24 December 2010

Mini E drivers charging without an EVSE

Todd and Kari with Mini E #140 just posted a link to a You Tube video with Josh from AC Propulsion.  If you look at 4 minutes and 50 seconds, you can clearly see that AC Propulsion has connected a 30 amp, 120 volt "Travel Trailer" plug directly to the charging cord for the Mini E.  This allows them to charge at 3600 watts at a Recreational Vehicle park in the US.  This is more than twice as fast as the usual 110 volt 12 amp yellow charging EVSE (Electric Vehicle Service Equipment) that Mini supplies in the US.  But I find it a bit odd that they are showing this, because the electrical code requires that drawing current at 100% of a connector capacity (30 amps in this case) should be limited to 3 hours, which is not long enough to fully charge the Mini E.  The code says to limit current to 80% of rated capacity when the load duration exceeds 3 hours.  But then again, AC Propulsion can probably set the current draw to 24 amps in their car, which the rest of us cannot do.  We have to live with 12, 32 and 50 amp settings.  (All of which actually draw slightly less than what the setting shows.)

Then I see that MINI-E Driver Stefan Reitmeier from Germany posted a picture of his car plugged into a wall outlet without an EVSE.  Maybe the regulations are more rational in Germany than in the US?

In any case, AC Propulsion has state of the art safety features built into the charging system in the car.  But only an external EVSE can provide the "dead front" connector to the car.  In other words, the connector face stays unpowered until it is actually engaged in the car receptacle.  So although I admit I have charged without an EVSE myself, we should all avoid it whenever possible and stick to the US rules and Mini guidelines.

It is interesting though.  Someday the US rules may change and charging will be more flexible.

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.

06 December 2010

The one thing electric cars need most but no one is offering

Every electric car, no matter the manufacturer (or start up), is offering one and only one power inlet.

Is this the only way it could be?  Gas cars have only one filler pipe for the gas tank.  So electric cars should have only one power receptacle, correct?

Wrong!  At least in the USA.  Much of the world has 220 volts as their standard supply voltage, which makes for a faster charging process.  But in the USA we stayed with 110 volts even after light bulbs switched from carbon filaments to tungsten one hundred years ago.  Since wires are more or less the same diameter in European homes as in US homes, this means there is less power available from US outlets, even if they are nominally safer.

There are many places in the US where it is easy to find multiple electrical outlets near each other that are on separate circuits. I always used two circuits in my garage in winter, one for charging the Mini E and one for keeping the cabin warm, which helps improve the battery performance greatly.  (Of course the charging circuit was usually the 220 volt wall box and the heater was on 110 volts, but bear with me.)

At my work place in the winter, I used two separate, dedicated 110 volt circuits.  One for charging, one for heating the car.  I have done the same thing when stopping to charge at the homes of several other Mini E drivers.  Plug the car into the charging box and run the cabin heater to a regular outdoor receptacle.

I have seen three separate 110 volt outlets at multiple shopping centers that have reserved parking spots for electric cars.  Truck stops with the "Idle Aire" system provide three 20 amp outlets right next to each other, all on separate circuits.  All sorts of camp grounds have multiple circuits side by side.

There is no reason not to provide a second connector, designed into electric cars, so that you can either run the cabin heating or cooling WHILE charging from a separate circuit, or simply double the charging rate if both circuits are 110 volts.

How to protect against someone plugging two cords into the SAME circuit?  This is a very easy engineering task.  If two circuits are out of phase with each other, they are guaranteed to be on different circuits.  This was the case I had at work, this is the case with "Idle Aire", and the shopping center parking lots.

So, why not provide even more than two power inlets on an electric car?  Actually the limit would be three.  In industrial or commercial locations where power is generally supplied in three phases, three would be the maximum that could be definitively distinguished from each other, and thus verified to be on separate circuits.  Idle Aire provides three outlets right next to each other, all on separate phases. Same in the shopping center parking lots.  The two outlets I had access to at work were on different phases of a three phase supply, although I did not get around to finding a third circuit.

In the long run, two (or three) power inlets in an electric car might not be necessary, but in the short run it strikes me as essential for flexibility.  And I don't hear any one talking about providing it.  This is an engineering crime of omission.  I cannot think of another thing that would improve the flexibility and even viability of early electric cars more than multiple power inlets.

And best of all, I don't see anything in the National Electrical Code or recommended practices of the Society of Automotive Engineers that forbids it.

So here is how it would work.

1) Plug in the first cord, the car starts charging.
2) Plug in cord number 2, and if the car can verify that the circuit is separate from the first, you either double your charging rate or use the added power to heat or cool the cabin, as you choose.
3) Plug in cord number 3, and if the car can verify that the circuit is separate from the first, you again increase your charging rate.

I understand that the coming BMW electric car will heat or cool the cabin from "shore power" but only after the battery is fully charged.  With a single 110 volt supply, that is about all you can do.  But with two circuits, it could be extremely useful at times to condition the cabin temperature BEFORE charging is complete.  I speak from experience.  25,000 miles of electric car experience in the Mini E, to be precise.  Much of it in cold weather.

There is a commercially available safety device that can combine two 110 volt outlets into a single 220 volt outlet.  But for practical purposes, it would be of limited use for an electric car although I have heard of a Tesla driver using one effectively.  These devices are popular for, say, contractors that need to operate a 220 volt floor sander in an older house, or operation of European instrumentation in a US facility.  But for outdoor use with an electric car, the omnipresence of Ground Fault Interrupters (GFIs) makes this "Quick 220" box unusable for the average electric car driver.  It only works without a GFI.

However, a properly engineered electronic interface in an electric car could easily take advantage of multiple separate 110 volt circuits to get faster charge times without special infrastructure installations in the early days of electric cars.  And I don't hear anyone talking about it!  Why?  Has no one noticed?  Are you guys asleep or something?  Hello?  Is anybody out there?  Don't make me do it myself!

04 December 2010

Why is it difficult to charge from a generator?

A dual section "Variac", 7 kVA maximum.  For use at 110 volt 12 amps, the minimum safe power capacity required is about 2 kVA.
I heard from other Mini E drivers that charging the car from a generator was usually unsuccessful. I never had occasion to try it, but it seems like a valuable backup plan if you could count on using a generator. So I wondered why it doesn't work. The story goes that large diesel generators sometimes work, but the Mini E always refuses to charge from a small gasoline generator.

I believe the reason is actually a safety feature built into the circuitry from AC Propulsion. The car measures the supply voltage before it starts charging, and then if the voltage drops too much as the car starts to draw power, it will stop charging. It figures you are using an extension cord that is too long, too thin, or has corroded connections or is somehow otherwise a fire hazard.  This is why Mini explicitly says not to use an extension cord.

I noticed this safety mechanism once when I was trying to charge from a 110 volt outlet at a considerable distance. I had some very heavy cable (10 gauge, rated at 30 amps) but even though I was only drawing 12 amps, the car would refuse to charge through this very long extension.  So after a long dry spell, I drove on the grass to get closer to the outlet and found that I could charge if I plugged in directly, or even if I used 100 feet of my heavy cord. But at 180 feet, it would refuse. If I recall correctly, the limit was about 8 volts of drop from no load to full load. More than 8 volts drop and the car refused to charge.

I had a large variable transformer for other reasons, so eventually I tried using it to correct for the voltage drop.  It worked, and I was able to charge the car even using 180 feet of heavy cord.  I would set the "Variac" (as it is called) so that the output voltage was equal to the input, which was about 110 volts. Then as the Mini E started drawing current, I would turn up the knob so that the output voltage stayed at 110 volts, more or less. And the car kept charging.

A Variac usually can adjust the output voltage over a range from +20% to -100% of the input
So my theory is that a small generator would have a significant voltage drop under load. A Variac could compensate for this drop. If someone who is still driving the Mini E has a small generator and would like to test this theory, leave a comment and I will get back to you.  Maybe we can try it sometime.

It might not work, since a small generator would also change its frequency with load. I don't know if the Mini E cares about power line frequency, but it might. And frequency is harder to compensate for than voltage is. The large diesel generators that have been reported to sometimes work for charging the Mini E would likely have less variation in both frequency and voltage than a small generator.

If you are curious about the theory behind this voltage drop measurement, see the technical discussion on Wikipedia about Thévenin's theorem.