question on inverter for system

aj-ky · January 2014

I am planning on installing some shop lights and a security camera in a remote barn and have a question or two related to selecting the inverter. First of all I am just now learning the electrical side or at least trying to.

When determining the wattage of the invertor should I just add up the max wattage of all devices ? (For example 2 lights + camera and maybe a radio) .

Also, for a basic setup like this should I go with a true sine invertor vs a modified sine invertor? I could possibly expand this at some point and want to make sure I don't skimp on something and end up buying something else a little further down the road. It seems like the more expensive true sine wave invertors come with more options for failover and readouts than the modfiied sine wave invertors. I've been looking at the Xantrex Prowatt invertors.

Any help would be appreciated.

thanks!

Cariboocoot · January 2014

Re: question on inverter for system

Welcome to the forum.

You're right about the inverter size: all the Watts that will be used together at any given time.
Considering the type of equipment you'll be using it will probably be a small inverter, perhaps something like the Morningstar 300. I would not bother with MSW for electronic equipment. It can induce 'noise' and perhaps damage the power supply (depending on how it is built). I just don't think MSW is worth the gamble for the price difference these days.

If you are thinking about future expansion, think carefully; increasing the size of an existing system is not easy even when you do plan for it. By the same token, putting in a 3kW inverter that will draw 20 Watts running when you only need 200 Watts that could be supply by an inverter that uses 6 Watts doesn't make sense either.

Put the plans down on paper and weigh the options. It saves a lot of headache ... and money.

aj-ky · January 2014

Re: question on inverter for system

Thanks Cariboocoot. I will check out the Morningstar and plan things out. I'm sure I will have quite a few more questions as I get further along in this project. Thanks again.

aj-ky · January 2014

Re: question on inverter for system

Are there any specifics I should look at when selecting the charge controller, battery and solar panel if I go with the 300w inverter?

westbranch · January 2014

Re: question on inverter for system

You can also use 2 or 3 inverters to run different loads, TSW for sensitive electronics and MW for old style incandescent lights, CFL's may or may not work with MSW, you just have to test them ... same for LEDs, motors like TSW but will run on MSW..... generally they may run hotter.

Ask away.

Cariboocoot · January 2014

Re: question on inverter for system

What you pick first is a battery or batteries that will supply the required Watt hours you need for running everything. Determining that can be difficult unless you can plug each item into a Kill-A-Watt meter (about $30) and really measure it beforehand.

After the battery capacity is determined the panel & controller will be sized to recharge that.

aj-ky · January 2014

Re: question on inverter for system

I do have the kill-a-watt meter. I will test the watt hours with a few devices and go from there. Thanks

jcheil · January 2014

Re: question on inverter for system

aj-ky wrote: »

I do have the kill-a-watt meter. I will test the watt hours with a few devices and go from there. Thanks

Remember at night, the security cameras will draw more power because the IR LEDS will be on. So, better off running the whole system for a day or two on the Kill-A-Watt meter so you see the total consumption.

aj-ky · January 2014

Re: question on inverter for system

the camera i was using was only registering 2 watts and 4 watts with the IR on. it was showing .036 kwh. does that sound correct?

also the lights i am looking at show a wattage 0f 145 watts. So 2 of those withe the camera doesnt leave much room for anything else using the 300 watt morningstar inverter. Should i plan on getting a bigger inverter and if so are there any recommendations? looks like the morningstar only goes to a 300w inverter.

thanks.

icarus · January 2014

Re: question on inverter for system

What lights are you using that draw 145 watts?

Can you use different lights?

Icarus

aj-ky · January 2014

Re: question on inverter for system

I am wanting to get 2 shop lights for the barn. I was thinking these LED lights would be sufficient and that they would be more efficient than flourescent

http://www.homedepot.com/p/Lithonia-Lighting-2-ft-White-LED-High-Bay-Light-IBH-11L-MV/203812710?N=5yc1vZwvZ1z115g2

aj-ky · January 2014

Re: question on inverter for system

The plan would be to have the camera on at all times (motion activated) and then the lights would be on a max of 5 hours twice a week (possibly more in the future).

PhilS · January 2014

Re: question on inverter for system

Nice lights!! The reviews are glowing.

Looks like you should be looking at 1000watt inverters?

Phil

aj-ky · January 2014

Re: question on inverter for system

Would you say a 1000w inverter just for expansion? or do you think the 300w would not handle those 2 lights and a camera?

Thanks.

jcheil · January 2014

Re: question on inverter for system

It's my opinion to never run anything at it's "max" all the time. Even for generators where it really starts to effect fuel consumption and engine life. Now with an inverter, I am no expert but I would think that running electronics like that near its max 24/7 would put more stress on it. IDK.

Cariboocoot · January 2014

Re: question on inverter for system

jcheil wrote: »

It's my opinion to never run anything at it's "max" all the time. Even for generators where it really starts to effect fuel consumption and engine life. Now with an inverter, I am no expert but I would think that running electronics like that near its max 24/7 would put more stress on it. IDK.

Yes.
And then again no.

An off-grid inverter is best kept below its maximum power rating because more power inevitably means more heat generated and electronic components don't like heat.

By the same token, running and inverter capable of 3.5 kW to supply say <500 Watts is a bit of a waste too as the inverter will consume the same 20 Watts of power for itself as it would at full output. So it's a waste of an inverter and energy.

On the other hand a grid-tie inverter is best kept 'over paneled' because whereas it may reach its maximum output, this will not happen all day long. So even though it may spend 4 hours running at full, the rest of the time it runs at less all the way down to zero. They're built (or should be) to operate this way. In truth the thermal cycling is harder on them than the constant output level.

The point being you have to consider both the peak load and the constant. Occasional peaks can be handled without difficulty. If you expect a constant load of >80% of the rated capacity, get a bigger inverter.

solar_dave · January 2014

Re: question on inverter for system

It doesn't say how much they draw but even 2 of the 300w morningstar should do the trick.

aj-ky · January 2014

Re: question on inverter for system

thanks fellas. I had to end up going to the manufacturers website to find the wattage on the light.

aj-ky · February 2014

Re: question on inverter for system

I decided to go with a smaller light that will max out a 128 watts. These lights would be on a max of 10 hours a week. I will also have the camera which is a max of 5 - 6 watts and will run continuously.

I believe I will go with the morningstar 300 as the inverter. How would I go about selecting the # of batteries, solar panels, etc.. ?

Thanks.

Cariboocoot · February 2014

Re: question on inverter for system

Math: it's your friend. No, really.

Total Watts * hours on = Watt hour demand.
Since this is AC you have to convert to DC using the inverter's efficiency rating. Then add in the inverter's own consumption. This will get you the DC Watt hours the batteries need to supply. Divide by nominal system Voltage (in this case 12) to get Amp hours used.
Amp hours of the battery is a matter of Amp hours used vs. DOD. Discharge should never exceed 50%, so the Amp hours used should be multiplied by 2 at least, and 4 is better. You should then round up to the nearest available battery capacity. You can round down only if you have some control over the usage.

Note the 'fudge factors': using nominal battery Voltage, rounding up, and discounting any power drawn directly from solar panels. It is better to have too much power available than too little, and it should be remembered that battery capacity will go down over time.

Once you have the battery bank size determined you can set the peak charge current as 10% (works for most cases) and select charge controller capacity calculate array size. For example if you were using two 220 Amp hour 6 Volt batteries (220 Amp hours @ 12 VDC) you'd go for 22 Amps peak current. That means the charge controller should be able to handle >22 Amps. The array would then be:
If PWM controller multiply Amps * Vmp for system i.e. 22 * 17.5 = 385 Watt array.
If MPPT controller multiply Amps * nominal Voltage and divide by 77% typical efficiency i.e. 22 * 12 / 0.77 = 343 Watt array.

Again you should round up to the nearest available panel size.

If you have adverse conditions to work with you may want to increase the array size.

BB. · February 2014

Re: question on inverter for system

I will guess at the loads as:
128 watts * 3 hours a day (lights max per day) = 384 WH per day
6 watts * 24 hours a day (camera) = 144 WH per day
6 watts * 24 hours a day (inverter tare) = 144 WH per day
=================================================
672 Watts of AC power per day (note quite true with AC tare losses--But just keep things simple/error on conservative side)

Battery size:

672 WH per day * 1/0.85 AC inverter eff * 1/12 volt battery bank * 2 days of storage * 1/0.50 max discharge = 264 AH @ 12 volt battery bank

A pair of T-145 6 volt @ 260 AH batteries wired in series would be about a perfect

To figure out the size of the solar array--First we need to size based on AH size of battery bank, and second is based on amount of energy used and hours of sun per day...

A battery bank should have around 5% to 13% rate of charge... Using typical rules of thumbs:

14.5 volts * 265 AH * 1/0.77 panel+controller derating * 0.05 rate of charge = 250 Watt array minimum
14.5 volts * 265 AH * 1/0.77 panel+controller derating * 0.10 rate of charge = 499 Watt array typical
14.5 volts * 265 AH * 1/0.77 panel+controller derating * 0.13 rate of charge = 649 Watt array "cost effective maximum"

In this case, you will be running loads during the day... So you should add the amount of power consumed by the constant day time loads too (especially if you go with a smaller 5% array, daytime loads can make the charging current too small for the battery bank):
12 Watt daytime load * 1/0.85 inverter eff * 1/0.77 panel+controller derating = 18 watt panel to support a 12 Watt 120 VAC load

So, you should take the above panel ratings and add 18 watts to get the amount of array to "charge" the battery bank... I.e., 5% array is 250 watts + 18 watts = 168 watt array minimum. Where day time loads are larger, the extra array needed will be greater.

And then there is sizing the array on energy used per day. Using PV Watts for Cincinnati Ohio, fixed array, tilted to 40 degrees from horizontal:

Month    Solar Radiation (kWh/m 2/day)
1      3.08     
2      3.54     
3      4.08     
4      5.17     
5      5.32     
6      5.54     
7      5.44     
8      5.68     
9      5.05     
10      4.79     
11      2.88     
12      2.36     
Year      4.41

Toss the bottom three months (use generator), gives you 3.54 hours of minimum sun for February:

672 WH per day * 1/0.52 system eff * 1/3.54 hours of sun per day minimum = 365 Watt Feb "break even" array

So, the array should be somewhere between 365 Watts to (649+18=) 667 Watts... Depending on how much power you use in winter/are OK with using a genset (more lights in winter, or not working there as often in winter/etc.).

-Bill

aj-ky · February 2014

Re: question on inverter for system

Thanks for all the info so far. I finally received the inverter and had a question related to the grounding since this is going to be an off grid setup. Do I just need to put an 8 ft. grounding rod in the ground and hook it up to the inverter?

Also, in the morningstar 300 setup guide. It says to "wire the white ac line wire to the earth ground". If I understand that correct I will have a ground wire on the AC side that will terminate to the grounding rod and also a wire from the grounding terminal on the inverter that terminates to the grounding rod. Does that sound correct?

With my setup I will have normal home wiring that will hook up to the inverter. So I assume the above will be the green ground instead of the white wire.

Thanks again.

vtmaps · February 2014

Re: question on inverter for system

aj-ky wrote: »

Also, in the morningstar 300 setup guide. It says to "wire the white ac line wire to the earth ground".
<snip>
With my setup I will have normal home wiring that will hook up to the inverter.

What morningstar is referring to is called "neutral-ground bonding". In most normal homes the bond is in the main circuit breaker panel and there is a ground rod near the main panel. You must only have one neutral-ground bond in your system. My first question to you (before I can answer the other questions) is "What sort of wiring and grounding do you have in the home already?"

--vtMaps

aj-ky · February 2014

Re: question on inverter for system

This is a completely new setup in an off grid location (barn) so no grounding at this point (nothing is setup). My plan would be to put a grounding rod in outside the barn.

Thanks.

aj-ky · February 2014

Re: question on inverter for system

If I go with 2 grounding rods off AC side. Is there any code for grounding the DC side as far as # of rods and distance apart or is it all the same? Also can I ground the AC and DC side to the same grounding rods or should they be seperate?

Thanks again for all the help.

Cariboocoot · February 2014

Re: question on inverter for system

aj-ky wrote: »

If I go with 2 grounding rods off AC side. Is there any code for grounding the DC side as far as # of rods and distance apart or is it all the same? Also can I ground the AC and DC side to the same grounding rods or should they be seperate?

Thanks again for all the help.

For one thing the two ground rods must act as one single grounding point. For another the DC grounding (if any) should go to the same point. I say "if any" because if the system is required to have DC ground fault protection there is no direct connection between negative and ground.

aj-ky · February 2014

Re: question on inverter for system

As far as the DC ground, I am thinking the DC ground is the ground on the morningstar inverter. Let me know if that is not a DC ground and just a ground off of the inverter.

Thanks Cariboocoot.

Cariboocoot · February 2014

Re: question on inverter for system

aj-ky wrote: »

As far as the DC ground, I am thinking the DC ground is the ground on the morningstar inverter. Let me know if that is not a DC ground and just a ground off of the inverter.

Thanks Cariboocoot.

Lots of people make this assumption. It is incorrect. The ground on an inverter case is the ground for the case and is not necessarily connected to negative. One of those things you need to check for the particular inverter involved. Easy to do though; with everything disconnected you just check continuity between the ground lug and the negative terminal or wire.

smatthew · February 2014

Re: question on inverter for system

The security camera can probably be powered directly from the 12v battery bank. Would reduce the power usage slightly.

BB. · February 2014

Re: question on inverter for system

check the DC input voltage range on the camera closely... You need to accept ~10.5 to 15.5 VDC. That is a realitively wide input voltage range and not all devices are happy with that range (and some have failed).

If the camera system is "cheap"--It may be worth the risk. If this is an expensive system--Then you may not want to experiment.

-Bill

smatthew · February 2014

Re: question on inverter for system

I do a bit of cctv installation on the side, and most cameras I run up against will accept a large range of DC voltages. Quite a few take both 12VDC and 24VAC on the same input. A lightly loaded 24VAC transformer can easily deliver almost 40V peak. After rectification, you're still looking at 39V DC.

I just pulled out a cheaper camera that I replaced last week. It's a 12VDC camera, and it's internal regulator is good up to 35VDC.

My experience: I have 3 different models of cameras, a DVR, and LCD panel directly connected to the "12V" bus on my solar trailer, so they've even experienced equalization voltages, no problem. Of course, Your Mileage May Vary.

question on inverter for system

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