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Alternator Question


reb78
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I have a standard 200tdi 45amp alternator, dual batteries connected with a T-max split charge.

The main battery runs the normal vehicle electrics, the eberspacher (when it is cold), an amp and my facet fuel pump.

My second battery was really installed to run the camping fridge and give me 4-5 days of juice when parked up at a camp site and not risk the main battery going flat.

Is the 45 amp alternator ok for my use? Its not like I have big drains like winches running. I am only asking as the current alternator is being a little odd on startup - no charge registering for 5-10 seconds on the voltmeter and the rev counter sits very low for the same period. So if I need to change the alternator should I change to a higher output one?

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It should be fine, provided that you are not doing continual short journeys and it is working properly, and you don't have loads of current gobbling accessories. Of course it will do no harm to upgrade if you want to.

Voltmeters are generally slow to react to any change, but assuming the rev counter gets its signal from the alternator, as many vehicles do nowadays, suggests that it is slow to wake up ?

Maybe poor earth, dirty or oily slip rings, worn brushes possibly, which is normally the main cause of alternator failure.

Try a multimeter across the battery and see if it makes around 14 volts with the engine running, and that it still does with the headlamps, heater blower , and rear window on.

 

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65amp lucas alternators aren't much bigger in physical size, but you get a bit more capacity. I did this upgrade years ago, I also shored up the wiring to it too. Land Rover do a standard engine loom upgrade for the bigger alternator. I'll see if i can find a part number.

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 It does sound like as L19Mud says the excitation is  not happening at start  - the revcounter is driven from  a phase of the output winding, so dead revcounter=no output definitely, but it is fed through the charge light (and usually a parallel resistor) so if the light comes on the current  must be going somewhere.Perhaps this a dead field diode, and it is OK once it has built some speed, and produces enough volts on  the remaining diode. Remember, a 45 amp alternator probably doesn't produce 45 amps till it's spinning at quite a decent speed. If you sit in traffic a lot, engine idling , eberspacher on, listening to a lot of deep bass etc perhaps demand exceeds supply sometimes

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If the split charge is wired to the charge warning light it may be loading the line down and delaying the excitation of the alternator, as long as it comes up eventually it's probably fine.

As for upgrading, if you're not using any more power than usual once you're running I wouldn't worry - all you'll gain is the 2nd battery will be refilled faster, but that could mean you need to drive for 15 minutes rather than 20 minutes to replenish it.

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1 hour ago, FridgeFreezer said:

If the split charge is wired to the charge warning light it may be loading the line down and delaying the excitation of the alternator, as long as it comes up eventually it's probably fine.

Other way around, the warning light is not supplying enough current to get the alternator up and running. If the light goes out when you come above idle, then stays out, then it's all fine.

As cackshifter said though, below about 3000rpm (alternator rpm not engine) you won't acheive 45Amp out. Expect half that or less at idle speeds. If your typical load at idle rpm is below 20A, there's probably no great benefit to an upgrade.

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12 minutes ago, TSD said:

Other way around, the warning light is not supplying enough current to get the alternator up and running.

That what I said :ph34r: the lamp limits the current, if you hang a relay off it there's even less going through the alternator.

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2 hours ago, FridgeFreezer said:

it may be loading the line down

... clearly has is different meaning to you. It is not 'loading the line down', but in fact 'not pulling it up'. If you removed the bulb entirely, would it then be loading it down to the greatest possible extent?

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I have a similar effect on my 109, using a fairly cheap Durite heavy relay rather than a pricey proper split charger, that takes its control feed from the alternator exciter/charge light terminal.  I need to momentarily blip the throttle to raise the rpm a little to get the alternator charging after start, maybe around 1000rpm.  After that, everything is normal.  I think it’s just a symptom of the relay being controlled from that circuit, like John said - with the relay disconnected, the alternator behaves normally.

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The weird thing is that this has only just started. I fitted the T-Max and second battery at the start of last summer.

As far as I can tell, the control unit controls when the relay kicks in - the only connection to the original system is the positive (main battery to relay unit) and earth (joining the two batteries). I guess the T-Max control unit detects a certain output going into the main battery and then switches the relay to allow charge to the aux battery.

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