watts and volts and amps question

pam · 07-08-2005, 08:41 AM

I'm trying to figure out exactly what I can power after Dennis hits with my 5500 watt generator. I know at the least i can do what I did last time (refrig, freezer, light and fan) but I'd like to add a small room AC to the list. I've checked my freezer and fridge and they don't have watt measurements. They're both shown as 115V, 50 amps, 60 HZ - does any of that translate to watts, or do I need to call the manufacturer?

Storm is 3 days away and I just heard another generator fire up in the neighborhood. Sounds like we learned our lessons with Ivan. LOL
Pam

W9GFO · 07-08-2005, 10:27 AM

Volts X Amps = Watts. That would be 5,750 Watts for your room AC which seems really high. Are you sure that the amps aren't 5.0? I would expect it to draw less than 10 amps.

Rich H

The Un-Official Segway Battery FAQ
http://www.spinfoot.com/SegwayBatteryFAQ.html

pam · 07-08-2005, 10:53 AM

You're absolutely right, 5.0. Thanks for this, Rich. The figures I gave were actually the freezer and the fridge. So that is 115 X 5.0 for each, which is not bad at all - .
Pam

citivolus · 07-08-2005, 03:36 PM

Pam,
One other thing to be careful of with three refridgeration devices (I count AC because it's functionally the same) is inrush current. Simply stated, inrush current is a current surge that happens when motors kick on. On a refridgerator, especially older units, when the compressor starts there is a brief but often substantial current required to start it due to loads that may be present. I've seen old fridges suck up 2000+ watts when starting but newer models are typically much better due to a sensor device that either won't let the motor start under load or relieves the load on the motor prior to starting. With 5500 watts on hand it would only be a concern if all three were rather old and came on simultaneously, even then most generators have surge ratings that will get you over the top. To give you some real numbers for comparison, my fridge is 7.5 yrs old, rated for 5.6 amps and draws 180 watts running and 1100 starting. Likewise my window ac unit is about 3 yrs old and draws 440 watts running on hot days and peaks at about 460 when starting, if using the energy saver mode those numbers drop about 90 watts. In short if both units started at the same time the instantaneous peak draw would be 1560 watts.

I should also point out that both of these appliances run with power factors of about 0.93. Power factor is a measure of the phase difference between the voltage and amp cycles, 1.0 is as good as it gets. If there are VA (volt ampere, kVA = 1000 VA) ratings on the generator the conversion would be VA x power factor = watts or going the other way VA = watts / power factor. You shouldn't have to worry about this but I bring it up because consumer electronic devices tend to be very bad here as they are often 0.5 - 0.7. What this means that a computer and monitor that uses 200 watts and has a power factor of 0.5, is drawing 400 VA. For resistive loads like lights and electric ovens use a power factor of 1.0. A typical home averages about 0.8. Again, it's not something to be concerned about, just aware of.

Good luck and stay safe.

pam · 07-09-2005, 05:53 PM

Thanks so much, citivolus. I think I've decided against the AC, will live with a fan, so that I can keep my HTs charged.

It's been a busy morning.

Pam

07-08-2005, 08:41 AM	#1
pam Last of the Early 30 Join Date: Dec 2002 Location: Yelm, WA Posts: 4,679	watts and volts and amps question I'm trying to figure out exactly what I can power after Dennis hits with my 5500 watt generator. I know at the least i can do what I did last time (refrig, freezer, light and fan) but I'd like to add a small room AC to the list. I've checked my freezer and fridge and they don't have watt measurements. They're both shown as 115V, 50 amps, 60 HZ - does any of that translate to watts, or do I need to call the manufacturer? Storm is 3 days away and I just heard another generator fire up in the neighborhood. Sounds like we learned our lessons with Ivan. LOL Pam

07-08-2005, 10:27 AM	#2
W9GFO Member Join Date: Jul 2003 Location: Seattle, Washington Posts: 758	Volts X Amps = Watts. That would be 5,750 Watts for your room AC which seems really high. Are you sure that the amps aren't 5.0? I would expect it to draw less than 10 amps. Rich H The Un-Official Segway Battery FAQ http://www.spinfoot.com/SegwayBatteryFAQ.html

07-08-2005, 10:53 AM	#3
pam Last of the Early 30 Join Date: Dec 2002 Location: Yelm, WA Posts: 4,679	You're absolutely right, 5.0. Thanks for this, Rich. The figures I gave were actually the freezer and the fridge. So that is 115 X 5.0 for each, which is not bad at all - . Pam

07-08-2005, 03:36 PM	#4
citivolus Member Join Date: Jun 2003 Location: , RI, . Posts: 562	Pam, One other thing to be careful of with three refridgeration devices (I count AC because it's functionally the same) is inrush current. Simply stated, inrush current is a current surge that happens when motors kick on. On a refridgerator, especially older units, when the compressor starts there is a brief but often substantial current required to start it due to loads that may be present. I've seen old fridges suck up 2000+ watts when starting but newer models are typically much better due to a sensor device that either won't let the motor start under load or relieves the load on the motor prior to starting. With 5500 watts on hand it would only be a concern if all three were rather old and came on simultaneously, even then most generators have surge ratings that will get you over the top. To give you some real numbers for comparison, my fridge is 7.5 yrs old, rated for 5.6 amps and draws 180 watts running and 1100 starting. Likewise my window ac unit is about 3 yrs old and draws 440 watts running on hot days and peaks at about 460 when starting, if using the energy saver mode those numbers drop about 90 watts. In short if both units started at the same time the instantaneous peak draw would be 1560 watts. I should also point out that both of these appliances run with power factors of about 0.93. Power factor is a measure of the phase difference between the voltage and amp cycles, 1.0 is as good as it gets. If there are VA (volt ampere, kVA = 1000 VA) ratings on the generator the conversion would be VA x power factor = watts or going the other way VA = watts / power factor. You shouldn't have to worry about this but I bring it up because consumer electronic devices tend to be very bad here as they are often 0.5 - 0.7. What this means that a computer and monitor that uses 200 watts and has a power factor of 0.5, is drawing 400 VA. For resistive loads like lights and electric ovens use a power factor of 1.0. A typical home averages about 0.8. Again, it's not something to be concerned about, just aware of. Good luck and stay safe.

07-09-2005, 05:53 PM	#5
pam Last of the Early 30 Join Date: Dec 2002 Location: Yelm, WA Posts: 4,679	Thanks so much, citivolus. I think I've decided against the AC, will live with a fan, so that I can keep my HTs charged. It's been a busy morning. Pam

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)