# Eu2000i-rectifier-MX60, charging

Registered Users Posts: 29 ✭✭✭
Hello All

I didn't want to hijack the other thread started by jnoble, but I have a sort of related idea. I know that is very dangerous for a fellow who knows less than nothing.

Brief system description:
12 sharp 123 watt panels wired 6 and 6
1350Ah Rolls battery bank @48 volts
10KW diesel generator
2 Outback vf3648's on FW100 panel
1 MX60

The system is still coming together, but I am concerned about winter production from the panels, I'm located in Seward, Alaska.

I am building a 10 foot otherpower turbine, that got me thinking about a way to top off the bank without running the 10KW diesel at it's least efficient.

Ok, here is my idea.

Run the EU2000i, 120 volt output through a rectifier and input it to the MX60 as DC??? Do the bulk charge with the diesel and finish it off with the EU2000i.

I understand that may be the craziest thing you have ever heard, if so please tell me to go back and stand in the corner some more.

Please keep it simple, as I'm way out of my depth.

Thanks

• Solar Expert Posts: 5,433 ✭✭✭✭
Re: Eu2000i-rectifier-MX60, charging

Why wouldn't you just run the eu into a big conventional charger, like a Xantrex or Iota or something similar? Or how about an inverter/charger?

I am certainly no expert on rectifying current, (only a potentate,,,what ever that is) but it seems like a solution in search of a problem.

Tony
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: Eu2000i-rectifier-MX60, charging

interesting idea, but don't do it as the peak voltage of 120vac is about 170v.
Re: Eu2000i-rectifier-MX60, charging

Regarding rectifier from the generator to the MX60... First problem is that rectified output of 120 VAC is sqrt of 2 * 120 VAC = 170 volts peak DC -- way over the input limit of the MX 60. So yo would need a ~2:1 step down transformer to bring the voltage down.

The other issue is a simple rectifier has very poor "power factor"... This will waste power, not work very well with the generator, and probably require a large capacitor (and perhaps inductor) to filter the rectified DC for the MX 60 to even hope to begin to function correctly... I would not recommend this process at all.

Your better bet, is to get a real 120 VAC battery charger that work well with your eu2000i (and/or whatever gensets you plan on using).

Using a proper battery charger with a "power factor corrected" front end will be better for the generator (more power, less waste).

The Xantrex line and probably the Iota have power factor correction. I would also like that the Xantrex has a battery temperature sensor option too (cold batteries need higher voltage to properly charge).

In your case, you probably will have to go with the Iota because they support 48 volt charging. Or, you may have to look around for a used forklift battery charger to run on your diesel genset...

You would want to charge your bank at ~5%-13% charge rate or ~68 amps (~4kW at 60 VDC output) to 175 amps (~11 kWatts)...

One eu2000i would probably be closer to a trickle charger range... Will work--but not very fast--and you would not be able to equalize your batter bank.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Re: Eu2000i-rectifier-MX60, charging

Plus, I should add, that the solar panels themselves are pretty small for that large of battery bank... Ideally, you would want closer to 4kW minimum of solar panels to charge the bank... And/or add in Wind and Generator power (especially when equalizing).

Do you have a good estimate on the amount of power you use during the "sunny months"? Will the panels be enough, or will you need wind+gen to make up for a deficit anyway.

Generally, it is recommended to size the battery to the load (6x your daily load is a good starting point). Then size the charging equipment to properly support the loads+battery requirements.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 29 ✭✭✭
Re: Eu2000i-rectifier-MX60, charging

Thank you for you responses.

The dumbest question is the one you don't ask.

I understand my system is a work in progress. I don't have a good estimate of our power use, however I am trying to build with efficiency in mind. We presently use about 10 KWH per day in the less than efficient house we are in now, which is grid connected.

The reason I came up with the idea is because I already have all the stuff and float charging with the 10 KW Northern lights seems like a waste.

I have already started the wind turbine tower but have run out of warm weather. The 10 foot turbine was for practice and back-up I will be building a 17 footer. I have other things that have to be taken care of before freeze up which is soon.

One other question, BB you wrote "First problem is that rectified output of 120 VAC is sqrt of 2 * 120 VAC = 170 volts peak DC". Is there a name for that theorem , equation, relationship or whatever? When I spin my wind turbine by hand , very unscientific, without any load, the voltage seems similar AC or rectified DC. I am not doubting your statement but my test procedure and results.

Thanks again
• Solar Expert Posts: 9,361 ✭✭✭✭✭
Re: Eu2000i-rectifier-MX60, charging
toothy wrote: »
One other question, BB you wrote "First problem is that rectified output of 120 VAC is sqrt of 2 * 120 VAC = 170 volts peak DC". Is there a name for that theorem , equation, relationship or whatever? When I spin my wind turbine by hand , very unscientific, without any load, the voltage seems similar AC or rectified DC. I am not doubting your statement but my test procedure and results.

Your meter is likely reading the AVERAGE voltage, not the PEAK voltages seen. You really need an O'scope to visualize this the first time. I don't have any images to post, but some of the equations are listed here: http://www.practicalphysics.org/go/Experiment_675.html
Another page here http://www.bcae1.com/voltages.htm has some sketches, but not really good ones.
Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,

Re: Eu2000i-rectifier-MX60, charging

Your average AC volt meter reads "Root Mean Square" voltage... Basically, this is the voltage of an AC wave form that has the same "energy potential" as a DC voltage would (sum of the squares, square root). Have to use RMS because power=(V^2)/R (power is equal to the square of the Voltage divided by resistance). If the voltage was linear (not raised to the 2nd power) the math to figure out the "power" would be like figuring out the area under a triangle 1/2 the base times the height.

The AC read the "peak voltage" of the AC wave form. And, using math, it turns out that the area under a sine wave is related to the peak by by the square root of 2.

A full wave rectifier just takes a the wave form that is centered around 0 volts, and makes it into a pulse train that goes from 0 to 170 volts DC--the RMS of which is still 120 Volts.

The other reason that this simple rectifier circuit is bad for using with a generator... When charging your filter capacitor, the current to charge the capacitor will only flow during the "peak" voltage (say from 150 volts to 170 volts)... This makes the peak current several times the "average current" that a normal generator/wiring would see... And because Power=I^2*R --- when you double the current, you get 4x the heating effect... This can cause your generator/wiring to overheat (this is also known as poor "power factor"). Over the last 10-15 years, many electronic power supplies (nearly all?) have been redesigned to have "power factor" corrected input circuits to get rid of this "peak shaving" effect.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
Re: Eu2000i-rectifier-MX60, charging

12 sharp 123 watt panels wired 6 and 6

Do you mean six modules in series (72 V nominal, ~103 Vmp STC, ~129 Voc STC) with two series strings in parallel?

If so, this is not a good idea in AK. The temperature-corrected array Voc on cold mornings will surely exceed the MX60's 150 VDC maximum input voltage limit spec. It may go high enough to damage the controller, and, since the MX60 records the higherst Voc it ever sees, it may also void the warranty.

The MX60 will suspend operation at ~141 V.

A "60 V" nominal PV array (five 12 V modules in series) is probably the ideal configuration for charging a 48 V flooded-cell battery bank in your location.

HTH,
Jim / crewzer
• Registered Users Posts: 29 ✭✭✭
Re: Eu2000i-rectifier-MX60, charging

Thanks for the information, reading them was easy, digesting them fully will be somewhat more difficult for me.

Thanks for the concern about max voltage output. I understand I am taking a small risk. Yes I have 6 modules in series with 2 strings. Seward has a marine climate, the coldest ever recorded was -19F the coldest I have personally witnessed was -6F and that was at night. I can't think of a daylight temp below 0 degrees F. If I have to shut the panels down for part of the day once in a while so be it. If I forget, that's called an idiot penalty and outback has a better quarter.

Thanks
• Solar Expert Posts: 9,361 ✭✭✭✭✭
Re: Eu2000i-rectifier-MX60, charging

I wonder if a simple 140V zener diode(s) would be enough to "load" an array down, so the open circuit voltage does not exceed the max input.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=751-1449-1-ND @ 14.5 volts, 65 watts ea, a string of 9 [ 130.5V ] might be enough to keep the panel loaded down, till they heat up enough to fall below the MX60's "kill" point. Once the MX60 fires up and seriously loads teh panels down, the open circuit danger should be gone for the day.

Solar Guppy - any thoughts on the matter, of using a hefty zener diode to "shave the peak Open Circuit" voltage ?
Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,

Re: Eu2000i-rectifier-MX60, charging

1.5 kW of diodes on heat sinks is going to be a problem...

And remember, that the Voc could still be an issue during the day--as the battery bank goes from bulk to float charging--the amount of current consumed by the MX60 will drop near zero (don't know if it goes PWM or what)... Other issues (like thunder storm, birds, etc.) quickly shading then unshading the panels will probably also cause issues with the array voltage moving between Vmp and Voc...

Remember that power FETs and Transistors are very intolorent of voltage extremes... Just milliseconds of over voltage can weaken/fail the devices. Add a little inductance in the wiring--who knows.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 1,973 ✭✭✭
Re: Eu2000i-rectifier-MX60, charging

You would need some expensive zeners ... on a large array, even trying to hold the voltage 10V below VOC can pull 100 watts in the early AM easily. I was doing extensive testing on a 100V design with my 54V array ( about 96 VOC in hot weather ) and used an electronic load with constant voltage mode to keep it under 100V , was regularly in the 100-150 watt range for a 2.8kw array until things warmed up

I've thought about this an come to the conclusion is not a reasonable solution ( zeners )
• Registered Users Posts: 29 ✭✭✭
Re: Eu2000i-rectifier-MX60, charging

OK, now you have me somewhat concerned about my cold temp voltage.

Is there a calculator or formula I could use to plug in my temp and panel specs and get a max voltage?

I tried a search but they only work if you ask the right question.

Thanks
• Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
Re: Eu2000i-rectifier-MX60, charging

There are several legacy Sharp 123 W PV modules. Worst case STC Voc spec is 21.8 V; best case is 21.3 V.

Worst case analysis, assuming -19 F low ambient temp, and using NEC 2008 690.7:
21.8 V/module x 6 modules x 121% TCF = 158.3 V
Best case analysis, assuming -6 F low ambient temp, and using NEC 2008 690.7:
21.3 V/module x 6 modules x 120% TCF = 153.4 V
Either way is a problem...

HTH,
Jim / crewzer
Re: Eu2000i-rectifier-MX60, charging

I use the Xantrex Panel Calculator... It lists all of the panels and their specs... Plus seems to do a reasonable job of giving voltage estimates (Vmp hot and Voc cold)... The Vmp/Voc Hot/Cold you have to do a bit of back calculation (basically, it will give you a chart of 8-20 panels--and you will have to divide out and multiply to get your string voltages--if they are not part of the chart.

2. Pick a system (I use the GT 3.0 -- just happens to be the one in my home)
3. Pick your temperature (units, low, high)
4. Read Voc at some easy multiple...

For Sharp ND-L3xxx 123 watt panels:

Max Power Voltage - Vmp 17.2 Vdc
Open Circuit Voltage - Voc 21.3 Vdc
Voltage Temp Coeff - Vtoc -0.072 V/°C
STC Rating - Pmp 123 Wstcdc
Max Power Current - Imp 7.16 Adc
PTC Rating 108.1 Wptc

Temperature Range:
Fahrenheit
0F low
80F high

Voc for 24 panels is 585.12 volts, /4 and get for 6 panels 146.28 volts @ 0F
Vmp for 24 panels is 349.44 volts, /4 and get for 6 panels 87.36 volts @ 80F air (around 144F panel surface temperature)

Voc calculated for 5 panels = 121.9 volts (cold) @ 0F
Vmp calculated for 5 panels = 72.8 volts (hot) @ 80F air (around 144F panel surface temperature)

The Vmp HOT seems to be pretty conservative (assuming ~a 35C or 64F rise above ambient--working the Xantrex numbers backwards)... Or that your 80F panel would be 144F on a windless day...

Long hand... Panels are spec'ed at 77F on a standard temperature and condition day...

Vxx (@STC) - Vtoc*(STC-Panel Temp)
21.3 volts (Voc) - (-0.072V/°C * {77F-0F}/1.8FperC) =24.38 VDC (Voc at 0F)
6 panels in series*Voc (@0F) = 6*24.38v=146.28 volts (6*Voc at 0F)

If you assume your panels will have a maximum surface temperature of 100F on a warm day, then Vmp would be:

Vxx (@STC) - Vtoc*(STC-Panel Temp)
17.2 volts (Vmp) - (-0.072V/°C * {77F-100F}/1.8FperC) =16.28 VDC (Vmp at 100F panel temp)
6 panels in series*Vmp (@100F) = 6*16.28v=97.68 volts (6*Vmp at 100F panel temp)

So--the calculated 0F Voc (open circuit voltage) is high---only 3.72 volts below the point at which your warranty will be voided...

Trying my guesses at what Xantrex does for Vmp Hot (80F, assume + 64F for temperature rise):

Vxx (@STC) - Vtoc*(STC-Panel Temp)
17.2 volts (Vmp) - (-0.072V/°C * {77F-[80F air +64F rise]}/1.8FperC) =14.52 VDC (Vmp at panel temp of 144F)

5 panels in series*Vmp (@144F panel temp) = 5*14.52v=72.6 volts (5*Vmp at 144F panel temp)

Still seems reasonable (you need at least 62-65 volts to charge/equalize your battery)...

So--5 panels in series looks OK... 6 panels in series seems to be cutting it awful close... But, on the other hand, the Voc is a physical property of silicon and should be pretty accurate... To go 3.72 (150VDC) volts higher, your 6 panels would have to go below 0F by:

(3.72V/6panels / -0.072V/°C)*1.8F/C=-15.5F below zero in full sun with a cold panel...

Perhaps Jim or Solar Guppy can give you a better idea of how close you can cut the 6 vs 5 panel voltage decision.

I am getting tired... I might have made one or more mistakes on the above equations (or ran the Xantrex calculator incorrectly, or even the Sharp 123 watt panel data is not the correct data for your panels)... But it all seems self consistent at this point.

The Xantrex calculator is easier--but you can put the above formulas into a spread sheet and play with them pretty easily too.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 29 ✭✭✭
Re: Eu2000i-rectifier-MX60, charging

Thanks for the information.

I have decided to get 3 more panels and make 3 strings of 5 panels each.
Better safe than sorry. My panels are Sharp ND-123UJF, VOC 21.78. I found a temp correction factor chart (NEC 2008, table 690.7) and I was going to be over 150v at anything less than 14 deg f, and we will surely get colder than that when the sun is shining.

I have already welded up the rack and will pour the feet in the morning.

Thanks for opening my eyes, I don't need anymore \$500 lessons.

Thanks