PhysicsGuy
Member
Here's a general capacitor charging and current curve so you have an idea:
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Here's a general capacitor charging and current curve so you have an idea:
There may be multiple capacitors in the inverter design, but for the purposes of the precharge circuit you only care about the lower voltage DC link capacitors, meaning the ones that are directly parallel to the input and are directly charged when you connect your low voltage power source (even with the inverter off).Nice. Thanks! Those curves are beautiful! But my question also is: what is T roughly for an 500 to 1200 VA inverter (typical)? If the capacitor is a microFarad then it would be just a few microseconds... right? But I don't really have a clear idea even to within an order of magnitude what the capacitance might be. Do you have a sense of that?
Additionally, I have little knowledge of inverter circuitry and don't feel completely confident that a single time-constant picture captures the complexity of actual inverters? I guess probably it does, I just feel a bit a bit uncertain about that...
I found the link again. This looks like a good way to do it:Nice. Thanks! Those curves are beautiful! But my question also is: what is T roughly for an 500 to 1200 VA inverter (typical)? If the capacitor is a microFarad then it would be just a few microseconds... right? But I don't really have a clear idea even to within an order of magnitude what the capacitance might be. Do you have a sense of that?
Additionally, I have little knowledge of inverter circuitry and don't feel completely confident that a single time-constant picture captures the complexity of actual inverters? I guess probably it does, I just feel a bit a bit uncertain about that...
Certainly it is much easier to use, but a bit more complex to wire and depending on how you configure and power it, the relay has a parasitic draw to keep the coil energized (which may or may not matter to you depending on your load).There was an automatic precharge circuit earlier in this thread that might be easier. Nothing to manually switch. And it would work if the car turns itself off and back on again.
Although, I would probably put the relay on the positive side, just because the chassis is negative ground. But, same idea. The resistor charges the input capacitors on the inverter. When they are charged enough, the voltage on the relay coil will reach 12V, turning on the relay and connecting the inverter to the 12V supply.I found the link again. This looks like a good way to do it:
Wouldn't a simple voltage relay likeThe car will throw a code as well.
Use a small DC to DC converter, plug into the aux acc receptacle (cigarette lighter thingy) and trickle charge a large 12 volt battery. Connect your inverter to that and you are good to go. Good enough for a fridge, freezer or entertainment centre for a couple or 3 days. You’ll need to leave the car “on”. So camp mode, keep mode, door open, whatever.
Not a great idea. Reasons: 1) the Wall Connector only allows 48 Amp max. The wires for the L1 L2 going into the panel are really big, much bigger than the 60A wires. 2) the car battery system must have an inverter to convert DC voltage to AC, that costs more and make the car more heavy. Bottom line: the EV car is not meant to be a PowerWall.Wouldn't it be great if the wall connector could be run in reverse to power your house? Charge during offpeak and use the Tesla for house power during on-peak!
Also, the HPWC has no neutral which is required to serve 120V loads. This limitation could be significant, depending on the rest of the system design. An autotransformer could perhaps create the 120V that is needed if that was part of the design.Not a great idea. Reasons: 1) the Wall Connector only allows 48 Amp max. The wires for the L1 L2 going into the panel are really big, much bigger than the 60A wires. 2) the car battery system must have an inverter to convert DC voltage to AC, that costs more and make the car more heavy. Bottom line: the EV car is not meant to be a PowerWall.
An relatively inexpensive power backup for home use is a gas generator. A PowerWall certainly can do but at very high cost.
That part is fine. You can supply power through a lower amperage generator. The problem is that the wall connector would also need a transfer switch.Not a great idea. Reasons: 1) the Wall Connector only allows 48 Amp max. The wires for the L1 L2 going into the panel are really big, much bigger than the 60A wires. 2) the car battery system must have an inverter to convert DC voltage to AC, that costs more and make the car more heavy. Bottom line: the EV car is not meant to be a PowerWall.
An relatively inexpensive power backup for home use is a gas generator. A PowerWall certainly can do but at very high cost.
Maybe for Tesla but not all EV's. F150 Lightning shows 10 PW's on wheels is more than doable.Bottom line: the EV car is not meant to be a PowerWall.
As I have already written, Tesla could easily make a charger/battery-less powerwall that would have the electronics but no extra batteries.Not a great idea. Reasons: 1) the Wall Connector only allows 48 Amp max. The wires for the L1 L2 going into the panel are really big, much bigger than the 60A wires. 2) the car battery system must have an inverter to convert DC voltage to AC, that costs more and make the car more heavy. Bottom line: the EV car is not meant to be a PowerWall.
An relatively inexpensive power backup for home use is a gas generator. A PowerWall certainly can do but at very high cost.
Mentioning this with 20/20 hindsight of course, but the battery-less Powerwall turns out to already exist as you describe, it is exactly the same Tesla Gateway from Powerwall installations - grid isolation, automatic transfer switch, at least 11.5kw support (max that the Cybertruck can output) - as announced as Powershare feature. Interesting to note the Gateway is itemized at exactly $1000 in Powerwall quotes, though there's already some suggestion that battery-less installation costs may run around $4K, which sounds expected given it's almost the same labor as doing a full Powerwall install. Already some discussion in the Energy subforum too about how Powershare deals with the lack of neutral in the Wall Connector portion as well....As I have already written, Tesla could easily make a charger/battery-less powerwall that would have the electronics but no extra batteries.
I'm not a hardware engineer, but I'm guessing such a device could be made in the range of $1000, even with a manual transfer switch and a 50A amperage limit which would be a healthy 10kW. My house uses 1kW on average.
No one is trying to turn a tesla into a full powerwall, but simply to use one for emergency use a few times a year at most.
In the meantime, we have my solution which is better than nothing, but not nearly as good and limited to 2kW
Incorrect, fuel powered generator will cost more fairly quickly, and have several more downsides....
An relatively inexpensive power backup for home use is a gas generator. A PowerWall certainly can do but at very high cost.
Incorrect, fuel powered generator will cost more fairly quickly, and have several more downsides.
Being a machine it will require regular operation to keep parts moving, annual oil changes, new filters, and cleaning.
Plus is noisy, exposed to elements (yes, generators can freeze), release CO2, CO, and possibly NO2 (others if using liquid fuel)
A neighbor had a whole-house propane generator and followed the manufacturer's CYA advice to run it once per month. That puppy was loud.