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Old 06-03-2019, 06:28 PM   #1 (permalink)
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Chargers that share available power

Which, if any, of the available quick chargers talk between themselves to share the available power?

Let me back up a bit. Much to my surprise, my workplace is looking to Green up their image by (among other things) installing some EV charging in our parking lot.

The general idea appears to be one lighting transformer to be shared by several chargers along one line of the parking lot. There are .. maybe 30? .. parking stalls in this line. I don't expect that the budget will allow for 30 quick chargers. But the stalls that don't have quick chargers should at least get a dedicated 20A 208V weather-resistant receptacle ... which is better than the existing 15A not-weather-resistant receptacles we use for our block heaters in the winter

The largest reasonable size transformer (fits into a parking stall, so we lose just one of them) appears to be about 250 KVA, if we are stepping down to 208V three phase ... but are we? Our input is 575VAC (Canada) three phase. Since some of the quick chargers are up to 800V (last I read) I'm not sure if we can actually step down the voltage. Perhaps I need to drop to 460V instead, or perhaps the chargers boost from 208V three phase? If the charger can be fed directly from 575 VAC three phase, we can use more power (the feeder is 600A) ... then the limiting factor would likely be the size of the cable we are willing to bury.

Having the feeder breaker trip or the transformer overheat is not reasonable. I expect that vendors have figured out a way to share the available power ... but I don't remember reading about that. I think I remember reading that the Tesla chargers measure voltage drop and reduce output based on that.

I'm confident that many people have investigated this and come up with good solutions. I'm not looking for a cutting-edge solution. But it would be nice if it was as future-proof as I can manage.

Thanks in advance!

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Old 06-04-2019, 10:38 AM   #2 (permalink)
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200 ish volt for charging seems universal, not fast but not week long slow so whatever you use up there for dryers should work for stock chargers. The quick charge people go exotic voltages. You might want to look at the appropriate specs because you dont need to go full blown tesla.

Block heater taps would even work. So what if you only half charge dring the work sift, it's free. Charging on 120 for 8 hours would still get me home and back.
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Old 06-04-2019, 12:56 PM   #3 (permalink)
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J1772 don't talk to each other or share the circuit as a as I'm aware.
Only tesla does that and I think they work in pairs.
Then you have 3 or 4 different DC fast chargers at the moment.

They are not going to pay to install DC fast chargers unless it's to do for profit charging. I occasionally see them used and they still run $8,000 to $10,000 each.
I don't know how much they are new.

Just put in some J1772 like everyone else.
Our nation electric code has guidelines for installing evse circuits.
In the US large numbers of public charging stations grouped together normally use 208v.
Then the chargers can be limited to anything from 6 amps all the way to 24 amps for a normal affordable j1772 charge setup.
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Old 06-04-2019, 01:53 PM   #4 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
Our nation electric code has guidelines for installing evse circuits.
In the US large numbers of public charging stations grouped together normally use 208v.
Then the chargers can be limited to anything from 6 amps all the way to 24 amps for a normal affordable j1772 charge setup.
I'm interesting in the 'Then the chargers can be limited to anything ...' part. Is that a manual setting on each charger, or can I install a supervisory controller that talks to these units ... or perhaps there is some other way?

There is presently one model X, a couple of chevy Volts, one Mitsubishi outlander ... I think that about does it for the parking lot survey.

I'd like to think that things will be getting better in the near future. One or two stalls that can give you enough juice to get home if you are only at work for a couple of hours (over-time call-out) would be nice. For the rest of them, I agree for now.

If 'this is important, for some reason, right now' and I have the budget to 'do it better', or have a plan to make it better later but I need to bury a bigger cable ... or whatever boundary condition will limit options ... Well, I'll go as far as I can with the budget I'm given.

Sounds like fast chargers are kinda non-standard. I'll contact the vendors directly and see what they say. I like to have SOME info before I go there
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Old 06-04-2019, 02:13 PM   #5 (permalink)
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J1772 is a simple, cheap, dumb charging protocol it doesn't have instrumentation and controls.
The J1772 sends a signal to the car telling the car how big it is, say a 24 amp capacity, then a car like my old leaf will accept up to 16 amps because that's all it can handle.
Newer cars will take all 24 amps.
The J1772 units don't talk to each other. If they did it would be some proprietary control and evse system. To me that's a waste of money.

The cheapest thing would be to run 4 wire wye 240/480v on 4 gauge wire. That way it can handle 70 or 80 amps.
Let's say 70.
So if you ran 30 charging spots and ran 1 line to 10 spots that would allow for 6 or 7 amp charging on each spot.
What I would do is run 9 spots, 1 line to 3 spots and limit the charging current to 20 to 22 amps or less.

Unless this is for profit charging?

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