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The mkiv Supra Owners Club

1 for the electrics experts alternator overcharge


hodge

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Hi guys

I've a 200 amp alternator fitted to the car but am seeing silly voltage.

My dash2 is seeing between 14-16 volts whilst driving which is way too high IMO.

Is there any cause for this apart from a faulty alternator?

 

Is there anything on the market such as a charge stabilizer/regulator or the like to say cap it at a steady voltage so I don't over charge the battery and fry it. I don't want to send the alternator back abd wait for a replacement if I can help it if they even agree to replace it at all.

So was hoping I could fit something inline between the alternator and battery to steady the charge at say 15 volts, which is the max an optima battery will take.

 

Any advice would be great.

Thanks

John

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It will be an internal regulator in the alternator, you'd know if not as you'd have had to wire up an external one, and I haven't seen one of those since the Lucas ones in Rover 2000's ;) Probably a faulty regulator. Why do you need such a huge alternator output? It may be possible to use the regulator from a lower output unit to test the theory. Whatever, that voltage is way too high, it'll boil electrolyte and maybe damage electrical items like bulbs or things without good over voltage protection.

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Does it immediately fall or does it hold at 16V+?

 

It jumps around a lot when I'm driving to be honest but never drops low. I'll take her for a drive with Bossco in the back checking the voltage on a multimeter at the weekend when this weather clears up.

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I've been through the Syvecs software and there is a section for alternator output. I'm not wanting to change anything until I speak to Ryan though incase I melt something. I'm hoping the Syvecs software could be the answer by clamping the voltage.

I've rang Ryan and left a message.

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Sorry Nothing you can do on ecu to solve this. Ricky is talking about his battery offset for his injectors.

 

My advise is to check all grounds on Intake manifold are good and also engine to chassis ground

 

Ryan

 

Ok bud. I'll get onto that tomorrow mate.

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you should have a sense wire marked s from battery to alternator.

you need to first measure across the battery, engine running and measure voltage - should increase as revs rise but not get to 16 volts

-the measure the battery engine off but on load -ie lights on

now back to the sense line, the voltage regulator within the alternator uses this to "sense" the battery voltage - if for example one cell is down or electrolyte is low then the regulator will up the voltage as it sees a low voltage in , or more likely the sense line has a poor connection or corroded connection at the back of the alternator(small contact) then the voltage seen by the regulator is lower(even thoughit is fine at the battery) so it pushes up the output .

fluctuating output as you say is likely with a poor connection

All assuming it is the correct alternator fitted ,with same wire connections?

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I'll check all the connections and earths in the morning.

 

The voltage on the dash2 display reads around 14v at idle and when the car is revved. The only time I'm seeing a high voltage is while I'm driving. And it jumps around between 14 and 16 volts.

I'll take the car for a drive with a multimeter on the battery and monitor the voltage getting there. I've got a feeling that the voltage at the battery will be fine but all will be revealed at the weekend. I'll post up my finding on here and hopefully I'll get to the bottom of it.

 

Thanks everyone for all your input I'll keep you informed.

Thanks again.

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