I got to witness DC arcing one day while trying to diagnose a solar array issue. I did what I wasnt supposed to do and unplugged a MC4 connector and had a inch long arc appear in the gap while pulling them apart. I had to replace the connector as it melted part of the conductor inside the connector. AC makes and breaks 60 cycles a second but DC does not.
EV developments
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BTW, if you the see the fuses up on power poles that are about 6" long with ribs on them, they have a charge inside of them, when they blow due to high current, the charge blows the connection apart so that an arc does not form. Lots of videos on You Tube of arcs and sparks with high voltage
I would not want to be around a DC charging station if there is damaged equipment that decides to go to ground.
I would not want to be around a DC charging station if there is damaged equipment that decides to go to ground.
25 years ago I worked on a physics project that had a large instrument that had different components that had to live at 50,000V DC difference form one another, in a high pressure gas containing methane. The gas was the primary insulator.
The problem was it was unstable. It would work fine up to some maximum voltage, and above that it was start to draw current (presumably from coronal discharge). Couldn't see inside a steel pressure vessel. And once it has started to discharge, it would hten discharge at lower voltages too, preventing operation.
When we opened it up (which took half a day with removing torqued bolts), it looked fine. When we put it back together, it worked again (no current), but if we went high, the same thing happened again... it started pulling current, and then it would pull current at lower voltage.
So something was happening that was irreversible, but was reversed by air.
In the end, we realized that the corona deposited carbon whiskers that drove more coronal discharge. So once the whiskers formed, the thing would discharge at low voltage too. And when air hit the whiskers... they disappeared by oxidation.
Solution... we looked at the thing under 50 kV in air, in the dark, and noted all the places where corona occurred. We then mounted little polished spherical conductors on all those locations to suppress coronae, verified they worked in air, and the thing worked in gas.
High voltage DC is weird.
The problem was it was unstable. It would work fine up to some maximum voltage, and above that it was start to draw current (presumably from coronal discharge). Couldn't see inside a steel pressure vessel. And once it has started to discharge, it would hten discharge at lower voltages too, preventing operation.
When we opened it up (which took half a day with removing torqued bolts), it looked fine. When we put it back together, it worked again (no current), but if we went high, the same thing happened again... it started pulling current, and then it would pull current at lower voltage.
So something was happening that was irreversible, but was reversed by air.
In the end, we realized that the corona deposited carbon whiskers that drove more coronal discharge. So once the whiskers formed, the thing would discharge at low voltage too. And when air hit the whiskers... they disappeared by oxidation.
Solution... we looked at the thing under 50 kV in air, in the dark, and noted all the places where corona occurred. We then mounted little polished spherical conductors on all those locations to suppress coronae, verified they worked in air, and the thing worked in gas.
High voltage DC is weird.
stoveliker
Minister of Fire
What you saw (carbon deposits) is still a problem in electron microscopes.
I once touched 7500 VDC. Failed connector (heated up too many times) that was normally enclosed (but rated for not being enclosed).
Luckily I was on an insulating platform (power and cooling underneath), on proper shoes, and I did not touch the steel vacuum system or frame. And most of all the current of the supply was limited to I believe 40 mA. Still considerable power.
I can tell you that it felt as in the dumb scifi movies where saint elmo's fire (-like) "lightning" crawls over ones skin. Very unsettling.
Back to EV charging: it would be very concerning if the vandalism would end up messing with the protective covers of these cables...
I once touched 7500 VDC. Failed connector (heated up too many times) that was normally enclosed (but rated for not being enclosed).
Luckily I was on an insulating platform (power and cooling underneath), on proper shoes, and I did not touch the steel vacuum system or frame. And most of all the current of the supply was limited to I believe 40 mA. Still considerable power.
I can tell you that it felt as in the dumb scifi movies where saint elmo's fire (-like) "lightning" crawls over ones skin. Very unsettling.
Back to EV charging: it would be very concerning if the vandalism would end up messing with the protective covers of these cables...
DBoon
Minister of Fire
I'll try to clear up some of the many questions and/or confusions about the voltage ratings posted here in the last few days (I have some experience in high voltage test and also in power electronics).
First, some background:
Power conversion systems (i.e., inverters and motor drives) convert input AC into a DC voltage and then use power semiconductors (MOSFETs or IGBTs) to switch that DC voltage on and off and create a pulse-width modulated (PWM) waveform that recreates an "normal frequency" sinewave. The width of the pulse equates to voltage (more width = more voltage) and the frequency with how the pulses go from their minimum width to their maximum width equates to the frequency (not always 50 or 60 Hz for a motor drive as the frequency is used to regulate the motor speed). The combination of voltage and frequency controls both torque and speed of a motor, but in a more complex way than can be described here.
AC, when rectified, becomes DC. 120Vac (RMS rating) single-phase becomes 170Vdc when rectified. 240Vac single-phase becomes 340 Vdc when rectified. 480Vac three-phase becomes 679 Vdc when rectified. 600 Vac three-phase (Canadian) becomes 976 Vdc when rectified. The 600 Vac "class" is generally referred to as "low-voltage" by those in the power utility or power distribution business (e.g., peakbagger). Engineers who work on printed circuit boards have a tough time with that designation
Car charging systems convert the AC (from your home 120 Vac or from a higher voltage utility supply, in the case of a DC fast charger) into a DC voltage matched to the charging voltage the battery requires. When you connect to the DC fast charger, it communicates first with the battery and then determines what the charging voltage (and current, based on battery temperature and other factors) should be and adjusts to that.
Power semiconductor MOSFETs are generally rated for 650 V or 1200 V. These 650 V MOSFETs are usually operated at 500 Vdc max. Most consumer-rated power conversion systems (e.g., lightweight wall warts, maybe lightbulbs, etc.) will convert 120/240 Vac into 500 Vdc with some sort of step-up so that these systems can univerally work with voltage inputs from a little less than 100 V up to 264 Vac (240 V + 10%). Thus, a 500 Vdc "bus" is pretty common and 650 V MOSFETs are used to create the PWM signals. You don't want to push the MOSFETs close to their safe limit because they can (and will) fail catastrophically at their hard safe limit.
If you are really curious as to how you get an AC low-distortion sinusoid out of a bunch of pulses, the simple answer is that you have to filter it. A motor winding is a great filter, so no problem there - you just need to insulate the motor windings differently for PWM inputs so the stress of the pulse impulse inputs doesn't degrade the insulation and cause it to fail. This is well known and not something that is hard to do.
Power semiconductor 1200 V MOSFETs or 1700 V IGBTs are usually operated at 1000 V max. Both 800 and 900 Vdc EV battery systems are both comfortably under 1000 V, though a 900 V battery charges at higher than 900 V, so this is probably why the China supplier stopped at 900 V for their system.
I don't know why original EVs were 350 V (Bolt and others) or 400 V originally, but the 800 V probably just came from doubling that - there was no reason why it couldn't have been 900 V initially, though the 800 V vs. 900 V could also be just a more conservative operating voltage, or was enough to deliver the maximum power using the maximum current of existing charging technologies (I don't know).
In regards to DC and AC voltage insulation differences, yes, the insulation systems for both need to be designed differently as DC and AC applied voltages stress the insulation system differently. Yes - some test standards may have specified some DC voltages to be equivalent to some AC voltage for testing purposes, but this was generally done to reduce the test cost (high voltage AC test systems must charge the system capacitance at the AC frequency, making them larger and more costly than a DC test system). If I were a lineman, I would want my protective gear (bucket trucks, rubber gloves, etc.) tested at AC and not at DC. High voltage AC-rated power cables are insulation tested with AC high voltages using specialized series-resonant test systems that use a tunable inductor to compensate for the AC capacitance of the cable under test, but these are expensive (and large, i.e., not very portable) systems. Impulses (e.g. lightning strike simulations) stress insulation systems differently from AC and DC.
First, some background:
Power conversion systems (i.e., inverters and motor drives) convert input AC into a DC voltage and then use power semiconductors (MOSFETs or IGBTs) to switch that DC voltage on and off and create a pulse-width modulated (PWM) waveform that recreates an "normal frequency" sinewave. The width of the pulse equates to voltage (more width = more voltage) and the frequency with how the pulses go from their minimum width to their maximum width equates to the frequency (not always 50 or 60 Hz for a motor drive as the frequency is used to regulate the motor speed). The combination of voltage and frequency controls both torque and speed of a motor, but in a more complex way than can be described here.
AC, when rectified, becomes DC. 120Vac (RMS rating) single-phase becomes 170Vdc when rectified. 240Vac single-phase becomes 340 Vdc when rectified. 480Vac three-phase becomes 679 Vdc when rectified. 600 Vac three-phase (Canadian) becomes 976 Vdc when rectified. The 600 Vac "class" is generally referred to as "low-voltage" by those in the power utility or power distribution business (e.g., peakbagger). Engineers who work on printed circuit boards have a tough time with that designation
Car charging systems convert the AC (from your home 120 Vac or from a higher voltage utility supply, in the case of a DC fast charger) into a DC voltage matched to the charging voltage the battery requires. When you connect to the DC fast charger, it communicates first with the battery and then determines what the charging voltage (and current, based on battery temperature and other factors) should be and adjusts to that.
Power semiconductor MOSFETs are generally rated for 650 V or 1200 V. These 650 V MOSFETs are usually operated at 500 Vdc max. Most consumer-rated power conversion systems (e.g., lightweight wall warts, maybe lightbulbs, etc.) will convert 120/240 Vac into 500 Vdc with some sort of step-up so that these systems can univerally work with voltage inputs from a little less than 100 V up to 264 Vac (240 V + 10%). Thus, a 500 Vdc "bus" is pretty common and 650 V MOSFETs are used to create the PWM signals. You don't want to push the MOSFETs close to their safe limit because they can (and will) fail catastrophically at their hard safe limit.
If you are really curious as to how you get an AC low-distortion sinusoid out of a bunch of pulses, the simple answer is that you have to filter it. A motor winding is a great filter, so no problem there - you just need to insulate the motor windings differently for PWM inputs so the stress of the pulse impulse inputs doesn't degrade the insulation and cause it to fail. This is well known and not something that is hard to do.
Power semiconductor 1200 V MOSFETs or 1700 V IGBTs are usually operated at 1000 V max. Both 800 and 900 Vdc EV battery systems are both comfortably under 1000 V, though a 900 V battery charges at higher than 900 V, so this is probably why the China supplier stopped at 900 V for their system.
I don't know why original EVs were 350 V (Bolt and others) or 400 V originally, but the 800 V probably just came from doubling that - there was no reason why it couldn't have been 900 V initially, though the 800 V vs. 900 V could also be just a more conservative operating voltage, or was enough to deliver the maximum power using the maximum current of existing charging technologies (I don't know).
In regards to DC and AC voltage insulation differences, yes, the insulation systems for both need to be designed differently as DC and AC applied voltages stress the insulation system differently. Yes - some test standards may have specified some DC voltages to be equivalent to some AC voltage for testing purposes, but this was generally done to reduce the test cost (high voltage AC test systems must charge the system capacitance at the AC frequency, making them larger and more costly than a DC test system). If I were a lineman, I would want my protective gear (bucket trucks, rubber gloves, etc.) tested at AC and not at DC. High voltage AC-rated power cables are insulation tested with AC high voltages using specialized series-resonant test systems that use a tunable inductor to compensate for the AC capacitance of the cable under test, but these are expensive (and large, i.e., not very portable) systems. Impulses (e.g. lightning strike simulations) stress insulation systems differently from AC and DC.
I read today that China has the opposite charging situation as the US. They have a glut of charging stations . Now their oil companies want a slice of the pie. "The state-owned oil companies together operate about 50% of the more than 100,000 gas stations in China and fuel sales account for almost half of their revenue." Most of the charging stations are grid owned, but the handwriting is on the wall and the oil companies want EV charging to supplement revenue. They have the properties set up for vehicle fueling in good locations. Now they are investing in charging.
So here's a thought, cut all subsidies to American oil companies except those earmarked for expanding the charging infrastructure here.
So here's a thought, cut all subsidies to American oil companies except those earmarked for expanding the charging infrastructure here.
EbS-P
Minister of Fire
Tesla sales missed expectations. Media seems to be really hitting them hard for this. We know now that EV sales rate increases are not to be expected in the short term. But inhale not heard anyone mention the the reduction of the tax credit for as a contributing reason for the lower than expected sales.
My take anyone wanting a new EV would have bought it in Q4 to get the extra tax credit. My parents did that. Model 3 is not eligible for any tax credit right now. That has to hurt sales in the short term. I assume that they will have it eligible again. The lease is still available with the full 7500 credit. Probably not a bad deal. But the value of used Teslas could see a big increase if Telsa get full autonomous approval.
My take anyone wanting a new EV would have bought it in Q4 to get the extra tax credit. My parents did that. Model 3 is not eligible for any tax credit right now. That has to hurt sales in the short term. I assume that they will have it eligible again. The lease is still available with the full 7500 credit. Probably not a bad deal. But the value of used Teslas could see a big increase if Telsa get full autonomous approval.
I just dont see Tesla getting and keeping full self driving anytime soon unless the congress gets its act together and passes some sort of blanket liability cap on accidents caused by self driving or go with the vaccine approach where lawsuits are not allowed but a government entity awards damages. There is still much case law to be made on what party is responsible for self driving accidents. My guess is its going to bounce around the legal system for a decade or so while firms like Tesla keep up the "wink wink nod" game of keeping the driver engaged and responsible. The problem is driving requires full concentration and if a driver is not actively driving, if there is an issue, its unlikely they will be able to shift focus quickly enough to keep an accident that the FSD missed from happening.
GIven the issue in San Francisco, FSD is not yet ready for prime time and may not be for awhile.
GIven the issue in San Francisco, FSD is not yet ready for prime time and may not be for awhile.
stoveliker
Minister of Fire
I thought Tesla's sales numbers were down because of lower sales in China - which does not relate to the US tax credit.
EbS-P
Minister of Fire
stoveliker
Minister of Fire
in 2022 Tesla's second largest sales volume was in China.
So if global numbers are going down, and China has competitive domestic models, it stands to reason that sales there are a big part of the problem.
Indeed, that's what's been reported by analysts - though I can't vouch for credentials and thus reliability.
Dan Ives (Wedbush Securities) said the biggest problem is likely Tesla’s sales in China, which he estimates fell 3% compared to a year earlier. He described Chinese demand as “very soft coming out of the gates for 2024.”
So speculation, but reasoned speculation.
So if global numbers are going down, and China has competitive domestic models, it stands to reason that sales there are a big part of the problem.
Indeed, that's what's been reported by analysts - though I can't vouch for credentials and thus reliability.
Dan Ives (Wedbush Securities) said the biggest problem is likely Tesla’s sales in China, which he estimates fell 3% compared to a year earlier. He described Chinese demand as “very soft coming out of the gates for 2024.”
So speculation, but reasoned speculation.
Sales numbers or sales revenue, or both? Didn’t they lower prices? That’ll drop revenue unless it is offset by higher numbers sold.
Looks like Tesla has dropped its low-cost car plans.
Ford has slowed down EV production and is making more hybrids instead. Kia will be making both with a potential more affordable EV in the wings.
electrek.co
Kia suddenly shifts to hybrids, affordable EVs amid 'waning global demand'
Kia is following in Ford’s footsteps after suddenly announcing plans to introduce more hybrids as it expects slower EV demand....
electrek.co
EbS-P
Minister of Fire
If true, Tesla has given into and acknowledged that BYD is the sole low cost manufacturer in the world. That will have dire consequences for the US.
I’m still skeptical if this is true. Partly because the robo taxi will could nearly identical to the small cheap call it model 2. Why not sell to two markets? My guess is they now know that they can’t sell the volume needed to hit the profit numbers for the next 5 years.
There are several nice, under $30k EVs sold in China in addition to BYD's. Geely, GM, GWM, MG, NEV, etc. are competing brands. It looks like Xiaomi will have one out soon too.
www.theautopian.com
I Went To China And Found These Incredible Electric Cars You’ve Never Heard Of - The Autopian
In the West, there is a lot of blabber about the future of electric vehicles. Some say that the future will never arrive, others say it is coming soon. In Europe, things are speeding up a bit, but many carmakers are wrestling with legacy cars and factories. BMW, for example, still offers a...
www.theautopian.com
EbS-P
Minister of Fire
Timing isn’t right here. Our protectionists trade policy which I mostly agree with right now will keep all those models maybe minus the Volvo from being sole here.There are several nice, under $30k EVs sold in China in addition to BYD's. Geely, GM, GWM, MG, NEV, etc. are competing brands. It looks like Xiaomi will have one out soon too.
I Went To China And Found These Incredible Electric Cars You’ve Never Heard Of - The Autopian
In the West, there is a lot of blabber about the future of electric vehicles. Some say that the future will never arrive, others say it is coming soon. In Europe, things are speeding up a bit, but many carmakers are wrestling with legacy cars and factories. BMW, for example, still offers a...
We will keep buying big tucks and suvs. Complaining about who’s in charge politically and about how insurance costs keep going up but never really caring enough to change. We’ll wait till 2050 meanwhile overshooting most emissions targets on the way then wonder why we didn’t do something sooner.
Small economy cars don't sell in North America, regardless of powertrain.
My brother just bought himself a Mitsubishi Mirage as a commuter car. Their sales numbers are pitiful compared to other larger models, like less that 5,000 units per quarter. And this after many competing cars (such as the Chevy Sonic) left the market leaving it essentially the only option.
I'd say it's a smart business move for Tesla, much the same way it's a smart business move for Ford to move away from EV's and to Hybrids, at least for the time being.
Sure EVs may be the end game but if electric tech has to be sugar coated with hybrid tech its a start. As usual some companies are gaming the system by meeting the hybrid classification for any incentives but just using the excuse to use it as a performance enhancer, I believe that is the Jeep approch and no doubt Dodge will do it. I would like the US to at least phase in plug in requirements and larger hybrid battery range. When someone figures out that they can drive 20 or 30 miles a day without going to a gas station, that is a nice way to get them used to it. Its a big step to go straigth to EV.
I know the topic of range anxiety is popping up with my friend with a new Ford Lightning. There are no DC charging options locally so he is unable to practice with them and will be charging in his garage. Not an issue with me with my plug in hybrid, run out of charge and I have 500 miles of gas range.
I know the topic of range anxiety is popping up with my friend with a new Ford Lightning. There are no DC charging options locally so he is unable to practice with them and will be charging in his garage. Not an issue with me with my plug in hybrid, run out of charge and I have 500 miles of gas range.
I think this is too dire. Tesla is a production cost leader across EV size segments, had been aggressively innovating in that space, and bringing that (derived in Shanghai) tech to the US.
They are just choosing to put their resources into other size segments (including cyber and semi) at this time, presumably because the projected margins are better than for the model 2. They are still cell limited, and the profit per cell is what matters.
And the US tastes and wealth means that they can sell 'cheap' Highlands and Junipers for years before anyone here cries bc they can't get a model 2.
They are only conceding the 'compact EV' segment in China, which is hugely overpopulated and CCP govt subsidized, seems like a savvy business decision to me.
Or folks will flock to Model Y, Model 3, Cyber and Semi for the next 2-3 years... the legacy brands will struggle to adapt to this competition, get bailed out, maybe get bought up by chinese brands in 2028, and electrification will continue apace.
After GM promised Ultium BEVs would launch and sell at scale for the last several years (looking at World Series and Superb Owl ads), and then delivered a pitiful number of, um, Hummers... I really doubt that they are going to be selling anything like a PHEV in the next couple years after this 'pivot to hybrids'.
In 3 years PHEVs will still be niche, and GM and Ford will be selling their next generation of BEVs with CATL-tech packs inside. They are likely licensing that tech for US production as we speak. Tesla has already recieved CATL production hardware in NV.
The 'pivot to hybrids' is a vaporware strategy intended to keep their investors, if not happy, from panicking en masse.
Stellantis? Still at the starting gate.
EbS-P
Minister of Fire
If it were full IRA tax credit eligible a decent small 5 seater sedan or hatch with 240 miles of range could be a great seller IMO. It’s not a replacement for those with cars less than 10 years old but as a supplement. You can keep the family truckster on the road for many more years if you are not piling on 10k miles a year of city/commuter driving. I had to fill up my van for the first time in 3 months. It’s seen some road trips. But not more than 2k miles since September. Wife isn’t happy about being seen in a 2011 Odyssey but it’s paid off and has a lifetime warranty with $100 deposit. Dealer loves me. Only once when oil pump had to be replaced/resealed were they not able to do it for what the warranty would pay. And I gladly paid the deposit and $75 difference. They tacked that warranty on 6 days after number 3 was born (a few week premature) and I laughed at him telling the sales man I would run it into the ground. 8 years later to the day 90k miles I need to take it in and have some more work done.
If true I think this choice sets the US adoption curve back 5 years. Tesla is setting the bar in the US. I read a Nissan exec said the magic number is 70 miles electric range without adding more weight. (Just make the car smaller dummy).
Thinking more about it. The pause/cancelation of giga Mexico is probably some evidence that Tesla is pausing the small cheap car.
I’m still skeptical that their is not enough demand to make a small EV profitable it if your still limited by battery production capacity you would put those batteries in the most profitable product.
I don’t think Ford and GM will have competitive products at volume over 75k units a year in 3 years. And the definitely won’t be a small BEV.
As down as the media is on Tesla their stock price probably did need a bit of correction. The new hybrids will roll out in the next 12 months based on the last generation teach with current battery tech and a range of 30-40 miles. Meanwhile all the products that were to be released 2022-2025. Won’t be competitive in three years. So effectively they/we have lost two BEV design cycles. And will have to wait for the hybrids to reach volume another 24 months. Then what…. Maybe Tesla will have a robo taxi and none of us need cars anymore.
EbS-P
Minister of Fire
A well reasoned take on where Tesla stands and could go.
www.autoevolution.com
Full Self-Driving Looks Cool but Tesla Betting Everything on a Robotaxi Is a Stupid Move
Full Self-Driving success may have blinded Musk to bet Tesla's future on the robotaxi even though the volumes for such a vehicle would be abysmal
www.autoevolution.com