I live in a condo. The main breaker is only 70A. Now what? [Resolved]

[andy92782]

Are you comparing that to your old system lasting another 26 years?!

The point is there is no financial incentive to replace it. I don’t expect it to last forever. When it dies, I’ll replace it, but likely not before.

 

[Big Earl]

And yet it works off a 30A breaker, same as a modern 2.5 ton AC unit. Yes, I know, duty cycles. I just doubt modern ones are twice as efficient.

8 or 10 SEER vs 16 or 20 SEER. Maybe not double, but not too far off.

 

[Watts_Up]

Yes you can do things like this, there are a few threads here on TMC that discuss hacking the HPWC load sharing protocol (New Wall Connector load sharing protocol), but the OP originally wanted something off the shelf that was up to code.

Personally, I think a little black box that turns off a HPWC via a signal cable would be a neat little product, but I don’t know how big the market would be or if anyone has built such a gizmo.

This is something I was thinking for a long time when reading about the Tesla HPWC load balancing capability.

It would be very simple to replace the expensive $1,000 DDC with a simple control box sending a signal to the HPWC when there is a surge of power.

 

[brkaus]

This is something I was thinking for a long time when reading about the Tesla HPWC load balancing capability.

It would be very simple to replace the expensive $1,000 DDC with a simple control box sending a signal to the HPWC when there is a surge of power.

I think a coil to measure load on the main and a control box for the HPWC would be great. Not sure it could react to a spike, but for other situations (oven plus dryer plus ac) it would keep the DCCC from tripping.

But I’m not sure an inspector would sign off of cobbled together hardware though. The DCC is self enclosed, tested, and listed.

I guess there is always a fuse...

 

[darth_vad3r]

The point is there is no financial incentive to replace it. I don’t expect it to last forever. When it dies, I’ll replace it, but likely not before.

Uh well, the financial incentive is the energy savings you are losing in the mean time, right? It depends on how long it lasts and the opportunity cost of the money required to upgrade. It is not an automatic that it better to continue using the less efficient one. The longer you use it the more you continue to pay the penalty of higher electricity usage while you only delay the upgrade cost, not eliminate it.

e.g. $100/yr for 5 years = $500 and then an upgrade of $X,000 vs $X,000 now.

 

[Cosmacelf]

e.g. $100/yr for 5 years = $500 and then an upgrade of $X,000 vs $X,000 now.

But if you buy a new unit now rather than five years from now, the new unit will have a five year shorter lifespan, which would easily eat up the $500 difference.

Usually the only time it makes economic sense to upgrade equipment is when the maintenance costs get out of hand on the old equipment, which doesn't appear to be the case here.

 

[darth_vad3r]

But if you buy a new unit now rather than five years from now, the new unit will have a five year shorter lifespan, which would easily eat up the $500 difference.

Usually the only time it makes economic sense to upgrade equipment is when the maintenance costs get out of hand on the old equipment, which doesn't appear to be the case here.

Right, and increased running costs must be factored in equally with maintenance costs is all I’m saying. The increased cost is guaranteed “maintenance” expense.

It’s not an automatic decision is all I’m saying.

How long should he aim to keep an old inefficient one running? 26 years? 5 years? 6 months? It’s complicated, it’s not automatic

 

[brkaus]

Interesting twist to the initial thread

I upgraded 3 systems when the first was in need of repairs. Saved a lot of money doing so.

I run AC 7 months and heat 3 months. Our heat was propane. Between the AC improved efficiency and putting in heat pumps to reduce the high propane cost we had a payback of 5 years. We had propane bills over $900 some months.

Also did other building envelope improvements.


Anyway - hope the hard start kit makes a difference. Gives more time to consider the finances of the HVAC.

 

[Watts_Up]

Do you really need the AC at noght?

I imagine that your AC thermostat has a timer.

So you could black out your AC let see from 2 am to 6 am and set your car to start at 2 am.

 

[Akikiki]

Update #2: Electrician #2 (aka the second opinion) says 4 gauge THHN copper wire *isn't* capable of 100A and he immediately quoted me the specific section of NEC that says so. So... It looks like I'm back to pursuing the DCC route. The good news is Electrician #2 is familiar with the DCC and has installed them before, so the only hurdle left to clear is the city inspector.

(the specific limitation of the THHN wire is the temperature rating. It has to be de-rated to the value used by the sub-panel where it connects, which is 75C. At that temp, 4-gauge THHN is only good for 85A, not 100A. The first electrician either didn't know that or skipped over it).

andy, have you considered bumping your service panel main breaker up to the 85a that your electrician stated it would support? That difference in amperage might solve your problem where one of your main components, i.e., AC and WC needed to be stopped to accommodate the other. (Sorry, I can't remember which one shutsdown when the other starts.)

Anyone agree that replacing a 30 year old circuit breaker would be a good idea anyway? I don't know, just makes sense. Seems to me that a 30 year old 70a breaker has been hot enough plenty of times that replacing with a new 70 or 85 would be a good idea anyway since he's increasing the load on it. I don't know for sure, but makes sense to me.

 

[andy92782]

A couple things while we wait for my startup capacitor:

First, I wish there was a way I could edit my posts after the fact. If so, I would like to update the very first post in this thread with the fact that I successfully resolved my issue with the DCC and provide direct links to the posts with pertinent information. If there's a way to do it then I apologize for not finding it (yet) - it's not as obvious as it is on other forums I participate at.

Second, I think it's pretty funny how some are so concerned over the environmental cost incurred when I operate my perfectly functional, 30-year old 9-SEER HVAC system for three months out of the year tops, and even then, not on a 24/7 duty cycle. I'm about to share a potentially unpopular opinion so bear with me, or perhaps tune out if you're easily offended. For me, buying the Tesla was mostly an emotional decision. I didn't do it to save the polar bears or protect future generations from environmental peril. I did it because the car drove awesome and it totally blew my mind. I LOVE my Tesla and the performance of the electric drivetrain, but in terms its environmental impact, I could make an argument that I'd have been just as well to to buy a Toyota Prius. Maybe a plug-in Prius Prime if I were super concerned about it. Without question it would have been a better decision financially. They cost half as much to buy and in terms of dollar-per-mile, a 50-mpg Prius costs about the same as a Tesla running on $0.30+ kWh juice from a Supercharger. But to me, cars have an emotional component in additional a practical one, so I was willing to spend the extra money on a Model 3 even though I didn't need it.

HVAC systems on the other hand are not something I get emotional about. I don't dream at night of Carrier, Lennox and Trane. All I care about is whether or not cool air comes out of the vents when I turn it on. My decision to buy a new HVAC system is driven solely by practicality and economics. If I replace it now, I'm guaranteed to lose out on the opportunity cost of $8K invested in the market for at least *some* duration. The existing system may die a week from now or it may run faithfully for another ten years. It's impossible to say. But there's absolutely zero emotional component involved with replacing it like there was with my (previous) perfectly functional automobile with a Model 3.

(trivia tidbit: $8K invested in an S&P 500 index fund ten years ago would be worth $32K today)

Tell you what: For those of you who can't sleep at night with the thought of an old AC system wasting electricity unnecessarily, I'm happy to start a GoFundMe page with a target of $5,000. Once reached, I'll go down to Costco and engage the Lennox guy who's always there right by the TV sets. Feel free to donate.

 

[andy92782]

This is something I was thinking for a long time when reading about the Tesla HPWC load balancing capability.

It would be very simple to replace the expensive $1,000 DDC with a simple control box sending a signal to the HPWC when there is a surge of power.

I agree. The DCC is pretty dumb in this aspect. In an ideal world, the EV charger could be tied in with the thermostat, or perhaps a really dumb one-wire signal could be sent from the thermostat to the EV charger to block it off when the AC needs to run. The present challenge has more to do with UL listings, the national electric code and obtaining building permits from local governments. Things move reeeeeeeeallllly sloooooooooooowly in this area. It took a LOT of planning and convincing just to get the city to sign off on the DCC. I can't imagine what it'd be like trying to educate them on what essentially amounts to a lesson in IoT.

The DCC may not be elegant but it enabled me to install a L2 charger in a dwelling where it would have otherwise been impossible - at least if I wanted to meet code, which I did (and did).

 

[brkaus]

@andy92782 you could wire a post with the updates to add to the first post. Then click “report” and ask the mods if they will update the first post.

If they have spare time, they will sometimes make the edit. Depends on how much snippiness is going around at the time.

 

[Big Earl]

A couple things while we wait for my startup capacitor:

First, I wish there was a way I could edit my posts after the fact. If so, I would like to update the very first post in this thread with the fact that I successfully resolved my issue with the DCC and provide direct links to the posts with pertinent information. If there's a way to do it then I apologize for not finding it (yet) - it's not as obvious as it is on other forums I participate at.

Second, I think it's pretty funny how some are so concerned over the environmental cost incurred when I operate my perfectly functional, 30-year old 9-SEER HVAC system for three months out of the year tops, and even then, not on a 24/7 duty cycle. I'm about to share a potentially unpopular opinion so bear with me, or perhaps tune out if you're easily offended. For me, buying the Tesla was mostly an emotional decision. I didn't do it to save the polar bears or protect future generations from environmental peril. I did it because the car drove awesome and it totally blew my mind. I LOVE my Tesla and the performance of the electric drivetrain, but in terms its environmental impact, I could make an argument that I'd have been just as well to to buy a Toyota Prius. Maybe a plug-in Prius Prime if I were super concerned about it. Without question it would have been a better decision financially. They cost half as much to buy and in terms of dollar-per-mile, a 50-mpg Prius costs about the same as a Tesla running on $0.30+ kWh juice from a Supercharger. But to me, cars have an emotional component in additional a practical one, so I was willing to spend the extra money on a Model 3 even though I didn't need it.

HVAC systems on the other hand are not something I get emotional about. I don't dream at night of Carrier, Lennox and Trane. All I care about is whether or not cool air comes out of the vents when I turn it on. My decision to buy a new HVAC system is driven solely by practicality and economics. If I replace it now, I'm guaranteed to lose out on the opportunity cost of $8K invested in the market for at least *some* duration. The existing system may die a week from now or it may run faithfully for another ten years. It's impossible to say. But there's absolutely zero emotional component involved with replacing it like there was with my (previous) perfectly functional automobile with a Model 3.

(trivia tidbit: $8K invested in an S&P 500 index fund ten years ago would be worth $32K today)

Tell you what: For those of you who can't sleep at night with the thought of an old AC system wasting electricity unnecessarily, I'm happy to start a GoFundMe page with a target of $5,000. Once reached, I'll go down to Costco and engage the Lennox guy who's always there right by the TV sets. Feel free to donate.

I hope I didn’t come across as hounding you about environmental stuff, as that certainly wasn’t my intent. I was merely pointing out that a new unit could potentially solve your current problem by reducing the inrush and overall consumption. Of course, your financial points are spot-on and there are much less expensive solutions available.

 

[davewill]

This would work, and even better, if you could get into the signal-lines of the HPWC you wouldn't need to get an enormous relay to essentially replicate the contactors built into the HPWC. I wonder if the power-sharing protocol of the HPWC's is published and could be used to turn the charge level down to 0 or some similar tiny current for a minute when the AC is starting.

You could use something like this WiFi controlled relay board to interrupt the pilot signal inside the wall connector, but honestly I don't see much point for the OP since the DCC is already doing the job. If both my EVSEs didn't already have timing smarts in them, that's what I would use to add it.

https://www.amazon.com/MHCOZY-Wireless-Switch-applied-control/dp/B0752P57ZG

 

[brucet999]

andy, have you considered bumping your service panel main breaker up to the 85a that your electrician stated it would support? That difference in amperage might solve your problem where one of your main components, i.e., AC and WC needed to be stopped to accommodate the other. (Sorry, I can't remember which one shutsdown when the other starts.)

Anyone agree that replacing a 30 year old circuit breaker would be a good idea anyway? I don't know, just makes sense. Seems to me that a 30 year old 70a breaker has been hot enough plenty of times that replacing with a new 70 or 85 would be a good idea anyway since he's increasing the load on it. I don't know for sure, but makes sense to me.

If that 70A SE panel includes the meter socket, I think there is no way to replace with a new 70 or 85. There are a few 100A panels with meter socket still available, but most are 125A or larger.

Definitely would be a cheaper alternative to replacing the HVAC unit, assuming that it would be physically possible to fit a new panel into the old space.

 

[andy92782]

You could use something like this WiFi controlled relay board to interrupt the pilot signal inside the wall connector, but honestly I don't see much point for the OP since the DCC is already doing the job. If both my EVSEs didn't already have timing smarts in them, that's what I would use to add it.



https://www.amazon.com/MHCOZY-Wireless-Switch-applied-control/dp/B0752P57ZG

One potentially interesting hacker project.... My thermostat is an Emerson Sensi Wi-Fi. There might be a way to tie it in to Alexa or IFTTT or one of those cloud IoT services. The idea would be to have the thermostat signal the Tesla Wall Connector to shut off and/or drop the charge current as low as possible and wait for a return confirmation/acknowledgement signal. THEN, and only then, turn on the HVAC.

Sounds cool, but I'm hoping the startup capacitor will accomplish the same thing for a lot less effort.

 

[Dana1]

Let's say a new AC system consumes $100/mo less in electricity than the system I have now. I use it approximately 3 months per year (again, the climate is mild here), so that's $300 in savings per year. The ballpark price of a new HVAC system is approximately $8000. Simple math says it will take over 26 years to recoup my investment.

Can’t you just charge at night with AC off? Guessing you probably charge every other night anyway.

 

[andy92782]

Can’t you just charge at night with AC off? Guessing you probably charge every other night anyway.

Yes, and this is what I normally do. But every now and then there's a heat wave and sometimes I want to run the A/C overnight.

 

[Akikiki]

Maybe one solution is adding a wifi/Alexa enabled heavy duty smart switch that rated high enough to turn the DCC on and off controlled by an Alexa routine via voice or timer. I would guess you have already found this, but here it is again. Being Model 3, you are charging at less than 40 amp anyway, right? And then adding the thermostat hack to bring the AC into the Alexa routine. Looks like an interesting device. Gonna bookmark this one while I know its there.

https://www.amazon.com/GE-Appliance...elay+for+240v&qid=1564274861&s=gateway&sr=8-3