Ok so I think I have asked this before but can't get to the bottom of it so all advice welcome. I have a new battery fully charged then occasionally, once every 10 times I take the car out the battery fully discharges all power leaving me stuck. Occasionally if I leave it for 10 to 15 mins the car will turn over quick enough to fire up but generally very slow cranking which then requires a full battery charge. Once charged cranks over really quickly and no problems firing up. I have cleaned and checked all the earth cables, replaced the battery, Alternator looks new so scratching my head here as the problem is intermittent with 9 out of 10 times the car fires up after any journey just occasionally virtually complete drain of the battery even after a 5 minute journey....normally school drop off... any idea on what to check/test or replace? thanks
To test, you need a volt meter.
The battery (when fully charged) will show around 12.5V test this with the battery still connected.
Get someone to start the car. Turning on and waiting for the heater lamp to go out and the relay to 'click' the battery will be below 12V, 11 point something is normal.
When the car started, rev the engine a little (1/4 throttle for example) and the voltage should rise up to 13.7 (or slightly higher).
This tells you that the alternator is charging ....
If the voltage stays around 12V (or slightly lower) it isn't charging.
Let us know.
The battery (when fully charged) will show around 12.5V test this with the battery still connected.
Get someone to start the car. Turning on and waiting for the heater lamp to go out and the relay to 'click' the battery will be below 12V, 11 point something is normal.
When the car started, rev the engine a little (1/4 throttle for example) and the voltage should rise up to 13.7 (or slightly higher).
This tells you that the alternator is charging ....
If the voltage stays around 12V (or slightly lower) it isn't charging.
Let us know.
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tottot
Well-Known Member
After you have done the above and found the charging is ok
Remove and clean the main live connection's at battery and at the starter. A poor intermittent connection at the starter can make it seem like battery has suddenly gone flat. If your headlamps are still bright when it does not start then likely a starter problem.
Remove and clean the main live connection's at battery and at the starter. A poor intermittent connection at the starter can make it seem like battery has suddenly gone flat. If your headlamps are still bright when it does not start then likely a starter problem.
If it's a calcium battery (many are) it needs to be charged over 14.5v.. usually 14.6 or 14.7, or it will slowly die. Most alternators are upgradable if you only get 13.6.
Also. You need to measure the charging voltage between the output post and alternator body to rule out issues elsewhere
Also. You need to measure the charging voltage between the output post and alternator body to rule out issues elsewhere
Please do. Once you have checked the things i've mentioned, and it's still not right, there is a set of stage 2 checks ....
So I’ve had a snap on tester connected to the battery and when reving the volts don’t go up so it looks like a alternator issue. Saying that the alternator is nearly new and correct for the car as confirmed by a Land Rover specialist near me. He suggested an earth strap from the chassis to the engine as it’s only earthed from the battery to the chassis? Does this sound right or could it be a dodgy alternator as all the belts etc are new
Good. Lets recap: - Tthe battery shows circa 12V when at rest, drops a little when starting but doesn't lift up towards 14V when running.
Which as you say indicates that its not charging.
If you look on the back of the alternator there are 2 connections. One is a thick brown cable (sometimes 2 together) to a large spade and the other is a smaller spade with a thinner cable.
That thinner cable/smaller connector should have 12V on it when the ignition is on and also when the engine is running - can you check the voltage on that smaller connector/cable and report back ?
Which as you say indicates that its not charging.
If you look on the back of the alternator there are 2 connections. One is a thick brown cable (sometimes 2 together) to a large spade and the other is a smaller spade with a thinner cable.
That thinner cable/smaller connector should have 12V on it when the ignition is on and also when the engine is running - can you check the voltage on that smaller connector/cable and report back ?
Sorry for the delay in responding I’ve been moving house and the turbo on my 335d crapped its pants. Anyway when volt meter is on either connector from the alternator I’m getting just under 12v then when revs are increased no change in output, still around 12v or just below. Based on this would we say the alternator is not putting charge back into the battery or is this something else.
You need to check the voltage between the connector on the back of the alternator and the alternator body.
It does sound like it's dead though, or at least the voltage regulator is dead
I’ve had the volt meter on the body of the alternator while attached the the spade connector and still doesn’t go above 12v when I rev it. As stated new battery which is the correct size and capacity and checked and cleaned all the earth straps. To be honest it feels like its discharging slowly when I’m driving rather than running down over days parked up. And obviously not charging even after a good motorway run. The next step I guess is to replace the alternator although this one looks new and is appropriate for the landy and see where I end up. This will be after fixing the brake lights which appear to have decided to stop working oh and the oil I’ve just noticed leaking out of the rear hub.
mick the builder
Well-Known Member
Just because it looks new doesn't mean it's working properly. You can get bad ones out of the box. Take it off and get it checked/ overhauled properly.
bluedog333
Well-Known Member
Sounds like a diode has packed in on the alternator. Get it tested with a multimeter, they are repairable, although I’ve never done this myself!
So never resolved this issue so any advice welcome. New alternator fitted kicking out over 13v when revving so working fine. Battery is new and is charging when engine running with volt meter. Charged battery cranks over fine. Go for a run battery will drain so it won’t crank over. Sometimes if I leave it for 10 mins or so it will crank over but labourer. I’ve no idea what’s going on. Checked all earth straps too
Right, so you're starting the day with a fully charged battery.. 12.5-12.7 is normal. You start up and you're getting 13 volts? That's not enough, 13.7 as a minimum but won't properly charge a modern sealed battery.. 14.5-14.7 is more normal.
While it's idling, turn on the accessories, lights, fan, rear heated screen etc, what voltage do you read then?
While it's idling, turn on the accessories, lights, fan, rear heated screen etc, what voltage do you read then?
