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Discussion Starter #1
I bought a Ford Focus Electric today. I want to use a fast charger but I'd rather not pay to have an extra 240v outlet installed.

Could I use a voltage step up/step down convertor to take 120v to 240v and then plug the fast charging cable into the 220 - 240v output?

122809
 

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Hi,

I doubt very much that transformer will be rated for the high load involved, but I'm not clear why you've got 110v to start with yet are talking about 240v sockets, what country are you in?

Plus, upping the voltage to 240 from 110 will have the result of halving the current and therefore the speed of the charger, even if you did get an appropriately-rated transformer.
 

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From the EV and Link + 110V standard I guess this is the USA.

Technically yes BUT the size of the transformer needed and the supply to feed lt mean it's cheaper to have a proper 240 outlet fitted.
The ford will have a 3.3 or 7.2 kw fast charger - not sold here so do not know. the 3kw unit is too small. The makers suggest the transformer be rated at 1.5 times the load so 4.5kw for a 3kw EV. 9Kw for the 7kw EV

Its a huge problem if the Ev takes 7kw you need to supply the transformer 8kw and at 110v thats about 75Amps which is not a normal socket! The Transformer would be huge in both size and cost
 

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I'm in the USA, if that matters. Our outlets are 120v so we'd use two breaker spots to install a 240v outlet. I find 2000w and 3000w voltage converters that will step 120v to 240 v does under $100. It's estimated to cost me $300 to get a 240v wall outlet installed.
 

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You need to check what power the car charger takes but a “granny lead” with a domestic plug is normally around 10 amps maximum i.e. 20 amps roughly feeder to your transformer and a 3000 kVA transformer say. Assume you have access to 240 volts somewhere in the house but it sounds as though the installation is difficult.
 

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I'm in the USA, if that matters. Our outlets are 120v so we'd use two breaker spots to install a 240v outlet. I find 2000w and 3000w voltage converters that will step 120v to 240 v does under $100. It's estimated to cost me $300 to get a 240v wall outlet installed.
However, your existing 120V outlet will be 15A max so 1750W max (and for continuous use rated 20% less than that).

So even if you can find a 3000W transformer of adequate quality at a low price, it would need 25A notionally and a 30A circuit for continuous use, so you can’t use the existing outlet anyhow.

Probably your car can charge off 120V and use the full capacity of the outlet without any voltage conversion.

(Note: USA practice is to quote breakers and wire sizes for typical use and apply derating for continuous use; in Europe we rate for continuous use and then apply diversity for non-continuous loads. The physics is obviously the same and the resulting wire sizes/breakers similar - we just put different labels on them).
 

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Discussion Starter #10
15 amps is needed for 1500w?

I just read that one of these converters suggested that a 1500w converter works for 800w continuous use. 3000w+ for 1500w continuous use.
 

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Assume you have access to 240 volts somewhere in the house but it sounds as though the installation is difficult.
I believe that more recently built USA houses do have 240 volts available, but not wired to sockets by default as it is normally used directly connected to cookers etc.If so, an electrician could advise and wire in a 240 volt socket.
 

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I believe that more recently built USA houses do have 240 volts available, but not wired to sockets by default as it is normally used directly connected to cookers etc.If so, an electrician could advise and wire in a 240 volt socket.
That's my situation for sure. It's just expensive, so I was looking for a cheaper alternative. I think I'm possibly asking for house-fire level trouble, though.
 

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It shouldn’t an electrician more than an hour or two, but of course in some places they do charge an arm and a leg.

Mine is Only £15 an hour but he won’t travel that far!
 

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15 amps is needed for 1500w?
Power = volts * amps.

So 1500W = 120V * 12.5A

A standard USA 120V outlet is rated at 15A normal use, 80% of that for continuous use so 12A.

I just read that one of these converters suggested that a 1500w converter works for 800w continuous use. 3000w+ for 1500w continuous use.
OK, so their nameplate rating assumes a very low duty cycle - might be appropriate for running power tools on a construction site or similar.

Anyhow, the bottom line here is that you have only 1500W available from your outlet without setting the house on fire (or, hopefully, tripping the breaker first).

A quick google search suggests the Ford Focus EV is capable of charging at 120V, so it will achieve that 1500W without any help from a voltage converter; in fact the voltage converter will just waste energy (by getting hot).

Another consideration is that most EVs charge slightly more than twice as fast at 240V compared to 120V even at the same current - there's a certain amount of fixed overhead (energy wasted) per hour of charging, so at very low rates of charging this dominates the (in-)efficiency. Therefore your 120V charging - even if it is just about enough overnight to make your commute - will end up costing you slightly more in electricity than 240V charging. Maybe not enough to cover the cost of the 240V wiring, but another reason to justify it.
 
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