Thoughts on Using Piggy Back Adapter

[sgmstr]

Hello - Have 220V 40amps Nema 14-50 receptable. I currently use this piggy back adapter (AC WORKS 1 ft. 50 Amp 14-50 Piggy-Back Plug to Household 15/20 Amp Connector Adapter Cord PB1450520 - The Home Depot). Nema 14-50 (220V) is rated for 50amps and Nema 5-20 (110v) is rated for 15/20 amps. I am currently using one end of Nema 5-20 for my refrigerator which draws 10 amps.

I'm wondering if it sounds reasonable to connect Nema 14-50 to the Model Y Mobile Connector and set charging current below 22 AMP (max 22 amps for Tesla and 10 amps for refrigerator) so the combined currents do not exceed 80% of 40amp my receptable is rated at.

The owner's manual (https://www.tesla.com/sites/default...bile_connector_owners_manual_32_amp_en_US.pdf) warns against:

1) "Do not use an extension cord, a multi-outlet adapter, a multi-plug, a conversion plug, or a power strip to plug in the Mobile Connector."
2) "If possible, use a dedicated receptacle with a single socket. If the receptacle has two sockets, do not plug any other items into the other socket."

Although there are warnings above, I see people using extension cords to charge their Teslas (using the appropriate gauge extension cords), for example. I'm wondering if I should be concerned about my set up. I welcome any suggestions or comments.

 

[davewill]

If this were an opportunity kind of thing at a relative's house or something, I'd say go for it. However, for daily charging, I say no. Instead you should run a new circuit. Run one for the fridge if this outlet is convenient for charging, otherwise, run a new charging circuit.

Setting the amperage lower in the car works great until a software update or the vagarities of GPS cause the car to forget and charge at full power. Also, each extra adapter is a chance for failure or overheating.

 

[Rocky_H]

I'll second what @davewill mentioned. If it's a one-off, sure, you set it up and pick the amps for that session, and you would be OK. But the memorized amp setting depends on accurate GPS position to know it's at your house, so that may not always be reliable. My car again last night with some rainy overcast skies couldn't get a very solid GPS signal, so it thought my car was a few blocks away in my subdivision and didn't pick up the location right to use my saved amp setting. So don't depend on that as a 100% reliable thing.

 

[Mrbrock]

Simple solution if you don't want to deal with changing settings in your car:

Buy the Tesla Nema 14-30 adapter for the mobile connector (this will automatically set your car to 24A charging) https://shop.tesla.com/product/gen-2-nema-adapters

Then a 14-30R to 14-50P adapter https://smile.amazon.com/ONETAK-Compact-Receptacle-Generator-Connector/dp/B08B66MB4J

Now you will have 24A charging + 16A available for your fridge. It is not a continuous load so I don't believe you need to stay under 32A total on the circuit (someone with more knowledge, please verify this).

Regarding the manual, I have a 10-30 adapter for the mobile connector that I then plug into TT-30 and L15-30R adapters, neither of which are supported through Tesla branded adapters so these go against the rules of the manual in terms of not using adapters. This rule is to prevent people using the wrong adapters. As long as all the pieces in the chain meet code and contain the proper safety devices (the Tesla 10-30 adapter with temperature sensor means I can plug it into any 30A or higher outlet of 120-240V single or 3 phase as long as the secondary adapter is wired properly and it won't draw more than 24A) then there aren't any issues with using them. Using my 10-30 adapter with another adapter to plug into a 15A or 20A outlet will cause it to trip without changing settings in the car so using adapters with lower rated outlets should be avoided at all costs (i.e. a 14-50R to 14-30P adapter would allow your mobile connector with 14-50P to draw 32A continuous on a 30A rated circuit, 24A continuous, a big no no).

 

[Rocky_H]

That's a good thing to bring up that maybe you weren't aware of. The Tesla plug adapters for the charging cord have chips in them that create a signal of the proper maximum allowable amps for that plug type. So that is a much more foolproof way to set an amp limit if you have to, rather than remembering to dial it down on the car's screen and hoping it gets the GPS position consistently right.

So if you want to plug adapt a Tesla 10-30 or 14-30 to some other thing, it will signal the car to have a 24A limit.