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PID/SSR controlled 4 bbl HLT runaway condition

 
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way2fastxl1200c



Joined: 08 Aug 2019
Posts: 5



PostLink    Posted: Thu Aug 08, 2019 1:13 pm    Post subject: PID/SSR controlled 4 bbl HLT runaway condition Reply with quote


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I built a simple PID control circuit to pre-heat a commercial 4bbl HLT.
The objective is to have a timer turn on a pid circuit that then raises the overnight resting HLT to 160 before the brew day begins on a 7 day schedule. It is set to come on at 5:30AM, when the tank generally is resting around 100f with 120 gallons in it.
When we arrive in the brewery in the morning, the tank is boiling, with the setpoint on the pid far exceeded and NOT calling for heat, the indications on the ssr's are off and the elements are still running full tilt. When we cool down the HLT and put it back in operation within a few degrees of the setpoint, it raises to its setpoint, turns off and runs perfectly. The ssr's seem to be latching shut during the long ramp up time from 100 to 160. This does not occur during shorter heating cycles with less temp change

Control is designed as follows:

Pid relay output ->timer->ssr->element

Regardless of PID tuning values, overshoot runs up to boiling and elements stay on full, so I dont think this is a pid issue. Even once the pid's control (primary) voltage shuts off, and the kill switch to the ssr control circuit is shut off, it still tries to run. Again, once we kill power to the panel, add cold water to the tank to get back down to 150ish, and turn the control back on, it stabilizes quickly at setpoint and all works well.

Is this an overheating SSR issue?
ssr's are mounted on individual heat sinks on a backerboard within the panel, the condition still occurs even with the panel door wide open and the 12v power supply cooling fan blowing directly on them.
Is this an inductive issue on the control side within the ssr forcing the ssr's into a runaway condition not allowing them to "unlatch"?

I realize these may be advanced issues but Ive spent 3 days trying to troubleshoot this doing hours of research. A prompt reply would be greatly appreciated, I'm stumped and I've got a very aggravated brewing crew waiting on a solution.
[b][/b]
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kal
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Joined: 12 Dec 2010
Posts: 10680
Location: Ottawa, Canada

Drinking: German Lager, Electric Creamsicle, London Pride, Kolsch, Belgian IPA, Red IPA, Russian Imperial Stout, Black Butte Porter

Working on: Weizen, Belgian Quad, Wit, English Pub Ale, Electric Creamsicle


PostLink    Posted: Thu Aug 08, 2019 1:23 pm    Post subject: Reply with quote

Welcome to the forum!

You'll need to determine where the issue is, and do it systematically, ensuring that each part works as it should. It should be fairly simple - you can see our TROUBLESHOOTING guide here: http://www.theelectricbrewery.com/forum/viewtopic.php?t=25460

Specifically the section "My heating element is not firing at all! (or firing continuously)". Assumption of course is that the setup's somewhat similar to our design (which it probably is).

Extra info:

Look at the PID first. Does it have an output "ON" light that shows when it's firing? If yes, and it's firing when it's not supposed to, the issue is the PID. You can confirm by measuring the output voltage on the PID to make sure it's sending a signal to the SSR when it's not supposed to. If that's the case the PID is defective or incorrectly programmed.

Otherwise look elsewhere, and it's most likely the SSR that is stuck "on". If the element's always firing even when the PID tells it no to, then the SSR is probably bad. I'd swap it out.

EDIT: It appears that once you hit the right temp things seem to work correctly, so sounds like it may be overheating issues somewhere. Most likely around the SSRs. Check your SSR sizing, use larger heat sinks, use fans, and/or put the heatsink(s) outside the case.

Pictures, a schematic, and/or parts list (brand/type) would help too. There's been issues with counterfeit SSRs out in the wild too (mostly from Fotek). If the price was too good to be true, it may be a fake.

Good luck!

Kal

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way2fastxl1200c



Joined: 08 Aug 2019
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PostLink    Posted: Thu Aug 08, 2019 1:32 pm    Post subject: Reply with quote

Yes, the pid operation is correct, even the indications on the ssr's go out once the pid goes over set point and shuts off, however the ssr's stay on. this only happens during large temp swings with long run times, so Im strongly suspecting SSR is overheating. Once we cool down everything, it works and operates as it should as long as the element doesnt run too long.
isnt there a large externally mounted heat sink available?
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kal
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Joined: 12 Dec 2010
Posts: 10680
Location: Ottawa, Canada

Drinking: German Lager, Electric Creamsicle, London Pride, Kolsch, Belgian IPA, Red IPA, Russian Imperial Stout, Black Butte Porter

Working on: Weizen, Belgian Quad, Wit, English Pub Ale, Electric Creamsicle


PostLink    Posted: Thu Aug 08, 2019 1:38 pm    Post subject: Reply with quote

Yes, I would recommend this one:

https://shop.theelectricbrewery.com/collections/heat-sinks

Kal

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way2fastxl1200c



Joined: 08 Aug 2019
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PostLink    Posted: Thu Aug 08, 2019 1:39 pm    Post subject: Reply with quote

https://www.amazon.com/gp/product/B07CZ5W8M9/ref=as_li_ss_tl?ie=UTF8&psc=1&linkCode=ll1&tag=theelectricbrewery-20&linkId=c2ad8bd4d28fd6e76cd3b4edb889d3e6&language=en_US

that is the relay i used.
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kal
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Joined: 12 Dec 2010
Posts: 10680
Location: Ottawa, Canada

Drinking: German Lager, Electric Creamsicle, London Pride, Kolsch, Belgian IPA, Red IPA, Russian Imperial Stout, Black Butte Porter

Working on: Weizen, Belgian Quad, Wit, English Pub Ale, Electric Creamsicle


PostLink    Posted: Thu Aug 08, 2019 1:47 pm    Post subject: Reply with quote

If you check the reviews, you'll see they suck. It would appear they may be fake SSRs. Some reviews:

Quote:
Junk, nowhere near 40amp
I both of these failed with about ~30 amp load, they were installed correctly and mounted to heatsink with thermal compound. They both failed on the first use, these are cheap knockoffs.

Not a 40A relay
Not only did I receive on AC and one DC relay, unlike what's listed - the DC relay can not support the advertised load. Inside is an International Rectifier IRFP250M 30A max (with good heatsinking) mosfet. The heatsink here isn't going to get you to a 30A rating from that FET either.

Not 40A at all
I was going to use this in my car to cut off power to the HVAC blower motor controller to prevent battery drain. It worked fine at low speeds but full speed was to much. The car filled with the distinct smell of burnt electronics and the casing stated to melt around the heat sink. I go to take apart the unit and the PCB is discolored. I look the MOFET they used and it's a irfp250m, they are ONLY rated for a ABSOLUTE MAX of 30A. So how can this Solid State Relay be rated for 40A if the core of it is only a max of 40A??? Hmmmmmmmm...


WARNING! not 40A
these solid state relays utilize the ST BTA24 triac which according to the datasheet from the manufacture are only rated for a constant 25A of RMS current


This would make sense given the ridiculously low price and is exactly the issue people are seeing with some Foteks with pricing that's too good to be true: They're lower current SSRs with fake cover stickers (or similar).

I'd recommend these 40A SSRs:
https://shop.theelectricbrewery.com/collections/ssrs-relays-contactors/products/40-amp-ssr-12v-dc-input-240v-ac-output

If you need 80A:
https://shop.theelectricbrewery.com/collections/ssrs-relays-contactors/products/80-amp-ssr-12v-dc-input-240v-ac-output

Use the recommended oversized heatsink and they'll basically last forever. Good luck!

Kal

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way2fastxl1200c



Joined: 08 Aug 2019
Posts: 5



PostLink    Posted: Thu Aug 08, 2019 3:39 pm    Post subject: Reply with quote

I found some inkbird 40a ssr's I had laying around, and will order the external heat sink. I currently have both legs of the elements switched as a safety factor against overflowing water from the hlt catching the remaining hot leg, etc. however I feel it may be generating more heat than is necessary in the panel, so I will be removing 2 relays and switching to single leg control with ssr. Between these 3 changes I feel pretty confident we can get the issue resolved. Hopefully the heat sink arrives quickly.
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kal
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Joined: 12 Dec 2010
Posts: 10680
Location: Ottawa, Canada

Drinking: German Lager, Electric Creamsicle, London Pride, Kolsch, Belgian IPA, Red IPA, Russian Imperial Stout, Black Butte Porter

Working on: Weizen, Belgian Quad, Wit, English Pub Ale, Electric Creamsicle


PostLink    Posted: Thu Aug 08, 2019 3:46 pm    Post subject: Reply with quote

Hi!

No need to switch both legs in the SSR as you mentioned. It also won't do anything extra for safety given how SSRs work and have leakage current. I recommend a physical disconnect using a mechanical relay or contactor. This is what we do in all of our control panels and is what we recommend in our build instructions. You can read more here in the "HOW IT WORKS" section as to why we recommend SSRs and mechanical relays be used together: http://www.theelectricbrewery.com/control-panel-part-2?page=13

Kal

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way2fastxl1200c



Joined: 08 Aug 2019
Posts: 5



PostLink    Posted: Thu Aug 08, 2019 3:57 pm    Post subject: Reply with quote

Adding a pair of contactors and a separate emergency stop to actuate them is on my list of to-do's with this project.
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