Standard Tests for Battery-electrics
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FTER lengthy negotiaeon with Athe . battery electric vehicle
• manufacturers, wit h t he co-operatioh of, the Electric Vehicle Association of Great Britain, The CoMmercial Motor" has been able to arrange a standard conrse for testing
pedestrian controlled and driveroperated. electric vehicles.
• There has always been a need for
established .conditions and a standard course for testing electric vehicles. These are fundamental requirements in measuring the potential range of a battery-driven Vehicle, because it, is obviouSly .unfair to observe .tbe perforrriance. of one medel in a hilly atea and of another in fiat country, or with
a variation in load. •
.A number ' of batteryeelectries -has
the-Ay been tested e. • by "Ihe Commercial Ivtotor" and the experience gained has been of great value in preparing a standardetat sh:2t. deciding the load conditions and generally establishing a course which can be termed representative of average country.
-The route and conditions have been ipproved by the manufacturers' com mittee of the E.V.A., and the local branch of the Electricity Board is :0-operating by installing a supply point for battery recharging in premises near. the starting and finishing point of the tests.
Two routes have been planned. One
is a I5-mile circuit for -driver-operated vehicles, andthe other is a shorter course of approximately two miles for pedestrian-controlled models.
Operational Conditions
Obviously, it would be unreasonable to test the pram over the longer circuit. because it is designed for operation close to the depot. Normally, the pram on retail delivery duty is required to run up to two miles to the first point of delivery and is theta engaged in door-to-door operation, possibly covering a total of five to six miles during the day.
The threeand four-wheeled driven models usually operate a greater distance from their base and during delivery make fewer stops per mile. Their compass usually extends to 15-25 miles.
The 15-mile route starts and finishes near the goods' yard at Watford Junction Station. Permission has been granted by British Railways for the use of the weighbridge.
From Watford Junction the route extends through the outskirts of the town to join the A.41 main road towards Aylesbury. This section of the road has level stretches where the balance current and speed can he ascertained both on the outward and return The difficult section starts at Langley Hill, where the first gradient when turnc.20 ing from the main road is 1 in 7. The coprse is then undulating and passes through Chipperfield. Bucks Hill and Ch'andleFs Cross before rejoining. the man road to return to the starting point.
The course for pedestrian-controlled vehicles, also starts from Watford Junelion, and embodies an estate circuit where the gradients range from 1 in 40 to 1 in 71. At the finish of the trials, the vehicle is presented with the climb. up an incline.
To simulate workine conditions. the most d:fficult being milk delivery, the test vehicle will carry three-quarters load for the entire trial. This is a compromise between Laving the depot with a full load and returning with half a load, such as empty bottles.
The first test will be a continuous run to determine the time taken to discharge the battery. This can be identified on the battery-discharge curve to obtain the effective capacity. The safe discharge point of the battery has been defined by the battery manufacturers, who advocate, in the first place, discharging the battery to 80 per cent., which will be measured by two amperehour meters, and checking the specific gravity after an hour's delay to allow for diffusion. Vehicle speed and current, amperage and voltage on level ground will be recorded during this trial, and the average and maximum current on the inclines will be noted.
At the end of this test, the batteries Will be recharged and a run will be made over the same route, with stops at the rate of 12 per mile, except for the first and final three miles. which will be run non-stop. This distance is approximately the average run from the depot to the point of first delivery
The effective range of a vehicle operating under these conditions can then be calculated from the meter readings taken throughout the trial. -Next, t further lap over the-same circuit will be made with 36 stops to the mile, again with non-stop running at the beginning
and end of the trial. As before, the effective range can be calculated and it graph can be drawn to show an approximate range for any number of stops up to 36 per mile. This covers most conditions, of service.
Data recorded during these trials will be reproduced in a standard panel.
A three-quarters load will be carried by the pedestrian-controlled batteryelectric vehicle, which will make a non. -stop run and perform other tests with
• stops at the rate of 50 and 100 per mile. These results will be compiled in standard form in the same manner as for -the larger' battery-electrics.
Assessing Performance
In testing commercial vehicles with oil or petrol engines, The Commercial Motor" has developed a performance factor as a measurement of efficiency. which is now accepted by technicians as a true factor. It represents the suni of the load, speed and fuel-consumption rate obtained during the trials, and has an equivalent in battery-electric per formance. This factor will also be calculated from the tests.
The performance factor for electric vehicles was first described in "The Commercial :Mot-or" on September 17, 1948, in an article by Mr. H. W. Heyman, managing director of Smith's Electric Vehicles, Ltd., and Mr. J H. Cansdale, of the British ThomsonHouston Co., Ltd. This factor is developed from two formulke, which arc derived from continuous-running and stop-start tests.
= Speed x Range x Payload Battery kW.-hrs.
with results taken from the continuous running test. Average
Sped x Stop-start range x Payload
Battery kW.-hrs.
with results taken from the stop-start test.
By deducting P.F.., from P.F., a figure is obtained which shows how far stops and star.s affect the overall performance of the vehicle. A small percentage difference indicates that. .the vehicle is well designed for the duty it is expected to perform.