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Thread: More info regarding poor battery charging ...

  1. #1

    More info regarding poor battery charging ...

    More info regarding my undervoltage/weak charging system.

    I went out to the plane today and am getting 13.0 volts at all times ( with heavy and light loads) . I learned today I have an ALE8406R Prestolite 40 amp alternator and Delco Remy adjustable voltage regulator.

    I attempted to do some diagnostics but the VR wiring connector is unmarked . There is a black boot with three spade type fittings inside . I was hoping someone could tell me what regulator this is and possibly which connections are which . To further complicate issues I have an AK-950 FTR filter on the main bus from the alternator, as well as an alternator filter on the alternator ( looks like a condensor ). I'm wondering if these could have some affect on the charging system. I will be seeking a mechanic to look into this situation but good mechanics where I live are few and far betwween. In the interim I was hoping to do some light diagnostics.

    Could someone please look at this attached photo and help me ID the

    Oh, and by the way, I was wondering if there is a 50 or 60 amp alternator that can replace my 40 amp unit down the road. Thanks again in advance for any help.

    Regards, Charles

  2. #2
    Charles, did you get some answers on this yet, from your MML posting?

  3. #3

    I'm not sure exactly what the problem is, but the picture you showed is the original Delco Remy Voltage Regulator for the A23-24. Beech shows it in the Parts Manual as Part Number 9000590, but I think the actual Delco part number is 9000591. Zeftronics shows a replacement part R251DR, but you may want to check out the info on their website or call them regarding whatever issues you have. (

    I'm not sure why you would want a larger capacity alternator. You would also have to change your ammeter, which is calibrated for 40 amps, and those gages are not easy to come by trying to find a 60 amp gage. With modern solid-state avionics, you don't pull much of a load. The biggest loads would probably be Pitot Heat, which is occasional, and your rotating beacon light.

  4. #4

    More info regarding poor battery charging ...

    I is from the overvoltage relay and ultimately the main bus. G goes through the firewall passthrough pin A and grounds onto the alternator case. F is field that goes through the alternator switch, then the firewall passthrough at pin H, then to the field. Hope the JPEG I sent you helps.


  5. #5
    With regard to the voltage regulator, I work at Remy and our prints show the 9000590 as a 12V unit and the 9000591 as a 24V unit. Hope this helps.


  6. #6
    I replaced my regulator this summer during the troubleshooting on the failed alternator. I went with the Zeftronics, which is PMAd for our birds. has a new web site that makes it very easy to search by airframe. The Zeftronics units have a fault light which can aid in troubleshooting.

    Interestingly, in running the circuit, we cannot find anything that appears to be the overvoltage relay; so it's on my list to do that.

    If you want to save a few ounces and simplify your wiring, Zeftronics sells an integrated unit that offers over/under protection integrated with the regulator.

  7. #7
    Charles, a couple more things for you. Don’t mess with the regulator adjustment, until you are more certain of what’s going on.

    The noise filters are unlikely to be a problem. If the either one shorts, you'll probably trip the field breaker almost instantly, as the regulator tries to raise output. If that breaker doesn't trip, the ALT breaker will trip if the bus filter shorts (though you may get smoke). The bus filter should be connected through a much lower amperage breaker than the ALT breaker; you might want to check on that, in case someone just connected it to the main DC buss. If the alternator-mounted filter shorts, and the field breaker doesn't trip, it will just melt the filter wire or something inside it. If the filters go open-circuit, they just won't take out the alternator noise.

    You have an ‘external regulator-grounded system’ to control field current (thus output), as opposed to an internally-grounded alternator field. Make sure you know what you are doing if you proceed with more self-diagnostics. This system works differently from the more common later system, in which the voltage is controlled by varying positive field current to the alternator (in which the field is internally ground within the alternator). In the older Delco-Remy design, full field current is always available to the alternator field through the regulator, and it varies voltage output by controlling the resistance back to ground (inside the regulator).

    If I were you, I would either put an oscilloscope on the alternator output (with both filters disconnected), or pull the alternator and take it to a parts shop for testing. Just tell them it is off an old Delco-Remy externally-grounded system on a dune buggy or something. What you need to confirm are that the alternator can produce rated current, AND that there is no significant output ripple. You are looking for a bad output diode. A bad diode will both reduce output capability, and will generate noise. So guess what I am suspecting, since you have found two added noise filters so far.

    To compound matters, if the regulator has been trying to compensate for a bad diode, it will have been feeding excessive field current all the time, trying to reach rated voltage. That often damages both the regulator and the alternator field (including the slip ring brushes), in part from excessive heat. If you do discover bad diodes, if I were you I would replace both regulator and alternator, unless a future in-flight charging loss would not be an issue (day VFR, uncontrolled airspace).

    The compact Plane Power alternators are a more effective choice, and will get some weight off the nose. The Zeftronics regulators are good; I did their initial 12V system testing for their STC application many years ago, for one of their first product offerings. However, I am not certain whether they offer a replacement for an externally-grounded system; and the last time I checked, they did not have a combined regulator/OV relay package STC’d for our planes (though they did have one that would work). Both situations may now have changed.

    Don’t take an alternator output upgrade too lightly. If you just put on a higher-capability alternator (or one comes with a PP package), and nothing else is changed, you’ll just have a higher likelihood of tripping your main 40A ALT breaker, if the loads go too high. You would probably need to replace the ALT main cable from the alternator the buss, as well as the main ALT breaker, unless both are already rated at least 50A. Then there is the issue of the ammeter gauge, which ‘should’ get upgraded; though that’s probably not too much of a major issue. The ammeter only shows the difference between demand and supply; not the actual alternator output. In other words, if you are using 30A while the alternator is producing 40A (due to 10A going into the battery charge), the ammeter will read 10A (not 40A). So as long as you are always flying with a well-charged battery, a 40A ammeter isn’t a real issue. And you should never just jump-start a plane and go flying, unless you enjoy the combination of in-flight electrical system loss, and the cost of alternators and regulators.

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