I need an under 20KW DC ChaDeMo Quick Charger

[hill]

So why isn't anyone installing those mono-phase DC chargers? Are they also too costly? Or otherwise not ready for prime time?

One simple reason is that the efficiency advantage goes to three phase. Mono phase requires much higher amperage loads (bigger, heavier, more costly, less efficient) than a three phase load of equivalent wattage.

I haven't needed a phase converter for over 2 decades - but I understand the digital models they have now days are a good 25% more efficient than the old style that I used. With a better than 95% efficiency, I still feel any home/residence can go 3 phase, if they don't mind eating the cost of the converter.

 

[Randy]

Half of our customers in San Diego are fed with a 25 kVA transformer. Of course, on average, there are several other customers connected to that transformer.

Then you get into the service drops and size of the panel that customers have.

There may be some newer homes that are better equipped, but many customers are not ready to connect a 20 or 25kW car charging load without some costly upgrades...

 

[edatoakrun]

So why isn't anyone installing those mono-phase DC chargers? Are they also too costly? Or otherwise not ready for prime time?

One simple reason is that the efficiency advantage goes to three phase. Mono phase requires much higher amperage loads (bigger, heavier, more costly, less efficient) than a three phase load of equivalent wattage.

In the long run, I think that existing infrastructure will play a major role in determining DC charger installations.

I expect that the vast majority of high-volume DC charge station locations will install 50 kW three-phase Chargers.

However, I'd still expect to see plenty of single-phase DCs, usually designed for lower kW, since, for many low volume charge sites, where the existing single-phase service to the business location, limits the charge rate. Lower kW charging will often be sufficient to bring additional customers to a roadside restaurant or coffee shop, without the large expense of upgrading the service to three phase, or to the higher single-phase amperage, that any 50 kW Charger might require.

 

[edatoakrun]

Half of our customers in San Diego are fed with a 25 kVA transformer. Of course, on average, there are several other customers connected to that transformer.

Then you get into the service drops and size of the panel that customers have.

There may be some newer homes that are better equipped, but many customers are not ready to connect a 20 or 25kW car charging load without some costly upgrades...

And why would any homeowner want to?

 

[Randy]

People are talking about it, so there must be some desire there....

And the new Tesla car will offer 20kW charging capability. Do people need it at home? Or do they just want it? I think there are people who are interested in getting that kind of charging at home...Probably not the majority of EV owners, though...

 

[DaveEV]

Half of our customers in San Diego are fed with a 25 kVA transformer. Of course, on average, there are several other customers connected to that transformer.
There may be some newer homes that are better equipped, but many customers are not ready to connect a 20 or 25kW car charging load without some costly upgrades...

What are the input/output specs of a 25 kVA transformer? Is this the typical transformer you see in the green boxes in underground utility residential areas and the cylinder transformers you see on poles? Your typical house these days has a 100-200A service panel at 240V single phase. That's capable of delivering 80-160A continuous or 19kW-38kW.

People are talking about it, so there must be some desire there....

And the new Tesla car will offer 20kW charging capability. Do people need it at home? Or do they just want it? I think there are people who are interested in getting that kind of charging at home...Probably not the majority of EV owners, though...

I do think we'll see people pulling 10-20kW to charge their car - we're already seeing 7.2kW being the norm - Tesla Roadster owners are already doing up to 19kW (though most charge at 9.6kW). I will not be surprised to see Model S customers doing it on occasion as well.

The question is - if you have 3-8 houses on a transformer - it will only take a couple customers charging their EVs at night to overload it...

 

[Randy]

While your whole house connection may be able to handle that many kw if other large items were off, you wouldn't be able to get a permit under those operating conditions. Remember the design ECOtality turned in to get your Blink permit? Some homes barely cleared those calcs...

 

[Randy]

True on the overload concerns...We are working on that...Probably will be handled on a case by case basis...

 

[DaveEV]

While your whole house connection may be able to handle that many kw if other large items were off, you wouldn't be able to get a permit under those operating conditions. Remember the design ECOtality turned in to get your Blink permit? Some homes barely cleared those calcs...

Mine was one of those houses. But if I upgraded my 100A panel to a 200A panel, that would surely imply that at least my house would be able to handle pulling 20kW (240V/80A) - even if the grid isn't able to handle it.

 

[edatoakrun]

..I do think we'll see people pulling 10-20kW to charge their car - we're already seeing 7.2kW being the norm - Tesla Roadster owners are already doing up to 19kW (though most charge at 9.6kW). I will not be surprised to see Model S customers doing it on occasion as well.

The question is - if you have 3-8 houses on a transformer - it will only take a couple customers charging their EVs at night to overload it...

Not to mention, what will happen, if they decide to charge during the day.

This sort of high kWh home charging behavior could require regulation by both mandatory TOU rates, and residential demand charges.

The wheels should tip you off to the fact that BEVs ARE MOBILE.

You do not need to bring the high kW to your garage. You can drive the BEV, to a public fast charge site. When you need a lot of kWh fast, you will almost always be far from home, anyway.

 

[abasile]

Ideally, I'd like faster charging at home for those evenings when I get home with 20% SOC and then want/need to drive somewhere else. On such days, I currently plan to leave work a bit earlier so as to allow time to re-charge at home at 3.3 kW. Yes, I think plenty of folks would like faster home charging. It's easy to imagine grid demand spiking around 5-7 pm.

 

[waidy]

Half of our customers in San Diego are fed with a 25 kVA transformer. Of course, on average, there are several other customers connected to that transformer.

Then you get into the service drops and size of the panel that customers have.

There may be some newer homes that are better equipped, but many customers are not ready to connect a 20 or 25kW car charging load without some costly upgrades...

My home which has a 400 Amp service is fed with a 25 kVA transformer. This 25 kVA transformer only feeds my property. I am interested to upgrade my feed from 400 Amp to 600 Amp (or 500 Amp). Other than pulling wires and service panel upgrade, what else is involved? What is the equation to determine whether a 25 kVA transformer is sufficient to give a 600 Amp feed? Any advise is appreciated.

 

[TomT]

Theoretically, a 25KVA transformer can supply just over 100 amps continuously at 240 volts... So, clearly power companies use some other formula to determine sizing...

My home which has a 400 Amp service is fed with a 25 kVA transformer. This 25 kVA transformer only feeds my property. I am interested to upgrade my feed from 400 Amp to 600 Amp (or 500 Amp). Other than pulling wires and service panel upgrade, what else is involved? What is the equation to determine whether a 25 kVA transformer is sufficient to give a 600 Amp feed? Any advise is appreciated.

 

[waidy]

Theoretically, a 25KVA transformer can supply just over 100 amps continuously at 240 volts... So, clearly power companies use some other formula to determine sizing...

Thanks for your comment. Does the 100 Amps continuously supply at 240V includes the 50% rule?

 

[Randy]

In our city, when requesting a permit for an EVSE, a design and load calculations must be turned in...There's probably differences from city to city, depending on the code they follow, but here are the load calculations that were used for my design:

General loads:
2469 sq ft x 3va/sq ft = 7407 va
two small appliance circuits = 3000 va
microwave = 840 va
electric oven 8.1 kw = 8100 va
garbage disposal = 840 va
dishwasher = 1000 va
evse = 7200 va
total general load = 28376 va

first 8 kva of general load at 100% = 8000 va
remainder of load at 40% = 8154.8 va
total net general load = 16155 va

hvac load:
1 unit x 29.8A x 240v = 7152 va

total demand load:
total net general load = 16155 va
total hvac load = 7152 va

total demand load = 23307 va
23307 va / 240v = 97 amps
panel size = 125 amps

 

[Randy]

Here is the residential and commercial transformer loading design standard for San Diego...

http://regarchive.sdge.com/documents/builderservices/elecstandards/5600/5625.1-2.pdf" onclick="window.open(this.href);return false;

Transformers can actually be loaded higher than nameplate rating for a certain duration with minimal loss-of-life...Of course, voltage issues can also occur that might require a transformer replacement...

 

[waidy]

Here is the residential and commercial transformer loading design standard for San Diego...

http://regarchive.sdge.com/documents/builderservices/elecstandards/5600/5625.1-2.pdf" onclick="window.open(this.href);return false;

Transformers can actually be loaded higher than nameplate rating for a certain duration with minimal loss-of-life...Of course, voltage issues can also occur that might require a transformer replacement...

Hi Randy, thanks for the document. My neighbor across from me has a 800 Amp feed. So I hiked over to his property and looked at his transformer. He has the same size of transformer I have (25k Va) but he has two boxes labeled PG&E connected to the transformer wires. I think if I am adding 100-200Amp to my 400Amp service, I do not need to upgrade my transformer. However, I am curious to know what are the two boxes for and whether if I need them. They are size of a wireless access point (small).

 

[ElectricVehicle]

Here is the residential and commercial transformer loading design standard for San Diego...

http://regarchive.sdge.com/documents/builderservices/elecstandards/5600/5625.1-2.pdf" onclick="window.open(this.href);return false;

Transformers can actually be loaded higher than nameplate rating for a certain duration with minimal loss-of-life...Of course, voltage issues can also occur that might require a transformer replacement...

Hi Randy, thanks for the document. My neighbor across from me has a 800 Amp feed. So I hiked over to his property and looked at his transformer. He has the same size of transformer I have (25k Va) but he has two boxes labeled PG&E connected to the transformer wires. I think if I am adding 100-200Amp to my 400Amp service, I do not need to upgrade my transformer. However, I am curious to know what are the two boxes for and whether if I need them. They are size of a wireless access point (small).

Those boxes are likely smart grid instrumentation, probably from Silver Spring Networks.

Just call up PG&E and ask them for an estimate. Whant type of large loads are you going to put on this and for how long? The reason I had trouble doing the 25 kVA math when we met is that I was not familiar with how high the ratio is that PG&E uses for service size vs. distribution transformer size! That 25 kVA transformer can probably supply 100A 24x7, but may only be able to supply 200A for a couple hours. If they let it go to 800A, I don't know what the number is, but I'd expect it to be less than 2 hours, probably more like 15 minutes... Expert answers welcomed!

100A * 240V = 24000 W = 24 kW.

 

[Randy]

Maybe there is an online PG&E Standard you can find? Down here it is 168% loading of nameplate for 4 hours max in a 24 hour period....The other 20 hours must be below 90% to allow cooldown...

 

[ElectricVehicle]

Maybe there is an online PG&E Standard you can find? Down here it is 168% loading of nameplate for 4 hours max in a 24 hour period....The other 20 hours must be below 90% to allow cooldown...

Hey Randy, thanks! Any info on what the load time is for 400% of nameplate?
Just being crude -168% is +68% for 4 hours. Doing a linear extrapolation, 400% is +300%, using the overload ratio to scale the time - 68% / 300% = 0.226, 0.226 * 4 hours = 0.9 hours = 54 minutes. That's assuming the fuse in the transformer doesn't trip. 54 minutes is optimistic, since the shorter the period is, the faster the transformer heats up locally compared to the heat dissipation through the case.

This also doesn't account for voltage droop at 400% load, which may well be excessive.

Waidy - get some more Coulomb stations that coordinate the load amongst each other.... We have to know your intended scenarios to come up with good answers.

I'm finding lots of neat studies, though none of them exactly address this situation.
Application of Distribution Transformer Thermal Life Models to Electrified Vehicle Charging Loads Using Monte-Carlo Method
http://www.nrel.gov/vehiclesandfuels/pdfs/48827.pdf" onclick="window.open(this.href);return false;

Peak loads in excess of 140% of design capacity or extended periods of time at peak loading can lead to localized electric service problems
– Voltage dips (dimming lights, damage to expensive electronics)
– Service interruption
– Transformer failure
http://ewh.ieee.org/conf/vppc/Speaker/KS02-4_H_Asgeirsson.pdf" onclick="window.open(this.href);return false;

We have to know what your planning - it looks like 200% load for anything over minutes is a problem and for the time it takes to charge an EV, 100% would be best - including the house loads, 120% sort of ok and 140%+ is getting into problem territory. If you really need that much load continuously - 500 to 600A for 4+ hours, it's going to be some serious distribution transformer and possibly network upgrades... I doubt practically and with some reasonable measures that you'll actually need anything like that unless your charging 3+ Tesla Model S at the same time.