Battery Vehicle Society

Just a quick question --- Just wondered why everyone seems to be using high voltage drive systems ?
Your comments would be greatly appereciated

Keeps the current down

Chris

But increases the costs -- g-Wiz for one only uses a 48V battery pack

Try getting a VW Scirocco to do 100mph on 48 volt.

Come to that, try doing on 96 or even 120 volt.

I needed a car that would cruise 10 miles down the motorway doing 70mph and you need a fair margin in hand.

Particularly with a series wound motor you need a lot of surplus voltage to get a flat torque curve over the rev range.

What are we after? Speed, Range, Both ( Cant Happen ) or basic longevity?
As we are all aware the chances of an electric vehicle being a true competitor to the combustion engine is a long way off.
Commuting cars only require low low voltages, mid range speed with ranges of upto 50-60 miles. So why go for hi speed very low range ? Whats the point ? To be honest the energy that has gone into producing the batteries for the abuse that they are being subjected in high speed/hi current loads/very short life span just dont add up to the green image. One would be better of going and buying a BMWX5.

Not trying to teach anyone to suck eggs here, but I thought the main reason for using high voltage was to keep the current down, as Chris said, and so reduce resistive heating losses (I squared R).

By reducing current draw you also reduce Peukert losses (especially with lead acid batteries) and so increase the useful energy capacity and life of your batteries.

Beg to dissagree regarding the Peukert losses. Yes there are high loadings put upon a low voltage traction battery but as we all know Evs are best suited to city environments whereby the loading might be high but for only short periods of time. As GG state the average speed of their vehicles in London is only 10MPH. That obvoisly must involve a lot of stopping/starting -- High loads for short times. Which on each occasion allow the battery to recover from its losses.

What a can of worms

I always understood from my physics days that it was more efficient to have high voltage and low current as you have less energy lost in cabling. Not only that but aren't you making life easier for the batteries if you have a high voltage pack with a low current drain?

No disrespect but, we're not all in cities either, There's a whole country outside the M25.

We have to do a mix of driving and quite a bit can be on Dual Carriageways so 70mph is actually often necessary. We may just do short journeys but it doesn't mean we crawl into the near by town at 10mph if we did we'd probably use a bike instead to be green.

One of the biggest advantages of high voltage - and preferably *AC drive system - is LOWER demand on the batteries. If you recall GM EV-1 or Solectria they were quite fast and reliable even with quality AGM/gem batteries, each cell 12V@50-100Ah not more. So in this way you can get 50-70.000km lifetime from Pb batteries, which is not achievable say at 48V or 60V in comparable sized vehicle..

There are some websites with advanced modeling of car consumption at batteries, you can tweak all the parameters to choose the right batteries for your particular setup..

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* here you can run into another set of problems, since highvoltage AC gives you higher regen efficiency hence your batteries have to be capable to take it..