurate and meaningful, I have always used a quick and easy short cut to alternator condition.

Once the engine is running switch on as many electrical circuits as you can to put as high a loading on the battery as possible. Now rev the engine and look at the brightness or intensity of the headlights. If they immediately get brighter the alternator is probably pumping out a good current into the battery.

I agree this method is far from foolproof, and no replacement for some proper measurements, but should give an initial indication.

[oragex]

Do you have one of these ? https://www.youtube.com/watch?v=IVDHzTkjHlc

It helps because the alternator output voltage varies depending if the battery needs charged or not. Basically, at start up the battery needs charged a little to top it up (i.e. until it reaches some 12.7-12.8V) so the alternator puts out some 14.5v for a few minutes. Then, once the battery has been fully charged, the alternator voltage drops to some 13.5v to power the various electrical car systems.

Now, the above is the ideal operation when the battery is in top shape.

However if the battery is old, it gets very slow to charge so you may see the alternator putting out 14.5v for long time while driving.

On the other side, if the alternator puts out always only 13.5v, even when right after starting the engine, then there is one or more problems:
1. the battery cannot get fully charged, which will damage it in the long term. 2. the battery may be already very worn and no longer accept a full charge so the alternator doesn't even try to charge it any longer.
3. the alternator may not be the correct one for the car and may not put out the correct voltage to properly charge the battery. For example, in these cars there are two different regulators: one for 2001-2004 and another one for 2005-2009. You need to have the correct one for your car year, or the alternator will not properly charge the battery. This is a site that has a good fitment section Fcpeuro.com

As for the starting problem, try once connecting the battery to a second vehicle, and try starting. See if the starter spins easier. That will tell you your battery doesn't provide enough ampers any more, so it may need replaced, but be also sure the alternator puts out the right voltage with the new battery. You may also definitely want to check for current drain when the car is parked overnight, because this can damage a new battery in the long term. If the starter still spins slowly even when connected to a second car, then there it may have a problem - look for the cables around the starter or the starter itself

[Symes]

+1 for checking the earth strap (low front of engine under starter). My battery would last a week or so after an off car recharge, its a cheap Tanya one and 4+ Years old so I was looking for replacements but thought I'd check the charging circuit first.
The alternator was outputting 13.5V checked with earth on the engine, but 12.5V when earthed to the body. The earth strap to engine surfaces were slightly dirty looking but a few minutes with some emery cloth got the surfaces nice and shiny, smear of copperslip on reassembly. Output measured with earth to body returned to 13.5V (rising with revs as expected), starter turns over quickly again and the battery seems as strong as ever!