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Author Topic: PV direct to battery temporarily  (Read 7546 times)
rithym
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« on: July 22, 2013, 07:35:54 PM »

Hi to all

My Tristar mppt 60a has gone phut  so am in the process of obtaining RMA for warranty return, apparently this could take a month or more has to go direct to factory in Germany. In the meantime is it safe to connect 8 x Hyundai 200W panels direct to 24v bank (4 x trojan L-16 435 ah) I can keep an eye on the voltage and disconnect if over 30V or so (or put air con on in house)

So, if this is okay should I wire 2 strings of 4 panels as they were to controller (120v dc) or should I re-wire individually 8 panels in parallel. According to tech sheet VOC for each panel is 33v

any help much appreciated this is only temp measure until I get controller back
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biff
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« Reply #1 on: July 22, 2013, 08:19:22 PM »

Be patient,
            There will be someone along in a minute.
          Once Rogerico finished his poundies and gravy he will tell you exactly what you need to know,
          Even Paul could put you on the right track if he was not too busy.
                                        Biff
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Justme
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« Reply #2 on: July 22, 2013, 08:22:29 PM »

Dont do it. All it will take is for you to take your eye off the ball for a short time & it could end up in disaster.


However if you do you will need to split the array up so its all in parallel. IE either each panel has its own wires all the way to the bank or to a central point that then has very thick cables to the bank. Either way it will cost you in copper.

How about buying a cheap controller & then selling it when no longer needed.

Just to rub the salt in, had you bought an Outback controller they send you one out first.
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rithym
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« Reply #3 on: July 22, 2013, 08:35:01 PM »

I am located in the Algarve, Portugal wire here is silly money compared to UK prices and a cheap controller just does not exist. I can get one from China off Ebay but that will take 2-3 weeks to get here. Looks like it may be cheaper to just pay the extra leccy bill for a month and stay on grid... such a shame with all this lovely sunshine   
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clockmanFR
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« Reply #4 on: July 22, 2013, 08:39:05 PM »

rithym, sorry to here, any underlying reasons for the failure, or just phut, I know that programing the MPPT's while they are working is not a good idea.

Just me, I agree, especially at only 435ah.

I have 2 Morningstar MPPT's but will phase them out. I am now fitting the Outback lite that can handle 200vdc on the input so I can reduce cable loss and achieve a better string output matching my 2kw Tracker higher voltage PV panels.

rithym, there is a guy in Spain that has Outback products, he is a heavy smoker so the stuff arrives smelling of fag smoke, but he' good on price and ships in a day UPS.
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rithym
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« Reply #5 on: July 22, 2013, 09:33:21 PM »

no idea why the phut... the controller was flashing red to show a fault, I turned off the PV array and the battery connect breaker... checked the connections and voltages all seemed normal... when I turned back on it went phut just like a fuse blowing and then dead. To make matters worse I disconnected the heat sink top part from the bottom part to gain better access to the PCB's to see if there was a simple fuse to replace... no fuses but an anti-tamper plastic rod which broke when I separated the two parts so I may be unlucky on the warranty now... what a plonker!

I do also have a Tristar PWM 60A problem is according to Mstar string calculator it's not compatible in solar mode with these Hyundai 200W panels. Perhaps I could use it as diversion control but that will involve buying resistors big enough to take the diverted load around 1600W at 24V. I was hoping to just connect batteries direct and open the breakers when battery bank reached 30V or so but even that involves a reel of 6mm cable to re-wire in parallel and wire prices tend to be double here compared to UK. 

the guy you referring too in Spain I believe is Nigel & his son Callum Prism Solar. I have bought some breakers and a Trimetric from them recently as you say good service arrived over the weekend on Moday via UPS. I see Mstar are bringing out a new version of the Tristar mppt... PV input is up to 600V DC that will be good for larger strings and long wire runs still only 60 amp total though.     
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billi
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« Reply #6 on: July 23, 2013, 02:49:21 AM »

CM , you mean  the Midnite MPPT or ?.....

Quote
I do also have a Tristar PWM 60A problem is according to Mstar string calculator it's not compatible in solar mode with these Hyundai 200W panels.
 , should work with pairs of two with 66 Voc ( well , with lots of losses )

But i reckon 66 Voc would be the better Voltage (VOC)  even for the Tristar MPPT when it comes back

I do not know  the temperatures in Portugal  in Winter , but i know that those panels  will scratch the high end VOC limit (150 VOC ?) of this controller when cold , if you keep 4 panels in series  ....

We have seen other Morningstar tristars MPPT here  fail in cold sunny conditions  (but may have been other reasons)


Billi








« Last Edit: July 23, 2013, 02:51:06 AM by billi » Logged

1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
rithym
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« Reply #7 on: July 23, 2013, 07:24:50 AM »

well, thanks for the info. I did wonder at times if having the panels in 4 series was a problem as the heatsink on the mppt used to get very hot sometimes in the 70's C. Checking the data log revealed everything was within limits max VOC I saw was 131V but generally around the 120 mark. Common sense tells me heat means losses of some sort and by the general theme on here I suspect Morningstar products are not as efficient as other controllers? I am on a hill here in the Algarve so no real frost but it does get down to around zero on clear nights in winter, as soon as the sun rises it's usually up to 15 again by 10am. I have to move the panels anyway, at the moment they are on a temporary ground frame about 10 meters from the battery bank but I now have some nice heavy duty 50mm English scaffolding and clips so my intention is to build up over the shipping container where the batteries are housed so the cable run will only be 3 meters or so. At the same time will re-wire the panels as 4 strings of 2 as you suggest. In the meantime today I will try a pair of the 200W panels on the Tristar PWM see what happens I take it a single panel would be too low at 33 VOC on 24V system?     
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clockmanFR
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« Reply #8 on: July 23, 2013, 07:44:45 AM »

Yes billi, my hearty, e589, Midnite Mppt Classic Light 200, It also has spare 10% extra extension capacity in emergency's.

My Morningstar MPPT 60 is working at max VOC with battery temp sensor active at only 120v dc input, if I disconnect the battery temp sensor all hell breaks loose. you know, Fault, Over temp, over voltage, auto disconnect, etc etc.

So with most 250w panels at VOC 38v to 40v the Morningstar MPPT as it stands will not cut the mustard.

ie My 2kw Tracker has 8 panels, split into 2 strings, giving me 152v per string, Mornigstar MPPT60 max is 150v.  sh*tfan

Its the sunny days in winter when I notice my Morningstar MPPT60 on my 2, 1.5kw trackers getting mighty close to limits.

So for the present Midnite MPPT Classic light 200 seems the way forward with these higher VOC panels.

And remember I am also trying to get max out of my PV trackers in ambient light so 5kw of PV gives me about 500w of steady juice even on dark dreary days. So Getting the MPPT stuff at max efficiency is very important.

Interesting ....  "I see Mstar are bringing out a new version of the Tristar mppt... PV input is up to 600V DC that will be good for larger strings and long wire runs still only 60 amp total though."
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rogeriko
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« Reply #9 on: July 23, 2013, 09:07:56 AM »

 In the meantime today I will try a pair of the 200W panels on the Tristar PWM see what happens I take it a single panel would be too low at 33 VOC on 24V system?     

What is the MPP voltage of those panels? if it is 28/29v then you don't need 2 in series just connect them in parallel. Try 1 panel with the Morningstar, how many amps does it charge at?

By connecting 2 in series you will lose half your power.
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rithym
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« Reply #10 on: July 23, 2013, 09:27:10 AM »

Tristar PWM is 60A

Spec taken from Hyundai sheet

Nominal output (Pmpp)  200W
Warranted minimum power   194W
Voltage at Pmax (Vmpp)   26.5V
Current at Pmax (Impp)   7.6A
Open circuit voltage (Voc)  33.1V
Short circuit current (Isc)  8.2A
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bxman
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« Reply #11 on: July 24, 2013, 03:53:06 PM »

I think you were probably right in the first place

The batteries I imagine are a reasonable size .

Well capable of absorbing   the 7.6 amps  output of a single  panel . (do not try a bank of panels )

A single panel connected to a 12v  battery  will sit at the battery voltage and gradually float up as the charge progresses

Unless it is well charged to start with the battery will take several hours to get above 14volts   which is where i would stop the process. 

 I seem to recall when my panels were installed they were tested by being shorted out through a circuit breaker  so they are reasonably robust and will never provide

more than the 7.6 amps regardless.

If your battery's voltage races up there is something wrong with it in the first place.

You must have a DVM  connect that and observe   If you have a spare airline ticket I will come and stand over it for you.

Be bold and experiment in the interest of Science .



This if nothing else  should bring out the real experts to shoot me down.

 they will say it is the battery temperature you should monitor I am sure 

best wishes Patrick
ps
I have a mickey mouse panel  downstairs on a AGN   at the moment with the AVO  needle gracefully swinging  between 15 and 70 mA
 and the voltage very slowly creeping up to 13v
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rogeriko
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« Reply #12 on: July 24, 2013, 04:24:33 PM »

The panels are fine. They are 26/27v panels just connect them all in parallel to the batteries. As the battery voltage rises towards 29/30v they will practically stop charging on their own because when the voltage goes over the mpp volts  the output drops rapidly. I know this from experience with these panels, everything will be fine.
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billi
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« Reply #13 on: July 24, 2013, 08:44:00 PM »

Quote
I will try a pair of the 200W panels on the Tristar PWM see what happens I take it a single panel would be too low at 33 VOC on 24V system?     
and please report when  panels are in full sun  and battery at 27 Volt how many Amps you get , i am very curious   and would like to believe Roger (honestly) .......................   perhaps 2  in series  to the PWM controller and the other 6 in parallel direct to the battery  as  a compromise Roger  ?  Smiley
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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
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« Reply #14 on: July 24, 2013, 09:44:43 PM »

If you look at the graph you will see how the current drops as the voltage increases. Of course connect them through the pwm controller but I am sure that they will never overcharge the batteries if you just directly connect them. In the heat of the sun they will only reach 29 volts at 1 or 2 amps each perfect for floating the batteries but when the batteries are low 24v or if you connect a load and battery voltage drops they will produce full power. Kind of self regulating these low voltage panels.


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