PhilRobinson

@SteamyTea thanks for your interest, and the current controlled switch tip. The chart shows a full hour - the "17:20" label is missing from the x-axis ( I suppose that counts as a bug), and as you see its at 2.8kWh (hard to tell accurately) at the end of the hour. It does look like more like 2kWh at 16:20 as you say; not sure why. Maybe the image compression? Anyway; the SA manual says 2800w, so that's what I have in the config. The logger allows you to put in any figure you like for kW because in summer when it's charging off our little PV panels, we charge the SA through a 110v site transformer. The PV only generates around 1- 2kw, so the lower current consumption means it takes longer to charge and therefore uses more sunlight and less grid elec.

Here's an update: I acquired a current activated switch as suggested by @SteamyTea - thanks. Wrote some code and added a bit of circuit to the logger, so I can now monitor the current consumption as well as the heater relay state. As @arg discusses (above), I'm interested in the idea that there could be a switch attached to the temp sensor(s) (probably just the bottom one) so that although the power relay is on, the SA could detect high local temperatures around the element and turn it off for a while until the heat has conducted around a bit, then turn it on again. This 'pulsing' would be undetectable in my previous version as it just read the state of the relay. The first graph shows temperatures and relay state (ON - the red line along the bottom). The 2nd one shows current consumption over the same 1/2 hour. If it was pulsing, the kWh line would be flat for some periods; in fact it just goes up steadily as long as the relay is on. The SA only outputs data every 12 seconds, so if it pulsed faster than that I might not see it, but that seems unlikely so I'm concluding that it doesn't pulse and the only control over the element is the relay. I've done this test (charging from empty via the electric heater) a few times, always, so far, with the same result. One interesting point is that temp 1 actually hits 93° and stays above 85° for about half an hour; reassuring given that the max temp given in their manual for a hot water charge is 85°. There are two other things I'd like to improve on the logger; 1. I have in mind a better way to calculate the current 'charge', but it will take a bit of writing and is on hold for now. 2. I may well add a relay to it so that I can switch the pellet boiler on when the charge drops below a configured level. For now though, it does what I want - indicate charge level and current consumption and allow me to download logs for spreadsheeting if I want to. http://whatsnormal.org/sunamp-logger/sunamp-logger.html

I'm very hesitant about saying how I did as I don't want to attract accusations from Sunamp that I'm encouraging people to mess with their boxes. Plus of course, whenever you reverse engineer something you may finish up with a system that works but is nonetheless not entirely correct; for example it's quite possible that the SA may one day output something which the logger doesn't understand. It hasn't yet (running about a month), but that doesn't mean it never will. I never noticed that modbus on the pcb - well spotted. No need for a Pi; the data is simple to read. But I did want a webserver with as little trouble as possible, so inside is an esp8266 chip. At the moment it's actually an Adafruit 'Feather Huzzah' (and some supporting bits and bobs) because it's easier to work with, but if I was making more of them I'd use a raw esp8266 - probably the 8mb robotdyn one (the logs are stored on-chip, so more memory is a good thing).

I was so excited I just ordered one without checking where it was coming from; China. So it'll be few weeks, but I'll report back when i get it working. Thanks again.

Wow I never thought of that; I've been toying with the idea of one of those ammeters where you stick the wire through a coil but a switch sounds a much simpler and more accurate idea. I'll look into it thanks. Also, @SteamyTea and couple of other people expressed an interest in the logger, so I made a web page for it.. http://whatsnormal.org/sunamp-logger/sunamp-logger.html

Thanks for your thoughts @arg In their 2016 brochure... https://www.sunamp.com/wp-content/uploads/2016/05/Sunamp-Heat-Batteries-Brochure-web.pdf .. they say their PV, Stack and Cube products are made from different amounts of cells, but I think you're right; I'd carried that assumption through to the UniQ range without thinking. Their UniQ pdf actually refers to "the cell" (singular) and their diagrams also indicate that its a single container too, so thanks for that. As for the pulsing thing; you don't see the relay in the controller switching on and off, but you do see the current consumption switching on and off rapidly right at the start. I expected to see that when the first temp. value reached its peak at 90+°C too, but I don't have a good way to monitor it (I just have to stand over an ammeter making notes). I'll do some more runs monitoring the current closely probably at the weekend and post the results when I have them.

Thanks for your replies! @Nickfromwales; I wasn't aware of Jeremy Harris's neon issue; I'll dm him and ask what happened in the end, thanks. The new SA box with LEDs strikes me as huge improvement, but of course no help to me since I have an older control box! Back to my original question; sorry, I don't have much experience of using forums and I now realise I should've been more specific in what I was asking. So... Here's a graph showing the 3 measurements from the 3 cells of our Uniq 12 as it charges up (from the immersion heater) from empty at 16:00 until the controller switches off the heater at approx. 21:30. (After that it's just sporadically discharging as we have showers and wash up etc.) The yellow line also shows an average of the three. I expected to see, as @SteamyTea suggests, a fairly quick heat up to 58°C, hovering around that temp for the majority of the time then a short time above that up to 75 or so before turning off. As you see, that's not what happens at all. I'd like to understand what's happening as I want to use this data to compute an accurate charge level. (It's further complicated by the fact that when you monitor the current consumption, it's clear that the SA is 'pulsing' rather than supplying a steady current. I need to look at his some more, but I don't think its very significant except when the store is pretty nearly empty.) So; cell 1 zooms straight up to 90°C in the first half hour. Since by this time its only consumed about 1.2kWh, this can't possible by the actual temp of the cell 'overall', so I figure the sensor must be very near to the heater element. Unless there's actually more than 1 heater element? The others then slowly catch up, presumably by conduction. The other cells also don't do anything particularly non-linear at 58°C. I'm baffled. Maybe the three readings the Sunamp outputs aren't temperatures at all! Answers anyone? I Someone must know than I do about this? Please?

When we got a Sunamp Uniq heat battery last year we were a bit surprised to discover that it had no lights, switches or user interface of any kind. You can't tell whether it's charging or not, how much charge it has in it at any time (i.e. can you have a bath or not) and you can't tell it to start or stop charging. It just sits there doing what it's configured to do (It does that very well and we're very pleased with it.). So to cut a long story short I made a little box that displays charging status and the state of charge and also has a little web server so I can see graphs of temp, charge state, kWh used etc. It works just fine and is very useful. BUT computing an accurate state of charge from just the reported temperatures is difficult I’m hoping someone here might know more about it than I do? Happy to provide more info as to how I do it at the mo. if anyone’s interested.

Very happy to… Basically, I’m trying to get it to report the charge state as a percentage. I ran all the hot water out of my sunamp uniq12, then set it charging at a slow current and had the logger monitor the 3 cell temp. readings. In the graph the x-axis is time, y-axis is °C. The series shown is average temp of the 3 sensors. As you see, its non-linear but not half as much as you’d expect. (I expected the temp to stay at or around 58° for ages.) However; if you look at the temps of the individual cells, they do show a much greater non-linearity around the phase change temp. The relatively sane average graph results from the fact that the cells heat up at different rates so they’re not all phase changing at the same time. So this makes the logger able to calculate the charge reasonably accurately for the 3 cell sunamp, while it’s charging or discharging (similar things happen during a constant discharge). However, my brother has a small sunamp which I think has only 1 cell (or maybe 2), so my simple algorithm which works out the charge % based on an average isn’t going to work so well for his. Also, in real life the temps seldom hit empty and/or full, and the cells are are constantly charging and discharging every time you turn the hot tap on or a radiator comes on, so it doesn’t work so well then either. So in practice, the logger can report the actual “charge” with some accuracy only in the top and bottom 20% or so. BUT, at least where you have multiple cells, I can’t help feeling that the differences between their temperatures must be telling me something useful about the charge state. I just can’t work out what. Does anyone know more about this than I do? Happy to post more graphs etc if anyone's interested.

We’re renovating a 1926 suburban 3 bed semi. Nothing flash, but we decided we’d try and make it as eco as possible on our limited budget. The first thing we did was asked for quotes from companies with names like “eco heat”, “green heating solutions” etc (these are just made up). They all suggested we install a gas combi, which was a bit disappointing. So we’ve found ourselves insulating external walls as we decorate and largely going it alone from a design POV. We now have a a small solar PV install on the roof, a 14kw sunamp heat battery and a pellet boiler and are working on how to integrate them so the pellet burner heats up the sunamp (in winter) and the sunamp then provides a ‘buffer’ of heat so the pellet burner doesn’t have to turn on too often. In the course of all this, I made a little monitor/logger for the sunamp as we were surprised to find that in spite of being quite pricey, the sunamp has absolutely no indication of the state of charge or even whether its currently charging or not. This is the primary reason for signing up to buildhub; I’m hoping someone here knows more about working out the Sunamps state of charge from its temperature than I do.