Q. for expert electronic's lurkers: Is there way using a simple volt/ohm meter to determine the discharge state of the automotive battery that I use to power my scope? Currently, I roughly judge the state of discharge by looking at how many amps my battery recharger shows when it is first plugged in. Kim wrote:

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I had to go to MalWart tonight for my son and I happened to notice a 12V, 22Ahr battery/power supply there for about $60. . . . Anyway, do any of you have recommendations?

I bought one of these portable automotive powertanks in the 20amp-hr range about two years ago and found them to not hold up in actual use. They are similar in amp-hour capacity to the 17amp-hr Celestron powertank. The main issues were: (1) cold weather, (2) steady voltage output and (3) heavy power draws when frequently slewing with a heavy mount. I am using a heavier Atlas (Synta) EQ-6 mount. 1) Cold-weather Cold weather can reduce battery capacity by 30%. So that 30amp-hrs with a lot of slewing on a heavy mount can quickly become 2 1/2 or 3 1/2 hours of steady 12 volts on a cold mountain ridge. 2) Good voltage regulation I understand that low-voltages can damage the electronics in some mounts, so I got hyper vigilent about having a good regulated voltage. So, I went back to using a car battery - an 51R coded battery - the R meaning it is supposed to stand up to repeated recharging. This was small enough to fit in a standard plastic battery box while leaving room to store my power inverters in same box. A cigarette lighter spilter gives me the same three ports usually included on the front of a commercial powertank. To adjust the low and varying voltage problem - and frankly not understanding electronics well - I bought a 120 volt inverter and then a Radio Shack regulated 120v to 12volt regulator converter. This was all on the theory that this would keep the dc output voltage steady at 12 volts as the battery's charge drained. Plus, that setup gives me both 12vdc and 120v ac at the scope as needed. Running the EQ-6 for 4 hours straight last Saturday with little slewing only drew the battery down by less than 1/4 (based on the 1.5 to 2 amp draw rate seen when charger was plugged in). 3) The amps that your mount draws Finally, the amount your mount draws is part of the equation of what battery setup is best. The Syntax EQ-6 draws, per the manual, 12vdc and 2 amps. A lighter mount will draw less power. Checking your manual for the load you are drawing for your various scopes is an idea. Joe Bauman wrote:

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The problem I've had is with keeping my computer and CCD setup going, which required AC. (I'll never be able to run a laptop for hours on batteries, I have concluded.

I run my scope off the home-grown powertank setup described above. I run the laptop and camera off the laptop power - generally with a 2 to three hour reserve. Then I supplement the laptop power with an extension cord and cigarette lighter AC converter to my main car battery. This gives me about 4 to 4 1/2 hours without having to worry about a drained car battery in warm weather and closer to 3 hours in cold weather. Finally, I still have that portable automotive powertank in the 20amp-hr range that I bought about two years ago. It has a air hose and compressor built-in, so I use it as flat-tire insurance on long trips. For astronomy, I only use it a couple of times a year to power my Kendrick dew heaters - generally just running the heaters until the battery drains. - Kurt _______________________________________________ Sent via CSolutions - http://www.csolutions.net