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2009 Megane mkIII hatchback 1.6 16v petrol
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Discussion Starter · #1 ·
Hi guys

I've just had my battery/alternator tested as I've recently noticed that the car is sometimes a little slow to start. It does always starts, but it just doesn't seem to crank and fire as efficiently as it once did, and I'm wondering if anyone can help me decode the test results....

Handwriting Rectangle Wood Font Parallel


I note that the alternator result of 13.40V says "TOO LOW", does this mean I might be looking at a new alternator at some point?

Is the 79% start capacity within the expected range?

The other thing I'd like to query is the "BATTERY UNSERVICABLE". Does this just mean it's a sealed battery that can't be serviced, or is it indicative of a potential fault/problem?

I'm just trying to be preventative of any future issues before the colder weather kicks in. And before anyone asks, I have no idea how old the current battery is! We've only had the car for about 18 months. FWIW - it's one of the best and most solid 2nd-hand cars I've ever bought, which is why I'm trying to keep it well maintained!!!

Any help or advice is greatly appreciated.

Cheers

sid (y)
 

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Grand Scenic 1.6 2007
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Hi Sid and Welcome:)
The regulated voltage looks low. I would expect 14+. That said some newer cars back off on charging to save something or other. That probably does not apply to a 2009 car? At that age I would expect that alternator brush wear is possibly affecting output and a diode or two might be not working. Diode failure would reduce output and cause drain from the battery. Perhaps part of the problem is that the car is not recharging the battery fully due to a combination of low regulator output and short trips. Not a new alternator but a new regulator and brush pack.
12.7 is high for the resting voltage. It was probably tested soon after driving and the battery had not settled to it's true voltage. A better test is first thing in the morning. 12.4 is about 75%, 12.2 about 50%. Ultimately sulphation reduces the current that the battery can deliver and the charge it can accept. Petrols can tolerate a lower battery capacity as the starting loads are much less. I reckon a large number are pottering about on 80% capacity or less quite happily. The battery date is most likely on the battery somewhere, either on a label or scratched into the plastic case.
 

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Technical Supremo.
Scenic II, 2004, K4MW761, DPO
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We can have huge War and Peace novels written here on the subject ..................



IMO:

Battery capacity is referencing the applicable measurement standard (EN in this case - value of 475A in this case - probably/definitely should be stamped on the battery and tested against THAT spec) ............... in general 80% starting current capacity when tested gets rejected by most testing appliances.
If you can cope with a failed battery only when it actually fails to start the engine, then it may still be "serviceable" for a few months - else replace

Alternator - that result quoted I find quite acceptable depending on the battery and alternator temperature at the time of testing.
On older alternators output voltage drops/compensates for "guessed" battery temperature (seen by the alternator) - I would not touch that alternator yet. I would however want to see around 13.8V+ when the engine is cold.
 

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Super Moderator Technical Supremo Platinum Member
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Forget war and peace, a poor battery can affect charging.
Assuming your battery test was a load test, replace it, if it is older then 5 years, it is on borrowed time anyway.
Shop about for prices
 

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2009 Megane mkIII hatchback 1.6 16v petrol
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Discussion Starter · #5 ·
We can have huge War and Peace novels written here on the subject ..................
Hahaa, I can see that!! I've done quite a bit of reading on it before making this post!!

Anyway, thank you both for the responses.

To add a little more, I've actually had the battery on trickle charge over the weekend, so that could be a factor in it showing fully charged for the test. And the car was at full running temp at the time of the test.

The guy who tested it for me advised to wait until the colder weather really kicks in, then go back and he'll re-test it for me, and in the meantime just use the charger to top it up occasionally if it's seeming 'dull'....

So, I'm thinking that I might wait until we get a proper cold snap, and then take it back for another test, first thing on a Monday morning before driving anywhere else. I'll also have a mooch and see if I can find a date on the battery (will it be the manufacture date or installation date?)

Not a new alternator but a new regulator and brush pack.
I've fitted new brushes to the likes of washing machine motors in the past, and I'm assuming that this will be a similar kind of job once you get clear access...?
 

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2009 Megane mkIII hatchback 1.6 16v petrol
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Discussion Starter · #6 ·
Forget war and peace, a poor battery can affect charging.
Assuming your battery test was a load test, replace it, if it is older then 5 years, it is on borrowed time anyway.
Shop about for prices
Cheers. I've already got a reasonable price sorted should I need a new one. I'll try and find the date on it tomorrow. I think one way or another, I'll be getting a new battery before the end of the year (y)
 

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Grand Scenic 1.6 2007
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I've fitted new brushes to the likes of washing machine motors in the past, and I'm assuming that this will be a similar kind of job once you get clear access...?
Mine stopped charging in the middle of the night 45 minutes from home and we made it on dips without radio or heater. The charge warning lamp was lit. It was tricky to extract the alternator. Some jack the motor up. I dismantled the alternator and took it out in halves. Turns out I could have replaced the brushes in situ. Someone here has done it. I would check all six legs of the rectifier pack.
 

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Discussion Starter · #8 ·
Mine stopped charging in the middle of the night 45 minutes from home and we made it on dips without radio or heater. The charge warning lamp was lit. It was tricky to extract the alternator. Some jack the motor up. I dismantled the alternator and took it out in halves. Turns out I could have replaced the brushes in situ. Someone here has done it. I would check all six legs of the rectifier pack.
"in situ" sounds more like my kind of approach!! :ROFLMAO:

I'm unsure of what you mean by "I would check all six legs of the rectifier pack."??

I'm hoping that the alternator won't be an issue. I'll address the battery first. However if it does, I will absolutely be looking into re-furbing it myself if possible....
 

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51 plate Laguna 2 1.6
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You mention poor cranking- if it doesn't fire in a couple of seconds the battery's on borrowed time, but it may well borrow another couple of years if, as I do, you charge it overnight every fortnight. But ours is in a garage- if you want it to start outside on the first freezing morning, you know what to do.
 

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I'm unsure of what you mean by "I would check all six legs of the rectifier pack."??
The alternator generates alternating current in three phases. This has to be turned around so it's all going one direction for the car DC system. Diodes are arranged to let the current in each phase pass only one way. You need six. They have a low resistance in one direction and effectively infinite in the other. When they fail, current goes the wrong way and battery can leak back through them and you may find an AC ripple at the battery terminals if your meter is up to the job.
Bottom line, find the six diodes and check low resistance one way and open circuit or very high resistance the other.
Your test said ripple okay so that would mean that the diodes are passable.
 

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We can have huge War and Peace novels written here on the subject ..................
I have given this some thought and Tolstoy may not fully represent the literary value of what we have.
Now, Dostoevsky is another matter, The Idiot perhaps? :)
 

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Discussion Starter · #12 ·
The alternator generates alternating current in three phases. This has to be turned around so it's all going one direction for the car DC system. Diodes are arranged to let the current in each phase pass only one way. You need six. They have a low resistance in one direction and effectively infinite in the other. When they fail, current goes the wrong way and battery can leak back through them and you may find an AC ripple at the battery terminals if your meter is up to the job.
Bottom line, find the six diodes and check low resistance one way and open circuit or very high resistance the other.
Your test said ripple okay so that would mean that the diodes are passable.
Ah right, that makes a bit more sense now. Basically check the resistance of each is all running uniformly in the same direction?
 

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Discussion Starter · #13 ·
Could issues with the serpentine belt/pulleys/tensioner cause low voltage from the alternator?

I have noticed that sometimes on a cold start there's a slight intermittent creaking noise that seems to be coming from the belt area, which dissipates within a minute or so. The belt itself is in decent condition, so I'm wondering if perhaps a previous owner has had the belt changed, but not the pulley and tensioner.... :unsure:
 

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Usually a belt issue that is enough to reduce charging will let you know in a rather loud way.
Sounds like a pig being slaughtered (or my daughter when I steal her chocolate)
Creaking would sound more like tensioner ????
 

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Discussion Starter · #15 ·
Sounds like a pig being slaughtered (or my daughter when I steal her chocolate)
:ROFLMAO:

Cheers(y)

I think I'll pop the belt off and have a closer inspection of the tensioner, and anything else the belt runs on. In fact I'll probably just replace the lot..
I'd rather swap out any failing components preventatively instead of waiting til they cause a real issue, and it will absolutely rule the belt out from being a cause of low charging
 

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Fair play.
My normal motto is if it aint bust don't fix it.
But belts are an item which are worth checking and sorting if in doubt, even if they look good.
 

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Discussion Starter · #17 ·
My normal motto is if it aint bust don't fix it.
I would ordinarily agree with that, and usually operate similarly myself, however this particular car is (relatively) low mileage, in very good general condition, and drives perfectly.

For the price we paid for it, we really got an excellent car, and I would like to think we'll get a good 4 or 5 more years out of it. (I know, I shouldn't tempt fate!! :LOL:)

As it stands, it owes us nothing really, so I'm happy to spend a bit of money, time and effort on it to try and keep it sweet.
 

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Discussion Starter · #18 ·
Just been looking, and there's not a lot of space to manoeuvre around the serpentine belt. I'm definitely gonna swap it out, but it looks like I might need to go in through the wheel arch to get to it...
I don't suppose there's a guide on here anywhere that shows how best to do it?
 

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Super Moderator Technical Supremo Platinum Member
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but it looks like I might need to go in through the wheel arch to get to it...
Deffo go through the wheel arch...all open for you that way.
Not sure about a guide but take a photo or two before starting so you don't forget where it goes.
Tensioner should be a spring loaded pulley...spanner or allen key on the pulley "fixing" and lean on it to overcome the spring...relax and it is tensioned.
 

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how to check each diode with multimeter, but given your results I think it unlikely a diode has failed.
It's very easy to predict when your battery will fail, it will be on the coldest day when it's snowing and you're in a hurry to get somewhere.
Rectangle Font Parallel Slope Diagram
 
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