Re: Separate power for mount - why?


Roland Christen
 

There is no risk to damage to the CP controller. The main problem is undervoltage, so if you run many applications from one battery, the terminal voltage might drop below the threshold for the CP to operate properly. It is almost always an issue when slewing, not usually during tracking.

There can be one situation that happens during tracking when a dew heater comes on or cycles on-off. They can sometimes draw so much current from a 12 volt battery that the voltage at the terminals drops below 11 volts (about 10.5 to 10.7 volts) and causes the CP to reset. This results in a momentary stopping of tracking during the undervoltage time. Having a battery that puts out more than 12 volts, like the Lithium batteries, will prevent this situations.

We have also seen situations where the power supply was situated some distance away from the mount and the wire was too small to carry the current of all the devices without causing a fairly large voltage drop. So even though the terminal voltage at the power source was high enough, the actual voltage at the CP controller was down near the 11 volt threshold and even lower in one case that we saw.

Roland

-----Original Message-----
From: ap@... <ap@...>
To: main@ap-gto.groups.io
Sent: Mon, Jan 10, 2022 11:55 am
Subject: [ap-gto] Separate power for mount - why?

First, I take all advice from AP seriously, and use a separate power supply for my mount now (AP1100AE). 

After my first attempt at night at a dark site, I need to redo my battery planning.  I ran dead before midnight with a Group 27 Lead Acid battery.  It was a bit premature due to a fallacy in the SOC indication I was using, but on further measurements I was way under sized and would have been completely dead before morning.  So a big 200ah LiFePO4 is on the way.

But that brings up the mount.  I have a Group 24 FLA for it, and that is more than adequate with its miniscule draw.  But it is about 50 pounds I lug around to the dark site.  I might replace it as well, say a 50ah LiFePO4, much lighter and smaller.  But expensive if not needed.

So here is the question: The recommendation is to have a separate DC power supply, due to noise from cameras, etc.

Is the recommendation based on trying to prevent damage to the CP4 or mount?

Or is the recommendation because it may create anomalies in tracking/guiding? 

Bottom line: Is there any reason not to give it a try off the same big battery, and so long as tracking is its usual near perfect self, not bother hauling (or buying) the separate battery?  If there's a risk of damage, obviously I'll keep two. 

I'm well aware in terms of investment the cost of another LiFePO4 battery is negligible, it is more about one more piece of "stuff" to haul out, back, etc.  The last trip I spent more time packing and unpacking than imaging.  Working to streamline other aspects also, but this one came up when I was debating whether to go ahead and order a second LiFePO4 battery or not.

Linwood


--
Roland Christen
Astro-Physics

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