False Positives With FW 5.8.4 Charge Current Reduction?

[FlasherZ]

Perhaps they consider the specs to be trade secrets. Perhaps they consider the specs to be non-final and subject to tweak, and publishing them would only create confusion before they are satisfied with the algorithm. Perhaps they are trying to rectify differences with ANSI standards. Your suggestion that it is due to Tesla not wanting to be questioned doesn't seem to line up with my experiences with Tesla.

 

[Larry Chanin]

Tesla uses ohm's law to determine when it appears there might be a high-resistance problem in the infrastructure. This serves to protect the infrastructure (whether wiring in the home, overloaded transformer, etc.)

Flasher I want to thank you for your thoughful responses in this thread.

In the above quote am I correct that it is your speculation that Tesla is using ohm's law to determine if high-resistance exists in the supply circuit to determine the trigger points of this lastest firmware upgrade? In other words, Tesla didn't actually tell you that they use omh's law to calculate the resistance of the circuit and they use some value to trigger the current reduction, correct?

The only thing I have seen on the record from Tesla is the following excerpt from a blog article:

A variety of factors such as corrosion, physical damage to receptacles, or inappropriate wiring or installation of electrical outlets can cause higher than normal electrical resistance when using the Universal Mobile Connector (“UMC”) NEMA 14-50 adapters to charge Tesla Model S vehicles. When charging, higher than normal electrical resistance connections to external energy sources may cause excessive heating of the adapter. In December 2013, Tesla released an over-the-air software update to address this issue, enabling the Model S onboard charging system to automatically reduce the charging current by 25 percent if it detects unexpected fluctuations in the input power to the vehicle. This fully addresses the issue by substantially reducing the heat generated in any high resistance connections outside the vehicle. This update increases robustness and safety considerably in the unlikely event that a home wiring system, receptacle, adapter or cord is unable to meet its rated current capacity.

My point is that all we know for sure is that unexpected fluctuations in delivered power to the car triggers the 25% current reduction.

I agree with virtually all of your main points, but don't you concede that other loads, both in the Model S owner's home and in other neighbors' homes on the same supply transformer, or even utility switching/voltage regulation, could also cause a fluctuation in power delivered to the car? If so, that could be responsible for false positives without there having to be faulty wiring or higher than normal electrical resistance in the owner's home or even the utility supply circuit.

In other words, you do accept that it is possible to encounter legitimate false positives due to load fluctuations?

Hopefully these situations are limited, but we don't really know for sure.

Thanks.

Larry

 

[FlasherZ]

Hi Larry,

Indeed I do not know the specific parameters that are used. There seem to be multiple components from the data I've seen in various forums - the absolute low-voltage component, a faster-than-normal voltage drop component (high-resistance), and a sudden voltage drop / voltage surge component (arc protection).

Technically, short of a supply-side generator problem, all of the fluctuations are load-induced somewhere. In the FAQ I address how to rule out appliances in your home that may have problems (such as a heat pump or A/C compressor with a bad start capacitor). If you combine an overloaded transformer (a common occurrence) with bad appliances at a neighbor's house, it can indeed result in the Tesla seeing a voltage fluctuation. If the transformer is properly sized, then an appliance at the neighbor's would have to be behaving extremely badly to cause the fluctuation required to trip the algorithm. It's certainly not out of the question, though, and if it happens more than just once in a great while, then it points to something in the system that is highly stressing the system.

Any time this happens repeatedly or regularly, it points to a problem in the infrastructure somewhere and will likely require the PoCo help to track it down.

I'm coming around to the idea that the "low voltage" element might need to be tweaked - Doug's comment that the car seems to be more sensitive to fluctuations at lower voltages has been growing on me a bit. It seems that if that is a part of the algorithm, I'd be in favor of eliminating it and looking purely at the ohm's law and arc prevention portions.