Another generator question

[PoP]

I've read the previous postings on using a generator in place of a regular mains supply, but really didn't take so much notice because I wasn't planning on buying a genny anytime soon. Regardless of that, I'm not now inclined to install a switch in front of the consumer unit thanks to the great information others have imparted here!

As luck would have it I have picked up a bargain on an ebay auction which ended a short time ago. The genny isn't anything fancy, just

850W. But that's good enough to give me light in the event of a power failure I think, and more than good enough to drive my power tools if I'm working out of reach of mains power.

Question is, will this genny be good enough to power the central heating system in our house if I isolate the CH from the mains supply? And does a CH load represent a particular risk factor on a genny supply?

Apologies if it covers ground which has been discussed previously, but I seem to recall that capacitive loads were the major problem area, and I think a CH motor is reactive - so I'm assuming it might be alright.

I have no previous experience of using a genny :)

PoP

[Dave Plowman]

They're strange things. We were using a 5000kVA Honda (it's our industry standard for a reasonably priced and not too noisy generator) to run a mobile rig for The Bill - a low loader with a car on it which was going to travel fairly long distances to shoot some scenes in the car without the actor having to drive - and this was powering a couple of lights and all the tech equipment - well within its loading. One of the lights failed, and the resultant surge wiped out three SMPS feeding cameras and sound.

If you had a basic old system with no electronics I'd think any old genny would be fine. With modern types, I'm not so sure.

[Steve Firth]

Hmm, two stroke generator blue or yellow or red fuel tank I bet. I hope you paid less than £69.99 for it. Firstly, it's not an 850W, it's a 650W unit, no matter what the spec says. Secondly those for sale on ebay are being sold by professional traders and they are getting their stock under £60 each. So getting a "bargain" is going to be difficult.

I have one that I use for charging the battery on a boat, they have a useful 12V output for charging as well as the 13A socket. Secondly, yes you can use it to run the CH. That's what I use mine for and the power is relatively clean for a small generator. Don't however go switching on an off other loads while it is in use. The power surges could do serious damage to sensitive equipment.

Once you have power from the genny it's not unknown for SWMBO to pop the kettle on which will definitely cause problems.

Good news, the units appear to be reliable, and at least you'll have paid less than the £199 that Screwfix were asking for one. It doesn't matter whose name is on the tank (I've seen Wolf, SIP and several others) it's the same generator. The engine is Yamaha and appears to be nicely reliable, two stroke means simple (almost no) servicing.

Watch out for oil dribbling from the exhaust though. That is the curse of 2-stroke gennys. If you want clean power under all circumstances you might consider running an online UPS from the genny and then run the appliance from the UPS. Note Belkin and similar off-line UPS's are no good for this. The UPS will of course cost more than the genny, ce la vie.

[Chris Oates]

sounds like you need 'crowbar' protection some zeners to measure (say) 260V which trigger a thyristor across the output which blows the fuse BTW is Gary dead ??

[BigWallop]

As long as the boiler isn't full of electronic circuits, then you should be OK. Automatic ignition units can be a problem because of the capacitor used in the charge / discharge that creates the spark. Pilot flame boilers are normally OK though.

The only main thing to watch out for is the pump running on its own accord even with the programmer in the off position. This sometimes happens because the live to earth on normal domestic supply is broken when the switch is flicked off, but because most generators don't have neutral potential on them and the pipes in house are all bonded together, you can get enough back feed from the black phase (neutral) on the generator to run the pump through to earth.

[The Natural Philosopher]

Should be OK. Switch on surges of pumps etc may dim your lights and cause the genny to slow down for a second or so, but should not cause it to actually stop, or trip.

[tony sayer]

In article , Dave Plowman writes

SMPS's are a very difficult load to drive from gennies and the genie needs quite some de-rating tho a CH pump isn't likely to be a problem. If its just that why not use a low power inverter and run it off a car battery?..

[N. Thornton]

Hi Bigwallop. I'm puzzled. I've done little CH wiring, but presumbly normaly the live feed to the pump is cut with a relay or a bimetal switch. And there should be no or very very little current flow from N to E in the pump itself. So how does current flow from N to E thru the waterpump? Unless there is large earth leakage it shouldn't AFAICS. I wish to understand this.

For the OP, a genny is not a low impedance supply like the mains, plus its an inductive supply. Result can be large surges in some situations. Much as I dislike those surge suppressor things, big fat ones could be genuinely useful on a genny supply where the loads are surge sensitive. It doesnt matter with motors, kettles etc, but when youre running electronics it does.

Regards, NT

[Dave Liquorice]

A while back, before my time in broadcasting, one EM would always use a particular generator "company". This was in the days of Pye PC60 cameras, they needed a fair bit of light. Anyway the job was a Songs of Praise so lots of lamps high in the knave and this generator outside to power the lot, probably in the order of 250kW.

Now the connections to the genny simply went through an open outsized "henley block" on the back of the truck. All was fine, if a little doubtful from the H&S point of view, until a large spanner fell across a couple of the terminals. The genny opens it's throttles and struggles just a little bit until it successfully makes this spanner act like a bit of 30A fuse wire shorting the mains. ie it explodes. Without the rather heavy load imposed by the spanner the genny volts shoot through the roof and blow every single bubble in the church...

Agreed anything that has electronics connected directly to the mains gets upset far more easily than a lump of iron wrapped in copper wire.

[Dave Liquorice]

Depends how big a motor you are turning on. Agreed a CH pump shouldn't upset a 1kVA or more genny but don't try the hoover.

Also it's not so much the dip when a load comes on but the surge when a load comes off. See my other posting...

[Tim..]

5kva? A 5000kva would need a low loader and weigh in at about 15 tonnes, didnt think Honda made single cylinder units that big... LOL

Tim..

[PoP]

It'd make the decoke easy though wouldn't it? Remove the cylinder head, climb inside, and use your SDS drill to take away the nasty stuff.

Wouldn't like to have to kick start it though.

PoP

[Dave Plowman]

Heh heh, must have had special k for breakfast.

[Dave Liquorice]

How does that function, under normal circumstances, *without* a big bang when you switch the pump on?

Can you post an ASCII art drawing of the circuit that allows the motor to run when using a genny?

[BigWallop]

Imagine having to hand crank that baby. :-))

[BigWallop]

Have a read through these pages PoP:

[Dave Plowman]

I could only tell you in person, as I'd have to kill you afterwards.

(If that sort of plot is good enough for them, it's good enough for me.)

[Mike Faithfull]

But you can start a power station by hand cranking! I did some work for a power company last year, and I had occasion to visit a power station that had two of its three generators off line for maintenance. Interested (ok, nerdy!) discussions around the plant's operation and getting the generators back on the grid etc. led to "so how d'you do a cold start?". The answer is "with a strong arm and a big handle"! If, for some reason, the station isn't connected to the grid, then it has no power, and without power for the control systems and pumps and machinery they can't fire up the boilers to make the steam that drives the turbines. Soooo .......

take one Mechanic with starting handle and plug it into diesel generator. Turn handle briskly. when power is available, initiate starting sequence for the big jet engine in that building over there, which involves connecting power from diesel genny to big electric starter on jet engine to spin it into life. then, when the jet-powered generator is producing electrickery, stop the diesel and switch on the systems to fire up number one boiler. as steam pressure becomes available, spin up number one turbine and bring its generator on line. At this point the station is more than self-sustaining and may be connected to the grid. All auxiliary power generation may therefore be shut down. The other boilers and turbines may then be fired up and brought on line as demand requires.

And it all began with a big bloke turning a handle ...

[Dave Liquorice]

I hope they never loose the handle. B-)

[Mike Faithfull]

(tee hee!)