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Old Jan 08, 2009, 09:05 AM
PLD
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Alan,

Thanks for the input. You're right, the symbols used aren't appropriate for the final product, more a case of me just quickly putting in something for the purpose of evaluation (the 16x2 display can suddenly become limited ).

My initial idea is to just offer a 2-pin input, the reason behind this is primarily that the cost of dealing with the multitude of possibilities and the electronics needed to switch the input cells one at a time blow the cost right out of the water (for a 6 cell pack you'd need at least 18 MOSFETs, 9 of which will ideally be low resistance types for minimal heating (2.5mR or lower).

With a simple 2 pin input, the cost can stay in the $50~$100 region, remember though I'm talking AUD, which is 0.70 USD, so $100 is $70 USD

Again, many thanks for your ideas - keep plugging away at them, while I sometimes may seem like I've brushed them aside, what's important is that they do get stored in the back of my head and help shape the development, even if I'm not aware of it explicitly.

Regards,
Paul.
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Old Jan 08, 2009, 09:08 AM
PLD
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btw, I do want to stress again that this is only prototype #1, I've already started work on #2 and there will most likely be a #3 before it even is considered going into production.

Actual production will be done here inhouse at NQRC (along with all the other electronics products made here), though the PCBs themselves will be outsourced as it's simply not ideal to keep the equipment around to produce quality masked/screened/multilayer boards. Solder-paste stencils and reflowing though are done in-house.

Paul.
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Old Jan 08, 2009, 03:57 PM
CamLight Systems
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Paul, I think this is a great idea for a great product and I'm looking forward to reading about its progress! Thanks for putting all of us in the loop.

John
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Old Jan 08, 2009, 04:07 PM
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Simple and cheap will be big sellers unless you can get a large mail-order place to sell it. Why not just a 3-digit led display? Don't need all the information and showing it on a screen costs money.
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Old Jan 08, 2009, 04:09 PM
PLD
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John,

Good to have you onboard, looking forward to making this a product that hits the "mark" appropriately for the right people.

Might try etch out board #2 today... quite a few more protection circuits on this one.


Paul.
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Old Jan 08, 2009, 04:16 PM
PLD
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biskit,

I looked at the 7-segment display option and I'm still umming and erring about it because of the extra circuitry required to support it. With the LCD it's a simple case for me to rig up the 4 datalines + 3 control lines and it's done (well, except perhaps for the contrast pot). 3x7 segment display needs either 7 data + 3 control/select lines, or if you add a 7-segment driver, 4 (BCD) + 3 control/select

I have found in the past bulk supplies of fairly suitable displays but the trouble is i don't want to end up in a situation where I can't keep getting the same display, at least not without fair warning.

I'll revisit the idea/option of the 3x7 segment display again later, at least with the LCD standoffs like i've designed, I could actually make a suitable daughterboard with the segments and plug it into the same place.

Paul.
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Old Jan 08, 2009, 04:35 PM
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Excellent project Paul. Now the trick will be to get lipoly manufacturers to test, list, and guarantee IR of their cells/packs rather than use 'C' rating as a marketing gimmick as is current practice with many vendors...

You've got my attention.

Mark
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Old Jan 08, 2009, 05:03 PM
PLD
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biskit,

I doubt I'll ever end up selling to large online stores (like UnitedH or what ever they call themselves now), moreso while I'm running NQRC actively online, though I do already have a few resellers. While I am all for simple/cheap, so long as it's quality.

As mentioned above, it's a case of seeing which one works out better between LCD vs 7-segment, right now they're so close when you weigh in the cost of producing the 7-segment system, for now at least the system is open-ended.

Paul.
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Old Jan 08, 2009, 05:48 PM
PLD
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Managed to find a suitable 16x2 display (LCD) at an acceptable price-point, so that's basically sealed the display choice for me. It's about the same size as the Wattup one afaik (52 x 19mm viewing area).
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Old Jan 08, 2009, 08:13 PM
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Current state of affairs

Here's a quick taste of what the IRM prototype is going to look like next.

The board size is about 75 x 30mm (2.9 x 1.2") and that's slightly oversize from the LCD panel itself.

What -is- nice about these LCD panels is that they all invariably follow the same pinouts which makes it easy to change them over to another type if wanted later (eg, OLED for the very rich ).
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Old Jan 08, 2009, 09:02 PM
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Paul I think the LCD gives you so much more flexibility than the 7-segment display that is is a no-brainer. I also think that many (most?) folk interested enough in a dedicated IRM will be interested in the additional info.

IMO while a multipin balance port interface with automatic switching would be nice to have, a 2-pin interface is acceptable. You might consider having two parallel sets of pins, one at 0.1" (2.54mm) spacing and one at 2.0mm spacing as that would cover pretty much all balance plugs AFAIK.

The PQ/Hyp balance plug wiring with the most positive pin separated from the rest is a pain and I guess those folks will have to buy/make a PQ-to-JST_XH adapter lead to remap the pins.

I presume this device is actually powered by the cell it is testing ? If so, what is the lowest voltage at which it will operate ? It seems to me there might be a risk when testing a discharged cell that the device will shutdown once the load is applied since the battery terminal voltage might fall below the minimum operating voltage. Not a big deal, just something to be aware of and to mention in the user guide.

As for comparing your measured IR with that reported by various chargers, it will certainly be interesting to see what you find. However, since the measured value depends on so many variables (state of charge, temperature, wiring, algorithm, tolerances etc) I will be surpsied if you get close correlation across devices.

Just out of interest, what is the price difference between LCD and OLED for the same size/features ? Other than price, is there any downside to using OLED in this kind of device ?
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Old Jan 08, 2009, 09:04 PM
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Of course if you did implement a multipin balance port all you would have to do is make it compatible with one of the popular charger ranges and then folks could use the adapter boards from those. For example the Hyperion adapters cover up to 6S or the iCharger ones cover up to 10S.
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Old Jan 08, 2009, 09:33 PM
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Paul,
I was going to have a plastic enclosure made in China for a 4x7 (inches) board I make. Tooling/NRE alone was over 4K USD. WHOA.
I can get 5 prototype 2 layer PCB's in 5 days to my door for under $100.00 USD and that is from China. I can't even get them that fast locally. LOL. I am sure you have connections like that from your experience there but for the enclosures, if you can find one already tooled you will save bank.
Best of luck to you and don't reveal too much, some people on here will steal you blind.

Rick
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Old Jan 08, 2009, 09:43 PM
PLD
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kgfly,

After this morning's search and discovery of the suitable LCD panel (the one which i've adjusted the board size to suit), the 7-segment option is completely out the door as the pricing was within 50c of each other, the LCD option is profoundly easier to route/assemble too.

I have decided also only to go with the 2-pin input option, and the 2.0mm as well, as you've suggested. They'll possibly have to exist on opposite sides of the PCB otherwise there's going to be too much of a 'distance' between the inputs and the measuring point.

The price difference between standard reflective LCD and OLED is about $20 AUD (in lots of 10), yes, it's a huge difference.

The IRM will be powered by an external source (namely between 6.5 ~ 12V input). I had originally considered being powered by the cell under test but I decided against it in the end as it limits the type of cells that can be checked. Right now the IRM will test any cell up to 5.0V voltage.


The sharp-eyed ones of you may have noticed that the revised board now has -two- loads on it, 1R and ... well I've not yet fully decided on the other, I was hoping perhaps to use 0.5R but I think another 1R should suffice, giving most lipo cells a 4.2A and 8.4A test load. There is one big advantage though of going to an 0.5R resistor and that would be that you can then in fact have three current tests, namely 1R, 0.5R and 1|0.5R combined ( 0.3333R, 12.6A ).

A lot depends on the cost/source/size of a suitable 0.5R load resistor, the other problem is that you're starting to really tax the balance plugs at that point, even though the test is only for ~0.01 seconds.

Paul.
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Old Jan 08, 2009, 09:57 PM
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Paul,

Thanks for the detailed response. To be clear, you are now considering having two inputs, one with 2.54mm spacing and one with 2.0mm spacing, possibly at opposite ends of the device ? Being at opposite ends could be considered a wise design choice, it prevents any mistaken attempt to plug something across the two sets of pins.

It would be very nice if the input DC supply could be up to 13.8V since this would allow for it to be run from a 3S lipo (12.6V) or directly from a DC bench supply (ie the one used to power a charger). A real stretch to 15V would cover a running car but that is a real corner case IMO.
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