Weak power or extension cord used warning/error

[yobigd20]

Just picked up my P85 yesterday. Characteristic of me, I procrastinated and still haven't finished my 240V 50amp NEMA 14-50 yet (it's almost done, just a long 100ft run and I need to shift some breakers down to make room for the new double pole breaker.) Garage and outlet is finished. Just need to finish wiring the breaker. I'll actually finish this later today after work.

That being said, in the mean time my garage has a regular 15 amp outlet. When I plugged in the UMC directly to the outlet, I get an error that pops up that said 'Weak power or extension cord used'. It does not charge the car. Shows 0/12a being used. (well, first it goes up to 12/12a, but then I hear a click and it goes down to 0/12a). Clearly I am not using an extension cord.

I don't know what else is on that circuit. I don't know if power is being used by something else on that circuit, or if its just a very long run from the breaker to that outlet and the voltage drop is too high.

I did figure out that I could 'turn down' the amps to use on the touch panel, and when I drop it to 9a (so it displays 9/9a), that it seems to charge at 1mile/hour, but that warning about weak power or extension cord is still displayed.

This does bring about a good point that I didn't really think about though - you can't really just "plug into any outlet" and expect to pull 12a and get 3/4mph charge.

None of this really matters to me much, just a bit surprised. Once I'm done with my NEMA 14-50 then all should be good.

 

[Robert.Boston]

@yobigd20: if you've got a multimeter, you might want to check the voltage at the outlet. That's the most likely culprit.

 

[yobigd20]

@yobigd20: if you've got a multimeter, you might want to check the voltage at the outlet. That's the most likely culprit.

Ok. What should I expect? 120V? 110V? What would be bad, 109V, 108V, or does it have to be much lower?

 

[FlasherZ]

Just picked up my P85 yesterday. Characteristic of me, I procrastinated and still haven't finished my 240V 50amp NEMA 14-50 yet (it's almost done, just a long 100ft run and I need to shift some breakers down to make room for the new double pole breaker.) Garage and outlet is finished. Just need to finish wiring the breaker. I'll actually finish this later today after work.

That being said, in the mean time my garage has a regular 15 amp outlet. When I plugged in the UMC directly to the outlet, I get an error that pops up that said 'Weak power or extension cord used'. It does not charge the car. Shows 0/12a being used. (well, first it goes up to 12/12a, but then I hear a click and it goes down to 0/12a). Clearly I am not using an extension cord.

I don't know what else is on that circuit. I don't know if power is being used by something else on that circuit, or if its just a very long run from the breaker to that outlet and the voltage drop is too high.

I did figure out that I could 'turn down' the amps to use on the touch panel, and when I drop it to 9a (so it displays 9/9a), that it seems to charge at 1mile/hour, but that warning about weak power or extension cord is still displayed.

This does bring about a good point that I didn't really think about though - you can't really just "plug into any outlet" and expect to pull 12a and get 3/4mph charge.

None of this really matters to me much, just a bit surprised. Once I'm done with my NEMA 14-50 then all should be good.

Did you take a look at the voltage on the screen when it's drawing 0A, and when it's drawing 9A or 12A? What's the difference.

There are a number of things to look at. I have my suspicions based on the information you gave:

What's the circuit size of your garage circuit that includes this 15A outlet, is it 15A or 20A? If it's 15A, you likely have #14 wire feeding it. You mentioned a 100-ft. run. 12A on 14 AWG for 100 ft will be pushing things a bit - you'll see a voltage drop of ~6% or so. If you have anything else on that circuit, it increases the drop to ~7-8%. This is likely to make the Tesla concerned you don't have the proper wiring.

- - - Updated - - -

Ok. What should I expect? 120V? 110V? What would be bad, 109V, 108V, or does it have to be much lower?

You need both loaded and unloaded voltages. You should expect unloaded to be somewhere between 110-120V and you want it to drop by no more than 5-6V when the car puts the charging load on it.

 

[mknox]

You need both loaded and unloaded voltages. You should expect unloaded to be somewhere between 110-120V and you want it to drop by no more than 5-6V when the car puts the charging load on it.

FWIW, the Canadain CSA defines "nominal" voltage at the service entrance (not utilization point) as 120 volts.

 

[yobigd20]

I'll go out and check with a multimeter soon. But for right now, the Tesla Mobile app is showing me 2mi/hr, 111V, 9/12A

 

[FlasherZ]

FWIW, the Canadain CSA defines "nominal" voltage at the service entrance (not utilization point) as 120 volts.

Same here, but there are older installations where you find 110/220 on old transformers... hence the Mr. Mom "220, 221, whatever it takes" line.

- - - Updated - - -

I'll go out and check with a multimeter soon. But for right now, the Tesla Mobile app is showing me 2mi/hr, 111V, 9/12A

That starts to align with what I'm thinking. My guess is that under no load you have around 115V, and that under 12A load you're dropping to 108 or so.

This could be compounded by an undersized main power feed if you have an older home. When was the home built and what is your main breaker size?

 

[yobigd20]

Home was built in 1980 and my main panel is 200 amps. I just finished wiring up the 50amp breaker and I tested it out the NEMA 14-50 receptacle outside using multimeter and looked good, plugged Tesla in and now the Tesla app is showing me 20mi/hr, 237V, 40/40A. Garage is on opposite side of house from the breaker. The run was about 100ft of 6/3 cable. (damn copper cost me $260 bucks, I wonder what an electrician would have charged for this job?). I have 180mi charged and it's showing me 2hr4min remaining so that all seems about right to me. From what others have said I'm sure I'll see that 20mi/hr go up eventually.

 

[FlasherZ]

Home was built in 1980 and my main panel is 200 amps. I just finished wiring up the 50amp breaker and I tested it out the NEMA 14-50 receptacle outside using multimeter and looked good, plugged Tesla in and now the Tesla app is showing me 20mi/hr, 237V, 40/40A. Garage is on opposite side of house from the breaker. The run was about 100ft of 6/3 cable. (damn copper cost me $260 bucks, I wonder what an electrician would have charged for this job?). I have 180mi charged and it's showing me 2hr4min remaining so that all seems about right to me. From what others have said I'm sure I'll see that 20mi/hr go up eventually.

Congratulations on joining the L2 charging club. Good to see you don't have that problem.

Mark up your parts cost by about 20-30% and add your labor at $80-100/hr for a rough reference to electrician cost...

 

[Robert.Boston]

now the Tesla app is showing me 20mi/hr, 237V, 40/40A. I'm sure I'll see that 20mi/hr go up eventually.

As has been discussed on another thread, the "mi/hr" rating appears to be based on projected miles. Screwy, unimportant measure. Just go directly to P = V * I to get your kW rate. The time to complete seems reasonably accurate.

 

[yobigd20]

As has been discussed on another thread, the "mi/hr" rating appears to be based on projected miles. Screwy, unimportant measure. Just go directly to P = V * I to get your kW rate. The time to complete seems reasonably accurate.

Yeah I read that thread this morning. So basically, the lower the mi/hr rating, the more irresponsible driver I am, right? LOL

 

[brianman]

Only skimmed the thread but in case it's helpful...

Try lowering the car to minimal (1A) setting. See if the charging is stable. If not, eep!

If the charging is stable at 1A, throttle up to 2A and wait 5 minutes. Repeat the process until you find the highest stable amperage you can use.

The first outlet I tried at home was a GFCI protected (yes, I know... ) and it was stable up to around 8A.

 

[FlasherZ]

Yup, at 120V or less voltage drop is more pronounced based on circuit length, circuit size, wire used, etc., and sometimes you don't know what the existing load is on a particular branch circuit. I probably wouldn't go amp-by-amp from 1, but would likely recommend the half-by-half approach -- start in the middle and based on indications, move by half the difference until you get to the one-amp increments.

 

[yobigd20]

Only skimmed the thread but in case it's helpful...

Try lowering the car to minimal (1A) setting. See if the charging is stable. If not, eep!

If the charging is stable at 1A, throttle up to 2A and wait 5 minutes. Repeat the process until you find the highest stable amperage you can use.

The first outlet I tried at home was a GFCI protected (yes, I know... ) and it was stable up to around 8A.

clearly you skimmed the thread, LOL. This is not an issue for me anymore anyway. But to comment, yes actually I did figure that part out myself. I started at 5A, that worked, then up to 9A, and it seemed stable there. When I went to 10A, it would kick back to 0A and not charge. So 9A was stable for me. BUT, I finished my 240V 50amp NEMA 14-50 yesterday, so all is good now charging at 40A.

 

[brianman]

@yobigd20 - Excellent. Life before 14-50R was very range-apprehensive for me.