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Old Apr 19, 2009, 02:29 PM
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Originally Posted by mrforsyth
The reason for this is that the voltage drop in the charge leads becomes negligible when at the end of CV mode when current tapers to 1/10th original charge value, resulting in a fully charged battery with or without charge lead voltage drop compensation.

In my opinion, if one wishes to have the benefit of slightly reduced charge times when charging packs without balance taps, it is best to reduce voltage drop by using either heavier gauge charge leads or shorter charge leads.

Mark
Good thinking, the end of the CV phase would have a very small drop, however we must still consider what happens to the cells right at the beginning of the CV phase. We are mainly concerned with damaging cells by pushing them beyond 4.20V.

Not that it matters much, but as kgfly and I noted, the voltage drop cannot be reduced with better/shorter leads because 99.9% of the voltage drop comes from the charger's FETs.

Kev
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Old Apr 19, 2009, 02:36 PM
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Originally Posted by Truglodite
Good thinking, the end of the CV phase would have a very small drop, however we must still consider what happens to the cells right at the beginning of the CV phase. We are mainly concerned with damaging cells by pushing them beyond 4.20V.
I understand and echo this concern. However, is there any reason to believe that the iChargers are even slightly going beyond 4.20V/cell as measured at the pack? I've read no such reports but even if they did go slightly beyond 4.20V momentarily there would be no ensuing catastrophe.

Even if this were a concern, the iChargers allow one to configure a slightly lower termination voltage that will put this to rest. I, for one, have configured mine to terminate at 4.18V/cell in hopes that I'll achieve slightly improved cycle counts.

Love my iChargers!

Mark
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Old Apr 19, 2009, 02:42 PM
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I've done the same, Mark!
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Old Apr 19, 2009, 03:23 PM
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Quote:
Originally Posted by Truglodite
Good thinking, the end of the CV phase would have a very small drop, however we must still consider what happens to the cells right at the beginning of the CV phase. We are mainly concerned with damaging cells by pushing them beyond 4.20V.

Not that it matters much, but as kgfly and I noted, the voltage drop cannot be reduced with better/shorter leads because 99.9% of the voltage drop comes from the charger's FETs.

Kev
How can the voltage drop push a cell beyond 4.20V? It's the other way around (premature entering av CV phase). ICharger is only allowing 'slightly' higher pack voltage if cell voltage is known. Trying to compensate for voltage drop for packs without taps is not worth the risk.

I fail to see what the FETs has to do with this. Voltage at output is total cell voltages and voltage drops over whatever is connecting the cells to the output. The displayed voltage on the display of the ICharger matches what you will get using a DVM at the output.

Fred
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Old Apr 19, 2009, 04:39 PM
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Quote:
Originally Posted by mrforsyth
I understand and echo this concern. However, is there any reason to believe that the iChargers are even slightly going beyond 4.20V/cell as measured at the pack? I've read no such reports but even if they did go slightly beyond 4.20V momentarily there would be no ensuing catastrophe.

Even if this were a concern, the iChargers allow one to configure a slightly lower termination voltage that will put this to rest. I, for one, have configured mine to terminate at 4.18V/cell in hopes that I'll achieve slightly improved cycle counts.

Love my iChargers!

Mark
Mark, I love my iCharger too!

I had that thought, about terminating at 4.18V/c, but I avoided saying it because it's almost like giving up on the problem. This is a good trade off between cell life and a full charge, so I plan on setting up an "Unbalanced mode"; saved settings with lipo termination at 4.18v just for use with those packs.
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Old Apr 19, 2009, 04:57 PM
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Quote:
Originally Posted by flarssen
The displayed voltage on the display of the ICharger matches what you will get using a DVM at the output.

Fred
Well Fred, you're 100% correct. I just checked with my BK meter and the voltage at the banana plugs was an exact match to the display (down to the 1/100V). The voltages taken from the unplugged balance taps (at 2A charge current) were about 0.03V lower. I knew there was some resistance, but I thought it would be much less than that.

Thanks for motivating me to get out my good meter and do some probing. My BK meter is stored so it's not easily accessible, so I mostly use my (not so precise) ratshack meter and other ppl observations in it's place. Now it's clear I was very wrong about the lead impedance being negligible.

Anyhow, I must retract everything I've said about the vdrop being a problem. The iCharger voltage measurement methods are in fact exact, wether or not you use a balance plug. I agree with Fred, the 0.05V/A correction is not worth the risk of having cells over 4.20V during every charge. While adding compensation would likely not damage a battery noticeably, it just seems like it would be going too far IMO.

Thanks,
Kev
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Old Apr 19, 2009, 05:42 PM
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Whoa! Have we come full circle? What does this mean in lay terms?
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Old Apr 19, 2009, 08:39 PM
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Originally Posted by Mighty Manfred
Whoa! Have we come full circle? What does this mean in lay terms?
It means to simply use your iCharger and charge happily ever after knowing that there's no charger in existence that will better care for your battery investment.

My 2 cents anyway!

Mark
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Old Apr 19, 2009, 08:49 PM
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Yes, that's what I thought. So, the sky isn't falling, right?
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Old Apr 19, 2009, 09:13 PM
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To use a fonz-ism, correctamundo. The sky isn't even a bit loose, let alone falling.

Mark
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Old Apr 19, 2009, 09:33 PM
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Status quo ante, my favorite charger!
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Old Apr 20, 2009, 01:28 AM
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Lol :d
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Old Apr 20, 2009, 11:28 AM
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Originally Posted by Truglodite
Anyhow, I must retract everything I've said about the vdrop being a problem. The iCharger voltage measurement methods are in fact exact, wether or not you use a balance plug. I agree with Fred, the 0.05V/A correction is not worth the risk of having cells over 4.20V during every charge. While adding compensation would likely not damage a battery noticeably, it just seems like it would be going too far IMO.
While I agree with your overall sentiment, the bolded part of your post is simply not true... if the balance leads were used to monitor the total pack voltage, this could NEVER happen.... for such a simple firmware change, the lead resistance is mitigated and the battery pack voltage is more accurate during charge... I agree that as the pack gets into CV mode, the difference essentially disappears, but it will take longer to charge...

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Old Apr 20, 2009, 11:37 AM
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Deja vu, all over again!
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Old Apr 20, 2009, 01:50 PM
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Originally Posted by FenceMagnet
if the balance leads were used to monitor the total pack voltage, this could NEVER happen.... for such a simple firmware change, the lead resistance is mitigated and the battery pack voltage is more accurate during charge...
Understand that individual cell monitoring and charge lead voltage drop compensation that you have described has always been an included feature on the iChargers since first release. This feature is active during balance mode lipoly charging. The charger will drive current at the set value until at least one cell hits the default 4.20V and then begins tapering current (CV mode). No firmware change needed.

The first time I witnessed this I was impressed.

Mark
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