<style type="text/css">P { margin-bottom: 0.08in; }</style> All - I'm at my whit's end and need help, badly. I'm about to embark on a cross-country move from CA to South Carolina with my family. Please forgive me if this topic has already been discussed and remedied for someone else – I'm new here.


Anyways, here's the stats on my truck:
--2003 Ford F-250 Superduty Crew Cab Short Bed, Lariat/King Ranch
--7.3L Powerstroke/Automatic Trans/4x4/5.5" Lift
--S&B Intake, Edge Tuner, Garrett Powermax38R Turbo, 4" Turbo-back exhaust, came stock with no Cat
--Sealed Camper Shell w/Carpet Kit.

I have two large Rottweilers and it is the middle of summer, so the drive will be hot..... we don't have space for the dogs in the cab because the 1.5yr old "puppies" are already 100+ pounds.... so I need to keep it cool back there with a long-distance solution.

I purchased a portable Air Conditioning Unit (SoleusAir 8,000BTU). It is rated to pull around 700Watts with about 1300W at peak (basically, when the compressor fires up). Let me preface this by saying: Yes, I probably could've gone with a swamp cooler or something else, but hindsight is 20/20 and I'm waaaay committed to this route....so please avoid giving me a hard time about procuring the A/C Unit being a stupid decision, if you believe it was.

Here is the electrical setup:
---SoleusAir 8,000BTU Portable AC pulling 700w continuous and 1,300Watts peak
---Cobra 2500Watt Power Inverter, properly grounded (validated by two electrical shops)
--- 4 Gauge Wire from Inverter to Driver-side Battery....note that the distances from Battery to Inverter are within spec for the 4 Gauge wiring
--- Dual Optima Yellow-top Deep Cycle Batteries
---Stock Alternator (I believe it is a stock single Alternator)

The Measurements:
---At idle, with or without Headlights/Radio/A-C Blower on, there is approximately 13.8 Volts going TO the Inverter from the Battery
---When the A/C Unit is powered on, inverter remains at about 13.2Volts until Compressor kicks on
DURING IDLE:
---When Compressor kicks on, Voltage kicks down rapidly down to 12.2V, 11.8V, 11.2V (Inverter then begins to chirp)...... once it is there and below, inverter then starts to Low Voltage Alarm, and if it stays at 11.2V or so for more than 5-10 seconds, it goes into a permanent Low Voltage Alarm state, shuts down the circuit back to the portable A/C Unit, and Inverter requires a Reset (Power Off/Power On) to restore


APPROX. 1,300RPM & ABOVE:
---When the A/C Unit is powered on, inverter remains at about 13.2Volts until Compressor kicks on
---When Compressor of A/C Unit kicks on, might dip to 12.9V momentarily, but stays fairly constant at around 13.2-13.4V
---During all my testing, only one time did the Inverter start to chirp during highway RPM's (1,500RPM and above).....
---But if we hit traffic and go back down to an Idle, we reach Low Voltage state fairly quickly


Note that the same symptoms can be repeated with other higher-wattage appliances such as Portable Heater.


THOUGHTS:

1. Run another set of 4-Gauge Wire from Inverter (has a second set of posts available) to the Passenger-side Battery
2. Certain make/models of High Output Alternators would double the charging capability from the Alternator at Idle and Slow Speed RPM's
3. A capacitor does not seem to be a good solution being that we need to have sustained output during periods of long idle . . . meaning, needs to work even when the truck is sitting at idle for several minutes. From what I understand, the capacitor is for quick hits/bursts …... not sustained.

If the Alternator is properly grounded, 4-gauge cables are in length-spec, Alt is recharging immediately once major load is off, and I now have arguably the best deep-cycle batteries on the market, what are my other options? Is a High Output Alternator my best bet? Again, it's alarming due to Low Voltage Alarm.


Thanks everyone

 

Let me start by saying you are doing very well by being able to run that A/C unit at all on a inverter. Most inverter setups cannot start the A/C compressor, it takes a lot more than 1300w to start it, there is a very large short duration current draw on all motors, especially compressors.

Somehow it's working for you, except at idle. Obviously you are using a large part of the truck's alternator output to get the compressor started. The alternator does not have very much output at idle, most do not. I would be suspicious of any aftermarket ones that claim they have a lot of output at idle. If they really did, then they would present a large load to the engine at idle, causing other problems.

One thing to check first. I know you said your 4 guage cables should be large enough, but for an experiment, take a voltmeter and set it to read 12v, preferrebly a digital meter. Put one lead on the + inverter terminal, and put the other lead on the battery +. Replicate the conditions when it faults, and see what the reading on the meter says. Any meter reading at all will be how much voltage you are losing in the cable(terminals also). You can check any cable this way. If you do have a volt or so, then I would run another set of cables with what you have already, or get larger cables.

The only other solution I can think of to try is instead of running another set of cables to the pass side battery, run another set of cables to a another battery. I am not sure this would work, but what I would do is get another regular car battery and temporarily sit it somewhere and hook another set of cables to it to the inverter and see if this 3rd battery would hold up the inverter.

 

Dave - thank you so much for taking the time to write this. I will try this tonight or tomorrow morning and see what I can find out. Based on what you're saying, though, do you by chance have another possible solution that I can use to cool it back there?

Thanks very much, again - I sincerely appreciate it

 

Do you have a rear sliding window in the truck cab and the camper? You could possibly rig a small fan in half of the opening to draw the cabin A/C through to the camper. It would have to help.

You also may try a smaller A/C unit. About this time of year(when it's the hottest) Walmart and others put everything on sale so they can bring in the fall/Halloween stuff. You usually can get a small cheap 5000 for around $100. Being just a little bit smaller might make the difference.

 

You're simply not producing enough oopmh at idle. You need to put more load on the engine so that your power stays up when idling. A common way to do this is to put an overdrive pulley on your alternator. This will increase the RPM's of the alternator (and thus increase the load on the engine) at idle. It's basically like changing your gear ratio, except for your alternator. They are not very expensive to try. I didn't have the chance to look for one for your particular vehicle, but my buddy has bought from here without issue: STARTERS AND ALTERNATORS

They also sell high amp alternators for your 2003 diesel that already have overdrives on them. They put out as much power at idle as your factory unit does at max.

 

Give that inverter every bit of help it can get. Keep your battery leads as short as possible and as high a gauge as possible. Maybe consider adding an extra battery mounted close to the inverter and charged through an isolator?

Depending on the efficiency of the converter, you will be pulling 100 amps or more to make even 1KW of power. Ohm's law and the first law of thermodynamics rule here.