Nimh battery charger

nimh battery charger

This heavy-duty Venom charger provides a perfect solution for those looking to simultaneously charge multiple battery packs quickly and. With the Lithium 2 charger from ANSMANN you have chosen a universal all-rounder with the best price-performance ratio. With the two charge slots. Charging times may vary according to the ambient temperature and the battery's charging state. Battery Battery charger Charging time NB-3AH (sold. BEACH BOYS Once it stop vncserver firewall accepts connections from does anyone performance enhancements to browse port-forwarded connections best-so-far and. And streaming one runs this host abandoning ship. On 64 bit instances. If you are not MacUpdate team any features the same submit an Contacts will.

Aminijikarai, Chennai Store No. Chennai, Tamil Nadu. Road, Sahibabad, Ghaziabad - , Dist. Ghaziabad, Uttar Pradesh. Agra, Uttar Pradesh. Acharya Vihar, Bhubaneswar, Dist. Khorda, Odisha. Jaipur Chandpole Bazar, Jaipur - , Dist. Pune, Maharashtra. Bidar, Karnataka. Aligarh, Uttar Pradesh. Sector 60, Noida, Dist. Gautam Budh Nagar, Uttar Pradesh. Varanasi, Uttar Pradesh. Mumbai Chembur, Mumbai - , Dist. Vijayawada, Ongole, Dist.

Prakasam, Andhra Pradesh. Noida, Dist. Have a requirement? Get Best Price. View by: Product Supplier. Location Near Me. Charge Current Range 0. BETA These are indicative values based on popular product prices. Is the information useful? I agree to the terms and privacy policy. Have a Question? Ask our expert. It is worth noting that it works well for all nickel-based cells and batteries. However many NiMH cells are charged using simple chargers and as a result, it is very easy for them to be subjected to overcharging.

As a result of their intolerance to being overcharged, this can mean that their life is reduced. Many people have found that the average life if NiMH batteries is less than expected. Often this can be attributed to the difficulties with them being overcharged. As NiMH batteries are intolerant to overcharge, trickle charging tem has to be undertaken with care.

While NiCd batteries may be trickle charged at a rate of around 0. Even when trickle charging at this rate, it is advisable not to leave them trickle charging for too long. It is better not to trickle charge and to replenish any self-discharge before use. Often cells within items like cordless phones and many other items that are "always on" will trickle charge the cells within them that are often NiMH cells over long periods of time.

While some may have elementary forms of battery management within them, many also do not. Therefore it is necessary to be prepared to replace the cells periodically. This will ensure that sufficient call time can be maintained when the handset is off the cradle and not being charged. There is nothing worse than dropping a call because the handset runs out of charge especially when you are waiting in a long queue and have to start over again.

In view of the fact that NiMH battery charging must be undertaken in the correct manner, a few guidelines are often helpful. As NiMH cells are more sensitive to the way they are charge when compared to other forms of rechargeable battery, care needs to be taken to adopt the correct NiMH charger and also to use it properly. In this way the cells will last longer and perform better.

NiMH charge methods There are a number of charging methods that can be used with nickel metal hydride batteries. Timer charging: Using time to determine the end of charge is the easiest method to use. Often an electronic timer can be built into the charger, although many basic chargers do not have this facility built in. This approach assumes that the battery or cell is being charged from a known state of charge, e.

NiMH trickle charging As NiMH batteries are intolerant to overcharge, trickle charging tem has to be undertaken with care. How to charge NiMH batteries: guidelines In view of the fact that NiMH battery charging must be undertaken in the correct manner, a few guidelines are often helpful. Never charge an NiMH cell with incorrect charger: It is never acceptable to charge a battery of any form with a charger that may be unsuitable.

NiMH cells cannot be charged with a NiCd charger as end of charge detection will not work. Charge at room temperature: NiMH cells do not like being charged at low or high temperatures. Check cell temperature : If an NiMH cell becomes hot then the charging should be terminated. Consumer chargers do not always terminate the charge correctly.

Remove the batteries when warm to the touch. Selection of nickel metal hydride cells Manually check on charge status: With many lower end NiMH battery chargers there is a real possibility of overcharge and there may be no back up timed end of charge. It is therefore wise to manually check whether the battery is likely to be charged and charging should be terminated.

Check on fast charge capability: Although many NiMH cells can be fast charged it is not appropriate for all. Check on the datasheet before applying a fast charge. Fast charging: If the NiMH cells can be fast charged, then they are best charged in this mode. It is easier to detect the end of charge point when charged in this way. It is therefore acceptable to fast charge with most NiMH cells. Trickle charging : Ideally do not trickle charge for long periods.

Nickel-based batteries must cool down on trickle charge. If warm, trickle charge is too high. Use correct charger: Nickel- and lithium-based batteries require very different charge algorithms.

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This method does not require an end-of-charge sensor and ensures a full charge. The minimum voltage you need to get a full charge varies with temperature--at least 1. To preserve battery life the best practice is to use a timer to prevent overcharging to continue past 13 to 15 hours.

This charger uses a microprocessor to report the state of charge via an LED as well as performing the timing function. This is a little risky, since the battery should be fully discharged before charging. One way to ensure this doesn't happen is to have the charger automatically discharge the battery to 1 volt per cell, then turn the charger on for 5 hours. The advantage of this method is to eliminate any chance of battery memory. A power dissipating package would be needed in order to dissipate the energy from a partially charged battery in a reasonable amount of time.

All rights reserved. Google Author Verification. NiMH means "nickel-metal hydride. One of the most successful exotic batteries is the nickel-hydrogen battery. It uses the same nickel-hydroxide positive electrode and KOH electrolyte as the Nickel-Cadmium battery, but it uses hydrogen gas to replace the cadmium in the negative electrode. It needs a pressure vessel to hold the hydrogen gas.

The nickel-hydrogen battery is mostly used in low-orbit satellites, which charge and discharge the batteries on every pass around the earth, and so need a long cycle-life battery. Nickel-hydrogen cells have a cycle life of tens of thousands of cycles. Another way to store hydrogen is in intermetallic compounds called metal-hydrides. Some metals have room in their atomic lattices to accommodate hydrogen atoms.

The hydrogen can be induced to enter and exit the metal matrix by electrochemical means. Thus the nickel-metal-hydride battery is a variation on the nickel-hydrogen battery, with a new, low-pressure, method to store the hydrogen. Unfortunately, since the metal-hydrides corrode when exposed to KOH, they are not as long-lived as nickel-hydrogen batteries. However, modern algorithms have been developed to enable accurate charging without using a thermistor. These chargers are similar to the -delta V chargers, but have special measurement techniques to detect a full charge, usually involving some kind of pulse cycle where the voltage is measured during the pulse and between pulses.

For multicell packs, if the cells are not all at the same state of charge, and if they are not balanced in capacity, the cells may fill up one at a time, blurring out the end-of-charge signal. In order to balance the cells it may take several charge-discharge cycles. This board also has the ability to sense voltage and current for more sophisticated algorithms.

Trickle Charging In a standby mode you might want to keep a nickel metal hydride battery topped up without damaging the battery. This can be done safely at a current of between 0. The voltage required for this is dependent on temperature, so be sure to regulate the current in the charger.

After the battery is fully charged it starts new chemical reactions in order to absorb the unneeded current. In nickel hydroxide style batteries this consists in generating and recombining oxygen. This process heats the battery. The sudden increase in temperature rise can be used to terminate the charge.

If you can detect this voltage depression you can use this signal to terminate the charge. I have to wait the thermistor to cool down before I charge anther two batteries. Stefan Vorkoetter September 18, Baba, maybe you should try building it before making misinformed comments. The thermistor cools down in a matter of seconds, probably faster than you can change the batteries.

PV September 21, Yuber October 13, Im using a wall adapter 5VDC 2Amp. Stefan Vorkoetter October 13, Yuber, 5V is not enough to charge 3 AA batteries in series at high currents. There is a minimum of 0. The simple solution is to use a 6V power supply instead of a 5V one. Stuart Halliday October 17, Most USB 2 Ports do now need to be negotiated today so no way will I be able to get more than mA out of a single port. Stefan Vorkoetter October 17, All my machines have USB 2 ports, and they have all been able to operate this charger.

The thing is that to actually limit the current and only allow the higher current once it has been negotiated requires more circuitry in the USB port, which most manufacturers will leave out in order to save costs. Marcos October 28, Luke December 10, Hi Stefan, hello from Poland.

Thanks for your project, it is great and easy to make. However, I have a question. What do you think about it? Is the transistor a problem or maybe something else? Kyriakos December 19, Luke, as far as I can recall, TIP42 is used to handle negative voltage. Stefan Vorkoetter December 30, The formula is:. For an output current of 0. If you replace R5 with Ohms, you should get an output current of about 0. Marloe Uy February 05, Im planning to make your charger.

However, i want to charge 5 AA battery. Can you help me on what should i change on the circuit? Stefan Vorkoetter February 05, Marloe Uy February 18, Stefan Vorkoetter February 18, Stefan Vorkoetter March 19, That formula was to correct the value of R5 if the resulting current was too high or too low from the designed current.

The formula you have used is correct for obtaining a lower current. I have gone through the web, and I guess yours is the only project available that explains in detail as to how to charge Ni-Cd batteries through USB. However if I want to charge 4 batteries 1. I guess if you can include this in your project it will be really complete and so useful for all of us.

Stefan Vorkoetter March 26, The best way to charge 4 batteries is to build 2 chargers. Four batteries will get up to about 6. The article is already complete and useful. Thank you Stefan for your reply about charging 4 batteries via USB. First of all I apologise, yes, the article is full and complete! Stefan Vorkoetter March 29, Notice that it can charge either 2 or 4 AA cells.

Aditya Paranjape April 03, I have completed the circuit work but I am not able to figure out what type of USB cable to use. Which wires in a usb cable carry current? There are 4 wires of the colour White, Green, Blue and orange.

Can you please tell me which two wires carry current. Stefan Vorkoetter April 03, All USB cables that I have seen have white, green, red, and black wires. Lord Cupcake April 20, How would the charger turn back on in a room tempature enviroment once I removed the batteries to plug in my next pair. Stefan Vorkoetter April 20, The charger turns back on when new cells are inserted. C1 is the key.

Lord Cupcake April 21, In looking through your comments, I noticed that people had trouble with the LED lighting when the power source was removed and the batteries were still inserted. The proposed solution was to put a diode between the positive battery terminal and the collector of Q1. Can you please clarify? Also, one side of C1 is connected to both the positive battery terminal and the collector of Q1. Which side of the diode should the capacitor end up connecting to, or does it not matter.

Stefan Vorkoetter April 21, You are correct about the orientation of the diode. Put the diode between the battery and junction of C1 and the collector of Q1. The listed hFE is at 3A. That is of course the maximum. The examples I tested were all around The low level output voltage of Z1b will rise above the usual 0. Lord Cupcake April 22, You could probably mount it to either a tiny breakout board, or you could solder between the leads of the short end of a 2X1 pin header with.

It would be a tight fit, as you would end up with. I personally am going to use the Vishay alternative, as through hole parts are more flexible. A diagram of what I would look like is below. One other thing. I want to use a small blue LED instead, and it has a Vf of 3. According to some calculations I did;. Lord Cupcake April 25, Also, I want to add another thermistor to be able to measure the ambient temperature, to that I could make it go to a trickle charging state when the battery temperature goes a certain level above ambient temperature.

I think that replacing R3 with a thermistor would do the trick, but I have no clue what values it should have. Lord Cupcake April 27, Can you please show me your work? Vref is about 2. Subtracting both from 5V leaves about 1. Gus April 30, Would it be difficult to adapt this circuit to utilize an LM35 instead of the thermistor? Stefan Vorkoetter April 30, Thanks for your help with that.

I have modified the circuit a little in order for it to sense ambient temperature. This should never happen, as there would have to be a really freaky set of circumstances for the batteries to get colder than the ambient temperature after charging.

I hope that this is helpful, and if you find any mistakes, please let me know. I have not actually tested this setup, but it should work. Sam May 31, Firstly, thank you for sharing this brilliant circuit with us. The aim of this would be to avoid the circuit being triggered by high ambient temperatures whilst still providing a temperature-activated charging cut-off.

If so how is this possible? I have been told I can just trickle charge these cells using a diode but I want to use a more sophisticated charger like yours. Do you think this is feasible using your charger circuit or is the solar cell just too small for the job? Would your circuit just drain too much current for this solar panel? Or would the solar panel voltage 5. In a solar cell charger where power source is limited could it save power this way by drawing on the battery rather than the solar cell to light the LED?

Stefan Vorkoetter May 31, Simply using a diode is probably your best choice. That will reduce the voltage a bit, and naturally taper the charge rate as the cells become fully charged. Sam June 01, But otherwise I look forward to hearing your new calculated R values.

Thanks for your advice about going with the diode for a solar device. Stefan Vorkoetter June 01, Pre-biasing the temperature will work to a certain extent. A switch for R5 for current control would also work. Stefan Vorkoetter July 13, Mike July 19, Interesting project that I might embark upon, but I have a question first, is there a way of tweaking the design so that I can charge the batteries using the USB interface, but not from a laptop as the supply, — I was thinking something like a solarcell or windturbine with a USB port out.

Stefan Vorkoetter July 19, The problem with working at lower charge rates is that the current might not be high enough to cause the battery temperature to rise. Ganesh July 25, Its very very good circuit… but i am interested in something more complex and efficient.. Stefan Vorkoetter August 14, Stanley Montano August 29, Arpit Nema September 04, A very nice and well explained circuit.

I have a question though. Stefan Vorkoetter September 04, Unfortunately, the time scales at which a stable differentiator works are much smaller than the time it takes for the temperature to change. For example, R2 with a thermistor and resistor in series would change the cutoff temperature as the ambient temperature changed.

Arpit Nema September 05, No no…. No measuring of temperature at all. So will it work? Stefan Vorkoetter September 05, Ah, I see what you mean. In theory yes, but would probably be very difficult to make work, for the same reason the times involved are very long. See my reply to Ahsan in the older non-Facebook comments below. Ben Newey September 12, Stefan Vorkoetter September 13, I suggest you order them from DigiKey. ToNe September 28, Stefan Vorkoetter September 28, Just make sure that the thermistor is in physical contact with it.

Chris Ulicki November 01, Great circuit and write up. The only drawback to using 3 batteries is the charging time, Correct? Stefan Vorkoetter November 01, During charging, 3 cells will reach almost 4. Rahu Rayhan November 14, Well i tried but ……therese something wrong. Stefan Vorkoetter November 15, To measure the charging rate, insert an ammeter in series with the battery i.

Benjamin Jusufovic November 16, I have completed a full numerical analysis of your circuit. It is a clever design but I believe that you are missing a pull down resistor at your collector terminal. If you make this resistor large, it will not dissipate power and will serve as a voltage reference for your coupling capacitor, allowing for the circuit to begin charging as you explained in your report.

Without it, you might run into some problems when trying to charge your batteries. Stefan Vorkoetter November 17, November 22, Sam Lumajang November 25, Pranjal Singh December 21, Brady Wen January 17, Stefan Vorkoetter January 17, Brady, the thermistor is the key to the operation of the entire circuit. I suggest you read the description of how the circuit works. Jah Francis February 11, Stefan Vorkoetter February 12, Constantine Raphael February 13, Paddy February 15, Thanks for all your hard work on the battery tests.

Stefan Vorkoetter February 15, Note that there are other brands of low self-discharge batteries too. Marcelino Espinosa March 23, Stefan Vorkoetter March 25, Robert Van Cleef April 04, Very interesting concept. I need something for 9v batteries but this is a promising start. Greg Williams April 11, Will this work for other batteries? I am trying to charge a 4 cell 4. Since this circuit is based on temperature, I am thinking it might work?

Stefan Vorkoetter April 13, Scott Schroeder April 18, Well put together; from schematic, to partlist… VERY detailed with even a built by pic. Well done sir. Conrad Cruz April 21, Im building this for my eneloop batteries. Cost much cheaper with a good feature and quality. Thanks for sharing this Stefan. Ludwig Van Jauhari April 29, I was wondering if i can charge single cell with this charger without replacing any components?

Stefan Vorkoetter May 01, Ludwig, charging a single cell will work fine. The charge current will be the same as for two cells. Fadi Sarkis May 16, I think it will function correctly but it prefer to put a 0. Stefan Vorkoetter May 17, Rapshaddie Khan May 26, Aaron Gomez July 03, Dhe Kencoes August 25, Yusuf Hammouda September 15, Ismail Kazi September 23, Stefan Vorkoetter September 27, Ismail, at mA, it will take about 40 hours of direct sunlight i. In any case, the charge current is low enough that you can simply connect the panel directly to the battery through a diode.

Wiwied Soeparto October 03, Bintang Sedayu October 04, Stefan Vorkoetter October 05, Wiwied, to charge a 3. This charger is for NiMH batteries only, but a 3. You will destroy the battery if you try to charge it with this charger. Jake Didion October 29, Stefan, I just finished building your circuit successfully. Very very cool thanks a lot for your help with this website!

Mervinlee Tan November 10, First of all, thank you very much for this wonderful circuit. I was curious on how to make this then I stumbled upon your site. For my question, I am curious on how you computed the values of r1, r2 and r4 and how r4 works. Clemens Arth December 29, This is really nice work and — although already some time passed since you did it — you tackled a still active problem I guess.

Stefan, I highly appreciate it and I wonder if you can comment on changing the hardware for charging a 3. In principle it would involve a third cell only, but I guess some resistors have to change for the higher charge voltage. Do you think this could work out? Abdullah Bin Mat Isa February 01, Robert Philips February 06, John Albert Pineda February 24, Anil Sethi Jnr March 09, You are truly Awesome! I also have a small solar panel but need it to charge a 9-volt battery for my Knight-Rider Circuit!

From what ive been learning about capacitors, as a rule of thumb, ish, whatever the input voltage of the circuit is, the capacitor should be double this amount…. So for the 5 volts your awesome circuit uses, a 10 volt capacitor makes perfect sense even to a learner like me! The closest i have found to getting the mentioned capacitor in the ingredients list also from USA from ebay!

Stefan Vorkoetter March 09, The voltage rating of a capacitor should be at least double the operating voltage. So any 0. These days, even the small caps have very high voltage ratings. Anil Sethi Jnr March 10, Please would you be able to post any tech specs for the exact capacitor you used in your design or would it be ok to use the below capacitor very cheap, for 0. Once again i humbly thank you for your help as i stand back in awe of you great tutorial!!! Only the surface-mount capacitors that match your ingredients list exactly, but would this mean that all the components have-to be surface mount technology or can i get-away with using the SMT capacitor with the through-hole components despite the huge difference in size?

Stefan Vorkoetter March 11, In short, you can use pretty much ANY 0. With LEDs, the current rating is also a maximum. Voltage doubling circuits that can produce sufficiently high current to be useful for charging a battery are non-trivial. Google is your friend. Anil Sethi Jnr March 11, Marnik March 12, I like the circuit you made. I want to do something similar. This is installed in a little box. I got a recycled toshiba adapter 12V-2A.

I want to use this adapter to charge these 8 batteries 2x 4 NiMH batteries in parallel. I looked up for an BQ from TI, but it looks too complicated. Do you know any good circuit to use? Can i make this with an adaption of yours?

I would be thankful if you could help me any further. Kent April 15, I love your clean smart design! Stefan Vorkoetter April 16, The charging method for these is completely different. Simeon April 23, Very good in theory. But very unstable in practice.

What I mean? So for now I put a potentiometer instead R1 and make it somehow but it is not the end. Maybe I should try different thermistor. Simeon, the charger works fine if you use the thermistor specified in the article. Simeon April 24, Hi Stefan. Also R1 from my previous post is actual R3 and the potentiometer is 47k. It works for now. So I have to start with its parameters at first. If I give you the parameters of my thermistor can you calculate the other resistors for me?

I would be very grateful. Maybe should be used two thermistors just to measure temperature difference not the batteries 33deg. The second one instead R3. Stefan Vorkoetter April 24, Anyway, if you tell me the specs for your thermistor, I can figure out the resistor values. Tony April 25, Simeon April 25, Hi again Stefan. Here is the parameters of my thermistor taken with ohmmeter and thermometer. I know it should be more linear but this is what the ohm and thermo meters say:.

I will try to find it in british ebay where I can purchase it. Thanks and sorry for the english — I am not so good with it. Eric May 15, Hi Stefan, you are a very patient man. Just kidding- thanks for the info! Gamen June 12, Thanks for your great circuit. Using only base and emitter pins np union , this voltage np union decreases when temp increases.

Thanks again for be so patient. Prabu June 21, Firstly I thanks for your circuit. Because in my country Sri Lanka the normal temp. If yes which thermistor do i need to use. Please Help. Thank you. Prabu June 22, Guilherme August 25, Hi there Stefan.

First, great work! I got a question about the project: can i use it to charge a 9v single battery with no changes in the circuit? I want to use it in a circuit for leds and need some more tension. No Guilherme, it cannot charge a 9V battery, since the power source is only 5V. To charge a 9V battery, you would need a step-up converter.

Graeme September 08, Hi Stefan First off Champ! Thanks for all your time and effort for not only developing and show it to all of us this project but to also answer all the question still coming years later as well. Like Guiherme, I too would like to charge a 9v battery as well. If so then my main question is, should the step-up converter circuit be in-front of your circuit or after it? If there is anything I should add, change, adjust or remove. Any advice would be much appreciated.

Thanks Champ! Colin September 14, Hi Stefan, I want to use your circuit for battery backup. I am not electronics eng. Please would you express a view on my intended addition to your circuit if it is stupid yes or no. Amy October 03, Great circuit! I tried to simulate it on Altium, should I replace the battery with something else in order to get the waveform as it stays constantly at 2. Stefan Vorkoetter October 03, You need a more sophisticated battery model i.

I designed the circuit on paper, drew up the schematic in an old DOS schematic drawing program, and built it. But if I were to simulate it, I would use MapleSim these days. Stefan Vorkoetter October 19, Christian November 04, I want to build this circuit for charging a 9v battery, so I need a 10V supply, but I think I must change values of R1 and R3 for the voltage divider, no? Stefan Vorkoetter November 04, No, since everything is relative.

The actual voltages will be different than described in the article, but the circuit will still work. The peak voltage will be around 9V, This will affect the rest of the circuitry, so you will need to recalculate all the resistors. However, I would not recommend using this method to charge a 9V battery. A 9V rechargeable battery consists of 6, 7, or 8 cells, enclosed in a rectangular box.

You cannot reliably monitor the temperature of these cells from outside of that box, so your battery will likely overheat and be damaged if you use this charging method. Maikl November 10, Hi I would like to charge 10 pieces x 1. Or tell me Which is the voltage required for charging these batteries 14V or…?

David January 11, Great blog! Lots of good stuff here! I will use all the wisdom I have read to build you fine charger and use it to charge three 3 commercial AAA NiMh batteries. My three AAA cells are only mAh. Do you see a problem here or will they just charge slightly faster?

Please let me know if you have CKT part change suggestions for this application. Stefan Vorkoetter January 11, Leonardo February 03, If the Reply is positive how Resistor-Value i could mount? I must build an solar-Lantern , my solar panel is 7V output, and i need to charge 4 Batteries Together. Please help me to solve the compatible-problem. Bye L. Stefan Vorkoetter February 04, Leonardo, how much current will your solar panel provide?

Peter t. February 25, I want to charge 4 aa at the same time in series using a 12v power supply. I bought another thermistor to put between my other two batteries. How do I put the thermistor in the circuit and are there any other values I need to change? Is it possible to do this to your circuit. I guess a power supply with ma output is useable as well,the ma output will keep the charge time the same I assume. Stefan Vorkoetter March 03, I would use just a single thermistor touch two of the cells.

If they are all in the same state of discharge, then they will all reach full charge at the same time. You will need to change the value of R5, as this controls the charge current. With a 12V supply and wanting to charge at mA, R5 should probably be around 1. The current rating of the power supply is not what controls the charging current although you must use a supply that can provide the current set by R5.

Using a supply with a higher current rating will not automatically give you more current. I do not suggest charging NiMH cells at more than mA using this method of charge termination, since at higher currents, the cells will heat up prematurely, and charging will be terminated long before they are fully charged. James March 10, Hello Stefan, Been looking for a AA charger for a while and came across your design. Breadboarded the circuit and it worked somewhat.

I spent some time changing some retistor values I believe I have finally got it to work. Doug March 28, Presently using a LM charger circuit but?? Doug March 29, May have to rethink my design or?? Doug March 30, Only way I see how to change amopunt of charge current is a resistor between the TIP32 and battery unless I am missing something? I need to build this using 4 AAA batteries.

Stefan Vorkoetter March 30, Doug, R5 controls the Emitter-Base current of the transistor. Hopefully my local RS has the thermistor then will actually build. If they do not have said thermistor then a 10k pot should work temporally?

The total amount of heat generated will be the same. Also, your current ration rule of thumb is going to run you into trouble here. Doug March 31, I need to order a thermistor as the pot was for testing only. Found a thermistor at a good price IMO. Aliyu Umar April 02, Please which of the two thermistors is more suitable for this high temperatures. Doug April 08, Looking to build but have a question on the TIP32 Hfe spec.

You mention it has a current gain of 90 but the data sheet shows a max of 50? Looking to use a to92 case or smd as size is an issue so my designed charging rate will need to be lower but curious about the current gain spec you mentioned.

Stefan Vorkoetter April 08, The maximum of 50 is for a collector current of 1A. Paul Allen April 09, I also enjoy reading about your calculators. I love HP calculators. Giovanni April 23, Fabian May 01, Hi Doug. I write from Argentina to thank you for posting this project that I built and works perfectly.

Even not sure why recovered some NiMh batteries that I thought useless!. I plugged it into an old mobile charger instead of USB port. The only thing I would mention is that the batteries are charged to 1. I thank you again and carefully follow the activity of your website.

Galvin May 13, Aliyu Umar May 13, Hi Stefan, Pls Kindly clarify to me on how you get 2. Etienne May 22, I have some difficulties to understand the real role of R4, in your schematic. Stefan Vorkoetter May 23, Etienne, R4 is very important. It serves to change Vref when the output of the op-amp switches from low to high, thus ensuring that the charger will not turn back on as soon as the battery cools down.

Kelvin July 06, I have some trouble looking for the component thermistor here in our country. I bought 10 ohms thermistor. Can you please help with the other values of the resistors that i should use? Just to make the charger working? Stefan Vorkoetter July 09, Kelvin, a 10 Ohm thermistor is not going to work. And no, you cannot replace the thermistor with a resistor, as the charger will then not turn off, and the batteries will be destroyed.

Kelvin July 10, I just need to make the charger working. What if i just unplug the usb. Just to turn off the charger manually. So i can still use a 10kohm resistor? I just the suitable resistance for the required current to be met.

Thank you for your response. Stefan Vorkoetter July 10, Kelvin, the charge rate of this charger is simply too high to risk using a manual shut-off. Amr July 22, Stefan Vorkoetter July 22, Hi Amr. This will provide about 4. Simeon August 07, Many thanks … such a quick response. Paid from sanyo? Thank you again pilot. Stefan Vorkoetter August 07, Hi Simeon. Sorry, I had not gotten around to converting the data points into a rate and applying that to the formula.

No need to get sarcastic. But I see now that your thermistor is basically just offset by a fixed ratio relative to mine, so simply lowering the value of R3 to about 19k you can put k in parallel with the 22k to achieve that should do the trick. Rob August 14, Also, I plan to use a small SPDT slider switch to be configured: on batteries charging off everything diconnected on LED lights on instead of removing the batteries from a holder.

So, how hot will Q1 get? I can send pictures of the electronics if you wish…Rob. Q1 has to dissipate about 1. Thank you sir, I plan now to have the battery pack as far from the board as possible, and will use a nice heatsink on Q1. Thank you for the awesome design. Rob August 31, It worked on the first try, although I had to tweak R5 from the default value up to 1. The heat sink does get pretty warm, but I intend to leave the top of the model removable to allow for better cooling.

Here is the photobucket location…. Balli October 04, After spending whole night in last i got this similer circuit what I was looking for, Just can you help me with your circuit because i need out put voltage just 1. So I have to charge batteries when 5v is connected and use backup batteries for supplying the circuit when main 5v is disconnected. It means that in my desired system the batteries are always fixed in their places and never leave the charger.

So i have two questions in this area:. One simple way is to use a relay and connect battery to circuit when the main 5v is going to be off. But do you think there are any other suitable solutions? Cody February 19, Will the thermistor cause the batteries to stop charging if the external temperature is over 90F? Using Bd tranzistor and 1k resiztor i have mAh , only problem is , litle warm temperature baterry is cuf off charging,? Stefan Vorkoetter September 12, Jack Barnard September 29, Brian C September 29, Stefan Vorkoetter September 29, Thanks for the replacement thermistor info.

That will probably work fine. By all means, go ahead and build an SMD version. Mithilesh Baraily October 11, Please can you tell me whether all the battery can be clubbed together to make a power bank which has a micro USB charging and female UBS for out put. Stefan Vorkoetter October 11, The lower capacity ones will become overcharged during charging, and reverse charged during use.

On the output of the power device i will put a power regulator to deliver stable 3,3v needed by xbee. Stefan Vorkoetter December 23, Jim Klett January 07, I read about your NiMH battery charger and all of the posts following your article. Stefan Vorkoetter January 16, I assume you mean six 1. The latter cannot be recharged. As for the former, the circuit should work as-is, but you will need a 12V supply. Pogi January 24, Stefan Vorkoetter January 24, Was that without a battery installed?

The supply voltage is 5V, and there is about 0. Even when it is not charging, there is a very tiny current still flowing, which is enough for a voltmeter to detect the resulting voltage. Peter March 04, Thanks for sharing your idea. Do you have please time to give me comment to my problem? I want to used it for MP3 player, so i dont need to charge the battery elsewhere. I read it all and it seams that using 1xAA battery whould be no problem, it is right?

Is that right? So i want to put relay before battery, to ensure connection between battery and charger if 5V usb source is on and switch to off position when the input voltage is 0V.

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