Correct wiring for a system with integrated inverter/charge controller

Re: Correct wiring for a system with integrated inverter/charge controller

dakaz wrote: »

This statement alone is making me think that this is not the right system for us! I will continue to explore other options but I do like the AC charger in the inverter and the ATS, is there another unit youd recommend for inverter/ATS/AC Charger or should I truly source them each independently?

We try here to first, spend your money (:p) on known good/reliable equipment. If your wallet (or spouse) does not agree, we will try to help you with other choices.

Second, I am on grid and just use a backup generator (have not had to fire one up for 20+ years--Yet). So, I can give you some equipment to look at--Others can help with their feedback--But it will have to be your choice (us moderators are not in the Solar Business, and we have no connections with NAWS other than as volunteer moderators on this forum).

• Schneider with the XW Hybrid inverter family has a pretty solid/reliable unit with lots of feature. A few have had isssuses. Most love their phone support, others not always.
• Xantrex (the consumer/RV arm of Schneider now)--Has their ProSine (sp?) series which a lot of people here have used over the years and found them to be very reliable and lots of surge capabilities.
• Outback has been a gold standard for years with their inverters and charge controller--And their tech support. They have been, at times, a bit slow to upgrading their product lines (difficult to upgrade firmware in the field) and you have to pick the "right inverter" for the optimum off grid+generator support.
• Magnum--Really like their product line. They were among the earliest that offered split phase 120/240 VAC inverter/chargers without needing external transformers and/or "stacked" inverters. Seems to be the 80/20 Rule--80% are very happy and 20% seem to be less than thrilled with voltage stability/surge.
• Exeltech makes very rugged inverters and if one ever fails, it is something like $100 to return to factory to get it repaired/rebuilt)
• Samlex (and their sister brand Cotec) are good quality at lower costs.
• MorningStar makes a killer 12 volt 300 Watt TSW inverter--But nothing else at this time.
• SMA products are always great German Engineering--And in the US, not cheap. Not a wide product line (at least in the US). The SunnyIsland is a wonderful product for what it does (and does it very well--using GT inverters for off grid/local power AC power networks).
• Victron (Europe) also makes good equipment too...

So, hardly any of what I typed will help you that much... So, I like to go back to what it is you need. 120 VAC? 120/240 VAC? You want an Inverter+Charger or separate Inverter + AC charger (pluses and minuses for both). Inverter+Chargers are usually highly programmable and can make it much easier to run a smaller (and more fuel efficient generator--If your loads are not heavy) vs a off the shelf AC charger and random genset.

Next, features. Remote metering/Control? 24x7 power (usually needed if you have an Energy Star refrigerators--they cannot have their AC power interrupted or they go into defrost mode when power is restored). Otherwise, you can use "search mode" on the AC inverter (sleeps for a second, then blips the AC line looking for >6-10 watts of AC load, inverter turns on if it "sees" AC loads).

Check the "tare" power of the inverter--Many inverters have very high "on/no load" current (10-20 watts or more). And TSW inverters usually have higher tare power requirements vs MSW. For smaller off grid system--this can be 1/3rd of your loads or more (inverter Tare). For larger systems, the 24 hour "always on" tare of the inverter is less of an issue.

All About Inverters
Choosing an Inverter - Home Power Magazine

You can pick an inverter with an Automatic AC Transfer Switch, or you can even get (or even make) simple ATS relays for not too much money.

Not sure I follow. The panels I am planning on using are these: http://solarsystems-usa.net/solar-panels/et-solar/et-p672280ww

That panel does have Maximum Power Voltage (Vmp)=35.54V

As long as you are using a 24 volt battery bank--That will work OK with either PWM (cheaper) or MPPT (more expensive).

If you have a fair distance from the array to the charge controller+battery bank--Then using an MPPT controller and putting 2 panels in series to raise Vmp-array can save you a lot on copper wiring costs.

Here are my loads, total is just shy of 150 aH per day.

Device    Volts    Watts    Hours / Day    Amp Hours / Day    Qty    Total aH/Day
                        
Inverter    24    1    24    1    1    1
Light    120    15    6    0.75    8    6
Fridge    120    360    24    72    1    72
Well Pump    120    600    3    15    1    15
Toilet    120    370    18    55.5    1    55.5

I am confused about your table...

Toilet 120Vac 370Wac average load? 18hours/day? 55.5 1 55.5

• 370 Watts * 18 hours per day = 6,660 WH per day = 6.7 kWH per day
• 6,660 WH per day * 1/0.85 inverter eff * 1/24 volt battery bank = 326 AH per day @ 24 volts

It may be you are confusing Amp*Hours at 120 VAC vs Amp*Hours at 24 VDC...

• 6,660 WH / 120 VAC = 55.5 AH @ 120 VAC

Both 326 AH and 55.5 AH are "accurate" answers... However, remember that energy is voltage dependent:

• Power = Volts * Amps = Watts
• Energy = Volts * Amps * Hours = Watt*Hours

But Amps and Amp*Hours are "missing" the voltage component:

• AH = Amps*Hours
• Amps= Amps

So, 2 amps at 120 VAC will look like:

• P=VI= 120 VAC * 2 Amps = 240 Watts load
• I=P/V= 240 Watt load / 24 volts = 10 amp load on your 24 volt battery bus (ignoring inverter losses)

So, you will need to rethink your numbers/loads up there... Stay with Watts and Watt*Hours until you need to pick a battery voltage (and inverter losses/efficiencies). You will not get in the trap where 24 VDC current is 5x larger than 120 VAC current (and therefore needs 5x as much battery AH for storage and 5x as much solar panels for "power" and "energy").

Watts and Watt*Hours (WH, kWH, etc.) a "complete" unit--Amps and Amp*Hours are "incomplete units" and need voltage to fully quantify what they "mean".

If you were working on a boat or a truck with a 24 VDC power system--You can stay in Amps and Amp*Hours because everything is at "24 volts". Not so when you throw a 120/230/240 VAC inverter and 12,24,48 volt battery banks. Confusion galore.

You can see my loads above. I was planning on buying 6 12V sealed batteries (lower maintenance for our occasional use cabin) like these http://www.apexbattery.com/12v-200ah-4d-deep-cycle-agm-solar-battery-ub-4d-also-replaces-210ah.html

Ignore the battery choices for the moment (AGM are "ideal" lead acid batteries--Their downside is that they are ~2x as expensive and typically last a couple of years less than flooded cell--But they still may be "worth it" for you).

Until we have your power needs nailed down--We don't need to go any further (farther?) down the battery+solar panels+hardware isle yet.

At this point, your 120 VAC to AH calculations (and probably your load watts) are not correct. As listed, just your toilet alone consumes about as much power as my 3 bedroom suburban home consumes in a day.

-Bill

Re: Correct wiring for a system with integrated inverter/charge controller

Just for an example with a typical Energy Star full size fridge that uses ~1.2 kWH per day... The average load is around 130 Watt*Hours:

• 1,200 WH per day * 1/130 Watts = 9.2 hours of "on time" per 24 hour day.

So--working with the above "knowledge":

• 130 Watt average load * 9.2 hours (per 24 hour day) = 1,196 WH per day = 1.2 kWH per day with rounding...

The DC AH energy per day would be (all in one formula):

• 1,196 WattHours * 1/0.85 Inverter Efficiency * 1/24 volt battery bank = 58.6 AH @ 24 volts

And this is why a Kill-a-Watt type meter is really nice... A frost free refrigerator may use ~120 watts 8.5 hours per day, 600 watts for 20 minutes per day, and 2 watts the rest of the day (plus 650 VA starting for a few seconds per cycle). You would go nuts trying to profile the detailed energy usage without a data logger.

For basic planning, you just plug in the K-a-W meter into the wall, and the appliance into the meter for 1-3 days and it will tell you kWH used over XX hours, you convert to what you need--For WH per day:

• 3,600 WH * 1/72 hour test * 24 hours per day = 1,200 Watt Hours per day (notice my units match :-))

I suggest you just collect appliance name, average watts and kWH per day (or per time period and convert to per day as above). You can also write down the VA and PF too (useful, but not required for sizing of system).

And then we just run it through the Rules of Thumbs equations... Don't even bother with 12/24/48 volt battery bus, conversion and storage losses, etc... It is just confusing you right now. The rules of thumbs will get a system design that is "close enough" for you to do a design/economic analysis... if you want to do the math--we can help you with that too once you have the 50,000 foot view of the project.

-Bill

Re: Correct wiring for a system with integrated inverter/charge controller

dakaz wrote: »

Lastly, do most DC Inverters with chargers charge from the same input terminals?

Just to be clear--The Solar Charger (PWM or MPPT) is one black box (mounted close to the battery bank to keep wires short) between the battery bank and the solar panels. Its job is to control the energy flow from the Solar Array to the Battery bank.

A PWM controller is a "simple on/off switch". Depending one how long the distance is and what brand/model/Vmp solar panels you get--You can use a PWM controller on a larger system.

However, once you go to a larger array (say over 800 watts), you really should be looking at a MPPT type charge controller (much more expensive, and usually a lot more bells and whistles too).

The two main reasons MPPT controller are really nice--One is they have a buck mode switching power supply which can take high voltage/low current and efficiently down convert to low voltage/high current needed by the battery bank (95% efficiency or so). This allows you to use higher Vmp-array voltages (upwards of 100 volts or more) and use smaller awg wire to ship the power back to the battery bank.

The other major reason is because solar panels provide maximum Power at a specific operating point (Pmp=Vmp*Imp)... Basically there is a "sweet spot for the voltage" that the MPPT controller "holds" and as the sun changes, the Imp moves about too.

For example, very common (and much cheaper) 240 watt panels may have Vmp in the range of 30 volts DC and Imp~8 amps. And you want to charge a 12 volt battery bank. Without the MPPT controller (PWM type), you would get:

8 amps Imp * 12 volts Vbatt-charging = 96 watts into teh battery bank or 8 amps

With a MPPT type controller, you would get (roughly):

30 volts Vmp * 8 amps Imp * 0.77 panel+controller derating = 184.8 Watts into battery bank
184.8 volts * 1/12 volt Vbatt charging = 15.4 Amps charging into 12 volt battery

These are real numbers and reflect why MPPT controller are very popular--especially with larger installations.

The "Inverter/Charger" is a completely different animal. It is very much like UPS you would buy for your computer (uninterruptable power supply).

There are one or two AC power sources (grid+generator for some units). Those go into the inverter and can pass through to power your AC loads (from grid or backup generator).

At the same time, the Inveter/Charger can bleed a little power from the AC power coming in, and recharge the Battery Bank (in parallel with the solar charge controller too--if one is present). If the AC power goes away, then the inverter cuts in and powers the AC loads from the battery bank (internal automatic transfer switch).

Some of the never AC inverter/chargers are getting very complex... They can "blend" generator AC power and charge the battery bank or even draw from the battery bank and supply power to the AC loads--"Generator Assist" is one term you can use. You program (for example) for the generator to output a maximum of 15 amps of 120 VAC--And the inverter will split the power between the AC loads and charging the battery bank. If the AC loads exceed 15 amps, the inverter will (seamlessly) starting pulling power from the battery bank and help power the AC loads (starting a well pump, running the microwave, even running an electric stove).

The options/capabilities of various pieces of hardware out there today are amazing... If you can think of what you want, there is a good chance that it can be done with off the shelf hardware. Chris Olsen wrote a nice writeup on generator support and some other generator topics (you will need a good genset and installation that far north):

Choosing a good generator
genset alternator failure (and if your generator is not generating AC? What to look for/do--Thread started by "Unicornio" from Spain)
Demonstration of Generator Support (A couple inverters that will share AC loads with the generator--smaller generator with large load support)

-Bill