11 December 2010

Multiple power sources

An isolation transformer from a surplus dealer in Brooklyn
It has been a week since I posted a blog about the need for multiple power inlets on early electric cars.  I have not heard a single product announcement yet.  What is taking so long?  Clearly I am going to have to explain how to do it.

Let's skip over the most obvious case, where you are charging outside in the winter, you have access to two outlets on different circuits at 110 volts 15 amps, and you have a small cabin heater that you bought from J.C. Whitney or the like.  Mount the heater safely, plug it in the second circuit, then your car is warm when you leave and you don't need to run the built in heater as much, extending your range.  If you have air cooled batteries like the Mini E where the air comes from the cabin, then you have even warmed up your batteries and significantly increased your range.  This is as trivial as it is important.

But now we turn to summer.  You have found two outlets that you know are on different circuit breakers, and you want to charge faster than you can from one 110 volt outlet?  First of all, Mini does not want you fooling around with their research car, so forget it.  But if you have a Tesla, a DIY electric car you built yourself, or an electric car you own, maybe you have some options.  The first and most obvious is the Quick 220 safety box.  This device is simple, safe and reliable.  It can detect two circuits that are on different phases and which therefore must be on separate circuits.  It is available in 15 or 20 amp versions and provides a 220 volt outlet, either the type you find on a 220 volt air conditioner, or a twist lock.  Tesla provides adapters for air conditioner receptacles, DIY types will have to make something.  I don't know what the options are for Leaf or Volt owners yet.  Maybe they will be like Mini and stick to the letter of the electrical code, maybe they will be advocates for changing the code to facilitate electric cars in a safe way.  We'll see.

Quick 220 safety box, Model: A220-20D Version 2

The limitation of this approach is that it does not work with Ground Fault Interrupters.  And just about every outdoor or garage outlet in the US has a GFI.  If you find one that does not have a GFI, it should be upgraded.  So what do you do now?  Or let's say you have found two outlets on separate circuits, but they are on the same phase?  The power is there, but cannot be stacked up to 220 volts.  What to do?

The low tech solution for combining power from two GFI outlets into one receptacle involves an isolation transformer in addition to the Quick 220 box above.  (It can also be used for two circuits on the same phase.)  If one of the GFI supplies is isolated and the neutral side of the transformer output is tied to the neutral of other GFI, then the Quick 220 box can safely combine the two 110 volt sources into 220 volts.  There are lots of things you have to get right:  the transformer has to be big enough, the phasing has to be correct, the neutral wiring is tricky.  It can be done, but don't try it at home as they say.  Get a professional to help.  And watch out for cheap Asian or Indian made transformers advertised on the Internet.  Many are not transformers, they are Autoformers.  The difference is that a transformer has electrical isolation between the primary and secondary windings.  An Autoformer does not.  An autoformer will not work here.  Period.

Topaz 91002-11 transformer 2.5 kVA, Dual Standard Electric F246 Powerstat 7.2 kVA combined variable autoformers with T5587 Choke
Once you do get a transformer setup like this working, your car still may not want to charge.  The Mini E is very fussy about the stability of the voltage source for charging, and this is a good thing.  It prevents charging from undersized extension cords, corroded outlets, and other fire hazards.  Nor would it like the voltage drop across a small transformer.  I do not know, but I would assume all electric cars from reputable manufacturers have similar discriminating tastes in electricity supplies.  So what to do?

There are several options if your car charger refuses to continue charging once it realizes the hokey setup you are trying to feed it with.  I have a large Variac that I used to adjust my 108 volt supply at my work place up to 125 volts to charge a little faster.  I expect that could be used, but it is expensive unless you have access to a surplus dealer like I did.  It might be possible to load the transformer with a electric space heater and turn the heater down as the car ramps up its current draw.  But this could cause you to trip a circuit breaker if you don't get the timing right.

All this is way too complicated for the average driver.  The only reason I bring it up is that it can be done.  And the people who should be doing it are the people bringing us the first generation of electric cars.  Modern electronics can do the combining efficiently and safely.  UL might have an aneurysm, and OPEC will probably bribe UL not to approve it.  But it can be done.  And someone should get working on it.

1 comment:

  1. Multiple chargers can be wired to charge different parts of a battery pack simultaneously, halving charge time with two chargers, say. Since chargers are small and light weight, this seems to be a better solution than uh, electrocution! lol
    On Ebay is a J1772 receptacle that can be wired to accept 110V plugs (running to 100-240V chargers), to get the best of both worlds.