Charger Circuit

[BRAKKIE]

Hi There.
Is there anyone who can tell me where I can find a circuit diagram for a 6 cell Nimh charger (3700mA each)? I would really appreciate the info.

cheers, brakkie.....

[ikraj]

There are different types of circuits available...some are microprocessor controled and you can use a BASIC STAMP to build it. YOu can search the parallax website and see if they still have a circuit there. Then there are allready afew chips made specificaly for NiMh chargers...

If you let me know what your background is and how well you understand electronics I will be more than glad to help you. I ask this to see in which direction to point you or in which way I may be able to help.

One thing is for sure, I can provide you with designs...

Thanks.
ikraj

[bizaare69]

Good old ikraj

man i love your knowledge wont you adopt me? and teach me everything you know lol....


Bizaare

[ikraj]

Hi BRAKKIE,

The IC that you need to get to buils a NiMh charger is the MAXIM MAX712/713 series. It is an integrated controller that has all the necesary circuitry to control the charge cycle on either NiCd or NiMh batteries. It has a very good detection cicuitry built in to detect the change in voltage specificaly used for NiMh. It is basically what is known as a ZERO VOLTAGE DELTA Detector...a very accurate dv/dt peak detection circuit.

Basically all you need to add to the IC is the drive circuitry to handle the desired currents that you want to charge the packs. MAXIM has a complete design guide for this family of ICs. The guide has all the tables need for the necesary resistors used to control the circuit.
I built a charger/discharger using the MAX712 and it worked great. I built a 6 cell integrated charger so that each cell in a pack would have its own charge circuitry.
You can find the MAX712 at DigiKey or JAMECO electronics. If you go to the JAMECO website you can download the PDF file with the MAX712 design guide. If you follow the specs and you know how to design electronic circuits you should have no problem building an excellent charger.

Just one recomendation, there are some excellent chargers available in the market and there is no way that you will be able to build a charger for less money. Unless you want to build your own charger just for the glory, it is not worth it.

If you need any help or further advice, just let me know.

ikraj
Axxis Racing (http://www.axxis-racing.com)

[BRAKKIE]

Hi Ikraj and Bizaare69....

Thanks for your quick response.

O.k. so here's the story... I am a Mechanical engineer and thought that I'd start playing with my knowledge of aerodynamics, drag forces and so on so I bought the MI2 schumacker rc car. I really enjoyed this untill my charger gave in. I've bought two and both failed on me.

I am really at a point where I just want to sell everything and give it up. Nowhere in south africa can I get a decent charger for a decent price so I thought it may be a good idea to build my own and broaden my electronic knowledge at the same time.

I got hold of a Max713 chip and I've downloaded the schematics from the internet. I am just not sure about the configuration and so on. Can you provide me with a circuit diagram that will be able to deliver the amperage that I need, with all the right transistors and so on. If you can I'd like an lcd display to see whats happening but it is not essential.

Please keep in mind that I struggle to get special components (like the max712/3) so if you can stick to common parts I'l appreciate it.

Once again thanks for the help so far.....

Regards, Brakkie

[ikraj]

Hi Ikraj and Bizaare69....

Thanks for your quick response.

O.k. so here's the story... I am a Mechanical engineer and thought that I'd start playing with my knowledge of aerodynamics, drag forces and so on so I bought the MI2 schumacker rc car. I really enjoyed this untill my charger gave in. I've bought two and both failed on me.

I am really at a point where I just want to sell everything and give it up. Nowhere in south africa can I get a decent charger for a decent price so I thought it may be a good idea to build my own and broaden my electronic knowledge at the same time.

I got hold of a Max713 chip and I've downloaded the schematics from the internet. I am just not sure about the configuration and so on. Can you provide me with a circuit diagram that will be able to deliver the amperage that I need, with all the right transistors and so on. If you can I'd like an lcd display to see whats happening but it is not essential.

Please keep in mind that I struggle to get special components (like the max712/3) so if you can stick to common parts I'l appreciate it.

Once again thanks for the help so far.....

Regards, Brakkie

Hi Brakkie,

I see what you want to do now. If we use the MAX712/3 I can help you with the design. However, you will need to build a good PC board or else you will get false charges due to induced noise. If you give me a few days I will provide you with the design for a 5 AMP charger. This is a very efficient design since I add to the MAX712/3 a power supply current regulator instead of just a pass transistor/FET to make it more efficient and reliable. If you do not have access to many ICs in SA, the I might just do it with a set of transistors.

What I need from you is a budget and how intricate do you want it. What kind of output data do you want from the charger....The reason I ask that is to see how complicated you want your charger... I don't know how familiar you are with charger design but it involves a lot more than just a current regulator and peak detector. Todays chargers are much more sophisticated...we can add microprocessors to conduct many operations and make smart decisions while charging. Axxis Racing makes a power module that we can integrate into the charger so that you can monitor MAHS, Current, VOLTAGE, WATTS, mwhr, and TEMP. We can design a very nice charger at a very good price if we integrate some of the Axxis Products into the charger...

I am also an engineer, I practice EE, ME, SE, and Architecture and have been involved with R/C cars since 1974.

Well, once you tell mw what your budget is I can decide which way to proceed. Just one thing, please give me a few days since we are about to launch our website for Axxis Racing and that has me extremely bussy.
Like I said, I will do everything I can to help you. Also, can we ship parts to you, I ask because I have the sources for ALL The parts needed. The package would be very small. I can get you most electronic components if they can be imported into SA...(Axxis Racing has a full time R&D department for R/C, we also manufacture).

Like I said before, I use a multipe charger that charges every cell in a pack individualy and it works great. I also use the MAX712 or 713 for all our chargers that cycle our batteries for production. Just a ?? how much did you pay for the 713? I am just wondering...

I have attached a simple block diagram that shows you the building blocks needed to build a charger. (Copyright 2003, 2005 Axxis Racing) This should help you with the basics of a charger. This diagram shows you all the diferent processes that can be added to a charger with inteligence...The 712/713 allready has a few of those monitoring circuits built in.

There are two methods to detect end of charge for NiMh. One is the standard peak detector set at a very low threshold level (around 3mv/cell) and the other method is the 0 DELTA V. If you know the differences you should know that the latter is better for NiMh, but both work very well as long as you use it right. I need to know what you prefer because then I have to select either the 712 or 713...or we could use both, but that gets more complicated and expensive...

I look forward to help you in any possible way..

TTYL
ikraj

[BRAKKIE]

Hi Ikraj...

Thanks once again.... Now thats alot of info. Just remember my knowledge of electronics is extremely limited, so please bare with me...

I really dont want anything too expensive and complicated, keep it as simple and ascheap as possibe. The only logics I need is to see what happens during the charge, I dont even need the temperature. I just want to see if it's charging and when its finished. If the lcd is too complicated an LED will also do.

O.K. I definetely need to use the max713 as this is the only IC I could get (I paid R50.00 for it, about 4 euro).

I would appreciate it if you can send me the circuit diagram with a list of components that I can buy. I can manufacture the pc board myself.

Just remember to give me as much info as you can so the electronic shop sales guy knows exacly what I need.

If you can send me a diagram of the same charger as yours with the part lists it would be great. I also don't want to keep you busy with unescessary things.

Oh yes, I would very much appreciate it if you can add a circuitry do use the charge with 220Vac. Will this be difficult?????

Thanks again, Brakkie

[ikraj]

Hi,

I will provide you with the diagram to build a charger that will do the job. just give me the time, pleae...but I will do it... Do you know how to design PC boards? Like I said before, if the PC board is not designed right you will have problems with the charger...

Regarding the diagram for the multi-channel charger, I am sorry but I cannot provide you with it as I am planning on manufacturing that charger for sale. Otherwise I would... Hopefully the muli-channel charger will be out for sale within a year...The same goes for the chargers I use for our battery matching and enhancing system...they are all proprietary technology that we use in-house. I am sure that being an engineer you understand that.

220Vac is not a problem because the charger will work from a 12VDC power supply. I recomend you get a good 12VDC - 10A or higher power supply for the charger. If you have been buying chargers with built in power supplies that might be your problem. Most commercialy available chargers that are AC operated have a very CHEAP power supply and that causes the majority of the problems.

If you need any additional info don't hesitate to ask...

Stay in touch.

ikraj
Axxis Racing

[BRAKKIE]

Hi Ikraj...

Hey thanks for all the help.

Off course I understand, thats no problem, really. Take your time, I know you must be busy, we all are and I dont expect you to spend all your time on my project.

The reason why I said I will do my own pcb is that ther is a place in town that's doing it for you. You simply take the design to them and you pick up the pcb the next day but if you think theres anything I ned to know, please, I'm all ears.

Hope to hear from you soon....

Regards, brakkie

[ikraj]

Hi Brakkie,

Can you check if you can get the following parts:
MAX472, MAX724, MAX507, and MAX713 (which I assume you allready have)

These are the primary components that we will be using, the rest are common size resistors, capacitors, diodes, transistors, and switches.

The way I will design it is to have a keypad or dip switches to select the current (variable from 0.5 to 5Amps), it will be digitally programable. I have the 5 AMP limitation because of the integrated PWM converter that I will use. By using this PWM DC-DC converter and a DAC the charger will be much more functional and efficient...The PWM Dc-Dc coverter will be used as a constant current source instead of linear pass transistors...much better solution. We might add a discharger to it, its easy to add that function to it...much easier than the charger design...
Please let me know if youu can get the parts I mentioned. These are the backbone of the charger.
Regarding the pcb, it is nice to have a company like that, its hard to find places like that anymore around here.
The only thingthat worries me is that I will design it but not test it to make sure that everything is working smoothly. Many times (most) we design and once we build and test we have to make adjustments and/or changes. That worries me. If you could wait some time untill I finish my ongoing projects, I could then design/build the charger and make sure it operates as designed. That is my opinion...I guess we can play it by ear...
One thing is designing a charger and another is to actually get it to work just right...there are temp variables, noise, impedance, the list goes on...it needs to be tested...it has to work just right...

Stay in touch.

ikraj
Axxis Racing

[BRAKKIE]

Hi Ikraj.

Yes, Ican get all the parts. The Max agents this side said that they'l order ne the ones they dont have (which was only the Max507).

Well, I'm prepared to wait untill you get time to do the thing propperly, lets get it right from the start.....

Just one question. I know it's difficult to tell exacly but how much current will this unit draw? I have a 12V 8A supply. Will this work or is it a bit small????

From which country are you???? It would just be interresting to know...

Best regards and many thanks, Brakkie

[ikraj]

Hi Ikraj.

Yes, Ican get all the parts. The Max agents this side said that they'l order ne the ones they dont have (which was only the Max507).

Well, I'm prepared to wait untill you get time to do the thing propperly, lets get it right from the start.....

Just one question. I know it's difficult to tell exacly but how much current will this unit draw? I have a 12V 8A supply. Will this work or is it a bit small????

From which country are you???? It would just be interresting to know...

Best regards and many thanks, Brakkie

Hi Brakkie,

Your 8A supply should be OK as long as it is rated for a 90%+ duty cycle at its rated output...The charger will operate at 5A max current, sp at the most we will use around 5.6Amps.

I am an American, and I live in Denver, CO. Now, in what part of SA do you live?
I have visited Johburg, Cape Town, and a few other cities by the ocean...
Well, hopefully I can get to work on the charger before years end. I will be working on similar projects around that time so I should be able to combine that project with another one.

You mentioned that you are an ME. In what area of work do you specialize? What kind of design work do you do? Now I am interested to know more about you.

Can you tell me who is the distributor for Dallas Semiconductors (Maxim) in SA.

BTW, can you give me your email, I rather exchange information with you directly. I do not think this is the right place to discuss the charger design and construction.

In the meantime, if you need anything do not hesitate to contact me.

TTYL

[BRAKKIE]

Hi Ikraj....

Well I am from Johannesburg (about 20 minutes away from the airport) and I work for a large aircraft manufacturing company. We manufactured the Rooivalk combat helicopter and are doing services for the South African air force.

I specialize in the field of metrology, force metrology to be more specific. I am the guy who's performing all the stress analysis on some components by using strain gauges, loadcells, torque transducers etc....

Who are you working for????

yes, you are right, this is not really the right place. My email edress is eduantech@yahoo.com

I cant remember the name of the agents of the Maxim IC's but I will let you know on monday or so...

Hey, have to go now. Looking forard to your mail...

in the meantime, keep well.

Cheers, Brakkie

[ikraj]

Hi Brakkie,

I work for myself, but I do consultung for many international companies... I am on retainer to 12 companies...so in a way you could almost say that I work for them...

I sold my A/E consulting firm 5 years ago to a division of Flour Daniel. At that time I had 1,300 employees and we specialized in the design and construction of mission critical structures. The work involved any structure from a simple (or very complicated) landing gear for a fighter jet to the structural design of nuclear plants and underground airport facilities. We conducted computer analysis and simulations to study the behavior of structures and systems under different loads/conditions...taking into consideration minute things like oxidation, material deformation, and material surface errors, not to mention the human error factor. We analyzed parts all the way to the microscopic level.

Anyway, my background is in 4 areas of engineering and business.

Like I said, I am involved in a few projects that will be finished soon and thereafter I will be more than glad to help you design/build your charger.

The design I suggested thus far is the quickest way to get a good charger working, the other route is to use a microprocessor to do all the control, but development time is much longer, and to be honest with you, you will not gain much. I know that using the MAX713 will be a good design since I have used it before, not only for the R/C industry but also for many commercial applications that had to have a built in charger that kicks in while the battery is still under load.

Since I have your email, I will be communicating w/you directly from now on.

Maybe we can exchange more than just the design of the charger...I am allways trying to find a better way to do things.

Stay in touch and CHEERS.

ikraj