How much voltage sag do you get when charging.?

[Riceball777]

I have a wall connector and I charge at 48amps. Voltage reads about 242-244 volts at the beginning about 1-5amps. During 48amps charging voltage is between 232-234 volts. So I have about a 10-12volts of voltage sag at 48amps. Is this pretty normal? Any way to lower voltage sag? Maybe run 4 gage wires instead of 6gauge to the wall connector? How much is too much voltage sag?

What’s your voltage when charging at 48amps?

 

[dafish]

Seems high. I'd assume something is getting hot, but of course you didn't show you run length.

Voltage Drop Calculator | Southwire

www.southwire.com

Might start by opening it all up and making sure connections are tight and right.

 

[DCGOO]

I have a wall connector and I charge at 48amps. Voltage reads about 242-244 volts at the beginning about 1-5amps. During 48amps charging voltage is between 232-234 volts. So I have about a 10-12volts of voltage sag at 48amps. Is this pretty normal? Any way to lower voltage sag? Maybe run 4 gage wires instead of 6gauge to the wall connector? How much is too much voltage sag?

What’s your voltage when charging at 48amps?

In my case, typically between 230-240. When not charging, typical is 250. It depends a lot on how your house is fed. If your utility is an arial drop from utility poles, the drop will be larger, because 200 amp service is typically delivered with AWG 2 gauge wire with higher loss. If you have buried service, you probably have 2/0 to 4/0 cable in a pipe, to reduce heating, which also provides less loss. But it doesn't really matter that much, because the car will charge fine with nearly any voltage applied.

You can run larger wire if you want. But most of the drop may be happening before it gets to your panel. To check, simply measure the voltage at your electrical panel while the car is charging. Picking up a volt or two is unlikely to make a noticeable difference.

 

[Genie]

Any way to lower voltage sag?

Easy, lower your charging current
10V drop x 48A = .48kW loss
(estimate) 5V drop x 24A= .12kW loss
The loss being resistive heat in the circuit

 

[DCGOO]

Easy, lower your charging current
10V drop x 48A = .48kW loss
(estimate) 5V drop x 24A= .12kW loss
The loss being resistive heat in the circuit

It should also be mentioned, this is perfectly normal and expected. There is really no need to reduce the voltage sag at all. While the word "loss" is often used, it is not an actual loss. Simply a slightly lower consumption, due to the voltage drop across the link to your utility.

The electric utility could reduce the voltage drop by using larger cable. But larger cable is far heavier, making it difficult to span the distance from the pole to your house. 2 gauge wire hanging out in the breeze can readily dissipate any extra heat generated by the increased resistance. Chances are good, your drop is made from aluminum wire anyway, because it is lighter, although aluminum causes somewhat greater voltage drop. Still all normal and expected.

 

[Benito1283]

You don't mention the length of run, but I second the latter responses. Seems normal and likely nothing to worry about. You'd probably never recoup the losses by putting in heavier gauge wire.

 

[bobbi_dooley]

Easy, lower your charging current
10V drop x 48A = .48kW loss
(estimate) 5V drop x 24A= .12kW loss
The loss being resistive heat in the circuit

But since they’ll now be charging twice as long the savings aren’t quite as dramatic. Although cooler equipment should last longer so there’s that.

 

[Genie]

But since they’ll now be charging twice as long the savings aren’t quite as dramatic. Although cooler equipment should last longer so there’s that.

It’s just pennies really, like turning off a light during the day. But saving pennies got me a Model X

 

[mr10012]

It should also be mentioned, this is perfectly normal and expected. There is really no need to reduce the voltage sag at all. While the word "loss" is often used, it is not an actual loss. Simply a slightly lower consumption, due to the voltage drop across the link to your utility.

The electric utility could reduce the voltage drop by using larger cable. But larger cable is far heavier, making it difficult to span the distance from the pole to your house. 2 gauge wire hanging out in the breeze can readily dissipate any extra heat generated by the increased resistance. Chances are good, your drop is made from aluminum wire anyway, because it is lighter, although aluminum causes somewhat greater voltage drop. Still all normal and expected.

FWIW, I have 3-phase 600-amp (3 x 200) service (buried, this is Manhattan) and I see a drop from 206V at min current to 193-200 (depending on time of day) at 40A. Almost all of it utility-induced (the incoming voltage is about the same as what the car reports). Once in the middle of the night I had 204V at 40A. So it seems to depend on what other demands the utility has...

 

[Riceball777]

Seems high. I'd assume something is getting hot, but of course you didn't show you run length.

Voltage Drop Calculator | Southwire

www.southwire.com

Might start by opening it all up and making sure connections are tight and right.

run is very short. The wall connector is less than 10 feet away from the breaker box

 

[Riceball777]

it seems like a 10-15 volts of voltage sag when charging at 48amps is pretty normal. What is everyones else voltage at and at what charge rate? if i lower the charge rate to 40amps the voltage sag is about 2-3less at about 235 volts and at 32 amps charge rate voltage is about 238volts and at 24amps i'm at 240volts

 

[dafish]

Again: Seems high.

My home, for reference:

249 @ ~600 watt load​

245V @ ~15.5 - 16.3KW (no voltage change between the loads)​

Assuming a 1.0 power factor that's 2.4 amps at baseline to 67 amps (all I could easily pull). Let's call it 65 amps of additional load over 4 volts lost.

The volts are right from an open 14-50. The current is at the panel. Seems to put "nope" to the conversation that it's related to the service from the pole. BTW, I'm aerial to the yard, below ground to the house, on only 200 amp service. I guess some folks, DCGOO as an example, consider roughly 20 volts of sag normal. I can only say it would be mighty darn odd in this house, but we all live in different area's and homes, so...

I'd bet your power company would be happy to send a guy to check your voltage at the meter at any amperage draw you want to present. Mind you I've already told you I'd check your connections, but if the power company guys confirms the sag is not to the meter you don't really have much left to consider. And at 10' it's going to be connections.

All this said I'm not an electrician. Having done what I can to help I'll respectfully bow out and wish you well.

atb,
-d

 

[appleguru]

I see maybe a 1-2v drop at most while charging, even with both EVs going at a full 48A. (With no load I usually see around 252V; under load it drops to 249-250V or so… a bit high!)

Our wiring is probably a bit oversized for the load though:

We have a 100kVA transformer across the street… it feeds our meter socket underground with approx 100ft of 500MCM copper. From there, we have about 5ft of 4/0 AL SEU to a disconnect, another 5ft of 4/0 AL SER to a main panel, about 80ft of 4/0 AL SER to a subpanel in the garage (which pretty much only has the EVSE loads on it), and then about 20ft of #6 copper THWN2 to the HPWC.

With that said, our setup is not normal. I’ve seen plenty of undersized utility feeders that often cause significant voltage drop under load (eg, #4 or #6 solid aluminum wire used for 200A service by the utility… its pretty comical mating a #4 wire to a 4/0 wire . Utilities play by different rules though/NEC does not apply… but most will update the loop wiring to something more reasonably sized if they’re out doing other work that requires a disconnect and/or if you’re having issues).

 

[Sophias_dad]

If you are comfortable in your main panel, measure the voltage at the input lugs to the panel while your car is using the 48A, and compare that to what your car is reporting. That'll tell you if the losses are something you can do something about or not. If its outside your house(therefore the input voltage to your home is dropping to 235V or something) there's really nothing you can or should do about it. The utility isn't going to be interested in fixing a few percent drop under load AND you aren't even getting billed for it(!). TBH, you are only seeing a 4.2% loss anyway.

I did have our utility come out and check when our voltage was regularly dropping below 220V and they replaced our transformer, which I think was only serving three houses. I vaguely recall they only get interested when they are consistently more than 5% off the 240 target and get really interested at 10%.

 

[DCGOO]

I'd bet your power company would be happy to send a guy to check your voltage at the meter at any amperage draw you want to present. Mind you I've already told you I'd check your connections, but if the power company guys confirms the sag is not to the meter you don't really have much left to consider. And at 10' it's going to be connections.

Most electric utilities can read the voltage remotely. So unlikely they would need to roll a truck.

 

[Riceball777]

I have an old nema 10-30 outlet in my garage that I don’t really use so I just use it to check the voltage. When my car is not charging it ready s about wr2 volts and when my car is charging at 48amps my nema 10-30 outlet reads 237colts. and my car reads 233volts. House was build in 1989 and has a 200amp service.

 

[Sophias_dad]

I have an old nema 10-30 outlet in my garage that I don’t really use so I just use it to check the voltage. When my car is not charging it ready s about wr2 volts and when my car is charging at 48amps my nema 10-30 outlet reads 237colts. and my car reads 233volts. House was build in 1989 and has a 200amp service.

So you are losing 4 volts due to resistance. 1.7% is well within even the recommended 3% loss of a branch circuit. Nothing needs to be done,

 

[ATPMSD]

Maybe run 4 gage wires instead of 6gauge t

If the wire you have is #6 Romex you are exceeding the wire’s continuous load rating. You should change the wall connector setting from a 60a circuit to 50a, or replace the wire.

 

[John in LB]

In terms of energy losses that matter to you: It's the difference in voltage between the utility meter and the car charger that counts. That voltage drop times the amperage is energy wasted and that you are paying for while the car is charging.

For example, I have a 6 volt drop at 48 amps - hence, 288W per hour is being wasted as heat in the wiring. This is 0.3kwh for each hour the car is charging that we are being charged for by the utility.

 

[EVSak]

I have a 48A Enel Juicebox wall charger, with about a 15' run from my electrical panel. I also cant park my car close to the charger, so had to purchase this Lectron 40' extension cable (Lectron J1772 EV Extension Cord | 40 ft). When charging at 48A, the Tesla app shows a charging voltage of 231-232v. If I dial back to 40A, which the cable says its rated for, I'm at 233-234v. At 24A I'm at 236-238v (but who wants to charge at 24A if I have a 48A charger?).

My cost of electricity is pretty low so I'm not really concerned about the loss of a few cents. Main question is: Is it detrimental to my 2023 Model Y LR (or my new Rivian R1S) to be charging at a voltage between 231(@48A)-233(@40A)?

Is ambient temperature of the cable and car also a factor in the voltage at the car? At what point is the voltage too low that it would result in damage to the car/battery?