February 24, 20179 yr Interestingly, have a rather similar issue at the moment with the balancing algorithm on the Multiplus. Might be helpful here or not. In earlier firmware versions, when running the hybrid ESS or hub4 modes, once you hit the minimum Soc the inverter would go into bypass and use all solar for battery charging, until your SoC was 5% above the minimum. Then it would go back to self-consumption (aka hybrid mix with the grid and try to zero out the meter) mode. But then in firmware version 2.01 an interesting feature came up: It would take into account the solar energy and work that into the calculation. So once it hit the minimum SoC, it would balance solar with consumption so that the batteries remain at MinSoC (ie it attempts to neither charge/discharge the battery, rather keep it there). Only problem was that the estimation was off: Attempting to hit zero on the battery is almost impossible, as the calculation has to be made using AC values and DC values, taking into account both inverter and charge controller efficiencies, and as we all know these things aren't exactly constant either. So it would overshoot slightly and continue to discharge the battery at around 20 watts even after hitting MinSoc. My initial idea was to just slightly change the scaling factors so that instead of slowly discharging the battery, it would instead slowly charge it. However -- and this is the point of me posting about it here -- I realised there is an inherent unstable convergence in that option. The problem is that if you underestimate the amount of available PV (to ensure that a small amount remains for charging) on a very full battery, it pushes the voltage up. When the voltage goes up, the MPPT pulls back current. Your algorithm once again pulls back even more to ensure that current remains available for charging, but this just causes the MPPT to back off even further. Left unchecked, this naive algorithm will eventually pull back completely. Allowing a small amount of discharge actually allows the MPPT to run at full capacity. As a proof of concept, I made a quick hack on my side: When the battery hits MinSoc, I slightly perturb the amount that is fed back by 40 watts. This causes the battery to charge slowly until it is just above MinSoc, at which point it removes the 40w offset. The effect is a saw-tooth right around the minumum SoC. I think some people will probably tell me I'm putting that battery through micro-cycles :-) So far my hack works very very well. Anyway, I have a further idea to make this sort of "self learning", or rather, a kind of binary search for the zero point. A bit like TCP/IP uses for congestion control. You slowly increase the discharge rate until you hit MinSoC. Then you halve the discharge rate, and repeat (again slowly increasing). When you hit MinSoc again, you take the halfway point between that rate and the previous one, and repeat. You should finally settle at a rate just below the available PV. No I don't know exactly how you'd implement this on non-hybrid inverters, though one way would be to widen the Soc levels you switch at. For example, say you switch to grid at 80% SoC, and back at 85%. When you reach 80% the second time on the day, you switch to grid, but this time you wait until 90% SoC before going back to battery. If you hit MinSoc again on that day, the new switch limit becomes 95%. And so on. Once you hit 100% SoC, you go back to the 85% upper limit. The effect: If you tune this properly, it should ensure that the batteries are fully charged every few days, avoid unnecessary switching, and help you adjust to seasonal changes.
February 24, 20179 yr I had a similar dilemma, although not as complex (was only interested in general load) and did solve with Software (but this was only a single load swtich over). My program was quite simple, and used the Axpert Serial interface and protocols: (POP00 is to Utility, POP01 is to Solar) On Solar - If (Load Wattage > 1000W battery draw for 2+ minutes && over 15 min since last switch) -> Send POP00 command (eg: Wife forgets and turns on something) On Utility - if (Load Wattage < 1000W && Solar Voltage > 100V && time between 09:00 and 15:00 && over 15 min since last switch) -> Send POP01 command (also allows for the problem of someone deciding to do ironing, so load is up/down - reset timer if load jumps over 1000W) That was simple enough to logically program and worked quite well for my purpose, but now that battery bank is only 1/2 capacity, I stay on Utility for now and Invertor is only acting as backup - Will have to wait till I am big to be able to afford more batteries
February 24, 20179 yr @The Terrible Triplett I may have created the impression that is a simple matter but as you know, that is only in concept. It will require much thought before one arrives at a viable solution to document. @plonkster is right, what we need are true hybrids but what to do if you already have two Axperts, like in my case, and really don't want to go through the whole rigmarole of installation again, not to talk about spending more of our ever more worthless Rands. Why was mankind ever so brain damaged to invent central banks. Oh wait a minute it, it was the bankers who needed a bankers bank to create money out of thin air, which at our time, is not possible with gold money. (I just could not resist that). What we need incorporated in the control program should be both easy to set up and not switch endlessly between grid and solar. Then of course it should be economically viable for the developer to consider or it won't happen. So a lot of thinking has to take place before a possible solution may materialize. In the case of ICC which I use, I hope other users will also give it a thought and that we will be able to persuade @Manie to incorporate it once we have a viable proposal. Already a lot of valuable information and experiences have been posted on this thread. One lives in hope. On that happy note, have a good weekend all after watching your shares drop like lead zeppelins all week.
February 24, 20179 yr Energy you're wily fox . You start a thread say you will get back to us and then watch the the ensuing chaos as the thread unravels and morphs. This tendency is what I so love about this forum.
February 24, 20179 yr 8 hours ago, The Terrible Triplett said: Or am I missing the obvious? Yes, a popup that tells you your inverters are not going to last long, hahaha.
February 25, 20179 yr Ok, so since "I know more than anyone else", I will try and say this with caution: Some appliances may suffer pre-mature damage, if switched on and off repeatedly like this. Fridges, some older PC's and TV's and even pool / borehole pumps could burn out when switched on and off, while under load.
February 25, 20179 yr 36 minutes ago, SilverNodashi said: Some appliances may suffer pre-mature damage, if switched on and off repeatedly like this. Fridges, some older PC's and TV's and even pool / borehole pumps could burn out when switched on and off, while under load. Glad you brought it up. I concur for I 'suggested' along the same lines. I would not switch a huge load on and off more than I have to, if I had one. Between summer and winter I add / take off loads to match and max my array and IF the batts have to produce a few amps now and then, so what. They are designed for that. At least Trojans are. And when my loads are switched at set SOC levels, the loads are running off a online UPS in any event. There is NO WAY I am running computer and other IT equipment unprotected, not even on Eskom. That lesson I learned over years. And my fridge and freezers are off grid in any event. So I am thinking that IF a feature is there to switch on parameters, it is assumed it is safe to use, right, what if it is indeed not? I mean I have doubt on the matter and down the line a user/s appliances start failing and it could be implied / suggested it was because of the switching, or a expert comes in and says it was due to the switching, who are they gonna call? And no T&C's are going to make that call easier. To now run a house off an inverter and then switch back to Eskom / solar / Eskom / solar, thinking of our house, grid tie or hybrid inverter seems to be the only way to go. Keep the power smooth and calm at all times. So to accommodate a Axpert with a large array and a smallish battery bank, the potential and unknown risks are not worth the few cents one may make out of the feature added to the software.
February 25, 20179 yr 35 minutes ago, SilverNodashi said: Ok, so since "I know more than anyone else", I will try and say this with caution: Some appliances may suffer pre-mature damage, if switched on and off repeatedly like this. Fridges, some older PC's and TV's and even pool / borehole pumps could burn out when switched on and off, while under load. Thanks Silver. This why I elected to have a resistive load as a dumpload. Plus if I shorten the geyser element's life they are under R200.
February 25, 20179 yr Just now, Chris Hobson said: Thanks Silver. This why I elected to have a resistive load as a dumpload. Plus if I shorten the geyser element's life they are under R200. Plus one on that. I also said geysers pool pumps hair dryers, curlers are fine to switch on and off. Previously I was called funny re. the hairdryer / curler being switched off. Today I have decided that if my wife and daughter keeps on using said devices whilst the entire kitchen is on, and we where on solar, no, it is a lifestyle change we ALL decided to do so they they are going to keep them tongues quiet in their mouth's or I am going to raise my voice for I am not listening anymore. My point. Using the wife and family as an excuse, we should stop doing that. Either they all bought in or they have not. If the decision was an autocratic or hobbyist one, then that is on the decision maker to solve. So either handle the situation with a said Axpert small battery bank or get a bybrid / grid tied system. BUT!!! That is not all. It still means that when they want to use the heavy duty elements, better do do it when the sun shines, and that boys and girls, is the biggest lifestyle change that is needed for no matter what happens, the sun shines best when we are not at home, at least, for most of us. Living in Cpt is THE best place to learn about the complications of solar for in summer we "gooi kole" from early in the mornings till quite late in the early evenings. But in winter, o boy, we have some serious complications for we not only have less sun hours, we have rain too. The rest of the country,lately, seems to have more clouds in summer due to lots of welcome rain. Welcome to our world.
February 25, 20179 yr 9 minutes ago, The Terrible Triplett said: Glad you brought it up. I concur for I 'suggested' along the same lines. I would not switch a huge load on and off more than I have to, if I had one. Between summer and winter I add / take off loads to match and max my array and IF the batts have to produce a few amps now and then, so what. They are designed for that. At least Trojans are. And when my loads are switched at set SOC levels, the loads are running off a online UPS in any event. There is NO WAY I am running computer and other IT equipment unprotected, not even on Eskom. That lesson I learned over years. And my fridge and freezers are off grid in any event. So I am thinking that IF a feature is there to switch on parameters, it is assumed it is safe to use, right, what if it is indeed not? I mean I have doubt on the matter and down the line a user/s appliances start failing and it could be implied / suggested it was because of the switching, or a expert comes in and says it was due to the switching, who are they gonna call? And no T&C's are going to make that call easier. To now run a house off an inverter and then switch back to Eskom / solar / Eskom / solar, thinking of our house, grid tie or hybrid inverter seems to be the only way to go. Keep the power smooth and calm at all times. So to accommodate a Axpert with a large array and a smallish battery bank, the potential and unknown risks are not worth the few cents one may make out of the feature added to the software. It's not so much a big load, as the type of load that's an issue. Motors, in particular, and badly designed power supplies. Some years ago, we had problems with our previous house' wiring. I don't remember what the problems were. It was a double storey house, with the DB downstairs and our office upstairs. An electrician came in to do some tests and the next moment my laptop PSU and an aircon blew. Didn't know what happened. They claim, all they did was to switch circuits on and off to test them. And that was probably true since the lights did go on and off the whole time and we left all the PC's off the whole time. Non of the UPS' took damage though, but the laptop (it has a battery, right...) and aircon (which is permanently on standby, never thought about switching off the isolator outside) blew. More expensive motor controllers generally have protection for this but cheaper electronics often don't. I used to work at a large printer company and services high volume printers. One particular client's printer's imager unit kept being damaged. Later on the building electrician came by and mentioned they had problems with their transformer in the street and one of the 3 phases had 170V. Turns out that kept burning out the imager unit. Moved the printer to another plug point (i.e. different phase) and never had the problem again.
February 25, 20179 yr 1 minute ago, SilverNodashi said: It's not so much a big load, as the type of load that's an issue. Motors, in particular, and badly designed power supplies. Agreed. But I am now putting it out there that as with what you said above and what we all have contributed, no-one can say for sure what will happen over time with some or all the loads in the house if one keeps on switching between inverter and Eskom power. A few hundred watts switching is one thing, a few thousand watts being switched over due to excessive load being drawn from the batteries, just cannot be good for anything. Reduce the load, or replace the inverter with one more suitable for your particular needs. More to the point. Don't force an Axpert into something it was not designed for.
February 25, 20179 yr Just now, The Terrible Triplett said: Agreed. But I am now putting it out there that as with what you said above and what we all have contributed, no-one can say for sure what will happen over time with some or all the loads in the house if one keeps on switching between inverter and Eskom power. A few hundred watts switching is one thing, a few thousand watts being switched over due to excessive load being drawn from the batteries, just cannot be good for anything. Reduce the load, or replace the inverter with one more suitable for your particular needs. More to the point. Don't force an Axpert into something it was not designed for. @The Terrible Triplett You will have this problem with ALL inverters, including Victron. Please stop making Axpert out to be worse than dog poo.
February 25, 20179 yr 21 minutes ago, SilverNodashi said: ALL inverters, including Victron. Again, I agree. Does not matter what inverter make. But this conversation is all about Axpert and 5000VA ontop of that the feature was asked to be done on Axperts. PLUS ... where did I knock Axpert? I thought I typed: Don't force an Axpert into something it was not designed for. EDIT: Correction. You don't have the problem with hybrids nor grid tied inverters or any scenario where the setup was designed so that it can switch based on parameters a few times per day as needed. Reading Plonks post above ... Victron falls into that category(?) if you add all the bits required.
February 25, 20179 yr Perhaps the answer lies in installing a battery bank that can cope with large loads. The more the switching to grid on large loads is discussed the more the complexity of the matter becomes clear. The programming may not be a train smash but arriving at appropriate parameters and switching factors surely seem to be. I suppose my 450AH T105 bank can cope with the odd load of about 65A for a few minutes which is all I have observed. With our sunny West Coast weather at present, it is impossible to determine the impact of intermittent cloud cover. So I am just going to live with it for now and see what happens during the winter months. Fortunately I have a base load of around 800W during the day and somewhat less at night when. It would seem that the right decision would have been to install an Infini but it is too late for that and I will just have to cope with my 2 x 4Kw Axpert cluster.
February 25, 20179 yr 13 minutes ago, ebrsa said: I will just have to cope ... Been there a few times myself. Paid a lot of school fees. How I solved my problems was to sell what I had on Gumtree. If it sells, problem solved. If not, I wait till it sells. Or, as I did the last time I decided 'nee wat', enough is enough. So I got more batteries (for free), split the loads and went off-grid. All I do is to ensure that the off-grid loads never go below 80%, unless I have to. At least now all the parts I have are being used. It is literally setup and forget bar me checking the 7 day SOC of both banks to balance the loads between seasons.
February 25, 20179 yr 33 minutes ago, The Terrible Triplett said: Again, I agree. Does not matter what inverter make. But this conversation is all about Axpert and 5000VA ontop of that the feature was asked to be done on Axperts. PLUS ... where did I knock Axpert? I thought I typed: Don't force an Axpert into something it was not designed for. EDIT: Correction. You don't have the problem with hybrids nor grid tied inverters or any scenario where the setup was designed so that it can switch based on parameters a few times per day as needed. Reading Plonks post above ... Victron falls into that category(?) if you add all the bits required. Grid tie inverters generally don't use batteries. But, set one up with batteries, and under the same conditions you will have the same problems. Looking at Ibiza's problem again: A cloud moves in front of the PV array, and the inverter then switches over to batteries - as it's instructed to. He wants to migrate some of the load to Eskom, and keep some of the load on Solar in this case. SO, in Victron's (using the Quatro - other's don't do this) defense you can have certain loads a emergency loads, and others as non emergency - so when solar is insufficient, the non emergency loads switch off, or switch over to eskom. I don't know if all the Grid tie inverters do this do, so in some cases like the infinisolar you either have full on solar, or a combination of solar + eskom / solar + batteries (depending on the setting, and whether you have Eskom or not). So, even with a gried tied inverter, if you don't have Eskom or batteries, and you don't have enough solar energy, you will run into problems. It cannot produce more than it have resources for. If you only have batteries as an alternative, it will use batteries. If there's eskom as an alternative, it will use Eskom. The issue here is not the fact that it's an Axpert inverter that wasn't designed for the setup, but rather, what do you do to mitigate some additional loads when solar energy is insufficient. Just about every decent inverter have a relay, referred to as "dry contacts" which can be used to switch other relays or contactors on, or off based on certain conditions. BUT, in this particular case, Ibiza wants to switch a whole DB back to Eskom, instead of off. All while still keeping solar for some of the load. Switching off a geyser, or two, as he suggest isn't difficult. Use the dry contacts with pre-defined values and switch off the contactors. The problem lies in the fact that he wants to switch off one geyser at a time, till it meets the power demand. There's only one set of contactors on most inverters so it will simply switch off everything conected to that contactror
February 25, 20179 yr 31 minutes ago, ebrsa said: Perhaps the answer lies in installing a battery bank that can cope with large loads. The more the switching to grid on large loads is discussed the more the complexity of the matter becomes clear. The programming may not be a train smash but arriving at appropriate parameters and switching factors surely seem to be. I suppose my 450AH T105 bank can cope with the odd load of about 65A for a few minutes which is all I have observed. With our sunny West Coast weather at present, it is impossible to determine the impact of intermittent cloud cover. So I am just going to live with it for now and see what happens during the winter months. Fortunately I have a base load of around 800W during the day and somewhat less at night when. It would seem that the right decision would have been to install an Infini but it is too late for that and I will just have to cope with my 2 x 4Kw Axpert cluster. True, but how much money to you want to throw at an expensive battery bank that will very likely never be cheaper than Eskom? Unless, of cause you're on a farm and already pay R4/unit
February 25, 20179 yr 2 hours ago, SilverNodashi said: Ok, so since "I know more than anyone else", I will try and say this with caution: Some appliances may suffer pre-mature damage, if switched on and off repeatedly like this. Fridges, some older PC's and TV's and even pool / borehole pumps could burn out when switched on and off, while under load. My idea is NOT to switch anything off but two geysers, the rest of high loads to divert to Eskom.
February 25, 20179 yr Just now, ibiza said: My idea is NOT to switch anything off but two geysers, the rest of high loads to divert to Eskom. Yes I understood that from the beginning. The problem is, you need to effectively switch off the load, from one source, then switch it on another source. A UPS generally does this, but between Eskom and batteries. So, one way of doing it, would be to look for something that can switch loads very quickly (10ms?) between two eskom feeds. My thinking is that perhaps you could use a high speed ATS (Automatic Transfer Switch), but would need to trigger it somehow. This is, again, where something like a Raspberry Pi which already monitors your load would help. BUT, what do you switch over? A whole DB, or just a geyser? As stated already, the dry contacts can switch off something, like a relay or contactor (SSR, preferably) - but won't do it one it at a time. Instead, you could have two or three appliances contacted to that contactor and then switch them all off at the same time.
February 25, 20179 yr 2 minutes ago, SilverNodashi said: Yes I understood that from the beginning. The problem is, you need to effectively switch off the load, from one source, then switch it on another source. A UPS generally does this, but between Eskom and batteries. So, one way of doing it, would be to look for something that can switch loads very quickly (10ms?) between two eskom feeds. My thinking is that perhaps you could use a high speed ATS (Automatic Transfer Switch), but would need to trigger it somehow. This is, again, where something like a Raspberry Pi which already monitors your load would help. BUT, what do you switch over? A whole DB, or just a geyser? As stated already, the dry contacts can switch off something, like a relay or contactor (SSR, preferably) - but won't do it one it at a time. Instead, you could have two or three appliances contacted to that contactor and then switch them all off at the same time. First to switch off one geyser, if it is not enough switch off another, then if needed whole subDB to switchover to Eskom and finally second subDB also to divert to Eskom
April 8, 20179 yr @ibizaI would suggest using a small separate PV panel (as in cell phone charger type) and measure the power derived from the panel with something like an LED power meter. The signal used to drive the individual LED's could also be use to drive relays. This would give you several logic points which you could use to switch loads between inverter and grid which would not depend on any info from the Axpert but rely purely on the level of insolation at any given moment. I leave it to others in the forum to determine whether this would be feasible and expand on the design...
April 9, 20179 yr thanks for the input @pilotfish and others who gave their view on my question. appreciated
November 12, 20187 yr On 2017/02/24 at 9:06 AM, ebrsa said: The last thing I would consider is using a bunch of relays and associated equipment to do the switching. That would be akin to a step back to the stone age and unnecessarily complicate matters,. After all less is more, always and in any respect. well said! did we spend thousands to make life more complicated?
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