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Topic: Thoughts on Inverters (Read 1125 times) previous topic - next topic

Thoughts on Inverters

Some months back Sue and I installed a 1500-watt PSW (Pure Sine Wave) inverter in the cubby below our refrigerator (where the vacuum lives). There is a lot of empty space in there (occupied by the vacuum hose) and is easily ventilated by leaving the door open (and taking the vacuum hose out) and it is the closest interior space to our battery bank (directly above). We will probably install the MPPT solar charge controller in there too but might add a muffin fan to help with air circulation at that point (though the inverter has 4 fans).

The installation of an inverter offers two basic choices: Install one big enough to power most everything in the coach or go with smaller inverters with specific roles. My choice falls into the middle of those, I guess. It's not quite big enough to power the entire coach (I'd probably need 3,000-watts for that) but is big enough to power most devices that plug into a 15-Amp household circuit.  And the cables, large anyway, don't have to be quite so big.

So far I have not actually wired the inverter into the electrical system (e.g.: wall sockets) of the coach; although I have a 15-Amp switch for that. I have, instead, a very good extension cord with 5 sockets. This turns out to work quite well because we haven't actually used that inverter yet. For anything.

Maybe if I can break the habit of putting a tea pot onto the stove for boiling water and using the microwave it would be more of an issue. But I'm surprised at how little we need shore power for our lives. Lights, radio, ham radio, fans, furnace, hot water heater, water pump... all of these work just fine on 12vdc battery power. The main issue, in fact, is just keeping the 12vdc system going... and solar power should solve most of that.

So, while I don't regret selecting the 1500-watt PSW inverter, I actually am starting to think that numerous smaller inverters that fill specific niches might be the best way to go. Of course, the elephant in *that* room is the microwave and any demestic-type of refrigerator we move to in the future. (Ok... that's two elephants.)

But so far our major use of any inverter has been for watching movies and it turned out that a little $20 cigarette-lighter-plug inverter from Walmart handled that load just dandy. No wiring problems, no expense, not even PSW.

Putting aside the issue of a rather inelegant conversion of DC to AC and then back to DC  (which nags at me, nonetheless... just not enough to buy DC television sets and BluRay players), it turns out that - at least for us - we could get along just fine with a collection of these little $20 inverters scattered around the coach plugged into 10-Amp cigarette-lighter plugs.

Until we wanted to use the microwave.

Craig
1993 U225 36' Unihome GV with PACBRAKE exhaust retarder, Banks Stinger and Solar Panels.
Toad: 1999 Jeep Wrangler 2-door soft-top.

"No one has ever had to evacuate a city because the solar panels broke."

Re: Thoughts on Inverters

Reply #1 –
Two more thoughts (comments, suggestions, whatevers)

When the previous owner of my boat (Letitia's Journey) installed the same 2500 watt Heart inverter my coach has, he didn't tie it into the existing AC house wiring. He ran separate wires to a new panel and separate wall sockets.

Thought 1)  just wire the small inverter to a new  microwave socket

'Skipper Bob' (Robert Rieb) wrote a number of cruising guides and acquired an almost cult-like following among folks doing long term cruising.

Thought 2)  he often espoused putting small inverters where you needed them.

Possibly you too can start a cult  :P

hth
Elliott & Mary Bray
ex. 1996 36' U295 - Build 4879
ex. 2018 Coachmen Leprechaun 319MB
 

Re: Thoughts on Inverters

Reply #2 –
The problem I see with inverters in multiple locations is the 12 volt supply wires for inverters must be thick due to high amperage, while the output wires from the inverter can be much thinner.

My solution to the inverter issue is to use one 1800 watt "pure sign" inverter supplying power to the "RED hot" half of the main 120VAC power panel. This allows use of the wires already installed, however some rewiring was required to provide additional 120 VAC receptacles in the kitchen and to provide more ability to be selective about what receives power. This solution for boondocking also requires that the on/off switch for the inverter is in a convenient location (mine is opposite the refer), such that it is only turned on when 120VAC is required.

"Pure sign" 1800 watt inverter because it will run anything you plug into a duplex receptacle more efficiently than a "modified" inverter without the risk associated with damage caused by poor power. This does require power management in that it will NOT provide enough wattage to run a toaster and a coffee maker at the same time. Larger than 1800 watt costs more to purchase, uses even more 12v amperage and is still limited in how many items it can power concurrently. 
Wyatt
96 U320 40 WTFE, build 4943
84 Toyota Supra towd
2015 Jeep Wrangler towd
Victoria, BC, Canada

Re: Thoughts on Inverters

Reply #3 –
Quote from: P. Wyatt Sabourin –
The problem I see with inverters in multiple locations is the 12 volt supply wires for inverters must be thick due to high amperage, while the output wires from the inverter can be much thinner.

This is certainly an issue with large inverters where you have to install the inverter close to the batteries and even then use 1/0 or 2/0 cables. But 200-watt and 300-watt inverters don't have that requirement. A 200-watt inverter will usually be able to plug right into a cigarette-lighter socket. I have those near both my front and rear tv installations anyway so I'm not going to bother hooking the AC plugs for those areas into an inverter.

I do like the separate panel-and-plugs idea. I don't like pulling wires - even 120vac wires - from the inverter (under the fridge) to the panel locations under the bed. I am looking at just tying the inverter (through a switch) into the wiring right there where it sits and then modifying the panel at the back. Really, it makes no difference where you put the 120vac; it can just as easily be in the middle as the beginning (or end) as long as you protect the circuits.

Craig
1993 U225 36' Unihome GV with PACBRAKE exhaust retarder, Banks Stinger and Solar Panels.
Toad: 1999 Jeep Wrangler 2-door soft-top.

"No one has ever had to evacuate a city because the solar panels broke."

Re: Thoughts on Inverters

Reply #4 –
Quote from: TheBrays –
Possibly you too can start a cult  :P

I tried doing that in the 70s... even got ordained as a Unitarian minister (still am, and can perform marriages; funerals, not so much).

But my wife warned 'em off.  :P

Craig
1993 U225 36' Unihome GV with PACBRAKE exhaust retarder, Banks Stinger and Solar Panels.
Toad: 1999 Jeep Wrangler 2-door soft-top.

"No one has ever had to evacuate a city because the solar panels broke."

Re: Thoughts on Inverters

Reply #5 –
Small inverters are usually modified sine wave.  Everthing is happier with true sine waves. 

It is always better to have inverter closer to house batteries to minimize 12-volt loss, and to have long 120-volt cables because the AC voltage drop is minimal.  So several small inverters is not necessarily a good way to go.

Re: Thoughts on Inverters

Reply #6 –
My experience with running small inverters from auto (or motorhome) cig sockets is not good. The 12 volt wiring in foretravel is larger than SOBs (I had to rewire cig sockets in my SOB to make them useable). Running a 125 watt inverter from the cig socket in my Suzuki caused the inverter to squack low voltage, and measuring at the inverter confirmed. There was a 15 amp fuse in the circuit, so draw was less than 15 amps, and while a cig lighter worked OK, wiring is undersized for an inverter.

I ran #8 wires from the battery to under the dash with a 40 amp fuse and two dedicated sockets under the dash. I am now able to run a 400 watt inverter in the Suzuki.

Running a 400 watt inverter which sees 12 volts requires 28 amps at 90% efficiency (25amps at 100% efficient) at full load. If the inverter sees 11 volts at full load, amps will be 40. To be safe, I would check the voltage at your inverters when drawing near full power. If you measure 12 volts, you are good to go, but less than 11 volts, watch for signs of over heating.







Wyatt
96 U320 40 WTFE, build 4943
84 Toyota Supra towd
2015 Jeep Wrangler towd
Victoria, BC, Canada