UMC Charging Rate Drop

clx · Apr 6, 2015

Hi,

Does anyone know if the UMC charges the car in constant rate? When I first plugged it my 240v outlet, my car had 140miles left (I have 85kwh) it start charging at 40Amp, and it said the estimated charge time was 3 hours 20 mins (set to charge 90% full). When I checked again 3 hours later, the battery was at about 80% and it shows I still have more than 1 hr left to charge; the dashboard is showing the warning message "Weak Power or Ext Cable Used", and the car is being charged at 30amp.

My garage has another EVSE charger for the Nissan Leaf, that charger plugs into a 6-50 outlet that I had an electrician installed last year. During the installation, I asked the electrician to put in the correct wiring to support up to 80AMP circuit since I was thinking getting a model s with dual charger at the time. When I took delivery, I bought a 14-50 -> 6-50 adapter from Tesla SC, when I need to charge, I unplug the Leaf charger and plugged my UMC into the same outlet. Could that be the culprit?

Thanks!

jerry33 · Apr 7, 2015

The drop in amps is because the car thought that there was a potential electrical safety problem. First thing to do is to check the various connection places, UMC, and breaker to see if any are overly warm (after a couple of hours of charging). Because you unplug and plug frequently, the receptacle may be wearing or need to have the connections tightened.

supratachophobia · Apr 7, 2015

It's the car thinking there is an issue when there most likely isnt. The severity or how often it occurs seems related to what firmware you are on. I will say that after 4 on-board chargers, two UMC's, and three charge ports it hasn't happened in two weeks. And no, it's not an electricity issue at the site.

FlasherZ · Apr 7, 2015

supratachophobia said:
It's the car thinking there is an issue when there most likely isnt. The severity or how often it occurs seems related to what firmware you are on. I will say that after 4 on-board chargers, two UMC's, and three charge ports it hasn't happened in two weeks. And no, it's not an electricity issue at the site.

This is not true, and you can't rule out an electricity issue at the site based on your experience.

For some people, it's the UMC. For some people, a component in the car (charger). For others, it's a larger than normal voltage drop due to long conductors or undersized conductors. For others, it's a misbehaving appliance or a load-related condition (transformer too small, etc.)

It is unlikely to be the wiring to your HPWC outlet, if indeed they used #3 wire to supply the outlet as you asked. However, it could be due to an overloaded transformer, long run from transformer to your panel on undersized conductors, etc. Can you start by giving us the voltage that the Tesla displays at 0A charging, and when it reaches 40A?

clx · Apr 7, 2015

Is there a quick way to find out if it's the electrical wiring issue without getting another UMC?

FlasherZ · Apr 7, 2015

We'll need some information. When you first plug the car in, look on the display and tell us what voltage it reports while charging at 0A and at 40A... that'll be a good first start.

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UMC Charging Rate Drop

clx

Member

jerry33

(S85-3/2/13 traded in) X LR: F2611##-3/27/20

supratachophobia

Active Member

FlasherZ

Sig Model S + Sig Model X + Model 3 Resv

clx

Member

FlasherZ

Sig Model S + Sig Model X + Model 3 Resv

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