RE: [Utah-astronomy] Portable power supply
Kurt asked the expert lurkers,
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.
On further reading and web surfing, I guess the way to size the needed battery is to: 1) Add up the total amps consumed by your mount and other gear. 2) Take the 60% of the battery's amp hour rating (for a cold weather and a general fudge factor). 3) Divide #2 by #1 to get the probable number of hours your battery will last. Example: If a battery has an amp hour rating of 17 amps and you have gear that draws 4 amps, 17 amps / 4 amps = 4.25 hours. The battery can carry a 4 amp load for 4 1/4 hours before it fully discharges to a 10.5 volt level. To determine the discharge state of a 12 volt battery (usually about 13.8 volts fully charged), plug the mount in so there is a load on the battery. Using a basic volt-ohm meter, measure the voltage across the two battery terminals. About 13 volts is fully charged, 10.5 volts is fully discharged. You can measure the likely percent of drain on the battery over time by plotting the battery's voltage - again always while under a load - as it declines towards 10.5 volts. This will give you a practical plot of the likely number of hours your battery will run your gear. To the electrically knowledgable, does this sound about right? - Kurt P.S. - I could not find any way to convert the automotive battery reserve capacity rating to an amp hour estimate. Any ideas? The best one I had was: The reserve cranking minutes for an automotive battery is based on a 25 amp load. So my 51R automotive battery has 70 minutes of cranking reserve. 25 amps / ( 70 mins * 1 hr / 60 mins ) =~ 21 amp / hours. See - http://www.1st-optima-batteries.com/amp_hours.asp _______________________________________________ Sent via CSolutions - http://www.csolutions.net
I used another (admittedly low tech) way to find out how long my set up will last in the field. After first charging the battery I plugged everything in (scope drive, video camera, VCR, time inserter and monitor) and started a timer. When the "Low Power" alarm went off on the power pack I noted the time. Crude but efficient. :) pw On 01 May 2007, at 13:47, Kurt Fisher wrote:
On further reading and web surfing, I guess the way to size the needed battery is to:
1) Add up the total amps consumed by your mount and other gear.
2) Take the 60% of the battery's amp hour rating (for a cold weather and a general fudge factor).
3) Divide #2 by #1 to get the probable number of hours your battery will last. Example: If a battery has an amp hour rating of 17 amps and you have gear that draws 4 amps, 17 amps / 4 amps = 4.25 hours. The battery can carry a 4 amp load for 4 1/4 hours before it fully discharges to a 10.5 volt level.
To determine the discharge state of a 12 volt battery (usually about 13.8 volts fully charged), plug the mount in so there is a load on the battery. Using a basic volt-ohm meter, measure the voltage across the two battery terminals. About 13 volts is fully charged, 10.5 volts is fully discharged. You can measure the likely percent of drain on the battery over time by plotting the battery's voltage - again always while under a load - as it declines towards 10.5 volts. This will give you a practical plot of the likely number of hours your battery will run your gear.
To the electrically knowledgable, does this sound about right?
- Kurt
participants (2)
-
Kurt Fisher -
Patrick Wiggins