Re: Servo Motor Current - follow-up

Me again,

I fitted a second cap in parallel so now I have 36,000uF across the
diode bridge and a 1000uF cap across the power-in terminals of each
Gecko. What I've observed is that the peak currents are still up in the
25amp range and during a big acceleration, the psu output voltage still
sags by around 5 volts. I would say that the addition of the 1000uF
caps right at the inputs terminals of the Geckos had more of a
beneficial effect than adding the 2nd big cap.

I've ordered a bigger transformer so we'll see how that affects
regulation during peak current draw. In the mean time I'll just run at
lower accel/decel settings - not as much fun...

Cheers, Peter

Peter wrote:

>Hi Mariss & Jon,
>
>Many thanks for your comments and insights. To clarify, I did look at
>my motor's no load RPM and then calculate the pulley/belt reductions.
> That's partly why I was happy with 65V DC rather than upping the
>voltage any further. Also, now I run out of steps from my Flashcut
>(with Lightning chip) controller before I run out of motor speed on
>rapids. I also selected my encoders to take into account my maximum
>step rate of around 35K steps per second. I'll be quite happy with
>around 1500-2000mm per minute rapids once I address my peak current demands.
>
>During rapids (steady speed), the pulsing current (drawn by all three
>motors) peaks around 5-7 amps. It is only during stops and starts that
>the current was peaking to around the 35 amp level. After an hour of
>exercises, the motors are only very slightly warm to the touch.
>
> I have ordered a big cap (18,000uF) which will come in tomorrow and
>which I will put in parallel with my existing big cap, but in the mean
>time, I fitted a 1000uF/100V cap across each Gecko power input. Now, I
>can observe the peak current coming out of the central 15,000uF cap has
>dropped to around 25-27 amps and the supply voltage only drops by about
>5-6 volts. I'm measuring the current coming out of the central cap and
>obviously some of the peak current now flows out of each 1000uF cap
>straight into the Gecko. FYI, my big cap is only about 6" from the
>Gecko's.
>
>Jon, you're right about the inductance of the resistor being a potential
>unknown (not to say it couldn't be measured) but at 0.1 ohm it should be
>"pretty" low. In any event, the exercise is still very helpful in
>understanding the peak current demands of the motors and observing
>voltage & current changes based on component changes..
>
>I'll report back after I fit the additional big cap.
>
>Thanks, guys,
>
>Cheers, Peter
>
>
>mariss92705 wrote:
>
>>Peter,
>>
>>I assume 20A is the stall or locked rotor current. Keep in mind your
>>motor is delivering no power at that point (lots of torque but zero
>>speed)...
>>
>
>
>
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