Weird Charging Curve

[derminghsieh]

Hi,
I have a 2012 es imiev with mileage of 55324. I used to charge at a Chargepoint Level 2 station with a single output. The normal charging curve shows currents drops to almost zero at least one time, then it would get back to full about 3KW (actually less than that) after about 10-15 minutes. This is unique to imiev because I talked to e Tesla owner who also monitoring the charging curve. He has never observed a drop down of currents in the middle of the charging process. Of course, there are reasons for that, but I am not interested in why imiev behaves like that, as long as it gets full charge.

A week ago, the old stations were replaced by new ones with dual output. I found that when the current drops to alomst zero, it could not recover to full charging strength. It only gets to half at 1.2 KW. Any thoughts on what happened? Thanks. I attached a screen shot of charging curve.

 

[derminghsieh]

Sorry the image does not show in my first post.

 

[phb10186]

I would have thought that even though the chart appears to show zero current for a time bucket of a good few minutes, in reality it's actually showing the lowest kilo-wattage in that time bucket increment. This, I would assume, would mean that rather than dropping down to zero for a few minutes,, it's actually only doing that for a split second, and the chart is misleading you.

I often see very brief current draw changes through my home smart electricity meter, and I would assume that the 'intelligence' of the on board charger does cause something of a re-boot periodically during charging, allowing it to very quickly re-check the pack voltage, and re-assess the power it then needs to draw for the next incremental part of the charging cycle.

The dip from 3Kw to 1Kw would be normally expected as the battery nears full charge, though from what I recall, it only does this during the 10-20 mins or so.

If this is a public charge point, then who knows what charging algorithm that EVSE is using.

 

[derminghsieh]

Thank you very much for your thoughts. I am aware of the final tapering down curve when the battery is nearly full. What puzzles me is that after the dip, the full charging power could not be recovered while the battery is still far from being full. It means I have to wait much longer to have a full charge. If it is due to charging algorithm, then I wonder what the solution might be. However, I can always restore the EVSE to full charging power as long as I unplug the connector and start a new charging session. I wonder if anyone has similar experience with a Chargepoint station like I do. I already make an appointment with Mitsubishi dealer to check if there is anything wrong with the battery system. Hopefully, there is nothing wrong.

 

[wmcbrine]

I wonder if that graph is just too crude to accurately represent what's happening -- like, maybe it's rounding to the nearest kW? Those lines are awfully straight.

On my JuiceBox, a typical session looks like this:

The location of the notch varies, but it's always there on a full charge. (A partial charge sometimes looks different.) The rest is pretty consistent.

 

[derminghsieh]

Yours look like the typical charging curve of mine with the old Chargepoint EVSE before the station owner changed to the new ones. The old curve shows a notch or two and then recovers to full charging power. It eventually tapers down as battery is nearly full. With the new ones as you can see, it shows several notches and no getting back to the full power. I contacted Chargepoint for possible explanation, they could not give me one. But they insist that their machine only accepts commands from the car's on-board charger, and never makes decisions as to how big a power should be getting into the car's battery. The output voltage of new Chargepoint EVSE is at around 220V, and the imiev's on-board charger should be able to sense that and decides a level 2 charging. Well obviously from my charging curve, it is a level 1 charging with 220 V. It really does not make any sense!!

 

[rnlcarlov]

That notch happens very often. The triplets usually have two notches where stey stop charging for some minutes. One at 30% SOC (lasts longer than 15min, usually) and one at 70% SOC, which usually is shorter.

If the car goes to 30%, that stopping point is almost 100% guaranteed. For the 70% pause, it doesn't always happen. In my experience, if the car starts charing below 60% there's a very high probability it will pause, but above that SOC it usually doesn't.

Those pauses are particularly troublesome for Portuguese people like me who use the public charging stations. Most of them are programed to terminate a charing session if no current is drawn for for than 5 minutes. This means we must go to the charging station to restart the charge. The 30% pause is particularly troublesome, since it can pause again immediately after restarting the charge and terminate the session again after another 5 minutes. And this can go on and on. Because of the I named it the "loop of death". I employed a workaround by adding an extra load (a lamp) in parallel to the EVSE to fool the charging station.

This is to say that notch is usual fare, but it doesn't always "talk" very well with charging stations

 

[phb10186]

That notch happens very often. The triplets usually have two notches where stey stop charging for some minutes. One at 30% SOC (lasts longer than 15min, usually) and one at 70% SOC, which usually is shorter.

If the car goes to 30%, that stopping point is almost 100% guaranteed. For the 70% pause, it doesn't always happen. In my experience, if the car starts charing below 60% there's a very high probability it will pause, but above that SOC it usually doesn't.

Those pauses are particularly troublesome for Portuguese people like me who use the public charging stations. Most of them are programed to terminate a charing session if no current is drawn for for than 5 minutes. This means we must go to the charging station to restart the charge. The 30% pause is particularly troublesome, since it can pause again immediately after restarting the charge and terminate the session again after another 5 minutes. And this can go on and on. Because of the I named it the "loop of death". I employed a workaround by adding an extra load (a lamp) in parallel to the EVSE to fool the charging station.

This is to say that notch is usual fare, but it doesn't always "talk" very well with charging stations

Makes perfect sense... clearly the man who devised the Portuguese EVSE pubic charging network knew nothing about how EVs charge, and rather worked on the current-drawing model of an electric kettle.

Your workaround is quite inspired.

 

[derminghsieh]

Wow, I do not not even know that much detail about stopping of the charge. Thank you for sharing. I thought the stop was due to too high or low a temperature in the battery or on-board charger. I will certainly ask the technician of the dealership if this is the way the on-board charger is programmed when I arrive there next week. Hopefully I can get some definite answer.

 

[JoeS]

derminghsieh, the normal 'timeout' dropout lasts anywhere between six and twenty minutes, and the reason for it is believed to be to determine if there is excessive voltage sag in the pack before continuing with the charging.

I like micarlov's explanations and his creative workaround!

wmcbrine's graph is of a normal condition although in my case I have not seen the gradual and slight power decline as the battery charges (which is logical) and I was surprised that my own TED monitor did not show this.

I have used all of the different ChargePoint public EVSEs (single, double, and CHAdeMO) and have never had any issues with them.

derminghsieh, your curve is normal UNTIL the second drop, and, as you point out, is really weird with repetitive drops at the reduced power level. What device/app are you using to monitor this J1772 input power? I presume that you have no problem L2 charging elsewhere?

derminghsieh, do you have CaniOn to be able to monitor the car's inputs and individual cells? Whereabouts are you located, as maybe one of our forum members with CaniOn could come over and check it out with you?

 

[derminghsieh]

JoeS, I checked into the owner's manual for "Regular Charging is discontinued" and there are 5 possible causes listed. The one that, I think, most reasonable for my case is "The temperature of the main drive lithium ion battery is too high or too cold to charge". Well, I think you have reminded me a more compelling cause "excessive voltage sag between cells" and it really gets to my nerve because it means " I have bad cells."

I do electric biking like you do and I remember one time while charging my 36V LiFePO4 pack, one bad cell popped and charging stopped. I did not use BMS because I considered it too tedious to use. But I use two metal wires to line up positive and negative terminals respectively after charging to balance out any differences between cells, no more BMS.

I am really interested in your suggestion of using CaniOn to have a real-time monitoring at individual cell voltage while charging to see how serious the sagging is. I am checking into CaniOn section of this forum. Maybe the super-smart on-board charger is saving my bad cells.

I sign in chargepoint website and key in USN and PSW, then I get to see the charging curve.

I am adding new charging curves recording the whole charging process, performed by Chargepoint EVSE, orchestrated by my imiev on-board charger for everyone to see.

This one is from the beginning to the time I unplugged the charger:

This one I started a new charging session until the end:

Total Energy into my battery pack is 8.835 KWh
Total elapse time is 2 hours 30 minutes

 

[derminghsieh]

Sorry there is a typo. The total elapse of time is 4 hours 30 minutes.; not 2 hours 30 minutes. It really talke a long time to charge.

 

[rnlcarlov]

Wow, I do not not even know that much detail about stopping of the charge. Thank you for sharing. I thought the stop was due to too high or low a temperature in the battery or on-board charger. I will certainly ask the technician of the dealership if this is the way the on-board charger is programmed when I arrive there next week. Hopefully I can get some definite answer.

It happens to all triplets I know. It was first described by Malm.
In the summer, when the cells are hotter, the 70% pause happens very rarely. No idea why.

Makes perfect sense... clearly the man who devised the Portuguese EVSE pubic charging network knew nothing about how EVs charge, and rather worked on the current-drawing model of an electric kettle.</span>

Your workaround is quite inspired.

To be fair, the portuguese public charging network is one of the first in the world. We already had hundreds of charging points before there were barely any electric cars at all. The problem is that is has remained in pilot phase for all these years and only now are they little by little updating the software. In the new version this problem seems to be resolved.

JoeS, I checked into the owner's manual for "Regular Charging is discontinued" and there are 5 possible causes listed. The one that, I think, most reasonable for my case is "The temperature of the main drive lithium ion battery is too high or too cold to charge". Well, I think you have reminded me a more compelling cause "excessive voltage sag between cells" and it really gets to my nerve because it means " I have bad cells."

I am really interested in your suggestion of using CaniOn to have a real-time monitoring at individual cell voltage while charging to see how serious the sagging is. I am checking into CaniOn section of this forum. Maybe the super-smart on-board charger is saving my bad cells.

There isn't any big voltage sagging in my car and it stops all the same. Actually, there was a study made with the fleet of electric cars (peugeot ion) of my city's town hall, and the charging data showed this as well in all cars. Like I said, with hot cell temperatures the 70% pause may not happen, but the 30% stops always does, no matter how hot or how cold it is.

 

[derminghsieh]

Hi all,

I went checked my car at the dealership and no error code was found on my car. Now it is becoming more difficult to pinpoint the problem of charging not able to restore to level 2 at 240 V after time out dropping. I am lucky, the technician I met did not stop in telling me the car is fine. Instead, he takes this matter into his own hand and contacts the Mitsubishi chief engineer to resolve this issue. I have provided all the information I have to the technician. Hopefully, there is a software update to rectify the problem.

I suspect this weird charging behavior is not unique to my car even though JoeS says otherwise. If you happen to charge your imieve using Chargepoint Dual , would you please check your charging curve to see if it shows similar characteristics to mine ? I would really appreciate your help.

 

[kevin1956murray]

I am seeing the charging reduction to 1.1 kW after the pause. I believe this must be some 'handshake' issue, where the station does not recognize that the car should get 240V again. I think maybe Chargepoint software/firmware is interpreting the i-MiEV's pause as an error, and they play it safe (hedge the bet) by only sending out 120V after that. I am trying to get Chargepoint to address this issue/problem, but it has taken 3 weeks to get replies to each of my 'opened tickets', so my hope for a fix is kind of fading.

The thread that I have been posting on is here: http://myimiev.com/forum/viewtopic.php?f=24&t=3977&start=20

 

[coulomb]

I think maybe Chargepoint software/firmware is interpreting the i-MiEV's pause as an error, and they play it safe (hedge the bet) by only sending out 120V after that.

I find it hard to believe that an EVSE, which already has a mechanism for controlling load (the pilot signal), would go to the trouble of adding another contactor, and interlocking with another contactor, to provide 120 V. Do you have evidence that it is doing this?

I suppose that providing 120 V would be a way to force a non-complying vehicle to take less load, while still allowing some charging. That would imply that the vehicle was ignoring the pilot signal, or at least there would have to be some disagreement between the EVSE logic and the vehicle's logic. But it still seems unlikely to me.

I note that per the last post on 2019/Feb/07 on the other thread, @ChrisEV is actually talking about a non-Chargepoint EVSE that is partnering with Chargepoint to use their card facilities. Is that the case for you too? If so, perhaps it's better to attempt to talk to them directly, rather than have Chargepoint talk to their partner.

 

[kevin1956murray]

I have no evidence of 120V. The reduced charge rate of 1.1kW equates to just about 4 miles gained per hour, down from the 12 miles gained per hour that I want (for the whole charge). 4 miles gained per hour is what my 120V cord can do.

The station is Chargepoint, with no third party involved.

 

[jray3]

Thanks Kevin1956Murray, I have this same issue with ChargePoint public EVSE, whether the unit is new or old, weather is warm or cold.
It's meant that I now only use ChargePoint L2 if I have several hours to stop there, otherwise I'll hit a DCFC.

 

[kevin1956murray]

When a ChargePoint station charges at just 1.1kW after a MiEV induced pause, I have found that calling ChargePoint and asking them to reboot that station will get the rate to return to 3kW, without having to physically go to the car to start a new session.

 

[JoeS]

When a ChargePoint station charges at just 1.1kW after a MiEV induced pause, I have found that calling ChargePoint and asking them to reboot that station will get the rate to return to 3kW, without having to physically go to the car to start a new session.

Wow! Good information. Guess we'll have to be paying attention from now on...