DIY Solar Energy: It’s Inverter Time!

By Dave Harris

I have purchased many diy solar energy inverters for my service truck, RV, boat, and emergency home backup, and this is what I have learned...

Buying a large inverter can be confusing! 

Most people want their inverter to run the "continuous" loads that they have, plus have enough surge power to start air conditioners, microwaves, sump pumps, etc. Seems simple enough, but when they purchase an inverter, usually it can't handle the startup surge they were hoping.  

This seems to be the problem: most people don't understand "Surge Duration".

Surge Duration

Most diy solar energy inverters can put out more than their rated "continuous" output for surge. But the question is: How long can the inverter provide that surge? The vast majority of consumer inverters can only provide surge for 2 seconds with most less than 1 second!

This is totally inadequate for hard starting appliances. I have measured the surge on my 2 hp air compressor, and it lasted about 5 seconds before it settled out to its "continuous" wattage. My 1000 watt microwave settles down at about the 3 second mark.

 So What To Do?

Always look for an diy solar energy inverter with long surge duration. The bigger inverter companies sell them, but they are usually labeled "Industrial" or "Commercial", and can be very expensive.

Which brings me to the Whistler Pro Inverters. Whistler Pro's have something they call "Smart Surge Control" that provides the surge wattage for close to 10 seconds. That is the longest I have found of any low priced consumer based inverter.

I gave several a shot, and they work as advertised! They have more than enough surge duration to start my hard starting appliances like A/C, microwave, air compressor, large power tools, sump pump, etc. My 3000 watt Whistler (5000 watt surge) can start my hard starting RV air conditioner with no problem while also running my microwave!

So add up your continuous wattage needs. Then find the wattage of your most surge hungry appliance.

 

Example:

  • Rated running watts ("continuous") of my lights + fridge + sump pump = 1440 running watts

 

  • Largest Surge wattage appliance is my big sump pump = 2700 surge watts

 

  • Pick the inverter that is above both ratings, in this case I would get a Whistler Pro 1600. It is rated at 1600 watts running continuous, 3200 surge.

 

Remember: inverters require VERY HIGH current, so the 12v cables have to be VERY large to work correctly. For larger inverters (1500 watt+) the cables need to be LARGER than the cables you see on your car battery.

Large cables are expensive, stiff and heavy, but are a MUST! Your inverter will NOT run correctly without them! Follow the cable sizing guides, and don't skimp or you will be disappointed with your inverter's performance! I cannot stress this enough. Also, keep the 12v connectors clean and tight for reliable power.

 

Let's Talk About Your Batteries

Home backup, off grid or RV (large) diy solar energy inverter use requires more than one deep cycle battery, usually many more. Check with an inverter pro to size your battery bank correctly BEFORE you purchase your inverter.

For those of you that are running an inverter in an idling single battery vehicle, the vehicle alternator makes your battery look bigger than it is. In my truck I have a 165 amp alternator with a 1600 watt continuous inverter.

It works terrific with the engine idling. I just don't use the inverter with the engine off. The continuous large current draw on an ordinary car battery will shorten its life considerably if the engine is not running. I could install a battery isolator with a second battery, but if I leave the truck idling, that isn't necessary.

Remember, BIG cables, TIGHT clean connectors!

I hope this was helpful, good luck with your diy solar energy project!

Whistler Pro-1600W 1,600 Power Inverter (affiliate)

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