Are such 12v batteries rechargeable? What type of small (alarm, motorcycle) batteries are rechargeable? What do I need to recharge them with? Is a gel battery preferable? What is gel?
I need it for a Celestron telescope, 6" mirror. I had a lead acetate for the scope, and it seemed like it could be charged with a jumper battery I have. In any case, it seems unusable now--after two years of occasional use. Maybe 12 uses for 2-3 hours each in that period.
Maybe this is the ticket. . It's lead acetate, so that answers one question. Maybe the one about a recharger too. Does a recharger service have to match up with the battery?
Yep. The charge/discharge cycle is bad for lead batteries. The lead atoms move around with every cycle and never reform into the nice neat plates of a new battery. Every cycle damages them. The deeper the cycle, the more damage.
Car batteries are usually the worst for this, it's perfectly possible to wreck one in 12 cycles.
You can get "deep cycle batteries" which are better.
I can't speak to lead acetate specifically, but Google is Your Friend.
Gel-cell batteries are sealed cells that use some additive to the electrolyte to make it into a goo -- and no, I haven't tried opening one up, so I couldn't tell you just how gooey. Google is Your Friend.
Improper use of any rechargeable battery will trash it. Letting them go all the way flat either through use or self-discharge is a pretty good way to seriously shorten battery life.
And yes, specific battery chemistries need specific charging strategies. Google is Your Friend.
The "Battery University" has some pretty good articles, although like anything on the web you should read them with a grain of salt.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
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Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
Haven't researched lead acetate abtteries, but have used a variety of lead-acid batteries, both flooded (removable caps to add water) and sealed (gel, AGM, etc).
The key to long life is proper charging and careful discharging, and ensuring the battery is kept charged.
Careful discharge means never discharging the battery below 50%, even if that means getting a higher capacity battery than the orignal.
I got PowerWheels cars for the grandkids several years ago (free on Freecycle and Craig's List when the battery dies) and replaced the orignal (%90) battery with a slightly higher capacity gel cell ad a smart charger (the original PowerWheels charger will overcharge the battery). I charged the batteries quarterly even if they were not used. The batteries I installed 3 or 4 years ago are still good.
Phil defines "friendly". Of course, he defines it in a way no one else in the universe does.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
A 12V lead acid battery is considered 100% discharged when the voltage at its terminals measures 10.5 volts. Discharging it that far causes damage. I don't know what the poster has in mind by his 50% figure, but if you figure it as 12V-10.5V * 50% it's 11.25V, which is a sensible cut off voltage. The cut off voltage is the level you set at which the circuit will disconnect the battery from the load so that no further discharge occurs.
Voltage is the easiest way to guess the state of charge, but the battery needs to be idle for some hours to get an accurate voltage.
The ultimate method is to use a "smart" meter that measures power in and power out and thus knows how much of the AH capacity has been used.
The simple method is to measure the current drain of the device being powered and multiply that by the time: 1.5 amps times 4 hours = 6 AH. If you started with a fully charged 12AH bettery, you're at the 50% point. If the battery is 10AH, then you shoukd have stopped at 3 hours, 20 minutes (5AH).
Man, I saw the acetate and assumed that the Battery Gurus had cooked up a new twist on the old chemistry.
If the OP just means lead acid -- well duh, of course they're rechargeable!
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
That presumes you know what the actual capacity is. With Nickle or Lithium chemistries this can easily be measured but finding the bottom of the pool with a lead battery will damage it.
1/4C will give a different number than 1/10C.
This assumes that your 12AH battery is good/new (and the supplier isn't lying).
A recharger with a built in meter doesn't fit in with what was being discussed, which was the level to which a battery was _discharged_. If you have to monitor a recharger with a meter, throw it away and get one that _automatically_ provides a proper charge to the battery, regardless of whether you're watching a meter or not.
With regard to the discharge cycle, you want an _automatic_ circuit to protect the battery - a meter provides only monitoring and measuring, not automatic disconnect. If all you have is a built in meter and you're not paying attention to it, you can easily discharge the battery too far.
A cheap VOM will likely be at least as accurate as a meter built into a power pack.
With regard to your Xantrex: the owner's manual states that the charge % indicator is accurate only when the unit has been disconnected from all loads and charging sources for at least
15 minutes. The manual also states that the unit will sound an alarm when the voltage drops to 11 volts, and automatically disconnect from the load when the voltage drops to 10.5, provided the AC outlet on/off switch is turned on. That's the right idea, but the wrong implementation. The voltage levels should be higher - 11.5 volts for the alarm, and 11.0 volts for the disconnect. In addition, the alarm and disconnect functions should not depend on the position of the AC outlet switch, they should operate any time current is being drawn from the battery. It is obvious that the Xantrex was not engineered for maximum battery life, nor the more or less permanent usage in your dome/telescope. That doesn't mean you can't use it for that - you can. But the questions you have asked over a long period of time have been more detailed in nature than something like: "What is the easiest way for me to power the dome?" If you want the easiest way, just use the Xantrex or equivalent to bring power out there each time. It still means you need to do some research to find out if your controller(s) and motors will work properly for long enough on the 12V DC that the Xantrex/equivalent can provide, and how often you need to recharge.
Per Google, I see they are probably called float (or automatic) float. Some are pretty pricey. I think I'll pass in favor of using my VOM, as necessary. For the 6" scope, I do not think this poses a problem. More below.
My (second) Xantrex turned out to be a stinker in that despite charging it every 3 months, it is barely in the game anymore.
Ah, you remembered my dome/obs. There is where I would need a (float) automatic recharger. It will easily run the 6" scope, but it sure is bulky.
I've run into a blank wall with regard to providing control of the dome shutter and rotation to keep the shutter open where the large scope is pointing. First though, I bought a hefty 12v Kirkland deep cycle battery from CostCo back around Feb or March. It has not been used, but I do not think has significantly discharged. The charger (float) need I mentioned in the last paragraph would probably be helpful there until and when I get the battery in use.
Regarding the dome control project, I think there may be one guy in the
50 states who knows how to do this, and he lives in Hawaii. He does it for a living. In the last 6 months, I've managed to purchase the Kirkland battery, soft start device, power inverter, aluminum sheets for shelves on the dome walls, relays, NEMA box, and a few other parts. In that time, I've had five people here who could likely do the job. Eventually, all but one showed up to do it. I've offered attractive money. The one who did show up got a real job and disappeared. My last resort now seems to be the fellow who built the obs. He tells me his son may have the skills to install the circuit cards, and wire up matters. I'll know in early Sept. If I knew more about relays, I could probably do it myself. If you or anyone lives near Sacramento, CA I have a job for you. :-)
Wish I could, because it is an interesting project, but I'm in NY.
Regarding the charger: if all you want is a float charger,you can build that cheaply and easily. Note that a float charger will not charge your battery properly, where properly means a 3 stage charge cycle. But it will work to keep a battery at full charge, and will charge a partly discharged battery to full charge, given enough time. If your battery usage is such that a float charger has enough time to recharge the battery between uses, then you can get away with that, and it doesn't need to be automatic. The float charger provides a fixed voltage at a low current, and won't overcharge your battery when it is properly designed. It's not as good as a 3 stage charger, but it may be perfect for your needs, and it costs way less.
To build a float charger, get Item Number 18724 PS from MPJA and Catalog #: 276-1141 from Radio Shack. Wire the two diodes contained in the package from Radio Shack in series with the + lead from the 15 volt regulated supply from MPJA. Like this:
Note that the banded end of the diodes must be as shown.
That will provide ~13.8 volts to the battery. It is not a *perfect* float charger, but is darn close. It's just
3 parts and is really simple to put together.
The diodes cost $1.59 for 2, the MPJA supply is $5.95. See:
formatting link
(watch out for line wrap above)
By the way leaving your Kirkland battery alone - that is, not giving it a charge every so often - will eventually kill it. Give it a proper charge once a month or so, or put it on float charge.
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