With two batteries and the size of the alternator, I think I have enough to run a breathing appliance I will need to use when pulling my TT.
I will be pulling about 33 amps off the truck through the converter if my math is right.
The unit uses 4 amps @ 120 volts.
Any thoughts or advice?

 

I think that would give you 480 watts, or about 40 amps at 12v, but that would be with a 100% efficient converter.

I'm having a hard time finding what the stock alternator puts out, but I believe there are also some aftermarket higher output units available.

 

Actually it would be 40 amps plus conversion losses so likely 45. Granted the 14VDC output from the alternator may lower it a bit. Leave at least 25% spare capacity so about a 750 watt inverter.

I don't know what kind of breathing unit you mean but do not scrimp on quality for your inverter. The process of converting DC to AC can produce "dirty" power that I have had destroy a few electronic devices in the past. Remember that this will take a new crcuit properly fused. The cigarette lighter won't do it.

As far as the system handling the load, you should have no trouble. It will kill the batteries pretty quick if you're not running though.

Good luck
Cya

 

Yeah, get a true sinewave inverter.

Looks like alternator output is 136 amps. A person would have to know how much the truck's systems draw in normal operation, but I think it should keep up as long as you aren't running every light and charging dead travel trailer batteries off the RV plug.

Don't scrimp on the cables to power the inverter.

If for some reason the truck doesn't keep up, you could likely upgrade the alternator. If you had a stick shift, a PTO driven generator could also be a possibility.

If the breathing machine is a life or death kind of thing (as opposed to keeping you feeling good), it might be a good idea to have a honda EU2000 as a backup plan. They are quiet, and handy while camping. Assuming you need to run the machine once you are camped and the engine is off, you would have to have a good generator anyway.

 

Standard alternator was a 136A unt in 2003. Don't know the other years.

Cya

 

Due to conversion loss, suspect will require in excess of 50 amps to handle constantlly. You would be well advised to upgrade alt to something in range of 200 amps in order to handle at low speed operation. You must be able to maintain a positive charge effort at idle with nearly all accessories powered. A direct replacement alternator is avaliable with that capicity at reasonable price. Do not recomend a different alt. If anything happens you need to be able to convert back quickly.

 

Better details & using the correct terms , is the 1st thing to do .
A converter , converts voltages , it would seem by what you have said in your post , that you are talking about an inverter , changes DC current to AC current .
Tell us what you mean by "breathing appliance" ?
Look on the id plat of that appliance , see what the rating is , volts , watts , amps , ect.
If this is an expensive piece of medical equipment , then getting it right is important for at least 2 big reasons , you health & protect the appliance .
So getting a quality - true syn wave inverter , if you need while engine is off , then many other issues , do not use your starter batteries .
I've been building alt energy systems for a few decades , so could point you in the right direction with all the right info .

 

Thanks for all the replies.
The appliance is an oxygen converter that uses 120V ,60 cycles,4 amps.
and yes, I should have said inverter, got hung up on converter because of the appliance.
This is not a life and death, but it sure helps.
I also carry oxygen bottles for back-up.
It is either the inverter or the small generator as was mentioned in one of the posts.
I usually stay at campgrounds with electric hook-ups, so it is just for the travel in the truck.

 

I do not know how the O2 appliance works , does it have a motor ?
If so , it can take at least 2-3 times the rating to start an electric motor .
120vac x 4 amp = 480 watts , to start a motor x 3 = 1,440 watts from inverter , a sign wave inverter starts motors easier [ motor will last longer ] .
Most of the cheap inverters will not start "some" motors at all , has more to do with being a square wave inverter , use at least a modified square wave inverter , the true sign wave inverters will put out better power than the utility / grid .
Now for what the truck batteries would see ,
1,440 watts divided by 12.5 vdc =115.2 amps -surge to start .
480 watts divided by 12.5 vdc = 38.4 amps continuous -running .
This would be enough load to draw down your starting batteries [ without knowing the amp hour rating of the batteries ] maybe over night .
Starting batteries are not designed to be drawn down more than 20% without shortening there life , so deep cycling over [ without battery info ] maybe 20 times can kill the batteries .