Inconsistent Charging Rate

EriCal said:

Now, I will admit that I have never gotten up in the middle of the night, gone out into the cold, dark garage and risked the return to bed when cold to check the charge rate indicator on the car. Have you?

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Won't the iPhone or Android app give you that information from the comfort of your warm and cozy bed? ;-)

Of course the car has to be online (via 3G or your wifi) to be accessible using the app.

EriCal said:

My Dear and Beloved Spouse has had her Model S -85 for six weeks. We charge at home with a 240v 50amp outlet during the super saver rate from midnight to 6 AM. The electric company gives us a nice set of graphs, etc. to help us monitor our usage.


MOST the time the car charges at 9.4 KW as expected but occasionally -about one night in five - it charges at about 4.6 kw. With this slower charge, it carries over into the higher-rate time of day.

Have any of you experienced this?? Cause?? And how do we fix it.

Now, I will admit that I have never gotten up in the middle of the night, gone out into the cold, dark garage and risked the return to bed when cold to check the charge rate indicator on the car. Have you?


Thanks, Eric

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If the model S detects a temporary voltage drop, it will drop the charging current for the rest of the charging session. I've seen this when I use the chop saw in my garage while I'm charging the car or if I'm charging at work and someone plugs into the other port on our charge point charger. In your case, perhaps something is intermittently causing a voltage drop and this is causing your car to reduce charging power. Running a REST data logger or visible tesla should help sort this out. If the voltage drop always happens at the same time each night, you could just program your car to start charging after the voltage drop so that it never reduces power. You could also drop the charge current so that the car just finishes charging as the electric prices go up in case you are normally just above the threshold for reducing charging power. You could also see if anything else like a large air conditioner or an electric oven is on the same circuit as the car charger.

You can determine if it's the Model S by looking at the charge rate after the charge. If it's where you set it, then it's something else. If it's lower than where you set it, it's because a voltage drop was detected.

voltage fluctuations will cause the Model S to drop it's amperage pull. The car detects this and as a safety precaution it'll reduce its pull. this is to prevent things like fires from faulty house wiring. if your wiring is good perhaps the electric companies' transformer is meeting the end of it's life.

It should not cut in half, however - from 9.4 kW to 4.6 kW. The automatic charge reduction will cut 25% of the power.

More information is needed. If you can tell us what your volts and amps shows during the 9.4 kW rate and 4.6 kW rate, we can try to help you. Check to be sure that the car isn't remembering a lower configured amperage based on location (my car used to sense my garage as 2-3 different locations in the past).