240VAC Toolbox Control Panel with Pics

[Walker]

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 @$$.)

You are correct.

Electricity needs a complete path to operate. Current must be able to go into the circuit and then come back out. The heating elements are connected to two wires, so cutting one of them breaks the circuit and no current can flow, so no hear is produced.

But, as you say, even though no current is flowing, that one line that is going out to the element (the line NOT going through an SSR) is energized. If you touch it, it will shock you and your GFCI breaker will trip.

I don't touch anything unless I flip the kill switch that cuts both lines compeletely. Even if I was using two SSRs, I wouldn't trust them and would flip a kill switch before I touched anything.

I do, however, trust the large mechanical device that connects or disconnects the wires completely.

 

[wyzazz]

It's DPST (Dual Pole Single Throw).

 

[passedpawn]

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 @$$.)

There's still voltage. No current. For the same reason you stated, no circuit.

It helps to consider the water analogy again:

voltage (volts) = pressure, (psi)
current (amps) = flow (gpm)
resistance (?) = resistance (ohms)
​

The heating potential of an element is rated in Watts. If you are using the voltage recommended for that element, you can calculate the current through it by I = W/V.

I.e., I = 5500W / 240VAC = 23A.​

 

[Walker]

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)

Nope.. DPST.

Double pole because you are simultaneously switching two lines.
Single throw because you want to connect or disconnect it.

A SPDT switch would be switching a single wire, but would allow you to connect that single wire to one thing or to another thing.

SPST would switch one wire, but would connect or disconnect it.

 

[wyzazz]

You are correct.

Electricity needs a complete path to operate. Current must be able to go into the circuit and then come back out. The heating elements are connected to two wires, so cutting one of them breaks the circuit and no current can flow, so no hear is produced.

But, as you say, even though no current is flowing, that one line that is going out to the element (the line NOT going through an SSR) is energized. If you touch it, it will shock you and your GFCI breaker will trip.

I don't touch anything unless I flip the kill switch that cuts both lines compeletely. Even if I was using two SSRs, I wouldn't trust them and would flip a kill switch before I touched anything.

I do, however, trust the large mechanical device that connects or disconnects the wires completely.

I myself will be using both a DPST switch and 2 SSR's, maybe I'm overly-cautious, but that's just me.

 

[Bjornbrewer]

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 dissipate, 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.

You are absolutely correct. However for clarification sake and to help others calculate power dissipation, the majority of heat is generated by the voltage drop across the device, not the resistance.

typical SSR and thyristors, triacs, whathaveyou have a very low ON resistance...in the neighborhood of 1.0 milliohms. but the voltage drop is around 1.1-1.5V. Do the math with 23A through it you have 25-35W dissipated because of the voltage drop and only 0.5-1W because of resistance. If you stick with 1.5V you'll be worse case when calculating heat.

 

[IrregularPulse]

Nope.. DPST.

Double pole because you are simultaneously switching two lines.
Single throw because you want to connect or disconnect it.
.

I think my confusion is how I say it. I say it as Double Pull , Pole makes sense d'uh. Believe it or not I do have an electrical background, but it's been about 5 years since I've used any of it short of simple home wiring.

 

[passedpawn]

I myself will be using both a DPST switch and 2 SSR's, maybe I'm overly-cautious, but that's just me.

That's what I did. Home depot sells 230V 30A DPST switches.

 

[Walker]

I myself will be using both a DPST switch and 2 SSR's, maybe I'm overly-cautious, but that's just me.

If you want to be overly cautious, then do you really want to touch a switch that is passing 240V/30A through it? (Are your hands ever wet when you brew?)

I actually don't use a DPST switch. I use a 2-pole contactor to do the switching of the 240V lines.

The contactor is triggered with a lower voltage, lower current signal, and THAT signal is the one I mess with with a simple SPST switch.

 

[IrregularPulse]

That's what I did. Home depot sells 230V 30A DPST switches.

Price on those?

 

[Bjornbrewer]

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.

correct. you don't have 120V at all going to the element...it's only 240V. You open one leg, the other delivers no current.

...well unless you are standing in water with a open cut on your foot and you touch it...then it will do plenty to kill your a$$. Hence GFCI breakers, contactors and two SSR's to open both legs of the 240.

 

[passedpawn]

but the voltage drop is around 1.1-1.5V.

Right. I figured out the difference between DC and AC SSRs a while back, then forgot. Thanks for that. I'll probably forget again though.

 

[passedpawn]

Price on those?

Hmmm.... maybe $10 - $15

 

[Walker]

Hmmm.... maybe $10 - $15

Yeah, that's about right from when I remember. You can find 240V, 30A DPST switches at mouser.com for a little cheaper than $10.

When I looked at 2-pole contactors (which take up a lot of space in the box) I found that the price of a 2-pole contactor and a simple SPST switch was about the same as a big burly 240V,30A DPST switch, so I went for the contactor. Overly cautious and all...

 

[IrregularPulse]

I can't find any 30A DPST switches on mouser or automation direct. I must not be looking right. I want industrial panel switches for my control panel.

 

[Walker]

I can't find any 30A DPST switches on mouser or automation direct. I must not be looking right. I want industrial panel switches for my control panel.

Hmmm.. I can't find them on there either... at least not ones rated for 240V. I do see 30A/125V, but not 240V.

I swear to god they had them 6 months ago when I started shopping, but I don't see them anymore.

 

[passedpawn]

I can't find any 30A DPST switches on mouser or automation direct. I must not be looking right. I want industrial panel switches for my control panel.

You could start with this thread. Lots of info

https://www.homebrewtalk.com/f11/buying-buttons-switches-ebay-pissing-me-off-can-someone-translate-96371/#post1048000

 

[Walker]

IP: mouser's database isn't accurate on everything.

This switch is listed on mouser as 30A/125V:
http://mouser.com/ProductDetail/NKK-Switches/S821-RO/?qs=sGAEpiMZZMvudeGI7i40XGort1gkgk11B7UtCDbC7nY%3d

But if you look at the manufacturer's data sheet, it can handle 30A/250V with a resistive load.
http://www.nkkswitches.com/pdf/stoggleshighcap.pdf

edit: just noticed that this switch is $22.

 

[IrregularPulse]

Hmmm.. I can't find them on there either... at least not ones rated for 240V. I do see 30A/125V, but not 240V.

I swear to god they had them 6 months ago when I started shopping, but I don't see them anymore.

You could start with this thread. Lots of info

https://www.homebrewtalk.com/f11/buying-buttons-switches-ebay-pissing-me-off-can-someone-translate-96371/#post1048000

IP: mouser's database isn't accurate on everything.

This switch is listed on mouser as 30A/125V:
http://mouser.com/ProductDetail/NKK-Switches/S821-RO/?qs=sGAEpiMZZMvudeGI7i40XGort1gkgk11B7UtCDbC7nY%3d

But if you look at the manufacturer's data sheet, it can handle 30A/250V with a resistive load.
http://www.nkkswitches.com/pdf/stoggleshighcap.pdf

edit: just noticed that this switch is $22.

Thanks all., I thought I'd gone retarded for a minute

 

[passedpawn]

IP: mouser's database isn't accurate on everything.

This switch is listed on mouser as 30A/125V:
http://mouser.com/ProductDetail/NKK-Switches/S821-RO/?qs=sGAEpiMZZMvudeGI7i40XGort1gkgk11B7UtCDbC7nY%3d

But if you look at the manufacturer's data sheet, it can handle 30A/250V with a resistive load.
http://www.nkkswitches.com/pdf/stoggleshighcap.pdf

edit: just noticed that this switch is $22.

The little rubber boot that I list on my schematic would probably screw right onto that (I think its a NKK boot).

 

[ScubaSteve]

Yeah, that's about right from when I remember. You can find 240V, 30A DPST switches at mouser.com for a little cheaper than $10.

When I looked at 2-pole contactors (which take up a lot of space in the box) I found that the price of a 2-pole contactor and a simple SPST switch was about the same as a big burly 240V,30A DPST switch, so I went for the contactor. Overly cautious and all...

Looking on mouser.com for relay contactors rated at 240vac/30A, they're all pretty expensive, like $20-$50. I know it's for safety reasons, but it could sure add up I guess you'd only use this for the "main" power swtich, right?

 

[IrregularPulse]

I feel like I've hijacked the thread enough and know enough to get started. I'll likely post a new thread once I get a parts list together for my own build. I think I too was confused o the switches not coming with the contactors.

 

[Walker]

Looking on mouser.com for relay contactors rated at 240vac/30A, they're all pretty expensive, like $20-$50. I know it's for safety reasons, but it could sure add up I guess you'd only use this for the "main" power swtich, right?

I did not get my contactors from mouser.com.

I found the contactors on ebay. They were $6 each. $5 shipping for the first one, and $1 shipping for each additional.

I ordered three of them, so my total price was $25 ($8.33 each).

edit: oh, and the contactors I got handle either 40A or 50A.

 

[Walker]

Here's the ones I bought (40A, 120V coil):
http://cgi.ebay.com/DEFINITE-PURPOS...tem&pt=LH_DefaultDomain_0&hash=item33581a4caa

The price has gone up since the time I bought them. They are $10 now. Shipping is still the same.

The same seller has other contactors with different load ratings and coil activation voltages.

The cheapest ones are here:
http://cgi.ebay.com/DEFINITE-PURPOS...tem&pt=LH_DefaultDomain_0&hash=item33581a293c

30A load and a 24V coil.... so you would need a special power source to get the 24V.

Anyway.... even for $10 (the ones I bought) they are still a pretty good deal. Remember, the other option is a DPST switch capable of handling the load, and those things are looking like something in the neighborhood of $15 to $20 anyway, so the contactor is still a price win.

 

[passedpawn]

Quick Test Results...

Brewed two large batches today. Everything worked flawlessly. I'm very happy with this new box.

 

[ScubaSteve]

SO I got two D2425's for 15 bucks each I've sourced some dryer cords for my elements, but I can't tell from your pics or schematic; are you using a 3 or 4 wire cord for your main line?

 

[passedpawn]

SO I got two D2425's for 15 bucks each I've sourced some dryer cords for my elements, but I can't tell from your pics or schematic; are you using a 3 or 4 wire cord for your main line?

Err... that is a GREAT deal. Those are the singles, right? I think the duals have a "D" after the number.

I'm using 3-wire, but you should build it with a 4-wire. I didn't have a ground wire in my 240 service (I will fix that later....). Neutral is only used for the 110V stuff, and the earth ground should not be used to conduct any current.

Take pics along the way and post them here after you've built it.

 

[ScubaSteve]

Just checked my dryer outlet, it's 4 prong, so I guess I just answered my own question On another note, I see that you used thermocouples with 2 wires and switched them. I'd like to use RTD's because they're more accurate and aren't affected by heat in the enclosure.....BUT, they have 3 wires. What should I do?

EDIT: I think I answered this too; a 4PDT switch...with on-off-on configuration....about the same price on digikey (I hate searching for stuff on there, they should take a cue from McMaster-Carr)....

EDIT SH!!!!!!!!!!T!!!!!! I ordered the wrong relays! You're correct, the RIGHT part number is D2425D....I just bought single ssr's.

 

[passedpawn]

Just checked my dryer outlet, it's 4 prong, so I guess I just answered my own question On another note, I see that you used thermocouples with 2 wires and switched them. I'd like to use RTD's because they're more accurate and aren't affected by heat in the enclosure.....BUT, they have 3 wires. What should I do?

Yea, that's a problem. RTDs are actually 2-wire devices, so you can use it that way (just leave one of the wires unconnected). However, when the wire to the RTD changes temperature, the wires resistance will change and affect the reading. I can't say how significant this would be. In an electric keggle, it might not be very much. Maybe someone out there has done some tests.

Or, maybe you can find a 4PDT switch. That'd be nice. Do a search on Digikey.com.

Or, just do your best to keep the inside of your control box the same temperature and stick with the thermocouples. Getting the heatsink and SSRs outside the box will help here.

 

[HoboJoe]

Do you have a parts list for this build?