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Charge rate and ambient temperature

Big Dunc

Member
Jan 5, 2021
36
4
Eastbourne, UK
I have searched for the answer on this, but cannot find anything related. Apologises if I have missed the obvious.

We have had the S since mid December and until have been charging it with a 3 pin plug (16 A 4 kw). It hasn't been an issue as it does a very low mileage, typically less than 50 miles a week.

Last week we had a Zappi charger fitted to coincide with the commissioning of our PV system. Initially I tested the Zappi on a fast charge and it put in 7 kw / 32 A as it should do. It is also very good at charging when sun is available and cutting in and out as required, albeit always at a slow state of charge (not a lot of Sun in the South of the UK this week!).

Last night, as an experiment, to prove the system works, we did a boost charge over night during the hours of cheap electricity. It did charge at the correct times, but only at half the rate I was expecting, i.e. 16A / 4 kw. At lunch time today, I set the Zappi off on a fast charge and it was straight up to 32 A / 7 kw I left it for 20 minutes to prove it could do it, then stopped it (expensive electric time). The ambient temp was around 10/12 C.

just now I thought I would try another overnight charge to test the speed, but before I did so I thought I would just check it was still putting in 7 kw / 32 A. Alas, no. Before charging it said 0/32 A. Once charging started it quickly went to 16/16A before ever going any higher. I stopped the charge, waited ten minutes and tried again. Exactly the same. Ambient temp about 2 C.

Is slower charging at just above freezing normal, or is there a fault with the car or the charger?
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,001
6,925
Boise, ID
Is slower charging at just above freezing normal, or is there a fault with the car or the charger?
Well, yes, if you start a charge and immediately look at it. It's probably still warming up the battery and may not begin charging right away in the first few seconds or minutes. But if you check it after 15+ minutes or so, it probably will be charging and maybe at a normal rate, because it has gotten to warm up some to get to charging without hurting the battery. Charging below about freezing point is harmful to the batteries, so the car won't let it do that until it gets to warm it up some.

But on the other hand, I am not at all familiar with this Zappi connector. It sounds like it has some detection and intentionally scales its power up and down based on some factors? I don't know if that is operating correctly.
 

Big Dunc

Member
Jan 5, 2021
36
4
Eastbourne, UK
Last night it charged for 7 hours, but never went above 16 A. I would have expected the battery to warm itself in that time frame?

I agree it may be the Zappi, but just wanted to make sure this wasn't normal model S behaviour before telling them they had a fault.
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,001
6,925
Boise, ID
Last night it charged for 7 hours, but never went above 16 A. I would have expected the battery to warm itself in that time frame?
Oh, no, that's definitely not an issue of warming. That would be up to the level that should be able to charge at your real 32A rate within the first hour.
What the heck? That's not relevant. This isn't 120V, and it's not a warming/cold problem. He has a real setup with 7 kW of charging power; it's just operating at exactly half the rate for some reason.

I might suspect there is a problem with the onboard charger in the car. @Big Dunc what kind of car and what battery size? This 16A is sounding familiar. The onboard chargers are internally made with modules of 16A each. The 32A onboard charger has two of them, and the 48A charger has three. If one of them dies, it will fail gracefully by still charging with the rest of it.
 

Big Dunc

Member
Jan 5, 2021
36
4
Eastbourne, UK
2014 85 kw. Over the weekend we had quite low temperatures and it refused to charge quicker than 16 A. However, yesterday it was warmer and it charged at 32A 7 kw which is what the charger is meant to do. Maybe one of those things?
This was the first week with the charger and before then the maximum charge rate at home was 16 A so maybe the car took a while to realise the change and that more power was available?
I will keep an eye on it and post back if it plays back again.
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,001
6,925
Boise, ID
That was short lived. Now it won't charge above 4 kw again. It is a lovely warm morning here, so I am not sure this is temperature related.
It's not. And here's a really obvious way you can tell:
Look on the charging screen. As it has been doing this, I am sure it has been showing either "16/16" or "32/32". That is showing how many amps it is currently using, out of how many the charging equipment overall is announcing are available. If it's doing that, as I suspect, the equipment somewhere (either external connector or onboard charger inside the car) keeps flipping back and forth about what it thinks the capability is. If it were temperature related and just the battery being a bit cold, so the car is charging slower for that reason, it would not be changing the number that shows how many amps are available. It might say something like 18/32 if it is only using 18 amps, but it knows the 32 is available when it can get warm enough to use more of it.
 

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