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Tesla Wall charger using DC input source.

Tesla Wall charger using DC input source.

The Tesla chargers should be updated to allow connecting to a DC source. I had to buy a $20,000 Chadeemo Charger for my Tesla,so I could charge my car from my 250kW Nickel Iron battery bank. I currently charge at 10kw, which is fine for home charging. It would require very little effort on the part of Tesla to update the chargers to allow for connecting directly to a Solar array and/or battery bank.

A slow 3kw charger would be sufficient for most daily charging needs, which would allow many Tesla owners to charge from a typical offgrid energy system, such as a 48v 50kw battery bank.

Earl and Nagin ... | 29/09/2016

@tommy,
I understand your need but it is a significant minority of all EV drivers so I can see how Tesla might not see it as being profitable to support that directly, expecially when other options usually exist. Even those of us who have solar PV with off-grid capability usually have it coming out as standard AC which we can use with our mobile connectors or J-1772 Level 1 charging cables. Just think of all the different DC input voltages this kind of system would have to support.

JAnnen | 29/09/2016

@tommy,
I am interested in your CHAdeMO Charger. Does it work? What DC input Voltage are you using from your Nickel Iron battery bank? Most Nickel Iron battery banks are set for around 48 VDC. Most CHAdeMO Chargers are set to input 450 VAC 3 phase and can easily be converted to input 450 or 500 VDC using the same Buck convert. The 48 VDC input requires a high current step-up converter.

It would be easier, more reliable and cheaper to use your Nickel Iron battery bank to drive a standard 240 VAC inverter which is probably in use on your system already. Why not use it?

The Tesla charger in the car converts 110 to 270 VAC to 400 VDC, but Tesla could easily modify it to also accept 150 to 300 VDC as input. Tesla would also need to convert the EVSE (HPWC) to input and output DC. Both modifications are easy, but I am sure Tesla will not do either one.

johndoeeyed | 29/09/2016

I expect the Powerwall2 (to be announced Oct 28) to have DC input to the car from the DC output of the Powerwall2.

tommy | 30/09/2016

@Earl and Nagin Actually, the circuitry and design change is very minor to adapt to a wide DC voltage range. The end user would have to set the maximum charge rate depending on the storage capacity and C rating of the battery bank.

@JAnnen My entire home operates only on DC power directly from the battery bank--no inverters here! :+)
I run multiple DC rails from my NIFE battery bank to power everything in my home--all appliances are DC powered. Yes, my Chademo unit works and was modified for my specific needs; I have it connected to 120v DC rail, but the unit can accept a wide input voltage range up to 500v DC. I have a 45kW solar array connected directly to the batteries--no expensive or sophisticated solar charge controllers; just a few home-brewed intelligent combiner boxes.

@johndoeeyed A likely assumption given the efficiency of avoiding the inverter step. But, a powerwall is still based on lithium technology, which requires sophisticated electronics to manage the cells and you have a battery that has a limited shelf life (3700 cycles). My NIFE battery bank does not sulfate or suffer from overcharging and deep discharging problems common with all other battery chemistries. I anticipate my Nickel Iron battery bank will last 100 years. I even eliminated the maintenance task of topping off the electrolyte with distilled water by collecting rainwater, which is passed through a solar distiller I built on my roof. The distilled watery is gravity fed into a storage tank which in turn gravity feeds the cells.

As far as I can tell, I have an energy solution that will operate for two or three decades without the need for any maintenance. However, I will probably flush the electrolyte every ten or 15 years.

Why am I not connected to the grid you asked!? well, I have zero interest in supporting power produced from nuclear, natural gas, coal, fossil fuels, or pig farts! The bad-ass nuclear reactor in the sky is all we need to power the world; it's time to start working towards putting all other producers of energy out of business!

@Dirty Energy Producers: Thank you nuclear and oil producers for being there when we needed you,but it's time to let solar take over--you can either invest in it and transition or be pushed out of business.

"The Tesla charger in the car converts 110 to 270 VAC to 400 VDC, but Tesla could easily modify it to also accept 150 to 300 VDC as input. Tesla would also need to convert the EVSE (HPWC) to input and output DC. Both modifications are easy, but I am sure Tesla will not do either one." -JAnnen

@Elon Musk / JB Straubel - Please make JAnnen eat those words, as I'm sure he would be happy to do so! :+) Send a memo and have your engineers make those updates to your chargers! I estimate it would take 20 or so wo/man hours to redesign the units. Us offgrid folks sure could use them! EVSE charging directly and affordably from a DC source is the only hurdle to taking entire suburbs offgrid. The ability to power a vehicle in remote locations directly from solar power will boost Tesla sales by a considerable margin! A bit of mppt support and the chargers could be connected directly to a solar array for daytime charging, which is a considerable saving in energy by avoiding charging a battery from another battery.

johndoeeyed | 30/09/2016

@tommy
I expect the Powerwall2 will take DC input directly from solar PV panels and convert it for the DC required for the car. I expect the Powerwall2 will have the car charger as part of it. It may therefore be possible that your existing battery bank can be connected directly to the Powerwall2.

tommy | 30/09/2016

@Johndoeeyed

"The main changes are a simplification to the handling and wiring requirements for installers, as well as the introduction of Powerwall compatibility with inverters from SMA.”

The home based powerwalls are not big enough to charge one or two EV's and power an entire home at night.

Also, Using lithium cells on stationary applications such as residential and commercial property is just wasteful. You need an average of 200kW of battery storage to have a usable system to actually power your home and charge your cars without supplementing with Nuclear and Coal produced power.

Inverters and Alternating Current is the real evil here! Inverters are what bastardize and drive up the cost of Solar and battery based energy systems.

The money I saved by not using inverters covered the cost of replacing all my appliances.

I have four 2ton Air conditioners that operate on 48v DC.

Modified 1500 Watt microwave oven using 120v DC input.

Modified washer and dryer using all DC motors and electronics at 48v DC.

Cat6A cabling powering a mix of electronics, computers, and televisions.

If I have a laptop that needs 24v DC, then I just go to the battery room and connect the port on the patch panel to the proper rail, then connect the laptop to the proper drop. Same goes for powering any device in my home. I just have to think about what I'm plugging in and what it's voltage requirement is and assign that voltage to the network drop.

No more need for AC power or inverters!

johndoeeyed | 30/09/2016

@tommy
I am talking about the next version of the powerwall, not the current one
I am talking about DC-DC conversion, not DC-AC-DC inverters
I am talking about bypassing the powerwall batteries for charging the car

makobill | 30/09/2016

@johndoeeyed - Agreed on your three points - and especially the third. Bypassing the battery charge with solar to charger is something I'm thinking is going to be built into the unit. I'm not expert by any means, but something I've been thinking as I ponder the October announcement...

Rocky_H | 30/09/2016

I do chuckle just a little at the optimistic attitude that everyone should do this, while wondering about the really large amount of space a 45kW solar array and 250kWh nickel iron battery bank takes up. Doesn't seem like there is the real estate available in most places for each family to deploy something like that.

tommy | 30/09/2016

@Rocky_H

Hi Rocky, the actual footprint is not large given the energy production of my system. My panels are 81"x41" and 435w each. My system is larger than required for most residential homes. 40 of my panels can fit on a typical rooftop. 16kW is all most people would ever need. My battery bank is a beast, but again, is more than most will need. I have 200 1200AH NIFE cells configured as a 120V 2400AH battery. The entire solution fits in a single 20ft shipping container. Depending on the locale and type of home, the battery bank could be designed to fit as an exterior wall or under a false floor. most homes have enough yard space to accommodate a battery room. NIFE batteries can be tightly packed and arranged in different configurations like Legos--no different than the designs seen with battery packs for EV's.

Rocky_H | 30/09/2016

Wow, that's still pretty huge. I'm getting the solar system put on my house in the next month or two. We're doing about a 5-6kW system, depending on how many panels can fit onto the roof. It's only a 1600 sq ft house, and that should account for about 90 to 96% of our annual usage. Grid tied and net metered still seems by far the most cost effective way to do solar right now.

tommy | 30/09/2016

@Rocky_H For me, it was more about boycotting the use of any energy produced from Nuclear, Coal and Gas--I didn't care what it cost to end my dependence on dirty energy. The last five years has been an interesting learning experience.

You'll harvest 25kW-35kw on average. a 5-6kw array using current panels should need no more than a third of your rooftop. I believe your solar array will only cover a third to half of your energy needs, not even close to your stated 90%.

Are you leasing or buying? Are you going with the solar city solution? I'm not really a fan.

JAnnen | 01/10/2016

@Tommy, I also use an off grid array and a patch panel to allow different outputs. Most of my house is still on the grid.

When I tried to get Solar City and others to install an array on my large low slope (flat, horizontal) roof, they said no. They can only install on my small area sloped conventional roofs that are in the shade. So I did it myself.

The PV modules are amazingly good and cheap, but the inverters seemed expensive. However, Google (Larry Page, good friends with Elon) had just announced "The Little Box Challenge."
https://www.littleboxchallenge.com/
https://eengenious.com/7500-2/

I decided to wait for inverter improvements. My hybrid system is working, but I will eventually use AC inverters.

Questions:
1. What DC switches do you use?
The common, 3 for a dollar, AC light switches are horrible for DC over 100V. Thermostats ( space heater, hot water heaters...) burn out from the DC electrical arc. Very bad. I use home brew IGBT switching circuits and big AC knife switches.

2. What PV module MPPT (Maximum power point tracking) do you use? This can make a factor of four difference is the power and energy a PV array can output, but optimizers can cost as much as the PV modules.
https://en.wikipedia.org/wiki/Power_optimizer

My guess is that you have such a large array and battery the you don't need to worry about efficiency. The SolarEdge DC/DC converter power optimizer on each module is the best, but optimizers are still improving.

Rocky_H | 03/10/2016

@tommy, Quote: "You'll harvest 25kW-35kw on average. a 5-6kw array using current panels should need no more than a third of your rooftop. "

I was a little off on my memory. It's closer to 7kW for the initial estimate, but that still may vary by a little when they design to see where and how they can fit the number of panels.

Quote: "I believe your solar array will only cover a third to half of your energy needs, not even close to your stated 90%."

Well, your assumption is wrong. This was calculated with the known annual solar intensity for this area, and for the amount of electricity we use per year, which is fairly low.

SUN 2 DRV | 04/10/2016

Tommy:

I have a 4400 sq ft house, drive my Tesla 22k miles a year and my 7kW solar array gives me a Net ZERO annual electricity bill. I suspect that Rocky will do just fine with his 7 kW system too.

And to preserve your credibility you should pay a bit more attention to the difference between kW and kWh...

tommy | 05/10/2016

@joehuber

"And to preserve your credibility you should pay a bit more attention to the difference between kW and kWh.."

Point well taken! I do know the difference thanks to Dr. Google. first thing I had to learn when I purchased a shipping container full of panels and started down this path years ago.

DISCLAIMER: I'm not an electrical engineer, I do not have a background in electrical engineering, whatsoever! Anything i discuss or communicate on this forum is merely opinion based on my experience.

Joe, do you mind posting what your electric bill looks like? monthly electric usage? solar pv array output for the month? Are you able to determine how much energy for the month was generated by the solar array versus the power company?

a 7kW array connected to the grid is actually more like a 5kW array given losses across the system. But, using 7kw as max energy production, you are looking at an average 38.5Kw peak production over 5.5 hours (depending on weather, time of year and where you're located). I estimate an additional 10kW total for morning and evening production, totaling 48.5Kw total energy production per day from your PV array. I would like to see if your bill reports different figures than my assumptions here. I've learned the panel sticker is a far cry from real world production.

My half empty P85 would consume your arrays total daily harvested power to just recharge the car. I assume your 4400sqft home has approx 96,000 btu (six to eight tons) HVAC system; which would also exceed your total solar pv production on a hot day.

In my opinion, grid tied solar helps marginally if at all with regard to the problem of Nuclear and Coal power plants. You are using most of your power at night when you are occupying the home and running all your household appliances and charging your cars. Therefore, you are primarily using dirty energy to power your zero emission Tesla. if this sounds judgemental it is not! :+)

Your electric bill netting zero dollars each month may not indicate that your producing more power than you're consuming ( I concede it can mean this) if you are likely taking advantage of a time-of-use metering plan. that is, producing power and selling it at peak rates and consuming during lower rates, such as waiting to charge in the middle of the night when your electric rate is cheaper than the rate your panels were producing and selling power back to the grid.

Because I HATE the actual dirty energy grid and don't really think of it often these days, I may be wrong about your actually household energy usage and what you are drawing from the grid versus giving back.

cheers.

tommy | 05/10/2016

@Rocky_H

I hear I'm wrong quite often!

Can you tell me what your monthly energy usage has been the past year? should be an easy copy and paste from your online account to the forum. :+)

tommy | 05/10/2016

@ JAnnen | October 1, 2016

@Tommy, I also use an off grid array and a patch panel to allow different outputs. Most of my house is still on the grid.

Questions:
1. What DC switches do you use?
The common, 3 for a dollar, AC light switches are horrible for DC over 100V. Thermostats ( space heater, hot water heaters...) burn out from the DC electrical arc. Very bad. I use home brew IGBT switching circuits and big AC knife switches.

2. What PV module MPPT (Maximum power point tracking) do you use? This can make a factor of four difference is the power and energy a PV array can output, but optimizers can cost as much as the PV modules.
https://en.wikipedia.org/wiki/Power_optimizer

My guess is that you have such a large array and battery the you don't need to worry about efficiency. The SolarEdge DC/DC converter power optimizer on each module is the best, but optimizers are still improving.

ANSWERS:

1: What DC switches do you use?

NONE. I do not use any dc-to-dc switches to power my household appliances and electronics. NO Alternating Current or inverts either! :+)

All my appliances and electronics connect directly to the battery bank with fuses to protect from over current.

How did I do that? I have one-hundred 1200AH Nickel Iron batteries connected in series and another 100 in parallel making a 2400AH 120V nominal battery bank.. Each cell is a nominal 1.2 volts and 1.5 fully charged.

I have DC rails coming off the battery bank to make up various voltages I need for my appliances.

I have five 24000btu mini split heat pumps that operate directly from 48vDC. My microwave oven is a modified 1500W electrolux that now accepts a 120V DC input and Same for my washer and dryer. I distributed the loads and staggered the rails across the cells to mitigate cell balancing issues. To further mitigate cell variance, I have a mix of panels that have varying open circuit voltages connected to respective DC rails on the battery bank.

some things were a real challenge like finding 4K tv's with the bridge rectifier (power brick) outside of the TV. Only a select line of Sony Bravia televisions still use a power brick, whereas all TV's now just have AC power cord coming out of them. my 4K tv's are connected directly to the battery bank 24V rails.

My 10kW Chademo charger connects to the entire 120V nominal battery bank. I can charge My EV's directly from solar power without the use of the grid or inverters day or night.

my 435W panels have an open circuit voltage of 86 volts, so I connected a dozen to the first 55 cells and another dozen on the overlapped other 55 cells (only 100 in series so 10 cells overlap). The panels can never overcharge the cells because the 55 cells at full charge will reach 82 volts and given line losses, the panels really never push more than 80 volts each. Also, my batteries are always under load, so it's impossible for the solar array voltage to damage the cells.

2. What PV module MPPT (Maximum power point tracking) do you use?

NONE. I use home-brewed "intelligent" combiner boxes (ICB's) that regulate the number of panels I have connected to the battery bank at any given time. Instead of using big IGBT's, I use heavy duty 400amp rotary DC disconnects that are controlled using servo motors to turn them on and off; my stab at my own little arduino project. Full 40kw array performs a bulk charge during the morning, and by noon the battery bank is fully charged and the Combiner Box begins to disconnect half the array by turning the DC disconnects using the servos.; This way, i can keep my battery bank charged even during cloudy days.

If you are grid tied, you can use the grid to cover the days your array is inadequate, but us offgrid folk have to oversize our arrays for this regular occurrence.

My solution has been working perfect for nearly two years now. In three more years, I will break even on the full investment, and will get at least another three decades of free energy. the batteries will last 100 years, maybe more.

milesbb | 05/10/2016

@Tommy

can you explain how you charge your 350 / 400 volt DC Tesla Battery using 120 volt DC. I understand the CHAdeMO connection and communication protocol gives you DC access to the battery. I just do not see how you charge with a lower voltage DC source.

PS you are still using kWh and kW interchangeably.

tommy | 05/10/2016

@milesbb

the charger is just a big boost buck converter using the chademo protocol.

"you are still using kWh and kW interchangeably."

I'm just being lazy. I don't see the need to communicate the amount of power over time, rather just how much power is being consumed or produced, hence why i just state kw.

milesbb | 05/10/2016

@ Tommy
What CHAdeMO unit you are using? I would like to research to better understand. Everything I have looked at uses 480v 3 phase as the source, not DC.

milesbb | 08/10/2016

@ tommy
wow I had no idea anyone was making this type of equipment. They have a car to car charger rated at 50 kW. Car to car charging has been mentioned a number of times on this forum and no one has mentioned ORCA products. I assume the car to car charger will not work with a Tesla as the Donor. Tesla's DC input is contactor switched between AC and DC. Without some override modification to the contactor you will be locked out of using the Tesla battery as a source.

ORCA also has direct solar to car charging, which also has been discussed widely in this forum.

I asume all of these ORCA products are priced way above what 99% of the folks on this site are willing to pay. At least they can be had for the person with no cost limitations.

You state you charge at 10 kW. The ORCA claims to operate up to 50 kW. Is this reduced charge rate due to your system limitation or is this due to the ORCA being modified to accept the lower 120 VDC input?

Interesting thought about using the existing onboard charger as a DC to DC converter. Tesla has not had good luck with the DC to DC converter that feeds the 12 volt battery. If done the contractor switching will have to differentiate between low power low voltage DC that gets routed to the onboard charger and the high voltage high power that gets directed to the battery DC.

Say Tesla came out with a modified onboard charger and a modified HPWC that would allow direct DC charging. I think Tesla would want a significant option price for this. Even if they include this in all cars they would likely charge those that want it turned on, just like the 75 kWh battery, auto pilot, and 72 amp charging. But if the alternative is purchasing a $20k ORCA they will have room to work.

Thanks

johndoeeyed | 08/10/2016

@milesbb
I expect the DC-DC converter to be in the Powerwall2, not the car.
I expect the equivalent of the HPWC to be incorporated directly into the Powerwall2.

milesbb | 10/10/2016

@johndoeeyed
I understand your position. @tommy argues that the power electronics that is needed to do the DC-DC conversion already exists in in the onboard charger. I believe his argument has some merit. Also the Powerwall solution would not work for a custom non Tesla system like @tommy has. I also believe the confusion that would come with this offering as @tommy suggests would be confusing and possibly misused by the general public. Using the power wall as you suggest could avoid some of the confusion and risk.

I believe the efficiency loss of doing the charging through an existing inverter using AC is not that significant. Better tools to control the charge current to match the solar panel output could be provided by Tesla. The new HPWC already has load share so load control is already being done. I do not understand why @tommy is so strongly against AC. All of the modifications he has done on every load in his house to accept DC seems like a royal pain. I do not believe the modifications you or @tommy are requesting will be available for a long time. But I wish you both luck in getting what you want.

johndoeeyed | 10/10/2016

@milesbb
The superchargers consist of multiple AC-DC inverters working in parallel and bypass the car inverter.
DC-DC converters can cater for a wide range of input and output voltages with high efficiency.
I expect Powerwall2 will cater for DC-DC, AC-DC and DC-AC.
We will find out soon :-)