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Charging Obs Batteries

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#1 averen

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Posted 03 February 2013 - 01:09 PM

I'm not really sure about the best place to put this...but since the batteries are going into my obs it seemed like my best option.

I'm planning on using some sealed lead acid or even deep cycle batteries to power the motors in my observatory. I'll have a battery that rides with my dome so it will only be connected to the charger when parked. There will also be another battery that is connected to the rotation motor and that battery can be connected to a charger 100% if need be.

So I'm wondering what the "normal" thing is to do here. I know a lot of folks use a solar charger and I would like to eventually go that way but initially I will probably go with an AC charger. So I have a couple of questions.

- Is there anything wrong with leaving a SLA or deep cycle battery always connected to a charger?

- Will it hurt the charger if I'm pulling power from the battery while the charger is attempting to charge the battery?

- Would it be possible to charge the SLA or deep cycle batteries in parallel (when the dome is parked)? What would be the affect of having a single battery on the charger and then having another battery get connected mid cycle? Am I better off having a separate charger here?


I think the simplest thing is to use 2 chargers. One that is always connected to the rotation motor/battery and another that is connected when the dome is parked for the shutter battery/motor.

Any thoughts or suggestions on this?

Thanks!
Jared

#2 Christopher Erickson

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Posted 04 February 2013 - 01:53 AM

Most important thing to do is to use a smart, multi-stage charger so you don't boil away your electrolyte with the charger connected all of the time. The best chargers have a temperature sensor that attaches to the battery being charged.

You could use one smart-charger for two batteries but it would be better (and both batteries will last longer) if you put a separate smart charger on each battery. Especially if the batteries have temperature sensors attached going to the chargers.

The chargers don't need to be able to handle the amperage it takes to actually run your observatory. However their rate of charge will need to comfortably-exceed your average daily (or weekly) Ah energy consumption. It won't hurt the chargers to use the batteries while they are connected.

#3 JMW

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Posted 05 February 2013 - 01:41 AM

I keep my small batteries plugged into Battery Minder smart chargers. They are designed to stay plugged in indefinitely. I have 1, 2 and 8 amp versions that can deal with AGM or Gel. I have a pair of 6 volt 220 amp-hour wet cell batteries on my astronomy trailer. They are charge via three 80 watt solar panels in series feeding a Morningstar Sunsaver MPPT charge controller. It is a 3 stage (+ monthly equalization) smart charger. I just add distilled water to my batteries about 4 times a year. I get almost 15 amps per hour put back into my batteries under full summer sun.

When you run a load on a battery with the charge connected, the load will be pulled from the battery and not the charger as long as the battery has a large enough amp-hour capacity and is designed to sustain the load. Larger wires help deal with voltage drops on the 12 volt DC load. It takes a lot more amperage at 12 volts to do the work compared to 120 volts. Thats why your car battery cables are so large.

#4 Midnight Dan

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Posted 05 February 2013 - 07:11 AM

Hi Jared:

Just curious, if you have AC power available, why run things off of batteries? You can just use a 12VDC supply instead.

-Dan

#5 averen

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Posted 05 February 2013 - 10:13 AM

Just curious, if you have AC power available, why run things off of batteries? You can just use a 12VDC supply instead.


The shutter will only have a power connection when parked. So I would prefer to have a battery that rides with the dome so that it can shut the shutter if something bad happens. (loses connectivity with the rotation controller, dome cannot park, etc)

I may end up using AC for the rotation controller as it will be hooked up all the time.

Another reason to use batteries is that they can generally withstand a fairly large amperage draw where an AC->DC converter of the same amperage could be fairly expensive. Thus using a battery and a medium sized charger would be less expensive than a power supply with a high amp rating.

Both of my motors are rated around 3A, but that seems low to me for the size motor they are. Getting a power supply to handle that load would be less expensive than a battery. However I'll still need a battery and charger that connects to the dome for the shutter.

Thanks,
Jared

#6 JAT Observatory

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Posted 05 February 2013 - 11:23 AM

<<Just curious, if you have AC power available, why run things off of batteries? You can just use a 12VDC supply instead.>>

I have AC mains but still make use of batteries where I can, because the batteries provide clean power. And when there is a storm and power goes out, I can still use my obs sans all the local skyglow when the sky clears.






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