Destination charge problem?

[-monky-]

So I’ve had my M3 LR for a couple of weeks, and what with covid etc home charging (tethered) is really all I need for the foreseeable. But I wanted to test the cable that came with the car and also get a feel for charging on the go, so today I took a little trip round the corner to the local leisure centre which has free destination charging.

They have 7.2kW / 32A Rolec Autochargers. So plug in and away we go...or not.

Once connected up, all the lights on the charging station and the car are correct. M3 shows charging status on the screen. After a few seconds, the mi/hr starts ticking up from zero, and the 0/32A starts ticking up accordingly. But when it goes above 16A, the whole thing pauses, and resets to 0 mi/hr and 0A. And the cycle repeats. Not actually charging, just looping through that sequence.

Tried 2 charge stations, they both behaved like that.

After a while I figured out if I manually limit the charge current to 16A, it does start charging properly (at 16A) ie half speed.

Is this normal? And if so, why?! Or have I misunderstood how these things are rated?!

 

[-monky-]

Here’s a video. It was just doing this over and over.

 

[LongRanger]

they may have limited the max charge current due to local supply issues, or never set the things up properly.

we have a local similar network and once it's been installed it seems nobody actually maintains it, the council has their EV chargers and they just forget about them, they have ticked the EV box

 

[Adopado]

So I’ve had my M3 LR for a couple of weeks, and what with covid etc home charging (tethered) is really all I need for the foreseeable. But I wanted to test the cable that came with the car and also get a feel for charging on the go, so today I took a little trip round the corner to the local leisure centre which has free destination charging.

They have 7.2kW / 32A Rolec Autochargers. So plug in and away we go...or not.

View attachment 588932 View attachment 588933

Once connected up, all the lights on the charging station and the car are correct. M3 shows charging status on the screen. After a few seconds, the mi/hr starts ticking up from zero, and the 0/32A starts ticking up accordingly. But when it goes above 16A, the whole thing pauses, and resets to 0 mi/hr and 0A. And the cycle repeats. Not actually charging, just looping through that sequence.

Tried 2 charge stations, they both behaved like that.

After a while I figured out if I manually limit the charge current to 16A, it does start charging properly (at 16A) ie half speed.

Is this normal? And if so, why?! Or have I misunderstood how these things are rated?!

I would say that comes under the general heading of Woeful Public Charging. 99% unlikely to be your car that's the problem.

 

[Glan gluaisne]

The screen is showing that the charge point is apparently signalling to the car that it is able to supply 32 A, hence the 32 A to the right of the slash (this is the available current taken straight from the charger reading the Control Pilot duty cycle from the charge point).

If I had to guess, I'd say that the charger is detecting something awry with the charge point, and reducing the charge current. It could be something like an excessive voltage drop (it's been rumoured that the Tesla chargers may be more susceptible to sensing this) or something like a tolerance problem with the CP signal. It's pretty well established now that the Tesla chargers seem to apply a tighter tolerance to the sensed charge point CP signal than the specification. This was mentioned recently in a post about an Ohme unit having this problem, plus I experienced it with my home brew charge points, which have worked fine on four different EVs, but needed modifying to work reliably with the Tesla charger.

 

[GRiLLA]

By any random chance is that the High Wycombe leisure center ? I tried there once, couldn't get it to work.

 

[phil4]

Is it worth trying to set a lower charge current, and seeing if it holds at that? I have idea of the old ADSL Syncing, BRAS profiles and the like.... or CPU overclocking. My thinking is if as you saw it tries for 32 but gets to 17 and drops back to zero, try setting a current limit of say 10 or 12, and seeing if it stays charging. If that works, try 16. And so on.

 

[Rustybkts]

Just look at the voltage dropping from 240v to 230v! 10 volts drop with only a 16A capacity on the cable is awful. How far would it have dropped on the full 32A?
Probably the car protecting the supply as it shouldn't drop that far.

Incorrect supply cable sizing for the distance or maybe a poor connection somewhere hence why the car is not pulling the full 32A......clever as most dumb chargers would simply suck away until something caught fire!

 

[Adopado]

Just look at the voltage dropping from 240v to 230v! 10 volts drop with only a 16A capacity on the cable is awful. How far would it have dropped on the full 32A?
Probably the car protecting the supply as it shouldn't drop that far.

Incorrect supply cable sizing for the distance or maybe a poor connection somewhere hence why the car is not pulling the full 32A......clever as most dumb chargers would simply suck away until something caught fire!

...but still well within spec when at 16A. Because of location my home charger will drop voltage to around 219/220 when pulling 32A and the car is happy to work with that.

 

[Rustybkts]

...but still well within spec when at 16A. Because of location my home charger will drop voltage to around 219/220 when pulling 32A and the car is happy to work with that.

Agreed it is within -6% of 230v which is 216v but the car may sensibly note the voltage drop and limit the current accordingly.

A drop of 10v on a 16A load that is rated for 32A is way too high if the cables are correctly rated.

 

[LukeUK]

Whilst I agree that the voltage is low, I've charged for a couple of hours at 30 A and 210 V, so I don't think that's the immediate issue, unless the car is specifically looking at the rate of change of the voltage, as it steps up the current.

As an aside, I don't know how the charger in question (Tesco, Port Talbot) was signed off. I'm guessing there's a long run of undersized cable, for the voltage to drop that low.

 

[-monky-]

By any random chance is that the High Wycombe leisure center ? I tried there once, couldn't get it to work.

Full marks!! Yes indeed. Amazing!

Glad it's not just me then

 

[-monky-]

Is it worth trying to set a lower charge current, and seeing if it holds at that? I have idea of the old ADSL Syncing, BRAS profiles and the like.... or CPU overclocking. My thinking is if as you saw it tries for 32 but gets to 17 and drops back to zero, try setting a current limit of say 10 or 12, and seeing if it stays charging. If that works, try 16. And so on.

That's what I ended up doing. If I set it at 16A, it was stable at 14mi/hr.

If I pushed it to 17, it reset to zero.

So I could basically charge at half intended speed, no faster.

 

[-monky-]

Thanks everyone for your insights...looks very much like the CPs in that location then. I'm going to try another somewhere else and will report back...

(incidentally, when I got back my home charger fired up fine at 30A)

 

[Glan gluaisne]

The issue of whether or not the chargers in Teslas are more sensitive to voltage drop than they need to be would be an interesting one to try and bottom out. I think it's been suggested a few times that they may be, but haven't seen any hard evidence. The spec for the UK LV grid supply is the same as that for most of Europe, as far as the lower voltage limit (as mentioned above, -6% of 230 VAC, so ~216 VAC). I'm not convinced it's the actual input voltage to the car that's necessarily the trigger, but it might be sensible if the car was able to detect a rapid drop in supply voltage as it ramps up the charge current.

It might do some form of loop impedance test as charging ramps up. This would be a good thing to do in terms of safety, as an increasing loop impedance might be an indication of a poor connection, or a severely under-rated, or damaged, cable, so reducing or stopping the charge under such a condition would be a sensible thing to do. I have a feeling that another make of EV does something like this, possibly the Renault Zoe? The Zoe has a pretty weird charger (IMHO) and is more sensitive to the supply than some other EVs.

 

[-monky-]

Thanks everyone for your insights...looks very much like the CPs in that location then. I'm going to try another somewhere else and will report back...

(incidentally, when I got back my home charger fired up fine at 30A)

Just to draw a line under this - I finally tried another 7kW destination charger today - a PodPoint at Tesco. Charged at 30A fine. Must be a problem with those Rolecs, probably just at that one location.

Thanks all for your input.