At 290 volts the model S charges at 37 mi/hr. I have been charging my 2012 RAV4 EV at 277 volts for three years with no problems. I put the boost transformer after the EVSE, because, 290 volts would most likely damage the EVSE. The newer charger in the model S are rated at 300 volts, the output is 11.5 kW at 290 volts.
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Ulmo
Active Member
I wonder if dual charger S or 72A charger X behave similarly. I'd be tempted to put the transformer on an interlocked open first and bypass switch (dual pole 4 way switch?), so I can charge without transformer losses when I'm not in a hurry. But having faster charging as an option is great.
Dual charger would work the same. Should get 23 kW, 74 mi/hr at 290 volts. Don't know about the model X.
Here us the link to the transformer i used. 1404D04 Auto Transformer
Warning: If you don't know how to use this transformer, you could burn down your house or die. Don't buy it, if you don't know how to use it.
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Yes, the high voltage will damage the UMC/HPWC circuitry if you boost before the EVSE.
The other issue that you have is that you're drawing a much higher current through the EVSE. To charge the car at 290V/40A after boost, the primary side of the transformer will be drawing 48A at 240V, and you're putting 48A through the EVSE -- your EVSE must be rated for that (the UMC isn't). This means you need a circuit sized appropriately (60A).
Note that the original (gen 1) chargers in Model S are labeled 85-265V, although we know they run them @ 277 in the older SC's.
This is a bad idea - even though the internals of the chargers may be rated higher, the warranty may not cover charging in this manner.
The other issue that you have is that you're drawing a much higher current through the EVSE. To charge the car at 290V/40A after boost, the primary side of the transformer will be drawing 48A at 240V, and you're putting 48A through the EVSE -- your EVSE must be rated for that (the UMC isn't). This means you need a circuit sized appropriately (60A).
Note that the original (gen 1) chargers in Model S are labeled 85-265V, although we know they run them @ 277 in the older SC's.
This is a bad idea - even though the internals of the chargers may be rated higher, the warranty may not cover charging in this manner.
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If you know what you're doing and you're willing to take the risk, then good luck to you. *Definitely* a recommendation against for 99.9% of people out there, though. Just a bad idea all around, so much that can go wrong. The EVSE signals a certain pilot current to the car, but if the car draws that same current through an autotransformer, it will overload the EVSE on the primary. So the car must never be able to draw more than the EVSE's rated current times input/output voltage ratio.
Mods: I'm recommending a thread subject change - lots of people are going to read this and wonder if they can hack something together. This is dangerous. Add "[crazy hack]" or something to the front please?
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Soolim
Member
The transformer you used is rated 120Vac primary, there is no 277V secondary tap, how does it work?
A raw transformer isn't really sensitive to varying voltage, to a certain extent - the only thing that matters is the ability for the insulating materials to handle higher voltages without burning through and shorting the coils, along with having large enough wires to handle the resulting currents on primary / secondary sides. From a voltage perspective, what matters is the ratio of number of coils in the windings.
At 240V, using a ratio of 120/158 (the likely best match for that particular transformer) would net you 315V. You'd need 220V input to get 290V using those same terminals (290V * 120/158 = 220V) - all of this without any line losses / voltage drop.
I'll agree this is a bad idea because the UMC cannot handle even the 240V/50A without eventual trouble. The Gen 1 chargers are rated at 277V not 265V, but the newer FW must allow charging at more than 10kW(old firmware did not, as anything over 250V would limit the amperage for a total of 10kW). Anyway, props to the OP, but this is not going to be realistic for many.
jcaspar
Member
Interesting idea. How much efficiency do you lose by using the transformer? Does this just provide slightly faster charging while using more electricity?
Autotransformers can be pretty efficient, up to 99% - they get more efficient the smaller the buck/boost ratio.
The reason you get "faster" charging out of it is that the Tesla chargers are current-constrained. So higher voltages can deliver higher power to the car. They don't use "more electricity" but rather have a higher current on the primary side to give the same current at a higher voltage on the secondary.
Power = current x voltage. You get 1 kW of power at 10 volts, 100 amps. You also get 1 kW of power at 100 volts, 10 amps. Effectively, this transformer will feed the car 290 volts @ 40 amps, while drawing 48.3 amps from 240 volts through the EVSE.
Autotransformers are pretty efficient, but also come with some big downsides. If the conductors in the transformer break down, because of the low impedance you get hellish short-circuit currents that will destroy things really quickly. Auto-transformers are particularly sensitive to overvoltage conditions and power surges will more easily affect devices attached to one. There can be phase-shift effects and power factor issues as the ratio of voltages increases.
It's not something the average person will want to deal with.
Canuck
Well-Known Member
"Risky" seems a better title than "crazy" to me. I saw the title as appealing, since a crazy hack usually means something so simple it's nuts, similar to these "crazy hacks":
Six Crazy Hacks That Will Change the Way You See Your World Nat Geo TV Blogs
Then again, anyone reading the thread will understand it's risky. I just don't get the crazy part, unless that's what we're calling pchilds...
Khatsalano
Member
This is a bad idea. Just buy dual chargers, go to a supercharger, or deal with 30mph charging. 37mph charging isn't exactly adding a life benefit now is it. Like the WuTang Clan said, "electricity ain't nothing to F with." Be safe.
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Electric700
Active Member
Note: Going along with other members' concerns outlined previously, there would be a risk associated with the below proposal.
What about using this: Simran AC-3000 - Step Up / Down Voltage Transformer 3000 Watt - CE Cer Voltage Converter Transformers
With this:
Tesla NEMA 6-15
Input is 120 V/12 A, output is 240 V/12 A. So, you'd get double the charging rate.
What about using this: Simran AC-3000 - Step Up / Down Voltage Transformer 3000 Watt - CE Cer Voltage Converter Transformers
With this:
Tesla NEMA 6-15
Input is 120 V/12 A, output is 240 V/12 A. So, you'd get double the charging rate.
Cottonwood
Roadster#433, Model S#S37
A lot of effort! Make sure you use a 120V/30A circuit; that derated to 80% is 120V/24A that the transformer will convert to 240V/12A.
It's a lot easier to just add a 6-15/20 outlet to your house.
I proposed this quite some time ago for other countries like Japan that have lower nominal voltages. Boosting from 200VAC to 277VAC is a much larger increase than 240->277, therefore much more likely to be worth the trouble. Also, if you boosted from 200->250, you could do it completely before the EVSE without any danger to its internal components.
