Leave UMC plugged in?

Leave UMC plugged in?

Do a lot of you all leave your UMC plugged in even when it's not in use? Anyone know how much power it draws just being pluged into the wall, but not connected to the car? | July 9, 2013

I leave it plugged in all the time and hanging on the wall. Do not know if it draws any power when not plugged into the car.

Bob W | July 9, 2013

The UMC draws only a tiny amount of power when when it is not connected to the car, so there's no reason to unplug it unless you're going to need a UMC at your destination.

Using a Kill-A-Watt meter and the 110V adapter, I just measured 0 W, 1 VA, which is as low as this device can measure. That's less than 1/117th of an amp. (<9 milli-amps). The UMC is only drawing enough current to power one chip and one LED.

olanmills | July 9, 2013

I unplug it since at least for me, the place it's located, it only takes me another second to plug/unplug it.

It definitely draws some power (the green light stays on), and also, it's a little more secure from damage should a power surge or something happen.

olanmills | July 9, 2013

Well dang, as Bob pointed out, it draws almost nothing apparently. I wonder if that's true regardless of what outlet it's plugged into. Anyways, I'll have the last laugh because when I die, I'll be $5 richer than all of you fools who leave it plugged in.

ORWA | July 9, 2013

I throw the 50 amp circuit breaker and just leave it plugged into the wall. Anyone see a problem with this method?

olanmills | July 9, 2013

I dunno, is it bad to flip the breaker so frequently? Maybe it will wear out or something? Or is there any danger of like a "mini power surge" every time you flip it back on.

nickjhowe | July 9, 2013

I leave it plugged in. Six months in no issues, and as per Bob W it draws essentially zero watts when not in use.

jbunn | July 9, 2013

Safer to leave it plugged in. Fingers are too close to the contacts on nema end.

ir | July 9, 2013

I leave one plugged in. Wearing out the socket or breaker = expensive visit from the electrician.

The other stays in the car.

Byong | July 10, 2013

So, looking at the kickstarter for a spare charger, so planning on leaving the Tesla UMC plugged into the wall and keeping the spare sharger in the car. Does anyone know a source for the Tesla charging plug? since the kickstarter is customizable, I was hoping to forego the J1772 plug if I can find a Tesla plug.

PaceyWhitter | July 10, 2013

The only thing constantly plugging and unplugging your UMC will do is wear out the 14-50 socket.

While they are not expensive, I wouldn't want to have to replace it unnecessarily.

Brian H | July 10, 2013

?? The charger is built into the car. The other requirements are a) a plug, and b) a suitable cable and plug. The purpose of a J1772 adapter is to enable use of public stations.

hamer | July 10, 2013

I don't usually leave it plugged in because there is always the possibility that I might want to charge some place other than my garage, and I don't want to accidentally go on a trip and leave it in my garage only to find out when I get there that I have no UMC.

I did that once and the nice Tesla owner who lived near my father-in-law was nice enough to let me use his.

And I'm not going spend $650 on a spare

Byong | July 10, 2013

@Brian: The kickstarter is for a L2 EVSE

Which looks like I the base model would be very similar to the UMC, but only cost me $99 + cables/connectors. J1772 connectors and cables seem very expensive, so looking at $250-$300 after it's all said and done, but thinking why go with J1772 connector if I'm only using it for a tesla.

Brian H | July 10, 2013

Charging stations are not relevant. The MS needs a 240V plug to get 40A, not a station.

Byong | July 10, 2013

My point is that I would like to have 2 UMC's one for my garage, and one for my trunk. Since I don't want to spend $650 for another UMC, figured this EVSE would be good enough. I'm pretty sure you can't just take a J1772 connector and wire it directly to a 14-50 outlet, otherwise, the UMC would be just a wire. There must be Relays and sensors inside to insure power doesn't go to the J1772 unless it's connected to the car, so this sounds like a reasonable solution.

Bob W | July 10, 2013


So are you going to put this homebrew Kickstarter EVSE in your garage and keep the UMC in your Model S, or vice versa?

Wouldn't it just be easier / cheaper to keep the UMC in your garage (even on a dryer plug), but keep the J1772 adapter with you in the car at all times, and use public chargers like Chargepoint to supply the J1772 cable? It's usually much easier to find J1772 charging stations than to find 240V 30A outlets in some friend's garage.

I mean, if your other car is a Nissan Leaf, than sure, a $300 EVSE in the garage makes sense. But if your only EV is a Model S, then I don't understand the compelling reason to buy a Kickstarter EVSE. You still have to plug it in to 240V somewhere to get decent charging speed.

docdac | July 10, 2013

My electrician advised me to leave it plugged in. He indicated that the NEMA 14-50 outlets are not designed for frequent plugging/unplugging and would wear out after a couple of years. Not a big expense to replace if you DIY, but with electrian charges it would be cheaper to leave plugged it. Throwing the 50A breaker doesn't seem like a bad idea if it is conveniently located - I would not expect the breaker to wear out (but I could be wrong!). The electric power to leave it plugged it seems trivial to me, though.

Bob W | July 10, 2013

Some circuit breakers are rated for high endurance use, but many are not.

According to this reference, if you intend to use a 40A circuit breaker on a regular basis, like a light switch, it should have an "HID" marking to ensure that it is suitable for such applications.

ramtaz | July 10, 2013

TESLA SERVICE MANAGER advised to leave the UMC plugged.

Byong | July 10, 2013

@Bob: I would likely charge at work as well as at home, hence, want to keep one in the car. We do have a 220 outlet at work. I plan on keeping the adapter in the car as well, so if there is a public charger, that would be fine as well. Guess I'll stick to the J1772 standard.

KendallPB | July 10, 2013

I left my 6-50 plugged in the whole time I used it, until the HPWC finally arrived and was installed. If I were still using the UMC, I'd leave it plugged in.

jagman_55 | December 27, 2015

Anyone know where I can get a 6-8 foot Cable for my 2014 Model S 60 to charge my car in my garage so I can leave my Tesla cable in the car so I don't forget it?
If I can find a 6-8 foot cable, with Tesla UMC plug on one end, and the recommended NEMA 14-50 MALE, for my wall connector, would just leave this in the garage and not worry about it. And it is not fun removing the 14-50 all the time, rolling up the cable........
I can get the Tesla UMC plug but only has a 9" pigtail.

Tola | December 28, 2015

Not sure why you are focused on a shorter cable. Why not do as most do in your situation and buy a second UMC?

jordanrichard | December 28, 2015

paulnevin30, and that has to do with the subject at hand, how.......?

jagman, it would be far safer to buy an extra UMC kit versus fabricating your own cable. | December 28, 2015

I use only a single UMC and leave it in the garage 99% of the time. On long trips I do move it into the car.

Of course on one 1000 mile trip I forgot it until I was 100 miles away. I pressed on anyway. I only used Superchargers and never needed the UMC. Still not smart to leave on a long trip without one. I do keep the J1772 adapter in the car, so I could have used an L2 charger if I had really got in a bind.

P.S. I've never run out of electrons in 3 years!

I agree with others, if you feel you need two UMCs, buy a second one from Tesla.

SUN 2 DRV | December 28, 2015

An even better idea is to buy the Wall Charger instead of a second UMC.

Lots of advantages to the Wall Charger for only a very slight increase in cost. And of course the Wall Charger works on any size circuit including the circuit feeding your existing 14-50 outlet.