Powering your lift truck
May 1st 2006

Which lift-truck power source should you choose? David Dobson C.Eng., managing director, Sidetracker Engineering explains The list of factors to take into account when choosing a lift truck can be long and complex, particularly if future developments are being taken into account. But one of the main decisions to be made concerns the power source and engine type. Batteries, gas and diesel all have advantages and disadvantages which make them more or less suitable for specific situations.

Before settling on any particular type of truck, it is important to decide what it is going to do:

• Will it be used indoors, outdoors or both?
• How many hours a day will it be used?
• What loads will it need to carry?
• How high will it need to lift the loads?

The shape of the loads also has a bearing on the lift capacity of the truck because a regular cube requires less effort to lift than a load that is particularly long, high or deep.

So changes in product dimensions or the installation of higher racking could reduce the usefulness of a truck in the future.

The two main types of motor to choose from are electric and IC (internal combustion), the latter being sub-divided for practical purposes in the UK into diesel-powered and gas-powered models.

LPG, propane and natural gas are all suitable fuels for gas-powered trucks, but LPG is clearly the most widely used at the moment.

A considerable amount of work is currently going into the development of hydrogen fuel cells, which combine some of the advantages of batteries and IC engines. Like batteries, they are quiet and create no emissions, but they do not need to be re-charged and can be refuelled as quickly as diesel or gas models. They could be the power source of the future.

Lifting capacity is one of the main differences between IC and batterypowered models. As a rule of thumb, ICpowered trucks are best for handling loads above ten tonnes, although specialised electric models are available for carrying loads above this weight. The practical limit for most standard electric trucks used for several hours a shift is around six tonnes.

The IC engines bring not only more lifting capability but also more speed and better performance on slopes. The extra power also enables a truck to cope with energy-sapping soft rubber tyres -- a useful feature where surfaces are rough, given that FLTs have no suspension.

Although the capital cost of a diesel model is generally around the same as its LPG counterpart, running costs are considerably lower, so over the life-time of a well-used truck there are some savings to be made with a diesel model. In addition, although a diesel generally requires more maintenance, the lowrevving engine should last longer and provide plenty of torque in the meantime.

The two big disadvantages of diesel trucks are noise and fumes. Planning authorities are increasingly outlawing their use near houses because of the noise of the engines, and it may well be that the same view is taken in future on the more up-market industrial estates. While the noise of a diesel engine is more a nuisance than a hazard, the same cannot be said of the fumes. These are carcinogenic, so indoor use is simply out of the question, and they can also produce sooty deposits, which may be a significant consideration in some situations.

At the other end of the spectrum from diesel IC-engined trucks are electric models, which are powered by large heavy lead-acid batteries that typically have enough power for five or six hours of constant use. The truck supplier should be able to propose a battery with the right capacity for each situation.

Electric trucks are very quiet, clean and emission-free, so they are ideal for internal use. They are also cheaper to run than IC models - around 85% of the cost of an LPG truck and 70% of the cost of a diesel - and require very little maintenance because there are few moving parts. The relatively low running costs off-set one of the main disadvantages of electric trucks - their higher capital cost compared with the IC models.

The use of batteries and electric motors allows a great deal of flexibility in the design of a truck, and this has resulted in electric models generally being more compact than their IC counterparts - a particularly valuable feature when they are used indoors where space may well be at a premium.

One disadvantage of battery power is the time it takes to re-fuel. Whereas filling up with diesel or changing a propane cylinder might only take 15 minutes, charging a fork-lift battery can take eight hours. A two-shift operation may need two batteries, so that one can be charging while the other is being used. A 22kW battery, a typical size for a 2.5 tonne truck, currently costs around £1600, but there is no fuel to store.

LPG-powered trucks are the compromise between diesel and electric.

They lack the low-revving grunt of a diesel, but they are faster than an electric model.

Their exhaust fumes are less hazardous than diesel, but they still cannot be used in fully enclosed areas because of the CO2 produced. They are quieter than diesels but noisier than electrics. They cost less to buy than electric but are much more expensive to run.

Diesel and LPG-powered trucks can be fitted with catalysts that treat the exhaust gases. Two-way or oxidation versions treat the two constituents traditionally considered the most harmful - carbon monoxide and hydrocarbons - and convert them into carbon dioxide and water. For LPG trucks three-way catalysts are also available, which convert the oxides of nitrogen (NOX) - a third potentially harmful constituent of exhausts from IC engines. As yet, these are not commercially available for diesel engines.

Although there are no specific regulations relating to the use of propanepowered trucks inside buildings, general health and safety considerations rule them out for most production areas and other buildings with relatively low roofs or little ventilation. Inside use is generally restricted to high-bay warehousing and buildings with plenty of ventilation.

Ultimately, the choice of engine type is nearly always a compromise between capital cost, running costs, performance and safety. The choice is even more complicated if possible future developments are also taken into account.

However, a manufacturer or dealer who takes the time to understand and evaluate a potential customer's situation should help him to prioritise his requirements and help him make the right decision.

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