Inverter Question

[Spitfire]

Just wondering what the biggest power inverter you can use with the standard 12V outlets on a FWC camper? Trying to figure some things out before I get my camper. Thanks.

 

[NorCalSteve]

It looks like my outlets have a 15 amp fuse. To avoid blowing the fuse, I probably would not go over maybe 10 amps current. Power = amps times voltage. So, 12 volts times 10 amps is 120 watts. But the inverter is not 100 percent efficient. It uses power to invert. You could plug a 200 watt inverter in as long as you did not plug a 200 watt device into the inverter. That would likely blow the fuse. I have a 75 watt and a 150 watt inverter. I use them both but only to supply 120 volts AC to a low power battery charger. I doubt I have ever plugged in anything higher power than maybe 50 watts, if that.

Hope this is correct information and hope it helps.

Steve

 

[Spitfire]

Thanks. I need about 100 watts to run my wife's CPAP machine. Looks like it might be doable.

 

[NorCalSteve]

Running 100 watts through an inverter through the night would be a large drain on the battery. You can probably figure about 70 amp-hours of drain after about 8 hours. The batteries may no longer be able to supply 12 volts at the outlet by morning. At 9 amps of current, you will also loose some voltage just from the long run of wire from the battery to the outlet. If the voltage gets too low, the inverter will probably automatically turn off.

Once you specify that you want the inverter to run through the night with the battery not charging, things get a little more complex.

My CPAP had a 12 volt adapter option, which I bought. I ran a dedicated 12 volt (fused) line up to the bed from the battery. I do not use the humidifier while camping. I do realize that not using the humidifier for many is not an option.

Steve

 

[Hittheroad]

Thanks. I need about 100 watts to run my wife's CPAP machine. Looks like it might be doable.

I wanted to be able to run a 500w vacuum cleaner. I have a 600w inverter hard wired into the battery and mounted nearby.
It works great and was easy to do. Also have often used a 150 watt inverter off the standard DC plug. Runs coffee grinder and I have used it for hours charging devices that only have an AC charger eg. Mac Laptop.

 

[Spitfire]

I did a little research and I found that they offer a 12V to 24V converter unit for my wife's CPAP which would be more power efficient than going through an inverter. I'm not sure how much current this unit draws yet. i think it depends on what settings she uses.

 

[Bosque Bill]

I did a little research and I found that they offer a 12V to 24V converter unit for my wife's CPAP which would be more power efficient than going through an inverter. I'm not sure how much current this unit draws yet. i think it depends on what settings she uses.

If the CPAP actually runs off of 24vdc, that might be more efficient. However none of these calculations are as simple as P = I x E as none of these devices are purely resistive loads, but some mix of inductors and capacitors. Let's just not get into complex math, please .

 

[NorCalSteve]

Well, you got me curious. I went out to my camper and connected my ResMed S9 CPAP to the 12 volt through the 12/24 volt adapter. It was a little over .1 amp on the 12 volt line while just plugged in with the CPAP lights still on (they take a few to go off). Running, it was maybe .6 amps (varies with the breathing) but, like you said, that would be based on the pressure setting. My pressure is pretty low. Bottom line is, if she does not need the humidifier running, things are looking good!

The humidifier is what will really drain a battery.

Steve

 

[Spitfire]

Well, you got me curious. I went out to my camper and connected my ResMed S9 CPAP to the 12 volt through the 12/24 volt adapter. It was a little over .1 amp on the 12 volt line while just plugged in with the CPAP lights still on (they take a few to go off). Running, it was maybe .6 amps (varies with the breathing) but, like you said, that would be based on the pressure setting. My pressure is pretty low. Bottom line is, if she does not need the humidifier running, things are looking good!

The humidifier is what will really drain a battery.

Steve

She has a ResMed S9 as well. They have a chart showing the different amp draws in this document: http://www.resmed.com/us/assets/documents/service_support/battery_guide/198103_battery-guide_glo_eng.pdf

Page 19 shows the draw using a converter for the S9.

 

[NorCalSteve]

Nice! Thanks for the link to the PDF file! Good stuff!

Steve