# Forums

## 20 mile daily commute: do I need HPWC?

My daily drive to work is only 7 or 8 miles. At lunch I typically go somewhere close by to eat. So an average daily commute for me is only about 20 miles. The Tesla website suggests I would be fine just plugging into the 110 V outlet in my garage. What have other people with low mileage commutes found? Is it OK to get the car without the HPWC?

stsanford | 8 agosto 2013

I have a 60 and routinely do 100-130 miles in a day, sometimes 180.
The longest my car has charged is 5 hours.

The other day, I had drained the battery down to 30 miles, had to do a 50 mile loop after work, so I came home, plugged in for a half hour into my NEMA 14-50 and was good to go... (8 miles left at the end , the closest I have ever pushed it).

PBEndo | 8 agosto 2013

Yes you definitely need the HPWC. As a matter of fact, you should buy mine!

So far it is the only thing I wouldn't buy if I had it to do over again. 9000 miles total with an 80 mile commute and I haven't had an occasion where it made a difference yet.

jat | 8 agosto 2013

@pbendo - how much do you want for it? :)

david.cheney | 8 agosto 2013

@jat

"125V * 12A * .86 / 265 Wh/mi = 4.87 ideal mi/hr"

Here is how I am interpreting these numbers: The 5m/h charge claim is at 110v, not 125, an immediate > 10% difference. The .86 is represents the 13% Amped mentioned, right?

265 Wh/mi is indeed roughly an ideal ("minimal") cost per mile driven - I am running just over 300.

But how is Wh/mi related to time-to-charge? I can see that it determines how many miles I'd get from some amount of electricity under ideal conditions. I'm not asking how many miles of any sort I can go, I am asking *how long does it take to get from N miles of rated range on the speedometer/powermeter to "Full"?*.

When a car is plugged in the Wh/m is either 1) not in the equation (if it measures only energy spent, as above) or else 2) the Wh/m factor of rate-of-charge is "ideally" accurate and some other factor is not living up: the simple fact is that the cars own measured rate of fill is about 2/3 of teh number they publish without any qualifications:

Sample deltaT deltaM m/h (the 5280' kind)
1: 9h25m -> 32m 3.4
2: 14h10m -> 46m 3.3
3: 7h -> 22m 3.1
4: 13h44m -> 44m 3.2
5: 18h30m -> 60m 3.2

I gathered these using this method: at the end of a drive I record the rated miles and start time, then I look at the same when I return to the car. If the car is full I toss the data out as I'm not sure when it reached full. If its not full, I record. The electricity has been flowing the entire time - and rate-of-fill is roughly 2/3rd what I used as a factor in my purchase decision.

For what its worth, I'm satisfied with my rate - because I took my absolute need and doubled it before deciding. At 66% of expected I have only 33% more than my need, and not a lot of flexibility. The rate-of-charge is by far and away the one thing that falls quite-a-lot short of my expectations for the car.

No doubt people will clamor about ideal miles. I'm fine with that, so log as Tesla adds the same kind of warnings about ideal miles to their rate-of-charge numbers as they do to the rated-vs ideal miles/energy-spent estimates. I saw the warnings about those. I use a 2/3-of-rated limit on my range, and I can accept a 2/3-of-rated speed of charge too. But that's me, and people ought to be able to decide for themselves from numbers that are clearly described.

If Tesla clarifies their rate-of-charge numbers, I'll be even more HAPPY WITH MY MS.

Brian H | 9 agosto 2013

I suspect the vampire drain is such a high percentage of the 120V feed that the 5 mi/hr is cut down to 3 by it.

jat | 9 agosto 2013

@david.chenney - it matters because you can configure the car to show ideal miles or rated miles. Up to 300mi range, 5mi/hr charging rate, etc are all in ideal miles. If you have your car set to display rated miles, then obviously the mi/hr charging rate is going to be lower because it takes more Wh going into the battery for each one of those rated miles.

rterry | 10 agosto 2013

HPWC is unnecessary. I have it but not quite sure why. Used the 240v while my HPWC was on backorder and that worked like a charm for my type of daily commute, @ 25 miles round trip. If I had it to do over, I would just install some type of garden hose bracket to keep my power cord off the floor of my garage for a neat storage solution. Will not install another HPWC when my wife gets her Model X.

Brian H | 10 agosto 2013

Yes you will, if you want it to come with twin chargers!
;p