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Post by Telemachus on Mar 12, 2021 15:54:36 GMT
Quite a lot of people advocate under 14v on the MPPT for LFP batteries. I've set mine at 13.6. I think this means a slightly lower capacity but more life. That's the theory. There is a lot of discussion about 14.5v+ being quite damaging specially if the batteries sit at this voltage for extended time periods, which seems likely in summer with solar input. I think one problem is that people only consider voltage (hang up from the days of LA). When in reality it is the combination of voltage and current that is important. Cells held at 13.6v until the current subsides to a low value, will be very close to 100% SoC. Cells taken to 13.6v and immediately disconnected on reaching that voltage at a charge current of say 0.5C, will be way down on SoC. Cells taken to 14.6v at a low current will be stressed unnecessarily (they were already at 99.5% when the voltage passed 13.8v). Cells taken to 14.6v at a high current which then stops as soon as 14.6 is reached, will be close to 100% but won’t have been held at a stressfully high voltage for long. Take your pick!
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Post by Deleted on Mar 12, 2021 15:59:11 GMT
I wonder what the effect of occasional power draw from a fridge would be.
It seems this might put the MPPT back into the absorb setting and result in the batteries going up to 14v+ again for however long the absorb time is.
On my Victron it is 2 hours but this is user definable to be fair.
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Post by Telemachus on Mar 12, 2021 23:41:26 GMT
I wonder what the effect of occasional power draw from a fridge would be. It seems this might put the MPPT back into the absorb setting and result in the batteries going up to 14v+ again for however long the absorb time is. On my Victron it is 2 hours but this is user definable to be fair. I think 2 hours absorb for Li is too long. 30 mins more like it.
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Post by kris on Apr 2, 2021 15:56:31 GMT
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Post by kris on Apr 11, 2021 14:01:21 GMT
So ive programmed my solar controller finally it took spending more money to buy the right cable, but at least its done know I am finally happy with the settings on every thing. ive fitted my new solar ill post some photos when I think about it. Ive bought another controller as I now have more solar power than I know what to do with, that turns up this week so ill have to rebuild it again, well not totally but move things around it seems never ending.
ps I forgot has anybody got any recommendations on switches to put inline with the solar panels, I think with these higher voltages id like to be able to isolate my panels.
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Post by Telemachus on Apr 11, 2021 15:06:21 GMT
What voltage settings did you go for in the end?
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Post by kris on Apr 11, 2021 15:38:21 GMT
What voltage settings did you go for in the end? absorption 13.8v, float off, equalise off, and HVD of 14.1v. I set absorption time at 1hr 30mins
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Post by Telemachus on Apr 11, 2021 16:45:39 GMT
What voltage settings did you go for in the end? absorption 13.8v, float off, equalise off, and HVD of 14.1v. I set absorption time at 1hr 30mins Sounds good.
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Post by kris on Apr 11, 2021 17:16:27 GMT
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Post by Deleted on Apr 11, 2021 17:47:35 GMT
ps I forgot has anybody got any recommendations on switches to put inline with the solar panels, I think with these higher voltages id like to be able to isolate my panels. I dont know what switch you would use- presumably an isolator switch that is rated to handle the maximum current that your panels can generate in 100% perfect conditions? I do remember the gas fitter who moved my inverter a few weeks ago saying that he didnt want to use an isolator switch, because he was worried about where all the charge would go when it was stopped from entering the batteries. He wasnt an electrical expert (as I think has been demonstrated already), but I think his theory was that the excess charge from the panels would be dissipated via heat through the fins on the rear of the MPTT. However, when I considered what he'd said, I realised that my isolator disconnects the solar charge before it reaches the MPTT, so there wont be any excess heat for the MPTT to worry about. But I am curious what happens to all that charge if you just throw a switch and stop it going into the batteries.
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Post by JohnV on Apr 11, 2021 17:54:39 GMT
ps I forgot has anybody got any recommendations on switches to put inline with the solar panels, I think with these higher voltages id like to be able to isolate my panels. But I am curious what happens to all that charge if you just throw a switch and stop it going into the batteries. nothing
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Post by JohnV on Apr 11, 2021 17:58:31 GMT
But I am curious what happens to all that charge if you just throw a switch and stop it going into the batteries. nothing should add though, it's not a good idea to switch off the batteries from the MPPT when the solar is still attached. MPPT's don't like it one little bit
switching off the panels just opens a circuit stopping the current ..... the solar potential is stil 60 volts or so but power is volts times amps ... open circuit is no amps 60 times zero equals zero watts
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Post by kris on Apr 12, 2021 11:18:43 GMT
Can anybody recommend isolator switches? Each string of three is running at 120v with a maximum of 80amps
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Post by Telemachus on Apr 12, 2021 11:34:02 GMT
Can anybody recommend isolator switches? Each string of three is running at 120v with a maximum of 80amps 120v at 80A is 9.6kw. Times three. Are you setting up a power station? I think you might be confused between the current coming out of the MPPT (80A at 12v) with the current in the panel wiring at 120v Which would be about 1/10th, ie around 10A. If you are not confused and it really is 80A at 120v, I think you will be struggling to find anything non-expensive.
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Post by Deleted on Apr 12, 2021 11:45:15 GMT
Can anybody recommend isolator switches? Each string of three is running at 120v with a maximum of 80amps This is what mine looks like (taken a few months ago). I cant see a manufacturer name on it, so I'm guessing its an industry standard electrical item that's been put into use, and the installer added the adhesive labels saying 'solar' and 'batt'. In my case the OFF positions seems to cut all power to the MPTT and it goes off, and the BATT position leaves the MPTT on, but stops it putting any charge into the batteries. imgur.com/a/xsuWGFg
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