When purchasing an inveter do I need to consider watts of draw as well as amps? I don't know anything about them and I want to run and oxygen concentrator for my wife. She's on oxygen and I want to be able to take longer trips without the need to take a large bulk oxygen tank along with her smaller carry tanks. The idea is that I'd run the oxygen concentrator in the truck while traveling since I can only get 8 hours or so out of a carry tank. My dad has a cabin that is about 3 1/2 hours away and that just doesn't leave much of a margin of error when traveling each way. Take the small tank for back up, run the concentrator in the truck then move it to the cabin with 110 power when we arrive. Any help would be appreciated.
inverters
- Thread starter 65 scout
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Watts and amps are, for your purposes, the same thing expressed in different ways.
(engineers, please don't yell at me for that ... I know it's not 100% true but it should be OK for what he's asking)
Either will tell you how much power you need from your inverter to run the device, but you'll need a little thing called Ohm's Law.
Watts = Volts x Amps
We know you are running at 120v, so if the concentrator is listed as drawing '5 amps', that would be the same as if it were listed as drawing '600 watts'.
Since most inverters are listed as a given wattage output, you'll likely want to use this number to figure your power needs.
The place you're more likely to use amps will be on the input side of the inverter, where you'll be dealing with (nominally) 12v from the truck's charging system. Here you'll probably find your alternator listed in amps output, such as 50 amp, 75 amp, 120 amp, etc, and your battery listed in amp/hours capacity - a common group 31 deep cycle battery is typically around 100 amp/hours.
(engineers, please don't yell at me for that ... I know it's not 100% true but it should be OK for what he's asking)
Either will tell you how much power you need from your inverter to run the device, but you'll need a little thing called Ohm's Law.
Watts = Volts x Amps
We know you are running at 120v, so if the concentrator is listed as drawing '5 amps', that would be the same as if it were listed as drawing '600 watts'.
Since most inverters are listed as a given wattage output, you'll likely want to use this number to figure your power needs.
The place you're more likely to use amps will be on the input side of the inverter, where you'll be dealing with (nominally) 12v from the truck's charging system. Here you'll probably find your alternator listed in amps output, such as 50 amp, 75 amp, 120 amp, etc, and your battery listed in amp/hours capacity - a common group 31 deep cycle battery is typically around 100 amp/hours.
Haf-E
Expedition Leader
If you have an amps rating for the load that is better to use - but I would advise a 2x multiplier for the size of the inverter compared to the load - it will operate more efficiently and will be more reliable.
So if the oxygen concentrator is rated at 5 amps - I would look for an inverter which is rated about 10 amps - which would be 1200 watts (120 volts AC x 10 amps AC = 1200 watts AC). If you'll only run it while the truck is running then a second battery isn't necessary - just be sure to turn it off when you stop or you'll end up with a dead battery the next day.
Maybe post the specs on the oxygen generator - whatever it says its electrical draw is - I am curious on the load level it puts on a system.
So if the oxygen concentrator is rated at 5 amps - I would look for an inverter which is rated about 10 amps - which would be 1200 watts (120 volts AC x 10 amps AC = 1200 watts AC). If you'll only run it while the truck is running then a second battery isn't necessary - just be sure to turn it off when you stop or you'll end up with a dead battery the next day.
Maybe post the specs on the oxygen generator - whatever it says its electrical draw is - I am curious on the load level it puts on a system.
1stDeuce
Explorer
I'm going to guess that the power consumption for the concentrator is rated in Watts, not amps. Watts is a constant measurement regardless of voltage. Amps depends HEAVILY on voltage. Just doing a quick search, I found a "portable" Invacare concentrator that's rated for 280 watts at 3LPM, on 120v A/C (wall) power.
I'd recommend you buy an inverter that is rated for at least 50% more watts than the concentrator will draw. That will ensure it isn't operating at it's max all the time, and a 2x "surge" rating should ensure adequate ability to start the machine, which sometimes takes double or more the steady state power. A 400 watt inverter should be sufficient, and will draw about 22 amps from your vehicle to make 280 watts of 120V. (280W/13V=22A) (The inverter will see ~13v most of the time from your vehicle as long as it's running.)
22 amps of draw means you won't be able to use the cigarette lighter for two reasons: 1: Most are fused at 15A, and 2: An ordinary cigarette lighter plug will begin to get pretty warm over about 15A, and pulling over 20 may melt some of them. You'll really want to hard wire the inverter. I'd recommend using 10 ga wire to keep voltage drop to a minimum, and put a 40-50A circuit breaker or fuse as close to the battery as possible. Connect BOTH the power and ground leads directly to the battery, not to some other source of voltage, unless your car has one of the large 12v taps fed by a large size battery cable, often covered by a red cap. That would also be OK for getting power.
This is the breaker I'm talking about. I just bought a few of these off Ebay for a solar setup, and they work great!
http://www.ebay.com/itm/INLINE-AUTO-WATERPROOF-40-AMP-CIRCUIT-BREAKER-MANUAL-RESET-SWITCH-12VOLT-4-8-AWG-/271244959834
If you overload them, you just reset them, and you can use them to switch the power off as well. If you use 10ga "Zip" wire, it has power and ground already run together. Like this: http://www.ebay.com/itm/10-Ft-10-GA-Gauge-Red-Black-Stranded-2-Conductor-Speaker-POWER-GROUND-WIRE-/161156437856?pt=LH_DefaultDomain_0&hash=item2585ac1760
Finally, as stated above, with a continuous draw of 20A, you'll probably want to leave the vehicle running as long as the concentrator is plugged in. Shutting it off for 20 minutes is probably OK if your battery is good, but longer periods may be at risk of not starting. (Ideally, a 20A load would drain a normal car battery to 50% in about 2 hours, but it's likely your battery isn't starting at 100%, and doesn't have as much reserve capacity as it is rated for anyway... If you really want to know how to figure out how long you can safely leave it with the engine off, PM me and I'll explain it. It doesn't sound like that's a concern though.
Chris
I'd recommend you buy an inverter that is rated for at least 50% more watts than the concentrator will draw. That will ensure it isn't operating at it's max all the time, and a 2x "surge" rating should ensure adequate ability to start the machine, which sometimes takes double or more the steady state power. A 400 watt inverter should be sufficient, and will draw about 22 amps from your vehicle to make 280 watts of 120V. (280W/13V=22A) (The inverter will see ~13v most of the time from your vehicle as long as it's running.)
22 amps of draw means you won't be able to use the cigarette lighter for two reasons: 1: Most are fused at 15A, and 2: An ordinary cigarette lighter plug will begin to get pretty warm over about 15A, and pulling over 20 may melt some of them. You'll really want to hard wire the inverter. I'd recommend using 10 ga wire to keep voltage drop to a minimum, and put a 40-50A circuit breaker or fuse as close to the battery as possible. Connect BOTH the power and ground leads directly to the battery, not to some other source of voltage, unless your car has one of the large 12v taps fed by a large size battery cable, often covered by a red cap. That would also be OK for getting power.
This is the breaker I'm talking about. I just bought a few of these off Ebay for a solar setup, and they work great!
http://www.ebay.com/itm/INLINE-AUTO-WATERPROOF-40-AMP-CIRCUIT-BREAKER-MANUAL-RESET-SWITCH-12VOLT-4-8-AWG-/271244959834
If you overload them, you just reset them, and you can use them to switch the power off as well. If you use 10ga "Zip" wire, it has power and ground already run together. Like this: http://www.ebay.com/itm/10-Ft-10-GA-Gauge-Red-Black-Stranded-2-Conductor-Speaker-POWER-GROUND-WIRE-/161156437856?pt=LH_DefaultDomain_0&hash=item2585ac1760
Finally, as stated above, with a continuous draw of 20A, you'll probably want to leave the vehicle running as long as the concentrator is plugged in. Shutting it off for 20 minutes is probably OK if your battery is good, but longer periods may be at risk of not starting. (Ideally, a 20A load would drain a normal car battery to 50% in about 2 hours, but it's likely your battery isn't starting at 100%, and doesn't have as much reserve capacity as it is rated for anyway... If you really want to know how to figure out how long you can safely leave it with the engine off, PM me and I'll explain it. It doesn't sound like that's a concern though.
Chris
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