What kind of extension cord can be used for charging my 2017 Prius Prime?

The internal car charger is the charger, so I don’t know what the evse can do to lower the charging rate.
I am thinking the 12 amps on the Toyota evse is the design limit rating.

 

Level 1 charging is precisely set to 12.00 A regardless of the voltage. This is to protect the 15-A circuits in North America. You can set it to 8.00 A if you like.

Level 2 charging is different if it is done by a Level 2 EVSE. The current will be higher to meet the kW-rating of the charger in the car.

The OEM EVSE is capable of 240 V using a plug adapter (even though not officially and Toyota does not allow it), but the current will still be limited to 12.00 A with the OEM EVSE when plugged in to a 240-V outlet.

The current is controlled by the charger in the car. There is a communication between the charger and and EVSE through the control-pilot and proximity-pilot pins of the charging plug, and the charger will set the current to 12.00 A (or, optionally, 8.00 A), if the EVSE tells it that it is a Level 1 EVSE, such as in the case of the OEM EVSE.

It looks like the resistor in the proximity-pilot pin is what signals the current capability of the EVSE, which would be 1.5 kΩ and 13 A, respectively, for the OEM EVSE, with the car charger setting the actual current to 12.00 A (or, optionally, 8.00 A) when 1.5 kΩ is detected.

SAE J1772 pins: control pilot—Wikipedia
SAE J1772 pins: proximity pilot—Wikipedia

 

I know this and gave an example in my post. At 100 volts the 12 amps is 1.2 kw., at 120v 1.44 kw. I also know you can set the onboard charger to 8 amps, if you like.

 

As Gokhan mentioned, the 12 amps is set to fit North American 15 amp circuits, under National Electric Code rules of 80% for long term loads.

My RAV4 Prime is listed as having an L2 limit of 6.6 kW. But the public J1772 charging stations have a variety of differing power ratings, both higher and lower. And watching their displays, I've seen a variety from 3.3 to 6.9 kW when charging at the station's full rate, and much lower as the car steps it down when approaching full. It is clear that there is a negotiation process happening between the car and the EVSE, choosing the lower of what the two components want or allow. And changing on the fly, rising when the other car on a shared station (with a combined power limit) unplugs, and falling as the battery fills.

The Prius Prime should be similar, just having a lower L2 limit a bit higher than 12 amps.

 

@ Joe Wall
Congratulations.

A noble profession.
Many extended stay hotels and other rentals cater to travel nurses and the best practice is to coordinate with the owner or manager to see where the best place to plug in your car.
This might keep you from interfering with other guests, their maintenance crews, etc while you're sleeping and charging after the night shift.

No.
Don't make this more complicated than it needs to be!!!

As mentioned by the 'plug whisperers' your car is limited to 12 amp charging - about as much as a toaster oven or a plug in hair dryer.
I was going to use a good vacuum cleaner as an example but then some electrical engineer would take us into a 3,000 word detour posting about the differences between inductive and resistive loading and how if you plug your Prius into an exterior outlet you might cause the next massive regional power outage.
Besides.
Most people use cordless vacuums these days.

SO....
It's always a good idea to read your car's owner's manual
HOWEVER (comma!)
The manual's contents have to be reviewed by their LEGAL department, and any mention of using an extension cord will cause ANY good lawyer to either salivate in anticipation of a million dollar judgement or break out in hives - depending on which side they are on.

Like I said.
Keep it simple.

You need a good quality extension cord such as the one pictured below.
12 AWG, or 12/3 (12 AWG 3 conductor.) Which they will proudly state is rated for 15 Amps.
"AWG" is American Wire Gauge and it works the same way that syringe needle gauges do.
Sometimes people in flyover country will say "12 gauge ware..." but this can be - um - 'triggering' to people who are sensitive about these kinds of things.

You can expect to pay between $50 and $75 for a proper 50' 12/3 cord and I would pay it!
The reason you don't want to cheap out on these is that a $50 extension cord is nearly always made from better materials than the $35 ones you get from Harbour Freight.
I personally would limit it to 50 feet only because 100 feet is a LOOOOOONG way to stretch a cord on someone else's property.

If you plan to be working in places where more personal property crime than is tolerated in other places - you may want to get a spare cord.
Travel nurses EARN their money for a REASON.


Good Luck!

 

Or you can do something like this to secure the extension cord to the charger.

 

I know it pulls 12 amps level 1, but the kw will vary by voltage. Last night I measured my use at a public outlet. The outlet read 120 volts unloaded, 107 volts when charging, and 1217 watts. So there must be 70 watts lost due to the charging cord as 12 amps @107 v is 1287 watts. So I am not disagreeing with Gokhan. Outlet wiring is sub standard or close to it.
On level 2 the charge rate goes to under 800 watts the last 10 minutes or so, tapering down gradually from the 3.3 at about the 20 mins to go mark. I think this is entirely internal to the onboard charger, not the ac supply box. I am not against learning otherwise.

 

Short term loads such as toasters and hair dryers can go to 100% current rating. Long term loads such as EV charging heat up the parts more, so must stick to just 80%.

Inductive vs resistive current doesn't matter to the wiring.

Shorter is always better for this, so if a 25 foot cord will work, buy a 25 footer instead of a 50.

 

Why - exactly?
12.5 amps is 12.5 amps.
If a 100-foot extension cord (I have two) is rated for 15 amperes - all day long, ALL WEEK long, what benefit would reducing the length to 25' provide except for providing a reduced trip hazard?

Are UL ratings based on a tower of lies?

PHEVS are designed to work with extension cords, and those are not an emerging technology.
I advised the OP to get a good quality cord because they have superior sheathing and (supposedly) plug connections - and the wire itself is a higher quality stranded copper - similar to the monster wire that all the kids are using in their tinnitus generators.
THAT will prevent the pitifully small heat loading up from a 12.5 ampere load from expressing itself in the cord.

Like I said in the post - people shouldn't complicate these things.

 

I have to check with my $12 watt o meter how much extension cables pull down the kilowatts at 12 amps.
Converting the neutral and hot wires on my $800 Toyota 120 volt 12 amp rated evse, to carry 13.75 amps on each wire, not doing that. Worse on G5, 14.58 amps, like ~20% over the rating.

 

Less voltage drop.

Where is this idea of 13.75 or 14.58 amps on a 12 amp EVSE coming from?

To get the Prius or RAV4 charging at 3.3 or 3.5 kW, one would not be using that Toyota 12 amp EVSE at all, but instead plugging in to a different L2 unit rated for higher current, such as all the public J1772 stations scattered around town. I'm suspecting that the EVSE hardware in nearly all these installations is built for 9.6 kW or higher, but set internally to cap to some value chosen by the installation's owner, according to their own policy or supporting infrastructure. Then the car and EVSE talk to each other, selecting a current / power rating acceptable to both.

 

The idea comes from using the Toyota evse on 240 volts. Converting it to run on 240. People do it and it apparently works on the G4 at least. I don’t believe the evse does any talking, just the car charger.

 

The protocol is the same whether the EVSE is an inline box plugged into a normal mains socket, or a dedicated charging station. And it's the same protocol in USA and Europe, despite the different physical connectors.

The EVSE declares how much current the car is allowed to draw via a PWM signal. (And presumably it shuts off the power if that's exceeded, as it indicates a fault). And when using a separate cable with a fixed charging station, current can also limited by a resistance-based indication in the cable indicating what it can handle.

My third-party charger lets you choose the current - it's got slow (6A, 1.4kW), normal (8A, 1.8kW) and fast (12A, 2.8kW for 2 hours) options. That only works because the EVSE gets to talk.

 

EVSEs very clearly talk to my RAV4, I see it every time any lower-rated EVSE, including the Toyota L1 unit run off-label at 240V, gives me less than the 6.6 kW my RAV4 can take. If it didn't, my RAV4 would be trying to suck 27.5 amps through that 12 amp Toyota unit. It very clearly does not.

I'd be very surprised if the Prius was different. (Lower trim 2021-22 RAV4 Primes were rated for 3.3 kW, same as their Prius Prime cohorts.) It is absolutely essential when charging real BEVs that can feed at higher rates, on EVSEs connected to lower capacity circuits.

I don't yet have hard data to show, but my feeling so far is that my Toyota 12 amp EVSE at 240V (2.88 kw), shows somewhat longer estimated fill times than when filling from a public station rated 3.3-3.7 kW. I'll have to collect some actual hard data sometime.

 

Good to know. I deal only with the Toyota evse and a couple others, which stick to the 12 amps on level 1, no adjustments except in the car menu. I wonder how the aftermarket evse overrides the Toyota setting in the car?
I read a good run down on the j1772 on wiki, interesting all that development was happening. Well time to charge and be happy.

 

The charger inside the car has control over how much current it pulls. It can pull a lot during bulk charging, tapering down as the battery gets close to full, according to the battery's specified charging profile.

The car's internal charger knows how much it wants to pull. As described in KMO's link, the external EVSE uses the CP pin to signal to the car how much the external side can (or is allowed to) supply. The car's charger then sets itself to draw the smaller of those numbers. (Details of how it controls input current, are a topic for a different discussion, including switch-mode power supplies and power factor controllers.)

If I am reading it right, the CP signal from the external EVSE is a 1 kHz square wave, encoded by pulse width modulation (PWM). That PWM signal tells the car the maximum current it is allowed to draw, between 6 to 80 amps, in 0.6 amp steps below 51 amps, or 2.5 amp steps above 51.

Numerous of the public charging stations I have used, display how much power they are supplying at any given moment. Some of the mobile apps will plot how much power was drawn for the entire charging, varying over time. Tapering down when near full.

When charging on a post with two cords sharing a 7.5 kW limit, I initially received 3.7 kW, the car on the other cord was getting the other half. The final plot revealed when the other car unplugged, freeing the entire 7.5 kW supply for my car, which then starting pulling its internal max of (slightly over) 6.6 kW.

 

I

Good explanation.
You probably can try a kill o watt between the toyota evse plug and your 240 adapter and measure the volts and watts on 240, up to 3840 watts or something. I see that number on mine as a high limit so assume it is for 240, but they don't want to advise using the 120 plug on 240.
But I am not advising it either, but with a probably.

 

I'm not going to risk my Kill-A-Watt on this experiment until others verify survival.

My rooftop PV system reads 244.8 V, a slight bit more stress.

 

I got one for $12. Search this on Amazon and they say its ok up to 3860 like expected as they are made to sell in other countries. I would try it but have no adapter and no need to use my 120 evse at 240 at this point. Pasting link not working.

SURAIELEC Watt Meter, Plug-in Socket Power Meter, Auto Cost Calculator, Backlit Large Display, Overload Protection, Kilowatt Wattage Voltage AMP Tester, Electricity Usage Electrical Energy Monitor

 

I purchased a 25' extension cord from Amazon and it works just fine. It's a heavy duty 12 gauge, 3 pronged (wires) extension cord. It's rated for indoor & outdoor use. It's available in 3 lengths (25, 50, 100 feet) long.

DO NOT BUY A CHEAPER LIGHTER GAUGE ONE. Here's a link to the one I bought and use.