Saturday, September 21, 2013

provided battery and charger tips

There was a discussion brewing on the RASC Yahoo!Group about batteries, how to recharge them, if they should be drained, etc. I sent out a detailed note.


The best type of portable battery for astronomical use is marine or deep discharge, with thicker metal plates.  While heavy, this type of lead acid battery is designed to be used over a long time with a slow and steady power draw.  Unlike a "booster" battery, with thin plates, used to start a car, with short intense bursts of power.

I believe the Nautilus battery itself is good.

The provided charger, like the Celestron wall wart, is putting out a lot of volts.  The proper voltage and amperage when recharging a lead acid battery is very important.  Each type of lead acid battery requires a different process.  Duration and temperature are other factors.

A well-designed battery and charger combination will charge the battery at the appropriate rate and intensity and protect from overcharging.  It sounds like the Nautilus is using a charger that tapers off, which is good.  But I would still not leave it charging all the time though, without knowing more about the charger or protection circuitry.

Someone have the manual handy?  Can they confirm the recommended charging process?

It is my understanding that the Celestron has no overvoltage protection at all.  If you leave it charging for days, you'll "cook" the battery. It probably should be charged for a few hours and then unplugged.

My old (15 years?!) booster pack with wall charger has overvoltage protection.  But when I recharge the booster in the car while driving there is no protection.  Had to be careful in-car.  Would only charge for an hour.


I would not fully deplete a lead acid!

Also I don't think that is specific to lead acid.  ANY rechargeable battery should not be completely emptied!  You should not run a battery very low.

I'd recommend charging your lead acid batteries with very smart chargers, if possible.  Or a good float charger.  If using a standard taper or constant voltage charger, recharge until full then stop.

Avoid completely discharging lead acid batteries.  If the Nautilus doesn't cut off automatically until 11 volts, I'd be mindful of this. For example, don't use it two nights in a row without recharging.

Recharge lead acid batteries immediately after use.  Don't leave it for a long time.  Don't forget.

Top them up regularly, say once a month, or once every two weeks, especially if outdoors in the summer when hot.  Top it up before the next observing session.  Put "recharging" on your pre-flight checklist!  Read the manual!


So, in the end, I think the Nautilus is a good solution for astronomers looking for a convenient, relatively inexpensive solution for portable power.  It's not perfect but I think of all the products at Canadian Tire, it is the best for us.  Do-It-Yourself people?  Build your own!

Review (on the old web site) my "powering your gear" presentation, handout, and notes for more info:

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