Inverter Question

spanel · April 2011

Im planning a smallish solar setup with a genertor backup... I will have a Transfer relay hooked up to the main breaker in the cabin.

So I know the genny get tied into one side of the relay and an inverter in the other...

My question is this..

Im looking at a 600 Watt Samlex Pure sine wave or maybe the 1000 watt. Both have 2 plugs for the 120. Do I just put a heavy duty cord in one outlet and splice the other end into the relay transfer switch?

Thanks!

p.s. All I would use the Inverter for is maybe 2 ceiling fans, 1/2 dozen CFL's.. I know the 1000 is overkill.. but maybe I want to use a microwave every now and then? Or just the 600 and get a small microwave or turn the genny on if i want to use that?

Thanks again!

Chris

Cariboocoot · April 2011

Re: Inverter Question

There's a couple of different ways you could go about this.

First off, never mind the 1000 Watt unit for running a microwave: chances are good it won't do it. I have a "700 Watt" microwave, but that is a cooking power rating; it actually draws over 1000 watts. Your best bet is to fire the gen when needed for this.

As to wiring it all in, if you don't want extension cords looped all over the place then yes you can feed a "main distribution panel" off a short, heavy cord plugged into the inverter. Remember that the inverter is going to "fault" before any breaker trips: 600 Watts is only 5 Amps @ 120 VAC and breakers tend to be 15 Amps.

You will need some method of recharging the batteries from the generator. The Samlex units do not have built-in chargers, so you'll need a stand-alone battery charger. You can use a cheap, automotive type to do the bulk charging and then allow the solar panels to finish charging to proper levels through the controller.

Another thing you might consider is wiring heavy loads to a distribution box, including a charger to feed the batteries. Then just connect the light loads to the inverter via a junction box. This way there is no transfer switch and the inverter's output is fully isolated from the gen's at all times.

If I were you I'd think long term too; what will you want the system to do in the future It is possible to plan ahead for expansion at least a little bit if you take that into consideration.

Most important is to get as accurate as possible numbers for expected use in terms of Watt hours per day. The whole design will hinge on that figure.

mike95490 · April 2011

Re: Inverter Question

NO ! Don't splice a suicide cord to the inverter/transfer switch. yet.

Please draw a line/block diagram of this, sometimes, just when you think you have it nailed, the smoke comes out of all the parts.

Can your inverter have one leg grounded ? Can your generator ? Don't cross the grounded legs in the transfer switch ! You say Off-grid cabin, does that mean it was never connected to the grid or a power panel ? I'm thinking of old, hidden ground rods wired somewhere, or a water pipe ground.....

Get a charger too, when you run the genset, use it's extra capacity to boost your batteries.

Cariboocoot · April 2011

Re: Inverter Question

As Mike said, "clean" wiring is essential to any install. That's why I mentioned totally isolating one AC system from the other. watching out for extra, accidental grounds and neutral-ground bonds can be a problem. Samlex is a pure sine inverter and should have no trouble with 'standard' house wiring practices.

If you get a handle on loads you might also consider a Morningstar 300 Watt inverter: http://www.solar-electric.com/mosu300wasiw.html They are well liked by many of the posters here, if that size would fit your needs.

icarus · April 2011

Re: Inverter Question

Even a pair od sure sine 300s, with each wired to one side of the buss of a split phase panel, each powering given set of loads. I second the notion of not powering the microwave. A big current draw regardless of the inverter size. Starting current is likey to be much greater than the battery and inverter can handle.

Tony

spanel · April 2011

Re: Inverter Question

This will be all from scratch.. the building is not even built yet.

Thanks

Chris

Paul54 · April 2011

Re: Inverter Question

I just checked the Samlex web site, and those particular models do not tolerate their "neutral" conductor to be grounded. If you are trying to transfer to existing branch circuits be sure your transfer switch can switch both hot and neutral. Also use a meter to be sure all the branch circuits are isolated completely from each other, with no hot neutral swaps or grounded neutrals downstream of the breaker panel.

If you are putting in the wiring, just be sure to only bond neutrals and ground at your main panel, but do your transfer switch such that you remove the neutrals form the ground bond when using the Samlex. Do keep the Samlex's equipment ground connection tied to your main system ground at all times.

icarus · April 2011

Re: Inverter Question

That is another advantage of the Suresine, it permits a grounded neutral.

Tony

mike95490 · April 2011

Re: Inverter Question

icarus wrote: »

That is another advantage of the Suresine, it permits a grounded neutral.

Tony

And, for short term (10 min) it's rated for 600W. That's sort of burried in the paperwork.

spanel · April 2011

Re: Inverter Question

So basically what you guys are telling me, Im better off with the Morningstar because 300watts/600 surge is good enough to run a few CFLs and 1/2 ceiling fans... and its also easier to wire because I dont have to worry as much about grounding issues?

Thanks!

Chris

icarus · April 2011

Re: Inverter Question

That would be my suggestion.

Unless you are routinely going to run near 300 watts of load, it is certainly would be my choice.

T

spanel · April 2011

Re: Inverter Question

After much thought.... a tv/sat might be added to the mix down the road. If I needt to go a bit more than 300 but less than 500watts.. what would you guys suggest as far as inverters?

thanks!

p.s. Was thinking.. worst case senario..

3 ceiling fans with 3 lights
26" led tv.. looked like approx 50 startup 25 avg watts
sat reciever 25 watts

50watts approx for the fans, 13 watts cfls..

117watts for the cfls, 150 for the fans.
75 watts for tv/sat

so we are at 342 watts.

Thanks again!

BB. · April 2011

Re: Inverter Question

What are you looking at for battery bank voltage and hours of usage per day...

You are still looking at a small system and 12 volts is still very practical, but as your power usage goes up, your solar array and battery bank will get larger.

You can save some significant money on higher voltage battery banks because many solar charge controllers are rated at 12/24/48 volt output. 24 volt will handle 2x the power as 12 volt, and 48 volt 4x the power as 12 volt...

Larger MPPT type charge controllers are not cheap, and upping the battery bank voltage can allow you to stay with one charge controller instead of 2 or more. Smallest good quality MPPT is 15 amps (Morning Star 12/24 volt output). And there are 30 amp, 45 amp, 60 amp, 80+ amp MPPT's too...

15 amp * 14.5 volts * 1/0.77 derating = 282 watts optimum maximum solar array
15 amp * 14.5 volts * 1/0.77 derating = 565 watts optimum maximum solar array
etc.

-Bill

spanel · April 2011

Re: Inverter Question

for the most part.. we will have a genny running during the day.. the load refered above...

at most all things would run 2-3 hrs. Maybe 1 fan all night (8hrs).

Looking at 4 -t105re trogans.
135watt solar panel
genny charging during the day when neccesary.

Chris

BB. · April 2011

Re: Inverter Question

Chris,

spanel wrote: »

for the most part.. we will have a genny running during the day.. the load referred above...

at most all things would run 2-3 hrs. Maybe 1 fan all night (8hrs).

117watts for the cfls, 150 for the fans.
75 watts for tv/sat

(117w + 150w + 75w) * 3 hours = 1,026 Watt*Hours
50 watt fan * 8 hours = 400 Watt*hours
==================================
1,426 WH of 120 VAC power per night

Assuming 2 days of no sun (1-3 days recommended) and 50% maximum discharge for battery bank:

1,426 WH * 1/0.85 inverter eff * 2 days * 1/0.50 max discharge = 559 AH @ 12 volt battery bank

Minimum solar array assuming at least 4 hours of full sun per day (usually around 9 months a year for many locations):

1,426 WH * 1/0.52 derating * 1/4 hours of sun per day = 686 watts of solar panel minimum

Optimal battery bank charging with solar panel (5-13% typical rule of thumb, ~10% rate of charge for flooded cell batteries as optimum):

559 AH * 14.5 volts * 1/0.77 derating * 0.10 rate of charge = 1,053 AH "optimum" solar array for flooded cell battery bank

Looking at 4 -t105re Trojans.
135watt solar panel
genny charging during the day when necessary.

Your 4xT105RE batteries at 6 volts each (225AH) would be 450 AH @ 12 volts... A bit small, but within reason.

Your solar panel is way too small for the daily loads--You would need to use the genset to get the battery bank recharged.

Unless you are thinking about reducing the loads somewhat... Most people underestimate their loads and over estimate what a solar PV system can supply.

-Bill

spanel · April 2011

Re: Inverter Question

It wont be a daily residence.... fri/sat night only when used.

Chris

BB. · April 2011

Re: Inverter Question

Personally, I would use a Honda eu1000i/eu2000i for the 3 hour evening loads and use the battery for fan/random lighting at night... And a smaller battery bank to better match the solar array, lesser needs.

You don't want to discharge the battery to 50% and then let it take 5 days to recharge with a small solar array--More than likely, the batteries will die sooner (year or so?) because of sulphation during the time it takes to recharge from 50% to >75%... Of course, you can use a genset on Sunday morning to quickly recharge the larger batter bank above 75% state of charge, and let the solar array finish them off (when needed).

-Bill

icarus · April 2011

Re: Inverter Question

Consider using two sure sine 300s each wired to one side of a slit phase buss.

Then wire your loads so that they are split between e two busses. The standby/idle current of the sure sine is small enough not to e a real problem, and they are quite efficient.

Tony

westbranch · April 2011

Re: Inverter Question

re: using the 300w inverter for a TV/Sat/ receiver,
you could test the inverter at home (use a car battery for 12v test) to see if it will handle the load. If not get a second slightly larger inverter...

hth.
Eric

Inverter Question

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