Dave Payne Posted January 28, 2017 Report Share Posted January 28, 2017 Output power1) : @ Ta=25°C Pnom 850VA P30 1000VA Psurge 1800VA I'm gonna fire it up shortly and listen to the beeps when it shuts down as I think it only does it once which means low power from the batteries. Link to comment Share on other sites More sharing options...
Alan de Enfield Posted January 28, 2017 Report Share Posted January 28, 2017 Output power1) : @ Ta=25°C Pnom 850VA P30 1000VA Psurge 1800VA I'm gonna fire it up shortly and listen to the beeps when it shuts down as I think it only does it once which means low power from the batteries. 850Va could actually be as low as 650 Watts. VA is not the same as watts - but manufacturers quote it so you think you are getting more that you really are Link to comment Share on other sites More sharing options...
Dave Payne Posted January 28, 2017 Report Share Posted January 28, 2017 Hmm it does say on the front 850watt Link to comment Share on other sites More sharing options...
mross Posted January 28, 2017 Report Share Posted January 28, 2017 That's unfair; they quote VA because they don't know anything about your load's power factor! Link to comment Share on other sites More sharing options...
WotEver Posted January 28, 2017 Report Share Posted January 28, 2017 (edited) Hmm it does say on the front 850watt That's not untrue, depending on the power factor. It would be 850W if powering a resistive load. Edited January 28, 2017 by WotEver Link to comment Share on other sites More sharing options...
Dave Payne Posted January 28, 2017 Report Share Posted January 28, 2017 Wooooosh. That's all this electrickery stuff going over my head. Link to comment Share on other sites More sharing options...
WotEver Posted January 28, 2017 Report Share Posted January 28, 2017 Wooooosh. That's all this electrickery stuff going over my head. Put simply... It could feed an 850W bar fire or maybe a 650W motor, or a 700W charger. There's no way of knowing in advance unless the equipment either states its consumption in VA or quotes a power factor. Link to comment Share on other sites More sharing options...
MtB Posted January 28, 2017 Report Share Posted January 28, 2017 (edited) Wooooosh. That's all this electrickery stuff going over my head. Just to explain, with a DC load the power is always V x A. So W = VA. With AC, it gets more complicated. There is something called inductance which explained simplicistically, causes the current in a circuit to lag behind the voltage that caused the current. The bigger the delay, the less work gets done by the voltage and current. The amount of the delay is measured using 'power factor'. When the current and voltage are perfeftly aligned the power factor is 1. When they are totally out of phase the power factor is 0. The thing is, whether the power factor is 0 or 1 or something in between, the voltage and current are still using the same energy to generate them. So if you have say a battery charger with a power factor of 0.8, the voltage and current multiplied together give you the power needed by the genny, but the maximum power delivered by the charger can only be the (input) voltage x current x 0.8. You may need to read that a few times! (Edit to correct a fundmental error!) Edited January 28, 2017 by Mike the Boilerman Link to comment Share on other sites More sharing options...
WotEver Posted January 28, 2017 Report Share Posted January 28, 2017 So if you have say a battery charger with a power factor of 0.8, the voltage and current multiplied together give you the power needed by the genny, but the maximum power delivered by the charger can only be the (input) voltage x current x 0.8. To put that in a possibly more useful form, you divide the wattage of an appliance by the power factor to find out the VA. So an 800W charger with a power factor of 0.8 would demand (800/0.8)=1000VA. Link to comment Share on other sites More sharing options...
MtB Posted January 28, 2017 Report Share Posted January 28, 2017 To put that in a possibly more useful form, you divide the wattage of an appliance by the power factor to find out the VA. So an 800W charger with a power factor of 0.8 would demand (800/0.8)=1000VA. Yes, exactly. This is what most explanations of power factor tell people, but I thought explaining why the power factor exists in the first place would help Dave understand what its all about. Link to comment Share on other sites More sharing options...
Rick-n-Jo Posted January 28, 2017 Report Share Posted January 28, 2017 So returning to the OP question, why not use a 12v-24v converter of sufficient capacity to run the pump motor? Efficiency not really an issue as it would only need to be switched on when the loo's in use. Link to comment Share on other sites More sharing options...
MtB Posted January 28, 2017 Report Share Posted January 28, 2017 So returning to the OP question, why not use a 12v-24v converter of sufficient capacity to run the pump motor? Efficiency not really an issue as it would only need to be switched on when the loo's in use. There was a longgggg previous thread discussing this IIRC Probably because the transient start current of the motor will be in the order of 30A, and such things are not easily found. Or maybe they are! Can anyone remember and point to the thread? Link to comment Share on other sites More sharing options...
Dave Payne Posted January 28, 2017 Report Share Posted January 28, 2017 (edited) Deleted Edited January 28, 2017 by Dave Payne Link to comment Share on other sites More sharing options...
Rick-n-Jo Posted January 28, 2017 Report Share Posted January 28, 2017 OP suggests specs give 7.5A locked rotor current, most Jabsco non-macerators seem to be 7.5 or 8A rated with a 15A fuse, so not a large motor, about the same as my domestic water pump which runs happily off a 360W dc-dc converter. Link to comment Share on other sites More sharing options...
WotEver Posted January 28, 2017 Report Share Posted January 28, 2017 There was a longgggg previous thread discussing this IIRC Probably because the transient start current of the motor will be in the order of 30A, and such things are not easily found. Or maybe they are! Can anyone remember and point to the thread? I can't be arsed to go looking for the thread but put simply a couple of small batteries and a small charger would be much cheaper than a very hefty psu. Link to comment Share on other sites More sharing options...
Chewbacka Posted January 28, 2017 Report Share Posted January 28, 2017 I can't be arsed to go looking for the thread but put simply a couple of small batteries and a small charger would be much cheaper than a very hefty psu. You might even get away with a big capacitor to supply the surge current, but as above couple of small batteries would be best, and you can even use a small charger. Link to comment Share on other sites More sharing options...
cuthound Posted January 28, 2017 Report Share Posted January 28, 2017 Just to explain, with a DC load the power is always V x A. So W = VA. With AC, it gets more complicated. There is something called inductance which explained simplicistically, causes the current in a circuit to lag behind the voltage that caused the current. The bigger the delay, the less work gets done by the voltage and current. The amount of the delay is measured using 'power factor'. When the current and voltage are perfeftly aligned the power factor is 1. When they are totally out of phase the power factor is 0. The thing is, whether the power factor is 0 or 1 or something in between, the voltage and current are still using the same energy to generate them. So if you have say a battery charger with a power factor of 0.8, the voltage and current multiplied together give you the power needed by the genny, but the maximum power delivered by the charger can only be the (input) voltage x current x 0.8. You may need to read that a few times! (Edit to correct a fundmental error!) Excellent explanation. I remember when power factor was first explained to me, years ago back at college, the lecturer rambled on about the companies running the power stations finding that they needed to burn more coal than they thought and eventually found that some customers had very inductive loads which needed more power to support. Link to comment Share on other sites More sharing options...
Dave Payne Posted January 28, 2017 Report Share Posted January 28, 2017 Just run the 700watt iron for ten minutes and no beeps or starts or the inverter, so must be the washer. Link to comment Share on other sites More sharing options...
WotEver Posted January 28, 2017 Report Share Posted January 28, 2017 Just run the 700watt iron for ten minutes and no beeps or starts or the inverter, so must be the washer. Yup. A 700W iron is a pure resistive load. The motor in your WM is an inductive load. Link to comment Share on other sites More sharing options...
Dave Payne Posted January 28, 2017 Report Share Posted January 28, 2017 So install a bigger invertor? Link to comment Share on other sites More sharing options...
Robbo Posted January 28, 2017 Report Share Posted January 28, 2017 So install a bigger invertor? If it only does it now and again, does it only do it when you load the washer too much? If you do a few half loads to see if that trips the inverter. Link to comment Share on other sites More sharing options...
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