Author Topic: 48 volts?  (Read 994 times)

BAndrews

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48 volts?
« on: September 04, 2016, 08:43:55 PM »
I have an opportunity to obtain (eight) 6-volt batteries and trade off the old 24 volt pack.  Would I be better off with two series strings in a 24 volt system or a single 48 volt string?  If 48 volt is better, what would be the minimum allowable PV  input voltage into the classic 150 charge controller?
4 Star Solar power center w/4KW Magnum inverter, (2) Midnite Solar Classic 150,  3.5 KW PV [(eight) Solarworld 265W, (4) Solarword 345W],  S550 (24 volt) Rolls Surrette battery bank.

mike90045

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Re: 48 volts?
« Reply #1 on: September 05, 2016, 02:56:50 AM »
in a balanced system
a 400a 24v battery has the same "power" as
a 200a 48V battery.   
 48V systems need about 70V to charge the battery, so 75 is the min coming off the array,  but there is little MPPT action happening there, unless the batteries are way low.    The lowest voltage array I'd have going to a 48V bank would be about 100Vmp
http://tinyurl.com/LMR-Solar

Classic 200| 2Kw PV, 160Voc | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph )| Listeroid 6/1, st5 gen head | XW6048 inverter/chgr | midnight ePanel & 4 SPDs | 48V, 800A NiFe battery bank | MS-TS-MPPT60 w/3Kw PV

Eleceng1979

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Re: 48 volts?
« Reply #2 on: September 05, 2016, 10:10:59 PM »
From a battery/inverter/wiring aspect...the higher the better.  Higher volts = less amps = smaller wires.

If you have enough pv voltage to support it...then go for it.  But you have not provided a detailed breakdown of your pv so a generic answer is all I can do

I would always default to the highest voltage system.  Higher pv volts = less loss and smaller wires...

1 battery string is always better than 2

12.96 kW PV = 48 x Canadian Solar CS6K-270M - 2 x SMA Sunny Boy 6.0-US - Ironridge Ground Mount
Record Day = 81.847 kWhr

B17 and 2x1700AH batteries on my Christmas list for santa

TomW

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Re: 48 volts?
« Reply #3 on: September 06, 2016, 10:27:36 AM »
In general, any system with substantial output you will want higher voltage.

I have done both 12V and 24V systems.

higher volts just makes sense with a higher power output set up.

As mentioned above one string of batteries is better than parallel strings for several valid reasons.

A lot of folks start at 12 volts for the wrong reasons and finally wise up and go to 24 volts and the really smart folks end up at 48 volts. Every voltage change generally requires new equipment somewhere in the system.  That is why I always suggest higher voltage to start when asked.

Anyway, my opinions.

Tom
Do NOT mistake me for any kind of "expert".

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24 Trina 310 watt modules, SMA SunnyBoy 7.7 KW Grid Tie inverter.

I thought that they were angels, but much to my surprise, We climbed aboard their starship and headed for the skies

Powerplay

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Re: 48 volts?
« Reply #4 on: October 19, 2016, 05:23:15 PM »
I'm planning to go to 48 volts next spring (2017) by reconfiguring my 12 batteries and installing a 48V inverter.  My 2 Awg (120A max) main battery charging circuit from my 2 Classic 150s is breaker limited at 100A and this limits the system to about 2500 W and it already is capable of more input than that at 3500W nominal PV.  So I limit output amps at the Classics.  I'm not worried about this since this system is charging the batteries very well even on overcast days.  I could put about 5000W through without changing any wires or breakers with a 48V battery bank. 

My question is, should I reconfigure my panels that are connected to my first classic (currently, input voltage on it is 57V) to match the second classic I installed last Sring which is 76V input voltage?

Would the first classic have a hard time charging 48V batteries at that input voltage?
41 degrees N, 255 Ah 48V AGM, MagnaSine 4448 Inv, 3500W PV, Midnite Classic 150 A (12/6/15), Midnite Classic 150 B (4/14/16), WBjr, BTS, MNPV6 X 2, SPD X 2, Apps: Mini Split AC, Car Charger, Water pumps, Lighting, -> 48V string plan 500W, 94.5VmP, 112.5VoC, -15C - 40C TCVoC -.3%, TCIsC +.04%

Vic

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Re: 48 volts?
« Reply #5 on: October 19, 2016, 06:05:51 PM »
Hi Powerplay,

IMO,  57 V input voltage to an MPPT CC,  (or even a PWM CC)  is not really sufficient on a 48 V ststem.

The Classic String Sizing Tool:
http://www.midnitesolar.com/sizingTool/displaySizing.php

...   suggests having 130% STC String Vmp above the highest battery charge voltage that you will ever need.

AGM batteries do not need as much margin over the battery voltage,  but,  still 57 Volts In would probably result in that Classic Resting quite a lot.

Expect that 57 V number was what the Classic was reporting,  and not the PV Vmp X 2 ...

Fewer parallel battery strings,  IMO,  is always better ...   FWIW,   Vic
« Last Edit: October 19, 2016, 06:07:38 PM by Vic »
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

TomW

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Re: 48 volts?
« Reply #6 on: October 19, 2016, 06:15:35 PM »
My question is, should I reconfigure my panels that are connected to my first classic (currently, input voltage on it is 57V) to match the second classic I installed last Sring which is 76V input voltage?

Would the first classic have a hard time charging 48V batteries at that input voltage?

I would say yes!

57 volts into a classic will not be able to fully charge 48 volts and is actually too low to charge 48 volts directly connected. It would need to be up closer to 59 volts.

It depends on the type and the manufacturer as well but 57 probably just can't get it done.

I recall a rule of thumb that a classic should have an input voltage at a minimum of 1.5X the battery voltage to work well.

So 48v is going to want 72+ volts so 76 is good.

I think.

Tom
Do NOT mistake me for any kind of "expert".

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24 Trina 310 watt modules, SMA SunnyBoy 7.7 KW Grid Tie inverter.

I thought that they were angels, but much to my surprise, We climbed aboard their starship and headed for the skies

CDN-VT

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Re: 48 volts?
« Reply #7 on: October 20, 2016, 01:50:01 AM »
tom's voltages are too low & Vic has my thinking for a classic MPPT .
Can you re string > V6 X 2
No info on your panels
3 in series instead of 2 & 2 strings ??
Guessing

VT
Canadian Solar 350W 37.6 VOC  30.6 VMP 8.22 ISC 7.87 IMP ,-15 c -30c max  4 strings in 2 in Series for 24v Classic 150 -1020 Ah  Freezers & fridges ~~~ Second Array same panels of 2sx3 parallel for 24 V Classic 150 -440 Ah  SS300 for lights & overhead door. Building the 33 panel 48 volt system now

Powerplay

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Re: 48 volts?
« Reply #8 on: October 20, 2016, 03:45:28 PM »
Thanks guys.  I can reconfigure the first Classic to 75.6V input (correct as reported by Classic by adding about 500W of PV to its combiner, hey one can always use more power  ;) ) which then matches the second one.  Or with a bit more work I can take them both to 94.5V input and still not be too concerned about cold winter temps but I'd want to check out lowest temps possible in my area and Midnite sizing tool regarding going to that voltage.  Everyone think 94.5 V is a better move?  Or 75.6 adequate?  I'd reconfigure the 12V battery bank as 4X3 to get to 48V if I designated that correctly.
41 degrees N, 255 Ah 48V AGM, MagnaSine 4448 Inv, 3500W PV, Midnite Classic 150 A (12/6/15), Midnite Classic 150 B (4/14/16), WBjr, BTS, MNPV6 X 2, SPD X 2, Apps: Mini Split AC, Car Charger, Water pumps, Lighting, -> 48V string plan 500W, 94.5VmP, 112.5VoC, -15C - 40C TCVoC -.3%, TCIsC +.04%

TomW

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Re: 48 volts?
« Reply #9 on: October 20, 2016, 05:06:46 PM »
Everyone think 94.5 V is a better move?  Or 75.6 adequate?  I'd reconfigure the 12V battery bank as 4X3 to get to 48V if I designated that correctly.

PowerPlay
Not exactly positive but I seem to recall that it is not good to have too high a voltage in.

Something to do with efficiency loss by downconverting too far. But, then, I am not sure if it matters unless you are just squeaking by with your incoming power?

Then maybe I am just overthinking the plumbing.

Another question that only the person asking can really answer based on the often subtle needs of the install. Things like cable size where a higher voltage will have less drop at the same power on a given cable gauge. 

All things equal I would go in the 76V range. Plus likely easier to do.

Never hurts to open a dialog on these things.

Sorry if I make things seem overly complicated but hopefully the discussioin will lead to better understanding of what is actually a fairly complex system.


There may well be a different opinion from every user.  :o

Tom

« Last Edit: October 20, 2016, 05:08:30 PM by TomW »
Do NOT mistake me for any kind of "expert".

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24 Trina 310 watt modules, SMA SunnyBoy 7.7 KW Grid Tie inverter.

I thought that they were angels, but much to my surprise, We climbed aboard their starship and headed for the skies

CDN-VT

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Re: 48 volts?
« Reply #10 on: October 21, 2016, 12:08:20 AM »
Thanks guys.  I can reconfigure the first Classic to 75.6V input (correct as reported by Classic by adding about 500W of PV to its combiner, hey one can always use more power  ;) ) which then matches the second one.  Or with a bit more work I can take them both to 94.5V input and still not be too concerned about cold winter temps but I'd want to check out lowest temps possible in my area and Midnite sizing tool regarding going to that voltage.  Everyone think 94.5 V is a better move?  Or 75.6 adequate?  I'd reconfigure the 12V battery bank as 4X3 to get to 48V if I designated that correctly.
Myself going off your posting on this thread (NO PANEL SPECS)  .
For 48Vdc & if you can reach  94Vdc , GO with Higher MPPT

 75Vdc is way low on a eq for a voltage of 60Vdc .. Your breakers (as I have 3 breaker posts going ) will still be the same amperage & your below the old 125Vdc type & if you have the newer 150Vdc your still good.

The Problem Tom is stumbling on is if it's a 94 Vdc down to 12Vdc is an over-work of the MPPT system .

If you could get it to the 2.5 X the battery Voltage so 12Vdc X 2.5 = 30 Min  to 12vdc X 3 .5  or so is fair for both @ 12Vdc , 24Vdvc  Id double 84 Vdc or so in , so 48Vdc you should be much higher for the equalization voltage for MPPT to work . 75 Vdc is just off Eq voltage on that 48Vdc bank for true MPPT to work well .
IMO

VT

Power play , update your sig line to include your panels , that would help .
« Last Edit: October 21, 2016, 08:06:17 PM by CDN-VT »
Canadian Solar 350W 37.6 VOC  30.6 VMP 8.22 ISC 7.87 IMP ,-15 c -30c max  4 strings in 2 in Series for 24v Classic 150 -1020 Ah  Freezers & fridges ~~~ Second Array same panels of 2sx3 parallel for 24 V Classic 150 -440 Ah  SS300 for lights & overhead door. Building the 33 panel 48 volt system now

Powerplay

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Re: 48 volts?
« Reply #11 on: October 21, 2016, 05:33:47 PM »
I just looked over the classic sizing tool and at the 94.5 VmP panel configuration my hyper-Voc is down at -104 degrees F so if it gets that cold here that'll be something different.   :D

I hear what you're saying about enough volts in.  Last winter I kept hitting my max volts on my old inverter at about 31V (24V system).  So by extrapolating 2X, and with max input volts being generally allowed higher on the Magnasine inverters, I can see needing to get to 62V absorb charging on the 48V battery bank just during absorb phase on cold days.  So 94.5VmP it is.  Now I have to think about how to reposition some panels that are pointing a bit wrong for a regrouping.  Sounds like some planning.  Fortunately all my newer string panels point exactly the same so easy to re-configure.  Learn as you go huh?

Thanks again for the opinions.
41 degrees N, 255 Ah 48V AGM, MagnaSine 4448 Inv, 3500W PV, Midnite Classic 150 A (12/6/15), Midnite Classic 150 B (4/14/16), WBjr, BTS, MNPV6 X 2, SPD X 2, Apps: Mini Split AC, Car Charger, Water pumps, Lighting, -> 48V string plan 500W, 94.5VmP, 112.5VoC, -15C - 40C TCVoC -.3%, TCIsC +.04%

CDN-VT

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Re: 48 volts?
« Reply #12 on: October 21, 2016, 08:15:55 PM »
Your classic 150 running a 48Vdc system would need to stay below VOC of 150 + battery system voltage  @48Vdc = 198Vdc  so when you update your Sig Line with panel spec's then we should know for sure.
My 3 series are VOC 112.8 & 91.8Vdc VMP , see my sig line. Im just above the 49p 100miles from the midnight plant & we see the same wet weather.

VT
Canadian Solar 350W 37.6 VOC  30.6 VMP 8.22 ISC 7.87 IMP ,-15 c -30c max  4 strings in 2 in Series for 24v Classic 150 -1020 Ah  Freezers & fridges ~~~ Second Array same panels of 2sx3 parallel for 24 V Classic 150 -440 Ah  SS300 for lights & overhead door. Building the 33 panel 48 volt system now

Powerplay

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Re: 48 volts?
« Reply #13 on: October 22, 2016, 05:43:13 PM »
At 25 degrees C, my series will be 94.5 VmP and 112.5 VoC so my numbers are going to be very close to your series numbers.  There are some 125V din rail breakers (Midnite) in my combiner boxes.  Thus VoC is getting fairly close to the breaker V limits.  Yours might be the same unless you switched out your old breakers.  TCVoC is -0.3 per degree C.  I can run my inverter at temps down to -20 C.  So -.3 TCV0C/C times -45 C =  13.5% TCV or  VoC + 15 which is 127.5 Volts just above breaker rating.  Anyone see any issues with this?  I can calculate my lower temp limit based on VoC or is it VmP?  Otherwise, the series PV are 600V max and 15A series fuse limited.  Still sounds like this setting is a winner for dropping current and allowing me to run some more power with the fewest overall changes.  Thank you for all of the advice and I hope others who are thinking along the same lines also get some useful info out of this.
« Last Edit: October 22, 2016, 05:58:20 PM by Powerplay »
41 degrees N, 255 Ah 48V AGM, MagnaSine 4448 Inv, 3500W PV, Midnite Classic 150 A (12/6/15), Midnite Classic 150 B (4/14/16), WBjr, BTS, MNPV6 X 2, SPD X 2, Apps: Mini Split AC, Car Charger, Water pumps, Lighting, -> 48V string plan 500W, 94.5VmP, 112.5VoC, -15C - 40C TCVoC -.3%, TCIsC +.04%

CDN-VT

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Re: 48 volts?
« Reply #14 on: October 22, 2016, 10:23:43 PM »
Sig add panels like this : Canadian Solar 350W 37.6 VOC  30.6 VMP 8.22 ISC 7.87 IMP
Then any configs can be made .

Thats why I said that the 125Vdc breakers are still in use , for a 48Vdc Battery bank & wired the way I assumed.


IN 20 YEARS TIME FROM NOW , WE MIGHT HAVE 72vDC OR 96vDC iNVERTER from Midnite B19 !!

VT
Canadian Solar 350W 37.6 VOC  30.6 VMP 8.22 ISC 7.87 IMP ,-15 c -30c max  4 strings in 2 in Series for 24v Classic 150 -1020 Ah  Freezers & fridges ~~~ Second Array same panels of 2sx3 parallel for 24 V Classic 150 -440 Ah  SS300 for lights & overhead door. Building the 33 panel 48 volt system now