Dennis O'Brien

So why don’t we drive them my dears?
These automobiles with no gears.
For speed they’re a match,
But there is a catch:
The problem, you see, is amperes.

Saw 2 Teslas on a trip to Brisbane and back, and I actually saw one on charge at my local Coles, which appears to be putting in more charging points — all is rosy on the EV front?

Well no, not really — see, despite what the snake-oil salesmen say, (and whisper in politicians’ ears) there are lots of problems with electric cars, otherwise we would all be driving one and would have been driving them for generations. The technology at its heart is nearly as old as the internal combustion engine but the problems have been there from the start.

I’ll only concentrate on the number one problem, which I have mentioned here before — charging times. Australia is a land of vast distances and many of us drive these distances, quite often completing the trip without an over-night stop but requiring a refuelling stop or 2 along the way. Time is often a constraint. Now I can "recharge” my petrol-powered car with a full tank of fuel in about 2 minutes, tank filled and payed for, and be on my way — 600 kms or more.

Were it a Tesla I could only safely run down the battery to around 30% and then charge it to around 90% (this by the way is the true range — only about 60 to 70 percent of the battery rating, perhaps only 400 kms or so; but that takes an over-night charge or an hour or so for a fast charge (not something you want to do to your $10,000+ battery too often as it will shorten its life). Clearly the Tesla is not suited to long-range travel.

The last time I looked, the Tesla battery (depending on the model) had a battery pack rated at around 250 kilowatt hours, so to go from 30% charge to 90% will require the injection of 150 kw hours of electrical energy (ignoring what will be considerable losses in the charging circuitry and battery). To give the layman (or laywoman) some idea of how much energy that is, how much it is sucking out of the already overloaded grid, imagine 150 single bar heaters all glowing red-hot for an hour. That’s how much mainly coal and gas fired electricity is getting pumped into that battery. But let’s just say for argument’s sake that the fast-charger can do this in an hour:
At 400 volts DC (voltage applied at the battery, and again round figures, don’t get nit-picky), the charger will deliver (I’ll average the current out as it will in reality not be a linear curve but will be considerably higher early in the charge cycle gradually decreasing as the battery becomes charged) 375 amps for the full hour — that’s why that charging cable is so thick! Power (in watts) is current multiplied by voltage, and this formula cannot be violated, it is set in stone, or if you like, Lithium.

By the way, a simple calculation shows that to charge the battery fully from flat to 250 kw hours capacity in 2 minutes as I can my car, and were it possible, it would require 18,750 amps of current for that 2 minutes — I haven’t calculated the cable size needed but the heat losses alone would melt everything, including the pole transformer and the operator.

So I hear the cries "But battery technology will make advances!” — makes no difference. We are stuck with Nature’s basic electrical laws — someone tell Albo, or (if you can find him) ScoMo.

Posted by: Timothy Birdnow at 09:08 AM | Comments (6) | Add Comment
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