240VAC Toolbox Control Panel with Pics

[passedpawn]

Did you do the boil with the box open?

On another note, let's try to keep this civil. Anyone building something like this is taking a risk. It's clear that you should err on the side of caution if unsure....

Passedpawn: Do you think the plastic box is better than a metal toolbox, a la "simple brewing"?

Boiled with the box closed. After more than an hour, I cut power and immediately measured temps (with an infrared temp gun) and also reached into the box and felt the wires, terminal blocks, etc. Nothing was hot at all.

I love the plastic box. Love love love. The metal box was a major pain to build and, in the end, felt a little clunky. I was concerned that the plastic wouldn't take the heat of the heatsink, but in testing this wasn't an issue. I considered adding a fan after I tested it, but I now see I don't even need that.

I'll be brewing 1 (maybe 2) batches this wkend. If there is anything else to add, I'll post here.

Yep, steve, err on the side of caution is great advice. BTW, did you look at my schematic? Do you see how I'm using the one PID for both elements?

[edit]

Here's the old crappy one. This one had 10 AWG wiring. I hated this thing, although it worked well.

 

[wyzazz]

Do you see how I'm using the one PID for both elements?

Dual SSR's, I like the concept but the 40A SSR's on eBay are cheaper when you buy 2.

 

[ScubaSteve]

Yeah, i read the schematic. I appreciate you listing the digikey part numbers I'm looking real hard at doing this for my rig...it just seems like it'll be at LEAST as expensive as buying an enclosure, plus I'll be able to move the box to compensate for the short 220v cord.

 

[Bjornbrewer]

I'm not sure where the chassis wiring comes in [citation needed]...NEC doesn't acknowledge it (that I can find or to my knowledge).

As far as general wiring is concerned we have to keep the temperature of the wiring under 75*C so as not to exceed the terminal block, breaker, relay, etc ratings. In section 310.15(B) (Article 310: Conductors for General Wiring), it says to refer to tables 310.16-.19. The table that we would use is 310.17 (free air at 30*C). The max ampacity for #14 is 25A, #12 is 30A, and #10 is 40A. However, all of these have a asterisk next to them saying to refer to section 240.4(D) in which is states the maximum over current protection device (OCPD) for these conductors must be 15A, 20A and 30A respectively. If you have 23A load current you need a 30A OCPD (23*1.25 = 28.75A so you go to the next higher which is a 30A breaker). With a 30A breaker you need #10 wire for you general wiring.

Again, it has nothing to do with the length of the run, but more to do with the conducted heat from conductor to component. And this is all at MAXIMUM CONDITION (think fault conditions, not just normal boiling). Really, what the temp is when you're just running it normal doesn't have any bearing on the temperature/current you should rate your wiring for.

Hope this helps.


PS Was I being uncivil? I apologize if I came off that way...not my intention.

 

[ScubaSteve]

Nope...you were quite civil. I just didn't want to ruin an awesome thread, and I hoped to keep it from escalating.

My next question is about those SSR's; the SSRD's are about $36 without heatsinks....but I can get two 40A SSR's with heatsinks for ~$10 a piece. With dual ssr's I guess you're paying for a compact build...but how much more space would 4 ssr's take up? I assume the heat output would be the same....perhaps it would be handled better through 4 heatsinks? Or, would it be cheaper to buy a bigger, more streamlined heatsink and hook 4 ssr's without heatsinks (even cheaper that way) up to that one main heatsink?

I hope that makes sense....

 

[wyzazz]

My understanding is that with the larger SSR's (40A vs 25A) you'll generate less heat, I took a look at the 40A dual SSR at digikey and it's like $77.

 

[passedpawn]

I'm not sure where the chassis wiring comes in [citation needed]...NEC doesn't acknowledge it (that I can find or to my knowledge).

As far as general wiring is concerned we have to keep the temperature of the wiring under 75*C so as not to exceed the terminal block, breaker, relay, etc ratings. In section 310.15(B) (Article 310: Conductors for General Wiring), it says to refer to tables 310.16-.19. The table that we would use is 310.17 (free air at 30*C). The max ampacity for #14 is 25A, #12 is 30A, and #10 is 40A. However, all of these have a asterisk next to them saying to refer to section 240.4(D) in which is states the maximum over current protection device (OCPD) for these conductors must be 15A, 20A and 30A respectively. If you have 23A load current you need a 30A OCPD (23*1.25 = 28.75A so you go to the next higher which is a 30A breaker). With a 30A breaker you need #10 wire for you general wiring.

Again, it has nothing to do with the length of the run, but more to do with the conducted heat from conductor to component. And this is all at MAXIMUM CONDITION (think fault conditions, not just normal boiling). Really, what the temp is when you're just running it normal doesn't have any bearing on the temperature/current you should rate your wiring for.

Hope this helps.


PS Was I being uncivil? I apologize if I came off that way...not my intention.

Here's where I got my numbers (for better or worse). There are good links there to some of the standards. The chassis wiring (I assume) comes from the handbook referenced at that site and not the NEC.

You're right about the breaker requirements. I don't understand allowing 30A in 12 AWG, but then also requiring a 20A breaker.

 

[passedpawn]

I bought the duals off ebay for a steal.

 

[Bjornbrewer]

You're right about the breaker requirements. I don't understand allowing 30A in 12 AWG, but then also requiring a 20A breaker.

ex) If you were wiring from, say a transformer secondary to full wave bridge power module, then you could utilize the full 30A. The protection would be on the primary side. The 30A can be realized if no immediate upstream protection is required.

 

[ScubaSteve]

I bought the duals off ebay for a steal.

I'm not sure what you consider a steal....the lowest I could find on Ebay for a D2425D is ~$36/unit.

 

[passedpawn]

ex) If you were wiring from, say a transformer secondary to full wave bridge power module, then you could utilize the full 30A. The protection would be on the primary side. The 30A can be realized if no immediate upstream protection is required.

That makes sense. Thanks.

 

[passedpawn]

I'm not sure what you consider a steal....the lowest I could find on Ebay for a D2425D is ~$36/unit.

I paid $28 each from a seller named "brinkercontrols". Shipping was $6. They are $64 each on Digikey, so I thought it was a good deal.

Also, here is the heatsink I used. It has a low thermal resistance ( deg. C per Watt). You can mount 2 normal SSRs on it. Click pic for link to Digikey.

 

[ScubaSteve]

So you went with the 25A SSRD's....has that caused any issues? I guess you're switching 23A, but it IS close.

You say you can mount 2 "normal" SSR's on the heatsink....but you obviously fit 2 SSRD's...any mods?

 

[passedpawn]

So you went with the 25A SSRD's....has that caused any issues? I guess you're switching 23A, but it IS close.

You say you can mount 2 "normal" SSR's on the heatsink....but you obviously fit 2 SSRD's...any mods?

No problems ever. Not a single one. I've made a lot of beer with this exact system. And no mods. the footprint of these DSSRs is exactly the same as single SSR.

The D2425D datasheet has curves for the power rating for this SSR. The 25A limit assumes a 5.0 C/W heatsink.

The heatsink I show above is 0.7 C/W. I used Arctic Silver 5 to join the heat sink and the SSR. According to the Crydom derating curves, I can drive nearly 50A per section. So, I think it's fine.

An improvement I just thought of: Right now, both 230VAC legs to the HLT go through the same DSSR (and same for the BK). So when the HLT is on, for example, both halves of the same DSSR are getting hot. What I should do is split the legs across the 2 DSSRs so that exactly half of each one is being used, the the heat is spread better across the heat sink. Did that make sense?

 

[Walker]

An improvement I just thought of: Right now, both 230VAC legs to the HLT go through the same DSSR (and same for the BK). So when the HLT is on, for example, both halves of the same DSSR are getting hot. What I should do is split the legs across the 2 DSSRs so that exactly half of each one is being used, the the heat is spread better across the heat sink. Did that make sense?

Yup, that made sense and sounds like a good idea.

 

[wyzazz]

Sounds like a great idea! And Arctic Silver rocks!!! :rockin:

 

[ScubaSteve]

Yup, that made sense and sounds like a good idea.

Sure, I guess you "criss cross" everything....it makes sense.

But isn't low thermal conductivity a bad thing? Seems like I'd rather have 5C/watt conducted through the heatsink and released into the atmosphere. Or is that bad, because you don't want the heatsink getting too hot?

It seems like a muffin fan with a splashproof intake and exhaust on the box would be easy and really effective. You could put it inline with the accessory 115v receptacle (vs the switched one for the pump) and it could always be on.

 

[Walker]

He's not talking about low conductivity but rather a more distributed production of heat on the sink; One really hot spot vs two not-so-hot spots.

 

[IrregularPulse]

So is the general consensus that you should have 2 SSRs per 240v element? One for each leg. Then do you need also 2 PID's per element?

 

[wyzazz]

So is the general consensus that you should have 2 SSRs per 240v element? One for each leg. Then do you need also 2 PID's per element?

Nope, just 1 PID. You want 2 SSR's or a Dual SSR so you can switch off both hot legs of the element, not just one. With only 1 SSR you still have 120V running through the element when it's "off".

 

[IrregularPulse]

Nope, just 1 PID. You want 2 SSR's or a Dual SSR so you can switch off both hot legs of the element, not just one. With only 1 SSR you still have 120V running through the element when it's "off".

that's what I thought. Just send the PID's one output to both SSR inputs then? I have the Auberin PID and 1 SSR for a BK build, but haven't looked at stuff yet. I'll have to pick up another SSR for it.

 

[ScubaSteve]

He's not talking about low conductivity but rather a more distributed production of heat on the sink; One really hot spot vs two not-so-hot spots.

I understand the discussion about heat distribution across the heat sink....I guess I was referring to the heat sink C/W "rating" that was mentioned earlier.

 

[Walker]

FYI: you do not *need* to use a second SSR. Some folks prefer it, but some don't.

I have a kill switch that cuts both hot lines going to the element when I want to power it down completely, and I just use one SSR controlled by the PID for the actualy automated heating stuff.

It's a personal preference. Neither way is right or wrong, but both ways have their pros and cons.

 

[wyzazz]

that's what I thought. Just send the PID's one output to both SSR inputs then? I have the Auberin PID and 1 SSR for a BK build, but haven't looked at stuff yet. I'll have to pick up another SSR for it.

Exactly!

 

[ScubaSteve]

I totally understand the concept of having 1 ssr for each leg...I guess it's a matter of how you want to integrate safety. Either way is fine, breakers/contactors are nice too. I guess I wonder if you decided to only switch 1 leg and you had multiple elements, would there be a current draw to factor in for the one that was not in use?

 

[IrregularPulse]

FYI: you do not *need* to use a second SSR. Some folks prefer it, but some don't.

I have a kill switch that cuts both hot lines going to the element when I want to power it down completely, and I just use one SSR controlled by the PID for the actualy automated heating stuff.

It's a personal preference. Neither way is right or wrong, but both ways have their pros and cons.

Right. I understand the 2nd SSR is thought of as a "safety precaution". Does having 120 through the element constantly effect the performance? You would think the PID want's to shut off the element because you are up to temp, say in an HLT, but the element is still on via 120VAC. So say with a 5500W element, when the it needs to be off to maintain a temp, you'd still have ~2500W running through it, over heating your water?

 

[passedpawn]

But isn't low thermal conductivity a bad thing? Seems like I'd rather have 5C/watt conducted through the heatsink and released into the atmosphere. Or is that bad, because you don't want the heatsink getting too hot?

Well, maybe that should have been thermal resistance; smaller numbers are better. You take the C/W (degrees C per Watt ) and multiply it times the watts you are trying to disappate, and you easily calculate the temperature rise over ambient. For example, if my SSR is 0.050 ohms, and I running 23A through one leg of it, the the power (watts) = I^2 * R = 23^2 * 0.050 = 26W.

Then, 26W * 0.7 C/W = 19 C (33 degrees F over ambient; if it's 80F, I would measure 113 at the SSR.

Now, since both legs are used at the same time on that SSR, I need to double that, so I would expect to see a 66F rise on the SSR: it would get to about 143F today. In fact, that is very close to what I am seeing.

 

[wyzazz]

you'd still have ~2500W running through it, over heating your water?

No, the element doesn't work that way. When one leg is cut there is no voltage because you're not completing a circuit. The danger is if you complete the circuit with that 120V running through the element by touching a ground/neutral/hot. (Someone correct me if I'm talking outta my @$$.)

 

[passedpawn]

Right. I understand the 2nd SSR is thought of as a "safety precaution". Does having 120 through the element constantly effect the performance? You would think the PID want's to shut off the element because you are up to temp, say in an HLT, but the element is still on via 120VAC. So say with a 5500W element, when the it needs to be off to maintain a temp, you'd still have ~2500W running through it, over heating your water?

Nope, you're confusing current and watts. Voltage does nothing; it's the current that creates the heat. by turning off one leg, you have clamped off the current.

If it helps, electrical current is analogous to water flow in a hose. If you step on one end of the hose, there is no flow. The pressure remains, though (pressure = voltage). No flow, no power (watts), no heat.

 

[IrregularPulse]

well then I gotta go with walker on this and I'll stick with one SSR but a SPDT switch to cut both legs. (Did I get that right on the Single Pull double throw switch? That always messes me up. I want one toggle to cut two contacts)