Dual HPWC thoughts

[billarnett]

Would depend on what those loads are, sure. But if they're unrelated to charging the car (and thus them being active or inactive has nothing to do with the charging of the cars) it would be difficult to argue that they'll be unlikely to be on concurrently for the 220.60 exception.

I'll stick with my original suggestion and that would be to get a dedicated 200A panel for two 80A (100A breaker) HPWCs.

Sure. (But the OP said that "would be a huge pain".)

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My house has 200A service. I have an HPWC set at 80A. And the usual plethora of little stuff for a big house (the sum of those breakers is far more than 200). But I'm about to remodel my kitchen and replace the gas cooking appliances with electric. That will add another 90A to my total. Can I reasonably argue that the cooking will never be concurrent with the charging?

 

[wk057]

Sure. (But the OP said that "would be a huge pain".)

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My house has 200A service. I have an HPWC set at 80A. And the usual plethora of little stuff for a big house (the sum of those breakers is far more than 200). But I'm about to remodel my kitchen and replace the gas cooking appliances with electric. That will add another 90A to my total. Can I reasonably argue that the cooking will never be concurrent with the charging?

I would say definitely not, as cooking and charging are completely unrelated and their concurrency would be random, not consistently not concurrent.

 

[FlasherZ]

Ok we are talking extreme what if's!!! Simply designate one car as primary and the other car that charges at between 3am to 7am. The primary car can plug in anytime prior to 11pm and suck down maximum power to be recharged.

In extremely rare off case where the primary car will charge outside of this time frame, you can modify the HPWC with a switch to over-ride the internal dip switch to charge at 40amps until morning!!!!

From a code perspective, modifying the HPWC disqualifies its listing and does not eliminate the load requirement. A user-selectable switch does not permit you to count it as a 40A charging load / 50A circuit requirement, if it is possible to charge at 80A (100A circuit) via a user-selectable switch. This is why it is based on DIP switches.

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If you set both HPWCs to 40A you can still charge both cars fully overnight so why worry?

There are times you will want to have the faster charging. Getting out a T20, looking up DIP switch setting, changing it, cycling power at the breaker, and then plugging in is a pain in the ass.

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Why is it ok for you to have two 80A loads on a 200A panel but not ok for the OP to have two 40A loads on a 100A panel? (I'm assuming the other loads are trivial.)

You can't assume other loads are trivial for NEC. See my post above for the ways to calculate lighting/receptacle loads other than charging.

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So the OP would be OK if he had no other loads concurrent with the two 40A chargers? Couldn't he reasonably argue that the other loads are unlikely to be on during the charging cycles? We're pushing the envelope here I guess. But given the OP's situation it seems like he doesn't have any other good options. I suppose he could limit the HPWCs to 35A each leaving room for 10A of other loads. That would still be sufficient to charge both cars overnight except when they're almost down to zero.

You'd have an easier time suggesting that 220.60 applies to 2 EV's than you would that other loads don't apply. Here's an example -- plug the car in, it starts charging, then you close the garage door. Boom - 5A motor load plus charging load.

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I'll stick with my original suggestion and that would be to get a dedicated 200A panel for two 80A (100A breaker) HPWCs.

That's what I recommend to anyone who is adding charging to an existing structure.

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My house has 200A service. I have an HPWC set at 80A. And the usual plethora of little stuff for a big house (the sum of those breakers is far more than 200). But I'm about to remodel my kitchen and replace the gas cooking appliances with electric. That will add another 90A to my total. Can I reasonably argue that the cooking will never be concurrent with the charging?

No inspector would ever allow you to say that.

The intent of 220.60 is to address things like large, high-HP tools. For example, it would be unlikely for you to use a 5 HP lathe and 5 HP planer at the very same time in a personal workshop. I don't necessarily agree with wk057 that EV loads should not apply to 220.60. There is also a provision in 220 (.53, I think?) that allows 4 or more appliances to have a 75% load factor applied to them. So 4 HPWC's installed @80A charging could be sized with 300A feeder.

There are specific calculations for a home, and you may end up needing a service upgrade.

 

[wycolo]

OP should build a new garage for the Teslas and let the one 250 ft away with the concreted feed evolve into other usage. One never has enough garages, right?
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[wk057]

I don't necessarily agree with wk057 that EV loads should not apply to 220.60. There is also a provision in 220 (.53, I think?) that allows 4 or more appliances to have a 75% load factor applied to them. So 4 HPWC's installed @80A charging could be sized with 300A feeder.

220.53 is correct, and certainly makes some sense for 4+ HPWC. It basically cancels out the continuous load up-sizing.

However I'll still argue a little for my point against 220.60 and EV charging. For one charger it definitely will almost never apply. EV will charge while you're home, and any other load can coincide with charging. But it seems logical to believe that if you're going to install 2+ EV chargers it's because you expect to be charging 2+ vehicles. Saying with certainty that they're likely to be noncoincident loads is probably wrong in most cases. The example I used earlier was my two Model S both kicking in at the same time to top off their packs after sitting for a while. The only real example I can think where 220.60 would apply to EV charging would be a HPWC and J1772 and/or NEMA 14-50 in a one car garage with 1 EV in the household. In that case I would consider them unlikely to be concurrent loads. 2+ EVs + 2+ chargers... pretty sure at some point they'll charge at the same time.

 

[FlasherZ]

However I'll still argue a little for my point against 220.60 and EV charging. For one charger it definitely will almost never apply. EV will charge while you're home, and any other load can coincide with charging. But it seems logical to believe that if you're going to install 2+ EV chargers it's because you expect to be charging 2+ vehicles. Saying with certainty that they're likely to be noncoincident loads is probably wrong in most cases. The example I used earlier was my two Model S both kicking in at the same time to top off their packs after sitting for a while. The only real example I can think where 220.60 would apply to EV charging would be a HPWC and J1772 and/or NEMA 14-50 in a one car garage with 1 EV in the household. In that case I would consider them unlikely to be concurrent loads. 2+ EVs + 2+ chargers... pretty sure at some point they'll charge at the same time.

Your final point is why I argue against writing it into code that EV loads can't apply on 220.60. That would make a lot of inspectors refuse to permit 14-50's as backups. That would be a giant disservice, IMO.

I still believe it is possible to configure 2 HPWC's so that it is "unlikely" (to use code language) that they would engage at the same time. Patterns have shown that the car tends to "wake up" and charge at a specific time of day every 1-2 days, and at 80A, the "topping off" behavior is going to be limited to a few minutes per day at best. Scheduled charging can be used to help ensure that likelihood even more.

I don't like relying upon large breakers tripping, either, but I think it's certainly within the intentions of 220.60. And, where there is a higher likelihood of coincident use, I wouldn't rely upon 220.60 (for example, my Model S + Model X will not rely upon it, I'm installing a larger 200A panel for the dual HPWC + 14-50's).

 

[Dave EV]

Sounds like what you really need is one of the Hydra variants
https://code.google.com/p/open-evse/wiki/Hydra
Hydra EVSE
But would have to be built with Tesla plugs good for 80A.
Not trivial, either.

 

[davewill]

Sounds like what you really need is one of the Hydra variants
https://code.google.com/p/open-evse/wiki/Hydra
Hydra EVSE
But would have to be built with Tesla plugs good for 80A.
Not trivial, either.

It could be built with 80a J1772 plugs as well. He could also use the cable and plug from his existing HPWC for one side.

 

[wk057]

It could be built with 80a J1772 plugs as well. He could also use the cable and plug from his existing HPWC for one side.

I plan on doing something similar, eventually, when I integrate my two HPWCs into my in-progress smart-off-grid-setup.

 

[Kardax]

It seems like Tesla could help everyone out if there was a way to run multiple HPWCs off a single 80-amp line with some kind of automatic balancing, similar to how the superchargers are paired.

 

[dirkhh]

It seems like Tesla could help everyone out if there was a way to run multiple HPWCs off a single 80-amp line with some kind of automatic balancing, similar to how the superchargers are paired.

I actually sent them email about that quite a while ago. My idea was to have a dual headed HPWC that would negotiate with the two cars and give the one with the lower SOC the higher power, keeping the sum of both <= 80A...
If you connect just one, you get 80A. If you connect to you get up to 80A, but as little as, say, 20A when you are at the a high SOC and the other car is very low.

 

[chuckd]

Great stuff here! I'm actually 'not legal' at the moment, but just struggling with how to add the second HPWC. I'd love to just replace the panel and run a larger feed, but it really is under 200 feet of concrete. That'd be awful.

i actually do have a second garage structure, but it's a long way from the house and I'm too lazy to walk that far to get the car (about 400 feet). It is setup for adequate power though, which is frustrating.

You guys were 'supposed' to say "go ahead, just don't use them at the same time"! Lol

 

[Blu Zap]

Hey, there may be a solution announced from Tesla on April 30th. (Stationary battery - rumor) That could play a part in multiple vehicle charges, even if you don't have solar.

 

[FlasherZ]

I actually sent them email about that quite a while ago. My idea was to have a dual headed HPWC that would negotiate with the two cars and give the one with the lower SOC the higher power, keeping the sum of both <= 80A...
If you connect just one, you get 80A. If you connect to you get up to 80A, but as little as, say, 20A when you are at the a high SOC and the other car is very low.

I suspect it's a little early in the market for such a device. While this forum will have a number of people with 2 Teslas, I suspect the number isn't enough to justify the investment when Tesla will donate HPWC's to businesses and has likely recouped its HPWC investment several-fold.

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You guys were 'supposed' to say "go ahead, just don't use them at the same time"! Lol

If you can arrange your charging schedules and such so that you are "unlikely" to have coincident loads from both, then yes, go ahead.

Seriously, you don't want to put yourself in a position where large breakers are tripping. Many of them won't survive several trips and will simply refuse to snap back into the "on" position.

Is directional boring an option? That's how I installed my generator on the other side of a 100' pad of concrete.

 

[chuckd]

In reality, anything is possible, like directional boring. However, the area that it passes under is all ornamental ponds (shotcrete style) and garden paths/deck areas. It'd be ugly, no doubt.

I would definitely install a HPWC at my office (only 13 miles from home), and that would probably take care of most situations. I would definitely arrange my schedules at home so that both cars don't charge at once if I decide to wing-it the way I originally described. If I could just set a charging time window (time range) on the car, I could almost guarantee no problems.

 

[sowbug]

I actually sent them email about that quite a while ago. My idea was to have a dual headed HPWC that would negotiate with the two cars and give the one with the lower SOC the higher power, keeping the sum of both <= 80A...
If you connect just one, you get 80A. If you connect to you get up to 80A, but as little as, say, 20A when you are at the a high SOC and the other car is very low.

Did you ever get a reply? With the Model X coming out, seems likely there'll be more two-Tesla households that would be happy to leave both cars plugged in and have the HPWC figure out the right thing to do overnight.

 

[Muzzman1]

I recently added a 2nd HPWC to my 100A sub panel in anticipation of my Wife's Model X in a few months (I hope).
I know that it's not "to code" but I opted to use 2-100A breakers on the panel, one for each car in the anticipation that both cars will never charge simultaneously. Ever.
Worst case scenario it will pop the main 100A at the main panel if both cars manage to charge at the same time. (which will never happen)

 

[Cottonwood]

As more and more households become multi-Tesla households, Tesla really needs to make a dual headed HPWC that does functions like the Hydra. For details see:

• open-evse: The Hydra
• TMC: J1772 Hydra - charge two vehicles with one charger

 

[ohmman]

Agreed; this is a clear need for a company that is garnering a lot of customer loyalty.

My plan when we get the MX is to put a 14-50 in place and buy an extra UMC. I am so used to having the cable in the frunk, having used a HPWC, I would hate to forget it on a trip.

 

[jerry33]

Of course, a dual heading EVSE might be almost twice as expensive