2 November 2001


How come the electric always goes in the middle of milking?

Mervyn Bailey finds out how to keep that crucial piece

equipment – the stand-by generator – ready for action

A STAND-BY generator is probably not the best-maintained piece of kit on the farm. Often ignored until a power cut, then dragged out of the shed in the middle of the night, the generator deserves a little care to keep it in good running order.

"On most farms, stand-by generators are properly installed or stored. But it is not unknown for them to end up buried beneath a pile of old sacks where they are forgotten until needed in an emergency," says Keith Fowler, customer support engineer at generator manufacturer, N J Froment.

"When this is the case, the first job is to dig them out and give them a thorough check-over to ensure they work properly and reliably when needed."

For the tractor-powered type, ensure there is ready access for the tractor and for the wiring that connects the generator to the electrical circuit.

Ventilation and lubrication are the key things for users to keep an eye on. Maintenance is otherwise minimal and no adjustments are needed while the generator is in use.

Mr Fowler emphasises ventilation is important when installing a fixed stand-by generator or positioning a portable version ready for work.

"There needs to be plenty of room for cooling air. Generators get hot and need a minimum of 18in clear space around them to ensure there is enough airflow to keep them cool."

Air enters through a grille at the back and is drawn over the alternator and other components by a cooling fan located at the front. It is therefore sensible to keep the area where the generator operates reasonably clean. Otherwise, leaves and other debris can be sucked in when it is started.

Ventilation screens should, therefore, be the first port of call when making a routine check on the generators state of readiness. They can be cleared using a brush and/or air line in the same manner as a tractor radiator. When they are left obstructed and airflow is restricted, the generator will simply overheat.

Having insufficient oil for the gear drive can also cause overheating. This is checked by inspecting the oil level indicator if fitted or by removing the level plug just below the power take off input guard – when loosened, oil should discharge from this plug.

To top-up the gearbox on Froment Magnate generators, remove one of the gearbox input plate fixing screws and use the hole as an inlet. A squeezable bottle will make the task of introducing the correct grade of oil – SAE 85w-140 automotive gear oil – a lot easier, advises Mr Fowler.

Signs of oil leakage are next on the check list. "Oil seeping from between the gearbox and fan housing at the front is caused by the seal drying out and perishing. This can be prevented by running the generator regularly.

"The best way to keep a generator in good condition is to run it on over 50% load for at least an hour. We also recommend using it to power the milking parlour once a month – perhaps on a Saturday morning as a matter of routine. This will also help the user remember correct operating procedures when the inevitable power failure occurs on a dark winter morning or evening."

Damp is another consideration for generators, especially those installed in buildings without heating. In these cases, it is recommended that an anti-condensation heater is fitted to prevent condensation causing the winding to become damp.

This takes the form of a small heating element (30-50W) fitted inside the generator and powered by the mains supply. It should be left switched on all the time.

Where a generator is installed in the same building as a compressor or vacuum pump, there should be enough warm air circulating to prevent condensation forming.

Incorrect brush spring tension can also cause arcing. So, if the generator has been left idle for a year or more, it is good practice to have the brush tension springs checked – by a professional electrician or a generator specialist – to find out whether they are still working well.

These will be checked as a matter of routine when a full service is carried out. This will also involve dismantling and cleaning the alternator, replacing oil seals and renewing lubricants.

The recommended frequency for a full service is every three years or 8000 hours of use. Again, Mr Fowler emphasises, this is a job for a qualified engineer.

For safety as well as performance, also remember to keep the powering tractors take-off drive shaft well maintained and in good order.

First, the input stub shaft on the generator should be kept lightly greased so the pto shaft will slip on easily. Second, keep the pto shaft universal joints properly lubricated – along with the guard bearings if these are of the lubricated type – and check the two sections telescope easily. It is important to ensure that protective guarding is in place and intact.

"Just because these machines are not in every day use, there is no excuse to skimp on either mechanical or electrical safety," concludes Mr Fowler. &#42

Keeping ventilation grilles clear of debris to ensure efficient cooling, maintaining the correct gearbox oil level and watching for oil seal leaks are the principal maintenance points on stand-by generators like the Froment Magnate.


&#8226 Check oil levels.

&#8226 Run every month.

&#8226 Keep safety in mind.

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