Xantrex inverter low voltage mod?

[BioHazard]

I have a Xantrex Xpower 3000 inverter that I bought a few years ago and has been collecting dust ever since. When I bought it, it was a "special" version, that had it's low voltage cutoff set to 11.3 volts instead of the normal 10.5. I thought this was a good idea, since I don't like to drain my batteries to 10.5v.

Today I hooked it up for the first time just to see if it works. I didn't have any proper cables, so I used three sets of old jumper cables hooked up to a new marine starting battery. Then another set of jumpers from my truck to the battery.

The biggest thing I could start was an air conditioner, about 500 watts, and it didn't sound right. I tried an air compressor, with a brush motor drawing about 10 amps and it would only run for a second before the inverter cut out. I also tried a 1500 watt heater, same thing, inverter shutdown.

This is a 3000w/6000w surge inverter. The inverter shouldn't draw more than 150 amps @ 11 volts using my 1500 watt heater, and there is little startup surge. My cables were kinda lame but I think they can handle 150 amps just fine, nothing got warm. The display on the inverter showed 13.9v no load, and shut down when it hit about 11v. I was not able to measure the voltage at the battery because my voltmeter was dead.

Is this happening because of my jurry rigged cable setup? Or is there something wrong with my inverter? Does anybody know if it would be possible to re-adjust the voltage cutout to 10.5v like normal? Would it be helpful to get bigger loads started if I had some big capacitor hooked up to the inverter? I feel like it's the surge load killing it...but a simple resistive heater doesn't have much of a surge does it? And the heater was still only a 50% load for the inverter...

[potter]

Cables cables cables Jerry rigged just does not cut it at high loads and low voltage.

   Potter

[BioHazard]

Hmm, well, I guess Xantrex says 4/0 as an absolute minimum. I never considered the voltage drop across the cable when I bought the high cutout version. (I wish it had a sense wire like an alternator!)

Does anyone think it is possible to mod the inverter to drop at 10.5 volts like normal?

Edit: I have some scraps of 2/0 cable just long enough to connect the inverter and battery, less than a foot. That should be plenty to test start a 1500 watt load for a few minutes, no?

[RogerAS]

You could also be witnessing a voltage drop within the batteries themselves. Combine that with the weak cables and...

R

[LowGear]

Dear BioHazard,

It's the connectors.  What's the first thing you check when your car clicks and won't start?  Even vice grip assistance may not be enough for these loads.

Casey

[BioHazard]

How about an aluminum bus bar with the inverter on top of the battery? My battery has bolt down mounting studs on it. How big would it need to be? I have some scrap 3/8" aluminum plate at the shop I might be able to use...

I just want to test this thing out before I invest a ton of money in some 4/0 cables!

What's the first thing you check when your car clicks and won't start?

I check to make sure my AAA card is paid up. 

[LowGear]

City Slicker!

[mobile_bob]

as mentioned by others you likely will have issues with both the cables of your choosing and the batteries
that you have to work with.

a typical car battery will dip below 11volt with 150amps of draw placed upon it, that works out to about
1400 output watts, which will require about 1800watts of input dc power or approx 150amps of input.

that is just the battery issue, the jumper cables are another issue, along with mutiple clamps etc. wherein
they alone would likely provide more than enough drop so that between the battery and the cable issue
i wouldn't be surprised to see a cutout occur at anything over 500watts of AC output.

or course motor starting surges will compound the problems.

while 4/0 might not be necessary for a very short couple, you will need probably two or more batteries
and at least 2/0 cable no more than 3 or 4 ft in length to be able to put anywhere near the output of the inverter
to a load test.

btw, do not mount the inverter over the top  of the batteries, unless they are true sealed batteries such as AGM or Gell cells
otherwise the offgassing which is corrosive will start the deadly destruction of the innards of your inverter,, the fan(s) in the inverter
will suck the corrosive fumes through the inverter case and everything will become exposed to these acid laden fumes.

this is to say nothing of the explosion hazards that would be present, the offgasses have a hydrogen component, and being lighter
than air will rise directly up and be sucked into the inverter, any spark and the gas will allow a flame front to reach down to the battery
cell tops and ignite the hydrogen rich gasses in the cells, and you then have a rather large explosion with acid and fragments everywhere.

lastly don't use buss bars for the above reasons and because they provide a rather large opportunity for shorts, if you have a suitably large
battery bank to operate the inverter properly there exists something around 1000amps per battery intermittent which is enough to make
a wrench melt which provides more gassing, vastly more heat, a positive ignition source and a likely explosive event. even if you insulate the bars
well they still will be so rigid that unless things are engineered well to account for real expansion and contraction, large forces will either break the inverter insulators or damage the battery posts to case seal interface or post to plate connections internally, which btw creates another opportunity for additional heat, more gassing, another ignition source with the same possible explosive result.

don't ask me how i know these things, suffice it to say i have in my younger days done things that have ended with a bad result and witnessed
many others.

so as the old saying goes, "do as i say, not as i have done"

bob g

[BioHazard]

Alright, I'm done trying to test this thing, even with a 100A battery charger I couldn't get it to do much without proper cables.

Question is, just how much battery do I need for this thing to be able to surge 6kw and NOT drop the battery voltage below 11.3v? Will 2 ~100ah trolling motor type batteries work?

I've decided I want to install it permanently in my truck, and that will only give me probably 50 amps or so charge at idle. I do have room for 2 extra batteries though....

Or maybe I'd be better off just selling this inverter and getting one with a standard 10.5v cutout?

[mobile_bob]

there is nothing wrong with your inverter, the reason it is set to cutoff at 11.x instead of 10.5 is to protect your battery bank
draining a battery to 10.5 usually does nothing to improve the lifespan of the battery and in some cases will damage the battery.

i would give up on trying to get 6kwatt surge from that unit, it is not within the realm of reality in my opinion, for a 12volt unit.

6kwatt surge will require 500amps at 12volts, which is something 4 group 31 950 cca batteries can deliver, and stay above
the 11.3volt cutoff, however starting batteries are not made to be deep cycled, so you will need to go with true deep cycle batteries
and probably at least 500amp/hr capacity, likely upwards of 1000amp/hr true deep cycle battery bank would do well.

anything less is asking for problems in my opinion, and likely will shorten the life of your alternator as well.

if you really need 6kwatt surge and 3kwatt continuous you really ought to step up to at least a 24volt unit, if not a 48volt inverter.

bob g

[BioHazard]

there is nothing wrong with your inverter, the reason it is set to cutoff at 11.x instead of 10.5 is to protect your battery bank
draining a battery to 10.5 usually does nothing to improve the lifespan of the battery and in some cases will damage the battery.

Right...that's the reason I originall bought the 11.3v version, I don't want to drain my batteries completely dead. But, I hadn't thought of the temporary voltage drop for such a large surge. I want to be able to run my air compressor with this inverter, I'm not sure what the total surge is, but it's around 10-11 amps running. The surge of course would only last for a short time...hopefully not long enough to drain the batteries.

I don't know if I "need" the full 6KW surge, but, when I bought this inverter, I wanted to be able to power just about anything I could plug into a standard 120v, 20A household outlet. That is my goal.

[mike90045]

Question is, just how much battery do I need for this thing to be able to surge 6kw and NOT drop the battery voltage below 11.3v?

The off grid rule of thumb is for each KW of power, add a series battery.
2Kw = 24V
4Kw = 48V     

6KW at 48V = 125A  Which needs a pretty stout battery to not fade.

6Kw @ 12V = 500A, which is way too many batteries in parallel.


I also suspect this is a square wave inverter, and not sine wave, which is even worse on motor starting loads.  Motors on sine wave = happy  Motors on mod-square wave = HOT with 20% excess current draw (which comes from your battery)