I have been using a Losmandy GM8 with Gemini GoTo, powered by 2 x 30amp 12V deep cycle batteries. As the night goes on (usually after about 2 hours, I often get the dreaded "RA (or DEC) motor lags" error message in the hc. I have found this is usually attributed to lower voltage in my power supply. In fact:
The solutions I have found so far refer to power supplies converting 240V AC to 13.8V DC. Only one site I use has the luxury of 240V.
I have found an alternative. Snaptec Australia Pty Ltd make DC/DC converters. I rang them and, while my power request was not made by them normally, they agreed to provide a 12V to 18V converter. The serial number on mine is 0001. The model is GB60-1218 (http://www.snaptec.com.au/dcdc/dcdc.htm#GB)
I have installed it into my battery box. When turned on, the amp meter does not move. While tracking power consumption is just below 1 amp, slewing about 2 amps. I wired the output through to a cig lighter socket mounted on the outside of the box.
The higher voltage has put an end to the "motor lags" errors
Looks excellent Geoff. RA stalls were always the bane of my experience with Gemini - which is part of the reason why I went back to the standard DigitalDrive/stepper system to begin with. This is a definite fix I hear.
Serial# 1 hey... Does that make you an early adopter?
Geoff, I gotta wonder if your worm mesh is too tight since I have used a G11 with a C11 + AT66 + camera gear, or a C14, and only got RA lags when balance was way out or while I was adjust the worm mesh. 60 Ah of capacity is quite a bit to drain, what else are you running off the batteries?
The problem wasn't the current drain, but the voltage drop as the battery went from being fresh off charging at around 12.8V to a lower state as the night went on - under 12.5V.
The other items do consume power (usual suspects - dew heaters, netbook), but this reduces the overall time available from the batteries.
Company7 does recommend the higher voltage, and it has solved the problem. If it reoccurs, I will look at the tightness you suggest.
We have never had trouble with voltage drop. We use a 13.8 V 5amp regulated AC supply. Gave up on batteries long ago and bought a "quiet" 2.6 KVA generator (it has remote electric stop start as well) for about the same price as decent batteries and inverters etc. Runs all night on 7 ltrs of fuel with a full load.
The generator makes some noise but at the end of a 25 meter cable and in a sound deadening box I can't hear it from 10 meters. If no noise is more important than a stable photography system then this may not be the way to go. In any case we share the AC power and get no complaints. ( we have had as many as 6 six way AC splitters running from the generator.)
Our problem Barry is that we don't allow generators at our remote club sites. This solution from Geoff is a good one given his and many others' problems with Gemini under-voltage issues causing RA lag errors and having to rely on a battery-only supply. This inverter that Geoff is introducing is a small and efficient DC-DC model, so we're not talking battery/DC-AC inverter/lab supply here.
It's also arguably easier lugging a 60 or 70 amp/hr battery in your boot than a smelly/oily/bulky 2.6kvA generator. Anyway - the smaller easier to carry Hondas and the like are very pricey in comparison - up around $1,300 or thereabouts. They do output cleaner power than your lounge room wall socket, but you pay for the privilege. I wouldn't use a modified sine wave model for any of my astro gear, even with spike protection.
The problem Barry is that we don't allow generators at our remote club sites - quiet or not. This solution from Geoff is a good one given his and many others' problems with Gemini under-voltage errors and a battery-only supply.
Yes Chris I know and it is a rather stupid regulation now that so much photography is done and quiet generators are the order of the day. Your club should look into its origins because they may no longer be important.
Yes Chris I know and it is a rather stupid regulation now that so much photography is done and quiet generators are the order of the day. Your club should look into its origins because they may no longer be important.
Barry
"Stupid?" - gee thanks Barry! A tad harsh? LOL! We just love the total peace and quiet - it's why we go. That's not stupid is it? "Quiet" generators are still loud in the night time bush setting - even at a distance and in a hutch. I have a Honda 1KVa which, on "Eco" mode, is way quieter than yours (I've heard it), and it's still considered noisy in a group session where we share the field with visual observers as well. No-one wants the noise - at whatever level. At MAS we don't have the luxury of split fields and on-site storage like we have at Wiruna. We lug everything in and then out again - every time.
I also run an auxiliary 120A/Hr deep cycle battery in my 4WD, and it sits there, charged, day in, day out. I run the fridge off it if I'm camping, and it's just always there. It will run my mount and small 22w lappy for three days. Smelly, oily, dirty & bulky generator - and fuel cans? Not required...
This solution has been around for a lot of years, the original Lacy 12 to 18 volt converter was around when the Gemini was in its early production runs.
Not required...
