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Generator / groupe électrogène


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The last serious power-cut in our area was in 1999 (before our time) and lasted 10 days.

Being the cautious type, I have been thinking that we should have a

generator (groupe électrogène) as a backup just in case... and mainly because our septic tank being situated higher than the house, we had to install a masticating pump (pompe broyeuse de relèvement) to carry the water and bits up the slope. I cannot imagine what we would do if we had a prolonged power-cut... [+o(]

Now, I'm not a technical person, not by a long shot, but I've been told that I should base the power of the generator on to the starting power of the pump, as it draws more when it starts...

The pump is a Flygt 3057 and on its spec sheet, it says: 1.5KW, 230V, 8.9A, 1PH, 50HZ, 2730rpm, 2KW.

It's located in a holding tank and only operates when the tank is full, then stops.

Can anyone tell me what I should be looking for in terms of generator power?

Would a 2.2KW generator be enough or should I look for a slightly more powerful one? or even a much more powerful one?

Thanks in advance.

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If you are going for a standby generator for the sewage, have you thought about catering for emergency lighting?  If you are ‘green’ and I am sure that you are[;-)], the extra load will not be that much.  The difference in price between say a 2.5KW and 3.0KW generator is not much as a percentage.  You can also go for a diesel rig and run it on bio-diesel!  To answer your question, the pump will present a ‘reactive’ load and you should therefore up the rating of the generator.  The VA rating from the information you have given is 2.047KVA.  So if the ‘spec sheet’ mentions both 1.5KW and 2.0KW it is *likely* that the latter is the starting power.  I would look for a 2.5KVA generator to be on the safe side.



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A 2.2kw generator should be adequate provided you are only using it to operate the pump.

As regards connecting it you have to be very careful here. Under no circumstances can the mains supply and the generator supply be allowed to meet, the result would be explosive in the full sense of the word.

You will need a specially constructed control panel incorporating current sensing relays, reverse current trips etc. which should only be done by a qualified electrician.

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Thanks for that Btuckey.

The main function would be the pump and I'm sure we would look at lighting too... [:)]

I know that diesel pumps are more expensive, so it's a question of knowing where to start to cover the basic function and then assess what else can/should be added for a small extra expense.

Your answer gives me a starting point and I will know what to look for and more specifically what to avoid!

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I bought a small generator and the box told me its maximum wattage AND the wattage if used with motors, pumps, amplifiers... anything that has a big coil in it. The engineers at work explained that in the instant that you put power through a coil, it doesn't actually have much resistance in it, so it's almost like a short circuit. However, within milliseconds it has created a magnetic field and the problem is solved, so a generator needs to be much more powerful than you really need it just for the moment that you trn the pump on (Unless your motor is soft start). So... look at the generator specification (I think mine was on the box). I believe that the more sophisticated the genny, the less difference there is (on my cheapy, I can have 1.2kw for lights etc, but only about 300w for things with coils).

What this means is...Once the pump is up and running, you actually have a lot more power available than it needs, so you might as well use that for lights, PC and Router etc!

Turning to the connection. If you want the genny to power up automatically and switch accross within seconds of the mains going, you do need very sensitive, carefully installed control systems. However, if you have 10 minutes to play with.... I would just have a plug on the end of the pump and once you've started the beast up you just un plug from the mains socket and into the genny. You then set about plugging up a few extension leads with table lamps on. (This may break a few rules of electrical insllation, but it's what I would do)



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I think this needs a bit more thought.  The 2 ratings on the motor will be running load and max overload.  They are nothing to do with the in-rush current on start up.  That will be many times greater than the 8.9A quoted running current.  The MCB feeding the motor will be a special one that allows a large in-rush current for a small period of time to stop it tripping during start-up.

A generator will max out at a certain load and if this is insufficient, ie less than the in-rush current of the motor, the motor will not start, buzz, and trip the breaker. This is assuming there are not some fancy electronics in line with the motor giving it a "soft start"?

Single phase motors are horrible things to start, more so, if they are fully loaded, just as in this application with a ton of sewage to shift from a stand still....

Clair, you need to look at some generator specs and see if any quote being able to start 2kW motors on full load.  It will need kitting out with a motor type MCB.  I suspect you will be into commercial stuff and the  price will be high (diesel, well you must have big pockets, but if its going to run for days on end, its the only way to go).  Also, try and find out the specs of the motor from the manufacturer, they should be able to tell you what the in-rush current is and that will allow you to spec a genny.

Is there not a manual pump handle you could use?  Or may be consider an additional manual  pump?

PS, Dont fancy being the man called out to repair that pump when its stuffed![+o(]

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To power a single phase electric motor you must cater for the starting or "Surge" current and the power factor.

Can I suggest that you PM Nick Trollope? he's the Guvnor as he is a fully qualified electronics engineer and working in France as a registered electrician. http://www.completefrance.com/cs/user/Profile.aspx?UserID=103841

If you are going to invest in a standby generator, it will pay to buy one large enough to provide power for not only the Fosse pump, but the lights (as already suggested) and the central heating boiler (if you have one) and also perhaps the freezer.

Most power cuts happen in Winter! Also look at an automatic changeover switch: not cheap, running at circa £650, but worth the investment.

If you have oil heating then buy diesel and run the genny on red diesel, 'cos it's far cheaper than pump fuel!

Plenty of new diesel gennys on the web with good endurance times. Last cut in the Nord pas de Calais was 24 hours! Small units only run for 5 or 6 hours.

I am also looking at this right now: no power no heat, no lights no nuthin'!


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There is also a user of this forum who is currently working as editor of a magazine for the on-site, standby and emergency power industry. But we are talking mainly about professional equipment here, which is seriously expensive.

If it was me, I'd spend reasonable money on a decent generator, probably diesel, and unless I was using it in something like a medical or data centre environment where an uninterrupted supply was essential, I would manually plug in things like the sewage pump, lighting etc. Automatic switchgear and controllers are very complex and expensive and are not totally necessary - but worth having if you can afford them.

You would probably find it worth looking at generators sold for marine use - high build quality, and able to cope with pump motor loads. And you can always use it on your boat (or in your camper van) in summer. Names to look for include Mase (sold by Barrus in Britain), Westerbeke, Kohler, or Onan (keep Dick Smith away from that one), or just about anything with Yanmar, Cummins, Caterpillar, Hatz or Lombardini engines (depending on the size). All will run happily on French heating oil (red diesel) and many can use biodiesel too.

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Page 33 of  Leroy Merlin <<Le Grande Guide>> includes a warning  about coeffcient of multiplication where start up load is 'N' times the running load. :

5 for 'fridges freezers and airconditioning  -------   3 for compressoirs, washing machines, cement mixers -------  2 for small tools and  1 for non neon lights.

I had no idea Dorothy Parker's friend's parrot made generators ( re above list above list of manufacturers) 

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[quote user="Gluestick"]

To power a single phase electric motor you must cater for the starting or "Surge" current and the power factor.

Can I suggest that you PM Nick Trollope? he's the Guvnor as he is a fully qualified electronics engineer and working in France as a registered electrician.


That is very kind of you.. Not exactly my field of expertise, but I will give it a go;

The rating of your generator is the maximum continuous load - 2.2KW - assuming a power factor of 1, a purely resistive load, such as an incandescent light bulb or an electric heater. Most electrical equipment includes inductive (motors, washing machines, fridges) or capacitive loads (power supplies for computers, flourescent lights, etc etc).

Your fosse pump, rated at 1.5KW is a measure of the maximum power that the motor is capable of producing (actually, it is 2 horse power). The actual power used by the pump depends on what it is doing. I have no idea, but shovelling a few litres of s**t a few metres wouldn't amount to much.

As has been previously stated, the "surge" or starting current of the pump is much higher than the running current, but the rating of your generator should be able to handle this - in theory, at least.

Small thing, these 2.2KW generators - almost inevitabley fitted with B&S, Tecumseh or Honda engines are cheap and chearful - they are reliable (I have had a B&S powered one for over 10 years, used it to run a 3HP fridge compressor and only got round to changing the oil a few months ago), but they ain't economical - the 1.5L tank on mine manages about 1Hr on full load. And they are noise, especially under load.

That said, this isn't the Transvaal - I wouldn't bother installing a very expensive diesel, auto-start generator for (perhaps) 6 hours use/year. You will find that your fosse pump chamber will take several hours to fill anyway...


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This is all very useful knowledge to have, even if some it it is too technical for me, and I thank you all for the advice. [:)]

The generator will not be used for the pump for any length of time during a power-cut and the idea is to connect the pump to the generator when the holding tank (250l) needs emptying. This would vary according to whether the gite is occupied (7-8 people) or not (2 people). I can hardly ask paying guests to nip behind the edge!!!!!!!!! [;-)]

I will review all this useful info and ponder before our next trip to the big town...
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Further info for you Clair:

I have a compressor in the workshop that is powered by a single phase 1.5kW/ 2HP motor (not dissimiliar to your motor I would guess).   The compressor motor will regularly trip a 20A breaker (non motor type), particularly if  its cold and its running to top up the cylinder - ie heavy/high load on start up.  It never trips the breaker when starting with an empty tank - ie light load.  When it does trip, resetting the  breaker, usually gets the motor running.

So from this I conclude that the in-rush current with a heavy load is around 20A, or is limited to 20A via the breaker.  A generator would have to be capable of supplying a minimum of 20A (thats 20 x 230V = 4600VA) to start this config.  In addition, I would allow say a 20% overhead, that takes the generator capacity up to around 5.5kVA!

Your motor is capable of delivering up to 2kW (2.6 HP), thats a big motor for single phase.  If the motor is heavily loaded on start up, it could very well be expected to deliver its full 2.6 HP.  However, I'm not sure you can simply pro rata the  above figures to suit your motor.  It may be perfectly happy to start with a 20A in-rush, then again, it could need a further 30% (1.5kW to 2kW) to be happy.  That would equate to (20Ax1.33x230 = 6.1kVA + 20% overhead)  =  7.3kVA!!!!!   Now thats a meaty genny.

 Also, bear in mind the conditions that you will be expecting the genny to do service. Power cuts happen at the most inappropriate times - heavy snow fall, followed by -15 deg temps. so forget buying a cheap generator, as it WILL let you down when you most need it.

I cant help thinking, we are using a sledge hammer to crack a nut here.  A 250l holding tank  is quite big, thats alot of flushes, even more if you can somehow divert the sinks/bath/shower etc waste.  It it possible to remove the motor from the pump?  If so, you could get Mr Clair to attach some from of manual drive - push bike may be!! or even a small petrol engine.  In an emergency, needs must!

I hope the above gives you something to think about.  There's no guarantees with the numbers however.

I have assumed that the motor in question is a 1500 or 3000 rpm machine.  It should say on the motor plate.  If its a high rpm / low torque job (10,000 rpm etc) then its a completely different story and a simple 3kVA genny would sufffice.

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Whoa! Lots of technical things to think about here... [geek]

Mr Clair announced today he's re-considering the problem...

Diverting the sink/bath/shower into the old unconnected tank would be totally illegal of course and I could never consider such a suggestion......... [:-))]
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