Two Teslas, Two HPWCs? Better for 12Vs for Both to Stay Plugged In?

[ForeverFree]

Just added a M3 and became a two Tesla family.

We had planned to add a second HPWC, having the two load-share our 100A circuit. Would be convenient: Come home, plug in, and forget. It would be nice to have a spare HPWC if one went down ... which has happened to us in the past. And, local utility rebate would cover cost of HPWC.

However, higher than expected installation cost ($850+, if properly permitted and inspected) has given us pause.

Neither my wife nor I have long commutes, so one HPWC provides plenty of charging capacity. We just have to remember to swap plugs at some point during the evening.

We do wonder, though, about the importance of “a plugged-in Tesla is a happy Tesla” advice. The high-voltage battery is supposed to connect and top up the 12V battery, as needed. However, is it clear that this happens as frequently and consistently when the car is not plugged in? Might the surprising durability of our 12V battery (almost three years, so far) be due in part to keeping the car plugged in all night every night?

Would love to hear people’s opinions (good) and experiences (better)!

Thanks!!

 

[TexasTeslaRacing]

We are two tesla house and one HPWC on a 100AMP circuit is plenty. We never have issues. Save the cash and stick with one. You can plug in the second car to a 12V outlet but we don’t.

 

[Tam]

....as frequently and consistently when the car is not plugged in

My guess is whether you plug-in or not, your 12V battery still get charged just as often.

Your main pack would stop charging your 12V battery to protect itself when its SOC is too low.

It's best to have 2 HPWC but there's nothing wrong by saving some money and rotate 2 cars for 1 HPWC.

 

[jaguar36]

Won't make a difference to the 12V whether its plugged in or not. On our 2014 we only plug it in once a week or so and its still on the original 12V.

We also have two Ss and only one 14-50 and it hasn't been a problem, does take a bit of coordination though.

 

[jbcarioca]

I'm probably more conservative than anyone else. I advocate plugging the one that needs a charge into the HPWC and the other one to a 120v outlet. That keeps the "vampire" at bay and adds some charge anyway. It also fulfils the "a plugged-in Tesla is a happy Tesla " edict.

 

[brkaus]

I have an S. Purchasing a 3 soon. Planning on a single 50a breaker HPWC (40a charging).

Why 50a? Electricity is cheaper with a EV rate if below 50a.

 

[Yinn]

We shared a single HPWC for a while, it worked perfectly fine. My wife and I get home at staggered times, so her charge is full by the time I get back. We didn't have any issues with our 12v while we did this. We did this for a while but then our garage door broke and limited our access to the 8' HPWC which forced us to explore other options.

Our local garage door company quoted us 6-8 weeks to get new doors since it was "unrepairable" Our local permitting and inspection office quoted 1-2 weeks for the electrical install, so I called the electrician to get a quote on a 2nd HPWC - which was reasonable and he was able to come the end of the week. Part of the reason for that was he did the first installation, and I had asked for a new subpanel to be installed in the garage, which didn't cost much more that a single HPWC install. So the 2nd run was really short and really only needed very little time to install.

While I waited, I used the 120V for a night, which wasn't enough. The nearest supercharger is about an hour away, so I needed to supplement with a nearby L2 charger, which happened to be near a Home Depot. Browsing around, I realized it was about $60 in parts to install a NEMA 14-50. So I ended up buying the parts - conduit, wiring, breaker, and contained 14-50 box/outlet and ran the 5 feet from the panel. We shared the NEMA 14-50 for two days before the electrician came and installed the second HPWC (20' cable). He also took a look at my install to make sure it was safe and said I should just leave it as is, even asked if I was sure I still wanted to run the 2nd HPWC. Since we didn't take it out, we made sure both items were included in the permit and inspection.

So all in all, sharing a L2 charger is 100% doable. Depending on your schedule, it might not even be a pain in the butt. But when things go wrong, and if all you have is electric cars without a nearby SC; then I would recommend having some sort of backup. A NEMA 14-50 run is pretty cost effective as a backup or secondary and would save a couple hundred over a HPWC even if it was installed by an electrician.

 

[bob_p]

Unless Tesla changes the documentation for Model 3, it's likely they'll have the same recommendations for charging as the S/X - plug in the car whenever possible, and charge above 90% for trips, only when needed.

We have two Model S cars. Our S 100D is on a 100A circuit with an HPWC. Our original S P85 (with 80A charger) used to be on the HPWC, and is now on a 50A circuit with Tesla's 14-50 mobile connector, providing up to 40A charging. Our S 100D only has the 48A charger, so it's not taking full advantage of the 100A circuit.

Using 48A on the S 100D is more than fast enough to fully charge the car overnight. We can spend $1900 to upgrade the charger to 72A - and don't plan to do that - charging faster (at least for overnight charging) isn't needed, even with Tesla's largest battery pack.

Even charging our S P85 as low as 32A (which is what Tesla's new mobile connectors support) is still more than fast enough to fully charge the P85 overnight.

The battery packs on the Model 3's will be smaller than the S/X batter packs, because the 3 is lighter and needs less energy to run.

My recommendation is to use 14-50 outlets for Model 3's - since that should be more than enough to fully charge an SR or LR Model 3 overnight.

A 14-50 outlet is less expensive to install - and if/when you ever decide to move - you avoid the additional costs for uninstalling an HPWC, which has to be connected directly to a power panel.

 

[jbcarioca]

...
So all in all, sharing a L2 charger is 100% doable. Depending on your schedule, it might not even be a pain in the butt. But when things go wrong, and if all you have is electric cars without a nearby SC; then I would recommend having some sort of backup. A NEMA 14-50 run is pretty cost effective as a backup or secondary and would save a couple hundred over a HPWC even if it was installed by an electrician.

When you have only BEV's redundant sources is always nice, obviously not essential. In the long run duplicate sources are cheap.

 

[AWDtsla]

We do wonder, though, about the importance of “a plugged-in Tesla is a happy Tesla” advice.

Only matters if you leave the car parked for weeks, saves Tesla $$$ on warranty battery replacements. Plugging in every day is unnecessary for almost everyone. You're just wearing out the connector.

 

[ForeverFree]

Thank you, everyone. Valuable food for thought!

For now, we're leaning towards continuing to make the shared HPWC work, especially if there won't be a significant impact on 12V charging.

However, redundancy does appeal. We've already had to go begging to a neighbor's HPWC when ours caught the flu once.

 

[gregd]

However, redundancy does appeal. We've already had to go begging to a neighbor's HPWC when ours caught the flu once.

If adding a second HPWC is too pricy, redundancy considerations would push me to consider adding a 14-50 circuit instead. If needed, the UMC can always connect to it, and it can be used for other things down the road, either an RV or a different brand of EV (just visiting, of course). The down-side is that it can't share the same breaker and wiring with the existing HPWC, so cost may be a wash.

When I added my 14-50, I threw in a set of dedicated 120 volt, 20 amp GFI outlets next to it. Since the parts are cheap and I did the labor, the incremental cost for the project was negligible. The outlets are available for whatever, but they can serve as a back up if the EVSE fails, or if a second vehicle needs some charging. I used 12-3 wiring (so, 2 circuits) and a double 20 amp breaker, providing 4 outlets.

 

[ForeverFree]

Makes good sense.

For us, though, the cost would be higher, not lower. Here in LA, a utility rebate covers the entire $500 cost of the HPWC.

The killer is the installation cost. We were quoted $890 by a Tesla SC-recommended guy who seemed completely legit. Another electrician, from Tesla's website, quoted $495 ... which was fine until I asked for confirmation that the price included permitting and inspection. "Permit. What permit? Why do you need a permit?"

Sorry, but living in a wooden house, in a chaparral-covered canyon, I think I want everything permitted on the wiring of a cross-communicating, load-sharing device that delivers up to 19,600W.

Permit and inspection hosting would have added $300.

 

[Mr T]

We had to upgrade our 100 amp panel to 225 when we put in our 11kw solar system. The added cost to go to to 400amps was only the cost of the panel and breaker so we went to 400. Southern California Edison required us to also run a separate feed prior to the main 400 amp panel to supply the 100amp EV meter and circuit. This main feed for the EV meter is completely unnecessary as you could easily run the EV meter off a breaker. This does however give our home 500amps. We then ran a 100amp sub to the garage to feed two Nema 14-50s and then another 100amp sub from the EV meter for two more Nema 14-50's. We have 4 Nema 14-50's in the garage, two on the EV meter for charging at 12 cents a KW between hours of midnight and 9am, and two Nemas for charging at anytime. We can charge the S and the M3 at anytime with the option to use the lower rate EV at night. We seldom need to charge both cars at the same time as the S gets supercharged frequently.

 

[gregd]

Makes good sense.

For us, though, the cost would be higher, not lower. Here in LA, a utility rebate covers the entire $500 cost of the HPWC.

The killer is the installation cost. We were quoted $890 by a Tesla SC-recommended guy who seemed completely legit. Another electrician, from Tesla's website, quoted $495 ... which was fine until I asked for confirmation that the price included permitting and inspection. "Permit. What permit? Why do you need a permit?"

Sorry, but living in a wooden house, in a chaparral-covered canyon, I think I want everything permitted on the wiring of a cross-communicating, load-sharing device that delivers up to 19,600W.

Permit and inspection hosting would have added $300.

Yeah, sounds like you have things dialed in right. Safety is the key reason I did my install, which ended up being over $2k because it involved a panel swap. The original 125 amp panel, besides being at capacity and with no free slots, turned out to be a model that had a tendency to "fail" (as in "catch fire"). The electrician was surprised to see mine still in service (thought they'd all been swapped out by now). So, even though I had enough charging current sharing a plug with the clothes dryer, the whole situation with the panel said otherwise. I ended up going with a 200 amp panel, added the 14-50 (giving the dryer sole use of its plug) and a set of 5-20's, and now the car and I are sleeping much better.

I also got to take advantage of the tax credit, which expired at the end of that year (2016), so net cost was a lot lower. If they extend the credit again, you might take advantage of it as well.

 

[scottm]

Model 3 and facelift model S don't need to be plugged in to spare the 12v battery excess cycling.
These cars have mini DC converters to feed parked loads, all night long. No cycling.

If your model S is older, then 12v cycling applies.

But here's the thing... keeping the charge cord plugged into the older model S doesn't prevent cycling either. You must install your own trickle charger on the 12v battery if you want to prevent cycling.

 

[ForeverFree]

Yeah, sounds like you have things dialed in right. Safety is the key reason I did my install, which ended up being over $2k because it involved a panel swap. The original 125 amp panel, besides being at capacity and with no free slots, turned out to be a model that had a tendency to "fail" (as in "catch fire"). The electrician was surprised to see mine still in service (thought they'd all been swapped out by now). So, even though I had enough charging current sharing a plug with the clothes dryer, the whole situation with the panel said otherwise. I ended up going with a 200 amp panel, added the 14-50 (giving the dryer sole use of its plug) and a set of 5-20's, and now the car and I are sleeping much better.

I also got to take advantage of the tax credit, which expired at the end of that year (2016), so net cost was a lot lower. If they extend the credit again, you might take advantage of it as well.

There was a tax credit for EV charger installation?

 

[swaltner]

There was a tax credit for EV charger installation?

Yes. The credit is claimed using IRS Form 8911.

 

[gregd]

There was a tax credit for EV charger installation?

Yes, 30% credit (with some limits), which was a significant savings given my total bill. That credit "ended" at the end of 2016, but apparently it got renewed retroactively for 2017 (only). The hope is that they will do so again for 2018 and beyond, but given that they can do it retroactively it's really hard to plan.

 

[stevezzzz]

@ForeverFree : if your daily commutes are both relatively short, the easy solution is to timeshare a single WC by the day rather than by the hour. Just plug one car in tonight, and the other one in tomorrow night; lather, rinse, repeat. I've got an S and a 3 that share a single WC: it works fine, and it's a lot less hassle than going out to the garage before bedtime to swap cars.