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Battery Equalization
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Jay



Joined: 02 Nov 2005
Posts: 37
Location: San Francisco, CA

PostPosted: Tue Feb 14, 2006 12:25 pm    Post subject: Reply with quote

I ran across this voltage equalizer diagram. It is incomplete but may work if we can determine components. Anybody want to tackle it?


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MajorWilson



Joined: 26 Sep 2005
Posts: 236
Location: Peoria, AZ

PostPosted: Tue Feb 14, 2006 6:08 pm    Post subject: Reply with quote

Jay, where did you find this. It has merit. I'm not sure of the components but I bet Tom might have some ideas. I'd give it a try. I have some good 12v Trojans in the garage that could be used as test bats. It does look like it's missing something. The diagram doesn't have resistors for R1 through R4 but starts with R5. Am I missing something?
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Jay



Joined: 02 Nov 2005
Posts: 37
Location: San Francisco, CA

PostPosted: Wed Feb 15, 2006 7:55 am    Post subject: Reply with quote

I did a search for these units and I found another site discussing them. It was an electric bike group. One of the members suggested it. I communicated with the originator who has 30 years in the electronics field. Their bikes have only 2 batteries so it wasn't worth looking into. His e-mail is: tbrown59@verizon.net. I'll ask your question. One refinement someone suggested is to add a resistor in series with the collector of each darlington transistor, so the resistors dissipate most of the heat.
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Jay



Joined: 02 Nov 2005
Posts: 37
Location: San Francisco, CA

PostPosted: Thu Feb 16, 2006 8:08 am    Post subject: Reply with quote

Updated info from originator of wiring diagram.


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MajorWilson



Joined: 26 Sep 2005
Posts: 236
Location: Peoria, AZ

PostPosted: Thu Feb 16, 2006 5:55 pm    Post subject: Reply with quote

Jay, has he tried this one and does it work? The parts aren't very expensive and its really straight forward and simple looking.
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Jay



Joined: 02 Nov 2005
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Location: San Francisco, CA

PostPosted: Fri Feb 17, 2006 7:22 am    Post subject: Reply with quote

He has not built one. I looked in the Digikey catalog and found most of the components for about $7. We have lots of small electronic job shops that we contract with. It is surprising how little we can get a piece done in batches of 20. If it works I think the cost would be reasonable. No lights, though I can see where LED's could be added to identify current flow, and they would be bare units that I would mount together on a board of plastic, put in a plastic case and mount under my hood.

His email is tbrown59@verizon.net

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MajorWilson



Joined: 26 Sep 2005
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Location: Peoria, AZ

PostPosted: Sat Feb 18, 2006 10:43 am    Post subject: Reply with quote

I'm not quite up to savvy on some of these like the LM4250. I noticed that Digikey has two in particular, on is the CM w/ 8-SOIC connection and the other is the CN w/8-DIP version. Would it make any difference which one was used?
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Jay



Joined: 02 Nov 2005
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Location: San Francisco, CA

PostPosted: Mon Feb 20, 2006 10:23 am    Post subject: Reply with quote

The CM is surface mount and smaller. The CN is through hole and larger. If I built these I would use the larger through hole and solder lots of wire. But you would want the 4250 vice the 4250C. The C version has an operating temp of 0 C to 70 C. The non C version is mil specs and can go down to -55C.

This design is not as efficent as the powerchecs. But once everything is ballanced I think the loses would be acceptable.

The transistors put out lots of heat but only one pair at a time so they could use the same heat sink to save space and money.

I pulled up the powerchec patent with diagrams. The designs are different. If we built one according to their diagrams but did it only for ourselves(not for sale) would we be infringing on their patent?

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MajorWilson



Joined: 26 Sep 2005
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Location: Peoria, AZ

PostPosted: Mon Feb 20, 2006 7:33 pm    Post subject: Reply with quote

If I understand patent rights, you are OK copying something for yourself as long as you don't provide others with the designed/finished product by either giving it to someone or selling it to someone. Much has been made of these issues recently with the music sharing on copyrights. The same rules hold true for patents as well... as I understand it.

I also downloaded the powercheq diagrams from USPO and their design is simple enough except they don't really lable the specific component values. I'm not that good to be able to figure out what they are using for the different transistors, diode, resistors and capacitors as well as the mosfets.

Any ideas? The design you found looks a lot like the powercheqs in function, just differs in components. Also, it looks like the powercheqs also have a pulse generator and gate drive to control the flow of power. Is that part necessary?

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Jay



Joined: 02 Nov 2005
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Location: San Francisco, CA

PostPosted: Tue Feb 21, 2006 3:32 pm    Post subject: Reply with quote

I started to look at parts for the home built equalizer. About $15. There may be some draw backs. Some of the parts are large; the 25 watt resistors are 2.5 x .5 inches. It will all have to be mounted on a hefty heat sink. Each unit would be about 20 square inches.

Each module could be giving off as much as 25 watts. For 22 modules that is a lot of heat and wasted power. Though I would estimate that it should be far less if kept balance and the batteries stay close. A bad battery would be a heavy drain.

Anybody have a Powercheq they opened?

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MajorWilson



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PostPosted: Tue Feb 21, 2006 3:37 pm    Post subject: Reply with quote

The powercheqs are encased in epoxy. I doubt they could be opened without severe damage. Why such a large footprint on the other ones?
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Jay



Joined: 02 Nov 2005
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Location: San Francisco, CA

PostPosted: Wed Feb 22, 2006 9:19 am    Post subject: Reply with quote

Heat sink. Each transistor requires 2 square inches x 4 plus spacing. Two of the resistors take up another 2 square inches each. the rest of the electronics need just a few square inches. This design is not as efficient as the powercheqs.

If the powercheq embeding is clear we could see the identification of some of the components and work from there.

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MajorWilson



Joined: 26 Sep 2005
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Location: Peoria, AZ

PostPosted: Wed Feb 22, 2006 10:46 am    Post subject: Reply with quote

They used a black epoxy. Can't see a thing.

I looked at specs on some of the components and see why it is so large. I was wondering why the two main resistors are 5 ohm 25 watt resistors. Couldn't we get by with less current flow? We really only need to pass through a small amount of current on batteries that are relatively close in balance. A couple amps would be adequate. In fact, I think that the powercheqs are limited to only a couple of amps of power flow. By using a smaller wattage, wouldn't the transistors heat be greatly reduced?

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Jay



Joined: 02 Nov 2005
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Location: San Francisco, CA

PostPosted: Wed Feb 22, 2006 12:44 pm    Post subject: Reply with quote

Thats a question for Tim Brown the designer. It was explained to me why they were there and their size, but it went over my head. But a 5 ohm resistor passing 12 volts(worse case) is a lot of heat to disipate. though only one resistor should get hot at a time.

Tim is one of our new members.

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browntimdc2



Joined: 23 Feb 2006
Posts: 4

PostPosted: Thu Feb 23, 2006 10:38 pm    Post subject: Reply with quote

Hi there,

I'm the guy that designed the equalizer circuit. It started as a casual mental exercise, not intended to be "ready for prime time". It's inefficient (0% really compared to the Powercheq's transfer method), but simple.

Quote:
We really only need to pass through a small amount of current on batteries that are relatively close in balance. A couple amps would be adequate.


The resistors are in fact sized for ~2A max current. If the batts were at 12V and the transistor drops ~2V when fully on that leaves 10V across the resistor. 10V / 5ohm = 2A. However, the circuit will only draw what is needed to balance the batteries.

There is an intentional 240mV dead zone, so if the batts are <240mV different the equalizer won't draw any current. Hopefully, if they are balanced well during charging they won't get enough out of balance during discharge to activate the equalizer. The idle current drain on the batteries is ~20uA.
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