Teamspeak January 31, 2012

January 31, 2012

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Homebrew Battery Chargers

One of the niftiest and cost-conscious things we can do for our various ham accessories on the bench is to use rechargeable batteries. But with the wide array of different battery types and technologies that we come across in the flea markets and online battery stores, figuring out the right way to charge them is sometimes (always?) a confusing matter.

Our discussion this week will be about the considerations and cautions in buying, building and using the right kind of chargers for the specific batteries you are trying to use.

73,
~George N2APB & Joe N2CX

Audio Recording ... (Listen to MP3 recording)

Text Log from this week's session ...

"Joe - N2CX": http://www.njqrp.org/teamspeak/Jan%2031.html

"George - N2APB": Lead Acid batteries charge at C/10 rate. The current that you pump into the batterey is 1/10th of its capacity ... takes a while to charge them up.

"George - N2APB": 2-stage charge is more practical. First charge faster until you bring the terminal voltage up to 10-12V, then switch over to a trickle charge at 13.5V.

"George - N2APB": A solar charger is a convenient way to do it simply.

"Frank N3PUU": might be worth mentioning how capacity is figured?

"George - N2APB": Bruce says: Take a 5V regulator and calculate a load resistor that would produce the desired current for charging. Example: 50-ohm load on output of 5V regulator will yield 100ma current. Now put your battery in series with the ground lead and you have yourself a constant current source that can be used to charge your battery nicely.

"Bruce - N1RX": linear lead acid battery charger IC Unitrode UC3906

"Bruce - N1RX": Application note for the UC3906 SLA battery charger IC: http://www.ti.com/lit/an/slua115/slua115.pdf

"George - N2APB": ALL: I just updated the web page with a number of IC parts and datasheets that can be used for smart charging batteries. Just "refresh" your web page if you currently have it up. (The web page.)

"George - N2APB": Linear Technology battery charger IC application notes:
http://cds.linear.com/docs/Application%20Note/an68f.pdf
http://cds.linear.com/docs/Design%20Note/dn395f.pdf
http://cds.linear.com/docs/Design%20Note/dn380f.pdf
http://cds.linear.com/docs/LT%20Journal/LTJournal-V20N4-02-df-LT3652-Jay_Celani.pdf

"George - N2APB": Texas Instruments UC2906 data sheet ... http://www.ti.com/lit/gpn/uc2906
National Semiconductor Battery charger ic's ... http://www.national.com/en/power/battery_charger_ics.html

"George - N2APB": Heat is an enemy of batteries. Don't let them get overheated!

"George - N2APB": Cold is a bad thing too ... If it gets to cold, especially if it freezes, the battery will fail.

"George - N2APB": Alkaline batteries particularly bad in the cold weather.

"Chris - w0anm": Here is a very simple NiMH float charger that I have been using once the charge is complete. Some interesting information on NiMH charging --> http://www.ka7oei.com/floaty_thingie.html

"George - N2APB": Commercial site for battery chargers ... http://www.batteryspace.com/batterychargers.aspx

"George - N2APB": Safer to store batteries at 56-60% charge. Don't top them off before storing them.

"George - N2APB": That is, specifically for Lithium batteries.

"Ray K2ULR": Hospitals are also a good source of used SLAs.

"George - N2APB": See your local security companies to try getting recycled lead acid batteries that were removed from emergency lighting fixtures.

"Bruce - N1RX": prolonging life of Lithium based batteries: http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

"George - N2APB": Anyone know the URL for a British hobbyist company that used to sell Lithium batteries and charger packs? They were around some 8 years ago but can't find them anymore.

"Joe - N2CX": Bruce Battery University is on CWTD rferencees - good site!

"Ray K2ULR": <http://www.hobby-lobby.com/batteries_102_ct.htm>

"Larry-W2HHV": How far can a lead acid battery that is not deep discharge type be discharged without damaging battery?

"George - N2APB": Polarity Reversal technique ... good to look up in order to rejeuvenate some types of batteries ... But be careful! and don't believe everything you see on the Internet.

"George - N2APB": Depth of Discharge (DoD) ...

"George - N2APB": Typically don't want DoD less than 40-50%

"Joe - N2CX": Long term charger puts it in float charge condition.

"George - N2APB": "Battery Maintainer" ... Won't charge the battery, but will keep the battery at the charge level without overcharging.

"George - N2APB": I think this is a feature of some of the modern chargers, such as from MAHA, etc.