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Home Forums Technical Discussion Inverter Suggestions for Fully Off-Grid System Re: Inverter Suggestions for Fully Off-Grid System

#64465
elnav
Member

Fast turtle said: , I’d like to avoid the types with built-in chargers, since we will be doing minimal charging from AC sources.

Why the aversion to being able to charge from an AC voltage source in a pinch?

I would assume you have done your homework and realize that combination charger /inverters are simply using the same components but running the current flow in reverse. There is no real savings by having a dedicated inverter only and then having to buy a seperate and inferior charger when you realize the need for some kind of charging after a proponged period of no wind or solar charging.

Internally the combination device only differs by the inclusion of a transfer relay and the neutral to ground switching required to make it safe. At most the total cost of components amount to maybe $50 worth of parts. Any greater price differential is simply due to markup not real cost. I know because I used to work for an inverter manufacturer. I won’t name names since this is not a sales pitch for any one brand.

What you should be looking for is the associated feature set each brand comes with.

For starters why so much power? Who guided you in developing a power budget? My uncle lives off grid and has a jacuzzci hot tub, a 52 in satellite TV plus every kitchen gadget you can imagine. He does this mostly on a 3kW Outback inverter. Because he is a stubborn logger who will not listen to good advice he does need a big diesel genset for his 300 foot deep well submersible pump. However there are technical solutions to overcome the start surge from a submersible well pump. I could show you how to do the same task with a 2 kW genset from costco or Walmart.

My point being you can save money by starting with a 2500 – 3000 size inverter which can be supplemented by adding multiple units in parallel should you really need the extra power. I design such systems for a living and the majority of clients are quite happy with 3kW.

Among the desirable feature set of the combi units is the inclusion of a battery monitor that acts like a fuel gage to tell you how much charger remains in the battery bank. Don’t believe the simple voltage bar graphs that really are not that accurate. The battery monitors actually count each watt extracted from the battery or add each watt added from wind or solar charging. In fact it is able to combine the total from multiple sources. Furthermore these combination chargers often have the ability to control the charge rate based in the size of the charging source be it an 800 watt little portable gasoline genset or a 10 kw Diesel generator, They have battery voltage alarms to warn you when its time to start the generator in a pinch. Believe me this does happen. Excessive snow fall, prolonged cloudy periods, and sometimes freezing rain even. I hear you guys really had a lousy winter this year.

Don’t kid yourself by thinking an automotive type charger is going to bail you out. They are usually constant voltage taper chargers and will take two to three times as long as the smart chargers found inside the combination models. Just think of the time and fuel burn involved.

On the subject of 230V submersible pumps don’t get sucked into one of the systems that require two inverter each delivering 120V being hooked in tandem to deliver 240V to a big pump. Either use a step up transformer and a soft start module to drive the pump or if your plans include full air conditioning etc. then select a 230V output inverter and use a step down transformer to provide the 120 V for utility outlets. The latter approach is what I now use because the systems of twinning two 120V to deliver 240V is still crippled if one of them has a problem. The result being you have no inverter at all. with my approach if one goes down you still have 50% capacity remaining.

Since you are just now building I would assume your electrical wiring is done to NEC code which insist on the usual North American NEC dictated center tapped neutral. Its the worst possible system approach but if you are off-grid you have some latitude to work around it. Manufacturers like Outback are committed to supporting this concept but there are other ways that are as safe and has more benefits.

Don’t make any final purchase decisions before you have completed your entire load budget to the nth degree.

You are right there are a gazillion inverter companies out there but not all of them will recommend a specific model for your benefit, more often they do so to enhance their own profit margin. And you can bet they are not going to recommend their competitor even if it has a better feature set that more closely meet your needs.