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Planning Conversion Which is Better AC v. DC System

5122 Views 4 Replies 4 Participants Last post by  kittydog42
I am trying to decide what system I should buy. Money is not a factor so I am considering an AC system, but I'm not educated enough to make a wise decision between the two. I need to go 40 miles a day and get at least 65 miles an hour, but don't need to burn rubber off the start line. Any help greatly appreciated. :D
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AC systems are generally considered "Better" from a technical perspective (all commercially made freeway-capable EVs such as the Tesla, and the GM EV1 from the 1990's and others used AC systems) but they are more complex from a conversion perspective and they cost more. The extra complexity comes from the fact that AC systems typically want a higher voltage battery pack than the DC systems and the components themselves are more complex. This means less "hackability" and less opportunity to mix and match components. For example, the motor and motor controller are typically a matched pair in AC setups, while with DC there are many controllers that will work with a given motor, and vice versa. For the extra cost and complexity of an AC conversion, AC makes it easier to get regenerative braking capability, the opportunity to build a direct drive conversion (no more transmission) and overall slightly better energy efficiency.

However DC is cheaper, and for the shade-tree conversion DC is much easier to work with if you want to build a higher performance car, and you can build a DC conversion using a lower voltage battery pack which can save battery cost and cost of peripherial components that don't need to be rated for as high of voltage.

Given the performance requirements you specified, either AC or DC could do it easily, provided you choose an appropriate lightweight, aerodynamic donor car.

All of this is IMHO of course. AC vs DC is one of the great holy wars in the EV crowd. (My car is DC!)
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It is true that a higher voltage system means you can use a smaller gauge of cabling. volts X amps == power; scale one up, the other can go down. I would contest the 35 miles vs. 45 miles statement unless it were a route where regen could be a major benefit however. Given those numbers, and if a well designed DC system is around 80% efficient battery-to-wheels (as is usually quoted) then the AC system would be, well... That's it. I'm done. Its written, therefore it must be true... :eek:

Anyway, yes if cost is no object... Go AC.
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