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Still Having Power Issues


Guest mcramsay

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Whats the voltage when the car us running, if its 12.3volts I'd suggest alternator not working. You should be seeing around 14volts with engine running. The alternator should be capable of providing the cars power without the battery draining. Just to add if the alternator output picks up when you rev then the exitation isnt working you need the charge light, in normal use the alt should kick in first time you boot it.

Edited by Jez Morton
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Guest mcramsay

Voltage does drop when the lights are turned on or fan starts and does increase with engine revs

 

Tonight I have done the following - added the correct wiring so that the alternator excite voltage is supplied through a 2.2w bulb as per the manual. (Just waiting on the bits turning up in the post for the warning light)

 

Wired the fan controller to its own switched 12v supply. This is only the wire for turning the unit on, and switching the relays, not the main supply cable for the fans.

 

I had the supply cable for the fans coming from the batt B+ post on the alternator ( along with the charge cable from the alternator) I am going to move this cable so it takes its supply directly from the battery.... I don't know if it makes any difference as the cable ends up terminating at the battery anyway but it will be as the instructions say to do.

 

I have also got a slightly smaller pulley coming aswell that should as said help the alternator put out a little more at lower Rpms, and I won't overspeed the alternator at higher revs.

 

This should put the system exactly as it should be and the alternator should cover the power supply required and charge the battery. As said if the alternator is 75A it should be able to make 30a at idle. Which should cover everything....

 

If not then it must be the alternator. Which even though is new, came from eBay and could be faulty.

 

On the battery front, of the alternator is giving out enough amps to run the full load of the car the battery should never be run down,

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Guest mcramsay

I know this calculator is no where near accurate

 

http://www.qualitypowerauto.com/pages/AmperageLoadCalculator.php

 

But going on this, for custom car electrics, with fuel injection and ignition then the output comes out at 25A which isn't far off what I'm getting

 

My conclusion is and I may we'll be wrong, but I have 6 individual coil packs, the ecu, 6 injectors, IACV, and a low pressure pump and high pressure pump running at 6 bar, so that is going to require a fair amount of amps....

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Because I'm sad I went out last night and measured my current drain, "ignition on & engine off" Pinto EFI with LP and HP pump running, struggled at first as the HP pump cuts off after a few seconds unless the engine is running and the LP pump pulses but the most I could get it draw at steady state was 11 amps. It would peak to 18 admittedly!

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Guest mcramsay

So I had a play tonight.changed the 53mm pulley for a 47mm one, added the charge light and went for it, initially the bulb went out and seemed fine, alternator was chaining output as I switched things on, I could run the lights and fan st the same time. Voltage to the battery was 14.2 volts and dropped to 13.7 when fan kicked in, after 20 mins of working the warning lamp then started to glow dimly, and again I was taking amps out of the battery rather than putting in.

 

I looked at the engine revs which had dropped from cold fast idle of 1100 to 850ish, things returned to normal with a few extra rpm from the engine.

 

The alternator must just be falling short of its required rpm even with the smaller pulley. But I think I can do something with the idle speed to sort this... if I put a few turns on the throttle cable I might be able to raise from 850 to 1000 which seems to be the sweet spot.

 

What has me stumped is that even putting 14.2 volts into the battery the warning light is glowing dimly even though it went off to start with. I am going through the stock BMW wiring loom that goes down to the alternator and looking on the wiring diagram there is a "decoupling diode" in the circuit... I don't know if this is causing the bulb issue.

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