Business Charger for Employees

[MrMassTransit]

Ha! That's not how a transformer works, though. It trades off voltage for current. So if they have a line providing 30A that is at 208V, that is 6.24 kW of total power. You want to buck that voltage up to 240V? Then you get only 26A, but the power is still 6.24 kW, so you get exactly the same charging speed.

What's being missed here is that the cars have an amperage limit so a higher voltage results in faster charging. For an SR+ car that accept 32 AMPs, that will result in 7.7 kW @ 240V, but 6.7 kW @ 208V. While the transformer is trading off additional current for voltage, since presumably the circuit and the transformer are nowhere near capacity, the car will be able to draw 32A at a higher voltage and thus charge faster. On a 50 amp circuit, the transformer is not going to limit to the car to 26A when boosting voltage to 240 unless I'm misunderstanding something.

I don't think they are really needed for employee chargers that are provided as a benefit. For any employee charging at home (even on 120v) and can charge during a normal workday, even in a situation with a lot of voltage drop the car should be able to pick up enough range for a fairly lengthy commute.

 

[miimura]

One thing to consider is whether your company's accounting department needs to track charging usage or not. They may need to track whether it's employees charging vs. visitors, total energy dispensed, amount used by specific employees, etc. I have heard that many companies pay the extra up-front costs and recurring fees for ChargePoint L2 stations because they provide the reporting that is required.

 

[Rocky_H]

What's being missed here is that the cars have an amperage limit so a higher voltage results in faster charging. For an SR+ car that accept 32 AMPs, that will result in 7.7 kW @ 240V, but 6.7 kW @ 208V. While the transformer is trading off additional current for voltage, since presumably the circuit and the transformer are nowhere near capacity, the car will be able to draw 32A at a higher voltage and thus charge faster. On a 50 amp circuit, the transformer is not going to limit to the car to 26A when boosting voltage to 240 unless I'm misunderstanding something.

I'm not missing that at all. I know that the car could get faster charging if you could just magically turn up the volts without lowering the amps, but that's not what a transformer does. This still goes back to my point about equipment build and cost. In order for them to provide for 32A at 240V, (a 40A rated circuit), they would have to start with a 208V 50A rated circuit, to have that level of power, which has thicker, more expensive wiring, and then put a transformer on each one of those lines somewhere, which steps up the volts and steps down the amps. That is a lot of extra equipment cost, putting an extra transformer on each line. Or, as I suggested before, they could put in one really large, expensive transformer farther upstream, on a really large supply like 300A or whatever, and then split that off into the separate lines for each station.

Here's an example of a 75kVA boost transformer that would do it for $3,114.54
Larson Electronics - 75 kVA Isolation Transformer - 208V Primary - 120/240V Secondary - Single Phase - NEMA 3R

Either way, the company isn't going to give a $#*t about the amp limits your car has if it is talking about costing them extra thousands of dollars in installation cost, just because of people being dissatisfied that their employee perk isn't perky enough!

 

[Sophias_dad]

Ha! That's not how a transformer works, though. It trades off voltage for current. So if they have a line providing 30A that is at 208V, that is 6.24 kW of total power. You want to buck that voltage up to 240V? Then you get only 26A, but the power is still 6.24 kW, so you get exactly the same charging speed. Except that would be only if a theoretical transformer is perfectly 100% efficient, which it can't be, so you would actually lose a little bit of power and therefore charging speed, just from trying to manipulate the voltage.

Maybe you're saying back at their source with 200A or 300A main supplies, they could boost it, and then split off a 40A or 30A line from there? But then that gets into much bigger and way more expensive equipment that the company definitely won't want to foot the bill for just because some people are whining that the charging being provided for them isn't as fast as they want.

Actually, I know full well how a transformer works... Thanks! The transformer wouldn't say "I want 30 amps input at 208V", leading to 6.24kw on the 240 side.... The HPWC or other equipment would allow let's say 30 amps of current to be drawn(more likely 32, 40, or 48, but whatever), and the transformer would then draw enough amperage(at 208V) to drive the output at 30 amps/240V.. I'm gonna say that's around 35 amps... Notably, the boost transformer doesn't need to be rated to the full 240v/30 amps, but rather a much smaller level.

Here's a handy URL...https://federalpacific.com/tools/buck-boost-transformer-calculator-selector/.....It shows you can get 240V/40A out of a 208V/46.9A line, using a Federal Pacific K1XGF16-1.5 transformer... Its $215 at 1.5 KVA Transformer Primary 120 x 240 Secondary 16/32 Federal Pacific K1XGF16-1.5 .... Its also notable that the transformer is only rated to 1.5KW.

You'd obviously put said transformer inside, as close as is reasonable to the supply, then run whatever wire is appropriate for 240V/40A out to the EV.

 

[yuhong]

Actually, I know full well how a transformer works... Thanks! The transformer wouldn't say "I want 30 amps input at 208V", leading to 6.24kw on the 240 side.... The HPWC or other equipment would allow let's say 30 amps of current to be drawn(more likely 32, 40, or 48, but whatever), and the transformer would then draw enough amperage(at 208V) to drive the output at 30 amps/240V.. I'm gonna say that's around 35 amps... Notably, the boost transformer doesn't need to be rated to the full 240v/30 amps, but rather a much smaller level.

Here's a handy URL...https://federalpacific.com/tools/buck-boost-transformer-calculator-selector/.....It shows you can get 240V/40A out of a 208V/46.9A line, using a Federal Pacific K1XGF16-1.5 transformer... Its $215 at 1.5 KVA Transformer Primary 120 x 240 Secondary 16/32 Federal Pacific K1XGF16-1.5 .... Its also notable that the transformer is only rated to 1.5KW.

You'd obviously put said transformer inside, as close as is reasonable to the supply, then run whatever wire is appropriate for 240V/40A out to the EV.

Actually, a 120/208V to 120/240V transformer can just boost 120V to 240V using the neutral. This is useful for NEMA 14-50 for example as this means that the line to neutral voltage is still 120V

 

[bosscat]

My company has 12 standard and 1 DC fastcharge units from Chargepoint, they also provided a Tesla chademo adapter for the fast charge station. Charging is free and unlimited but locked down to employee chargepoint accounts only.

 

[IronQQQ]

We have a couple of PHEVs and BEVs. My 3 LR is the only one that can charge higher than 6kW. Our charger maxes out at 2x 6kW with 208 VAC 30 amps, but bear in mind our charger is 6 years old and installed for cars of the 2013 timeframe. I would suggest getting a J1772 charger that can sustain 11 kW as that's the max for any Tesla. However if you want to future proof that, might want to go to 15 kW.

Second, You want some kind of easy security access. For instance we have a Schneider 2 station charger that is RFID card accessed. Problem is that ppl keep on losing cards. We currently have more cars than cards. Someone lost my card last week! Company doesn't want to spend money to get service provider to supply more cards and then for them to program the system to accept the new cards.

 

[Sophias_dad]

Actually, a 120/208V to 120/240V transformer can just boost 120V to 240V using the neutral. This is useful for NEMA 14-50 for example as this means that the line to neutral voltage is still 120V[/

We have a couple of PHEVs and BEVs. My 3 LR is the only one that can charge higher than 6kW. Our charger maxes out at 2x 6kW with 208 VAC 30 amps, but bear in mind our charger is 6 years old and installed for cars of the 2013 timeframe. I would suggest getting a J1772 charger that can sustain 11 kW as that's the max for any Tesla. However if you want to future proof that, might want to go to 15 kW.

Second, You want some kind of easy security access. For instance we have a Schneider 2 station charger that is RFID card accessed. Problem is that ppl keep on losing cards. We currently have more cars than cards. Someone lost my card last week! Company doesn't want to spend money to get service provider to supply more cards and then for them to program the system to accept the new cards.

I like the idea of RFID access. How much can the cards cost? Make the people charging pay for their own cards, they'l be less likely to lose them if they paid for them. The value of a charge session or two should more than make up for the cost of their cards.

 

[frnkblk]

My company has 12 standard and 1 DC fastcharge units from Chargepoint, they also provided a Tesla chademo adapter for the fast charge station. Charging is free and unlimited but locked down to employee chargepoint accounts only.

Can a non-employee charge ... at their own cost?

 

[Bill25cycle]

Ha! That's not how a transformer works, though. It trades off voltage for current. So if they have a line providing 30A that is at 208V, that is 6.24 kW of total power. You want to buck that voltage up to 240V? Then you get only 26A, but the power is still 6.24 kW, so you get exactly the same charging speed. Except that would be only if a theoretical transformer is perfectly 100% efficient, which it can't be, so you would actually lose a little bit of power and therefore charging speed, just from trying to manipulate the voltage.

Maybe you're saying back at their source with 200A or 300A main supplies, they could boost it, and then split off a 40A or 30A line from there? But then that gets into much bigger and way more expensive equipment that the company definitely won't want to foot the bill for just because some people are whining that the charging being provided for them isn't as fast as they want.

Sorry Rocky that is total nonsense - no offense. If you present a 30 amp wall box with 183 volts it will draw 30 amps. If you boost the voltage to 240 volts it will draw 30 amps. What you are forgetting is that when you 'boost' the voltage from 208 to 240 you are using a 32 volt, 30 amp transformer (which, with a 208 volt primary winding, would draw around 4.6 amps). The load on the feed to the wallbox and boost xfrmr system would then be 34.6 amperes with a 30 ampere load. The currents add arithmetically since there is no change in time (phase) between the boost transformer and the load.

34.6 ampere load at 208 volts is around 7200 watts, which is what the car happens to be drawing (30 amps at around 240 volts).

Another thing: You are using the terminology wrong. They are called 'buck/boost transformers' since you can reconnect them to do either. You either BUCK the voltage lower (through a lower effective voltage at the load), or you BOOST it higher (as in the scenario I just gave) where you are RAISING it higher.

As my nick name indicates I've done many voltage conversions using buck/boost transformers on several different frequencies (25, and 60 Hz). What you claim is magic... How would the car 'know' to lower its current to 26 amps when it is provided with 240 volts? I don't know about you. But my ev will draw 30 amps at 240 volts when hooked up to a 30 amp wall box at 240 volts at either the home or the office. It has no GPS to tell it that the power originally came from 240 or 208 or 277 or whatever. It only works on what it itself sees.

 

[Bill25cycle]

I'm not missing that at all. I know that the car could get faster charging if you could just magically turn up the volts without lowering the amps, but that's not what a transformer does. This still goes back to my point about equipment build and cost. In order for them to provide for 32A at 240V, (a 40A rated circuit), they would have to start with a 208V 50A rated circuit, to have that level of power, which has thicker, more expensive wiring, and then put a transformer on each one of those lines somewhere, which steps up the volts and steps down the amps. That is a lot of extra equipment cost, putting an extra transformer on each line. Or, as I suggested before, they could put in one really large, expensive transformer farther upstream, on a really large supply like 300A or whatever, and then split that off into the separate lines for each station.

Here's an example of a 75kVA boost transformer that would do it for $3,114.54
Larson Electronics - 75 kVA Isolation Transformer - 208V Primary - 120/240V Secondary - Single Phase - NEMA 3R

Either way, the company isn't going to give a $#*t about the amp limits your car has if it is talking about costing them extra thousands of dollars in installation cost, just because of people being dissatisfied that their employee perk isn't perky enough!

Wrong again, sorry...… When someone wants to make a small change in voltage, they in the 30 amp case (drawing 960 watts through the boost transformer) use a 1 kva unit which is CHEAP. Reason? There is no need to 'isolate' the primary from the secondary - the voltage only needs to be raised 32 volts. The 208 is already there so the 'transformation' only happens on 0.96 kva of the load, not the full 7.2 kva.

Now sometimes in industry, you will see large 75 kva 208 volt primary transformers where there is a feeder with no neutral, and it is desired to run a 300 ampere 120/240 volt load. That is not the case with car chargers as they work on 208 volts or 240 volts ONLY and if a 6-50 cord is used with the wall boxes there is no 'neutral' anywhere.

Other times isolation transformers are needed between main feeders and variable speed motor drives, to keep the crap generated from one drive from affecting other drives or other sensitive equipment. Putting a load through an 'isolation' transformer 'cleans up' the ratty load waveform by a factor of 10.

 

[swaltner]

I like the idea of RFID access. How much can the cards cost? Make the people charging pay for their own cards, they'l be less likely to lose them if they paid for them. The value of a charge session or two should more than make up for the cost of their cards.

The RFID cards for the Schneider EVSE are $8 each (I see packs of 10 for $80 on the Internet). The programming module is something like $200, but that can be used on multiple EVSEs. I don't know if these RFID EVSEs are still being made. They have a benefit of having access controls, but not having a monthly service fee like the ChargePoint systems. The have a drawback in that you need to program each EVSE independently (there is no networking function). Each card apparently gets programmed into each EVSE manually. Sounded like a hassle. There are some other access control systems that may not be as labor intensive to manage.

I had thought about adding an RFID function to the OpenEVSE system. That would be difficult with its onboard Arduino system because the RAM is already close to full. It would likely require something like a Raspberry Pi to communicate with the OpenEVSE/Arduino over the serial API connection. I never got past the stage of researching options for RFID readers to add to Arduino/Pi systems....

 

[frnkblk]

The RFID cards for the Schneider EVSE are $8 each (I see packs of 10 for $80 on the Internet). The programming module is something like $200, but that can be used on multiple EVSEs. I don't know if these RFID EVSEs are still being made. They have a benefit of having access controls, but not having a monthly service fee like the ChargePoint systems. The have a drawback in that you need to program each EVSE independently (there is no networking function). Each card apparently gets programmed into each EVSE manually. Sounded like a hassle. There are some other access control systems that may not be as labor intensive to manage.

I had thought about adding an RFID function to the OpenEVSE system. That would be difficult with its onboard Arduino system because the RAM is already close to full. It would likely require something like a Raspberry Pi to communicate with the OpenEVSE/Arduino over the serial API connection. I never got past the stage of researching options for RFID readers to add to Arduino/Pi systems....

What about leveraging the RFID on modern mobile phones? Then no cards are needed at all.

 

[Rocky_H]

Actually, I know full well how a transformer works... Thanks! The transformer wouldn't say "I want 30 amps input at 208V", leading to 6.24kw on the 240 side.... The HPWC or other equipment would allow let's say 30 amps of current to be drawn(more likely 32, 40, or 48, but whatever), and the transformer would then draw enough amperage(at 208V) to drive the output at 30 amps/240V.. I'm gonna say that's around 35 amps... Notably, the boost transformer doesn't need to be rated to the full 240v/30 amps, but rather a much smaller level.

Yes, that is what I was saying. You can look at it either way. If you have a fixed supply coming in, then boosting the voltage would lower your output amps. You're just stating the other case, that if you want to establish the fixed output that you want, then you do have to provision a higher amp input circuit. It's the same thing; I just didn't spell out that reverse case.

Sorry Rocky that is total nonsense - no offense. If you present a 30 amp wall box with 183 volts it will draw 30 amps. If you boost the voltage to 240 volts it will draw 30 amps. What you are forgetting is that when you 'boost' the voltage from 208 to 240 you are using a 32 volt, 30 amp transformer (which, with a 208 volt primary winding, would draw around 4.6 amps). The load on the feed to the wallbox and boost xfrmr system would then be 34.6 amperes with a 30 ampere load. The currents add arithmetically since there is no change in time (phase) between the boost transformer and the load.

34.6 ampere load at 208 volts is around 7200 watts, which is what the car happens to be drawing (30 amps at around 240 volts).

See my explanation above, which is exactly what I am saying about a larger circuit before the transformer. If you are talking about establishing the output at the fixed continuous 30A and 240V, then that is 7.2kW that has to come from SOMEwhere. So the circuit they have to run prior to the transformer would also need to be able to supply 7.2kW, which at 208V would need to be at least 35 continuous, which would need the oversized circuit, like a 50A, instead of a 40A 208V, which could have given you the same 7.2kW without the transformer. I guess if there is a really long wiring run after the transformer, then it might possibly offset the cost of the transformer if you could use thinner wire for the lower current.

Another thing: You are using the terminology wrong. They are called 'buck/boost transformers' since you can reconnect them to do either. You either BUCK the voltage lower (through a lower effective voltage at the load), or you BOOST it higher (as in the scenario I just gave) where you are RAISING it higher.

Wow--seriously? Did you bother to read where I immediately made that correction to my terminology on the same day on Thursday, before you tried to correct me on Saturday?

Whoops, I just realized I used "buck" when I should have used "boost".

As my nick name indicates I've done many voltage conversions using buck/boost transformers on several different frequencies (25, and 60 Hz). What you claim is magic... How would the car 'know' to lower its current to 26 amps when it is provided with 240 volts? I don't know about you. But my ev will draw 30 amps at 240 volts when hooked up to a 30 amp wall box at 240 volts at either the home or the office. It has no GPS to tell it that the power originally came from 240 or 208 or 277 or whatever. It only works on what it itself sees.

Great--that is cool that you have done this before. I never said the car would "know" to lower anything. The EVSE will signal what the amps are. The part I said was supposedly "magic" was this thinking people seem to be promoting, where they can take a 208V 30A input and have it somehow come out of the transformer with 240V and still 30A with no explanation of where it got that extra power.

Wrong again, sorry...… When someone wants to make a small change in voltage, they in the 30 amp case (drawing 960 watts through the boost transformer) use a 1 kva unit which is CHEAP. Reason? There is no need to 'isolate' the primary from the secondary - the voltage only needs to be raised 32 volts. The 208 is already there so the 'transformation' only happens on 0.96 kva of the load, not the full 7.2 kva.

Now sometimes in industry, you will see large 75 kva 208 volt primary transformers where there is a feeder with no neutral, and it is desired to run a 300 ampere 120/240 volt load. That is not the case with car chargers as they work on 208 volts or 240 volts ONLY and if a 6-50 cord is used with the wall boxes there is no 'neutral' anywhere.

Other times isolation transformers are needed between main feeders and variable speed motor drives, to keep the crap generated from one drive from affecting other drives or other sensitive equipment. Putting a load through an 'isolation' transformer 'cleans up' the ratty load waveform by a factor of 10.

OK--cool. Now this is actually informative. Having not actually purchased transformers, I did not really know the type that should be used for this type of application. I was thinking nameplate rating based on the voltage, but I hadn't thought about this, that they would be sized more cheaply for just the difference of how much you are trying to move the voltage. OK, so I guess the equipment would be cheaper than I was thinking.

 

[Bill25cycle]

Yes, that is what I was saying. You can look at it either way. If you have a fixed supply coming in, then boosting the voltage would lower your output amps. You're just stating the other case, that if you want to establish the fixed output that you want, then you do have to provision a higher amp input circuit. It's the same thing; I just didn't spell out that reverse case.


See my explanation above, which is exactly what I am saying about a larger circuit before the transformer. If you are talking about establishing the output at the fixed continuous 30A and 240V, then that is 7.2kW that has to come from SOMEwhere. So the circuit they have to run prior to the transformer would also need to be able to supply 7.2kW, which at 208V would need to be at least 35 continuous, which would need the oversized circuit, like a 50A, instead of a 40A 208V, which could have given you the same 7.2kW without the transformer. I guess if there is a really long wiring run after the transformer, then it might possibly offset the cost of the transformer if you could use thinner wire for the lower current.


Wow--seriously? Did you bother to read where I immediately made that correction to my terminology on the same day on Thursday, before you tried to correct me on Saturday?


Great--that is cool that you have done this before. I never said the car would "know" to lower anything. The EVSE will signal what the amps are. The part I said was supposedly "magic" was this thinking people seem to be promoting, where they can take a 208V 30A input and have it somehow come out of the transformer with 240V and still 30A with no explanation of where it got that extra power.

OK--cool. Now this is actually informative. Having not actually purchased transformers, I did not really know the type that should be used for this type of application. I was thinking nameplate rating based on the voltage, but I hadn't thought about this, that they would be sized more cheaply for just the difference of how much you are trying to move the voltage. OK, so I guess the equipment would be cheaper than I was thinking.

No need to get snarky - I don't read every post you ever wrote, and I obviously missed your mistatement. But you have way too arrogant an attitude about things 'telling people how things work' - when you have no actual experience with any of this by your own admission.

As far as expense - these things trivially add additional cost. If you have to run a 50 ampere circuit and use #6 aluminum wiring as opposed to #8 aluminum wiring for a 40 ampere circuit you are talking about pennies. Copper romex still has the archaic 60 degree centigrade limitation even though the wire is good for 90 degrees - so using BX or MC (metal clad), or copper SE cable with the same wiring automatically makes #8 copper wiring good for 50 amperes at 75 degrees centigrade, which happens to be the temperature limitation at most terminations. That wire will work 24/7/365 at 35 amperes. If the layout allows, its smarter to put the boost transformer back at the loadcenter, then the long feed to the wall box can be sized for the 30 amperes going through it and the 35 amperes drawn from the loadcenter will only go 2 feet to the colocated transformer. This scheme (keeping the long wiring at the highest voltage) reduces the percentage voltage drop of the entire installation.

In a large installation (say, 30, 30 ampere wall boxes), a 208 volt Y-connected autotransformer with an output voltage of 138Y/239 could either be purchased, or else made in the field with 3 - 18 volt secondary, 120 volt primary transformers (9.4 kva transformation per phase, or 3 - 10 kva wall mount transformers). The 208 volt load to the 3 boost transfomers and feeder to the distant wallbox distribution would be 600 amperes at 208 volts 3 phase will all boxes loaded at full capacity (216,000 watts), the 'boosted feeder' amperage at 239 volts would be about 520 amperes. To the uninitiated this seems low, however it is to be remembered that on a Y connected feeder the loads of the wall boxes are AS SEEN FROM THE FEEDER as 26+J15 amperes in one of the legs feeding any individual wall box, and 26-J15 amperes in the other leg.

Now, you might say this is unrealistic to feed so many wall boxes from an originally 120Y/208 volt system. It is not if the parking lot with 30 ev's is in the downtown area where, per the utility's 'Network' system this is only voltage available without expensive special construction, or at large apartment complexes.

Ideally, If 277Y/480 or 347Y/600 (in Canada) was available as in a new construction project, it would usually be easier to start from those voltages with an addition of a few dozen wallboxes. In fact Tesla Superchargers in Canada all have individual 3 phase autotransformers to lower the voltage line to ground from 347 to 277.

Simply put, If you run 3 - 30 ampere wall boxes L1-L2, L2-L3, and L1-L3 off a 3 phase feeder, the 'apparent' 90 ampere load will actually be 52 amperes. A 30 ampere wall box at 208 draws 6240 watts and 7200 volt-amperes off the feeder at a power factor of 86.6% leading off of one leg and 86.6% lagging off the other due to the time displacement. since the feeder thinks it is merely supplying 2- 120 volt loads per wallbox. Balanced, the leading and lagging power factors cancel out at the 3-phase loadcenter in the parking lot. 52 amperes at each 120 volt leg is 6240 watts per leg or 18,720 watts total.

Now, there is a complication with SOME wallboxes that do a line test from each leg to the grounding conductor to see if the ground integrity is good, and SOME may trip their protection circuits should L1 to GND differ substantially from L2 to GND, which a SINGLE (boost) autotransformer would cause (such as boosting the voltage from a 2-wire, 208 volt feed), if the boost is substantial, say from 190 to 250 or something along that range. But in the general case its not worth worrying about - especially since most people just want a 'moderate boost', say from 208 to 230.

 

[Rocky_H]

No need to get snarky - I don't read every post you ever wrote, and I obviously missed your mistatement. But you have way too arrogant an attitude about things 'telling people how things work' - when you have no actual experience with any of this by your own admission.

My self-correction was literally the very next comment in this thread after the one you did read and were criticizing me for. It does not require anything as dramatic (and snarky) as reading "every post I ever wrote".

I just brought up the very broad and accurate principle about transformers that there would have to be oversized input current if you want to have a certain output current at a boosted higher voltage. You called that "total nonsense", which seems wrong (and snarky).

I do really appreciate your further detail about how to design and build a system that would accomplish this. I still don't really see much of the benefit, especially to the company that would be footing the bill for this. The vast majority of companies just send the 208V out to the EVSEs in the parking lot, so there must be good reasons why they don't want to bother with boosting the voltage.

 

[yuhong]

Now, you might say this is unrealistic to feed so many wall boxes from an originally 120Y/208 volt system. It is not if the parking lot with 30 ev's is in the downtown area where, per the utility's 'Network' system this is only voltage available without expensive special construction, or at large apartment complexes.

Thinking about it, I assume that many of these "network" systems already run closer to 127/220V anyway, right?

 

[vickh]

we have 3 Teslas at my work but not sure how to best approach landlord about charger value.

I have put the neighboring hotels on Teslas destination charger contact form. Not sure if Tesla still initiates contact or hotel cares

 

[Bill25cycle]

Thinking about it, I assume that many of these "network" systems already run closer to 127/220V anyway, right?

Standard network voltage is 125Y/216, as this mimics the archaic 125/250 volt DC network almost all such systems replaced. I'm not familiar with anything higher but there's no law against it.

In the EV world, Baker Electric 'Car chargers' in public downtown areas were merely 'Toasters' which dropped the voltage from the nominal 125 to the 84 volts or whatever was required by the car. No rectification necessary as the juice was already DC. Jay Leno showed his, stating he was afraid the thing would burn down the place, and used a modern battery charger for his. Home charging solutions in AC areas 110 years ago were Mercury Arc 'Glass Bottle' rectifiers mounted on a 'shaker' to initially strike the arc. An Inductor past the single-phase power transformer kept the current running past the zero-crossing point so that the arc never needed to be re-struck, it varying at power line frequency between the 2 anodes every half cycle.

Any homes in the 'dc network' area merely used Jay Leno's Toaster.

 

[Bill25cycle]

Yes, that is what I was saying. You can look at it either way. If you have a fixed supply coming in, then boosting the voltage would lower your output amps. You're just stating the other case, that if you want to establish the fixed output that you want, then you do have to provision a higher amp input circuit. It's the same thing; I just didn't spell out that reverse case.


See my explanation above, which is exactly what I am saying about a larger circuit before the transformer. If you are talking about establishing the output at the fixed continuous 30A and 240V, then that is 7.2kW that has to come from SOMEwhere. So the circuit they have to run prior to the transformer would also need to be able to supply 7.2kW, which at 208V would need to be at least 35 continuous, which would need the oversized circuit, like a 50A, instead of a 40A 208V, which could have given you the same 7.2kW without the transformer. I guess if there is a really long wiring run after the transformer, then it might possibly offset the cost of the transformer if you could use thinner wire for the lower current.


Wow--seriously? Did you bother to read where I immediately made that correction to my terminology on the same day on Thursday, before you tried to correct me on Saturday?


Great--that is cool that you have done this before. I never said the car would "know" to lower anything. The EVSE will signal what the amps are. The part I said was supposedly "magic" was this thinking people seem to be promoting, where they can take a 208V 30A input and have it somehow come out of the transformer with 240V and still 30A with no explanation of where it got that extra power.

OK--cool. Now this is actually informative. Having not actually purchased transformers, I did not really know the type that should be used for this type of application. I was thinking nameplate rating based on the voltage, but I hadn't thought about this, that they would be sized more cheaply for just the difference of how much you are trying to move the voltage. OK, so I guess the equipment would be cheaper than I was thinking.

Thanks Rocky_H for marking my "Baker Electric" post informative. I was always intrigued by the 'charging infrastructure' existing 110 years ago for the electric cars back then. A third way to charge the cars was in Commercial Garages, where they would charge multiple Baker Electrics at the same time from a small AC powered (usually 3 phase in the 'larger' installations) Motor-Generator set, with quick connect cables existing in each 'stall' for each vehicle. Too bad we had to wait 100 years for Electric cars to get going again.