504 alternator question
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  1. #1
    Fellow Frogger!
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    Default 504 alternator question

    I have one of those digital voltmerers which plug into the cigarette lighter. Today I stuck it into the Pug. Very interesting! At its peak the alternator was charging at 15 V at start up but the volt meter in the dash was just out of the red. In general running it was charging at about 14.7- 14.8 V at about 2000- 3000 RPM with the guage at the top of the red or just past it. At idle with the lights on it fell to about 11.7 V and the built in guage was in the bottom of the red zone. Is all of this typical or does it tell us anything other than that the in-dash volt meters are terrible pessimists? The battery , by the way is just on 7 years old and was switched from my Toyota Prado 3 years ago before a big outback trip. It has no trouble starting the Pug even after a week or 2 and appears to hold charge ok. With all of this is there any advantage in putting in a 75-80 amp alternator to replace the standard 40 amp job? Neil

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    Budding Architect ???? pugrambo's Avatar
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    the guage in the 504 is a battery condition meter,not a volt meter
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  3. #3
    Fellow Frogger! Bruce Llewellyn's Avatar
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    Quote Originally Posted by pugrambo View Post
    the guage in the 504 is a battery condition meter,not a volt meter
    Um, nope. It's a thermal volt meter. The mechanism is a bi-metallic strip which heats up in relation to the current. Since it has a fixed resistance, it's temperature is proportional to the voltage. Ambient temperature doesn't have a noticable effect.
    The response time for a reliable reading is two minutes, from memory, according to the 404 owner's manual.

    15 V is too much. Normal should be 13.8 so I'd expect that the voltage regulator is getting a bit sick, especially if it is the original points type. These are usually found on the firewall near the center in the engine compartment. other things to check.

    1) That the voltage and ground wires are still connected and in good condition- if the voltage regulator has a dirty connection on either side it thinks the alternator is putting out 13.8 where the rest of the electrical system is seeing 15V. The alternator can produce 90 to 100 v if the regulator loses its ground but keeps supplying the field coil.

    2) Don't trust digital voltmeters that don't have a calibration certificate.

    3) 40 amps is heaps for a 504 unless it's got aircon. Fitting larger alternators is no problem usually. Some late cars had 55A

    4) If it is starting well and not boiling the battery it is probably OK.

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  4. #4
    1000+ Posts robmac's Avatar
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    Quote Originally Posted by pugrambo View Post
    the guage in the 504 is a battery condition meter,not a volt meter
    Sorry to burst your bubble, both 404 and 504 had thermal voltmeter.

    Volt meter refers to the fact it connected to measure the electrical system voltage. Thermal refers to the fact that it is "hot wire" instrument.

    Bruce adequately describes how it works. The meter reading is dependent on the "stretch" of a piece of resistance wire which is heated by the applied voltage/current. Hence a substantial lag in the reading stabilising.

    Yes it acts as "condition meter" but only because system voltage varies depending on the battery state-of-charge (read internal resistance). The occurs because the alternator output is determined by the voltage regulator. When the alternator is "on charge" the system voltage is high to pass a higher current through the battery and charge it.

    FWIW I'm of the opinion that 504 alternators run far too slow - a limitation of the crank pulley size versus the smallest alternator pulley that allows sufficient belt wrap.

    The mechanical regulators are sh!t and prone to all kinds of problems. The solid state RE55 are a better option.

    Before rooting around with regulators et al consider an alternator change. At $40 from DIY wreckers it is a sensible option. Plus the advantage of better low revs current output, accurate regulation, charging line voltage drop sensing adjustment and a cheap plentiful supply of spare parts.

    The details are here : http://www.aussiefrogs.com/forum/sho...sion&highlight

    The Holden alternators bolt up to 404/504/505 by simpy making spacers for the mounting bolt and the tensioning bracket.
    You need to refit the old vee pulley.

  5. #5
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    Thanks, chaps. That makes it simple for an electrical nong. I will check out those earths. The whole shebang appears to be working fine and I will go the Holden/magna alternator route when this one ceases to work. The thing that intrigued me was the 15 volts when on every other car in the house the same guage reads about 14.2-14.3 v. at start up and then quickly drops as the battery charges. Rob, are you saying that a bigger [or smaller] pulley on the alternator would be better to overcome the low charge at low revs? Neil

  6. #6
    1000+ Posts robmac's Avatar
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    The output current of an alternator is dependent on shaft rpm

    For most claw pole alternators charge current at 1500 rpm is about 20% of the maximum. Maximum current is at delivered at 6000RPM.

    Most alternators will safely run at 18.000 rpm without damage.

    So. consider the 504 Bosch alternator with a 35 amp max output. If it's running at 1.5 engine speed, 1325 rpm shaft speed, at idle it may deliver around 7 amps. This is hardly enough to cope with ignition and park lamps. However because of the safe max speed of 18000rpm it could be run at 2.5x engine speed. However the crank pulley diameter limits the speed because the alternator pulley would be too small to wrap a belt to achieve that drive ratio.

    Compact claw alternators (the squat type) have much better low RPM out characteristics and that is why many luxury cars with aircon and electric cooling fans use them. They would be ideal for a conversion, but are too hard to mount in most cases.

    EDIT: If the alternator is charging at 15 volts keep an eye of battery electrolyte level. 15 volts will a bit high and likely to "boil" the battery.
    Last edited by robmac; 28th October 2012 at 07:43 AM.
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  7. #7
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    Thanks, Rob. The level in the battery is ok but I will keep an eye on it. The car rarely does more than 15km at a time so I guess it doesn't get a chance to cook the battery. What I find amazing is that this battery is 7 years old and still going strong!

  8. #8
    1000+ Posts Beano's Avatar
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    Wow ! Which brand is it, Neil ?

  9. #9
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    Beano, it is the original battery which came in my Prado. Not sure of brand but it will be standard Japanese Toyota fare. I will have a look tomorrow. I hope I haven't jinxed it.

  10. #10
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    I've found the OEM batteries in many new cars to last extremely well - Almost 4 years down the track in our 307 Touring the original battery is fine & going well. The previous 307 lasted the four years we had it on the Original battery. My 2000 Ford Couriers' (thai built including battery) battery lasted ~8 years, and my current Thai-built ute is coming up for three years on the battery - early days yet, but I have no reason to think it won't last, it's the same battery (externally at least) as the previous one.....

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