derminghsieh
Posts: 19
Joined: Mon Sep 10, 2012 10:10 pm
Location: Bellevue, Washington

Weird Charging Curve

Sun Oct 15, 2017 8:28 pm

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.

Image

derminghsieh
Posts: 19
Joined: Mon Sep 10, 2012 10:10 pm
Location: Bellevue, Washington

Re: Weird Charging Curve

Sun Oct 15, 2017 8:31 pm

Sorry the image does not show in my first post.
Image

phb10186
Posts: 290
Joined: Fri May 13, 2016 12:58 am
Location: North London suburbs, UK

Re: Weird Charging Curve

Mon Oct 16, 2017 11:44 am

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.
2012 I-MIEV Keiko Silver 16K
2010 Insight ES-T 43K
2001 Accord Type-V (F23 manual)
2009 Hornet CB600F
2008 SH300

derminghsieh
Posts: 19
Joined: Mon Sep 10, 2012 10:10 pm
Location: Bellevue, Washington

Re: Weird Charging Curve

Mon Oct 16, 2017 1:13 pm

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
Posts: 350
Joined: Wed Apr 29, 2015 10:26 am
Location: Laurel, MD
Contact: Website

Re: Weird Charging Curve

Mon Oct 16, 2017 9:10 pm

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:

Image

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
Posts: 19
Joined: Mon Sep 10, 2012 10:10 pm
Location: Bellevue, Washington

Re: Weird Charging Curve

Mon Oct 16, 2017 10:11 pm

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
Posts: 72
Joined: Wed Apr 13, 2016 8:30 am

Re: Weird Charging Curve

Tue Oct 17, 2017 4:04 am

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
Posts: 290
Joined: Fri May 13, 2016 12:58 am
Location: North London suburbs, UK

Re: Weird Charging Curve

Tue Oct 17, 2017 9:58 am

rnlcarlov wrote: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.
2012 I-MIEV Keiko Silver 16K
2010 Insight ES-T 43K
2001 Accord Type-V (F23 manual)
2009 Hornet CB600F
2008 SH300

derminghsieh
Posts: 19
Joined: Mon Sep 10, 2012 10:10 pm
Location: Bellevue, Washington

Re: Weird Charging Curve

Tue Oct 17, 2017 11:04 am

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
Site Moderator
Posts: 3482
Joined: Thu Dec 15, 2011 5:47 am
Location: Los Altos Hills, California

Re: Weird Charging Curve

Tue Oct 17, 2017 11:22 am

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?
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

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