Re: Failover generators

[James Fidell <james@xxxxxxxxxxxx>]

Nigel Giddings wrote:
> Paul,
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>
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> Using generators can open a whole can of worms...
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>
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> I have a 'medium' size generator which I have incorporated in my self
build. It is rated at 11KVA and should allow the house to function normally
if I lose the grid connection. We use Gas for Heating and Hot Water.
>
>
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> Things to consider:
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>
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> Noise - I have a full acoustic canopy
>
> Fuel - Petrol (Highly flammable loses it punch after 6 - 12 months),
Gas (easy to handle bottles or connect to local mains supply) diesel (red
diesel cheaper, less volatile, doesn't go off with age)
>
> Fuel Storage - (How long before refuelling, I have 400 Litres, fuel
delivered in 205 litre drums. Genny can run for 2½ to 3 days)
>
> Location - Mine is 30 Metres from the house in the garden which helps
deal with Fuel, Storage and noise.
>
> KVA - You may need to run things as well as computers (monitors,
routers etc. Lighting, cooling?) Gennys like to run at 80 - 90% load. A
Genny at no load uses 50% of the fuel used at 100% load. A light load will
lead to carbon build up.
>
> RPM - 3000 is typical for smaller sizes, mine included. 1500 for large
units this gives less wear.
>
> Stability - Small gennys can be noisey on the o/p and this upsets some
UPSs. I have heard it said no more than 50% of load should be UPSs due to
harmonics created by SMPS and effects on frequency stability circuits of
Genny. I have 6KVA of UPS with no issues.
>
> Self Start - Definitely the way to go. By using a small genny you will
need to split the wiring between protected load and un-protected load at a
cost.
>
> Maintenance - Annual Oil and filter change or after a number of hours
of use. Air cooled reduces fluids to monitor.

There are a few people running generators for backup (or even as the
main source for) power based around the old Lister CS diesel engines,
often running on vegetable oil.

These run at ~600rpm and are very simple, yet massively over-engineered,
so service intervals are huge even when running full time, and most
maintenance is very straightforward.  They're also fairly quiet (I've
heard stories of people sleeping next to them and you can quite easily
hold a conversation standing next to one even with no exhaust system).

Where they're used for backup power they usually seem to be coupled to a
230VAC generator head, whereas when they're the main power source a
12VDC alternator is often used, charging batteries connected to the
mains using an inverter.  In the latter instance there's also the
potential to link the coolant system to your DHW/CH.

The down-side is that it's all a bit Heath-Robinson.  But not everyone
sees that as a problem :)

James