iCharger 1010B+, 106B+, 208B, 206B, 306B and 3010B - Page 215 - RC Groups
Apr 11, 2009, 05:05 AM
Registered Aircraft Offender
OK folks, I just completed the updated spreadsheet. I think I added in all the features that everyone has mentioned. While I was on a role, I decided to get resistor tolerance in the picture (in a very crude way, but it works fine for us). I focused a few hours of my night on putting all the equations involved on paper, so I sure hope I don't have any errors.

Please download and try it out; let me know what you guys think. I'd like to hear everyone's questions and comments so I can polish it to a shine before Junsi links it to post#1.

Cheers,
Kev

[edit: There are actually 4 factors that constrain the D+ process: 1) max power rating for charger cannot be exceeded, 2) charger cannot output negative voltage, 3) current cannot exceed max rating, and 4) resistors cannot exceed max power rating. This spreadsheet accounts for everything, and I added notes so anyone who is interested can learn the math involved in this. Whew!!! I'm going to bed.]

{edit edit: I moved the spreadsheet file to my blog so you won't accidentally download an older version. You can find it in my blog.
}

Images

Last edited by Truglodite; Apr 12, 2009 at 12:36 AM.
Apr 11, 2009, 05:44 AM
Registered User

Why not optimise for zero discharge in the charger ?

I think there is a confounding factor here which is that you are assuming the goal is to dissipate maximum power inside the charger. IMO the optimal solution dissipates minimal power inside the charger and all the power in the external load. This maximises the possible discharge power while placing minimum stress on the charger electronics. In this optimal mode the charger FETs are essentially fully on and the charger simply acts to control the current and monitor the voltage. The only requirement is to not exceed the maximum discharge current (7A for 106B+/10101B+, 20A for the 208B).

Since 100% of the power is dissipated in the external load, calculating the resistance is as easy as R = V/I where V is the initial pack voltage and I is the desired discharge current. I believe this is the guidance given in the manual.

Now it becomes much easier to calculate the minimum external resistance for any voltage pack and target discharge current by assuming a fully charged pack. A resistor larger than the calculated minimum will be safe and simply mean you get less than the target discharge current. A resistor smaller than the minimum will force the charger to start limiting the current and dissipating power internally, which is sub-optimal but the charger will always protect itself from overload.

Images

Apr 11, 2009, 06:43 AM
Registered Aircraft Offender
Quote:
 Originally Posted by kgfly I think there is a confounding factor here which is that you are assuming the goal is to dissipate maximum power inside the charger. IMO the optimal solution dissipates minimal power inside the charger and all the power in the external load. This maximises the possible discharge power while placing minimum stress on the charger electronics. In this optimal mode the charger FETs are essentially fully on and the charger simply acts to control the current and monitor the voltage. The only requirement is to not exceed the maximum discharge current (7A for 106B+/10101B+, 20A for the 208B). Since 100% of the power is dissipated in the external load, calculating the resistance is as easy as R = V/I where V is the initial pack voltage and I is the desired discharge current. I believe this is the guidance given in the manual. Now it becomes much easier to calculate the minimum external resistance for any voltage pack and target discharge current by assuming a fully charged pack. A resistor larger than the calculated minimum will be safe and simply mean you get less than the target discharge current. A resistor smaller than the minimum will force the charger to start limiting the current and dissipating power internally, which is sub-optimal but the charger will always protect itself from overload.
I included minimization of Pc in my spreadsheet bro.

BTW, are you sure the charger will limit the current in D+ mode so it won't fry itself? Speedflyer's experience has me wondering whether there is protection against using too small of a resistance.

Even if it did protect itself, it's nice to know exactly what's happening. For example, I have a single resistor setup that will safely discharge 3s from 1-5A (all I need anyways). Not by chance, but by design. If I optimized for Pc=0 for one current, I could be in trouble at other currents in the desired range. Plus I'd hate to spend money and put time in to an array only to find out my current range is limited by a poor choice of resistors.

Anyhow, I'm going to bed.

Kev
Last edited by Truglodite; Apr 11, 2009 at 07:00 AM.
 Apr 11, 2009, 07:41 AM Asks too many questions I must be honest and say I haven't the first idea what all the calculations and spreadsheets are about but it sounds like you're doing good work so well done! The 208B is an exciting addition to the range, I wonder when it will hit the shops. What other additions might we see in future? I would like to see a 2012B with the onboard logging, higher power and ability to balance 12 cells.
Apr 11, 2009, 08:32 AM
Registered User
Quote:
 Originally Posted by Truglodite I included minimization of Pc in my spreadsheet bro. BTW, are you sure the charger will limit the current in D+ mode so it won't fry itself? Speedflyer's experience has me wondering whether there is protection against using too small of a resistance. Even if it did protect itself, it's nice to know exactly what's happening. For example, I have a single resistor setup that will safely discharge 3s from 1-5A (all I need anyways). Not by chance, but by design. If I optimized for Pc=0 for one current, I could be in trouble at other currents in the desired range. Plus I'd hate to spend money and put time in to an array only to find out my current range is limited by a poor choice of resistors. Anyhow, I'm going to bed. Kev
OK, I think I am getting the hang of your model now. Nice improvements. I note that the combo boxes for the charger model and the battery chemistry are not operational.
 Apr 11, 2009, 12:44 PM Registered User I am cycling a few new lipos right now to wake them up. I have the discharge set at 7amps but it is only showing 1.9 amps on the dissplay. When I push start to get the discharge current to flash (edit mode) it shows I have it set for 7 amps. Why wont it go to 7 amps?
Apr 11, 2009, 12:50 PM
Registered User
Quote:
 Originally Posted by Mera'din I am cycling a few new lipos right now to wake them up. I have the discharge set at 7amps but it is only showing 1.9 amps on the dissplay. When I push start to get the discharge current to flash (edit mode) it shows I have it set for 7 amps. Why wont it go to 7 amps?
If I recall correctly, the 106B is limited to 20 watts in discharge mode. The 1010B is limited to 30 watts. If you want higher power dissipation you must use an external load.
 Apr 11, 2009, 01:15 PM Intensely Calm Excellent work on the resistor calc. sheet Kev! Very exciting stuff. Thanks for your work on this - I'll be ordering some resistors soon. - David
Apr 11, 2009, 02:05 PM
Registered User
Quote:
 Originally Posted by mrforsyth If I recall correctly, the 106B is limited to 20 watts in discharge mode. The 1010B is limited to 30 watts. If you want higher power dissipation you must use an external load.

Now that you state that, it makes sense after rethinking it. 1.6 x 12 = 20 watts or so. So the only way to get to 7 amps discharge is to use the discharge + that everyone is talking about?
Apr 11, 2009, 03:26 PM
Registered Aircraft Offender
Quote:
 Originally Posted by kgfly OK, I think I am getting the hang of your model now. Nice improvements. I note that the combo boxes for the charger model and the battery chemistry are not operational.
Cool, so it looks like I achieved my goal of making my model more accessible.

Thanks for pointing out the combo box problem. The problem is now fixed; I lost the data verification for those drop down boxes while I was moving things back and forth across sheets. Cell references for both data verification and conditional formatting become orphaned once copied to a new sheet; good 'ole excel.

David, thanks, and you're welcome!

Mera 'din, you're right! This is why we're all hankering over this D+ stuff. Regular discharge is very limiting, and D+ is a very exciting feature. With discharge reduce activated, it sure beats the heck out of soldering dedicated relay circuits like I used to do.

Kev

[edit: BTW, I noticed the spreadsheet was not discarding the irrelevant imaginary roots for the minimum current limit, so in some cases the calcs were undefined. The minimum safe current will now show the correct value instead of "#NUM" for these cases. The sig fig setting for resistance input on the analysis page was too low as well. These problems are fixed as of this edit. ]
Last edited by Truglodite; Apr 11, 2009 at 04:19 PM.
Apr 11, 2009, 05:40 PM
Registered Aircraft Offender
Quote:
 Originally Posted by natterjak I must be honest and say I haven't the first idea what all the calculations and spreadsheets are about but it sounds like you're doing good work so well done! The 208B is an exciting addition to the range, I wonder when it will hit the shops. What other additions might we see in future? I would like to see a 2012B with the onboard logging, higher power and ability to balance 12 cells.
Wow, 50.4V is ton of power. I'm curious, what are you using 12s for?

Thanks BTW.

Kev
 Apr 11, 2009, 06:08 PM Registered User Getting better Some more suggestions. * The graph axes have fixed limits that are tied to expected values for 106B+. Ideally the limits would be adjusted when you choose a different charger or perhaps set for automatic scaling (I think this would OK on both graphs work if the plot range only went up to 20A instead of 40A). * Draw horizontal red lines on the graphs showing the maximum allowable value (must be sensitive to the current charger selection) for internal charger power and load current respectively.
Apr 11, 2009, 08:26 PM
Registered Aircraft Offender
How does this look?

I added all the possible data lines I could think of, and combined the 2 charts on to one. I wouldn't be surprised if someone says it looks more confusing.

I can't figure an easy way to make the chart automatically scale the axis in a reasonable way without adding a bunch of extra conditional items to the data table itself (I'm thinking a bunch of "if" functions that set any out of range/invalid data point to 0). I may get around to this if it's a big enough deal for enough ppl, but it would take me a while.

Now that I'm in to aesthetics, I'm saving each previous version separate from the updated one, since backward changes are likely. Let me know if there's any lines you'd rather do without.

Kev

[edit: The resistor comparison page is left the same, since adding similar detail to it's charts would make the white background barely visible.]