9-Volt 150 mAh battery

[Crockett]

Does anybody have a schematic or link to a free schematic for charger that will charge this battery?
I'm sure some discussion might be necessary, so ....   

[Psi]

na, no discussion needed. 

Any old switchmode wallwart that's 12-19V  + one resistor.

Resistor value in ohms = (Vpsu - 9) / 0.015

0.015 is 1/10 the battery capacity (0.150) so will take 10 hours to charge.

Done.

[Balaur]

Safest way is to use a slow, trickle, C/10 constant current charger.

(You cannot/should not use a fast (i.e dv/dt, or dT/dt termination) charger.)

Basically, use a 15V+ power source, then build a 15mA constant current with a TL431 (figure 31 from this datasheet) and let the battery to charge during 15 hours or so.

(431s can be easily found everywhere, especially in broken PC PSUs)

Best regards

[Crockett]

I'm not sure yet how I want the design to go. I'm thinking I'd like to be able to have a 9 volt power supply that I could leave usually plugged in. And then when I want I can unplug it and the battery take over. (Remember, I'm here in the "newbe" section. Also, I have not yet determined the application for this power supply, but I'm sure I've got more parts to play with.

[Paul Price]

This simple circuit will work with about any wall wart power supply that is unregulated >8V  or regulated up to 20V and will not harm the battery and the LED's set  the correct charge voltage so will not damaging the battery or your equipment.

[Crockett]

I like this, but I have some questions.
I've been working with a AD-101ADT (wall wart) that is rated at 10VDC 1A output with 120VAC 60Hz 18W input. (I presume this will work to charge the battery). But, it seems this is an unregulated supply, since in measuring it I get 13.22VDC (unloaded). Applying a simple 5ohm (cement) resister as load I get ~7.7V and 1.53A. (Should this be like that?) I haven't checked the specs on this model wall wart so I don't know if it is supposed to be regulated or not, but regardless of that I want to build into this power supply a regulator for it. (Aside: I was even thinking it might be a good idea for Dave to do a vblog about loaded and unloaded voltage divider circuits with and without control circuit on a "Fundamentals Friday" episode)
So, as it is, we have a beefy wall wart to power this thing that as yet still has unspecified application. Bummer.
Another question; does it have to be LEDs? How do they control charging. I am assuming the LEDs light up as the battery charge maximizes to keep it from overcharging?

[Paul Price]

The rather precise voltage of each RED LEDs are added together to set the correct voltage to charge the battery, the red LEDs have the correct voltage and other colors, green or yellow or blue LEDs certainly do not. This charger does not care whether you connect this to an unregulated or regulated power supply, so long as the power supply is working, it regulates the voltage and current. 
If you have a volt meter you power up this circuit and connect it to a charged NiMH 9V bat and you can measure the voltage at the battery or at the emitter of the power NPN transistor with just a 1k load connected, and you should read between 9 and 10.5 volts, and  this is right in the range to charge the battery to full capacity without over voltage. The current itself is limited by the gain of the transistor, and a low gain 1w power transistor (with low beta) is preferred that can handle 25V or more.

If you want to gild the rose:

If somehow you compulsively think you need to have to so precisely control everything in life,  you may want to fine tune this circuit according to the discarded wallwart power supply of  your choice and to fit the Beta characteristics of your luck in winning the current gain lottery of the BD139 transistor:

Calibration Procedure:

(1)Replace the 100K fixed resistor with a 68K resistor in series with a 50K tiny pot connected as a rheostat. Apply wallwart voltage to the circuit and using a 1-ohm resistor as a current shunt in series with your discharged 9V NiMH batter, adj. the 50k pot for 14 to 28mA, whichever level you think you like. I have mine trimmed to 20 mA...a compromise between the two extremes.
(2)Replace the 10K fixed resistor with a 20K pot in series with a 1k resistor. Now, with a 10k ohm  load at the emitter of the BD139(no battery connected), adj. the Max full charge cutoff (output) voltage to 9.3V or whatever else arbitrary voltage you might think will please you and the almighty god of NiMH batteries.

Once you've set these values you can remove the adj. pots and insert the closest value of a fixed resistor or two to match their actual resistance setting...pots are too expensive and handy to keep around the experimenter's shop, why sentence them to a life of neglect???
 
Myths:  All NiMH batteries cannot be trickle charged after cut off voltage or charge completed voltage has been reached.
             A circuit needs to be complicated to work well.
             A simple circuit cannot work as well as a very sophisticated and elegant design.
             A NiMH battery such as 9V 150mA type must only be charged so as to achieve a precise voltage at a precise current.
             A  9V NiMH battery will be damaged by "float charging".  Truth:  if the charger current limit of the "float charger" is set to the correct charging current and float voltage, then the float charger automatically switches mode from constant current to float charge as the cutoff voltage is reached.             

The proof of a pudding is in it's tasting. 

I have been using this charger for 8-years for my two NiMH 9V batteries and they are both still giving great service.
 

[Crockett]

A "glowing" power supply/charger! Cool!

[RPBCACUEAIIBH]

Well I don't think that circuit ever stops charging... Slowing down yes, but stopping no...
Look at my Lithium battery charger (https://www.eevblog.com/forum/beginners/3-6-v-li-ionli-po-battery-switching-and-charging-circuit/), and make it with a little difference. 1. If you need only the charger, loose the entire switching part 2. replace the 7809 with a 7812 or find a suitable 12 V power supply and loose the regulator part. 3. replace the BD 139 with a BC 547 or 847 because you don't need that much current. you find description there about the rest.
You will need a Voltmeter to calibrate it. Connect the voltmeter's ground terminal to the ground, and the other to the 555 timer's pin 5 and set the upper limit with R7 where it stops charging. Set it a little bit 0.2 - 0.5 V higher the battery's rated voltage at a 9V battery sized accu is about 8.2 V. Then hook up the voltmeter's positive terminal to R8's middle terminal, and set it with about 0.2 V below the battery's rated voltage, and you're about ready to charge your battery. the LED will be illuminated while it is charging, and will turn off when the battery is charged.

[Crockett]

Thanks, RPB...  I'm definitely going to study your diagrams. I may build both and compare results. I know I want to regulate the supply to furnish other constant voltage levels and then have the battery take over when it is unplugged.

[ivan747]

Wait a minute everyone.

What kind of battery is this? I assume alkaline, but he mat be using something else like NiCd or NiMH or even Li-ion (charging Li-ion with a resistor will burn your house down without supervision and will burn itself with supervision).

[RPBCACUEAIIBH]

Thanks, RPB...  I'm definitely going to study your diagrams. I may build both and compare results. I know I want to regulate the supply to furnish other constant voltage levels and then have the battery take over when it is unplugged.

Well if your circuit needs to run without interruption when you pull out the plug, then you need to build the modified switching part as well.

If you are using 12 V as external power and your circuit is supplied with 9V, you need to replace the 7805 with 7809 at the switching part, eliminate the 7809 at the charger part, and change the C4 with a big electrolitic one. 100 uf I think will do well.

if you are not using 12 V as external power, you need to re-calculate the values of R2 and R3, because you can't exceed 5V at the BC's base and GND. You need to replace the 7805 with 7809 at the switching part, and the 7809 with 7812 at the charger part. I advise no less den 12V external supply, and no more then 24 V external because the 78xx ICs supports until 24V.

What kind of battery is this? I assume alkaline, but he mat be using something else like NiCd or NiMH or even Li-ion (charging Li-ion with a resistor will burn your house down without supervision and will burn itself with supervision).

Alkaline can't be charged, and Lithium can be 3.6-3.7 V/cell which excludes this 2 kind at 9V, so it may be NiCd or NiMH only.

[Crockett]

 
Ok, battery specs are:
Name: Power One Rechargable - p7/8h 150mAh
8.4 V 150 mAh
No. 5522
(IEC 6LR61 size/taille)
Charge: 14 h 14 mA
rapide: 7 h 28 mA
up to 1000 times
Blah blah
Made in Germany
VARTA Microbattery GmbH

That's it folks!

[RPBCACUEAIIBH]

Yeah, I thought so... it's 8.4 V I had one and I remembered 8.2 V
Please note that my design is not tested yet, if you build it than please leave a note there with your modified schematic and if it works well or not. Thanks!

[Crockett]

Will do

[IanB]

Ok, battery specs are:
Name: Power One Rechargable - p7/8h 150mAh
8.4 V 150 mAh
No. 5522
(IEC 6LR61 size/taille)
Charge: 14 h 14 mA
rapide: 7 h 28 mA
up to 1000 times
Blah blah
Made in Germany
VARTA Microbattery GmbH

That's it folks!

Looks like NiMh with 7 cells in series (7 x 1.2 = 8.4).

The charging current is given (14 h at 14 mA). Or 7 h at 28 mA if you feel lucky.

na, no discussion needed. 

Any old switchmode wallwart that's 12-19V  + one resistor.

Resistor value in ohms = (Vpsu - 9) / 0.015

0.015 is 1/10 the battery capacity (0.150) so will take 10 hours to charge.

Done.

This. This. This. This. This.

Forget fancy charging circuits with current transistors, LEDs and voltage regulators.

A battery like this has simple needs. Feed it a constant current of about 15 mA for about 12-16 hours. Measure the voltage from time to time if you like while it's charging and when it reaches somewhere over 10 V and stops rising the charge is done.

If you try to charge it at higher currents like 30 mA or more you will increase the risk of damaging  the battery by overcharge.

If you try to use any kind of voltage controlled circuit at 9 V you will fail.

Read the good advice from Psi and follow it.

[IanB]

This simple circuit will work with about any wall wart power supply that is unregulated >8V  or regulated up to 20V and will not harm the battery and the LED's set  the correct charge voltage without damaging the battery or your equipment.

I disagree. This circuit is not suitable for charging NiMH batteries.

[IanB]

I'm not sure yet how I want the design to go. I'm thinking I'd like to be able to have a 9 volt power supply that I could leave usually plugged in. And then when I want I can unplug it and the battery take over. (Remember, I'm here in the "newbe" section. Also, I have not yet determined the application for this power supply, but I'm sure I've got more parts to play with.

Unfortunately this is not simple to do with NiMH batteries. You can't successfully "float" them as you can with lead acid batteries for example.

There are generations of cordless phones out there that have routinely run their batteries into an early grave by trying to keep them on charge when the handset is in the base station. The underlying issue is that putting NiMH batteries on permanent trickle charge severely shortens their life.

Charging NiMH batteries has special requirements. You can't use a constant voltage based charger because the battery voltage is not stable. It changes with age, battery temperature and manufacturer. Therefore applying a constant charge voltage will overcharge the battery in the worst case, will undercharge it in the best case, or will subject it to constant trickle charging in the middle case. None of these results are optimal.

What you need a circuit to do is to charge the battery, detect when the battery is fully charged, and then completely disconnect the charger until the battery is discharged by some significant amount before trying to charge it again. It will involve some kind of voltage window comparator (see Dave's latest video), a charge control circuit with full charge cut off, and some logic to drive the thing. It is not the simplest thing to put together for a beginner.

[Crockett]

Cool! That's why I'm here. Good to see the viewpoints... And I don't mind the challenge. I think the other post on building a charger makes sensè for this one since it cuts off charging at a designated level

[IanB]

Cool! That's why I'm here. Good to see the viewpoints... And I don't mind the challenge. I think the other post on building a charger makes sensè for this one since it cuts off charging at a designated level

But "cutting off charging at a designated level" is not appropriate, and does not work, for NiMH batteries. (That other post with the LEDs is a bad design.)

To charge NiMH batteries you need to feed them a constant current and then measure parameters like voltage, temperature and time while charging.

For batteries with one or two cells (1.2 V or 2.4 V) the charging circuit can use a large charging current (from 1 to 4 hours) and look for a drop in voltage at the end of charge.

But for batteries like yours with 7 cells this is not as suitable. It is necessary to use a smaller charging current (the 10 hour rate) and charge for a measured time like 12-16 hours.

So to repeat the advice above: you should construct a constant current supply of about 15 mA, you should charge the battery for 12-16 hours, then you should disconnect the battery from the charger until it is used and needs charging again.

Of course, if you have a large supply of batteries and you don't mind replacing them when they fail, then you can use some other poorly designed charging arrangement.

[Crockett]

I was actually referring to RPB...'s thread on battery switching and charging circuit. I don't know if it can be modified to achieve the points you address or not, but it does cut off charging and does not trickle charge

[NiHaoMike]

There are plenty of charger chips for NiMH.

[Crockett]

There are plenty of charger chips for NiMH.

And that is a point well suited for this area of the forum,"beginners." It is good to see advice from some that points out fire hazards. It's good to see the various concepts like red LEDs being used to set a voltage level. (I still want to play with this circuit). And all in all I'm just exploring what I can do with an old 9-volt Rechargable I found in one of my boxes of parts
 

[IanB]

I was actually referring to RPB...'s thread on battery switching and charging circuit. I don't know if it can be modified to achieve the points you address or not, but it does cut off charging and does not trickle charge

Right, but that circuit still has a problem because it is still trying to use an adjustable voltage to stop charging:

You will need a Voltmeter to calibrate it. Connect the voltmeter's ground terminal to the ground, and the other to the 555 timer's pin 5 and set the upper limit with R7 where it stops charging. Set it a little bit 0.2 - 0.5 V higher the battery's rated voltage at a 9V battery sized accu is about 8.2 V. Then hook up the voltmeter's positive terminal to R8's middle terminal, and set it with about 0.2 V below the battery's rated voltage, and you're about ready to charge your battery. the LED will be illuminated while it is charging, and will turn off when the battery is charged.

NiMH cells read about 1.2 V open circuit when discharged and they reach a peak voltage somewhere between ~1.45 V and ~1.50 V when under a low charge current (say C/10 rate). The voltage profile is very flat, so the peak voltage is very difficult to pin down; it varies by battery and it varies with temperature.

If you set the full charge threshold at the lower end, about 1.45 V, then your 7 cell battery would reach a voltage of 7 x 1.45 = 10.15 V at this point. It might be a little less than fully charged, but this only matters if you want the absolute maximum run time afterwards. The lower you set the threshold voltage the more sure you are that charging will switch off, but at the same time you are leaving more unused capacity in the battery.

[IanB]

And all in all I'm just exploring what I can do with an old 9-volt Rechargable I found in one of my boxes of parts

If it's an old battery it might not even perform very well, so that adds another layer of uncertainty to your enterprise. You would probably want to analyze the battery to see how well it works before devoting time to making a charger for it. And building a battery analyzer is a whole new kettle of fish...