Driving a 4.5A Pump from a 2KVa Generator?

[C00P]

Hi folks,
I have a house pump Connected to water tanks which could double for fire fighting if the need arose. The pump is an Onga and the motor is rated at 4.5A (0.75kW) single phase.
According to my High-school physics, Power = A x V, so 4.5 x 240 = 1080W. I know it isn't that simple with AC, and that the starting current is likely to be considerably higher for a brief period.
S0, could a 2KVA inverter generator (Honda) start and run such a pump?
The idea is that if the power goes off, and the mains pressure drops (both probable if the bushfire is nasty), then we would switch to the generator to drive the pump and take our supply from the tanks.
Cheers

C00P

[bee utey]

Ohms law only holds for DC systems or in the case of AC the instantaneous values of A and V (or pure resistive loads, not motors). There's this thing called the phase angle between the voltage and current waveforms that messes entirely with that simple calculation.

Anyway a 2kVA genny won't deliver 2kW for the same reason (power factor), and the only way to find out if the genny will start the pump is to get an idea of the pump's starting current and compare it with the genny's maximum output current. You could of course try by plugging said pump into said genny. It'll either work, pop a breaker or stall. It depends also on what kind of motor it is, a variable speed one will be OK but a capacitor start one likely wouldn't.

[C00P]

Thanks bee utey, much appreciated. I knew Ohm's Law wasn't entirely applicable in AC, but I thought it might give a rough approximation.
I suppose the 4.5A cited on the pump's specification plate would be the RMS figure, once the pump was running?
Anyway, giving it a go isn't an option as I don't yet have said genny. I was thinking of buying one for other purposes, and wondered if there was some way I could find out in advance if my cunning scheme would work before outlaying the cash. Or perhaps buying a larger one (if necessary) so it could cope with this job as well.
Would an electrician's meter be able to tell me what the starting current might be? ie do those meters that they use have a "peak reading" feature?
Cheers

C00P

[Fluids]

Hi C00P ... Your 1080watts calc is correct as that is the input power (P1) .... To give you an output power (P2) of 750watts. About a 70% efficiency.

The EU20i Honda inverter generator will go 50% over it's rated maximum output for 1 - 3 seconds for motor starting duties. It will start and run your Onga without any issues. I have been able to start and run 1500watt pump sets from an EU20i.

I would leave the Eco throttle setting at OFF so the EU20i is running at full speed when the pump starting load is applied. With Eco throttle on, the time it will take for the EU20i to respond to the starting demand the pump is asking for, and get up to a suitable operating speed, may cause the EU20i to go out on fault. There's no issue with the Honda Inverter generators if you overload them as they will just disconnect the power output, requiring a stop/restart.

How do I know this ? I have a Honda Power Equipment dealership, and the other half of my business is pumps, irrigation and plastic plumbing supplies .... Been doing this for 28yrs.

If you don't have the EU20i yet, suggest you look at the EG3600 unit. It's bigger, a bit noisier, but is 3600watts output for around the same money, and will will leave plenty of extra capacity to run other appliances simultaneously ... Also runs a large long range tank.

Cheers
Kevin

Sent from my iPad using Braille

[tailslide]

Hi COOP,


In regard to the starting current, the rule of thumb is six times the full load current for the motor. In this application the generator will not be able to supply this starting current. The actual current supplied is limited by generator.


So it is then a question of is the limited current available from the generator sufficient to start the motor, only testing will confirm... For fire fighting duties I would recommend using a bigger generator.


Cheers
Ron

[Homestar]

If you have access to the genset, then try it. There are a lot of calculators on line to check these things, and my own one I use for work (which is based on 20 years of real world work) says its borderline...

It could work, it may not. If you are still deciding on what size genset to get, go bigger.

[Blknight.aus]

It'll do it but it won't start the motor under full load.

You might get lucky with it being a centrifuge non positive displacement pump that the. "slip" is enough to let it start and run without issue.

My.math says the inverter will be running at about 70% capacity with the pump under nominal max load and will spike to around 190% for start up. Running the Honda on Mon eco mode will help it get you a start. The honda may still pull it off as most inverters have a max rating (which is your 2kv) a momentary limit which is usually 1.5 times normal max for up to five seconds and max instamt limit anything up to 5x normal max for about 1/10th of a second.

I regularly run an 800w drill on a 600w inverter. It will trip out every time.if I try to start it under load or if I try to drive a big bit at a high feed rate.


My gut feeling is that. If the pump is gravity Fed and you have some way to unload the discharge side during start up that the Honda will get it going. It may not run it for normal.domestic duties where the pump will be expected to. Start and stop against. pressure

The last thing you. red to.sorry about is heat. Those inverter type gennies are only.hit their advertised specs at a certain ambient conditions, I'm going to guess that in the middle of a bushfire is somewhat out of those specs.

[C00P]

Many Thanks to you all, the feedback has been exactly what I was looking for.
The pump sits alongside the main tank and is connected to a common line that links three other tanks. Most of the time the tank level is well above the pump level, so input pressure should be positive most of the time and only slightly negative (about a 300mm lift) if the tank is really low.
In common with most household pumps, this one senses a drop in output pressure which triggers it to turn on. There's no pressure vessel. If the output line comes up to pressure (ie the tap is turned off) it runs for about another 7 seconds, and then switches off, maintaining the pressure in the line. So I guess it is starting under some load. If we are about to fight a fire, then we will open the tap onto a hose which is larger than normal (1") so the output would have little resistance to begin with,and then turn the pump on manually and let it run.
Seems you all reckon it would work, but that it is likely to be marginal. Given Blknight's comment about the heat (if there's a nasty fire, it will probably mean 35 degrees C or more) it seems like the best idea is to follow your advice and go for a slightly bigger unit to give a safety margin.
So a bigger genset it is.
What triggered this thinking (apart from the recent fires) was a deal with a local tool shop offering a Honda EU20i at $1599. They are also offering a Yamaha 2.4 kVA (EF2400IS) at $1799.
The primary use for the genset is to support our caravan in our retirement, and will rarely be asked to run very much as we like to keep things simple. Lighting will be all LED, we might have a small microwave. If things get too hot we'll park where there is power and run the Airconditioner. I don't expect to use the genset to run that, although I believe it could (if the A/C unit is small enough). So mostly it will be charging the batteries if the solar system can't keep up, and we'll be running computers, so need a smooth output. Lightness, quietness and ease of use are the primary requirements. I believe the Yamaha is about 10kg heavier than the Honda, but still pretty quiet. The EG3600 weighs over 40kgwhich is going to limit its utility for our purposes.
The fire-fighting capability is for emergencies only, and we may never use it. But like a parachute, if you actually need to use it, it really has to work!
It looks as if the Yamaha might be the way to go....

C00P

[bee utey]

To be honest, I'd think a little sideways here. A nice big battery and a quality 2000W+ power inverter attached, and a multi stage charger and/or portable solar setup to keep the battery full. Your pump can then start in an instant, and you can run a selection of 12V LED down lights inside off the battery. It means you're essentially blackout proof. Then you can purchase a small quiet generator to run the charger off in extended blackouts. You won't need a bigger genny as the inverter and battery will supply the surge. All the components will transfer well to a camping setup. Even your vehicle can be used with jumper leads to charge the system. Very flexible all round. I've got similar at my place, it's been very helpful over the last few years.

Oh and if you want fire sprinklers to do some good, perhaps a 5hp petrol fire pump would be more suitable. 750W isn't a lot.

[C00P]

Thanks Bee utey, there's some food for thought in that. I hadn't thought of using an inverter to supply the surge. (Maybe even some large capacitors?).
As for fire-fighting, we are in a relatively safe area, but there are two houses between us and a large national park (Sturt Gorge). Our main risk is ember attack, with a tiled roof and fine dry crap that gets in through the gaps (and is vacuumed out of the ceiling space every couple of years). A sprinkler on the roof keeping it wet would probably cope with that and the hose to deal with any spot fires. We can stand and fight because we have a nice green oval directly across the road to escape to if it all goes bad, so we have no cause for panic.

C00P

[Blknight.aus]

For the same.money as the Honda you could set that up very nicely and stop have enough left over to get a second. hand old school genny that will quite. happily run the pump.


Look hard enough and you could prob a my get all.of that and a cheap second hand. petrol ph.p or an eBay petrol powered pump.

[C00P]

For the same.money as the Honda you could set that up very nicely and stop have enough left over to get a second. hand old school genny that will quite. happily run the pump.


Look hard enough and you could prob a my get all.of that and a cheap second hand. petrol ph.p or an eBay petrol powered pump.

Hmmm. YOu could be right. MIght have to do some more research....

C00P

[C00P]

Well, when I went to the shop they'd sold all the Yamahas, so I bought the Honda.
I set it up, had it running with the eco switch off, turned on a tap to ensure the pump had limited load when it started, and plugged the pump in. The overload indicator gave the briefest flicker as the pump started, and then it settled down with the Honda obviously loaded, but certainly not struggling.

I was pleased with the result, because the Honda really is the best unit for it's main task, and having it able to run the pump in an emergency is a bonus.Thanks folks for all your helpful suggestions and information. Special thanks to you, Fluids, because your contribution from your experience was what convinced me to go with the Honda when the Yamaha wasn't available.

Cheers

Coop

[Fluids]

Thanks Coop.

The O/L indicator operation observed is normal as the gen' is doing over it's 2000w rating. Try the same thing with Eco ON and see what the O/L indicator does :) You can't hurt the gen', if it's overloaded the inverter out put will just disconnect, requiring a stop/restart.

Here's a bit of advice. Fuel the gen' up, plug in a 60% load (1200w - fan heater on low or similar is ideal), turn Eco OFF, and run 3x tanks of fuel through it ... to bed the rings in. Then do your first oil change (that should be around 20Hrs). Then every 100hrs (or 12 months). Mineral grade 10w/30 only. NO synthetics!! Use ULP 91 Ron ... E10 is OK, but E10 has it's own unique issues ... Premium ULP (unless your running the gen' balls-to-the-wall constantly) will carbon up the top of the piston and cylinder head. If you have to use a tank or two of Premium or E10 because it's all you have to hand, do it, it won't cause any issues for short term use.

Extened running (tank after tank after tank) with Eco ON under light loads will glaze the bore (ie:running a battery charger, unless it's a BIG arse battery charger). If it's doing this sort of duty (very low speed with Eco ON), every 3 to 5 tanks, run a tank of fuel through with Eco OFF.

These things are great, but a bastard ("time consuming") to work on IF something goes wrong. Regular oil changes are your best friend, and don't store your fuel for extended periods - FRESH FUEL !! - Don't let the gen' sit around for extended periods unused .... start it up every month or two AND run it for 30-60min with a load (get it to full operating temperature) before putting it back into storage. Store the fuel tank FULL to the brim (as little as / or no air space as possible). I use fuel stabilizer in my EU generators.

Regarding the output light (green). If it flashes once at startup, the unit has done MORE than 100hrs but less than 200hrs ... twice at startup, MORE than 200hrs but less than 300hrs, etc, etc .... easy way to check run hours and track oil change intervals.

Cheers. :twobeers:

[C00P]

Thanks Fluids, much appreciated. I've got some other questions in a PM.
Cheers

Coop