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Forum Index : Electronics : 150V 45A MPPT - roll your own
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| azhaque Senior Member  Joined: 21/02/2017 Location: PakistanPosts: 117 |
Valid, but the issue with that topology is that a separate supply with a floating ground is needed. SolarMike and Warp put me wise on that in the thread MinimuMPPT. I guess the way to go along the KISS philosophy for this machine, Schottky diodes maybe the best solution. Nick has already tested it. However it shall require reworking the board which can be minimized if these diodes are off-board and just have two thick wires going to their paralleled anodes and cathodes. High voltages may require an additional pair in series, but that aspect requires further examination. Solution if you want to use reverse protection mosfet - just duplicate the TLP circuit already being used here and use it to bias the reverse protection mosfet. The ACS/LEM will tell the nano when to shut it down or switch it ON. azhaque Edited 2020-05-08 19:36 by azhaque |
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wiseguy Guru  Joined: 21/06/2018 Location: AustraliaPosts: 1156 |
Can someone enlighten me what sort of current do panels draw from backfeed ? Assume a single line of panels say 250 or 300W. If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
An external relay module would be the most reliable, something like this:  The contact rating being the determining factor, I have used these relays before and they seem reliable 80 amp , 60 amp .I would be a bit wary about the ratings of some relays on Aliexpress, but that manufacture seems to make quality stuff. The resistor allows pre-charging of the electros to prevent the contacts burning up. CPU should turn off PWM so, so no current load prior to opening at night. Mike your question about back feed current, not much... a 60 junction panel (24v) and 50v battery has say 3 series panels for mppt = approx 100v and 180 reverse PN junctions applied across the 50v battery, so their will be some 10's ma leakage, probably wont be noticeable on a large bank. Cheers Mike |
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| nickskethisniks Guru Joined: 17/10/2017 Location: BelgiumPosts: 458 |
It's dark over here at this moment, so I went measuring. I have 20 panels connected (each 280W), they are with 2 in series and 10 groups in parallel, let's say 2p10s. They are consuming just not exactly 100mA @ 53V, I've measured with a clamp meter on the 2A setting. For the design files I just checked and I can convert the files to Altium format if you want Mike. At this moment I would recommend for backshed members to make an account on Easyeda and sent me a private message with your account name. That way I can add you to the project, I can give you acces to copy the project and do whatever you want with it. That way we have time to write proper description before exposing it to the world if we want to. Edited 2020-05-09 06:33 by nickskethisniks |
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| wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156 |
Thanks Nicks and Mike, if I divide Nicks 100mA by the 10 parallel strings, I guess that's of the order of ~10+mA that Mike suggested. This is a whole lot less than I was expecting, it appears that for an average say 3 strings in parallel ~ 1A is lost in ~3 days or ~ 50Wh for a 48V system. It almost sounds like a non event to me. For a 1kWh storage 5% for 10kWh 0.5%. To put into perspective 0.5% is 1 hours use in 200 hours. Nicks I have almost finished creating all the symbols required for Altium and just have the current sensors to go and the schematic will be finished. Can I assume you can also convert from Altium to easy eda? That would make it a whole lot easier for me. If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike |
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renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Almost every panel in existence would have blocking diodes on the back already wouldn't they? Cheers Caveman Mark Off grid eastern Melb |
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| wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156 |
Fair comment (I wouldnt have a clue - google seems to suggest they do) but it seems like Nicks and solar Mikes don't or maybe the blocking diodes have this much leakage? There seems to be two takes on this, some suggest they are in the panels so external blocking is not necessary, the other says that the charge controllers perform this function so blocking diodes are not needed. I dont know which one is right....yet. If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Open up the black box on the back of the panel and you'll see them there, they have been in every one I inspected. Be careful opening them though the little tabs break easily. Cheers Caveman Mark Off grid eastern Melb |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
All my panels have blocking diodes already there. Cheers, Tony. |
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Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1026 |
Most of mine have Bypass Diodes only. Cheers Aaron Off The Grid |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
Mine have bypass diodes, not blocking ones; generally if blocking diodes are used it is one diode per string of series panels. Mike |
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| shallowal Regular Member  Joined: 26/07/2018 Location: AustraliaPosts: 58 |
I thought the diodes were normally for bypass rather than blocking.  Allan |
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poida Guru Joined: 02/02/2017 Location: AustraliaPosts: 1420 |
Feel free to put it all up here on the forum. wronger than a phone book full of wrong phone numbers |
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| azhaque Senior Member Joined: 21/02/2017 Location: PakistanPosts: 117 |
I can try and export it to Kicad if there are people interested. Haven't actually done it but remember something to this effect in Easyeda. azhaque |
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| azhaque Senior Member Joined: 21/02/2017 Location: PakistanPosts: 117 |
Wiseguy, Here is the file exported from EasyEDA (Thanks Nick for forking it over) to Altium.(I assume that is what you meant  )Pls try it out and tell us. Regards BuckConv.zip Edited 2020-05-09 15:22 by azhaque |
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| wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156 |
I just finished creating the schematic in Altium - here it is. MPPT SCH.pdf Please critique away. I just added bits for 2 snubbers and RC filters for 3 analogs before sending to the nano via the ribbon cable. Edited 2020-05-09 15:37 by wiseguy If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike |
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| azhaque Senior Member Joined: 21/02/2017 Location: PakistanPosts: 117 |
Thanks Wiseguy. Consider putting the input side capacitor bank, upstream of the ACS758. Also pls consider a 2nd connector for the power lines instead of the ribbon cable. azhaque Edited 2020-05-09 15:40 by azhaque |
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| wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156 |
Considered and discarded - unless you really want to see all the switching noise superimposed on the low level current signal ? Am happy to try for a 10 way inline connector if it fits - I reckon the 48V to 12V converter feels like it belongs on this PCB too. Edited 2020-05-09 15:43 by wiseguy If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike |
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| azhaque Senior Member Joined: 21/02/2017 Location: PakistanPosts: 117 |
But then it is just the thick wire inside the ACS. Wouldnt the noise leak thru anyway? |
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| wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156 |
If we did it your way on the LHS input of the current sensor we have smooth DC on the other side of the current sensors we hav a node jumping from Vin to Vout with current spikes from 0 to 60A ? why would we not see this ? Iin is the current from the solar Panels not the P-P current of the high side switch. Edited 2020-05-09 15:51 by wiseguy If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike |
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