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Old Jan 09, 2009, 03:04 AM
PLD
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rampman, missed your post there, sorry about that (and it's a good post too!)

Quote:
Originally Posted by rampman
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.
Yes, found the same What I have done in the past is use laser cut acrylic for cases in a sandwich type layout using nickel coated standoffs etc. Cost an absolute fortune per case (about $6 for me) which of course nearly killed the whole project.

As for PCBs, yes similar costs here, also from China, though normally I pick up 100~155in.sq on a 2 week delivery (for some reason stuff is just slow getting to AU )


Quote:
Best of luck to you and don't reveal too much, some people on here will steal you blind.
Trying not to, there's also some very deliberate faults in the show board layouts, so any would-be copycats will have to start from scratch after a few head-scratching days. Good advise none the less, I agree.

Thanks for your well thought out response.

Paul.
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Old Jan 09, 2009, 06:39 AM
PLD
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Well, I think I'm pretty much done for now, at least until I get to the next physical incarnation of the IRM. I'll look over it some more tonight, sleep on it, then if I still feel cozy with the layout/schem I'll etch a new proto in the mid-morning tomorrow.

Paul.
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Old Jan 09, 2009, 06:51 AM
Southern Pride
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Quote:
a device like the one propused here probably will need to priced at less then US$40 to be marketable.

Just my 2 cent. I seen too many good idea that failed to become commercially viable product becasue it was priced way too high for the general public.

You can purchase LiPoly chargers for 60-$ 80 or pay 150-$200 for chargers with very similar capabilities. I have many chargers which cost 200-$300 and few that cost less than $100.

This IRM is to be a precision device not a 30 cents on the US Dollar third world country knock off.

Charles
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Last edited by everydayflyer; Jan 09, 2009 at 07:57 AM. Reason: added a quote . several post separated my response
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Old Jan 09, 2009, 07:35 AM
PLD
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Charles,

Sincerely hoping that it does turn out to be sufficiently accurate.

One thing that I was pondering on the last couple of hours was the possible need for offset calibration for the load resistors, however the ones I'm using are 1% tolerance, so the load resistance will be wandering between 0.99 and 1.01R with and additional 100ppm temperature coefficient. Even with these two combined the resultant error is quite small, especially when you start to see 20mR or more added just from dirty contacts (I fear this is something that could end up bringing the sanity of the values into disrepute). I can either calibrate the IRM after assembly and store the possibly required values into EEPROM on the microcontroller, or I can use a trimpot onboard to basically do the same thing. My original idea was to have a stable, fixed current source built in onboard for the device to calibrate itself against periodically, however that's something that am going to have to leave for the 'benchtop' version due to size/cost constraints.

Paul.
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Old Jan 09, 2009, 08:05 AM
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Hi Paul

Yes by using a external Cal Box you could take the board variables
out. The external could have a known resistance.
What if you took a large cap. and used a fixed low current regular
to change the cap and then once it charge . The board could test
the resistance of the cap. It should be the same as if you let it
become full charged.
Yes I'll store the offset/error into the EEproms.

Just a though.

Charles
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Old Jan 09, 2009, 09:57 AM
HAL... Open the damn doors!
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Paul,

What is mR? I am familiar with resistance but I've always seen it expressed as mΩ, is "R" equivalent to the "Ω" symbol?

As for the measurements you've quoted, I have packs with cells reading more in the range of 20 mΩ, I've seen other folks using the CellPro chargers with readings in the single digits (4.2 mΩ per cell for example). This seems to point out a huge variance in readings, likely not caused by the LiPo's actually being all that different but rather the different meters being at fault. How can one obtain the "real" value, is the CellPro correct, I know for a fact my Hyperion is reading WAY high (it's not factoring in the internal wiring and circuitry)? I'd buy it in a second but I'd want to know it's accurate...

Jack
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Old Jan 09, 2009, 10:16 AM
Southern Pride
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FYI Hyp. 720i Net is a lot more accurate than the DUO was(is) which was off by approx. 250 to 300%.

My experience Cell Pro 10 is very accurate per cell and Hyp. 720i is accurate per battery.

IR is calculated by applying two difference loads , taking voltage reading under load and using Ohms law.

Be aware that all cells will have different IR at different temperatures. LiPolys are very tricky to get accurate(?) IR readings as they change not only with temperature,but state of charge and cell condition. To make matters more confusing size matters. A given C rated LiPoly cell will have different IR depending on its' capacity, greater capacity ,lower IR.

I for one would like to know how closely increased IR relates to reduced capacity as in aging cells.

Charles
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Old Jan 09, 2009, 05:03 PM
CamLight Systems
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Old Jan 09, 2009, 05:15 PM
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Just for everyone's info, the Emeter II does pack IR. Not sure how many folks know that, since it isn't due out until the 20th of this month.
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Old Jan 09, 2009, 05:26 PM
PLD
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Just a quick question everyone (I see there's been a lot of activity since I went to sleep), do any of the chargers being mentioned have the facility/ability to test individual cell resistances, as apposed to whole packs?

jfetter, yes, 'R' is routinely used in place of the omega symbol to represent ohms, a matter of convenience when using only the ASCII charset (or US-keyboards).

Paul.
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Old Jan 09, 2009, 05:31 PM
CamLight Systems
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My iCharger 1010B+ tests pack IR and individual cell IR (only for Li packs).

John
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Old Jan 09, 2009, 05:37 PM
Southern Pride
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FMA Cell Pro10 does individual cells for LiPoly and A123 (LiFePO4) will charge and IR a single cell.Alos has nice PC interface graphing. One possible drawback wity CP10 is that it requires 12 min in the CC stsge of charge to get an IR. Sometimes I have to use a reduced charge rate as most often I charge A123s at 10A (4C) and this will cause CC to end to soon.
Hyperion DUO and 720i Net does battery only,LiPoly ,A123,Ni. You can charge / check a single cell. Start IR reading at 1 min and recalculates each minute it would appear judging by Graphed charge.

Charles
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Old Jan 09, 2009, 05:38 PM
PLD
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John,

Thanks, saved me having to google/read more than I wanted to.

One thing that the IRM will be able to do of course is test -any- cell chemistry so long as the cell voltage is below 5V, so that covers NiCd, NiMH, NiFe , Lipo, Liion, LiFe, LiS, .... so many possibles.

Paul
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Old Jan 09, 2009, 05:58 PM
PLD
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Charles,

Looks like we both posted at the same time (or close enough) hence I didn't see your response.

As for PC graphing, the IRM does have a serial port on board, so logging to a PC can be done if required.

Paul.
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Old Jan 09, 2009, 06:19 PM
CamLight Systems
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Quote:
Originally Posted by pldaniels
John,

Thanks, saved me having to google/read more than I wanted to.

One thing that the IRM will be able to do of course is test -any- cell chemistry so long as the cell voltage is below 5V, so that covers NiCd, NiMH, NiFe , Lipo, Liion, LiFe, LiS, .... so many possibles.

Paul
LOL, I know what you mean. It's sometimes hard to just stop thinking about other features and build the darn thing!

I'm excited about the possibilities for the IRM. Something to consider as a future feature....selectable test types and current levels. This would allow the user to select a static 2-point DC test at different discharge levels, a "standard" 1KHZ impedance test, etc. Each use could then compare the IR results for different tests and see how they compare. It also might allow for a user to select the test that best matches their application...high current, low current, intermittent, continuous, etc.

John
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