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Charge Doctor - Cutoff Settings


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Hello,

I need help to determine optimum Charge Doctor Settings for.

1. King Song 14c 840wh -- What you recommend for Voltage Cutoff

                                        -- What you recommend for Current Cutoff

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2. Gotway Msuper Vs+ 84v 1600wh -- What you recommend for Voltage Cutoff

                                                          -- What you recommend for Current Cutoff

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Thank-you,

 

 

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For these big batteries, cut-off by voltage gives you much more fine control (or current may not work at all), so forget cut-off by current. Use cut-off by voltage.

Voltage also has the advantage you can easily predict what charge percentage a certain voltage gives you. A usual cut-off would be 80% or 85% battery, for example.

--

IN THEORY:

  • A standard battery cell is at 0% at 3.2V and at 100% at 4.2V.
     
  • 67.2V wheel (16 serial cells) like the Kingsongs: 3.2V*16 = 51.2V means 0% charge (empty battery), 4.2V*16 = 67.2V means 100% charge (full battery)
    So the formula is: target voltage for x% charge = 51.2V + x% * 16
    For example: to get 80% charge on your 14C, set a cut-off of 51.2+0.8*16=64V.
     
  • 84V wheel (20 serial cells) like the 84V Gotways: 3.2V*20=64V means 0% charge, 4.2V*20=84V means 100% charge
    So the formula is: target voltage for x% charge = 64V + x% * 20
    For example: to get 85% battery on your 84V msuper V3, set a cut-off of 64+0.85*20=81V
    84V computation actually is easy, 1V = 5% battery, so for example 80V is 4V missing from 100% battery (84V), so that means 4 *5% less, so it's 80% charge.

IN REALITY:

  • If you look which voltage (charge doctor cut-off) gives you which battery percentage (what the app displays), there's quite a discrepancy between theory and reality (but the theory is approximately right, of course).
    So you have to do your own experiment to see which exact numbers work for you. Luckily you only need to do that once, and you can predict with theory.
    For reference, here's a picture of my list from my 84V ACM measurements, to give you an idea (no guarantee for these numbers!!!). "Theoretisch" is theoretical, "echt" means real (measured) numbers.

    35179.jpg

    I usually charge to 85% battery with a 82V cut-off on my charge doctor (81V in theory).

    [The difference between theory and reality can be explained by the battery cells not going exactly from 3.2V to 4.2V, or maybe the charge doctor not showing the exact voltages or the app not showing the exact battery percentages. If you cared enough, you could do such measurements, and estimate the real voltage range of the cells in "your" battery from that.]
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7 hours ago, meepmeepmayer said:

For these big batteries, cut-off by voltage gives you much more fine control (or current may not work at all), so forget cut-off by current. Use cut-off by voltage.

Voltage also has the advantage you can easily predict what charge percentage a certain voltage gives you. A usual cut-off would be 80% or 85% battery, for example.

--

IN THEORY:

  • A standard battery cell is at 0% at 3.2V and at 100% at 4.2V.
     
  • 67.2V wheel (16 serial cells) like the Kingsongs: 3.2V*16 = 51.2V means 0% charge (empty battery), 4.2V*16 = 67.2V means 100% charge (full battery)
    So the formula is: target voltage for x% charge = 51.2V + x% * 16
    For example: to get 80% charge on your 14C, set a cut-off of 51.2+0.8*16=64V.
     
  • 84V wheel (20 serial cells) like the 84V Gotways: 3.2V*20=64V means 0% charge, 4.2V*20=84V means 100% charge
    So the formula is: target voltage for x% charge = 64V + x% * 20
    For example: to get 85% battery on your 84V msuper V3, set a cut-off of 64+0.85*20=81V
    84V computation actually is easy, 1V = 5% battery, so for example 80V is 4V missing from 100% battery (84V), so that means 4 *5% less, so it's 80% charge.

IN REALITY:

  • If you look which voltage (charge doctor cut-off) gives you which battery percentage (what the app displays), there's quite a discrepancy between theory and reality (but the theory is approximately right, of course).
    So you have to do your own experiment to see which exact numbers work for you. Luckily you only need to do that once, and you can predict with theory.
    For reference, here's a picture of my list from my 84V ACM measurements, to give you an idea (no guarantee for these numbers!!!). "Theoretisch" is theoretical, "echt" means real (measured) numbers.

    35179.jpg

    I usually charge to 85% battery with a 82V cut-off on my charge doctor (81V in theory).

    [The difference between theory and reality can be explained by the battery cells not going exactly from 3.2V to 4.2V, or maybe the charge doctor not showing the exact voltages or the app not showing the exact battery percentages. If you cared enough, you could do such measurements, and estimate the real voltage range of the cells in "your" battery from that.]

Interesting... i just finish to install an extra battery pack on my V3S 1300Wh 84V and i found something very interesting, yesterday while charging the extra pack 20S, same as original battery (2900mah panasonic), using charge doctor (setup to cut off at 84.4V) stopped charging at the cut off and when i measured i got only 76V... when measuring the original batteries I had 83.3V... dont understand what is going on, but i need to run a few more tests, but in none of the cases the charge doctor, matched the battery voltage. 

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I have absolutely no idea about such stuff. The charge doctor guy says he calibrates each one before shipping.

Is it maybe the new batteries stop charging at some point at first charge? This happened with a few new wheels (my ACM included), the first charge stops at a lower percentage (like 70%=78V) despite higher charging voltage (charger without CD). If you ride for a few seconds and plug the charger in, it will charge higher. Once you reach 100% after a few steps, it always charges to 100% from then on and does not stop prematurely. So maybe your new batteries will charge further if you plug them in again? I assume they already have a BMS (which maybe caused this behavior)?

This does not explain your measurement for the original batteries, though.

--

Always a good idea to add bigger batteries:thumbup: How much are you adding?

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On 8/4/2017 at 3:43 PM, meepmeepmayer said:

I have absolutely no idea about such stuff. The charge doctor guy says he calibrates each one before shipping.

Is it maybe the new batteries stop charging at some point at first charge? This happened with a few new wheels (my ACM included), the first charge stops at a lower percentage (like 70%=78V) despite higher charging voltage (charger without CD). If you ride for a few seconds and plug the charger in, it will charge higher. Once you reach 100% after a few steps, it always charges to 100% from then on and does not stop prematurely. So maybe your new batteries will charge further if you plug them in again? I assume they already have a BMS (which maybe caused this behavior)?

This does not explain your measurement for the original batteries, though.

--

Always a good idea to add bigger batteries:thumbup: How much are you adding?

Hi @meepmeepmayer found the issue, i'm charging with a parallel 2xcharger and i got one charger with green light while the other one, that i didnt saw was still red, but as soon one turned green the charge doctor gave the full charged message. a bit weird and difficult to explain... solution i charged everything with a single charger... and got the 84v across all packs.

 

For me this was just an experiment and managed to get 20S2P pack (40 Panasonic 2900mah cells) that should grant me additional 418wh together with the standard 1253wh (officia) i will have a total of 1671Wh, advantage is since is 2 more parallel i should keep higher current margin available, can have Cmax 80A... although the engine shouldnt handle more than 45A... just gives a nice buffer to have all this power available.

 

1st Tests runs very well, but i only tried going fast fro a long time... 26km round at approx. 40km/h and arrived back home with still 60% battery. I guess that for long range i should get real 100km at 25/30 km/h average.

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On 04/08/2017 at 2:18 AM, meepmeepmayer said:

The difference between theory and reality can be explained by the battery cells not going exactly from 3.2V to 4.2V, or maybe the charge doctor not showing the exact voltages or the app not showing the exact battery percentages. If you cared enough, you could do such measurements, and estimate the real voltage range of the cells in "your" battery from that.]

 

59 minutes ago, Noillek said:

but as soon one turned green the charge doctor gave the full charged message

Hmmm. Guys, things are being overthought here it seems to me.

First of all when talking about a certain voltage equating to a certain state of charge we are talking about resting voltages. I absolutely do not think it is due to any limitations in the CD. If 84V AT THE CHARGER was 100% charge then we wouldn't have a constant voltage phase where the current slowly drops, yet we know we can set the charge doctor to cut off at (say) 1 Amp (at which point it has been at 84V for some time) and still be some way below 100% charge. So, actually using voltage as a cut-off only works really well if it is done in the way that @Jason McNeil implemented it on his fast charger, I.e. The charger has a lower maximum voltage and still does a constant voltage phase where the current gradually lowers to a small value and then the charger goes green.

Secondly, unless the software has radically changed on the Charger Doctor since I got mine (?). Full does not mean full. It means the charge doctor has reached the threashhold (either voltage or current) that you set it to and it has turned of its output to the wheel. So of course it would say full as soon as one of the chargers turned green - it has to have reached the voltage threashold you set on the charge doctor if the current was already lowering, as that only happens once it has reached full voltage.  This was why previously I said setting the CD cut off voltage to the full charged voltage was a bad idea in my earlier post. All you do is prevent balancing (and by the way make it LESS likely both packs are at the same state of charge - is it is impacted by the internal resistance of the packs - a bigger or newer pack will be fuller than a smaller or older pack)

As @Hansolo has said, the internal resistance, voltage and current thresholds, etc of two chargers will never be exactly the same so one will indicate full before the other - it is no problem whatsoever as you are down to current levels easily supported by just one charger at that point.

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On 04/08/2017 at 3:18 AM, meepmeepmayer said:

I usually charge to 85% battery with a 82V cut-off on my charge doctor (81V in theory).

There is a relevant difference between the voltage displayed by the CD and the battery voltage for two reasons: i) the charge current, ii) the diode (preventing that current can revert through the wheels charge plug, not all Gotways have one). The diode makes an estimated difference of about -0.6V (true battery voltage minus displayed voltage). Per 1A charge current I see roughly -0.7V voltage difference (true battery voltage minus displayed voltage). For example, if I see 1.3A charge current at 82V, I estimate the battery voltage to 82 - 0.6 - 0.7*1.3 = 80.5. If the CD displays voltage without being plugged to the charger, then there is no diode and the voltage reading should be rather accurate. 

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Thanks guys! I noticed the CD shows a lower voltage when you plug the charger in later again (e.g. cut-off at 82V, plug it in later and it's maybe 81.7V or so displayed). In the end, I only care about what voltage cut-off I have to set so the next day my wheel will be at x% battery, and you explained [I guess:P] why the cut-off needed for that is a bit higher than the theoretical number:thumbup: (so some experiments are necessary).

@Noillek An extra 430 Wh (I prefer 3.7V nominal so the numbers look better;)) is quite a lot. So your "just an experiment" gives you extra 25 km which is really awesome!!! You may have the third best range type of wheel after the 2400Wh Monsters and the "world famous ACM 2040"!

@Keith Isn't the constant voltage/decreasing current phase just when the batteries are getting full? Aka you no longer increase the voltage to push more power into the batteries (because that would be more than they can take), but you keep it constant and the batteries getting fuller automatically decrease the current via their own counter-resistance? I'm a bit confused why Jason's chargers do an artificial(?) constant voltage/decreasing current phase at lower % numbers then...

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1 hour ago, meepmeepmayer said:

Isn't the constant voltage/decreasing current phase just when the batteries are getting full? Aka you no longer increase the voltage to push more power into the batteries (because that would be more than they can take),

Lithium batteries are over stressed and damaged much above 4.25V/cell so the charger absolutely must not go higher than that or risk a fire. However they are nowhere near fully charged at that point so the charger enters a constant voltage/diminishing current phase which can last as long as the constant current phase of charge. 

See: http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries look at figure 3. In the example they show the battery is not much over 50% charged when the charger reaches 4.2V/cell and goes into constant voltage mode. It does depend on how high the charge current was in the first place, and this example is at 1C which is worst case, a 0.5C charge will, obviously reach a higher state of charge before reaching constant voltage - but still very much below full.  

This is actually a lot lower a charge level than I thought it was and might well explain why @Noillek's battery settled at 3.8V/cell after taking it off of charge when charging was cut as soon as it hit 84V.

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I've yet to play with my Charge Doctor but because of this constant voltage/decreasing current phase provides a significant proportion of the final charge I was going to try to use current level cut off rather than voltage. I understand that current level cut off becomes increasingly viable the higher the current the charger can provide. I think it provides greater granularity for control. I got the 2.5A fast charger from eWheels for my V8 and think I should be able to control via current cutoff quite well given the 2.5A supply and the smaller 480Wh battery.

This is just from what I have learnt on here and battery university. I could be totally wrong.

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56 minutes ago, WARPed1701D said:

I understand that current level cut off becomes increasingly viable the higher the current the charger can provide. I think it provides greater granularity for control.

The main difference is that current provides fine control at a different charge level, namely at the end of charging (for a 500Wh battery above 90%-or-so). If you want to finely control the charging cut earlier, say below 85%, you have to use voltage. The larger the battery, the further up goes the transition point.

In short, as long as the voltage is below the nominal voltage, current changes remain marginal. A bigger charger will indeed reach the nominal voltage a little earlier.

The reasons become more clear when looking at this chart (charging +600Wh with a +3.5A charger).

59889cdf7f143_ScreenShot2017-08-07at18_58_45.thumb.png.37cab73d824fac1d551de9f6506e9214.png

source: http://hobby16.neowp.fr/fr/category/batteries/

 

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24 minutes ago, Mono said:

The main difference is that current provides fine control at a different charge level, namely at the end of charging (for a 500Wh battery above 90%-or-so). If you want to finely control the charging cut earlier, say below 85%, you have to use voltage. The larger the battery, the further up goes the transition point.

In short, as long as the voltage is below the nominal voltage, current changes remain marginal. A bigger charger will indeed reach the nominal voltage a little earlier.

The reasons become more clear when looking at this chart (charging +600Wh with a +3.5A charger).

59889cdf7f143_ScreenShot2017-08-07at18_58_45.thumb.png.37cab73d824fac1d551de9f6506e9214.png

source: http://hobby16.neowp.fr/fr/category/batteries/

 

Thanks for this. So to summarize, and to double check my understanding, a faster charger brings the battery to max voltage sooner in the charging cycle allowing a longer time in the constant voltage/decreasing current stage thus allowing current to be used to halt charging in the capacity ranges we typically want to stop them at.

The bigger the battery (assuming the same input current) the transition from increasing voltage to decreasing current is the further along in the charge cycle (basically the inverse of the above, as by increasing the battery size you have decreased the "C" rate of charge).

If you have a large battery then unless you have a very high powered supe charger (that would likely melt connectors and harnesses of the wheel) the point at which decreasing current is experienced will likely be too far along in the cycle to be useful (over 90% capacity) hence voltage is preferable (the only option).

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On 07/08/2017 at 6:39 PM, WARPed1701D said:

Thanks for this. So to summarize, and to double check my understanding,

@WARPed1701D, yes good summary, higher charge rate really gives you more flexibility rather than really changing the percentage charge you get. For example, Taking @Mono's example graph above and my battery university link figure 3 (reproduced below) a 600Wh 16 cell battery at 1C would be a little over 10 Amp charging and, as per fig 3 on the battery university site would reach 4.2V per cell at not much over 50% charge. In @Mono's example graph above 3.5Amps is around 1/3C and constant Voltage starts at around 85% charge.

However if cut-off was set when current had dropped to (say) 2 Amps that would, from the above graph be around 90% (roughly 550Wh on that graph.) Now on battery university's figure 3., then 2 Amps would be about 20% of 10Amps on that graph which looks to be - surprise, surprise - around 90%. Of course with a 1C 10 Amp charge you could cut charge at (say) 5 Amps (50%) and that would be about 80% charge giving you a bigger range of percentage capacity that can be controlled by setting a current level cut off than if a much lower charging rate is used.IMG_0341.JPG.647b81839279dee8b8d09a3f60a02852.JPG

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So is it true then that the charge level (in %) where the transition between constant current and constant voltage occurs depends only on the C-value? Then we could draw a single graph of the transition point vs C-value, which would be applicable to all wheels.

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1 minute ago, Mono said:

So is it true then that the charge level (in %) where the transition between constant current and constant voltage occurs depends only on the C-value?

Unfortunately, as with all of these things the answer is probably "almost"?. Internal resistance of the pack, a property that varies by cell type, manufacturer  and also age will have an effect. What I'm not sure about is exactly how big an effect?

I think it is safe to say that your statement is probably good enough as an approximation.

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My V8 has 40 cells in a 2 x 20 cell parallel configuration. The cells are LG MH1's, nominal capacity 3200mAh (manufacturer spec). The "fast" charger is a 2.5A supply. Am I right in saying that I'll be looking at about a 0.4 C rate in this configuration? And 0.23 C for the standard 1.5A charger. Ignoring any losses in both cases.

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I guess you were computing C = 2.5 / (2 * 3.2) and C = 1.5 / (2 * 3.2) which looks like the right thing to do to me ;). I usually do it the hard way via Wh and never know which voltage applies, C = 2.5A * 80V / 460Wh and C = 1.5A * 80V / 460Wh.

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  • 8 months later...

Allows you to see the charged Wh, set charge cutoff by voltage or current (so you can charge to x% after trying what voltage/current that is), and the dual input ones (highly recommended if you get one anyway) allow you to plug in 2 chargers (make sure the overall current isn't too high, 5A max for Gotway charge ports). And some other functions like data logging to PC.

http://hobby16.neowp.fr/buy/ - the 32.10€ one is the right one for your Tesla.

Not strictly needed, but a nice gadget to have. If you regularly want to charge to 90% or so, it's helpful.

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3 hours ago, meepmeepmayer said:

Allows you to see the charged Wh, set charge cutoff by voltage or current (so you can charge to x% after trying what voltage/current that is), and the dual input ones (highly recommended if you get one anyway) allow you to plug in 2 chargers (make sure the overall current isn't too high, 5A max for Gotway charge ports). And some other functions like data logging to PC.

http://hobby16.neowp.fr/buy/ - the 32.10€ one is the right one for your Tesla.

Not strictly needed, but a nice gadget to have. If you regularly want to charge to 90% or so, it's helpful.

hmm. Its just i have seen titles as "how to make your euc battery last 3000 cycles instead of 500" and "how to double your euc range"  i mean.. I just use a timed wall plug:P

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1 minute ago, Shad0z said:

hmm. Its just i have seen titles as "how to make your euc battery last 3000 cycles instead of 500" and "how to double your euc range"  i mean.. I just use a timed wall plug:P

That is great if you already have a full understanding of the charging curve and characteristics of your wheel and a specific output charger it is hooked up to. If your charge rate is slow enough to allow a voltage cutoff then you can measure the minutes per volt charge rate and set the timer to cut off accordingly. Very simple if you always only charge when you get to a specified low voltage as the time will always be the same. But for people who charge more frequently, from differing starting charge levels, need charging cut-off during the decreasing current stage, or who must ensure they don't accidentally end up fully charged (those who must ride downhill at the start of a ride) the Charge Doctor just make life a lot easier. Turn the charger on and then forget about it.

A luxury for sure. But a useful tool to those with desire to manage their battery with some precision or want to understand the process.

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