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Power Joiner Step


Marginally-Known Member
Mar 28, 2015
Houston, TX
Thoughts on this??

Power Joiner Step Up Inverter Electric Car Charger Converts Dual 20amp 120volt Outlets To 240volt

Looks interesting and was thinking about doing something like this myself for when I visit the relatives over the holidays :) Certainly not to code but is electrically equivalent to a Nema 14-50 that is hardwired. Given the gage of the wires you probably wouldn't want to pull more than 30 Amps..

The device is obviously not to code, but neither are the various extension cords that I've sometimes used to charge (that convert 14-30 to 14-50, for example). It's safe to use to charge the car as long as you carefully follow some rules:

1. You must test each outlet you intend to use the device on with one of the pictured outlet testers to make sure the outlet is wired correctly. Standard 120V devices are somewhat tolerant of mis-wired outlets, but this device is not. Both of the outlets you intend to use have to pass the outlet tester's tests.

2. This device cannot be used with GFCI-protected outlets, it will immediately cause them to trip. Be aware that some outlets are GFCI-protected even though that outlet itself doesn't have the GFCI protective circuit in it (i.e. no "Test" or "Reset" button). The protection device for these outlets may be in another outlet on the circuit or the entire circuit may be protected with a GFCI breaker in the panel. In all of these circumstances, this device cannot be used with those circuits or outlets.

3. Once you plug the device in, you have to press the test button to make sure that the two selected 120V outlets are on different phases. The light will light up green if they are -- it won't light at all if they're not. By definition, outlets on different phases are on different circuits, so if the light comes on green, you're good. If it doesn't come on, you have to move one of the extension cords to a different outlet, and it has to be checked with the tester as in #1 before you plug in.

4. You must set the current limit in the car manually. The limit will be either 12A (if one or both outlets are on 15A circuits), or 16A (only if BOTH outlets are on 20A circuits). You can identify the current rating of the circuit on each outlet by looking at the receptacle's slots. 15A circuits use outlets with straight vertical slots. 20A circuits will have one of the slots capable of taking a horizontal prong -- the slot will be a sideways "T" shape.

Having said all that, you need to determine if this device is really worth it.

1. If you have to set the current limit to 12A, the charge rate is 2.8 kW, or only about 8 miles/hour. Current limit of 16A has a charge rate of 3.8 kW, or only about 10.5 miles/hour.

2. By comparison, a plain public J1772 will do 6.2 kW for 17 miles/hour.

3. Even just using a 14-30 dryer plug and extension cord will get you 5.7 kW for 16 miles/hour.

4. 14-50R to 14-30P adapter plus a 50' 14-50 extension cord will cost less than this device.
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