On 5/23/2013 8:45 AM, Zeke Yewdall wrote:
So... a client of mine got a converted VW bug with the wilderness EV kit --
the kit#2, so it's a 6.7" series DC, 450 amp alltrax, 72 volt system with
six 12 volt 100AH gel batteries, no DC-DC, very little instrumentation,
crude offboard transformer 10A charger. Right now, the car can move
itself around the yard, and that's about it. They said they did get it up
to about 40mph on the flat before it died though. Only 20mph even on very
slight upgrades.
The Wilderness EV kit is pretty crude. Still, I would think its
performance should be better than you're describing. I had a ComutaVan
with a 72v system that weighed even more and had the aerodynamics of a
brick, and it would do 50 mph.
Look for the usual culprits. Soft tires, dragging brakes, poor
alignment. You should be able to easily push the car with one hand.
Get at least a voltmeter and ammeter in it for instrumentation. See what
the pack is sagging to, and how much current is being drawn from it. I'd
expect the pack to sag to around 60-65v at 250 amps. 60v x 250a = 15kw =
15hp (approximately), and 15hp will push a bug at 50 mph.
If the voltage sag is more, you may have bad batteries or wiring. If you
can't draw 250 amps, the Altrax controller may be programmed with too
low a current limit, or there may be bad wiring or connections to the
controller or motor.
Here's what I'm thinking of for upgrades.... they want a good solid
50miles range, and enough speed to keep up in city traffic (45mph, a few
small hills, but not climbing big ones).
Figure out if any of the current batteries are any good.... (some are brand
new, so they should be).
*Some*? If it's a mixed pack, the weakest link limits the performance of
the whole pack. One bad apple spoils the lot. Gels are not high current
batteries, and this low-voltage setup is likely to overstress them
unless the driver keeps the current down. Don't draw over 100 amps
continuous, or over 250 amps for more than a few seconds.
Better charger (not sure the old one is working at all, which could explain
why the main bank is not doing well).
That should be easy to ascertain with a meter. Gels do not like crude
chargers! They will quickly be murdered by a typical unregulated
charger! You *have* to limit the maximum charging voltage.
Think about lithium batteries/smart charger/ and higher voltage
That could certainly work, but will cost a lot. Not only the batteries,
but also for a BMS, new charger, new motor and new controller as well.
Is your client prepared to put $10k into this vehicle?
Is the Alltrax any good?
Alltrax are good controllers, though pretty small. They are intended for
small, light, low-speed vehicles.
Lithium batteries? Not sure that getting solid 50 miles on lead is
possible in this car without seriously overloading it.
Sure it is. *Lots* of people have done it. But with lead, it's done with
lots of big golf cart batteries. Six 12v 100ah batteries is a pitifully
small pack, whether lead or lithium.
Is the 6.7" series DC motor enough for this heavy of a car?
Possibly. Which 6.7" motor does it have? If it's an ADC, there is the
little A89 (10.39" long, 6.4hp), K91 (11.34" long, 10hp), and L91
(15.25" long, 15hp). The A89 would only be good for low speeds, like 40
mph or less. The GE motor in my ComutaVan was equivalent to the K91, and
was adequate for 50 mph. The L91 in my LeCar is more than adequate to do
70 mph.
--
Progress is the product of human agency. Things get better because we
make them better. Things go wrong when we get too comfortable, when we
fail to take risks or seize opportunities. -- Susan Rice
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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