Installing a Back up Power System

Submission by Nigel Giddings – I am currently building a house in North Kent and have caught the Home Automation bug. The intention is to live in the house for the rest of my life (a bold statement?).

I would like to be able to say that no expense has been spared but that would be an exaggeration. I have, however, included many things that you probably would not expect in a typical new house, at least in it’s price range. As I want all the usual HA toys the design calls for the usual items like servers, amplifiers, receivers, and a wide range of detectors of various types.

Early on you realise that one important item that all this automation requires is power. Without power 24/7/365 the hardware becomes useless and the software non-existent. It is also a well known fact in HA that things fail when you are least ready. If like me you live in a rural location with your supply by long lengths of overhead cable the failures are regular. Not something that happens every week or month, but based on the last ten years we experience 2 – 3 failures a year. Sometimes these are short, 5 – 10 minutes, more typically 1 – 2 hours and on several occasions 12 hours plus. In one particular year we had 3 consecutive days of power cuts during daylight hours while emergency works were carried out on supply lines. These outages typically occur during the autumn and winter when there is a high requirement for heating as well.

Sitting in a house with no power feels quite strange. I personally like something in the background, either TV, radio or a favourite playlist, and being ‘disconnected’ during bad weather feels even worse. Having an automated home with no power is like having a F1 car off road.

What is worse is that a sudden loss of this lifeline can have damaging effects on Hardware and Software, Databases can be corrupted and application data on Hard Drives can be damaged meaning that when the power is restored you have to work at bringing your system back to life, possibly resorting to backups with the inevitable loss of something. Sometimes during the restoration of power damage to Hardware can occur due to power surges and voltage fluctuations. All this is bad news for the Home Automater and does nothing to help that all important WAF (Wife Approval Factor).

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The requirement – To maintain the power supply to the house during the occasional power disconnection. This should be able to be maintained for several days, possibly longer if fuel can be sourced and delivered.

Enough power should be provided so that all systems function. A slight modification of use to reduce overall load is acceptable, such as using light scenes less bright than normal (more dimming or less lights on). Part of the supply should be ‘Uninterruptible’ so that sensitive equipment, servers, routers, LAN Switches, TiVo, satellite receivers, projector, clocks etc. do not suffer. Other less sensitive systems can experience a disconnection during a short changeover period (<30 seconds) such as Immersion heaters, Kitchen appliances, Central Heating, Koi Pond pump, TVs, Pin Ball Machine, Juke Box etc.

Considerations – The house is provided with a ‘Grid’ supply of 100 Amps. This was requested from the supplier so as to be able to deal with unusual peaks in demands, such as Parties in the Garden! And if we ever get that Hot Tub I promised myself.

I expect typical peak demand during a day, a winter’s evening, could reach 30Amps or about 7KW or 7KVA (assuming a power factor of 1 for easy maths). Switching on a the Kettle could add 2 to 2½ KVA so I have assumed a maximum of 10KVA flat out. Please note the Heating and Cooking is by Natural Gas. We had researched a Heat Pump for heating but as we have mains gas the running cost of a condensing boiler into a heat store compared with the high initial cost of a Heat Pump suggested the Gas route. The balance was swayed as Heat Pumps have a very high start up current which would probably stop an 11KVA generator dead.

The house is located in a rural location and does not have any near neighbours; however, the prospect of a generator running through the night keeping the occupants awake would not provide high WAF so a proper acoustic enclosure is important.

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There are several choices for fuel, each has its pros and cons.

Petrol. Advantages: Fuel relatively clean (doesn’t leave an oily residue like diesel), not affected by temperature. Disadvantages: Highly Volatile, loses its punch after 6 to 12 months, dangerous to store in large quantities, storage tank requires bunding, not readily available Tax Free (unlike Red Diesel). High Maintenance Oil, Filters, Ignition System.

Gas. Advantages: Fuel easily available (either bottled Gas or direct connection to Natural Gas supply),clean, not affected by temperature. Does not require bunding for storage tank. Disadvantages: Cost of connection to Mains supply. High Maintenance Oil, Filters, Ignition System.

Diesel. Advantages: Tax Free Fuel available in Bulk 205L barrels or pumped on site (500L plus deliveries), low maintenance (Oil and Filters only), Diesel engines more bullet proof than Petrol/Gas engines, Lower fuel consumption, fuel is fairly inert when stored. Disadvantages: Fuel Storage requires bunding, non winterised fuel can wax at low temperatures. Cold starting can be an issue at very low temperatures.

The runtime of the generator is important. A period of 60 – 72 hours without intervention is required. This is so that if the maintenance man (me) is not on site the system can still be used. It is also felt that this would deal with 95% of outages. Extended outages would require inspection of the Genset to check on fluid levels and probably the delivery of additional fuel to ensure continued running.

Fuel storage is determined by a number of factors. Large half empty tanks can suffer from condensation contaminating the fuel supply. It is therefore better to keep tank 90% full. This has to be offset against how much fuel you expect to use and issues with Petrol where it may not be of any use after 12 months. Fuel delivery should also be considered handling 205 litre drums is best done with two people. Access for a delivery vehicle has the same constraints as heating oil delivery (30 metre delivery hose). Delivery of large Gas bottles probably with a system of two bottles to enable switch over without interruption. Mains gas connection deals with all these issues, but you may suffer a loss of Gas supply?

Fuel tanks require Bunding, a catchment system that can hold the fuel should a leak occur. Oil tanks now come with a double skin to provide this. However, if the leak happens between the tank and the generator contamination of the area can occur. A design that allows the generator, tank, filler point and temporary storage to be within the bund is preferable.

All generators require a regime of maintenance. This is based on either hours run or a fixed period of time, which ever occurs first. Air cooled engines eliminate issues with the cooling system such as, annual maintenance, loss of coolant, thermostat issues and radiator leaks. Petrol and Gas engines have an ignition system where as diesels do not have this additional point of failure. All the engines will require Oil, Fuel and Air Filter changes as well as Oil changes. Regular checks to Oil levels should also be made although self filling systems are available to keep the sump topped up.

Generators tend to use about 50% of their maximum consumption while not producing any useful power and in fact like to run at a load of 80 to 90% to prevent a carbon build up. A bit like cars in that they don’t like doing just the local school run.

Options – Generators fall into several types, these were relevant to me.

Portables: Not typically a fixed installation, require placement and connection at time of failure.

Small size Petrol upto 5 or 6 KVA, short run time, noisy, high maintenance.

Medium size Diesel, 5 to 10 KVA, short run time, very noisy, medium maintenance

Installed: Integrated in building, automatic or manual start and switch to load

Gas domestic units 5 to 15KVA, self contained units, acoustic hoods, small, straightforward maintenance, designed for non technical user.

Diesel medium sized units, 5 to 20 KVA large integrated fuel tank, medium maintenance, acoustic hood.

My Decision – The solution is one of UPSs and a Genset. I believe it is good practice to install UPSs with or without a generator. My server hardware also has dual PSUs so by using dual UPSs and controlled shutdown software this offers as much protection as I can think of. The UPSs can provide 2 x 3KVA for in excess of 15 minutes allowing a controlled shutdown should the Generator fail to start.

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The idea of a portable Generator was discounted early on because one of the requirements is autonomous starting and stopping with long run times without intervention.

The choice of fuel was also quite straight forward. Petrol was quickly discounted on the basis of cost of running (less efficient, and more expensive to buy), more dangerous to store and issues with the life of the fuel (6 to 12 months) as well as higher maintenance. I’m not sure an 11KVA petrol unit is available anyway. Probably for the reasons just mentioned.

Gas was tempting, especially when connected to Mains Gas but this would not be fully autonomous. Bottled Gas also offers a clean alternative but access to additional bottles during bad weather may be an issue as well as the higher maintenance requirement for a Spark Plug equipped engine.

This left the Diesel option. Most Medium sized generators are diesel powered, gas may become more popular for domestic situations. Availability of Diesel is high, worst case you can buy it at a ‘Petrol Station’. Alternatively delivery in Oil Drums by a local plant company is straightforward. Diesel is relatively inert although ‘oily’ when filling and transferring fuel. Engines tend to be robust and maintenance is very straightforward.

The Solution – A new 11KVA autonomous Genset with acoustic hood and extended fuel tank could cost up to £10,000. Not being adverse to buying second hand and also as a fan of E-Bay I located a unit that met my criteria for £2,700.

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I was told the unit was ex-Cellnet and used at an important Node site, loss of this one site could have affected several base stations and therefore a large geographic area.

The unit was almost 10 years old having been operated for just under 100 hours, this means the unit is not worn. Typical maintenance procedure is to run the Genset for approximately one hour per month just to check operation.

The unit is located 30 metres plus from the house and will be housed in a shed in the future which will incorporate the bunding and space for additional fuel storage in two 205 Litre Oil Drums. Transfer from the Drums to the Fuel tank is achieved by the use of a hand pump and hose.

The unit is powered by a Lister Petter LPA2 two cylinder, direct injection, normally aspirated axial fan air cooled diesel of 726cc developing 13.9bhp / 26.8 lb/ft @ 3000 rpm (its operating speed).

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The engine’s sump is also connected to an engine oil reservoir via a ‘Murphy Oil Fill Level’ which maintains the sump oil level in case of oil being lost (burnt?) during normal operation. Can be seen in bottom left of engine picture.  The brushless alternator was manufactured by Stamford and is rated at 45 Amps.

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A 380 litre fuel tank is built into the enclosure, under the Genset. This provides sufficient fuel to run the engine for in excess of 3 days. Refuelling is achieved through an external filling point. Refuelling does not require the engine to be stopped.

There are no manufacturer’s plates on the acoustic enclosure so I don’t know where this was sourced and the control panel is also lacking in any identification. If anyone can provide any information on this I would be very grateful.

The control panel is custom built using mainly electro-mechanical devices, a number of controls are on the panel, a rotary switch allowing it to be switched between Automatic and Manual mode as well as a position for OFF. Push buttons to start and stop the unit in Manual mode, a button to reset Low Oil Pressure and High Temperature alarms and indicators showing On Load, On Grid and Oil and Temperature alarms. 3 meters also show Frequency, Voltage and Current when the Genset is operating. I have added a fourth DC meter to show battery voltage. An hour meeting also measures run time so that maintenance periods can be observed.

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The internals of the panel are made up of contactors and relays with octal bases. The panel does have 3 electronic timer modules used in the starting and shutting down sequences. A battery charger / DC supply unit is also located in the panel. There is no low voltage DC alternator on the Genset although the panel / Genset is operated by 13.8 VDC (a conventional 13.8V 6 cell lead acid battery AKA a car battery is located in the Genset).

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Connecting the Genset – With the Genset located in the garden the control panel has been located in Node Zero with the main power distribution.

One of the requirements was that the Genset should power the whole house. This actually makes installation easier with a single Distribution board. Smaller Gensets which maintain only a part of an installation require the loads to be feed through two distribution boards, one for Maintained and one for Non-Maintained.

The incoming supply to the house connects directly to the control panel where it is monitored for health. The Genset output also connects directly to the control panel. A third connection is made from the Panel to the house distribution board. Connections from the panel to the Genset are also required for the 12 volt control lines and charging circuit.

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How it Works – Under normal conditions the ‘Grid Supply’ feeds through the panel and on to the Main Distribution board. A light on the panel indicates the supply as healthy and the panel mounted charger provides a float charge across the battery located in the Genset. It is important not to overcharge the battery.

As soon as the ‘Grid Supply’ fails 12 volts is applied separately to two relays in the Genset, the first operates the Fuel Solenoid (supplying fuel to the distributor and injectors) and the second operates the starter motor and inlet manifold heater, cranking the engine and pre-heating the incoming air. The starter motor is operated for 5 seconds and then stopped. If the engine continues to turn (under diesel power) and the alternator produces 240v AC the panel determines that the engine has started.

During the start cycle the Charger / DC supply unit in the panel is disconnected from the battery so as not to draw too much current during cranking.

If the engine fails to start first time power is applied to the starter motor/inlet manifold heater a second time for a further 5 second cycle. If the engine still does not start the panel produces an alarm and waits for human intervention.

Once the engine has started sensors on the Genset monitor Temperature and Oil Pressure. If a problem occurs with these measurements these are shown on the panel and the engine is stopped by shutting off the fuel solenoid.

During normal engine running power from the 240v Alternator is used to power the Charger / DC power supply which maintains the battery and the DC power required to operate the relays and solenoids. You will remember there is no DC alternator on the engine.

Once the ‘Grid Supply’ is restored the panel waits five minutes to ensure the restoration is permanent and then switches over and shuts down the engine. This is a simple changeover that occurs very quickly such that you don’t see it in the lights and PCs don’t reboot.

The switching between ‘Grid Supply’ and Genset supply is achieved with the use of a pair of Lovato Contactors with mechanical and electrical interlocks. This maintains separation between the Grid and Genset connections, preventing the Genset becoming connected to the Grid (this would damage the Alternator and possibly the Engine due to extreme forces generated if the two sources where out of phase). More importantly the Linesman up his ladder would not appreciate the Genset back feeding 240 volts up the line to where he is working.

Maintenance Schedule – Oil change, initially at 100 hours then every 250 hours (or 12 monthly if sooner)

Fuel Filter 250 hours (Sooner if fuel contaminated)

Air Filter 500 Hours (If dusty environment then sooner)

Fuel Pump Diaphragm 1000 Hours (Sooner if fuel contaminated)

Replace Fan Belt 2000 Hours

Major Overhaul 6000 Hours

Things to add – A strange problem to have is that the generator can start and you may not know it has happened. If we are not in the house during the start-up or it is during the day you may not see the lights go off for the 5 seconds or so it takes for the Genset to start. The first indication would be when the unit runs out of fuel.

To deal with this and so that I can be notified when I am not in the house I intend to connect it to Homeseer via spare contacts on a VIOM or NetVIOM, typical inputs could be Fuel Solenoid, Starter, Low Fuel Warning, Temperature Warning and Low Oil Pressure Warning . I may also connect a VIOM o/p to the reset switch which would enable me to try a reset remotely if an alarm has occurred and I won’t be home anytime soon.

An alternative could be a ‘Web Brick’, especially useful would be the analogue inputs to monitor Fuel level, Voltages and Currents as well as the temperature interfaces to monitor temperatures inside and outside the enclosure.

Addition of an automatic load or shunt to keep the load nearer the optimum 80%. Using a 3 KW Immersion heater (or two) fitted to the Heating Systems Heat Store which would convert the power to useful heat for the DHW and UFH.

The housing for the Generator needs to be built in the garden, this is combined with some rain water storage tanks and will cost more than the Genset in the first place.

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I will also look into providing a socket directly into the garden for ‘special’ events so that if we need to power a Marquee in the garden I can run the Generator manually providing additional power for the stage show.

Further Reading

Originally posted on the UKHA_D mailing list by Phil Harris

Murphy oil level switch

Selfbuild photos

Node0 photos

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