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Old Sep 08, 2006, 03:32 AM
PLD
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Looking for parallel lipo charger schematic

Hello everyone,

I'm looking for a schematic, or outline on how to do lipo cell charging in parallel using the existing 'balancing taps' that are found on most packs these days.

From what I can gather, one needs to have isolated chargers but on a correctly staged input supply (ie, charger for cell #2 has to be 4.2V above charger for cell #1 etc)

Looking for hints/guides...

Paul.
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Old Sep 08, 2006, 07:46 AM
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Bruce Abbott's Avatar
Hastings, New Zealand
Joined Jan 2001
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It can be done with isolated chargers (example) but this requires a lot of circuitry and changing current is tricky.

Another way is to use a single multicell charger combined with a balancer.
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Old Sep 08, 2006, 08:01 AM
PLD
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Bruce,

Surprised I didn't recall your setup - since I frequently visit your site for great ideas.

Thanks for that!

Paul.
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Old Sep 11, 2006, 09:13 AM
Don L.
Old Lyme, Connecticut
Joined Feb 2006
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Quote:
Originally Posted by pldaniels
Hello everyone,

I'm looking for a schematic, or outline on how to do lipo cell charging in parallel using the existing 'balancing taps' that are found on most packs these days.

From what I can gather, one needs to have isolated chargers but on a correctly staged input supply (ie, charger for cell #2 has to be 4.2V above charger for cell #1 etc)

Looking for hints/guides...

Paul.
Paul,

Here's a schematic and board layout for the parallel charger that I built. It uses a Microchip MCP73843 LiPo/Li-Ion charge controller and independent 5 volt power supply for each cell. It will charge 1 to 4 cells.

The MCP73843 is a constant-voltage, constant-current, single-cell charger with built-in safety timer, cell preconditioning, and status indication. The constant current is set by the value of an external sense resistor and the constant voltage is a function of the controller itself, which comes in 4.1 and 4.2 volt versions. I pretty much followed MicroChip's application note for the design.

These drawings are lacking in detail, but if you (or, anyone else) are interested, I'll do a more comprehensive post.


- Don
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Old Sep 13, 2006, 11:39 AM
Don L.
Old Lyme, Connecticut
Joined Feb 2006
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Quote:
Originally Posted by dleroi
... if you (or, anyone else) are interested, I'll do a more comprehensive post.

- Don
Ok, then, I'm going to unsubscribe.
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Old Sep 14, 2006, 03:56 AM
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FlyingDan's Avatar
Paris, France
Joined Jun 2006
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Quote:
Originally Posted by pldaniels
Hello everyone,

I'm looking for a schematic, or outline on how to do lipo cell charging in parallel using the existing 'balancing taps' that are found on most packs these days.

From what I can gather, one needs to have isolated chargers but on a correctly staged input supply (ie, charger for cell #2 has to be 4.2V above charger for cell #1 etc)

Looking for hints/guides...

Paul.

Hi Paul and Don,

Please consider as well electron_head's circuit in thread http://www.rcgroups.com/forums/showthread.php?t=130567
In particular, you would find there a similar approach to Don's, but with a much mower budget (i.e. only two LM317 instead of a special IC, per cell). Also, Don's and electron_head's circuits share the problem of the common ground plane, that calls for isolated power supplies (which is expensive). Some of us are still looking for a solution that would overcome this difficulty (as in commercial chargers).

Dan
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Old Sep 14, 2006, 11:20 AM
Don L.
Old Lyme, Connecticut
Joined Feb 2006
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Quote:
Originally Posted by FlyingDan
Hi Paul and Don,

Please consider as well electron_head's circuit in thread http://www.rcgroups.com/forums/showthread.php?t=130567
In particular, you would find there a similar approach to Don's, but with a much mower budget (i.e. only two LM317 instead of a special IC, per cell). Also, Don's and electron_head's circuits share the problem of the common ground plane, that calls for isolated power supplies (which is expensive). Some of us are still looking for a solution that would overcome this difficulty (as in commercial chargers).

Dan
Hi Dan,

You would think that a dedicated IC and pass transistor would be expensive, but the MicroChip part is just under $1 USD and the MOSFET is just over $1 USD - not much more than LM317s. The rest of the components will cost about the same for the two designs. With the IC, you also get automatic shut off, a built-in safety timer, charge indicator, and precharge conditioning (trickle charge for over dis-charged cells).

Yes, the power supplies are still an issue. For mine, I found some 5V, 13A switching supplies on sale for $5 each at Jamco and purchased a dozen of them. I'm currently building a single switching supply with multiple isolated outputs, though.


- Don
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Old Sep 18, 2006, 07:31 AM
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FlyingDan's Avatar
Paris, France
Joined Jun 2006
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Quote:
Originally Posted by dleroi
Hi Dan,

You would think that a dedicated IC and pass transistor would be expensive, but the MicroChip part is just under $1 USD and the MOSFET is just over $1 USD - not much more than LM317s. The rest of the components will cost about the same for the two designs. With the IC, you also get automatic shut off, a built-in safety timer, charge indicator, and precharge conditioning (trickle charge for over dis-charged cells).

Yes, the power supplies are still an issue. For mine, I found some 5V, 13A switching supplies on sale for $5 each at Jamco and purchased a dozen of them. I'm currently building a single switching supply with multiple isolated outputs, though.


- Don
Don, that sounds interesting. However the "rest of us" still rely on very simple, ubiquitous parts, as I'm sure I won't find this IC easily in my surroundings.
Mmmh I am very curious about your new design (multiple isolated outputs sounds VERY good)...

Dan
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Old Sep 18, 2006, 08:42 AM
Don L.
Old Lyme, Connecticut
Joined Feb 2006
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Quote:
Originally Posted by FlyingDan
Don, that sounds interesting. However the "rest of us" still rely on very simple, ubiquitous parts, as I'm sure I won't find this IC easily in my surroundings.
Mmmh I am very curious about your new design (multiple isolated outputs sounds VERY good)...

Dan
Dan,

MicroChip sells directly to the public from their web site, as do many other manufacturers these days. In fact, I order directly from MicroChip because they sell single units, whereas their distributors often sell only in large quantities. You do have to register, but that's a very simple process that greatly simplifies subsequent ordering. Of course, even though they sell single units, it's much better to order more because of the shipping. Here's a link, in case you want to see it first hand:

http://www.microchipdirect.com/Produ...words=MCP73843

I'm also excited about the new circuit. The parts are ordered. I'll keep you posted.

- Don
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Old Sep 18, 2006, 06:01 PM
PLD
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I actually received my samples of this microchip yesterday.

It's an interestingly simple chip, I got the MSOP-8 type (surface mount - don't get this unless you really want it ). Of all the parts on the board, the most expensive is actually the current/voltage sense resistor (0.1R~0.5R) since it's typically a precision 1% type. They cost me about $0.90 each from RS and you have to buy at least 10, worse, if you want to have variable currents you have to have different resistors or change the supply voltage (according to their formula).

Incidently, those wondering why there are multiple entries on the WWW site for the same chip, you want the -420I version (4.2V).

Paul.
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Old Sep 18, 2006, 07:58 PM
Don L.
Old Lyme, Connecticut
Joined Feb 2006
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Quote:
Originally Posted by pldaniels

Of all the parts on the board, the most expensive is actually the current/voltage sense resistor (0.1R~0.5R) since it's typically a precision 1% type.

Paul.

Paul,

I'm glad to see someone else using the MicroChip device. I'm very pleased with my 4-cell charger.

Did you go with chip resistors? I found them to be much less expensive than the other types. I would think the resistors in Electron Head's circuit would be substantially more, albeit easier to find.

At what rate will you be charging? How many cells?

Have you done a PCB layout? If not, are you interested in seeing mine?

Regards,
Don
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Old Sep 18, 2006, 08:16 PM
PLD
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Don,

I'd love to see your circuit/PCB. I was wiring mine up to use the MSOP charger chip and an accompanying IRF7501 P&N MOSFET MSOP 8 pin chip as well (will handle 3~6A no problem). Basically it means the entire circuit should fit within a 15x10mm area without any real issues - the biggest issue will be sorting out these floating-grounds / isolated PSU's.

Paul.
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Old Sep 18, 2006, 09:55 PM
Don L.
Old Lyme, Connecticut
Joined Feb 2006
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Paul,

Oops, I used the IRL5602 in the D2Pak. I wasn't concerned with board size. I put 4 chargers on a 99.5 x 63.5mm board. The schematic is above, in post #4.

ExpressPCB doesn't print a nice looking image of the PCB because they don't want us using their software without using their PCB service. I had forgotten about that when I said I'd post it. Here it is anyway, though.

Regarding the power supplies, I found some 5V, 13A switching supplies on sale for $5 each at Jamco and purchased a dozen of them. I mentioned above that I'm working on a single supply with multiple isolated outputs. I'll have more on that when it's working.

- Don


- Don
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Old Sep 18, 2006, 10:52 PM
PLD
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Don,

I see you've gone quite fancy there and using double-sided board with vias. I was doing a single-sided one myself ... only because I'm lazy and like to work purely with SMT (less holes!), even my connectors are SMT. The biggest trouble though (expense rather) when it comes to pure SMT is the larger capacitors.

When I've done my SMT PCB (using Eagle CAD on linux) I'll post it up here.

Paul.
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Old Sep 19, 2006, 08:48 AM
Don L.
Old Lyme, Connecticut
Joined Feb 2006
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Paul,

I, on the other hand, was anxious about using SMT components, this being my first SMT project. In fact, had the MicroChip IC come in a through-hole version, I never would have attempted surface mount. As it turned out, it was much easier than I ever thought it would be and now I'm sold. I wouldn't want to go much smaller, though, given I have no special equipment other than an old Pace desoldering station.

I look forward to seeing your layout when you've finished it. Do you make your own boards?

Cheers,
Don
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