I am looking to run one, maybe two air blowers (to inflate bouncy castles) using a generator. (Constant blow needed) The spec of the 1.5HP fan is 1100w/220v/50hz. It also states 550 CFM @ 5.5" wg (whatever that is ?) The Kw and Kva ratings of generators are a bit confusing.
Anyone know if a 2.8Kva would run the fan comfortably ? What size needed to run 2 fans?
It depends on the fan power factor. If it is near unity, then kW is the same as kVA. If it starts getting inductive on you, the kVA increases. Basically, if the generator can produce 2.8kVA (and at least 2.2kW, too), then it might be able to run both the fans.
However, you need to examine the fans to see what their kVA rating is. They could be quite inductive, or they might be power factor corrected and present no problems.
I'm not sure which ampage it is. If it is 6.8A on 220V it would be 1.5kVA. If it is 6.2A on 220V, it would be 1.4kVA. Depending on motor type, you may be able to correct it with capacitors, although this would require knowing more about the motor, to select a suitable value.
Having been through this before... a standard decent quality 6.5hp Honda ~3kva will fairly comfortably run two fans, once the castles are blown up, as motor load eases as the pressure builds up. (thus current draw drops)
Initial motor starting load might be an issue, rather than the running load. Put simply Kw and Kva are the same, except that Kw is a resistive loading and Kva is inductive. The power factor of the motor could make a difference to its apparent load presented to the generator.
Best guess would be to aim for the next size up in generator which should be adequate with a better margin. Start one motor then delay a few seconds before starting the second one.
Could you not hire a generator to see how it works out in practise?
Motors need lots of humph to start 'em much less when running. Rule of thumb is for reliable quick starting have at least double the motors rating available. So I would say 2.8KVA genny will start and run one fan no trouble, it might complain for a few seconds when you switch the second on but once it's running it'll be fine. I'd expect problems if you try switching both fans on at the same time.
This is what I thought before seeing Tims post which backs it up. B-)
I have a home-made gen based around the same Honda GX200 engine that the one on ebay has. In my experience it will run a 3kw (resistive) load like floodlights OK, but you know from the engine note that it's running virtually flat out to achieve it.
So, as your 3kw load (with unknown power factor) will be similar (or a bit more than my resistive loads) it will run it, however will be working hard to do so. As I assume you'll need to run this for many hours at a time, I'd suggest going for a bigger gen to give it an easier, longer life, and maybe consider a small diesel one as the running costs will be less, especially if you can get your hands on red diesel - no point paying road fuel duty on fuel to go into a generator!
If going down the petrol route, Honda engines are pretty bullet proof, with decent service intervals. If you look for a gen rated at ~4 KW it will run the load with ease, and last well too.
Also consider that these open frame generators *are* noisy - this may be an issue for you. If so look at the enclosed reduced noise types about, I have recently bought one of the smaller "Kipor" units available on eBay for quiet tasks and it is much quieter than my Honda.
Yup, its starting surges that will be the issue. There is a simple workaround though which would enable you to run your fans on a gen of half the kVA rating. Wire 2 sockts and a switch such that when running
2 fans you power the 2 up in series, and when theyre upto (half) speed then switch them to parallel.
Also as has been mentioned, parallel cap on each blower may improve pf thus reduce kVA requirement. You'd have to calculate or measure to determine cap size.
I'm in favour of electric fans and a generator. It's a more versatile setup. The electric fans will be very reliable. There'll sometimes be power locally available to save the use of a generator. You also get to have a generator which has other uses. It's also more easily replaced than a petrol blower.
If you can lift 90Kg, which is as near as damn it 200lbs or 1 3/4 cwt...
It's also open frame and will be as noisy as the SMD jobbie you posted before. Between the two I'd go for the SMD, that has a genuine Honda engine and you'll be able to get spares and/or service for it easyily.
The Chinese clones maybe cheap but how about spares and servicing? And by spares I don't mean new valves or major parts but "consumables" like air filters and spark plugs.
Most likely going to be open frame and noisy...
If you want quiet look at (sitting down) the Honda EU series I think they go up to 3kVA or the similar Chinese clone Kipor models on eBay and elsewhere. For their power output the Honda EU series are remarkably light weight.
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