# overdriving the alternator?



## kismetcapitan (Nov 25, 2005)

it's summer, and there are times when I'm stuck in traffic, idling at 1000rpm, and I've got the A/C cranked, the electric fan is on (engages whenever the A/C is turned on) and to pass the time I'm listening to my stereo, which can draw up to 80 amps of power on its own. On a couple occasions, after 30-40 minutes of being in said traffic jam, the car would stall. I'd have to restart, and shut down everything, sometimes even the headlights, just to keep spark flowing to the engine.

So the thought has just occurred to me - why not put in an OVERdrive pulley, to spin the alternator faster. The regulator will then think that at a given rpm, it's spinning faster, and then peak output would come in at a lower rpm, say 2500rpm or less (engine speed) than the usual 3000rpm.

What's the downside to this? Finding a four-ribbed pulley of a different size and a belt is easy, and the swap would take an hour or two. At 8000rpm the alternator's regulator has the thing limited anyways. I guess...the alternators parasitic load on the engine would come in at a lower rpm, when the engine is making less horsepower.

How much horsepower does an RB26 in vacuum, at 2000rpm make anyways? The 160 amp alternator that I have in my car apparently (as far as I've been able to glean from the internet) saps around 11-14hp at peak output. That could be a significant number if the engine is only producing a very low-torque 50-odd horsepower while puttering around in traffic. If I had to guess, I'd say the horsepower of the RB26 at 2000rpm, basically running N/A as the turbos aren't spooled, may be even lower than that.


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## blue34 (Jul 28, 2005)

er just drive around the problem, turn the stereo down... hold the revs slightly higher occasionally on the throttle when your in traffic. 

I wouldn't have thought that increasing the rpm of the alternator was a good idea at high engine revs


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## miragev (Apr 11, 2007)

at what rpm does you alternator achieve peak output ?


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## DeanN (Jun 2, 2007)

Depends on a lot of things, like how high and how often you rev your engine when driving hard.
It's generally not a good idea to run the alternator faster.
None of this can be helping your battery. They're not designed for a lot of discharge cycles, so it might also be getting tired.

Maybe a better battery. I know that we are restricted as far as batteries are concerned by the physical size, but you could get a better battery with more reserve capacity.

From the sounds of it though, you could do to fit a second battery and an intelligent split charger to run the stereo


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## Cris (Sep 17, 2007)

space issues aside I'd put in a bigger battery in. stick it in the boot loads of space there. however I would suggest that you have another problem. what voltage care you seeing prior to the problems?


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## kismetcapitan (Nov 25, 2005)

well here's the weird thing. My battery is in the boot, and since I was unrestricted by space, I bought the biggest damned thing they had. I'll see 13.8 volts at the ECU, 12.8 volts as reported by the Apexi turbo timer. When I start the car, it dips down to, say 11 volts, then takes about 20-30 seconds to stabilize. If I try to drive, the car will try to stall, unless I'm really giving it gas to keep it from stalling. The voltage drops during those stall moments. If I can get the car rolling, it's enough to get the juice flowing, but there is ALWAYS some goddam slow-ass car in front of you in Seoul.

I replaced the battery just a few months ago and have started using a battery tender regularly. Maybe I should throw some big money at a audiophile-grade AGM battery. Or maybe two.

How would the wiring of an "intelligent split charger" look like, if I were to run two batteries in the boot? Since my car never leaves Seoul, the added weight would be negligible compared with the ability to run all electrical accessories at will.


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## vennuth (Aug 2, 2001)

kismetcapitan said:


> well here's the weird thing. My battery is in the boot, and since I was unrestricted by space, I bought the biggest damned thing they had. I'll see 13.8 volts at the ECU, 12.8 volts as reported by the Apexi turbo timer. When I start the car, it dips down to, say 11 volts, then takes about 20-30 seconds to stabilize. If I try to drive, the car will try to stall, unless I'm really giving it gas to keep it from stalling. The voltage drops during those stall moments. If I can get the car rolling, it's enough to get the juice flowing, but there is ALWAYS some goddam slow-ass car in front of you in Seoul.
> 
> I replaced the battery just a few months ago and have started using a battery tender regularly. Maybe I should throw some big money at a audiophile-grade AGM battery. Or maybe two.
> 
> How would the wiring of an "intelligent split charger" look like, if I were to run two batteries in the boot? Since my car never leaves Seoul, the added weight would be negligible compared with the ability to run all electrical accessories at will.


Why do you have so many strange issues!? :runaway:


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## kismetcapitan (Nov 25, 2005)

vennuth said:


> Why do you have so many strange issues!? :runaway:


my car is possessed. I haven't had a major failure in nine months. But during that time, the car has been ritually exorcised by Korean shamans, and various luck charms have been "installed" at critical locations within the car.

Can't hurt


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## Cris (Sep 17, 2007)

kismetcapitan said:


> well here's the weird thing. My battery is in the boot, and since I was unrestricted by space, I bought the biggest damned thing they had. I'll see 13.8 volts at the ECU, 12.8 volts as reported by the Apexi turbo timer. When I start the car, it dips down to, say 11 volts, then takes about 20-30 seconds to stabilize. If I try to drive, the car will try to stall, unless I'm really giving it gas to keep it from stalling. The voltage drops during those stall moments. If I can get the car rolling, it's enough to get the juice flowing, but there is ALWAYS some goddam slow-ass car in front of you in Seoul.
> 
> I replaced the battery just a few months ago and have started using a battery tender regularly. Maybe I should throw some big money at a audiophile-grade AGM battery. Or maybe two.
> 
> How would the wiring of an "intelligent split charger" look like, if I were to run two batteries in the boot? Since my car never leaves Seoul, the added weight would be negligible compared with the ability to run all electrical accessories at will.


Hmm I'd get the multi meter out. Mine has 14.1v in normal operation. If I switch on everything then I'm seeing 13.9v at worst. If your best is 13.8v then it sounds me like you have a problem somewhere.

I would suggest checking your voltage at the alternator. Then trace the cabling from there to your battery checking voltage as you go. If it's any help I saw a 0.01v drop between the stock loom (under the bonnet) and my extended loom etc at the battery.

Given your higher capacity alternator the voltage sounds low to me. Perhaps you have an earthing problem?


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## pupsi (Aug 29, 2006)

Dual batteries with a split charger is the way to go.


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## DeanN (Jun 2, 2007)

kismetcapitan said:


> well here's the weird thing. My battery is in the boot, and since I was unrestricted by space, I bought the biggest damned thing they had. I'll see 13.8 volts at the ECU, 12.8 volts as reported by the Apexi turbo timer. When I start the car, it dips down to, say 11 volts, then takes about 20-30 seconds to stabilize. If I try to drive, the car will try to stall, unless I'm really giving it gas to keep it from stalling. The voltage drops during those stall moments. If I can get the car rolling, it's enough to get the juice flowing, but there is ALWAYS some goddam slow-ass car in front of you in Seoul.
> 
> I replaced the battery just a few months ago and have started using a battery tender regularly. Maybe I should throw some big money at a audiophile-grade AGM battery. Or maybe two.
> 
> How would the wiring of an "intelligent split charger" look like, if I were to run two batteries in the boot? Since my car never leaves Seoul, the added weight would be negligible compared with the ability to run all electrical accessories at will.



Without actually looking at your car it's difficult to diagnose, but you shouldn't see you battery voltage dropping to 11v after you have started the car. It's common to see quite a drop as the engine is cranking, but as soon as it's it's fired (and the alt light is out) unless the idle speed is very low, the alternator should be making some output (maybe not peak) and you should see high 13's or around 14v depending on the state of charge of the battery.

What alternator is fitted? Are you sure it hasn't got regulator issues?

I would definately start by checking all the wiring,connectors and grounds.

BTW an intelligent split charger is just a relay with some electronics in it that senses the main battery/alternator voltage and sends power to an auxiliary battery when all is well with the main system,unlike the old fashioned split charge relays, it needs no connection to the alternator warning light, just straight battery to battery and a ground. There are some 100amp ones on ebay at the moment.

Oh and if its the case your alternator isn't charging, your car shouldn't try to stall. You should be able to drive a car without an alternator fitted if there is a reasonably charged battery on it and you aren't drawing all it's reserve capacity with other things.

Can you see if the voltage is dipping significantly just before it stalls? I would expect that the even at 10/11 volts the engine would run ok, maybe even down as far as 9v, I've seen plenty of engines that dropped to 9v during cranking and still started, so there was obviously enough for the fuel and ignition systems even at that.


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