4-9-06 Re: AC vs DC; Newbie Question

Hello to All,

Mike Phillips wrote:

The biggest thing that bugs me about most DC systems is the huge
amount of current the battery’s have to supply just to leave a stop
light. That’s hard on everything involved.

Huge amount of current just to leave a stop light? Where do you get that from? The average 144V-192V DC systems do not have to use ‘huge currents’ just to leave a stop light. My 156V car takes just 50-100 amps to leave a stop light at speeds matching traffic flow. In order to match the not-too-exciting 100 kw AC system’s ‘maximum’ leave the stop light capability, it still only takes about 300 hundred amps through a transmission, something most everyone uses with these DC systems. The huge currents (really not all that huge) only come into play when one wishes to demonstrate the 144V-192V DC system’s 6-7 second 0-60 acceleration capabilities, such as when wanting to dust off one of those lower powered 100 kw AC systems :-)   Using quality AGM batteries (wimpy gel cells need not apply) like Optimas, Hawkers, or Orbitals, the high currents are not a problem at all, in fact, these tough batteries seem to thrive under such treatment…witness my Optimas that finally died after 6.5 years of nearly constant high current acceleration blasts! Witness the Exide Orbitals that never, ever failed under repeated 1/4 mile drag strip runs. Witness the Hawkers in White Zombie that never, ever failed throughout the 2005 racing season.

With most AC systems you
need higher voltage to get the watts up, but the battery pull 500 amps
max on the high powered systems I am familiar with. Many limit to 200
amps. That makes battery and interconnect choices easier.

You can get the exact same results in a high voltage DC system, so I find this comparison you’ve made interesting, because it’s an apples to oranges thing. High voltage AC to low voltage DC? If you want the low current battery thing you ‘seem’ to be saying is the AC’s advantage, then simply run a high voltage DC system….you know, apples to apples.

In White Zombie, at 348V, it only takes about 50 amps from the battery pack to accelerate as a normal car does in average street driving, and it takes a whopping 20-25 amps to cruise at 55-60 mph. Driving as if I were in a 96V Rabbit or a Solectria Geo Metro, the car uses about 40 amps from the batteries to accelerate up to speed. The difference of course, is that my high power DC setup gives me the option of pulling 1000 amps from the high voltage pack (if I so deem it necessary and have it programmed the max battery amps this way) for extreme acceleration, something the 100 kw AC system you are comparing to, cannot remotely achieve.

The beauty of the 144V-192V DC systems is that you can afford these, they give superior acceleration when compared to the 100 kw AC systems that are double the cost, and using quality AGM style batteries, in particular the three brands I’ve mentioned that have a proven track record (pun intended), there really are no cabling or connector issues.

The only AC failure I’ve ever known was when the 12v accessory battery
got hooked up backwards ;)

The AC powered S-10 (Hughes Dolphin 50 kw) I had in my possession years ago failed, big time. The repair would have been so expensive that the truck was salvaged by the owners instead of being repaired. A DC truck would have been back on the road at minimal cost. The AC systems Victor (Metric Mind) sells have a very good reliability record.

It seems odd that you would favor an AC system at twice the cost, twice…because it ‘bugs you’ to pull high amps from a battery pack, when a DC system at the same voltage does the same thing while also giving you far more available power at far less dollars.

See Ya……John Wayland

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