Sunamp temp vs. charge

[PhilRobinson]

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.

[SteamyTea]

It is to do with the nature of phase change materials.

 

When a block of ice changes to liquid water, there is a phase transition at 0°C.

During this change, the energy that can be released.

Water as a liquid has a specific heat a capacity of 4.2 J/g.K, when it is solid (ice) it is 2 J/g.K

When it is actually changing state, is it ~325 J/g.K

 

Now the Sunamp does not have water as the phase change material, so the numbers will be different, but it works on the same principle, it draws the majority of the energy while it undergoes transition.

This is why it is hard to use Temperature as a state of charge indicator.  It is not linear, but stepped i.e it drops at one rate, levels off, then drops at another rate.  The same is true for charging it up, but in reverse, obviously.

[Nickfromwales]

@Jeremy Harris fitted a neon indicator to his and was told ( iirc ) that it was responsible for the PCB blowing, and he was warmed off doing anything similar again or his warranty would be void.......

The new UniQ’s have inboard electronics with a wealth of 4 x LED’s to show various guestimates. Think they’re more for silencing the crowd vs giving accurate data tbh. 

[PhilRobinson]

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?

 

Edited November 1, 2020 by PhilRobinson

[SteamyTea]

I don't know the inner workings of a SA too well, only seen an early version.

I suspect that for material longevity, and very little performance gain, the heater cuts out at the optimum charge temperature. So a little above 58°C.  This will also reduce expansion.

Phase change materials are odd things.  They can be charged up i.e. change from solid to liquid, then allowed to cool while still in the liquid phase.  Then they can be activated to change phase, releasing the energy at the phase change temperature.

This partly accounts for the low standing losses of the SA units.

If they did overheat the material, that extra energy would relatively quickly be lost to the atmosphere (the small amount of vacuum panel insulation is to brilliant at retaining a 55°C temp difference).

So this heating regime may account for the pulsing, it is just limiting the power being inputted, which also limits the overall temperature.

Edited November 1, 2020 by SteamyTea

[arg]

On 01/11/2020 at 17:57, PhilRobinson said:

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?

 

Are there actually 3 separate cells?   I don't know anything other than what I've read from others, but I had understood that there was a single volume of the PCM material with 3 sensors at different heights within it (and the heater at the bottom).

 

So it would make sense, starting from cold as in your graph and hence all the PCM in solid state, that the heater initially melts a small volume of liquid that's very close to the heater.  Further heat will then rapidly spread through the already-liquid part (by convection) but more slowly through the rest of it since there's a limited surface area of the frozen stuff in contact with the hot liquid and also there's a large amount of energy absorbed as the surface layer melts - think ice floating in a cup of warm-ish water.  So you'd have a gradually increasing volume of hot liquid that's much warmer than the average of the whole thing, until everything has melted and you are just putting in the small amount of extra energy stored in the difference between it all being at the melting point vs all being at the max permitted temperature.

 

I didn't think the sunamp controller (at least the original separate unit which has had photos shared) had any means of finely pulsing the elecrical supply to the heating element - it appeared to be a simple relay switching the element on and off.   It could potentially pulse slowly (seconds) during the initial warm-up to avoid that small volume of liquid near the heater from exceeding the maximum permitted temperature as it takes time for heat to spread through the mostly-solid content; that should be less necessary later in the charge process as there's a larger volume of liquid and less convection.  But it's possible there's also a thermostatic mechanism in the heater itself (independent of the three temperature sensors used by the controller).

 

As above, these comments are 99% speculation, though I'd be interested in any info to confirm or deny...

[PhilRobinson]

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.

 

 

[SteamyTea]

I bought, for about a fiver, a current activated switch. Using that you could count the pulses, and if you know the power of the heating element, you will know what is going on.

I suspect, but don't know the chemistry that well, heating is limited to stop phase change when it is not needed. The thermal conductivity of the PCM will be different when it is a liquid and when it is a solid, and not just because a liquid can flow.

Normally when a PCM changes state, it cannot be easily stopped. SA have got around this somehow, and that somehow may be to do with how the material is 'conditioned' during the heating process.

[PhilRobinson]

9 hours ago, SteamyTea said:

a current activated switch

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

[SteamyTea]

49 minutes ago, PhilRobinson said:

Wow I never thought of that

Was a tenner, but after I ordered hound them cheaper.

They also do DC activated ones, could be useful for PV 'suff' i.e. diverting power.

 

https://www.ebay.co.uk/itm/SelfSupply-Adjustable-Normally-CloseAC-Current-Sensing-Switch-SZC25-NC-AL-CH/114352241908

 

I got it to turn a fan on so that I can put my new oven under my induction hob.

Edited November 4, 2020 by SteamyTea

[PhilRobinson]

13 hours ago, SteamyTea said:

https://www.ebay.co.uk/itm/SelfSupply-Adjustable-Normally-CloseAC-Current-Sensing-Switch-SZC25-NC-AL-CH/114352241908

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.

[SteamyTea]

Only took a few days for mine to turn up. China warehouse in Southampton probably.

I have used an ordinary relay in the past. Just hook the coil up to the switched supply, then sense the contacts closing.

Edited November 5, 2020 by SteamyTea

[ProDave]

I have been reading this thread and would like to know more, purely from an academic point of view:

 

You have tapped into some data on a "TX" pin.  How the hell did you figure out what it was transmitting and in what format?  hours with an oscilloscope?  I bet SA don't publish that information.

 

And once you have found what format it's transmitting, how did you work out what all the data was saying?

 

And last question, what did you use for your monitor?  I will guess a raspberry pi?

[joth]

5 hours ago, ProDave said:

I have been reading this thread and would like to know more, purely from an academic point of view:

 

You have tapped into some data on a "TX" pin.  How the hell did you figure out what it was transmitting and in what format?  hours with an oscilloscope?  I bet SA don't publish that information.

 

And once you have found what format it's transmitting, how did you work out what all the data was saying?

 

And last question, what did you use for your monitor?  I will guess a raspberry pi?

 

To get you started, there's a nice little clue stenciled on the PCB next to the Comms header....

 

Nice work Phil ?

[joth]

... that said I also see I2C on the header and 5V supply and a 3.3V regulator so there's plenty of alternatives to explore

[PhilRobinson]

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).

[SteamyTea]

I find all this very interesting.

I like logging data, and analysing it even more.

[PhilRobinson]

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

 

 

Edited December 28, 2020 by PhilRobinson

[SteamyTea]

So is the heater 3 kW?

(reading from chart 17:02 - 16:20 = ~0.40[minutes] and 2 kWh)

[PhilRobinson]

2 hours ago, SteamyTea said:

So is the heater 3 kW?

(reading from chart 17:02 - 16:20 = ~0.40[minutes] and 2 kWh)

 

@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.

 

[SteamyTea]

@PhilRobinson

Only reason I questioned it was that I thought the SA had small, 1 kW heating elements.  No idea where where I picked than up from, so may well have been wrong, or maybe some old units do have small elements.

The chart looks fine to read off.

Edited December 29, 2020 by SteamyTea

[DamonHD]

3 hours ago, SteamyTea said:

@PhilRobinson

Only reason I questioned it was that I thought the SA had small, 1 kW heating elements.  No idea where where I picked than up from, so may well have been wrong, or maybe some old units do have small elements.

The chart looks fine to read off.

Sunamp was happy to supply with smaller-than-3kW elements when I asked some time ago.  But maybe that option has evaporated in favour of keeping production simple.

 

Rgds

 

Damon