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Do not order a ChargeDoctor for now!

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7 hours ago, Boogieman said:

Ok, so i measure

1) with wheel NOT connected to charger

2) directly on + and - on the charger plug from the charger (godda figure out which those pins are on my gotway tesla charger)

But the BMS comment i dont understand? The BMS is in the battery pack and since battery pack is not connected when meassuring the voltage (as described ABOVE), the BMS has nothing to do with the charger output voltage?

Or am i missing something here?

Thanks a lot for the QUICK reply :-) Hope you can clarify above. My father allways tought me to measure with load when doimg charger measurements back im the days when we were charging ni-cd batteries, but that was basically to check the batteries (charge and life). But to check the charger, it still fells like there should be some kind of load (except only the fluke internal resistor or maybe thats enough? I mean normaly voltage drops tremendeously as load is applied = charging, so even if 84 with "no load"(except internal resistor to get voltage measurement) looks ok, it might not be able to output 84V even at 0.25A, depends on how robust the china charger is...and i Guess not that robust LOL)

Boogie

You measure the charger unloaded (or specifically very lightly loaded just by the 10 megaohm or similar input impedance of the meter) to see that the maximum voltage is correct. Under load, it starts to drop the output voltage so that only a specific maximum amount of current (constant current mode) flows to the packs. Once the voltage has risen high enough to reach the maximum, the constant voltage mode starts, where the current will drop as the battery voltage gets closer to the charger voltage, dropping to 0 when the battery has reached the same voltage as the charger (which happens much, much later than when the LED changes from red to green in most chargers).

The BMS-comment refers to what the charger voltage should ideally be. The balancing circuitry in the wheels is based just on slowly "bleeding" charge off the cell through a resistor once a certain voltage threshold has been reached (which could be up to 4.2V), so for the balancing to occur, the battery pack must be charged until it reaches high enough voltage for all the cells to "catch up" and charge to the same maximum voltage. For example, if your 20S-battery pack was charged to a voltage of 83V, you still don't know whether all the cells have charged equally (83V / 20 cells = 4.15V per cell), or if 19 cells were at the full 4.2V and the one was at 3.2V, or a mixture of these. The previous is a bit bad example, if there really was one cell that 1V behind all the others, likely that one cell would already have been so degraded that it should be replaced, but even much smaller differences cause some of the cells discharge faster than the others, causing extra stress on them and they will die sooner. But ideally the charger voltage should be high enough to fully charge and balance all the cells if left charging for long enough, which basically should be the amount of cells * 4.2V. 

Should, but, most wheels have some form of reverse polarity protection in their BMSs (apparently at least Gotways don't, some other older wheels like Firewheels don't). The idea is to protect the battery from a charger with reversed polarity (wrong type of charger) or external short circuit through actual diodes or mosfets. If there are BMSs that use diodes for this protection, they will have a "side effect" that the diodes cause a drop of their forward voltage (around 0.3-0.7V depending on type of diode even at low current) before the cells. Thus if you have a diode dropping 0.7V before the actual cells, and your charger outputs 84V, the batteries won't charge but to around 83.3V. I originally thought that the Firewheel charger was set to 67.8V (for 67.2V wheel) because there are protection diodes dropping around 0.6V in the BMS, but in reality it was just a badly adjusted / drifted charger.

For your Gotway you can simply check that the charger's at 84V, since there are no protections. But, in case there were protections and you wouldn't actually know whether there are diodes or mosfets there, it'd probably be better still just to adjust the charger to the typical 4.2V per cell voltage, or at least not much above it. The only reason for higher voltage, while still avoiding overcharging which can cause a fire or explosion at worst, would be to ensure that the cells reach their full voltage when leaving it on charger for balancing to occur. But there you'd be better knowing the protection circuitry, or even better, being able to measure the individual cell voltages, it would be so much easier if the wheels had BMSs that report the individual cell-voltages (or even better, active balancing, but likely that won't be seen). ;)

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On 8/2/2019 at 3:22 AM, Boogieman said:

How did you measure the charger.
With no load (wheel not connected) directly on the charger pins on the contact?

exactly

I already went to the shop where I bought the wheel and they gave me a working one ;)

So imagine you want to charge up to 67V, would you expect a loaded charger to go to a higher voltage than an unloaded one? I do not know if that is possible, but in my charger it wasn't. I ended up measuring the voltage while loaded + green light, and still, it couldn't reach the 67V.

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Posted (edited)
7 minutes ago, Struck said:

exactly

I already went to the shop where I bought the wheel and they gave me a working one ;)

So imagine you want to charge up to 67V, would you expect a loaded charger to go to a higher voltage than an unloaded one? I do not know if that is possible, but in my charger it wasn't. I ended up measuring the voltage while loaded + green light, and still, it couldn't reach the 67V.

If you charge the wheel from low battery (say 10%) the meassured voltage at the charge pins will be lower during charge load.

Why?

Simple, battery is maybe 61V at 10% charge state (empty meaning discharged battery, not 0V)

Charger unloaded output voltage is 67V.

Battery is adding a resistance to the circuit dropping the LOADED output charge quite significant (depends from case to case but lets estimate in the middle) to around 64V.

(Measured my own charger during load and not, and it is just like in the old lead battery,NiCd battery days...no magic has happened)

And then we can add BMS to the equiation, but thats beyond the area where i feel fairly confident to say anything with a reasonable amount of facts and experience behind me. I am really intrigued to learn me more about the circuitry though :-)

Edited by Boogieman

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I am a little bit lost here. I do not know if we are disagreeing on something or not. My charger could not give 67V, and therefore the wheel was never fully charged. First way to check if it was giving 67V? By measuring the thing unloaded.

I can measure the charger voltage and use the app to measure the battery voltage , and they differ by 0.2V, I do not know how much is because neither of them is perfectly calibrated, but I think it is a pretty good  measurement

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Posted (edited)
On 8/4/2019 at 11:17 AM, esaj said:

For your Gotway you can simply check that the charger's at 84V, since there are no protections. But, in case there were protections and you wouldn't actually know whether there are diodes or mosfets there, it'd probably be better still just to adjust the charger to the typical 4.2V per cell voltage, or at least not much above it. The only reason for higher voltage, while still avoiding overcharging which can cause a fire or explosion at worst, would be to ensure that the cells reach their full voltage when leaving it on charger for balancing to occur. But there you'd be better knowing the protection circuitry, or even better, being able to measure the individual cell voltages, it would be so much easier if the wheels had BMSs that report the individual cell-voltages (or even better, active balancing, but likely that won't be seen). ;)

Ok, i measured charger output 82.5V before and battery nominal voltage is 84V on the Tesla, so too low.

Hence opened charger, removed tack from trim pot vr 1 - then suddenly charger is at 83V.

Tried adjusting slightly like 1/50 of a turn at a time and boom now it charges 84.2V and regardless if I turn the trim one FULL revolution cw or ccw it stays at 84.2V. i wonder if i killed the pot when i removed the tack?

So now i have started balancing allowing 5-6hours with green led. Reported voltage from wheel log after roughly 15h charging from 20% was 83.5-6V (before 82.3-7 when full / green after maybe 12hours).

I have stopped over the night and now charging again at green LED for a few hours and it now at 83.6V as reported  by the app (can i measure more exact right at the charger input pins of the Tesla, i mean will that show battery voltage or is there electronics in between the f up the value?)

As you say, a voltage measurement of each battery would be optimal and a automated battery fault checking in the app would be lovely.

That will not happen now, but if they dont kill EUC through governments, more companies and people will join and quality will increase.

If they kill it, all EUCists will "go dark", quality wil fail and people will get hurt or die. But that's up to politicians to decide, which outcome they want for us human beings ;-)

Edited by Boogieman

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17 minutes ago, Struck said:

I am a little bit lost here. I do not know if we are disagreeing on something or not. My charger could not give 67V, and therefore the wheel was never fully charged. First way to check if it was giving 67V? By measuring the thing unloaded.

I can measure the charger voltage and use the app to measure the battery voltage , and they differ by 0.2V, I do not know how much is because neither of them is perfectly calibrated, but I think it is a pretty good  measurement

1. Check the deviation of your meter. Mine is pretty good but at 0-400V the max dev is +/-0.7V and app, noone know for sure ad it likely differs between wheels (and how app interprets it)

2. My charger also gave less than nominal, read this thread and other threads on charging, its all in there already. Also read on https://batteryuniversity.com/

3. From what i have read, wheel should be fully charged at least every 10th charge cycle for balancing. In between you can double or tripe total amount of charge cycles (before battety dies) by only charging 80-90% (or less,but...why). Read more on http://hobby16.neowp.fr/2016/12/01/voltage-threshold-on-charge-doctor/

 

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my charge doctor attempt. 

1B532978-2548-4848-98D8-D887BDFCAFE4.jpeg

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