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Alternator clarification

GeekOKent

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So, I seem to have a wires issue. Came to the 105 this morning to find the battery reporting 12.10v , so put it on the charger for a few hours , went for a drive. But when I got back after a 2 hr drive, no starts after setting off from home, the battery was only at 12.15v.

Spent a bit of time and I seem to have this going on:

Starter battery is 'low'. It turns the engine, starts up ok. I read 12.66v across the terminals. After about 5 min, it jumps to the 14.4v expected.

But the moment I put some load on with the engine running, eg. Headlights or heater/blower, the voltage across the terminals drops back down to 12.5/12.6v.

If I drive around without any electronic load, lights off, heater blower off etc. The voltage does stay up, and the battery is happily charging. Given time of year, and weather conditions - I don't want to drive without lights or heating. So, what's up? Alternator on the way out?

Battery is from battery megastore, 750cca, starter, 2 years old, and the health indicator is 'green'.
 

stumog

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Thats a odd one. Maybe the battery isn't that good. Have you tried disconnecting battery and giving it a good charge up.
 

Grimbo

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Crude but...
Try giving the alternator a loving tap with a hammer....
I've known brushes to be worn and sticking so they just make contact ...bit of a shock can let them make good contact for a while ... at least long enough to diagnose ....
 

karl2000

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Does sound like the alternator to me tbh... as soon as it gets a load, it cant put out enough amps?
 

nick_the_fish

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How many miles on the alternator GoK? Is it still the original?

I had something kinda similar on my 105 a few years ago. Bear in mind you don't necessarily need a full new alternator. I had mine rebuilt and it was as good as new. I can't remember who did it and can't find the e-mails in my inbox. Probably got the recommendation from someone on here.
 
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Ben Stratford

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Check battery clamps not cracked and tight and grounds are all secure too. Does alternator body get warm or hot in any circumstance?
 
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GeekOKent

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Appreciate all the comments and feedback.

Had another run today, the alternator is not super hot - mildly warm, after a 120 mile drive. I have a new battery on its way, and new clamps.

@nick_the_fish this is the original alternator as far as I can tell, milage is 120k

@stumog I left it on charge the last 2 days but after the drive this morning is again showing 12.3v so suspect it's on the way out.

@Grimbo just tried the gentle hammer, let's see if it makes a difference.
 

GeekOKent

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Worth noting that the 105 is a single battery setup. Since I have the space, is there much more to adding a second battery than just drop it in, and wire it in parallel with the first one ?
 

stumog

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Worth noting that the 105 is a single battery setup. Since I have the space, is there much more to adding a second battery than just drop it in, and wire it in parallel with the first one ?
It really is that simple. Or you can fit a volt sensitive relay between them for extra protection and split what comes off them
 

flint

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Excuse my ignorance on the 105, but does it have a heater grid on the inlet for cold starts like the 80 ?
 

karl2000

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Since I have the space, is there much more to adding a second battery than just drop it in, and wire it in parallel with the first one ?

You can wire a battery in parallel easily enough, but what are you looking to achieve with a second battery?

It wont really add much to reliability, as if one battery goes bad it will pull the other one down soon enough. You're also doubling your chance of a battery failure, by having twice the number of batteries that can fail.

It would increase the cranking amps, so if its a bit slow to start in cold weather, it might give it a bit of a boost. But you probably don't need it.

If you leave your lights on or run electrical stuff without the engine running, it will power your electrical kit for double the time (say)....
 

uHu

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Because of the voltage going down that much with load, sounds like a blown diode in the alternator. Take out the alt, disassemble and measure. Probably the diode bridge can be purchased separately.
 

nick_the_fish

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Worth noting that the 105 is a single battery setup. Since I have the space, is there much more to adding a second battery than just drop it in, and wire it in parallel with the first one ?
It is that simple, although due to the size of the cables you'll need some heavy duty crimpers etc. But as Karl says it won't solve the underlying problem, which seems to be the alternator.

It's a very easy job to take out the alternator on the 105 (assuming you have the unaltered 1HZ). IIRC there are 2 wires that you need to disconnect from the alternator, undo the tensioner bolt to remove the belt, and undo the lower bolt holding the alternator in place, although its been 8 years since I did mine.
 

GeekOKent

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A quick update here. I have an 100A alternator on its way from Australia. In the mean time, I did some gentle tapping and reseating all the main cables etc. Things have been working ok. 3 weeks of driving and it's actually been fixed.

Except this morning again it's gone into this made state. Trying to now see what is going on and it feels like something to do with the lights. I might have a parasite drain that only gets activated when things are very wet and very cold.
 
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