Charging batterys?

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Pugsley
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Charging batterys?

Post by Pugsley »

Ok I know lots of stuff about electronics.. but one thing i never learnt was how do you charge batterys?

I know it probbly depends on the type.. but dont you just apply the rated voltage and it will charge?

This is somting ive been wondering for years now and just never got around to looking for the awnser, and now i need to know for an upcomming mod.
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Post by DocSilly »

You don't apply the rated voltage, you apply the rated current. That method alone is only used by the very cheapest "dumb" chargers, it's unreliable and will damage your batteries over time.

Those chargers deliver only a set current, like 200mA, and you have to calculate how many hours your 2000mA battery needs to be full. That method only works when your battery is completely discharged, otherwise you wouldn't know how much capacity is left and you couldn't calculate the needed time.
Those dumb chargers continue with the rated current even when the battery is full. A full battery can't store more current than its rating and will heat up when the charging continues (which isn't healthy for the battery).

- Some of the lower priced chargers are built with a simple timed charge. For instance, a charger may say that it charges AA NiMH batteries in 6 hours...so it charges the batteries for 6 hours and then shuts off. If a battery has a higher capacity than the example (i.e., 2000mAh versus 1600mAh), and the battery is fully discharged, you are likely not going to have a fully charged battery at the end of the cycle.

The smarter chargers offer more options to care for your battery.

- Most chargers will switch to a trickle charge once the charger determines that the battery is done charging, or once the charger's timer completes. The purpose of this trickle charge is to keep the battery topped off to the optimum capacity. This is standard in most chargers, but is still something you should look for.

- Minus Delta V
Chargers that test for -dV monitor the voltage over the cycle of the charge. When a battery is fully charged there is a drop in voltage (hence 'minus delta v'). When this is detected the charger will either switch off or switch to a trickle charge, depending on the specifications of the charger.

- Some chargers monitor the temperature of the batteries as they are being charged. This is a basic safety measure to prevent overcharging and is typically included in fast rate chargers.

- Channels
The most common number of channels you will see in AA & AAA chargers is 2 or 4 channels. A 4 place 2 channel charger treats each set of 2 batteries as a single unit. It is important to charge and discharge each 'pair' of batteries together, since the voltage is measured as a total voltage for the pair and so you can easily over charge a battery if you attempt to charge two batteries at different states of discharge. A 4 channel charger will charge each cell independently for complete charging.

- Conditioner
Some chargers are built to charge both Nicad and NiMH batteries. You will find that some of these chargers have a 'conditioner' designed to remove the 'memory effect' in NiCad batteries. This conditioner basically discharges and recharges the cells a couple of times to remove the voltage depression that NiCad batteries sometimes develop.

- "burp charging"
That method stops the charging periodical for a few millisecs and dischargers the battery during that time. This is to minimize the developing of gases inside the battery while charging with high currents. It's mainly used for NiCd high-current batteries that RC-fans often use.

- CCS (Computerized Charging System), check BTI CCS for more detailed info. They can identify each battery type and charge them correctly, they can even handle the rechargable alkaline cells.
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Post by BillyGoat »

Thats some good info doc- most hobbiest who run rc stuff know about that- do you drive or fly?
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Post by DocSilly »

I'm not into rc stuff. The C'T (german pc magazine, best in the world) had recently a four page story about battery chargers. They covered everything from the basics of charging batteries to comparing the different options of todays chargers.
The C'T is a biweekly magazine with 200+ pages before the adblock. They cover pretty much everything that's interesting for the advanced computer user. That goes from software/hardware to service test, from current technologies and research to more exotic topics like the battery chargers or electronic gadgets in cars today and in the future.
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Post by Pugsley »

well.. all i want to know is how do i build a simple dumb charger for a 12V lead acid battery? just have it pump like say 200mA @12V and it will take a charge? cause i only need to charge my chair up for lans.
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Post by Shadow250 »

sure you could do that but you might want more than 200ma if its a large battery more like 2-5 amps. possibly one of those power supplys from ratshack would work or a rigged at atx psu. i have one of those as a car trickle charger. :D
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Post by Pugsley »

what I have for the chair:

YUASA

Sealed Rechargeable Lead-Acid Battery

MP7-12FR 12V 7.0Ah
flame retardant


I Plan to use that.
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Post by Shadow250 »

i have 2 of those batteries. 1 i have rigged with a handle and a car headlight. (one hell of a flashlight) i charge it with a 2amp output radioshack power supply. takes about 5 hrs. i dont think you could charge it with 200ma charger i tried with a 400ma transformer plug but it blew after 3-4 hrs.
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Post by canton_kid »

Is this a vibrating back massage chair or something your modding with leds el cable and cathodes :)

Maybe some fans for those hot lan buildings?

If the battery is easily removeable how about plugging an adapter to your car lighter (12v) and the battery or one of those cheapy chargers that plug in like that. Charge while you drive, or sleep for those weekend parties :)

I'm not familar with that battery. Is that like a UPS battery?

I think most 12v batteries charge at about 13.5 V and when fully charged will read higher than 12v with a meter.
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Post by canton_kid »

Shadow,

I used a 12v cordless aircompressor with a halogen driving light for a flashlight too. Connected a lighter plug to the light and used the cigerette lighter style plug. Works great!! Just plug it in to turn on.

Do you by any chance live in the woods like I do? Best flashlight I ever had, rechargeable too and even airs up your tires :)
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Post by Pugsley »

im just puttin some cathodes under my chair... they should run for several days if not a week on a single charge.
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Post by Shadow250 »

yep i live in the woods pretty much. only have dailup available here or that direct tv satelitte thing. the battery and car headlight light up quite a lot :D dont have a air pump on it though.
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