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[Specter]

Yesterday I was charging my bike at home,  and I got to the end of the charge with 96 percent left and it said it was 'Balancing' but pulling zero amps.  Umm... ok.... an hour and a half later, it's at 96 percent charge and 'balancing' at zero amps being brought in.  Umm, that's not right.

So exactly HOW does the balancing thing work here?  In my world, there should be a 'balancing' circuit installed which is there all the time anyways.  Essentially it's a wheatstone bridge type thing that when one bank of cells goes up or down from the rest, it trickles current from the others to 'balance' it all out.

This 'balancing circuit' is pretty much passive, and works ALL THE TIME, anytime there's a cell imbalance, and when everything is happy it will pull about nothing to stay idle.

So what does Energica do when it says balancing?  Does it just reduce charge current to a few amps while letting this thing do it's job for the most part and when the cells eventually trickle up to the 100 percent charge by voltage, it says 'charged' shuts off and what little imbalance might be there just 'fixes' itself over the next hour or so, or does it actively monitor and control the cell voltages somehow?   

What I did was I unplugged the bike, waited a few seconds then replugged it in, it re initiated the charge cycle, went straight to 'balancing' mode, but this time it was pulling 4 amps.  Fairly soon after, I hit 100 percent and it ended, but the KEY thing was it was grabbing power this time around.  I have a feeling if I were to have left it, today it'd still be balancing, at whatever percent it dropped to, sitting there all night with the fan and light running but no power coming in....but still balancing !!

Is the act of balancing, something that is going to occur no matter what, because there IS a balancing circuit in there that for the most part, acts passively, OR is it something that has to be initiated at the very ass end of the charging cycle to physically happen?.

If I were to only charge my battery up to 90 percent each time, and do this 20 times in a row, is that going to really wank them out of balance, or will they trickle balance in the back ground?  Do I HAVE to actually push them to 100 percent each time I charge?

Aaron

[DonTom]

Do I HAVE to actually push them to 100 percent each time I charge?

NO! In fact, it is best if you normally only charge to 80% but once in a while to 100% for balancing.


There is more than one method to balance cells. IIRC, Tesla can balance at any SOC. But IIRC, that method has a cost in battery drain when the car is not being used. It draws some current when the vehicle is not being used. Tesla is bad to let sit. Discharge is almost 1% per day. Must be left plugged in for long periods of non-use. Unlike my Chevy Bolt that I can leave NOT charging for months. I believe it balances only near the full charge, as do motorcycles.


Motorcycles all seem to do their balancing after 80% SOC. I find it normally comes out if I only charge to 100% when I really need it, 80% other times is about right. So even if I don't think about it, they get balanced well enough from my normal riding.


Also, if on a trip, it is faster to make more stops and recharge in the range of 20-80% every time. The charge slows down a lot above 80% soc.


So only charge to 100% when you know you have not done so for quite a while. Expect it to take a lot longer as you get nearer to 100%.


-Don-  Auburn, CA

[Specter]

thank you Don.
That is what I was getting to.  Cycling a battery FULL cycle is not the best practice on it.  If you can keep it at a 80 20 for the most part is the best as for longevity etc etc.  Yes if you NEED to, suck it dry or push it to the top.   The very 'tips' of the range cycle on a battery tend to be lower density watt/volt anyways so it's not worth the bother unless you just have to.  As you said, charging takes longer because it drops way off at the top because it needs to let the battery settle off a high C rate to get the chemical reaction to slow down a bit to see what the real SOC is.   If they are self balancing in general then you wont' have to worry about one cell going way crazy out of line with the others.

I have batteries in my truck, (goofy nerd project with solar panels on my flip back for the bed) and a balancer on them.  Once they are balanced it only draws like 5 milliwatt idle current or something very negligible on a 8kw battery pack.  They can sit for months with virtually no drain.  The ONLY time this becomes a problem as I have found is, when the temps might get around freezing.  The batteries have a heater in them and that apparently is NOT on the DMZ side of the BMS and will suck them to zero if you let it.  My thoughts were that if the Energica is set up with a similar 'passive' type of balancing, then it happens anyways and topping off is not critically important.

Thanks for your input.

Aaron

[jotjotde]

The bike not getting to full occasionally is a bug that the update …042 should fix.
So I assume you still are on 041.

[Specter]

I'll have to look and see what firmware I am on.

Charging it again today so we'll see how it behaves. IT's a cloudy day so my inverters are chattering a bit because they aint happy going thru the make .vs. take threshold with the constant cloud passing changing the production levels.

Ill get back to you later after it's had a chance to run a complete cycel

aaron

[PWM]

Yesterday I was charging my bike at home,  and I got to the end of the charge with 96 percent left and it said it was 'Balancing' but pulling zero amps.  Umm... ok.... an hour and a half later, it's at 96 percent charge and 'balancing' at zero amps being brought in.  Umm, that's not right.

So exactly HOW does the balancing thing work here?

Aaron

What you describe is normal.

There's only (2) choices to balance cells in a pack, low-side or high-side, Energica employs high-side.

For high-side, the weakest cells (ones w/ the lowest capacity) will charge the fastest and hit their 4.2V full charge state first, therefore on an iterative basis, the cell groups that are full need to be discharged while the stronger sibling cells take on more charge.  This is why 0-amps is displayed, the cells are being discharged.

Also, Energica does not employ a separate 12V battery for system keep-alive and I'm pretty sure the DC/DC converter is deactivated when ignition is switched off.  That means a select group of cells and not the entire pack supports the 12V keep-alive and that is probably why the 315mA fuse exists, to limit the keep alive voltage discharge rate should a fault occur. 

Depending on storage duration, the keep alive cells are the ones that take the longest to fully charge, therefore the balance session time is variable and proportional to storage duration. 

While balancing, the charge rate is limited to 4-amps to manage surface charge otherwise an accurate sense of full capacity cannot be determined.

So, balancing on a bi-weekly basis is necessary.  More frequent than that is not necessary.  LPR @ 80% is healthy for the keep-alive cells to ensure they never deplete too far from the rest of the pack.

Eliminating a separate 12V battery is a feature, but there's a maintenance element that must be recognized.

[Specter]

PWM, ideally though, each bank of cells should be dynamic really.  Yes at first the lowest voltage ones will charge the fastest, and get more charge, because the voltage difference is greater between them and the charging voltage, allowing more current to flow.. but as their voltage comes up, they'll eventually catch up and even out with the others, and from there is probably a millivolt dance as each bank takes what it needs.  Yes at the end, as the charge current is reduced to let the batteries 'relax' a bit and get back down to a real voltage and not a charge excited one, they will eventually settle out, and sip here and there until it's all ready to go.

I understand the 0 amps because the balancing is occurring inter battery, and thank you for that info, but 2 hours? and ZERO percent change in charge status after all that time??  With no power coming in, any balancing, ideally should make my state of charge appear even less because voltages are overall lowering to balance out the entire pack.  With that scenario, the bike will never reach 100 percent until they put more energy to them, so how does it determine 96 percent,  98 percent, 100 percent?  Is there a timer too?

As a related note, this is another thing that really irks me is, Lithium cells are NOT lead acid cells, yet almost everyone wants to apply the same Lead Acid "Battery Lore" to them, especially when it comes to charging, strings, and the likes.  Each battery or bank really, pretty much has it's OWN management system.  Don't need the hooman manually sucking water out to check the balance etc, as an example, they take care of themselves.   If they are in series, then YES you can get in big trouble fast w/o any sort of management or balancing, but in parallel, not so much.

Question for the masses?

As a lithium cell ages and eventually dies.  Does it's terminal voltage die off significantly like a lead acid does,  or does it just for the most part lose capacity until it's pretty much at a percent or two? and the battery just crashes when you try to use it?

Aaron

PS. Morgan I hear is on and offline a bit with storm issues, so may not be able to answer folks right away who asked him questions.

[PWM]

Question for the masses?

As a lithium cell ages and eventually dies.  Does it's terminal voltage die off significantly like a lead acid does,  or does it just for the most part lose capacity until it's pretty much at a percent or two? and the battery just crashes when you try to use it?

Aaron

Lithium cells degrade over time which results in higher internal resistance.  Terminal voltage is not impacted because it is measured open circuit but under load the cells will exhibit a greater voltage drop for same C-rate discharge as when they were new.  There's a minimum voltage the terminals should not exceed (for doped anode NMC chemistry, this is likely around 3.0 volts).  Below this value, the degradation increases significantly, that's why the BMS will invoke a throttle inhibit signal to traction drive should any cell fall below this value.  The degradation in both cases is caused from a plating effect to cathode (positive terminal) preventing ions from being absorbed during discharge.

[PWM]

I understand the 0 amps because the balancing is occurring inter battery, and thank you for that info, but 2 hours? and ZERO percent change in charge status after all that time??  With no power coming in, any balancing, ideally should make my state of charge appear even less because voltages are overall lowering to balance out the entire pack.  With that scenario, the bike will never reach 100 percent until they put more energy to them, so how does it determine 96 percent,  98 percent, 100 percent?  Is there a timer too?

Aaron

PS. Morgan I hear is on and offline a bit with storm issues, so may not be able to answer folks right away who asked him questions.

No, the shunt current used to discharge cells that have reached full capacity is not regenerated but burned off as heat.  Balance session time is inversely proportional to state of unbalance and 2-hours is perfectly normal as I have also experienced.  If the balance session times out before the pack is fully balanced, the fuel gage will read short of 100% at completion, this means cells are not fully balanced which makes sense since full capacity is not reached.

True SOC is determined by counting coulombs while charging or discharging, this is NOT how the fuel gage works on an Energica.  I would expect in 6-8 years my fuel gage will still register 100% when fully charged but w/ depleted capacity compared to new.

[Specter]

The bike not getting to full occasionally is a bug that the update …042 should fix.
So I assume you still are on 041.

Just looked a little while ago  im on 42

aaron

[DonTom]

Question for the masses?

As a lithium cell ages and eventually dies.  Does it's terminal voltage die off significantly like a lead acid does,  or does it just for the most part lose capacity until it's pretty much at a percent or two? and the battery just crashes when you try to use it?

In many cases, it is just like your KWH dropping off. IOW, your 20  KWH battery becomes a 10 KWH battery after MUCH use. Then 5KWH, etc. Will even charge faster to full at the same charge rate, in most cases.


In fact, when my Zero DS battery crapped out during warranty, it had less than half its normal range and charged to full more than twice as fast. Also seems that Regen works much better (same charge rate but with smaller battery).


But perhaps not all failures fail in the same way, but normal aging should be just like your battery getting smaller as it ages.  Still useable, and if the charge stations are close together, it makes little difference because you stop twice as often for half the time when the battery KWH capacity is half.


-Don-  Reno, NV