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No longer cuts down to 30 amps... delayed start...

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SabrToothSqrl

SabrToothSqrl

Active Member
Dec 5, 2014
4,579
4,154
PA
#1
So, after fighting with my power company, and tesla, in that nothing is 'wrong' with my wiring...

And having the charge cut from 40 to 30 all the freaking time...

I now set the charge start to 10:00 PM. 40 amps.

it's been fine at the full 40 now for almost two weeks.

I always knew it was PP&L...

if it was my house it would still have the issue...

just FYI for anyone else in the same boat...
 
#3
some nights, when plugging in at 40 amps, it would cut down to 30 amps. Either within 10 min, or after an hour, or after two... or not all.

All random and annoying as f___ because you'd have to unplug, replug, and crank it back up. Weeks of calling and yelling at Tesla, and PP&L (power company). Who installed a 'monitor' to verify I had 240v... well they gave me a 8.5" x 11" PDF of a MONTH of voltage levels. all "within spec"...

Magic how when I start at 10 PM it holds 40 amps just fine... validating that my outlet and house wiring are just fine. Else it would kick down..

I'm hoping when we have two cars sucking down power we can bend that voltage so low, it forces PPL to do something to improve service.

It's not a theory :) It's correct, you are on the same grid as your neighbors... who are running A/C dryers, ovens, heat pumps, hot tubs, TVs, who knows... I may play with they start time to 9 PM just for fun, but so far 10PM works for me...
 
#4
The other alternative to moving your start time around is to lower your amperage. That usually works for most people. The heavy draw of 40A is pulling hard on the voltage. Turning it down to 35-36 or so will probably keep it up a couple volts higher and give enough margin that it won't trip the safety lowering thing. Yeah, I know, lowering the amps is not what you wanted to hear, but 35 is still higher than 30.
 
  • Informative
Reactions: linkster
#5
I had a problem charging the other morning. I have a 2X 50A breaker that feeds a subpanel with the 2X40A for the UMC outlet but I also have a couple of 15 and 20A breakers for other stuff on the sub panel. I think when I have a big load on the 15/20's it makes the 240 unbalanced and my UMC doesn't work at all, not even dropped to 30A.
 
#6
I think the OP has just shifted to a time period when his utility has fewer demands and thus less voltage sag.

The root problem is more likely the UMC in that when the voltage sags, the current will increase to deliver the same power to the charger (which really doesn't care too much about volts or amps, it just wants power). The UMC is only rated for 40a so I suspect the sagging voltage pushes up the current over 40a which causes the UMC to tell the controller in the car to stop charging or lower the current (really lowering the power demand).

For example, I charge a Tesla and BMW i3 off the same panel/meter at the same time (and my house panel/meter is on the same wire from the utility pole). The Tesla HPWC is charging at 80a and the voltage will sag a bit from 245 to 242 with a load. The i3 wants to draw about 7.2kW which is normally just under 30a, but when the Tesla is drawing 80a and the voltage sags a bit, the amperage to the i3 climbs to 30.x (as reported by the EVSE). This is not a problem because the i3 EVSE is a Juicebox rated for 40a.

I don't think the power company will ever do anything about sagging voltage, I suspect their spec sags way down towards 220v or even 215v. I used to get "220" for my boat a few blocks from my house and it was normally more like 210v.

Now maybe the OP can get a TOU program from the utility and get lower rates by charging at night!
 
#7
Here in PA, power is about $0.113 (whole bill) kWh

Any time of use stuff I've seen actually costs a lot more.

I currently pay $0.535 kWh generation

Still no issues w/the 10 PM start. holds 40 amps for the whole charge. I did try 35 before, it wouldn't hold that, and would always cut to 30.

When my wife gets her 3, I guess we will tell it to charge about midnight or 1 AM. Still more than enough time.

or, is 30 amps better for the battery anyway? I guess I could just do 30 at home... but that always makes me think something is 'wrong', when it's just PP&L...
 
#8
I've had this occur randomly, since I got the MS last year. My incoming voltage is always high, as it generally runs 252-256, so I am convinced that it's not a magic number at which the current is derated. It's most likely some percent of voltage sag, from the starting voltage.

I think there's likely a number of factors at play, which all lead up to the car sensing too much voltage drop; some of which could be related to the utility's distribution, but also certainly related to the service entrance cabling and wiring in your house. All wires act like resistors and create some voltage drop...the more current pushed through the wires and the longer and smaller the wire gauge, the larger the voltage drop. I suspect that it's the coincidence of something else kicking on (ie. A/C, refrigerator compressor, etc.) that causes an increased momentary voltage sag which trips the charging minimum threshold (or maximum allowable voltage drop).

Honestly, I just think it's one of those things that we'll have to live with for a while. It's there for a good reason (to prevent overloading circuits), but with only one value to monitor, is very difficult to discriminate nuisance trips.
 
#9
Zextraterrestrial said:
I had a problem charging the other morning. I have a 2X 50A breaker that feeds a subpanel with the 2X40A for the UMC outlet but I also have a couple of 15 and 20A breakers for other stuff on the sub panel. I think when I have a big load on the 15/20's it makes the 240 unbalanced and my UMC doesn't work at all, not even dropped to 30A.
Click to expand...

I see the badges on your account that you have been to Tesla Connect in 2013, 2014, and 2015, which even includes when it was called Teslive, so you’re not a new guy. So it surprises me a little bit that you have what seems to be an install that violates code.

“I have a 2X 50A breaker that feeds a subpanel with the 2X40A for the UMC outlet but I also have a couple of 15 and 20A breakers for other stuff on the sub panel.”

The 75A worth of circuits being run from a 50A subpanel may be OK, depending on load calculation. It’s the outlet that is wrong. You say that is a 40A breaker for the UMC outlet. There is no 40A NEMA outlet type, so I am wondering what you have. There is a special exception in NEC because of this lack of some outlet types. If you have something like a stove that is specifically marked as a 40A appliance, then you are allowed to use a 40A breaker with a 50A outlet type. But since the UMC is specifically marked as a 50A device, and the install instructions (which NEC requires you to follow) say it needs a 50A breaker, that exception doesn’t apply and that install is in violation of code.
 
#12
The cut to 30A happens to me frequently as well. One of these times it is going to bite me - if the car hasn't completed charging by morning when I have to head out. I emailed Tesla, but they haven't offered a solution. I also suspect that it may be related to a slight voltage sag when my (and my neighbors) A/C's come on at night after my car begins charging. I haven't contacted my utility as yet to see if they can monitor my voltage. If the sag is only a few volts, I doubt the utility would do anything.
 
#13
jf2go said:
The cut to 30A happens to me frequently as well. One of these times it is going to bite me - if the car hasn't completed charging by morning when I have to head out. I emailed Tesla, but they haven't offered a solution. I also suspect that it may be related to a slight voltage sag when my (and my neighbors) A/C's come on at night after my car begins charging. I haven't contacted my utility as yet to see if they can monitor my voltage. If the sag is only a few volts, I doubt the utility would do anything.
Click to expand...
The localized voltage sag is likely totally independent of the utility's infrastructure. This all depends on where your transformer (and if it's shared with your neighbor) and the sizing (length, gauge, and material) of the incoming secondary feeders running from the transformer to your house. Depending on how things are handled with your utility, they may consider that everything beyond the transformer is "your property" - in which case, they are only responsible to provide you with x voltage at the transformer's secondary terminations. Otherwise, you may have a meter socket installed on the side of your house, and the utility may "own" everything up to that meter socket. In this case, if your secondary feeders were undersized for the load, they could possibly be willing to do something about it.

You can find some online calculators that are helpful to understand this a little better.... Voltage Drop Calculator

In my experience, the 40 -> 30 amp charge reduction only occurs about once every few weeks and hasn't been a major issue. I have my charge scheduled to end about 30-60 minutes before I usually leave in the morning, which provides a buffer in case this happens.
 
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#14
I saw my charge rate drop from 79 amps on a regular basis. This began after an early software update (forget which one) that added detection against 'faulty wiring'. In my case, as the car started to charge, the voltage would drop from 240 to as much as 218. This drop triggered the car to reduce the charge rate. I had our power utility come and check the situation but they happened to come when I was not home with the car. Their test of the line showed everything within spec. Eventually I persuaded them to come again to test while the car was placing a load on the line. Sure enough, they could see the problem. The solution was to add a new transformer on our street. There were simply too many homes getting power from one transformer. Charging is now 100% reliable.
 
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