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Planning Conversion Which is Better AC v. DC System

5118 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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Derka Derka Jihad! :p

If money is no object, then you should DEFINITELY go with an AC conversion. If you can get 35 miles out of a DC conversion, then you should be able to get 45 miles out of an AC conversion.

madderscience is absolutely right though, AC systems are more complicated. However, if you can afford to purchase a matched motor and controller, then the added complexity only equates to added $$ out of your pocket, so go for it.

One nice thing about Ac systems is that they run higher voltage. Rather, they run lower amperage. With lower amperage, the system can use smaller gauge wiring (perhaps 6 gauge vs 00 gauge). Less copper = less weight which further increases the system's efficiency. Less amperage through the motor = less heat in the motor on start-up. Less energy converted to heat energy = more energy converted to kinetic energy. Yay!

Look at this thread too. I blather on and on (sorry about that :) ) about the benefits of AC in there too.

Again, if money is no issue, then AC systems are the way to go.
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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.
I would say there is no "better". The two systems are fundamentally different.

DC systems are mainly preferred for reasons of cost, or performance. If you are on a budget or want 1000A, tire-spinning performance, you generally have to use a DC system.

If you want regenerative braking and more efficient use of the power, you generally have to use an AC system. Let me also say that generally, regen is only going to add 5% to the range; it is not the regen that accounts for the majority of the extra range, it is the increased efficiency. Where the regen is really helpful is with it's braking effect.

The AC systems begin at about $8000, which is a little more than double what DC systems begin at. A really nice DC system, with a WarP 11" motor and Zilla 2K would not even cost $8000, and the AC systems that cost that much are low performance models. The really nice, high end AC systems that places like Metric Mind sell will begin at over $10K, easily. They are nice if you can afford them, but once you go into that territory, it would be downright cheap not to couple it with a premium battery pack, and then you are into the 50K range. If you can afford to go there, you will be able to make a very nice, showpiece conversion.

There is a reason that many DC conversions are being completed every day. They make an excellent cost effective electric vehicle for most people, and are probably the only type of conversion that will actually pay for itself if the costs are compared.
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