Charging station

[funkymonkey]

Someone asked a question on here about whether a higher current charger would charge a ni-cad etc faster - another person's reply suggested it wouldnt.

This is not the case as far as I understand. (The following is based on my understanding, if its wrong, someone please correct me)

Any rechargable battery depending on its capacity has a recommended maximum charging current. A flat rechargeable is greedy, it will try and gobble up as much current as it can get (its like pouring water into an empty container, you could trickle it in, or blast water in really fast) - that doesnt mean its healthy for the battery to accept current at that rate.

Imagine a battery with a 500ma capacity. If you charged it with an adapter rated at 50ma, it would take somewhat over 10 hours to charge (it takes longer than 10 hours, cos some of the power is lost in heat)

That would probably be a healthy charging rate for such a battery.

If you supplied it with 500ma, it would take a little over an hour to charge - the battery would gobble up all the current. However you would shorten the life of the battery because it would be accepting a high current.

I dont know this for sure with Ni-Cads, but this is the case with lead acid car batteries. If you have a 40Ah car battery that was flat, you could charge it real fast with say 20amps of current - but its not healthy, in fact you'll probably boil the electrolyte.

Its the same way in reverse. A ni-cad can deliver quite a sizeable amount of current - it will deliver its full current if shorted, which is usually enough to start melting stuff. That will also likely do permeant damage to the battery.

So to summarise, using a 2Amp adapter with a tiny battery will probably charge it fast, but also shorten the battery's life.

Also, just to backup what others have said, mAh is a measure of current used over the period of an hour. So a battery rated for 500mAh means it can deliver 500ma for an hour, or 250ma for two hours. Thats not strictly true, because in reality the rating is usually calculated based on the battery being discharged over a 20hr period.

So if the battery is 10Ah, that means you could draw 500ma for 20hours. You'd actually get less if you tried to draw the entire 10A over an hour.

Hope I havent confused you all. Im drunk afterall

[funkymonkey]

One more geeky addition, as far as know Lithium Iron batteries are a whole different kettle of fish. For a start they should be pulse charged - short pulses of current. Also, they are pretty dangerous things. If it werent for the safety aspect Li-Ions would have an even higher capacity than they do, but because of their volatile nature they have to be made in such a way that they are safe by giving them pretty thick sturdy casing.

Ive heard a report of one of the early li-ions in a cell phone exploding and causing nasty injury to the users face.

[rrvbl]

So, what's the easiest way to limit the current going to the battery? Place a resistor in parallel with the charging circuit? Or if you charge more than one car at a time (all in parallel), the current would be split equally between the cars.

[funkymonkey]

Not sure if a resistor would work cos it also has a habit of dropping the voltage too, but you are right in saying that if for example you had a 100ma charger and connected it to four (flat) batteries they should consume 25ma each.

Someone posted a link somewhere on here to a Vellerman kit (the type you just solder together onto a ready made PCB with instructions) for a charging circuit that depending on where you put some jumpers will charge from 1.5-9V at anywhere from 15 to 750ma (if I recall correctly). That looked pretty handy.

In fact if you wanted to make a complete charging station, it probably wouldn't be a big job to modify that board slightly so that you could cram it in a hobby box and use a couple of dials for voltage and current, and have a charging pad coming out of the top. Voilla - you could charge anything from stock to multi-cell jobs at the flick of a switch.

[bitbeater]

Heres what I did..

[JaredR420]

If you want to drop the charging current but not the voltage this is how you do it. You must place a resistor in parallel to the charging pads. Every supply will need a different resistor value to cut it down to the proper level. There are ways to figure this out , it's just hard for me to explain to you. I hope this helps
JaredR420

[rrvbl]

Jared,

Thanks, I'm patient if you want to try to explain it to me. You can send me an email.

Thanks

[Spanky]

so how long should you leave your car on the charger if you have 2 50mah batteries wired in series... does this depend on the nubmer of batteris in the charger? what is ideal for this setup, and can this be accomplished by charging through the controller?

[Squishy]

hmmm... this stuff is a little over my head.(and i thought all you did with little toys is play with em...)

[RIGD1]

I just got done building my stand alone charger. It uses 4- AA batteries.
Now I can finally build a 3 cell NimH pack and charge the sucker!

[RIGD1]

Just in case you guys are wondering what I used for the battery harness. It came from a HPI Micro RS4 kit. It is the AA battery harness for the Micro RS4, so you can use either AA or even AAA batteries for a power source. All I did was cut the plug off of the battery harness and solder on the Bit charging piece. I charge for about 2 minutes. Works great!

Do they sell Micro RS4 or whatever in the TinyRC shop?

[techno]

What do you think of this idea using a Nicad battery charger that you get at Wal-Mart ect...
You would have places to put 8 cars and could put a selector switch on for 2-3cell cars wired in series it is 1.2 volt charger right and you could race any time just leave them on they trickle charge get them when you want them don’t know if its peak charging but I think it should work


I got the initial idea off of Devedander on another site just looking for input or ideas on it?

[RIGD1]

Originally posted by got BITS?
Do they sell Micro RS4 or whatever in the TinyRC shop?

No, I don't think so. You should be able to get this harness at either your local hobby shop or on a internet hobby shop. Here's the part # if you're interested. HPI part# 73408

SAdly enough I don't have an LHS I can get to on my bike without taking a freeway. Could you make me another charging station just like that? I'll pay for it if its $5 or under (thats all the $$ I'll have left)

[RIGD1]

Sorry man, but I don't have an extra charging pad to mod and the charging pad cost $10 alone. Mine came with my Micro RS4 kit.
Radio Shack should have something similar to my battery harness and much cheaper.

I'll look in my closet and see If my friend's Micro RS4 kit still has this harness.

I can send you a charging pad. I can't get to an RS on my bike. I'm pretty much on my own in modding my bits & stuff (my dad wount move a finger to help me) I'll pay for the wire & the 4 AA box if it cost under $5. I may be able to get my friend to help me out. His dad has a soldering iron & maybe we can learn how to solder

I can send you a charging pad. I can't get to an RS on my bike. I'm pretty much on my own in modding my bits & stuff (my dad wount move a finger to help me) I'll pay for the wire & your friend's old micro rs4 box if its under $5. If you can't do that then nevermind. I may be able to get my friend to help me out. His dad has a soldering iron & maybe we can learn how to solder

[Lord_Nick_D]

2.5 A is equal to 2500mah
mah = miliamp hours
there is 1000 mah in a full amp

[Duratrax]

I just wana ask u smth.. if i make a dual selland my car runs faster i connected the bats in series, right? And i cant charge it with my controller.. So i need 4 AA bateries in series to charge my dual sell?