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Questions about charging at 120v block heater outlets

Rocky_H

Well-Known Member
Feb 19, 2015
8,569
11,119
Boise, ID
I'm not sure what you mean by "50% duty cycled". Do you mean there is actually a timed switch inline with the circuit that makes the circuit live and disconnected for alternating periods of time?
1. If the power cuts off like that, I think it will automatically resume charging when the power comes back on, but I'm not totally sure.
2. It won't mess with the battery, but if charging doesn't resume, the UMC and/or charging system may think the circuit is unreliable and be sitting there waiting for you to tell it that it is OK to start charging again.
Anyone confirm how that behaves from a power interruption?
 

mknox

Well-Known Member
Aug 7, 2012
10,104
1,900
Toronto, ON
One thing to be aware of with block heater outlets is that the voltage is not always "reliable". When all you're doing is powering a resistive heater, concern for a nice even 120 volts is not a high priority. I believe there are even some block heating systems that manage loads across numerous vehicles in a parking lot by throttling the voltage. Not 100% sure on that last point, but I recall seeing something about this for shopping centers and other large parking lots some time ago.
 

Duma

Member
Nov 16, 2014
169
72
I wouldn't worry too much about other cars plugged into the circuit. The only time other cars will plug in for the block heater will be in winter. In winter there is no point to trying to charge a Model S on 120 V because all the energy gets diverted to heating the battery rather than charging. In other seasons, might be helpful to have a trickle charge to add a few miles overnight.

(Whether it is worth plugging in to keep the battery somewhat warm on a very cold night is a different question.)
 
...and it could be an "intelligent" block heater plug as well. Many of these are being installed - they won't function above 40 F, 4C. See: https://www.iplc.com/files/IPLC_Fleet.pdf . Great for block heaters, not so great for charging.
Thanks for all the responses. The block heaters near work and home are both older style and they do have power all the time (tested with a multimeter).
 

efusco

Moderator - Model S & X forums
Moderator
I wouldn't worry too much about other cars plugged into the circuit. The only time other cars will plug in for the block heater will be in winter. In winter there is no point to trying to charge a Model S on 120 V because all the energy gets diverted to heating the battery rather than charging. In other seasons, might be helpful to have a trickle charge to add a few miles overnight.

(Whether it is worth plugging in to keep the battery somewhat warm on a very cold night is a different question.)

I'd argue that that is the very best time to keep the S plugged in. I use a 120v at work in the winter all the time for that very reason. I still get at least 2-3 miles/hr of range AND the battery is much warmer, I'm able to operate at nearly full power instead of being power and regen limited as it would be if I let it cold soak for the entire 9 hours of my shift. I plug in in the warm weather just because I can, but the benefit is minimal other than a few cents worth of free juice.
 

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