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Hi Darryl, yes I’m little pedantic. But in this case it is warranted. I actually own this unit. When I purchased it about three years ago from Andrews, Lee warned me not to use it with rechargeable batteries, because in his words – they blow up and can not be repaired. RA drive kit consists of small unipolar stepper motor, large brass gear and hand controller. Naturally I was curious why would those controllers blow up when used with rechargeable batteries so I open the controller. From the memory (it must be about 3 years ago) it consists of PIC microcontroler, LM7805L, crystal, and ULN200x (again I don’t remember which one) Darlington Array driver. After analysing the circuit I come to conclusion that most likely reason for damage when used with rechargeable batteries is ULN driver. This device can sink/source about 600mA of current. There is little copper on the PCB to provide adequate heatsinking. With increased voltage provided by SLA battery and if the mount hits hard stop with corresponding increase of current this IC will most likely fail. Also there is no reverse polarity protection on this unit. Those two design shortcomings are understandable because unit was designed for use with non-rechargeable batteries so it is extremely unlikely that some one would insert all the batteries wrong way around and internal resistance of those batteries would limit the current.
Saying all that, I was using this RA drive with 7AH SLA battery until recently (I had converted mount to Autostar GO-TO) without any problems. But, I’m using power lead from the battery to the controller with small bridge rectifier wired in to it. It drops up to 2.5V and I can connect the power lead to the battery in darkness whichever way around and still have correct polarity going to RA drive. I’m also mindful not to let mount to hit had stop.
Jinxsta, wire or have someone to do it for you, W02 bridge rectifier to the power lead to your RA drive. As Darryl said, don’t use it while charging battery. And don’t let you telescope to hit something solid.
Karl
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