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Andreas

Vac-Star SousVideChef

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Hi,

Keeping with the recent SideKic Thread, I wanted to ask you for your thoughts about the Vac-Star circulator.

To me it seems to have enough power etc. and might be a cheap alternative to the pretty expensive ones we know. Also the given value for temperature consistency seems to be quite ok... (but since till now I used a big pot on my stove, regulating myself with ice & hot water...)

Has anyone tried the thing? Any thoughts based on the provided data? Is it a good alternative for the more expensive circulators or should I still go for those?

Regards,

Andreas

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I'm also interested in this device: my home-brew cooker is a little more temperamental than I'd like. However, the price is still above the 'frivolous spend' level.

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See in the main SV topic egullet.org/p1859926:

There is another iphone app that is free called sous vide pro (created by Vac-star who make the circulator that I have just purchased and am awaiting delivery of). Their time for a 70mm sirloin to medium rare (water temp 58C) is 3 hours 30 minutes. Given this time and temp, you'll most likely wind up with a core temperature of 57C, which should be rare-medium, rather than medium-rare.

and wait for nickrey's report.

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An acquaintance in German cooking forum recently purchased the Vac-Star SousVideChef. Using an uninsulated, uncovered polycarbonate container (1/2 GN), she measured an overshoot of 0.3 °C at a nominal 65 °C. After adding some jury rigged insulation and covering in the form of bubble wrap and aluminium foil, the overshoot dropped to 0.2 °C.

Apparently, In her setup the controller never reached a steady state and continued to oscillate between 64.9 and 65.2 °C for the duration of the cooking. I may be misreading her report however, and she's gone Barcelona for the week (including dinner at 41°, I've been told), so I cannot ask her for clarification at the moment.

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I've got a Greisinger Pt1000 reference thermometer. Will post results once my unit arrives.

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@pep. It would be nice if you could post a link to the report so that I could read it myself?

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@pep. It would be nice if you could post a link to the report so that I could read it myself?

Sorry, so far it's all in PM. But I'll ask her to post a public report when she gets back from Barcelona.

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Apparently, In her setup the controller never reached a steady state and continued to oscillate between 64.9 and 65.2 °C for the duration of the cooking. I may be misreading her report however, and she's gone Barcelona for the week (including dinner at 41°, I've been told), so I cannot ask her for clarification at the moment.

A tolerance of ±0.2⁰C is a lot better than the ±1⁰C I get from my homebrew rig. As I don't cook near dangerously low temperatures anyway, that tolerance sounds acceptable to me. Not ideal, but acceptable.

But yes, more reports are always good. Thanks, everyone.

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Apparently, In her setup the controller never reached a steady state and continued to oscillate between 64.9 and 65.2 °C for the duration of the cooking. I may be misreading her report however, and she's gone Barcelona for the week (including dinner at 41°, I've been told), so I cannot ask her for clarification at the moment.

A tolerance of ±0.2⁰C is a lot better than the ±1⁰C I get from my homebrew rig. As I don't cook near dangerously low temperatures anyway, that tolerance sounds acceptable to me. Not ideal, but acceptable.

But yes, more reports are always good. Thanks, everyone.

This is not a science experiment nor are we making high tolerance drugs that may need extremely high thermal accuracy.

We are cooking.

Can anyone give me any sensible rationale that requires temperature to vary less than the reported tolerances?

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Can anyone give me any sensible rationale that requires temperature to vary less than the reported tolerances?

It's the principle of the thing ;-)

I'm a bit surprised by the results my acquaintance got, but maybe the problem is the lack of proper insulation. I'd like to do a side-by-side comparsion of the VacStar SVC and my Polyscience SVP, since the VacStar basically looks like a clone of Polyscience's device.

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Can anyone give me any sensible rationale that requires temperature to vary less than the reported tolerances?

It's the principle of the thing ;-)

I'm a bit surprised by the results my acquaintance got, but maybe the problem is the lack of proper insulation. I'd like to do a side-by-side comparsion of the VacStar SVC and my Polyscience SVP, since the VacStar basically looks like a clone of Polyscience's device.

If you can't get a hold of both, once I get mine, let's see if we can replicate the cooking vessel as much as possible and run the experiment in tandem.

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I just looked again at the manufacturer's website, and they claim the temperature stability of their device is ±0.2⁰C. It looks like Pep's friend's unit is working as intended.

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nickrey: I also don't think that a temperature variation of 0.2°C should matter that much... The only procedure where it might matter that comes to mind would be "6x eggs" cooked at the higher end of the 60s range. But cooking in that range seems to be quite inaccurate anyhow (at least when I look at the errors graphs in the appropriate paper).

My question was more along the lines: "Does the unit really work as advertised", and that it seems to do, at least according to pep. One other question that came to my mind would be if you can configure the controller parameters yourself + is it PID controlled. From the description it might be a bang-bang controller. I sent an email to VacStar asking about the control algorithm, I'll post their reply when I get it.

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One other question that came to my mind would be if you can configure the controller parameters yourself + is it PID controlled. From the description it might be a bang-bang controller. I sent an email to VacStar asking about the control algorithm, I'll post their reply when I get it.

I think I can answer your first question, whether it is possible to configure the controller parameters yourself: I'm quite sure you can't. Too many things that could go wrong and result in commercial liability. What could exist (but I'm not too confident that it does) is a setting for a temperature offset (since the Polyscience has that feature).

The answer from VacStar regarding PID or no PID will interesting, however. I had assumed that it would be PID controlled, but you are right that the demonstrated behavior doesn't look like a (well-tuned) PID.

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I just got the answer:

Hi

the unit is equipped with a PID controller.

All settings are fixed on the PIC (configuration can be done by the software eng. only).

Please fell free to post my answers.

Maybe just a tuning issue?

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I've received mine. Shopping for a suitable cooking container on the weekend.

Will post pictures and measurements once I get to using it.

I know from the sous vide magic that the PID settings vary depending on what you are driving. Obviously the PID settings for this machine will vary according to the type of container used (insulated or not, conductive of heat or less so, thermal covering on top of water, etc). If they have fixed settings, it has to be for a choice of one type of container. Vac-Star sell a polycarbonate container as well as thermal balls to sit on top of the water so my bet is that they have optimised tuning for that. If you use anything other than this, I'd say you have to live with some variance. However, as I said above, 0.2C variance has no impact on cooking. If you want less variance, it's easy: spend more money and get a unit that costs many times as much.

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I just got a follow-up mail where the guy from VacStar said something interesting: He told me that they do not do any power regulation on the input power to the heating element (For cost reasons). I have asked for clarification, since this does not really go well together with his comment that the unit is PID controlled. A PID controller does not really make sense if you don't do any power regulation...

You are surely right that it won't hinder any cooking process, but I like to know what I'm getting, hence I followed up on the report that the controlled temperature was oscillating. Even with a cheap PID controlled setup you should get a stable temperature.

Another reason for my curiosity: I'm an electronics engineer, so it's always interesting what I get when I want to buy something ;)

I will also order the unit and report when I get an answer or the unit.

(edit: pressed send button too early)


Edited by Andreas (log)

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Ok, first report. Got myself a 20l polycarbonate tub today and ran the SousVideChef. Started with water around five degrees below target (which was 59.5C). Time to heat up 20l of water up 5C was less than 10 minutes. I was a bit concerned as my Greisinger reference thermometer appeared to be reading .5C less than the unit. As the unit approached the target temperature, this levelled out. When it reached the set temp (59.5C), the reference thermometer read 59.4C, and once every 45 seconds or so clicked over to 59.5C. This pattern of temperature readings on the Greisinger was steady over a 45 minute period. In my opinion, it was rock solid, possibly .1 lower than set temperature, but nothing of note. What happened on the LCD thermometer on the unit, however, was different. On that the unit seemed to oscillate between 59.4C and 55.7C, which seems to be exactly the behaviour that your friend reported Pep. Please note, however, that the reference thermometer was much more consistent, and that included measurements taken anywhere in the 20l container.

So we have a stable temperature according to the reference thermometer but an oscillating temperature according to the unit. I think this is the way that I prefer it to be.

Moreover, this level of stability cannot be achieved by a simple on/off controller so it must be a PID as advertised.

One last comment is that the switch for turning the heating unit on and off has quite a loud click, which could be distracting especially given the level of thermal loss from the uncovered polycarbonate container.

If this performance level is consistent, I'm a very happy purchaser.


Edited by nickrey (log)

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I just got a follow-up mail where the guy from VacStar said something interesting: He told me that they do not do any power regulation on the input power to the heating element (For cost reasons). I have asked for clarification, since this does not really go well together with his comment that the unit is PID controlled. A PID controller does not really make sense if you don't do any power regulation...

Ah, no. These are pulse width (PWM) or pulse frequency (PFM) modulated. The control loop controls the percent of time the heater is on. This allows a cheap relay or SCR to switch the element. They all work this way including my old analog PolyScience unit.

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I just got a follow-up mail where the guy from VacStar said something interesting: He told me that they do not do any power regulation on the input power to the heating element (For cost reasons). I have asked for clarification, since this does not really go well together with his comment that the unit is PID controlled. A PID controller does not really make sense if you don't do any power regulation...

Ah, no. These are pulse width (PWM) or pulse frequency (PFM) modulated. The control loop controls the percent of time the heater is on. This allows a cheap relay or SCR to switch the element. They all work this way including my old analog PolyScience unit.

That explains the clicking noise when the relay switches.

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@sreeb: I would consider PWM a power regulation, especially when the thing you are driving in the end is as slow changing as a 20l pot of water.

+ I hope they do not use a traditional relays to PWM control the heating element


Edited by Andreas (log)

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@sreeb: I would consider PWM a power regulation, especially when the thing you are driving in the end is as slow changing as a 20l pot of water.

+ I hope they do not use a traditional relays to PWM control the heating element

The "regulation" thing is a matter of semantics. They are regulating when averaged over time.

I don't know if the Vac-Star uses a traditional relay but it is done. If your system is using a relay, you want the period to be at least 10S and maybe longer for best life. I have a cheap Chinese PID controller that can either using a internal relay or drive a external solid state one. Period is adjustable from 2-199S with the recommendation that it is >10S if the relay is used. Assume a 1 million cycle life and 10S period. Relay life would be 1M cycles * 10S period/ 3600S/Hr = ~3000 Hrs of operation. Maybe longer if you increase the period or start skipping cycles entirely when you reach equilibrium.

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I think semantics should not be our problem, I think we know what we mean :smile:

Btw. yes if you use a relays it will not break for some time when controlled "correctly" (though even 3000h are not that much considering the 72h cooking marathons those device have to withstand). I would not use one because of the scenario that might happen when the relays malfunctions and gets stuck, and the heating element run continuously on full power. But on the other hand...for the electronics I design it's not a requirement that they are as cheap as humanly possible...

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