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# 9V battery charger schematic?

Anybody have a tested schematic for charging 9V battery?

Thanks.

R11 sets the charge current

R9 sets the charge voltage

Thanks for replying. Can you provide more info on the schematic? Values of the components, input voltage, etc?

C1/C2 = 1uF ceramic or film

R10 = 221R

R11 = depends on what charge current you want.

R9 = 2k or 5k trimmer

You don't really need D1 if this is a stand alone charger.

Input voltage is at least 2 volts higher than you max charge voltage.

What are the ratings on the battery you want to charge?

How many cells?

What capacity?

Q1 = 2N3904

Edited by Avro_Arrow - 2/11/14 at 6:19pm
Quote:
R11 sets the charge current

I've seen this schematic on the net somewhere before. It is straightforward, the only thing

nobody seems to be able to come up with is the formula for calculating current .

Even the datasheet of the LM317 doesn't give a clue...

The PIMETA v2 includes a simpler LM317-based trickle charger, suitable for "9V" NiMH batteries. Schematic link.

There's a whole section in the docs explaining it.

An LM317, one or two diodes, and a resistor. Done.

Thanks for replies. The battery I am going to be using is Rayovac 9V 200mA NiMH rechargeable battery.

trickle charge is the safe level for indefinite connection time - and NiMH don't like continuous charge as much as other battery chemistries - C/10 is too much if you want full cycle life

to get the full recharge cycle life you may have to be below C/20, down to C/50 by some manufactures NiMH datasheets

to do a faster charge you need to have a circuit smart enough to disconnect the fully charged battery - many cheap chargers just use fixed current with a timer that cuts off after 8-12 hours

in higher performance applications - laptops, phones - where battery life is really a customer satisfaction issue even smarter charger circuits look at V and temperature to cut off charging just right so they actually achieve many hundreds of recharge cycles without major loss of capacity

for hobby circuits you can just go with overnite levels of fixed charge rate and try to remember not to leave it plugged in forever - and you will forget, will not get 100s of cycles of battery life

Quote:
Originally Posted by tangent

The PIMETA v2 includes a simpler LM317-based trickle charger, suitable for "9V" NiMH batteries. Schematic link.

There's a whole section in the docs explaining it.

An LM317, one or two diodes, and a resistor. Done.

where would you find an LM317? I wanted to get it from mouser but they don't seem to carry it....I /think/ I found it on amazon but it had 4\$ shipping (if I plan on building more of these I'd like to get the components from the same place so that I only pay one shipping fee)

You mean this?

Quote:
Originally Posted by backspace119

where would you find an LM317?

The LM317 is one of the most common ICs around. You can probably find them for sale in Outer Mongolia.

Quote:
I wanted to get it from mouser but they don't seem to carry it...

Seriously??

I get 19 results, just in TO-220 type packaging, or over a hundred if you are willing to look at other packages. The TO-92 style is suitable for DIYing a 9V trickle charger.

The PIMETA v2 parts list even gives you a couple of Mouser part numbers.

How hard did you look?

Edited by tangent - 2/12/14 at 7:54pm
Quote:
Originally Posted by stixx

I've seen this schematic on the net somewhere before. It is straightforward, the only thing

nobody seems to be able to come up with is the formula for calculating current .

Even the datasheet of the LM317 doesn't give a clue...

The voltage across R11 is set by the diode forward voltage of the B-E junction of the transistor it is in parallel with.

So you could use a rule of thumb 0.6V, or get it from the datasheet, or measure the voltage.

This voltage will stay the same, even when you change the value of R11, and applying ohms law you'll be able to figure the rest out yourself.

Quote:
...and applying ohms law you'll be able to figure the rest out yourself.

Sure! Thank you!

Quote:
Originally Posted by drabina

Thanks for replies. The battery I am going to be using is Rayovac 9V 200mA NiMH rechargeable battery.

Do you know how many cells are in the battery?

It could be 6, 7 or 8.

It might say something like 7.2 volts, 8.4 volts

or 9.6 volts on the battery.

For 200mA charging current, R11 would be about 3.25 ohms.

If the battery has 7 cells, charging voltage should be set to 10.5 volts.

Quote:
Originally Posted by tangent

The LM317 is one of the most common ICs around. You can probably find them for sale in Outer Mongolia.

Seriously??

I get 19 results, just in TO-220 type packaging, or over a hundred if you are willing to look at other packages. The TO-92 style is suitable for DIYing a 9V trickle charger.

The PIMETA v2 parts list even gives you a couple of Mouser part numbers.

How hard did you look?

Quote:
Originally Posted by Avro_Arrow

You mean this?

ok I swear to god that wasn't there when i searched it. I searched lm317 and it did not come up! I swear! I did search before posting I promise both of you.

Thank you for the replies though