Fun With Batteries

A couple years ago, with the help of a nuclear scientist who is handy with a soldering iron, i built a largely American astronomy power supply. 

What is an astronomy power supply? Amateur astronomers need typically a 12V power supply to power their equatorial mounts and the increasingly complex gadgetry for modern astrophotography. These are pretty much all made in the PRC, so after the last stopped recharging, i said I would make my own.

The  LiFePO4 battery was from Dakota Battery in Seattle. Very little of the other parts seem to be made anywhere but the PRC now: a 12V cigarette lighter socket, and a really cool digital voltmeter display. It works with most of the mounts that I have that need 12V power.

A couple years back, I bought a Losmandy G811G mount. This is a very fancy go-to mount. Pick an object and across this sky it roams. I was never able to get it to work, partly out of frustration because thousands of others use it just fine. (SuperGrok may have figured out what I was doing wrong.)

So I rolled it out a couple nights ago, and before doing the needed setup, I grabbed the hand controller and told it to slew across the sky. Beep! RA STALL. This usually means you do not have enough voltage.  The port says 12V-18V but moving those motors actually needs more like 14V. The battery was at 13.3V. After a couple attempts, it was down to 10V. It turns that this little power glutton tucked more ampersand than it could give. 

SuperGrok said get a larger capacity battery. I ordered a 20Ah Dakota. When it arrived, the built-in voltmeter said 13.1V. The Dakota 3A tender could not raise that at all. It turns out something called the Battery Management System decided to protect by refusing to charge. After much study, I learned you defeat BMS by wiring a higher voltage battery positive to positive and negative to negative then disconnect and resume charging. So no astronomy tonight?

The older Losmandy GM8 mount is far less demanding. It runs just fine on 13V. Do I rolled the 5" f/9 apochromat out. I had forgotten how sharp and crisp it is. With a 50mm eyepiece (22x) Jupiter's cloud bands were easily visible. At 32x, even more details.  Then I remembered the last time I used it, i had some focuser difficulties that I did not adequately address. Evening over.

Also, the tripod at its lowest position. This is good for sitting in a chair to look at stuff below 45 degrees altitude, but the Moon was  almost at the zenith and Jupiter was not much below it. I was down on my knees and rear.  Clumsy.  I think i will raise it up tomorrow.  It will still be some work looking at the zenith but it will be worth the effort to be standing up.