What Do You Need In An Inverter?

Last time I mentioned I was swapping out the inverter aboard Sun King and last night I climbed aboard to do just that. I was fussing about UPS bringing the package after supper, but that may have been a blessing. Sometimes the temperature drops below 80 at night.  First things first, I had to do some clean up as the coon has been in there, leaving chewed food packages and greasy footprints.  I hope he got a good buzz from the instant coffee packet he ate.  No more stashing MREs under the seat and the boat is getting a new food locker.

The old inverter has been a good one, sort of.  It has survived thousands of miles of travel and about 8 years of seafaring.  It’s main problem is that the maker fibbed a bit on the specs.  Otherwise, the short time I run stuff in the galley or use the shop vac to dry out the deck it works fine without melting the transformer mount.  It had what would have been some desirable features, had they actually worked.  But what did I really need?  I will go over my selection process and some criteria you might use in selecting an inverter of your own.

I have some very advanced and expensive inverters, but those stay inside.  The inverters in my boat and golf cars I consider expendable.  Weather and dirt are the hazards on the buggies, whereas water and salt spray are the hazards aboard Sun King.  I either need some super expensive mil-spec all weather gear or I need something I can afford to replace on occasion.  Budget is a factor at my house and that works well with what I actually need.  I need a box to convert low voltage DC to 120 vac.  I could get by with only 1000 watts if the ratings are honest and I only operate one appliance at a time.  2500 watts would let me run the coffee machine AND the microwave simultaneously.  I spent a little more and got a 3500 watt inverter because I have some non-boating things in mind.  In case you are wondering, Sunelec sells some very capable and inexpensive Kisae inverters, but none on hand quite met my spec.

We are in hardcore a/c season and when you combine constant running with cloudy weather, the main system gets a little stretched.  I plan to use the boat’s solar power system to charge all of the electric vehicles, reducing battery load at the Solar Shed.  I will probably put some of the chargers for yard tools, too.  That can all add up.  It will give the boat solar something useful to do when not roaming the rivers or bays.

Last time I talked about the standby feature of some inverters.  I don’t really care for that, but one big selling feature on the new one is a remote control panel.  The inverter is tucked away and it is not easy to reach the switch.  I could leave it on all the time, but idle on an inverter can add up to quite a bit of power.  In addition to “Really, really off” with the main switch, you can turn it mostly off with the remote control.  I can mount it anywhere the cable will reach.  My Trace PS2524 that I used for many years as backup power was mounted in the attic, but had a remote panel in the laundry room wall.  That was a handy feature.

Used to be, you had a choice of square wave, “modified sine wave” and, rarely, sine wave.  The stuff coming from the power company is sine wave and that’s the best.  It really does not cost any more, these days.  You hardly see square wave inverters any more and that’s good.  Motors hate them and other things don’t go quite right.  Modified sine wave inverters work pretty well with anything, but boy will they buzz your ceiling fan!  Maybe that’s not a problem as I don’t have enough overhead clearance for a ceiling fan aboard.

Do you need a charger built in?  I don’t, but it is a necessary feature if you are using your inverter as a battery backup for the house.  This is about standard in the bigger units, but not usually on the smaller ones you use in vehicles.

The new inverter, in my case, needed:

  1. Suitable input voltage for my onboard solar, which is 26 volts.
  2. A good operating range on the input voltage, though not a big deal with lithium.
  3. Power output sufficient for what I think I need, plus more for what I didn’t think about.
  4. Reliability
  5. A remote switch
  6. Expendable price
  7. Has to fit the allocated space

I like to try new stuff.  There are brands I trust, sure, but I am not going to put a $3000 inverter in a boat that didn’t cost much more to build.  Besides, I like hunting for buried treasures, like cheap, but good, solar gear.  It does not always work out—case in point, the old inverter.

Shopping Ebay is always an adventure with the Chinese sellers’ fanciful mathmatics to embellish the specs.  Or shifting decimal points.  Want to buy an inverter that cranks out 50,000 milliwatts?  That’s big enough to charge your phone!  The photos all look about the same in the 2″ space allotted on the web page.  Even though modern electronics keep getting smaller, actual kilowatts require a certain volume of electronics.  Sometimes the seller will give the dimensions and that is a big help.  Yes, a lot of times it is in metric, but I have been able to translate that to real ‘Merican inches in my head since grade school. 30cm is a foot and if they are hawking a unit that is only 15cm long it is probably only 300 watts capable.  My new inverter is better than a foot long, maybe 6″ tall and 10″ wide.  A key if no numbers are given is to look at the scale of the outlets.  If a single outlet is a third of the panel, then the thing isn’t very big and they aren’t figuring you can plug much into it.  Mine had 4 outlets across and plenty of room to spare.  Below, we can compare the old (left) and the new.

What Do You Need In An Inverter? 1

The old one was bigger, owing to its low frequency design and it had comfortingly huge battery lugs.  Two sets made it a handy junction point.  They are connected internally.   Unfortunately the unit was not big enough to contain a proper transformer to maintain continuous rated output and it would often smell of burning rubber.  The new one, with lower wattage rating and high frequency design (which I have come to embrace) is smaller.  I was dismayed by the single set of M6 screw terminals.  That’s roughly a quarter inch, but pretty much standard, even in some of my batteries that are rated to crank out 900 amps!  The big worry with terminals that size, though, is to keep them tight enough for a cool connection, but without snapping them off.  Using a torque wrench is not a bad idea.

So far, the inverter has worked well and I am pleased.   I have run it for hours at 1500 watts in 97 degree heat and will soon step that up.   There was an issue with the new lithium batteries’ weird behavior and the old circuit breakers that I will write about separately, but the inverter is fine.  This may well turn out to be one of those elusive treasures.  (No, I won’t tell you the brand.)


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