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Hi Erwin
Also found this via google:
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I have a GP mount with dual motors and the Vixen DD-1 controller. I noticed that when running the controller from a 12V supply (as is the case when using the 8 D cell holder or running from a 12V lead acid battery or car cable), the RA motor would "stutter" with the controller set to the 32x position.
I found out that the DD-1, when set to 32x, powers the drive motors with whatever voltage the controller is being fed. At 1.5x and 2x, it drives the motors with a regulated (5v) voltage.
The stepper motor controller Vixen uses (Toshiba TA8415P) is rated at a maximum of 400 mA per phase. The motors have 20 ohm windings. So with a +12V supply, the chip was being asked to deliver 150% of it's maximum rated current. Worse, at 12V, the chip is being asked to deliver TWICE its recommended maximum or 300 mA. Vixen claims the controller can use 7.5 - 12 volts, and realistically, many people will want to use a "12" volt lead acid battery or car cable, which is actually closer to 13-14 volts.
In my case, the controller chip was overheating with the higher voltage, and unable to reliably step the motors. Worse, the driver for phase 1 was blown.
So what I did was to wire a 7808 1A voltage regulator into the input. This means that the motors will never be driven with more than 8 volts regardless of the input voltage, and the driver will remain at or below its rating. This will allow me to reliably use a 12V lead acid battery for field power. (regarding the blown output, the Dec drive uses a different chip [Toshiba TD62103, which has a higher rating of 500 mA, although it is also being used beyond specification], and I was able to rewire the bad phase 1 output through this chip to get everything working properly.)
I recommend that anyone with a Vixen DD-1 controller either not use the 32x setting, or only use an 8 volt power source. I got mine second hand, but if you bought your's new, this obvious design flaw is definitely a "defect in material or workmanship," so
demand that Vixen correct the issue under warranty.
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Cheers
Dennis
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