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Forum Index : Solar : Solar buck converter
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| rogerdw Guru  Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Hi Nick, thanks for this post, I had forgotten seeing this thread before. Looks very tidy and easy to read with all the displays lined up. It's good to see how others are putting their systems together. What sort of diodes are you using on the outputs, you mentioned schottky but do you have a part number please? All three outputs then charge the one battery? Cheers, Roger |
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| nickskethisniks Guru Joined: 17/10/2017 Location: BelgiumPosts: 458 |
Apparently not really a shottky diode, partnumber is UFB200FA20P, I'm using 2 of them, 1 is only half used. Yes the outputs from the diodes are tied together and go to one battery. Yes it's good to share ideas and learn from each other. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Thanks Nick, that's very helpful. I've had a look at a few datasheets and comparing what's available and what's not. Still a lot of components on back order. Do yours get very hot ... and I assume you have them on a heatsink. Cheers, Roger |
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| nickskethisniks Guru Joined: 17/10/2017 Location: BelgiumPosts: 458 |
I used what I had, one of my addictions is to buy small lots of genuine components :) These were 5€/each. So today after a few hours running at minimum of 60A through one sot227 package (40+20A), I could still hold the package and heatsink and it felt warm, so I think around 35°C. They are mounted on a big heatsink, the same as the 3 controllers. Doing total of minimum 70A. Heatsink is not active cooled, but room is like 18°C. I must say it has a massive heatsink, (30*55cm with 5.5-6.5cm fins) At the moment, 24A has 0.774V voltage drop and 5A has 0.65V drop. I like those packages for these kind of application, they have a great thermal heat transfer. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Thanks Nick. I've been checking out similar items from element14 and RS and have been shocked by the prices. Up to $200 and more and many are on back order for months and months. I really like the package too ... and being isolated lend themselves well to the task. It's a bit of a trap when they say a eg. 104A diode ... but when you read the datasheet ... that is only when run as one in parallel. Just figured I should go look through all my scrap inverters and see if there's anything suitable amongst that. Should be cheaper.  Cheers, Roger |
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| nickskethisniks Guru Joined: 17/10/2017 Location: BelgiumPosts: 458 |
You should find simular around 10-15€ each. Poida is not using series diodes so they are optional. Use a breaker or fuse on the output and you've included a safety measure. You can always make a small pcb and put tht diodes on it as alternative on an isolated piece of aluminium. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Mmmm ... best I could find was here ... Still want $46.52 each for them. I do have circuit breakers on the inputs and outputs, so maybe I don't need to worry. I kinda started to think I need them when I saw your original post ... but also because even though I was careful in my calibration etc ... I find that often one output is quite high (maybe 1,800 watts) and the other throttled right back to a couple hundred watts ... and yet other times almost equal. Maybe I should go through the calibration again ... or any other thoughts? Maybe that is normal? Thank you. Cheers, Roger |
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| nickskethisniks Guru Joined: 17/10/2017 Location: BelgiumPosts: 458 |
You are right, they are more expensive then I thought. Did you split the input? ( one solar array/ controller) No, unless they are out of MPPT algorithm, and/or are in bulk/float. If you are entering bulk phase or float then it's normal I think, the battery can't except all energy the solar is producing. You can try to set them with each a little bit different settings. If you did calibration right, a new calibration will not help, my first controller was put on the wall and I never did a new calibration. I found these: still expensive and on the other side of the world for you https://www.ebay.de/itm/374948019548?hash=item574ca4bd5c:g:dEsAAOSwSEllECDX https://www.ebay.de/itm/372752131075?hash=item56c9c22403:g:4pEAAOSw5MllEqAa https://www.ebay.de/itm/372752131892?_trkparms=amclksrc%3DITM%26aid%3D1110013%26algo%3DHOMESPLICE.SIMRXI%26ao%3D1%26asc%3D259211%26meid%3D8c4afabdd2bb45c48eba9b8c3a091745%26pid%3D101196%26rk%3D4%26rkt%3D12%26sd%3D375100942934%26itm%3D372752131892%26pmt%3D1%26noa%3D0%26pg%3D4429486%26algv%3DPromotedRVIPbooster%26brand%3DIXYS&_trksid=p4429486.c101196.m2219&amdata=cksum%3A3727521318928c4afabdd2bb45c48eba9b8c3a091745%7Cenc%3AAQAIAAAA8JsbtOKd5uIU0OgsJNCgXCNZoJnSlqKTzN4YnXE4mpdYKusuurKZg1dbZ5OUhncUiPVBQrZQ8D%252BEFuyiv1uISXTh3orlnanagDE0sjahS%252Fji6%252FlQN6Ra67HYiZ3lG5szQc0EdT4uA2s%252BVJdP1Ii%252FNVcWFScalb3iPI8IHGu7hV7ITiFFcbaGrHvG7KaKfqWuon1xyg9N6F0W9cdMaDIMRbio9BKBcZQ3tbgImJ3Lzm%252FDdD4zjdP0%252FfxCA1itEXHOJhoFtxKLyo5rsdxsk3tMVGpqRXjdI7Tj--wlGCusdjfQC%252Ffpkq2xf1YvMFnhLZIAUQ%253D%253D%7Campid%3APL_CLK%7Cclp%3A4429486&epid=1442703376 |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
Sometimes I have 3-4 mppt controllers feeding a single battery bank, each has its own circuit breaker, have never used extra output isolation diodes, all they do is waste heat.... If you want to use them, Schottky types would be preferable, 100V 100 amp Like These Big high current bridge rectifiers are pretty cheap on AliExpress. And you are correct, its difficult to get them to current share, I normally have each controller programmed for a max current limit, so under bulk charge they share current equally. Your controller looks very good. Cheers Mike |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Thanks Nick. No, I have 3kW of panels 3s4p into each controller. I don't think there is a major problem then, I'm just getting used to how they work. I might still go through and check the parameters, though pretty sure they were all consistent. Thanks Mike, looks like I was expecting the diodes to fix something that isn't an issue anyway. I also have cct breakers on the inputs and outputs of each mppt. The more I watch the displays at the various stages, the more sense it makes. Cheers, Roger |
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KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1679 |
Sorry for breaking up the lines below, for some reason it's forcing the view in my browser to scroll across three times the screen width if I don't?? and at the moment, only in this thread. Hi Rodger. I thought I would chime in on paralleling MPPT solar charges. You likely know that I've had four mppt in parallel for years, soon to be five in parallel. I initially had one mppt feeding each battery bank. I made sure that all mppt negative cables were the same length back to a common ground point. All battery and other charge cables were also the same length to the AC inverter connection bus. The 60A "Make Sky Blue" mppt controllers, like most I assume, are incredibility sensitive to output voltage tracking. The manufacture shows them connected in parallel and goes to length to emphasize equal cable lengths, that was mainly to ensure equal individual bank charging and I once did it like this. I now have two common solar charger connecting bus bars, one for positive and one for negative, these go via 53mm2 cables directly to the Junction connections of the AC inverter and Battery connection Bus bars. Solar charger "load sharing" tracks a lot closer than before, but that was not the reason for the change, just a byproduct. Tracking really makes no difference to the operation of mine. I sized the panels to produce a max of 40A from each controller, this gives me plenty of headroom for solar input flaring. One mppt may be running at 23A and the other three at say, 12A, 9A and 7A. As soon as the load demand increases, they obviously have no choice but to start to equalize current sharing. I would imagine that yours runs like that as well. No diodes and I have had no faults after years of running it like this. I did calibrate the voltage display on each mppt, they use that calibrate voltage point to accurately set the mppt charge output regulate voltage. This system runs an average of 1.5kw all day, there is some running time at 3kW and short surges up to 10kw or 13kW. In my situation, any diodes would be problematic and wasteful. It's the "Solar chargers" that power the AC-Inverter all day long, when each battery pack charges to a set point, it disables its charge input. So the only time the battery packs might show any discharge current is from load startup surges or from falling solar input, but for 90% of the day the solar chargers run the house and shed by themselves. The batteries sit floating with almost no charge input and almost no discharge until the evenings, when the batteries run the property at night, repeat cycle. . Edited 2024-02-02 11:10 by KeepIS It's all too hard. Mike. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Thanks very much Mike that explains a lot. The ultra wide screen is a fault that shows up if a very wide image is posted or in this case a very long link a few posts up. Sounds like I'm aiming for the same thing as you with my charge controllers. I have four though only the first two are connected so far. All outputs are paralleled immediately and then head over to the inverter/battery lead connection via 70mm cable. It's odd but since I first complained out it, the system has been a lot more even ... though I won't get so concerned if I see big variations when I fit the other half of the panels. I'm also hoping for the panels to provide the bulk of the daytime power, direct to the inverter ... and the battery to take care of evening and overnight. Thank you again Cheers, Roger |
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