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Forum Index : Microcontroller and PC projects : Current measurement of solar panel output
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| BrianP Senior Member  Joined: 30/03/2017 Location: AustraliaPosts: 292 |
Hi all I have accumulated over the past few years a variety of 180-280w of solar panels & currently there are 3 separate MPPT regulators in use feeding a multiple battery bank in a series-parallel combination (it is a 24v system). Consequently it is quite a pain to monitor the various daily solar production as only one of the regulators can store KWH history on a weekly basis. One of the regulators can output up to 100A, the others 60A each (on a really really really good day). An ideal task for a 'Mite to monitor? Requirements: Measure battery voltage, measure each regulator output current, & calculate KWH for each day using the measured voltage & current values. The energy output for each day can then be read & reset at a convenient time. Dilemma: What to use for current sensing? I would rather not use shunts in the negative regulator output lines if I can avoid it, which then leaves the use of hall effect sensors clamped to the output cables. Is this idea practical? Are there sensitive enough hall effect modules that could be just clamped to the regulator output cables? If anyone has experience in this area your advice & recommendations would be very much welcome. Incidentally, how many can remember what we were told when solar panels became available, i.e. they would pay for themselves? Because mine are all installed by me there is no qualification for any taxpayer subsidy (I'm OK with that though). Latitude here is 36 degrees south, so winter & trees don't help. So far with an expenditure of about $30k I reckon I've saved about $2k! (Solar panels were double the price they are now & nearly double the capacity than when I first started out). Needless to say, I am NOT off-grid. Thank you in advance  Brian P. |
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TassyJim Guru  Joined: 07/08/2011 Location: AustraliaPosts: 5900 |
I use the ACS712. They are analogue output but there are other chips that are digital. Jim VK7JH MMedit  MMBasic Help |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 639 |
G'Day BP There are a lot of split core devices particularly under raspberry current monitoring. However I did notice one was +/- 3% from 10% to 120% so who knows what below 10% A bloke did suggest we install a system here on our existing system for about $500 I think. We have had a $8k, 5kW system for 7 years. The house is all electric and our beaut gum trees do a wonderful job of shading the panels all winter. We use a lot of electricity, at our age comfort is more important than money. According to my "estimate" our system will have paid for itself in 5 to 7 years. That is based on how much we would have paid for the energy we generated and used ourselves. The credit is trivial. Peter |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
Thanks Jim I've ordered 4 ACS712 modules (Jaycar/Electus) to give them a try. I'll still need to use some form of shunt to reduce the max current through the module though. I know it's possibly fraught with potential problems, but I'm thinking of a parallel connection for the module with the regulator output cable - this will have several milliohms resistance & hopefully can share the total current. Any thoughts? Calibration should not be an issue - adjust the 'Mite software to match the indicated regulator output. Or am I dreaming/  @PeterB What's the latitude at your place? We get heaps of cloud here, so I need heaps of solar capacity to make the most of the little we get  We don't/can't bother with a grid feed-in - would lose the quite reasonable discount we currently have & it would be very un-economic. Because the house has a 3phase supply (back in the day using lots was encouraged so we have electric floor heating which is now too expensive to use - split system aircon is very efficient) I just run separate feeds from the inverter to the areas that use 24/7 power - computer, fridge, etc. etc. We also have a couple of standalone induction cooker units which I connect on the days when the batteries get near full - doesn't happen all that often though. And I'm trying to be environmentally friendly  B Edited 2019-08-16 13:29 by BrianP |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 639 |
34.7476. I really don't understand the effect of cloud. Sometimes it's a killer and at other times it has very little impact. If you want to use the actual cable as a shunt that should not be a problem unless there is a significant temperature change with current and even then I'm not sure how significant it would be. Peter |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
Yes already thought about temperature changes - but I'm not looking for 100% accuracy. Just hoping the regulator output cable has enough resistance to share with the 30A module... B |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 639 |
There is the TSC1031 which uses the cable as a shunt and removes the common mode stuff. I wish some of these things were available when I worked for a living.  Peter |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 5900 |
I should have read your post closer. I use the ACS712s on my little solar setup. For high currents you need the ACS758LCB-100B That gives you +/- 100Amps. There are unidirectional ones but I haven't seen them in modules. I used some 50A ones in my caravan but you can get up to +/-200A. The modules I used had nice big bolt holes but I can't find them on eBay any longer. This one is OK but no big bolt holes: https://www.ebay.com.au/itm/Current-Sensor-IC-ACS758LCB-050B-100B-PFF-T-ACS758LCB-Current-Module-AU/263478819354?hash=item3d588fba1a:m:mGHl37aBVtJ7tQah5Dxll-Q&frcectupt=true Jim VK7JH MMedit  MMBasic Help |
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panky Guru Joined: 02/10/2012 Location: AustraliaPosts: 1094 |
Like Jim, I have ACS758 50A units in use in my caravan Only limitation is they are 5V devices so you will need to scale the sense output. At some possible loss of accuracy, you can shunt some current by using a parallel shunt across the hall element - as long as you initially measure the ration of currents and compensate in software, this can increase the current capacity. Panky ... almost all of the Maximites, the MicromMites, the MM Extremes, the ArmMites, the PicoMite and loving it! |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
Yes, this is what I'm going to try with the 30A modules, using the cable as the shunt. They quote 66mV/A as a resolution so hopefully there will some usable measurement down to 1A or maybe a little less. We'll see... B |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1123 |
A suitable circuit for this was posted some time ago, see Current Sensor Module Scroll nearly to the bottom of the page. Cheers Mike |
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| PicFan Senior Member Joined: 18/03/2014 Location: AustriaPosts: 133 |
Maybe is this a solution ? Link |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
A reasonably low cost off the shelf solution would be a Turnigy power meter. These measure volts, amps, watts, cumulative watt hours, and cumulative amp hours. Max input typically 60v and 150 amps, all for about $20.00 https://www.ebay.com.au/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=turnigy+power+meter&_sacat=0 Cheers, Tony. |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
@PeterB Yes, clouds! What ever happened to the solar panel development that was reputed to produce usable output under moonlight? (probably bought out & killed by other vested interests)  @Solar Mike, @PicFan, @Warpspeed Guys thanks for your input  The issue I have is I would like to separately monitor the output of the three individual MPPT controllers which should make me aware of any developing issues (like cleaning bird crap & othe detritus off the panels). So I need 3x separate monitoring units which is why I'm thinking of using a 'Mite to independently handle the info. Would also easily allow for any future expansion. Why do I have 3 separate controllers? Well, this journey started in January 2013 with just 3 or 4 panels & controller (not MPPT back then) feeding a 24v battery & 3KW inverter system. Over time more panels have been added, but of varying characteristics so they are not suitable for a series connection. These now 16 175W panels (which don't have isolating diodes to prevent back feeding) individually feed into an array of schottky diodes mounted on a common busbar (fan cooled) & all output to a 100A MPPT controller. In December 2014 4 200W panels of identical properties were installed, parallel fed to another (smaller) controller as the original controller was up to capacity. In February 2019 I installed another 6 275W panels in a 120v series/parallel combination feeding into yet another MPPT controller. I'm planning on adding another 6 of these panels into the latest controller (Because of PeterB's "beaut gum tree shading" this extra bank of panels will be physically distanced from the others as far as possible). All these new panels of course have isolating diodes. All controllers are parallel fed into the common storage battery bank with 3KW inverter (I do have a 5kW unit not yet installed. I'm planning on using this unit in addition to the 3kW one for short-term high-peak loads such as the washing machine (3kW for 30minutes) & full-on cooking sessions (4kW)) Both these inverters are the "old school" transformer variety which handles peak overloads better & produce a cleaner sine wave output than the all-software ones. (I've perhaps started a flame war here...)  Re-stating the need for maximum solar output to get the batteries reasonably charged. In winter they seldom get a full charge & even more infrequently receive a necessary equalization charge. Yes, if this project was to be started all over it would be done differently. As per the old saying "like Topsy, it just growed".  Cheers Brian P. |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
To give some idea of the solar profile here... (from February) Image.pdf B Edited 2019-08-17 14:36 by BrianP |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 639 |
Here I go again. You young blokes never listen. The TSC1031 does exactly what you want for a couple of dollars. No need to cut cables, just connect the chip to each end of the existing cable, there, all done. (That is until you read the fine print) But I think they are the answer to a maiden's prayer. Good luck Peter P.S. our 5kW system was generating 2.2 kW at 9am but dropped to 500W when Bill's red gum got in the way. You can't have it both ways. P |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
Consider me suitably admonished  My only excuse is that you said "young" blokes - definitely does not apply here... It certainly looks the goods - I'll follow up. Where to get them? ta muchly B |
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| erbp Senior Member Joined: 03/05/2016 Location: AustraliaPosts: 186 |
RS Components have the TSC1031IPT (if this is the same beast) at $3.30 ea ex GST for a minimum qty of 5. If you order via the web they offer free delivery with no minimum order value required - see RS Components Note: I have no connection whatsoever with RS Components aside from buying stuff from them occasionally. Cheers, Phil |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
Thanks Phil - I have often used RS for various stuff What has always bothered me about RS Components is that I'm from an era where "RS" meant something else altogether B Edited 2019-08-17 17:59 by BrianP |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 639 |
Sorry. I missed the where to get them ?. If you Google them every man and his dog sells them and one offers to supply a free sample. I hope they do the job. Peter |
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