Stephen A. Lawrence
Tue, 08 Jul 2008 09:28:00 -0700
Terry Blanton wrote:
Came through fine. I gather that's it's umbilical cord sticking out the trunk.
Yup.
Hows about some more info: 1) DC operation? 2) Voltage? 3) Motor type/rating? 4) Propulsion control? Kewl.
It was converted from gasoline to electric by Richard Lane, http://www.revconsultants.com/ , last spring. Richard likes Jettas; they're apparently easy to convert and have beefy enough suspension that they can carry the weight of the batteries without going over the manufacturer's gross vehicle weight. At the same time, they're pretty light, so they perform acceptably afterwards. It's a (nominal) 96 volt system, using 16 6-volt "flooded" lead-acid batteries (golf cart batteries). It's got a 9" DC motor; I don't recall the rated horsepower, unfortunately. But in any case the limiting factor with regard to power is the batteries. If you "grease it", it'll take off pretty respectably, but it'll also pull 300 or 400 amps from the batteries in that case. They're rated by the manufacturer at something like 75 amps max, and though golf cart batteries are pretty rugged it's still better not to fry them: they heat up awfully fast with that kind of drain. So, we try to hold it to no more than 200 amps (keep a close eye on the ammeter while accelerating or going up hill!) and that limits the power to about 19 kW (with charged and happy batteries), which is something like 25 or 26 HP max regardless of engine and controller type. The controller is a Curtis PMC 1231C, rated at 500 amps peak and 225 amps continuous with a battery pack producing from 96 to 144 volts. It's bolted to an absolutely enormous heatsink. It's possible to build EV's which run on higher voltages, and that has advantages; in particular higher volt battery packs require less current from the batteries, as a result of which they may last longer. If you can keep the current down, you also have the option of using "marine" batteries, which can handle deep cycling but "burn up" if you draw a couple hundred amps from them for extended periods. However, Richard doesn't like to go much over 100 volts due to the wet, salty conditions which we have all winter in Ottawa -- he feels a 300 or 400 volt system is just asking for trouble in this area. Speaking of the weather, there is an issue with lead-acid, which is that it performs badly when cold. So, this car -- like many which operate in this climate -- has insulated battery boxes with heaters built into them. It's kind of like a diesel that way, but rather than plugging in a block heater to heat the oil, you plug in the box heaters to heat the batteries up before you go out in the winter. The charger is a simple one, which charges them all in series. A fancier arrangement which charges each battery individually would extend the battery life and would give the car better range. Its range right now appears to be about 45 km before the batteries are "technically run down", which is when the battery pack voltage drops under about 85 volts while under load. Running it down flat (and then calling a tow truck) will get you substantially more range but it's very bad for the batteries. That was done to this set of batteries once or twice before we bought the car, which is unfortunate; Fred (former owner) got lost and drove 'till the car stopped, waited a while for the batteries to recover, ran 'till it stopped again ... and made about 99 km that way. But these batteries will never do 99 km between charges again, except straight down dropped from orbit. "Where are the batteries?", you may well ask; position of the batteries can affect car balance and performance. The answer Richard gave when I asked that was "everywhere" -- some in front and some in back. When you open the hood or trunk, you don't see bare batteries, though; you see the metal battery boxes, which are lined with about an inch of Styrofoam. (Attached are photos under the hood and in the trunk, if the attachments come through.) The battery box in the trunk is actually on wheels, and runs on a pair of rails; it rolls forward until it touches the back of the back seat in "driving" position, which leaves some useful trunk space in back of the box. To get at the batteries (to check the temperature or water level) you roll the box all the way to the back and pop off the lid. When it's rolled forward and you're about to drive off, you put a couple of moby pins through the rails to hold it in place while moving: it weighs about 600 pounds, so just letting it rattle back and forth would be a bad plan. (And don't pull the pins out if the car's on a hill...) Let's see, what else is there to say about it? It's got one additional battery: A normal 12 volt automotive battery. A DC-DC converter keeps the 12 volt battery charged. The 12 volt system is used to run the headlights, wipers, horn, cigarette lighter outlet, and any other 12 volt accessories there may be on the car. There's a vacuum pump for the power brakes. There's an electric heater for use in cold weather (can't steal waste heat from the engine, there isn't any -- or rather there isn't enough and it's not in a theftable form). It's got an automatic transmission and power steering. The auto trans may not be ideal (a lot of EV websites recommend against it, because it reduces the range) but from what I've read in "conventional" car publications about the efficiency of automatics I doubt it has a big impact. Modern torque converters are pretty efficient. When you turn the car on the motor starts up, which one might not expect! You might think the electric motor would just stop when the car's stopped, rather than "idling". The problem, though, is that the automatic transmission and the power steering are designed to work with continuous mechanical power applied to them. So, if the car isn't set up to "idle", then you need to add a couple of additional motors to run the transmission and steering pumps. It has ordinary tires, but we keep them pumped up to 40 pounds, to reduce rolling resistance.
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