# Balanced MPPT system?

• Solar Expert Posts: 180 ✭✭✭
Re: Balanced MPPT system?

Bill,
I was just about to order marine 6/2 awg marine shielded cable when I remembered the slight confusion about wire runs

3 36v (nominal) panels each run separately to the Morningstar TS-45-MPPT controller. Connected directly to the lugs on the controller.

Assuming a max distance from the panels to the controller of 24 ft (likely a bit less)

What is the proper AWG to minimize loss? I believe its 6 AWG for .34 %loss....but before I order I would like to be sure as the cable is expensive!

Also will 3 6 AWG cables even FIT the lugs on the Morningstar controller??

Thanks!

I'm getting close.

Rick

BB. wrote: »
Assuming 3x panels in parallel with Imp-array~15 amps @ 36 volts and using a generic voltage drop calculator, with ~1-3% voltage drop on a 24' one way cable run:
• 36 volts * 3% = 1.08 volts max recommended drop
• 36 volts * 1% = 0.36 volts min cost effective drop
And using the calculator (trial and error) with 24' one way run:
• 24', 10 awg, 15 amp=> 0.9 volt drop
• 24', 8 awg, 15 amp=> 0.55 volt drop
• 24', 6 awg, 15 amp=> 0.34 volt drop
-Billl
Re: Balanced MPPT system?
Wanderman wrote: »
I was just about to order marine 6/2 awg marine shielded cable when I remembered the slight confusion about wire runs

3 36v (nominal) panels each run separately to the Morningstar TS-45-MPPT controller. Connected directly to the lugs on the controller.

Assuming a max distance from the panels to the controller of 24 ft (likely a bit less)

What is the proper AWG to minimize loss? I believe its 6 AWG for .34 %loss....but before I order I would like to be sure as the cable is expensive!

Also will 3 6 AWG cables even FIT the lugs on the Morningstar controller??

From the manual:
Wire Size
The four large power terminals are sized for 14 - 2 AWG (2.5 - 35 mm2) wire. The terminals are rated for copper and aluminum conductors. Use UL-listed Class B 300 Volt stranded wire only.

Good system design generally requires large conductor wires for the solar and battery connections that limit voltage drop losses to 2% or less. The wire tables in the appendix on pages 51-54 provide wire sizing information for connecting the solar array and battery bank to the TriStar MPPT with a maximum of 2% voltage drop.

I am not sure you need 3x parallel runs of 6 awg cables... The calculations, if I remember everything correctly, are for 3 panels paralleled together, then 1x 6awg (pair) run of 24' carrying 15 amps total. (see bold in quote)

Just to be clear, you are looking at 6/2 as 6awg x 2 wire cable.

And, if you put three panels in parallel--you are probably supposed to put a series fuse between each panel + wire, through a combiner box with fuses/breakers, then they wire to the common + bus to go back the 24' to the solar charge controller.

That fusing/combining is the job of a combiner box. The fusing should be around 1.56 x Isc of the panel (round up to next standard size) if Series Fuse rating is not provided.

Something like one of these (box+breakers, or box+fuses):

Midnite Solar Baby Box Enclosure for 1-4 Din Rail Breakers
Midnite Solar MNPV6 Breaker Busbar
Midnite Solar Fuse Busbar Four Terminal

I am not in this business--so talking with your supplier and getting their suggestions will probably helpful for a small combiner box...

It is also possible that a small fused/breakered combiner box for this application is way overkill...

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 180 ✭✭✭
Re: Balanced MPPT system?

Yes 6/2 AWG is a pair of 6 AWG sheathed conductors inside a another sheath.

Since the wire run is pretty short, I figured I could run 3 separate pairs of cable down directly to the controller.

By:

"The four large power terminals are sized for 14 - 2 AWG (2.5 - 35 mm2) wire"

do they mean 14 TO 2 AWG or 14/2 wire???

Either way based upon my panel specs what wire size SHOULD I use?

Thanks for the help!

Rick
• Banned Posts: 17,615 ✭✭
Re: Balanced MPPT system?

He's saying 14 AWG minimum to 2 AWG maximum, I think.

None of your panels are over 200 Watts, right? And 36 Volts? The Isc under 10 Amps per panel? If you're running parallel wiring - one set per panel - it shouldn't be any trouble on a short run like that.
• Solar Expert Posts: 180 ✭✭✭
Re: Balanced MPPT system?

Yes, they are:

Given the panels spec at:
Peak Power(W) 170
Open Circuit Voltage (V) 44.00±1
Short Circuit Current (A) 5.30±0.2
Max. Power Voltage (V) 36.00±1
Max. Power Current (A) 4.72±0.25
Max. Rated System Voltage (V) 1000
Working Temperature -40℃——90℃
Net Wight (kg) 8.5
===================================
*2 of these*
Peak Power(W) 140
Open Circuit Voltage (V) 42.12±1
Short Circuit Current (A) 4.16±0.2
Max. Power Voltage (V) 36±1
Max. Power Current (A) 3.89±0.2
Max. Rated System Voltage (V) 600
Working Temperature -40℃——90℃
Net Weight (kg) 7

Likely a BIT higher than that since those were preliminary specs.

So for three separate runs all the way to the controller (20 ft-ish) what size should I use?

Thanks,

Rick
• Banned Posts: 17,615 ✭✭
Re: Balanced MPPT system?

Argh! Forgot to answer the question!

Doesn't run on my Linux netbook (neither does PCWatts, et cetera ). Otherwise I'd do the calc for you.

I'll hazard a guess that 12 AWG is plenty, considering how short the run.
• Solar Expert Posts: 180 ✭✭✭
Re: Balanced MPPT system?

Wow! That calculator is precise!

A few caveats for my installation.

I will not be using a combiner box, simply wiring directly into the Morningstar TS-45-MPPT controller. I still have to figure out how to fuse this...3 (one for each panel) or 1 for all three. (of course could do none as well..but I am a bit cautious.

So the run from the combiner box is eliminated on both sides. From controller to battery is a distance (around 10 feet) but already has 2/0 cable wired in.

I will likely have shunt issues here as the wiring is a bit convoluted. I'll take some pictures at some point....when the RV isn't buried in the snow!

I wonder if any experts are near 12428 zip code. Since it's an RV I could drive it to them!

Rick
Re: Balanced MPPT system?

We need to backup a moment... If you want three separate runs... could probably use a ~8-10 gauge run for each panel and still be way under the 1% voltage drop.

And, yes, I believe the max single wire would be 2 AWG. You can always clip a couple strands (evenly from the 3 cables), if needed, to fit them into the connector. I believe you could fit 3x 8 awg wires into the the 2 awg hole with room left over.

So--which is your preference? 1x 24' of 6/2 cable or parallel of 3x 24' of ~8-10/2 cable? Would not make much difference either way (costs should be similar, overall will take up more space because of the extra insulation on 6 wires vs 2; thinner cable may be easier route as it is more flexible).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Banned Posts: 17,615 ✭✭
Re: Balanced MPPT system?

Since you're putting three panels in parallel each panel should have its own fuse. The Isc on these panels is very small; you're looking at 5 Amp fuses. Note: most automotive fuses are not rated for 36 Volts. This could be a problem. Otherwise bringing the three panel wires to an automotive fuse block and then running a common wire to the controller would work nicely.
• Solar Expert Posts: 180 ✭✭✭
Re: Balanced MPPT system?

Is there a convenient 3 or 4 space fuse block that I can place close to the charge controller? The household sizes are really large and I'd like to keep the sizes down to a minimum since I have so little space to work with.

Ventilation distances are fine though,

Rick
Re: Balanced MPPT system?

If your battery bank is 24 volt or less (the higher voltage fuses tend to be larger foot print), look around for marine fuse blocks. They have some interesting variants.

http://bluesea.com/category/5/21

This series uses automotive fuses:

http://bluesea.com/category/5/21/productline/126

What size current/circuits are you looking for?

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 180 ✭✭✭
Re: Balanced MPPT system?

These would be protecting the 36v nominal panels that feed the charge controller on a 12v bank.

Rick
Re: Balanced MPPT system?

I believe the Bluesea are 32 volt maximum fuses--so they are too small for 36 volts...

Other than the old glass tube type fuses, I am not sure there is a small fuse block that would work for you with the proper voltage ratings.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 180 ✭✭✭
Re: Balanced MPPT system?

Hmmmm. OK SO anyone know where I can get the proper fuses for these panels. Three of them??

And What kind?

Springis getting close. Almost time for the install!

Rick
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: Balanced MPPT system?

i believe these fuses fit the voltage requirement you need with ease,
http://www.solar-electric.com/mnatm.html
now they are designed to go into this fuse holder for midnight products,
http://www.solar-electric.com/mnts.html
but if i miss my guess these are 5ag fuses which are designated 13/32 inches x 1.5 inches and fuse holders are available for them. for example,

to be sure, talk it over with naws or hopefully somebody else can chime in to confirm what i've said here.
Re: Balanced MPPT system?

3AG glass fuses are rated 250 volts for up to 8 amps and 32 volts for 10 amps and over... Will 8 amps maximum be enough?

Here is a Bluesea glass fuse holder.

For higher currents, there are MNTS fuses and holders:

fuses
Midnite Solar MNTS Touch Safe Fuse Holder
Midnite Solar MNPV3 Three-Breaker Busbar

Or, skip the fuses and holder, and get breakers of the same size and about the same price) plus the above busbar:

Midnite Solar AC Breakers, 10 to 60 Amps

and mount on a DIN rail or DIN breaker box.

I don't know what size a MNTS fuse is and if it would fit a 3AG panel but from looking around the web, they are not the same size.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 180 ✭✭✭
Re: Balanced MPPT system?

I'll be at no more than 50v at 8 or so amps for the panels (I believe), the AG style fuses look fine, but someone must make a simpler holder for them. I need a 3 fuse version (okay maybe a 4 or 5 for expansion to ground based movable panels in the future. Who knows?)

I didn't see any on the web sites.

I am amazed at how difficult it is to find, what seems to me, to be simple electrical bits.

I wish I could find a Morningstar TS-45-MPPT for less than 420 shipped.... ah well.

Rick
Re: Balanced MPPT system?

The Bluesea 6 fuse holder is around \$32 each...

This Prime 6 fuse holder is around \$10...

http://primeproducts.com/electrical-c-43.html

I just Googled and found these less expensive guys.
• 3ag fuse block -bluesea -"blue sea"
Got rid of the more expensive Bluesea brand holders (using the "-" to remove from google search).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 180 ✭✭✭
Re: Balanced MPPT system?

It's odd how many times I end up on the Prime Products web page for odds and ends!

That 6 fuse holder is perfect. gives me some expansion for later circuits.

Now to select the correct fuse.

Thanks,

Rick
• Solar Expert Posts: 180 ✭✭✭
Re: Balanced MPPT system?

OK...I cannot figure out what size and style of glass fuse to purchase for this installation.

Help??

Rick
• Banned Posts: 17,615 ✭✭
Re: Balanced MPPT system?

Short circuit current * 1.25 as per NEC, round up to nearest size.
Your panels are 5 Amps? *1.25 = 6.25 = 7.5 Amp fuse. Be sure wire is adequate for at least that current.
• Solar Expert Posts: 180 ✭✭✭
Re: Balanced MPPT system?

The fuse type description on the holder reads "Will accomodate both AGC and SFE fuses." So which ones (of the correct values) should I buy???

Rick
Re: Balanced MPPT system?

AGC fuses are all one length (for different current ratings) and have higher voltage ratings for the under 10 amp fuses:

1/4 in x 1-1/4 in
1/100 amp to 8 amp 250 V
10 amp to 30 amp 32 V
UL, CSA thru 8 amp

SFE fuses are different lengths for different current ratings (so you cannot mix up fuses in the application) and have only one rated voltage:

1/4 in diameter
32 V

I probably would just go with the AGC.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 180 ✭✭✭
Re: Balanced MPPT system?

Looks like AGC is the way to go. The panel is inexpensive and the fuses are easy to get. I'll have to make sure they are accessible from inside without major disassembly.

On to Wiring!

Here is my best thought on wire running from the panels to the Morningstar TS-45-MPPT controller:

This is 8/2 marine duplex. They also have 6, 8, 10, 12, 14, 18AWG duplex wire. Overkill is OK, and the runs are all pretty short (max 12-15ft one way)

Which one would be the best??

Thanks,

Rick
Re: Balanced MPPT system?

Outside wiring needs to be UV rated.

What is the array going to be wired as? Series/parallel, voltage, current, battery voltage, maximum current you expect to run, etc.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 180 ✭✭✭
Re: Balanced MPPT system?

The 3 panels (450w) will be run parallel outputting ~36v into a Morningstar MPPT 45 amp charge controller feeding 3 130a/hr Trojan batteries (wet cell/deep cycle, likely SCS225s) at ~12v

Wire runs from the panels to the controller never exceed 12ft (1 way) and the batteries are at most 8 ft from the controller.

That's the entire concept

Rick
Re: Balanced MPPT system?

Try to keep the wiring between Controller and Battery bank short... Voltage drop is not your friend (a couple 1/10's of volt drop can slow down the battery charging as the controller thinks it is almost charged).

However, you are in luck. The MorningStar TS family does include remote battery voltage sensing... You run a couple small wires from +/- battery to +/- Battery Sense on the controller--and it automagically adjusts for voltage drop in your heavy cabling (verify the MS TS MPPT family does have remote battery voltage sense--I don't have time at the moment to verify my memory).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 26
Re: Balanced MPPT system?
BB. wrote: »
Try to keep the wiring between Controller and Battery bank short... Voltage drop is not your friend (a couple 1/10's of volt drop can slow down the battery charging as the controller thinks it is almost charged).

However, you are in luck. The MorningStar TS family does include remote battery voltage sensing... You run a couple small wires from +/- battery to +/- Battery Sense on the controller--and it automagically adjusts for voltage drop in your heavy cabling (verify the MS TS MPPT family does have remote battery voltage sense--I don't have time at the moment to verify my memory).

-Bill

I have run a very similar system as you and am using the MS Tristar MPPT-45 as well... It does have the voltage sensor included with the digital display faceplate (if you purchased this aftermarket piece instead of staying with the 3 LED faceplate that is included with the controller) You will have to run 2 small wires that do not come with the controller. The temperature sensor is included with the aftermarket faceplate.

I purchased from this website, it was the best deal when I purchased mine, it may still be a good deal depending on what you find
http://www.altestore.com/store/Charge-Controllers/Solar-Charge-Controllers/MPPT-Solar-Charge-Controllers/Morningstar-MPPT-Solar-Controllers/Morningstar-TriStar-Digital-Meter-for-TS-and-TS-MPPT-Controllers/p7732/
Rory
• Solar Expert Posts: 180 ✭✭✭
Re: Balanced MPPT system?

OK, I was definitely going to run both the temp sensor and voltage sense wires.

Still, What gauge wire should I be using for the runs?

Panels to controller = 12 feet (one way, MAX)

Controller to battery = 8 feet (one way, MAX)

Panels total 450w

Controller max is 45Amp

Battery bank is 390a/hrs.

Thanks,

Rick
• Solar Expert Posts: 26
Re: Balanced MPPT system?

I'm sure someone more experienced can ultimately give you a better answer than myself, but I can tell you what I did and assure you that I have not had any problems with my equipment.

Although my panels are about 30' away from my charge controller, I used #8AWG wiring (I believe this is standard size of the pigtails that come off your panels, or it looks that way to me anyway) You could probably get away with #10AWG unless someone here can correct me on this.

From your Controller to your battery bank I would say #6AWG would be fine (Its what I use anyway)

From your Battery bank to your inverter I ran #2AWG to my 300ANN fuse (I have a 1500W pure sinewave inverter so this is the recommended fuse size) and then I ran #2AWG from there to the inverter.

As a general rule of thumb it is better to run heavier gague wiring from place to place if possible... Most people refrain from doing this because of the associated cost of #2AWG... Pretty pricy stuff... BUT since you have the luxury of running very short distances you could probably get away with using some bigger wiring to avoid having a power loss between your components... then again, I don't think you will have much with such short distances anyway... If you private message me I can take some pictures of my system and send them to you if you think it will help with visualizing a finalized product... Sometimes a picture says 1000 words...