Battery Basics 101
 

There's been quite a lot of Forum traffic with questions pertaining to Batteries, so let's try and makes some sense of it all...

In this thread we're going to touch on the following subjects:
- Bit Battery Dimensions
- Nicad vs. NiMH
- Voltage & Amperage
- Charging

-Bit Battery Dimensions
The stock Bit Char-G/Microsizer battery is a 1/3AAA scale, 50mAH Nicad battery. One of the most common upgrades for the Bits is a higher capacity NiMH battery (like a 1.2v 150mAH NiMH battery).

The '1/3AAA scale' size is very misleading because that is NOT an industry standardized size and that means there can be a significant variation in actual physical dimensions between one manufacturers 1/3AAA size vs. another. The best way to shop for an upgraded battery is to go by physical dimensions...In order to fit (without modification) into a Bit chassis, the size has to be '10mm Diameter x 16mm Height' (or smaller). This is IMPORTANT to note because there has been some talk about a company that offers a 210mAH 1/3AAA size battery...But it has a height of something like 21mm (which is too big to fit a Bit).

- Nicad vs. NiMH
IMO, go with the NiMH batteries. They have higher capacity, no toxic chemicals, and prices are relatively cheap. I won't go into full details about the differences, there's PLENTY enough info out there on the Net about the 2 types and their differences.

Also note that while the stock battery on a Bit Char-G is NiCad, the charger on the remote handles the NiMH batteries without problems.

- Voltage & Amperage
Okay, let's put some sense into what 1.2v and 50mAH means...To simplify things:
~ Voltage(abbreviated as 'v') = Speed
~ Milliamps (abbreviated as 'mA') = Runtime and Torque/Acceleration

The PCB (aka circuit board) of the Bit regulates the Milliamps (aka current) going to the motor, which means having a higher capacity battery (like a 150mAH battery vs. a 50mAH) will make no impact on motor performance except to be able to maintain that regulated current for a longer time (meaning longer runtime between charges). If you were handy/brave enough to tamper with the resistors on the PCB and change how much current was going to the motor, then you’d in turn change how much torque was imposed (think of torque as acceleration).

On the other hand, the PCB does NOT regulate the Voltage to the motor, so putting a higher voltage battery in the Bit will equate to ALL the voltage going to the Motor and in turn the motor will produce more revolutions, faster (in other words, SPEED!).

A term heard often around the Forums is ‘2.4v’ or ‘Dual-Cell’ or ‘Dual-Battery’ Mod…They are talking about taking 2 batteries (make SURE they’re both the same voltage and milliamperage) and connecting them in Series (when connecting multiple batteries in ‘series’ the voltages add together, but no change to the milliamps. If you were to connect the multiple batteries in ‘parallel’, then the opposite is true; the milliamps add together, but the voltage stays the same)…Considering the information above, you know that this 2.4v Mod means lots of SPEED increase right? :)

- Charging
Here’s the rule of thumb when charging batteries…First, set the voltage as equal as possible to the cell/pack voltage. Then take the capacity of the battery (in milliamps) and divide by the charge rate (in milliamps) and then add 20% and the result is how long (in hours) it will take to fully charge the battery. Let’s take, for example, a 2.4v Dual battery pack with a 150mAH rating. Now, let’s say you had a 2.4v charger that charges at 500mA…[150/500 = .3] then [.3 + 20% = .36] so it would take .36 hours (or a little less than 22 minutes) to fully charge the pack…Roughly

The 20% is a sort of ‘leeway’ given because charging batteries and the chemistries and variations make this NOT an exact science (as a matter of fact some people say to actually add 50% for inefficiencies!)

The stock charger on a Bit puts out 2,500mA at 1.5volts for 45 seconds, per charge cycle. If you do the math in reverse, you’ll see that a single charge only fills a stock battery to about ½ capacity! So doing 2 consecutive charges will produce a SIGNIFICANT increase in runtime!

Alright, I think that should give a decent idea of how it all works with Batteries.

If you have any questions, concerns or corrections, feel free to post.

very nice.

again tho ive said this before. they are really cheap and dont get all bent out of shape over not charging enough or charging too much. they cost 2 or 3 dollars(us) and even with heavy wear will last probably 6months.

Great summary of a lot of information thats been posted on the boards. That should help clear things up for lots of people.

excellent info! thanx alot, you've answered alot of Q's. this thread needs a sticky!!

Also thanks for the correct battery dimensions, i was all set to buy a handful of 210mAh ones, I checked the dimensions at they were 21mm height just like you said. Phew!

Great post
So if you made a stand alone charger how do you figure out how long a charge should take if your using 3 AA batteries? Or should you not use 3 AAs if you have a 2.4v dual battery with a 150 mAH rating?
Thanks alot

i got the nkok micro sea explorer for xmas. it comes with a 4aa charger that works with bits.*you gota put the bit on backwards*

plus the boat is pretty cool.

L3V3L1,

How are you planning on doing that standalone charger? If you're thinking of connecting the wires straight up to the batteries (with no circuitry in the middle to regulate voltage and current) then you're sending 4.5v (if you're using 3 Alkaline AAs) at the highest current that the AA alkalines can chemically put out...Which i'm thinking is in the neighborhood of how the stock charger works on the Bits (so ~2,500mA).

It doesn't matter what voltage you use, the formula stays the same (time for charge is figured by amperage).

Use 2 batteries. While the 3 will work, you'd be sending more voltage than needed and could be detrimental to the batts.

great info,

thanx heaps

making a 2.4v battery pack
 

hey is there a special way or putting the batteries together my brother tried to make a battery pack a while back any for some reason when he tried to charge it it didn't work can anyone give exact details on what to do or know what was wrong that could cause the battery charging not to work?

another thing has anyone ever tried to use a plug for their bit battery pack so u can take it out to externally charge it? i was thinking those mini d.s. deans plugs are small enough to fit in the bits right?

what sorta ways are there to increasing torque? i have a 2.2 motor and i've had my thunderbolt for a few days. it seems to be slowing down. but it could just be my eyes deceiving me. i've cleaned it and all, oiled it, done pretty much everything to make it slicker. suggestions?

I have been looking for this information for SO Long. THX
I am in the process of building a AC bit charger but didn't know the specifics of how a battery being charged worked! So if i used my adjustable voltage at 3v and it has 500 amps it should work fine?

what if i used a 4.5 at 800ma?
(this is on a 2.4 v battery system)

Oh my god, the same old damn questions...In answer to every single one of your Qs masterjin, YES.

Just an update about using AA battery packs as a charger...I now STRONGLY suggest you DON'T do it (for anything more than 2xAA anyway)...Or at the least be VERY careful and keep a CLOSE watch on the battery temperature (of the car) when charging.

Why? Because I took my meter out and measured how much current output a 4xAA pack was putting out as a charger...5amps man! That's 5,000mA!!!

Just to put some perspective on that; Charging a 150mAH battery at 5,000mA is like baking a cake (that's suggested at 375°) at 12,500°!!!

Crispy on the outside, batter on the inside baby.

another perspective that's also how much the electric chair uses LOL

Oh, that sounds like my wife's rule of thumb.
Just add a little, it will make it bake faster.


-Nox

I found an ac adapter which gives 800mA dc at 3 volts to a battery. Do you think that would work ok on a 150mah battery at 1.2 V?

Also, the adapter does not say it in mah, but rather just in mA, it is one of those radioa shack ones like this: LINK.

i think 800mA might be a little high... i think 300-400 is max.... for not blowing out the battery..

A friend and I built AC chargers. I first used an 800mah 3v adapter, but my friend had a 1000mah adapter, and we concluded that a double charge from the 1000mah adapter was better than the 800mah adapter. In fact, a double charge off of the 1000 was better than a triple charge on the 800. This is all with stock NiCads in the cars. Haven't noticed any ill effects on the batteries.

whoa... that's scary... lol, hmm i guess they Wont burn the batts out then

What length of charge are you giving them? and how long are they running?

Because I was wondering if the 800ma adapter is not millamp hour. What's up with that? Is it like ma per second or instant?

I can only imagine they didn't give AC Adapters the 'mAH' rating so as to keep folks from being confused...Even though that's what it means...

An 800mA AC Adapter, means it'll charge to 800mA in 1-hour

So just do the math if you want to know by minutes (800/60 = 13.33mA per minute)

sweet, thanks. Stupid radio shack. Oh well, I think I have a few different adapters at home.

So Namuna, given your maH equation, would you conclude that a 3v/8oomAH adapter would need 11 minutes and 15 seconds to fully charge a 150mA NiMH battery?

basicly a AA battery puts out 1250mah acording to your past (4xAA=5000mah) and considering the charger puts out 2500mah at 1.5 v and doing qfm's duel cell chager mod on the controller dosnt change **** but volts and you said volts dont really matter am i correct?

1250mah means total capacity of the battery. it doesnt dump it all at once.

errr could someone set this straight how much mah does a AA put out

volts do matter somewhat(depending on internal resistance of the batteries. they have to hit a certain thresold(i belive roughly 1.5x of what you want to charge). thats why 3v doesnt charge 2.4v batteries.

The math is right, but charging batteries ain't an exact science...So add like 20% to your final time and I'd say you're fine with 13 to 14 minutes.

As far as the AA ratings...I haven't tested a single Alkaline AA, but I'd say 1250mA would be about right.

Let's use the classic Water to Electricity comparison, hopefully this helps with understanding what's going on...

If Electricty was water; Current (mA) would be the volume or amount of water flowing and Voltage would be the pressure or how fast it was flowing at.

For comparison sake, using an AC Adapter at 3v/500mA would be like getting shot by one of those big Super Soaker guns...Whereas using a 4xAA Alkaline battery pack would be like getting shot by a Firehose...They'll both get you wet, but one hurts less...ESPECIALLY over time.

So, the hog is right in saying that Voltage matters (somewhat)...But you need to be careful with the Current

also i did a big battery no-no by adding a 3rd battery to my toys-r-us truck and its not the same capacity or brand as the other two. no problems so far so maybe its pretty close.

lol

hogjowlz and babykiller, you're treading on some dangerous ground when trying to figure out what an AA NiMH batt puts out. If you look up the differences between alkaline batts and NiMH or NiCad batts, there is a crucial difference in the way they put out power.

babykiller, your question about how much mAH an AA batt puts out, if it's a NiMH or NiCad, it will be listed on the side of the battery. The highest rating at the moment for a AA NiMH is the Sanyo 2100 mAH batt. Meaning it can supposedly sustain a 2100mA output for one hour.

However, and this is very important, hogjowlz, your statement about the 1250mAH batt being the capacity and that it doesn't output that all at once is incorrect. The actual output of the batt is dependent on current draw. Most circuits regulate the draw, but if you ever short circuit a battery, i.e. just take a wire and connect the 2 terminals, then current draw is dependent on the battery's internal resistance. An alkaline batt has relatively high internal resistance so even if you short it out, it has a limited current output. Also, because of an alkaline batts chemistry and construction, these batts don't perform well under load. The performance drops quite significantly in fact, the greater the draw.

NiMH and NiCad batts though have very low internal resistance which makes it VERY dangerous to short these batteries out. They can put out tremendously high currents if you short them out. Yes, even AA size batts. If you link 4 AA-size NiMH or NiCad batts in series and short out the +ve and -ve terminal of this pack with a screwdriver for instance. It won't take very long, just a few seconds to get the screwdriver really hot, and if you leave it connected, the current draw is high enough to MELT the screwdriver. Be careful with these batteries!

If you don't believe me, try it, but try not to burn the house down in the process, and I take no responsibility for anyone crazy enough to try this.

Also, Namuna, a small point about the rating of the output on that radio shack adapter. It is actually correct to state that the output is 800mA and NOT 800mAH. It means that there is an output of 800mA constantly. Thus an 800mAH battery would take one hour to charge, then theoretically be able to output 800mA for one hour. If current draw is higher or lower, than the battery would be able to sustain output for a shorter or longer duration. In practice of course, the inefficiencies of a battery never let it maintain the constant rated output, so if you had a device which draws 1600mA, the 800mAH battery would not run for 30 minutes. It would probably run less than 30 minutes.

This is why NiMH and NiCad batteries are so dangerous. shorting it out means near 0 resistance across the terminals. Because the battery itself also has near zero internal resistance, in theory, I believe I've read, NiMH and NiCad batts can put out near infinite current when shorted out. This massive flow of current heats up whatever is shorting it out and the battery itself. Keeping a fully charged NiMH battery in your pocket with a whole lot of loose change can short the battery and start a fire in your pocket.

BTW here's a link another forum member put up to a site with NiMH and general battery info
http://www.extremetech.com/article2/0,3973,15710,00.asp

P.S. sorry, can't remember which member posted the link.

I just ran through this thread, and now I'm a little confused. Hog says that 3 volts won't charge a 2.4 volt battery (dual cell mod). You actually need something closer to 3.6 volts. Yet Namuna recommends getting as close in voltage, between the charger and the batteries, as possible. Who is right, assuming that you're charging NiMH batteries?

I ask this because I'm thinking about adding a regulated AC adapter to my Motorworks charging base, but I'm not sure which adapter to buy. I was all set to use a 3V, 700mA Radio Shack adapter, and using the timed (50 second) charger to make 13 consecutive charges to my dual cell car, modded with two 110mAH NiMH batteries.

But if a 3V adapter won't do the job..... Do I step up to a 4V adapter?

And while we’re on the subject, what would be the highest safe current to use? At 4V, Radio Shack can provide adapters rated at 300mA, 800mA and 1000mA. At 300mA, I’d be charging for almost a half hour, which is a long time to wait. Stepping up to the 800mA adapter would cut things down to 10 minutes. It’s also a lot easier to count 12 charges, as opposed to 31 charges.

when we charge of my ee buddie's power supply its usually 4v @ 3-500ma.

as far as shorts go ive never seen my stuff get that hot. i have shorted a car once by hitting a door(really hard) and the shock jabbed a solder connection through the insulator on a battery and all kinds of strange stuff happened but it didnt get super hot right away.

you wana see a lota heat play with photography power packs.
my friend repairs them and a switch shorted one night and vaporized part of a screw and it arked allover the place and well "blam" it sounded like an m-80. i was about 5 feet from it and he was about 1foot from it. you can always run an auto fuze in your car if you are worried about shorts.

and well namunas statments are all on theory and the most efficient way to charge a cell. if you are charging an expensive industrial battery or even a cell phone id listen to him.

in theory you want just enough voltage to overcome internal resistance and trickle the current into the battery. and yes thats the proper way to charge a cell.

but these things cost about 2bucks a piece and if you charge the "proper way" you will be waiting a long time to play with your car. i cram the juice in so i dont wait more than a few mins to run my car at top speed. i have a few dual cells that still run hard after several months of use and they hold just as well as when they were new. when they do go bad it will cost me 4bucks to replace.

you guys should not get ulcers over 2 dollar batteries.

When it was mentioned that you need a voltage roughly 1.5x that of what you're charging to overcome internal resistance it was said based on the assumption that what you're charging has a high internal resistance. Now that it has been established that NiMH and NiCad batteries have a miniscule internal resistance it should be more understandable as to why it is fine to charge them from a 1.5v source.

I do have a question for the more technically inclined people here. What if the charging source were to be a rechargeable (NiMH or NiCad) AA? It is my understanding that we're able to charge NiMH and NiCads w/ alkaline batteries due to the high internal resistance of alkaline batteries causing only a partial short allowing current to dump into the battery you intend to charge without all cycling back to the battery you're charging from. If I were to use a NiMH AA to recharge a NiMH 1/3AAA directly wouldn't that cause a full short resulting in bubbly batts due to the miniscule internal resistance on both ends (< 1ohm)?

Oh, and don't alkalines have an approximate internal resistance of about 1.2ohms? (this would make sense if they're putting out 1.25amps on a full charge, while their voltage is still at 1.5v ... I = V/R .... I = 1.5/1.2 ... 1.25 = 1.5/1.2).