Towing and charging

[Luke42]

Sure, you could run it to a box that handles only the most important loads during an emergency, but that's not what we were talking about.

Critical loads panels (and transfer switches) are a standard part of a backup power installations.

The hard part is deciding what belongs on the critical loads panel.

For me, that's the wifi, the furnace fan, and the fridge -- I can do without everything else for hours or days. But, then again, my parents were back-to-the-landers, so my idea of "roughing it" is likely different than yours.

If you call an electrician to have a backup generator installed, a big part of the conversation will be determining what belongs on the critical load panel to address your particular needs in your particular circumstances.

Using a truck+inverter in place of a standby generator doesn't change that.

 

[ajdelange]

I thought we were talking about whether the CT would handle a whole house in an emergency. I am saying that based on the fact that I weathered many a power outage on a 7 kW generator for years and that I expect, therefore, that I would be able to do it with the 7 kW inverter in the CT (as long as the battery lasts anyway). It is so obvious that some sort of load management is/would be
required that I didn't feel it necessary to discuss it explicitly until it appeared this was an unfamiliar concept to you and so I didn't until No. 29.

So let's go a bit more into how you would manage loads manually if running my whole house on a 7 kW inverter. In particular let's talk a bit about how I would have done that on the most demanding day of last winter which was February 7th on which day average consumption was 5.71 kW with a crest factor of 2.5 (peak demand 14 kW). Load was less than 7 kW 61.4% of the time but it was over the remaining 38.6. Here's the history:

The long pole in the tent is the heat pump. It's probably obvious that its compressors are the cause of the 5 kW "pulses". It's clear that in the middle of the night the baseline load is 1.5 kW and it is also clear that loads other than the heat pump climb to around 4 kW later in the day. To run on the 7 kW generator or inverter we have to keep the total load below 7 kW (unless the duration is very brief).

So we suppose that on that day we awake and it's colder that a well diggers behind because the power went out. What do we do? Haul out of bed, go out to the garage, fire up that generator, go outside and open the disconnect to the panel. Go to the panel, open its feed breaker and all breakers except for some light, comms, the well, some outlets, the refrigerator and the heating systems control transformer. This removes all the loads except the baseline 1.5 kW and you should be able to go 100 hrs on 100 kWh from the battery. But no heat? Not acceptable. What would happen chez mois is that the thermostats would detect that their calls for heat are going unanswered and they would call for E-heat thus firing up the backup propane boiler and the house would come to temperature.

So what happens now. The heat pumps won't run and you have no heat. After a few minutes of no heat the thermostats will call for E-heat. That doesn't do anything for those heatpumps that have electric E-heaters but the one in my house that is backed up with an gas boiler (which also does instant on DHW) fires up and the part of the house you are in warms up (and warms up faster than it does with the heat pump).

Given this I would hope you would be able to see that I could have run my house on that coldest winter day on a 7 kW generator and did so many time largely because the heat pump gets taken out of the equation. In summer time there is no gas backup for the heat pump so the solution is to not run the A/C or run it when all the other loads have been turned off by flipping their breakers. This clearly requires a lot of manual intervention and is a big PITA but it can be done. I've done it. The ability to do it depends in no small measure on the fact that the system is designed to be operated on backup power supplies. That's why the DHW and heating backup are from a gas boiler which operates on only a few watts of electricity.

I will comment that if you have an electric whole house instant on hot water heater you are pretty much out of luck with respect to emergencies. Some of these things draw 36 kW and to run it you need a 36 kW generator. This is not a small generator but many houses do have them in that size and even larger.

 

[Crissa]

As I said, a central AC unit will use almost all the power it can supply. If the water heater kicks on at the same time, it's not going to be able to handle the load.

You A) need a more efficient A/C system. B) can have these two not kick on at the same time. They're both controlled by little computers.

Personally, my plan is to have two layers of critical loads: stuff on uninterruptible power, like the expensive PC and the network; stuff on the critical loads panel. Which will just be a special outlet in each room, for the most part. That way I can choose what's critical at the spur of the moment.

Eventually I want a whole-house backup, but I need to be able to handle extended outages and ration power.

-Crissa

 

[Luke42]

Personally, my plan is to have two layers of critical loads: stuff on uninterruptible power, like the expensive PC and the network; stuff on the critical loads panel. Which will just be a special outlet in each room, for the most part. That way I can choose what's critical at the spur of the moment.

Hospitals do this by color-coding the outlets:
https://www.backupbatterypower.com/...d-outlets-in-hospitals-and-medical-facilities

It was fairly clear from the context what the colors meant the last time I was in a hospital. (Though I probably wouldn't have noticed if I had been the patient.)

 

[ajdelange]

Critical loads panels (and transfer switches) are a standard part of a backup power installations.

The hard part is deciding what belongs on the critical loads panel.

For me, that's the wifi, the furnace fan, and the fridge -- I can do without everything else for hours or days. But, then again, my parents were back-to-the-landers, so my idea of "roughing it" is likely different than yours.

If you call an electrician to have a backup generator installed, a big part of the conversation will be determining what belongs on the critical load panel to address your particular needs in your particular circumstances.

Using a truck+inverter in place of a standby generator doesn't change that.

The tendency today is to approach the problem from the opposite direction. Instead of picking a handful of circuits which you consider essential you pick the biggest loads, prioritize them and connect them to your panel(s) through contactors. Everything else is connected directly to the panel(s). The big loads are few. They are things like E-heaters, heat pumps, clothes dryers, EVSE, electric ovens and any special purpose things like pottery kilns. While the average consumption due to these loads is often not much more than the average baseline load the peak demand when several of them are on at once can be 7 - 10 times greater. The strategy is to keep several of them from coming on at once. This is done by monitoring the emergency power source load and if it rises above say 80% of the supplies capacity the lowest piority big load will be shed. For example, if the heat is going full bore all over the house, there's a load in the drier, cookies in the oven and someone plugs in 2 Teslas to charge the generator will shut down the E heat for a couple of heat pumps, the ovens and the clothes dryer to keep the generator loaded less than 80%. The main heat pump stays on as do the refrigerators, lights, phones, computers, TV's, toasters, blenders,...When someone notices the generator is on, says "Hey the Telsas are charging" and goes goes and unplugs them the generator senses the load has gone down and starts restoring those loads it has shed. I have 96 kW service. All the loads I just mentioned plus the baseline (all the other loads) total 74 kW. I have a 48 kW generator and the inspector is happy with it because the system can shed 50 amps worth of loads if it needs to getting me down to 24 kW. This makes it clear that my 48kW genny is twice as big as it needs to be! It would not be twice as big as it needs to be if I had a 36 kW instant on water heater.

 

[ajdelange]

Hospitals do this by color-coding the outlets:

This is yet another level of sophistication where UPSs are involved for critical loads which cannot be interrupted for even the briefest period of time. When the utility goes down a relay connected to it deenergizes closing a pair of NC dry contacts. These are wired to the generator which using its battery operated controller starts counting. After about 30 seconds the controller starts the generator and when the generator voltage, as sensed at the transfer switch, has been stable for about 5 seconds, the transfer switch operates. During this 35 second waiting period there is no primary power. A critical load like your home computer or a respirator is often powered by batteries (within a UPS) charged by the primary power. If it goes down for a few minutes the load runs on the batteries.

 

[ReddykwRun]

Why I heat my house with a wood stove, it's cheap, I understand it, and no batteries required and independent of the grid. Oh, and the best part, the pretty colors put me to sleep.

 

[jhogan2424]

This is yet another level of sophistication where UPSs are involved for critical loads which cannot be interrupted for even the briefest period of time. When the utility goes down a relay connected to it deenergizes closing a pair of NC dry contacts. These are wired to the generator which using its battery operated controller starts counting. After about 30 seconds the controller starts the generator and when the generator voltage, as sensed at the transfer switch, has been stable for about 5 seconds, the transfer switch operates. During this 35 second waiting period there is no primary power. A critical load like your home computer or a respirator is often powered by batteries (within a UPS) charged by the primary power. If it goes down for a few minutes the load runs on the batteries.

That’s exactly the setup at my house. Whole house backup with auto switch and then I have several UPS placed in a few places I don‘t want to shut off for the short time the generator is starting and switching like internet router, POE security cams, DVR, PCs, and just a couple led table lamps. You can get away with the super cheap UPS because you only need it to hold power for the 30 seconds or so before generator kicks in.

 

[Ogre]

We just built our house my two big focuses were minimizing maintenance over the next 50 years, and minimizing power we need to survive. Didn't do "Great" at either, but did well enough at the latter than we've gone through the hottest summer in the Willamette valley in decades (ever?) with more than half a dozen 100 degree+ days with no AC. (Heating I didn't do quite as well on unfortunately)

Personally think it's irresponsible that builders are allowed to make new houses which require high powered HVAC systems during normal weather. It means during extreme weather events, homes need extreme amounts of heating or cooling. A modern built home should not turn into a furnace or a freezer if the power goes out.

... sorry what were we talking about again?

</triggered>

If your home can get by with minimal HVAC, you don't need a ton of power to keep things running if the power goes out.

 

[Luke42]

Why I heat my house with a wood stove, it's cheap, I understand it, and no batteries required and independent of the grid. Oh, and the best part, the pretty colors put me to sleep.

I grew up with good stoves.

They are simple, but have dirty emissions and are labor-intensive.

They make sense in a rural setting where you have enough trees to harvest that you can make your own fuel.

But, unlike my back-to-the-lander parents, I live in town where both maintaining a supply of firewood and managing the emissions are show stoppers. Natural gas and geothermal are much better suited to my current surroundings.

If I still lived in the rural place where I grew up, wood heat would make sense -- but there were never any jobs there for people like me, and the area is relatively unfriendly to remote tech workers.

P.S. My dad got a nifty wood heater which was essentially a 2000 gallon water tank with a supercharged wood stove in the middle. Hydronic heat from biomass. You could run a fire for 45 minutes or so and keep the house warm all night on the hot water. It required grid power for fans and pumps though, just like the gas furnace in my house.

 

[Crissa]

Hospitals do this by color-coding the outlets:

Yep! I ordered a bunch of colored outlets ^-^

-Crissa

 

[Ogre]

P.S. My dad got a nifty wood heater which was essentially a 2000 gallon water tank with a supercharged wood stove in the middle. Hydronic heat from biomass. You could run a fire for 45 minutes or so and keep the house warm all night on the hot water. It required grid power for fans and pumps though, just like the gas furnace in my house.

Requires what, 110v and maybe 250 watts?

 

[Crissa]

Requires what, 110v and maybe 250 watts?

House fans can be amazingly inefficient. Mine uses 5a at 110v. I really need to make it more efficient.

-Crissa

 

[Luke42]

Requires what, 110v and maybe 250 watts?

I don't have the specs handy, but it was in that ballpark.

But there were also hydronic water pumps and fans in some of the mini-radiators he used, so the total system power consumption may have been higher than intuition would imply. But those energy-costs would be different in other installations of this type of heater.

This is the company which made it: https://www.garn.com/

I thought adding a solar hot water heater to the boiler would have saved a lot of wood. Adding SHW to the system (located in the garage) would have been straightforward, except that he would have had to take down an apple tree that he happened to like.

It was his house, he got to do it his way -- some of the things he did were clever, and some were things I would have done differently. ??‍

 

[AZCYBER]

I hope running the inverter and charger at the same time will be an option on the Cybertruck. That would certainly make all of the questions go away.

I don't yet have any information to suggest that this is possible.

Being able to charge the truck and use the inverter (ePTO?) would make things easy and safe for those without EE-skills.



I went as far as to read a bunch of electrician-educators who interpreted the NEC sections about campground wiring.

The wiring going to the campsite is only required by be able to carry 50A (with breakers to match), even for pedestals with 50A, 30A, and 20A outlets. The assumption that you will only use one outlet is baked in to the NEC.

I'd go as far as to say that almost all campgrounds are wired based on the assumption that the 50A and 30A outlets will not be used at the same time.

It's also assumed that the full 50A load will only be used intermittently, especially at larger campgrounds.

Plugging in a full 50A EV charger + a 30A TT (mine is 30A) really should start tripping breakers when the devices pull the full load -- because one leg could pull as much as 80A.

It's really on me to manage the load to keep it below that 50A limit.



Nice!

I've done some paper designs of something close to that 14kWh battery pack, but haven't bought parts or built it yet. (I have a relevant engineering background -- so my electrical/fire safety is my responsibility.)

I've also been considering the Delta Pro portable battery pack (it has a 30A RV plug).

Is your battery pack (partially) custom built? Or is there a commercial unit I haven't encountered yet?

P.S. My wife and I both assume that campgrounds will eventually start adding an EV surcharge for those who tow with electric trucks. I'll be happy to pay it when that happens, assuming it's somewhat related to the campground's cost. I'm fine with them billing me for an extra 180kWh of electricity just because I brought an EV -- I just don't want to be price-gouged. With the marginal cost of electricity being $0.07/kWh at home, an extra $20 tacked on to my stay would be reasonable, because I'm likely to arrive with an empty battery and leave with a full battery.

Isn't a NEMA 14-50 rated for 40 amp continuous (80%x50)?