Should I go AC or DC?

[Heather Poe]

I plan to convert a 3000 pound car to EV, 24 mile daily commute without recharging (charged by solar at my home) and I want some "pep" for the highway portion.  Any opinons or advice would be appreciated on any part of the conversion process.
thanks,
Heather

[ev-supply]

Heather, there is quite a bit of price difference between the two systems.  The motor and controller for a DC system cost $3,000-$4,000, and run off of a 120V or 144V system normally.  The same AC components with comparable performance will probably begin at $10,000 and will run off of a 300+V system.  There is one lower cost AC system out there that runs off of 144V, but it still costs $7,500 and generally performs slowly in comparison to the DC systems.  My opinion is that you would be best off going with the DC system, and stash the extra money away for the day when you need new batteries.  Your 24 mile range should be easy to obtain with the typical lead acid batteries.  Hope this provides some information.

[aviken]

I plan to convert a 3000 pound car to EV, 24 mile daily commute without recharging (charged by solar at my home) and I want some "pep" for the highway portion.

This is not far from my criteria...what is your 3000lb car you will be converting?
Ken

[leitmotif]

Heather

As a former submarine electrician who worked with AC and DC distribution and motors I am definitely biased in favor of AC.  So are the railroads, electric forklift manufacturers, industry in general.  I am still an electrician in industry and definitely favor AC.

There was nothing wrong and still is nothing wrong with DC motors as such.  They are still an excellant choice for variable speed application.

AC is just better no brushes, commutator, difficulty with flashing arcing contacts, AC motors are much more resistant to running wet, with a VFD the starting current is less, you get regeneration braking with no added controls, good torque control (ice in winter ??).

I do NOT like going above 250 Volt DC battery bus voltage to get to AC drive
BUT I know high voltage work (440 3 phase is meat n spuds for me), and have insulated tools and hot gloves.

Everyone says the cost of DC is lower than AC and I agree especially when you use Curtis controllers which are least costly
-BUT  just try getting factory  support - they will not even sell direct to you (NOT DEALER - ASSUME -- he does not care he got your money).  Look at all the posts citing problems with Curtis.  Curtis is widely used in forklifts and I guess they have done OK but there are horror stories of them failing - such that motor goes to full speed.  IF you go with a good controller then I think the prices start to even out.

So to answer in short
IF you go with the crowd go DC.
IF you are short of bucks go DC
IF you are worried about high voltage DC with the AC crive then go DC.

I predict that in 3 to 5 years AC prices will be competitive with DC and you will get some really neat options like all wheel drive with four independent in wheel motors (supposedly on the market or soon to come but oh boy the price tag).

As a side note
 you may have solar at home, but you are still going to recharge those batteries regardless of what your power supply is.  I would plan on using the solar generated energy to supply house loads, sell any excess to utility (if you want) and use the utility to charge.

Dan Bentler

[Monermaje]

Voltage has little to do with power.
Voltage is energy (Volt = Joule/Coulomb)
Power is energy flow and is a product of voltage and current
P=V I (Watts = Joules/ sec)
AC is easier transmitted over long distances since it can be stepped up to a high voltage, transmitted and stepped down just before the consumer. High voltage AC is used for trains that run long distances. Local trains may employ DC. DC is 'safer' than AC, but that is another story.

No we can't say that "...25k V AC is equivalent to 750V DC " in terms of power since we don't know how much current is used in each case.