Amp draw

Discussion in 'Discussion Forum' started by dragonsgate, Jul 10, 2018.

  1. dragonsgate

    dragonsgate True Classic

    Anyone know what the amp draw is on X19 A/C motors?
    This one in particular. I think it is from a 1975.
  2. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    Not a direct answer, but what size fuse is the heater blower circuit on? That will cover it.
    My understanding is fan motors draw quite a bit more than one might think. Especially when they first start up, then it backs down once they are spinning at a constant speed. These older motors were not particularly efficient either, and it's resistance would have likely increased with age. You can always put a amp meter inline to test it. Sorry I don't have any specific spec though.
  3. dragonsgate

    dragonsgate True Classic

    You voiced my thoughts but I am just looking for the easy way out.
    Someone to do my home work so to speak.
    Motors do have a surge on start up. That is what capacitors are for on bigger motors.
    I am guessing the draw could be as high as ten amps on this motor.
    I am running the original 1984 fan motor for extra air flow on the traction motor.
    Kind of redundant, an electric motor to cool an electric motor.
    I rebuilt it with roller bearings as you might remember and I believe the bearings reduced a bit of drag there.
    I am already putting load on the electrical system as it is and it has been working fine up till now.
    This motor is for my A/C project and while I am happy with the cooling part when I hit the switch the motor buries the battery gauge and it stays buried until I turn it off.
    I get 13.5 volts under normal condition and it drops to 12.3 with the with the A/C motor on.
    This is the problem with using old stuff.
    I guess I am going to have to spring for a newer more efficient motor if that is possible.
    I am also planning to pull the old alternator and go through it. I have a feeling it might not be up to snuff.
    Last edited: Jul 10, 2018
  4. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    I'd bet it draws over 10 amps, just a guess. But my assumption might be closer to 15; maybe that or a bit more on startup and a little less as it runs. From my experience they are really heavy consumers. Seems a lot of my older cars have a 20 amp fuse for the blower. The reaction of your battery gauge tells the story.
    I do remember your bearing installation project, still admire it. But the bulk of the amperage loss will be from the old windings, weakened field magnets, etc, more than the friction of the bearings (although they will certainly help).

    As you know there are efficient brushless motors that draw a lot less, but expensive. This is on your electric car so power consumption is somewhat critical. Yes you could increase the alternator output, but that will also increase the load to drive it...increasing the draw on the main drive motor (a bit of a vicious cycle).

    Funny, I do the same with one of my compressors. It's an older large-capacity model and the electric motor has a lot of resistance and gets hot. So I run an electric fan on it to help keep the drive motor cool.

    Very interesting project though.
  5. dragonsgate

    dragonsgate True Classic

    Did some testing and the older motor I am using for A/C is a lot more drag than the blower motor from the 84 X.
    With just the 84 fan motor running and I spin the alternator up to 2000 to 3500 rpm I get 13.35 volts on the multi meter.
    With everything unplugged I get 13.5 volts and it drops to 12.2 when I hit the A/C switch at 3500 rpm.
    One would think I would have electrician tools but I don't have anything but a multi meter that only goes up to 10 amps.
    Everything in the electric drive system is pretty much plug and play so I rely on the expertise of others.
    I just ordered a better meter for when I work on the old motor and am looking for a newer more efficient setup that I could possibly adapt.
    Dr.Jeff likes this.
  6. LarryC

    LarryC LarryC-Albuquerque

    All of the AC stuff runs off an 8 amp fuse. So presumably.....But, yes, a significant voltage drop is common. If you can find a proper replacement for that particular motor, which was also common in the '79, I am happy to hear more about it. The ball is in your court!

    Here is a challenge: If you can find someone who can really rebuild that motor - or any electric motor for that matter-I would be especially happy to learn who that is. So called electric motor builders appear to be a myth as far as my attempts have shown. They say they do, but they don't.
  7. dllubin

    dllubin True Classic

    You can make your multimeter into a high current ammeter if it has a reasonably accurate low value resistance measurement function. You could measure the resistance across the fuse for the circuit with the system off. Then you can measure the voltage across it with the motor running and use Ohm's Law I = V/ R. To improve the resistance measurement accuracy, measure the resistance of the leads touching just each other and subtract it from the value measured across the fuse.

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