# DIY recharging a battery

I am using this circuit without the diode. My resistor is 50 ohms, Can it charge a four cell, 4.8 volt, 300mAH, Ni-MH battery? My input voltage is about 18 volts. Any help? I am not sure how long to leave the battery charging or anything about this. Thank you

In conjunction with your other post about these cells, this sounds even LESS likely.
Last time they were 500 or 250 mAH. If they really are 300 mAH cells, they are
more likely to be Nicad rather than NiMH.

Secondly, your charger is going to be driving 1.2V/50ohm = 24 mA into the cells. If
they are 300 mAH, it'll take about 300mAH/24mA = 12 hrs or more to charge. This
isn't really the best sort of charger for either NiMH or Nicad. Commercial chargers
have a lot more electronics inside.

However, you really need to figure out what you have here. Knowing any of these will
help a lot.

AA, AAA, 1/2 AA cells?
The actual mAH rating.

The op has his charger set to output 360 ma 18/50 = .360 amps divided by cels 4 is 90ma a cel.
It will take 3.3 hours to charge and he better keep a eye on it there not anything to stop it from over charging.

Once the pack hits 5.6 volts you'll need to stop changing the pack. Thats if it is Ni-MH

be80be:
The op has his charger set to output 360 ma 18/50 = .360 amps divided by cels 4 is 90ma a cel.
It will take 3.3 hours to charge and he better keep a eye on it there not anything to stop it from over charging.

Once the pack hits 5.6 volts you'll need to stop changing the pack. Thats if it is Ni-MH

Wrong.
The four cells being charged are wired in series, Whatever amount of current that is leaving the regulator, each and every cell is also having that same amount of current passing through them. That is one of Kirchoff's laws, current is a series circuit is the same at every point in the circuit.

Lefty

I don't think that's for charging batteries.

At any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node, or:

That word sum means you added some thing to get a total in this case we are charging 4 cels we only have a set current of 360 and each will charge to that just like a cap

be80be:
I don't think that's for charging batteries.

At any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node, or:

That word sum means you added some thing to get a total in this case we are charging 4 cels we only have a set current of 360 and each will charge to that just like a cap

Your making little sense. The circuit shown can only charge all four cells at the same identical current rate, there is no 'division' of current for each cell as there is only one current path for the current to flow through.

Lefty

Lefty is right. Look at the OP's diagram. Whatever the current is, coming out of the regulator, it is going through all four cells before it goes to ground. No division into quarters anywhere in that diagram.

Would be nice if someone would verify that the charging current for the ckt as

oric_dan:
Would be nice if someone would verify that the charging current for the ckt as

I believe that is correct. As long as R is 50 ohms, then the output current of the regulator is 1.2V/50 = 24mA.

Here is a nifty calculator:
http://english.cxem.net/calc/lm317_calc.php

Going to a 13 ohm resistor would increase current to almost 100mA.

majenko:

Arduino Forum

Very good write up. I would only add the information that some 'fast chargers' monitor the battery terminal voltage while charging and can tell when the cell(s) have reached full charge and either turn off the charger or switch to a C/20 or so 'trickle charge'. These are/were called 'peak chargers' in the R/C hobby world. There are also even more advance chargers that can fully charge a battery pack then discharge them into a resistant load and actually measure the mAH that the battery held, these were/are called cycle chargers by some manufactures.

Lefty

retrolefty:

majenko:

Arduino Forum

Very good write up. I would only add the information that some 'fast chargers' monitor the battery terminal voltage while charging and can tell when the cell(s) have reached full charge and either turn off the charger or switch to a C/20 or so 'trickle charge'. These are/were called 'peak chargers' in the R/C hobby world. There are also even more advance chargers that can fully charge a battery pack then discharge them into a resistant load and actually measure the mAH that the battery held, these were/are called cycle chargers by some manufactures.

Lefty

Yeah, at the time I wrote that I didn't need to go into charge termination detection techniques etc. I know "peak charger" as a "delta peak" charger - one of the two main types of fast charger; the other being "delta time" - charge at a high current for a specific time.

Yeah, at the time I wrote that I didn't need to go into charge termination detection techniques etc. I know "peak charger" as a "delta peak" charger - one of the two main types of fast charger; the other being "delta time" - charge at a high current for a specific time.

OP should spend some time with google, learning about battery chemistry, basics of
electronics design, and proper design of chargers.

oric_dan:

Yeah, at the time I wrote that I didn't need to go into charge termination detection techniques etc. I know "peak charger" as a "delta peak" charger - one of the two main types of fast charger; the other being "delta time" - charge at a high current for a specific time.

OP should spend some time with google, learning about battery chemistry, basics of
electronics design, and proper design of chargers.

Or just some time on Battery University...