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the problem is the panel volts VOC today was 55 volts (have them 2 in series)
regulator said NOPE not happy, volts to high...
the upper max upper limit from the book is 48V and Working volts 29-38v
what can i do? in series gives me up to 55v on a sunny day and that is to high.
in parallel i`m only going to get 23.7v so it wont feed the MPPT regulator with enough volts...
What to do?
DC-DC voltage converter? expensive...
drop volts over large power diodes? (wasteful?)
????
Thanks.
davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499
Posted: 04:52pm 04 Mar 2015
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Just checking ... are you trying to charge 24V batteries?
Your Vpm of 23.7V seems a high for one panel to charge 12V, I think mine is about 17Volts. Were the panels designed for 12V charging?
For my 24V system the charge controller can handle up to 90-100Volts, so an upper limit of 48Volts for a 24Volt controller does seem low.
I would consider putting a dump load (shunt regulator) that kicks in at 45Volts, if you didn't want to buy any controller. Seems a waste unless you could use it to heat water or something. How much current do you have "shunt" to get your panel voltage down to 45Volts, it might not be a lot.
Tracer 30A controller is about $200US from China.
rgormley Senior Member Joined: 22/02/2006 Location: AustraliaPosts: 245
Posted: 09:52pm 04 Mar 2015
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it is a 24v bank i run.
after lots of playing, yes have come to the same conclusion.... need a better regulator....
now the Ebay/local hunt for a unit..
need a 40Amp unit to be safe....
rgormley Senior Member Joined: 22/02/2006 Location: AustraliaPosts: 245
Posted: 09:14am 05 Mar 2015
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problem will be solved...
just bought a 40Amp tracer MPPT unit 100Voc input...
KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178
Posted: 10:19pm 06 Mar 2015
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Ebay or Au seller?
Apolloenergy sells them here is Aus with a proper warranty
vs ebay your mandatory 30 days.
Luck favours the well prepared
rgormley Senior Member Joined: 22/02/2006 Location: AustraliaPosts: 245
Posted: 11:17pm 06 Mar 2015
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$259 vic seller
Although i just spied on the Apollo website 2nd generation unit at $236
Really?? bugger it!!.....
Ps Karl , you installed my orig on grid system (i think?) via energy matters..
rgormley Senior Member Joined: 22/02/2006 Location: AustraliaPosts: 245
Posted: 11:25pm 06 Mar 2015
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jey Karl, why is the older tracer more expensive than the new generation?
normally the newer stuff is more expensive?
Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333
Posted: 03:31am 07 Mar 2015
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I would suggest you follow Karl's advice, as he is hands on in the industry, and not a guru due to post content, like many here.
I have used the TriStar MMPT in the past and I would assume they are about the same technology. I really like the TriStar unit because it has a RS485 Modbus slave feature. This allows you to adjust and monitor almost every aspect of the panel without any extra hardware. You can monitor the input power and the output power and see the controller loss.
Inside the MMPT controller generally consists of a buck regulator that does a quick voltage sweep to automatically find where the power is the highest.
P=IV. As the voltage increases you get more power until the current starts dropping off.
On my cells with a 30 VOC it sits at around 26 volts on a sunny day.
If you go with double the voltage on the output of the solar cells, you can literally 1/2 copper area of the wire size and still have less loss. Because P(loss)=I^2xR it's a very big advantage (you are decreasing I).
Also on a cloudy day, the higher the input voltage, the more room the controller has to synch down to create the amps.
The VOC rating is the voltage open circuit so there is very little current at this voltage. As soon as you put any load on it - it will drop fairly quickly to it's higher current rated area. Try to find the cell's data sheet and you will see what I mean. At this point you can decide what is 'safe'
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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