Re: Mach2 Slew Speed, Power, and Voltage Question #Mach2GTO


Greg McCall
 

Hi Mike,
The first two things are that I don't use a keypad and I don't use or need a 3 stage charger. But I was also not just trying to solve my particular issue but to provide info so anyone who needs it is armed with the information. So an answer specific to me while very helpful, would be better for all if I could get AP to document the area.

While I've seen many discussions of the power bricks, I only do portable Astrophotography as I live in the centre of Sydney and must drive to a location. I currently use 12v (nominal) LiFePO4 batteries but was considering a 24v battery to power my Mach2. The alternative, a 12v to 24v booster (readily available from China) could be used, but I wonder about the quality of those available and the noise produced on the 24v output. This also seemed an obvious solution and wonder why AP has not suggested it leading me to think it may not be a good idea.

Lead Acid batteries, typically AGM or Gel construction for astro stuff, need a 3 stage charger with the absorption voltage at about 80% charge level which is around 40% of the charging time.
I use Lithium Iron Phosphate batteries (LiFePO4) which are a type of lithium that are close to matching Lead Acid voltages. 
These are a safe type of Lithium battery (compared to Lithium Cobalt-based batteries is used in say a mobile phone) and also used in Recreation Vehicles, camping etc. They also charge at full charge current for 100% of the time, can be safely discharged to around 80% compared to 50% of lead-acid, are under 1/2 the weight and have way more charge-discharge cycles.
I particularly favour some locally made (in Australia) high-end batteries (read trusted brands) that have a built-in state of charge and current monitoring as part of the internal battery monitoring system, that I can BlueTooth too with an app if needed during the night.

LiFePO4 batteries have some slightly higher voltages compared to Lead Acid.

The reason I would have liked to see a definitive specification is that I know what gear I have and AP know what they have. I then can choose a solution that meets both specifications.
I didn't expect AP to test the variations (particularly on a world stage). Specs take the guesswork out of decisions and not rely on what the world seems to be moving to opinion-based decisions based on numbers of votes. Many opinions actually don't override facts and I would have liked to see the facts from AP in the form of a spec or definitive recommendation.

I also understand voltage drop and the need to err for thicker cable with shorter runs. I also have multimeters to confirm the various voltages. I typically use oversized cables, quality fuses and powerpole connectors to reduce the voltage drop.

I also only use quality chargers. In my case, I favour Victron smart chargers with the Bluetooth app.
The charger also has its own cabling and fuse to the battery.

regards
Greg

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