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OFF GRID POWER; various thoughts on...

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I spoke with an Outback Power Systems engineer recently. I had some specific questions about one of their inverters. He answered them quite clearly. I've always thought their products to be top line, if not the best. Anyhow he confirmed my main concern about the inverter I had a chance to buy on a deal. He also clarified one point that I was also wondering about.

The question relates to inverter/chargers, like Outback, Magnum Energy, Trace/Xantrex. Plain vanilla inverters, like most square wave inverters, are just inverters. They do not have battery charging circuitry incorporated within them. You need a separate charger to recharge the batteries from a generator or other AC power source when you have an economy inverter. Inverter/chargers have a battery charger incorporated into the unit. In the case of my Outback VFX3524M the charger has a maximum charge rate of 85 amps at 24 VDC.

These inverter/chargers all are setup so when the connected generator is fired up, the AC power to the inverter causes the inverter section to switch out. The AC power to the cabin then is coming from the generator. The generator power is also powering the battery charger section. I have wondered why this was? Why was the generator power not just used to power the battery charger section, while any AC loads would still be supplied by the inverter section?   ??? 

Since I have a small generator this was of concern. By past experience I know that when my 2800 watt generator (derated by altitude to about 2300 watts) is working hard enough to power the old 75 amp Iota charger, it is not a good move to use the microwave at the same time. There's just not enough power available from the generator. Buying a larger generator would be a solution, but that's not a part of this scenario. Ideally I would like to be able to use the generator power to charge the batteries and leave the inverter to supply any cabin electrical needs.

Outbacks engineer supplied the answer. Keep in mind I have a planned 24 VDC system. The Outback 3524 inverter is designed to operate with an input voltage maximum of 32 volts. There are similar limits with other brands. Some are even less, like 30 volts maximum.

Batteries should be subjected to an 'equalization charge' about once a month to assist in achieving maximum battery life. An equalization charge is a higher than usual voltage, low current, charge rate. An equalization charge is done at 2.57 to 2.68 volts per cell (in a wet lead acid cell battery). In a 24 VDC system that is 31 to 32 volts.

Do you see the issue? The voltages are getting too close for the comfort of an engineer. In a real world situation it might happen that the charging voltage could spike higher than 32 and thus it might cause damage to the inverter/charger. Hence, the inverter manufacturer usually elects to program the inverter to drop out when the AC power in, is active.

I am not certain, but I do believe I killed my Exeltech 1100 watt inverter when I was equalizing the batteries. The Exeltech does not have a charger built in. I left it connected to the batteries. At the same time I bumped my stand alone charger into high voltage mode. It might have exceeded the design input voltage for the inverter. Poooof!    Or maybe it was 'just one of those things'.  ??? ???

Anyhow, I thought it was interesting.

I think this would be a good place to talk about good things, bad things, odd things, that we have encountered in alternative power systems.

glenn kangiser:
My Trace inverters go off at about 21 volts low or  30 volts max. I have two 4024 Trace sine wave inverters stacked to make 240v.  They are also over-current protected internally so that any short will trip them out and a manual reset is required if a short happens.

I know as I sometimes equalize and bulk charge with my DC welder.  I doubt I am treating my batteries as well as possible but when doing it I monitor them pretty closely.  I generally charge at between 60 to 100 amps but the welder does not taper off on charge as the batteries get full therefore monitoring is necessary.  This is across 12 375ah batteries or 1125ah at 24v.

Excellent information guys and maybe Glenn, you could start up a separate section on off grid power? I love this idea.
Just some FYI, I had some free time between Christmas and New Years and decided to take a little road trip, just drive alone for hours and see some country to try to get rid of all the crap in my brain from the past year. Anyway, as I traveled west on old Route 66 as I was coming into Tucumcari, NM, I saw this huge wind turbin and as I got closer I could see that I could get right up to the base so I did. This thing was huge, I'm guessing 20' or more at the base and at least 150' tall with blades that had to be 100' long.
I took a bunch of pics if anyone is interested. On my way home a few days later, I was a billboard on I-40 eastbound that said it was the largest wind turbin in the world!!! Suspect that maybe it was when installed but, maybe not anymore. It is 1.6Megawatts!
I had heard that these big turbins were quite noisy and that is way some people object to them. Well, let me tell you this monster was so quiet I couldn't hear it running at all.
I was also amazed at the 100's of wind turbins I saw in Oklahoma, Tx, NM and even AZ. Someone sure believes in them!
PS: I went all the way to the Grand Canyon. Highly recommend the trip on the old Mother Road.
Okie Bob

glenn kangiser:
Lets just go ahead and add our thought's , pix and everything to this thread, BoB.  :)  It will be easy to find here and this thread can expand endlessly on off grid power.

glenn kangiser:
Getting ready to change my solar tracker cylinder to a larger one so I have to rotate the panels to the sun in the morning after which it tracks all day.

Readings .... set 1 in light but 160 degrees away from the sun at 8 AM(back of tracker toward the sun) -  1 amp  immediately change to 16 amps when toward the sun.

set 2  .5 amps away     10 amps when toward the sun.


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