# Re: [EVDL] Citicar tech



## EVDL List (Jul 27, 2007)

*Re: [EVDL] Citicar tech*

Although I would like my Citicar to have the ability to go 45 MPH or so, it
is probably too squirrely at that speed to keep going for 15 miles of a
commute. Perhaps some suspension upgrade will be the solution. One
additional thing to keep in mind is that if the speed limit is 45, people
are probably driving 55.

If you have a Dana axle, you probably have a 5.17:1 ratio with 13" rims. At
45 MPH, the motor will be turning about 3,500 RPM. This is nearing the
maximum of about 4,000 RPM I'd use for this motor, but mechanically it will
probably be OK at that speed. (The GE 6HP motor in Dana-axle C-Cars has one
bearing at the brush end, and is suspended at the drive end by the
differential. This isn't exactly a high tolerance fit, which reduces the
top RPM limit a bit.)

On Terrell axle CitiCars, the ratio is 7.125:1 and they have 12" rims. The
3.5 hp GE motor has bearings at both ends, and is rated for a higher RPM
than the newer 6HP model. I have run my motor at 5,000 RPM, and so far it
seems to be OK. 5,000 RPM is about 45 MPH in a Terrell-axle CitiCar. I
would not recommend exceeding 45 MPH, and only 45 for brief periods of time
with the Terrell axle setup because of the probability of overspeeding the
motor.

I've tried 145R13 tires from a Comutacar on my Citicar, and found the top
speed (measured by GPS) was about the same as when it has 145R12 tires.
This speed - about 37 MPH in my Citicar - is probably a point where the poor
drag characteristics (about .82 or so) of the Citicar require more power
than the motor at 48v can put out.

As far as voltage is concerned, all 48v Citicars I've driven (either axle
type) won't go much over 40 on a flat road, most will only go 35. You'll
need 60 volts or so to get to 45 MPH. There are a couple of options:

10 X 6v batteries for 60 volts. Will get some Citicars to 45, but may not
be a reliable speed due to the weight. Range would likely be over 40 miles.
You'll have to find room for two extra batteries, and the odd-voltage 60v
charger.

8 X 8v batteries for 64 volts. Will get you to 45, and have about 30 - 35
miles range. Difficult to find chargers for 64 volts (I only know of one
manufacturer that makes a 64v charger).

6 X 12v batteries for 72 volts. Will get to 45, but you'll only get a max
of about 16 - 20 miles before you need a charge. This is the lightest
setup, and folks that have done this like the acceleration. The suspension
is particularly harsh when only six batteries are used.

9 X 8v batteries for 72 volts. Will get you to 45, but you'll have to find
room someplace for the 9th battery. Would probably have about 35 - 40 miles
of range if you kept the speeds down. With a Dana axle C-Car, the
acceleration is sluggish, even at 72 volts. Terrell axle CitiCars
accelerate well at 72 volts, even with the extra weight.

8 X 12v batteries for 96 volts. I haven't seen this done, but would get you
to 45 and probably have about 25 - 30 miles of range.

As far as controller amperage goes, I believe that my acceleration with the
Alltrax 7245 is about the same as it was when I had the contactor setup in
most conditions. It may be slightly slower from zero to 3 MPH because I'm
not dropping all the current the batteries can provide across the stock
small F/R contactor points, the teeny stock brushes with their single-wire
leads, and the stock #4 or #6 battery cable... 

In a stock Citicar, I believe that the second position (24 volts - normally
2 parallel banks of four 6v batteries) will provide more current and
accelerate faster up to about 15 MPH or so, but no one seems to drive that
way. Most people will just floor a 3-speed contactor setup and use whatever
amperage the 48v single-string pack can provide to the motor - about the
same as a 500 amp controller.

After about 3 MPH, the motor, batteries, cabling, brush leads, and motor
probably can't use much more than about 450 - 500 amps. If you're slogging
at 3MPH up a steep hill and full power, you're likely to burn something out
very quickly - Steep hills aren't a CitiCar's forte... 

Amperage falls off quickly as speed increases. IMHO, You'd have to do some
significant modifications to the motor and other power components to need
more than a 500 amp controller in a CitiCar.

Tom Keenan

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