Amp, gauge, duty cycle recommendations

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Spintab

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I'm putting together a really simple boil kettle electric build. I'll build the PWM controller myself to regulate the element load. So I have a few questions:

1: Building the controller myself I can use just about any cycle length I want. I think most PID's use a 60hz cycle but I don't see that being necessary and rough on the SSR. I was thinking more like a second or so. So 50% would be .5sec on .5sec off.

2: This is going in my garage and I'd like the kettle to be stationed about 15ft from the breaker box. I was planning on running wire from the breaker down low in the wall space then through a conduit along the base of the wall then up to an outlet above the level of the kettle. What gauge wire do people recommend to run a 5500 watt element that far from the breaker? I was going to go with 8 gauge.

3: What size breaker should I use? I was thinking 40 amp.

4: What rating SSR should I use. I was thinking 50amp if possible to minimize heat.

Thanks
 
5500w is ~23 amps at 240vac. You will want some headroom on the circuit as you only want to really pull about 80% max of the amperage load on the breaker or you will trip it often. 30A minimum for just the BK. 10 gauge wire is the minimum code requirement for 30A. If you put a 50A breaker on the panel, you need to run 8 gauge wire to the outlet on the wall. I would highly recommend just doing a 50A circuit with 8 gauge. I only did 30A with 10gauge to my garage and I already wish I had spent the money to just do a 50A from the beginning.

-Steve
 
What voltage?

240

5500w is ~23 amps at 240vac. You will want some headroom on the circuit as you only want to really pull about 80% max of the amperage load on the breaker or you will trip it often. 30A minimum for just the BK. 10 gauge wire is the minimum code requirement for 30A. If you put a 50A breaker on the panel, you need to run 8 gauge wire to the outlet on the wall. I would highly recommend just doing a 50A circuit with 8 gauge. I only did 30A with 10gauge to my garage and I already wish I had spent the money to just do a 50A from the beginning.

-Steve

Good to know. Thanks

Another thing. 240v comes in 3 and 4 wire flavors. I'm assuming the element will only have 3 connections. Is that what I should be running to the outlet?
 
240



Good to know. Thanks

Another thing. 240v comes in 3 and 4 wire flavors. I'm assuming the element will only have 3 connections. Is that what I should be running to the outlet?

Depends on what you want it to do.

3 Conductor - 2 Hot, Ground
4 Conductor - 2 Hot, 1 Neutral, Ground.

The three conductor is fine if you ONLY want 240V. If you want 120v also available in your control panel then run 4 conductor. For example if you want to also run a pump at 120V.
 
usually the latch time for a SSR is 1-2 seconds. most PIDs dont let you set it lower than 2 seconds if i remember. you dont want the thing pulsing 25amps on and off several times a second. 1-2 seconds is good.

i agree with the rest of the suggestions. use 8 gauge wire, 50A breaker, and 40A or higher SSR with heatsink. the more you overprovision your SSR, the less it will heat up.
 
5500w is ~23 amps at 240vac. You will want some headroom on the circuit as you only want to really pull about 80% max of the amperage load on the breaker or you will trip it often. 30A minimum for just the BK. 10 gauge wire is the minimum code requirement for 30A. If you put a 50A breaker on the panel, you need to run 8 gauge wire to the outlet on the wall. I would highly recommend just doing a 50A circuit with 8 gauge. I only did 30A with 10gauge to my garage and I already wish I had spent the money to just do a 50A from the beginning.

-Steve

8Gu is good for 40A so you'd need to move up to 6Gu wire to cover the 50A breaker. 6Gu should be good to 55A.
 
Depends on what you want it to do.

3 Conductor - 2 Hot, Ground
4 Conductor - 2 Hot, 1 Neutral, Ground.

The three conductor is fine if you ONLY want 240V. If you want 120v also available in your control panel then run 4 conductor. For example if you want to also run a pump at 120V.

Is it compliant to tap a 120vac outlet from the 240vac circuit? Or does this split have to happen inside the appliance/control panel? Could the box at the end of the conduit have a 3 prong 240vac outlet and a 120vac outlet both derived from the 4 wire line? I could run a separate 120vac line from a separate breaker at the box but then the question is can this wire be housed in the same conduit as the 240vac wire? I do need both. 240vac for the bk element, 120vac ~20amp for an element in an hlt, and 120 (ultimately 12vdc) to power the controller.

My original plan was to run the two separate. Come out of the wall into a junction box with two conduits along the wall to a box at the end with both outlets. Obviously I'm trying to cut costs so if I can eliminate a conduit and put both lines in one, cool. If I can only run one and split it at the end into two outlets, even better.

BTW thanks for the help. I'm sure this comes up a lot but at least I'm not asking why my airlock isn't bubbling after 24 hours.
 
It all depends on your supply. If your plugging into an old dryer outlet that has a 3 wire supply, then you will only have 240 to use. If you have a newer outlet, or are running directly from the panelboard, and have a 4 wire supply then you use the neutral to get your 120v.

If you have the 3wire, and need 120v the easiest option is to just use a second cord to connect to a 120v GFCI, just be sure to keep you circuits separate in your control panel.

About the SSR cycling too much and wearing out from 60hz, dont give it a second thought . Solid state has no mechanical parts to wear out. Heat is the biggest killer of SSR, so make sure your relay is rated for the load, and is properly cooled. (40 amps for the 5500 watt is sufficient)
 
Is it compliant to tap a 120vac outlet from the 240vac circuit? Or does this split have to happen inside the appliance/control panel? Could the box at the end of the conduit have a 3 prong 240vac outlet and a 120vac outlet both derived from the 4 wire line? I could run a separate 120vac line from a separate breaker at the box but then the question is can this wire be housed in the same conduit as the 240vac wire? I do need both. 240vac for the bk element, 120vac ~20amp for an element in an hlt, and 120 (ultimately 12vdc) to power the controller.

My original plan was to run the two separate. Come out of the wall into a junction box with two conduits along the wall to a box at the end with both outlets. Obviously I'm trying to cut costs so if I can eliminate a conduit and put both lines in one, cool. If I can only run one and split it at the end into two outlets, even better.

BTW thanks for the help. I'm sure this comes up a lot but at least I'm not asking why my airlock isn't bubbling after 24 hours.


You're overthinking this. Buy the 50 amp spa panel from Home Depot, it comes with a gfci breaker 240v in it. This is the cheapest way to get a gfci breaker and it comes with a panel to boot.

Then put either a 50 amp or 30 amp breaker in your main box (I went with 50 but I have a 150 amp main so I had plenty of spare current - I don't anticipate running the water heater, range, dryer, and brewery at the same time).

Next, run some romex cord in a conduit to your spa panel, you want 4 wires, not 3 so you can have both 120 and 240v in your control panel..

Then install a 240v 4 wire outlet from (or in my case - 'on') the spa panel. Now you run a 4 wire range/stove plug from that outlet to your control panel. I went with a sturdy plastic tool box from lowes, it was $20. I prefer plastic to metal because drilling metal sucks as I found out when mounting the outlet on the actual spa panel itself.

Once inside the box you can split up the current as necessary but fuse it down first. At a local true value hardware store I found a terminal block with the fuse posts built right in. I ran one of the hot lines to this block and then ran all my 120v connections off of that (fused down appropriately). I used 14gauge wire to route the 120 around the box and used 8 gauge for the non fused stuff.

So one hot wire goes right to the switch, contactor, element or whatever. The other goes there as well but makes a pit stop first at the terminal block where you branch off your 120v stuff. I installed a 120v outlet into the side of the toolbox so I could plug in my HLT stirrer and my single pump. I also installed 2 240v 3wire outlets on the box so I could plug in my 2 elements. I wired my elements to some dryer cord (which is 3 wire, rated at 30 amp).. I then plug these into the outlets on my control panel when ready to brew and use a switch and contactor to switch between the element in the brew kettle and the element in the HLT (the switch switches between outlet 1 and outlet 2).


Note, the 5500w camco elements I and others are using cannot both be run simultaneously on a 50amp circuit, it's still 1 at a time. So you really don't gain much by going much by going 50amp over 30amp.. but I did because I could, it didn't cost much more, and it gives me more room for future expansion.

There's a really nice diagram by PJ here that I followed (minus 1 pump).
https://www.homebrewtalk.com/f170/simple-eherms-following-pjs-diagram-w-only-1-pid-221403/

You can also get all the switches at lowes or radio shack. I didn't see a need for fancy lighted push buttons from automation direct when regular old bat switches work just fine. I would also suggest that you choose switches which require circular rather than rectangular holes since that makes installation a snap with a drill.
 
Are you planning to use a GFCI breaker in the panel? If not I'd highly recommend it or using a spa panel to add GFCI protection to the circuit. I wouldn't want to touch anything in a e-brewery running at full power without a regularly tested GFCI breaker somewhere upstream from your control panel.

You could install a 30 amp breaker in your panel, run 10 gauge/4 wires to a spa panel ($50 at Home Depot), then run more 10/4 from the spa panel to the control panel. Then you'd have a 30 amp circuit with a neutral available to use if you want to wire in a pump with 120v. That's how I wired up my e-brewery.

EDIT: It looks like Lost snuck in ahead of me with the winning answer.
 
It all depends on your supply. If your plugging into an old dryer outlet that has a 3 wire supply, then you will only have 240 to use. If you have a newer outlet, or are running directly from the panelboard, and have a 4 wire supply then you use the neutral to get your 120v.

If you have the 3wire, and need 120v the easiest option is to just use a second cord to connect to a 120v GFCI, just be sure to keep you circuits separate in your control panel.

Actually, the common 3-wire dryer plugs (NEMA 10 style) are ungrounded. They offer 240V and a neutral, not 240V and a ground. The lights and buzzers on the dryer are usually 120V, and make use of the neutral, and the chassis of the dryer is 'grounded' via the neutral.
 
EDIT: It looks like Lost snuck in ahead of me with the winning answer.

He did, but that's cool. Both answers were totally helpful. The spa panel is clutch. Thanks for pointing that out. GFCI good, zappy bad.

Edit:
This is how I wired up my e-brewery.

This is awesome BTW. Probably pretty close to what I'll end up doing. The only difference being that my PID is an Arduino. I have it hooked up to my chest freezer right now and I move it into the garage when I brew to run the HLT. This will be more permanent though so I need to figure out a way to keep the chest freezer happy if I semi-permanently house the Arduino in the garage. I'd just move the freezer out there but then I have to worry about heating it in the winter. The house stays warm enough that I always have it set to cool with no problems.
 
I think you are ok with 8 gauge inside the control panel if you are only running 30 amps to the outlet, which you will be if you use a 5500w element.

8 gauge will handle over 50 amps for chasis wiring applications such as this and it will never even see that unless you have a short.

The risk is that the 8 gauge wire will catch fire in the event a short draws all 50 amps through the wire. The thing is, a short will quickly trip the breaker anyway.

The 8 gauge wire is not a fire hazard at 50 amps. Remember the other reason for gauge ratings is voltage drop. 8 gauge results in excess voltage drop in long lines, which is why 6 is needed for power transmission but 8 is ok for chasis wiring.
 
I love pinching pennies as much as the next guy but with something like this I'll spend the extra jing and get the larger gauge wire. Just add on an extra few feet to the wire you're already buying for the run to the outlet and run that in the Control Panel.
 
I respect that position but I would point out that 8 gauge is overdoing it, really you could get away with 10 gauge, that will carry 55amps chasis wiring.

I would also point out that if you plan to use the convenient and cheap 3 wire dryer cord to run from the element(s) to the plug(s) on the control panel then that too is 10 gauge so you'll want to use 6 gauge there too I guess.

Really though, I don't think 10 gauge running even a few feet through open air will burst into flames if 50 amps were briefly run through it. But I am not an electrician.

If you're really that concerned about it, and again I appreciate that position, then you should fuse the 2 240v hot wires as they come into the box. Put a 30 amp fuse on each of the two hot leads. Then you could use 10 gauge around the box and from the box to the elements.

If you haven't priced out wire yet you'll see that the expense of 6 gauge is substantial. It's not just "pinching pennies," more like burning bills. You'll also find that 8 gauge is a b!tch to work with and 6 gauge is even worse.

In the end though you should do what you think is safe because I couldn't live with myself if my bad advice resulted in the serious injury or death of a fellow homebrewer :mug:
 
I love pinching pennies as much as the next guy but with something like this I'll spend the extra jing and get the larger gauge wire. Just add on an extra few feet to the wire you're already buying for the run to the outlet and run that in the Control Panel.

I'm totally with you on this one but...hang on now. How many watts are ample to boil a 5 gallon batch? Not sure if I mentioned it but I don't intend on doing more. Let's go with a good rolling 7 gallon maximum boil. Can I get that with a 4500 watt element? If that's the case I can run a 30 amp circuit.
 
I'm totally with you on this one but...hang on now. How many watts are ample to boil a 5 gallon batch? Not sure if I mentioned it but I don't intend on doing more. Let's go with a good rolling 7 gallon maximum boil. Can I get that with a 4500 watt element? If that's the case I can run a 30 amp circuit.

You can easily get it with a 4500W element. Most people around here only have to run a 5500W element at about 60% to get 12 gal boiling nicely. That's 3300W, (averaged over the duty cycle...note that really it's 5500W for 60% of the time, 0W for 40% of the time), and that's 12 gallons.
 
Looking around I found a report at Electrical Wiring Faults – Fire Hazards

It suggests that overloading the wire results in fire when the current is at least 3 times the rating for wire. Here's the quote, "Experimental studies on the gross-overload ignition mode are meager, but they indicate that currents 3 – 7 times the rated load are needed for ignition."

This would indicate that with 10 gauge wire generally rated at around 30 amps, you would have to run at least 90amps through it to generate enough heat to start a fire. Since in practice you'll be running less than 30 amps I think you're fine. If you were to have a short that permitted the full 50 amps through the wire too would be insufficient for a fire (at least one caused by overheating the wire).

Moreover, the 50amp breaker would quickly trip quickly before the wire could heat up anyway. Here's what the article says about that, "In a bolted short, heating is not localized at the fault but distributed over the entire length of the circuit. A bolted short can readily be created by mis-wiring a circuit and then turning on the circuit breaker. The circuit breaker then typically trips before anything ignites. It is, in fact, exceedingly hard to create a fire in branch-circuit wiring from a bolted short."

The other sort of short is an arcing short which creates fire, as you would suspect, by heating and melting the material at the site of the arc. Wire gauge, in the context we are discussing it here (overheating by overloading), would seem to be irrelevant to this sort of short.

More food for thought.
 
I'm totally with you on this one but...hang on now. How many watts are ample to boil a 5 gallon batch? Not sure if I mentioned it but I don't intend on doing more. Let's go with a good rolling 7 gallon maximum boil. Can I get that with a 4500 watt element? If that's the case I can run a 30 amp circuit.


A 4500 watt element will be more than sufficient for a 5 gal batch (7 gal boil). But if you go that route then you could run 2 4500watt elements on a 50 amp circuit. So there's one good reason to go 50 amp instead of 30 amp, if you can that is.

2 elements running simultaneously would allow you to do back to back batches. Heat strike water and begin mashing your second mash as you boil and chill the first. I don't personally ever do back to back batches but I might if I did tiny 5 gal batches :ban:
 
Lost said:
I don't personally ever do back to back batches but I might if I did tiny 5 gal batches :ban:

Hah, I see your schwarz is bigger than mine. I drink a majority of my beer myself. Most of my friends that would really appreciate it live elsewhere so I only go through 5 gal every few weeks. I'd love to make larger batches but I'll save that for the day I can legally sell it somehow.
 
I'm totally with you on this one but...hang on now. How many watts are ample to boil a 5 gallon batch? Not sure if I mentioned it but I don't intend on doing more. Let's go with a good rolling 7 gallon maximum boil. Can I get that with a 4500 watt element? If that's the case I can run a 30 amp circuit.

FWIW, I can get a good rolling boil (if it's not 20F outside) with 3000W on 7.5 gallons. A 4500W element will do you just fine, it'll just get you to a boil more quickly. You could easily do 10gal batches with a 4500W element.
 
I've got 5500 watts in my HLT and kettle. I have the ability to do 10g batches, but I like to brew a lot of different styles so only do 5 gal batches. But I went for the larger watt elements cause I'm an impatient b*stard, so I like my stuff to heat quickly. :D
 
Lets not give someone advice that goes against the National Electric Code. They are very clear that to be code compliant you need 6 gauge wire for a 50A breaker going to a subpanel or outlet.

National Electric code says:

14 gauge = 15 amp
12 gauge = 20 amp
10 gauge = 30 amp
8 gauge = 40 amp
6 gauge = 60 amps

Please don't try to cut corners by overloading your wire putting too large of a breaker on it trying to pull more current through it. This is dangerous.

-Steve
 
sjwelna said:
Lets not give someone advice that goes against the National Electric Code. They are very clear that to be code compliant you need 6 gauge wire for a 50A breaker going to a subpanel or outlet.

National Electric code says:

14 gauge = 15 amp
12 gauge = 20 amp
10 gauge = 30 amp
8 gauge = 40 amp
6 gauge = 60 amps

Please don't try to cut corners by overloading your wire putting too large of a breaker on it trying to pull more current through it. This is dangerous.

-Steve

You are right, but in practice a 5500watt element pulls less than 30. You would only overload the wire in the event of a short and that's why you have the breaker in the first place.

As I said before, if you are really concerned then put a 30 amp fuse in the line.

This wiring isn't going through the walls and I don't personally plan to have my control panel UL listed. But again, do what you consider safe.
 
New plan. After spending an hour in Lowes tonight I realized this is going to get really expensive really quick. I already blew 300 bucks on a couple kegs and a new kettle so I'm running out of budget pretty quick. So I'll go with all 120vac. Three 20 amp breakers at the box to three 20 amp gfci outlets near the brew area. One 2000 watt element in the hlt and two in the boil kettle. 2000 watts is pushing the headroom of a 20 amp circuit but it should be ok. I haven't had a problem using it in my hlt thus far. I already have one gfci outlet and two mechanical relays well rated for the job. The one in the HLT is on a 30 second cycle which works well and if I keep one in the kettle fully on throughout the boil I think I could get away with a several second cycle for the other. That's still rough on a mechanical relay but doable and without the heat issues of SSR's. Even running 3 lines to the brew area, I think the cost of wiring would ultimately be less, let alone the cost of 240 volt recepticals, switches, contactors, etc. We'll see. Still have some figuring to do to confirm this.
 
Lets not give someone advice that goes against the National Electric Code. They are very clear that to be code compliant you need 6 gauge wire for a 50A breaker going to a subpanel or outlet.

National Electric code says:

14 gauge = 15 amp
12 gauge = 20 amp
10 gauge = 30 amp
8 gauge = 40 amp
6 gauge = 60 amps

Please don't try to cut corners by overloading your wire putting too large of a breaker on it trying to pull more current through it. This is dangerous.

-Steve
Perhaps it might help you to better understand wire ratings if you did a little more research instead. Take a look at this wire chart:
http://www.armstrongssupply.com/wire_chart.htm
Please note that #8 copper wire is capable of carrying 50 or 55A depending on the wire's insulation.
Oh - and the information is from NEC.
 
New plan. After spending an hour in Lowes tonight I realized this is going to get really expensive really quick. I already blew 300 bucks on a couple kegs and a new kettle so I'm running out of budget pretty quick. So I'll go with all 120vac. Three 20 amp breakers at the box to three 20 amp gfci outlets near the brew area. One 2000 watt element in the hlt and two in the boil kettle. 2000 watts is pushing the headroom of a 20 amp circuit but it should be ok. I haven't had a problem using it in my hlt thus far. I already have one gfci outlet and two mechanical relays well rated for the job. The one in the HLT is on a 30 second cycle which works well and if I keep one in the kettle fully on throughout the boil I think I could get away with a several second cycle for the other. That's still rough on a mechanical relay but doable and without the heat issues of SSR's. Even running 3 lines to the brew area, I think the cost of wiring would ultimately be less, let alone the cost of 240 volt recepticals, switches, contactors, etc. We'll see. Still have some figuring to do to confirm this.

You are greatly increasing cost by using multiple breakers, elements, and line to feed each outlet. 240v outlets are about $10 and the SSR from Auber is less than $20 and the heatsink is about another $20. You only need 1 ssr. And you could do with a single outlet for the element. Just unplug the element from the HLT and plug in the element from the boil kettle, this would save you the cost of the switch too (which isn't too bad anyhow).

For your prosed 120v setup, the two gfci outlets you'll need to buy along with the 3 breakers will probably equal the expense of the HD spa box ($50 if I remember correctly) and the single double pole 30 or 50amp breaker (~$10) needed for the 240v system. Plus you have the added expense of the additional element, nut to secure it (from bargain fittings) and time to drill the extra hole.

It looks to me like a more complicated system that isn't any better and isn't going to be any cheaper. I don't see what you save by going with 120v. That said, I will agree the expense of an electric system is hidden. It doesn't look pricey until you start adding up all the little things (outlets, wires, switches, heatsink, fuses, fuse holders, etc.). I speak from experience.

You could use the mechanical relay but I sure wouldn't expect it to last long. There are some around here who have or are toying with the idea of a PWM to control the element. It would be like adjusting the heat on a stovetop element - you turn it up and down until the temp is where you like it. There's no setting it for 150F and leaving it, you would have to monitor it constantly and 'learn' your system (i.e. how far to turn the dial to maintain the temp you seek).

I think the PWM is cheaper but I'm not positive about this, it's worth looking into though. I would consider a PWM if I wasn't doing HERMS, with HERMS I really need to set the HLT at a specific temp and maintain it there. If I were just heating the strike and sparge water and boiling the wort then I would definitely consider a PWM if it were cheaper and it may be.

Anyhow, food for thought.
 
You are greatly increasing cost by using multiple breakers, elements, and line to feed each outlet. 240v outlets are about $10 and the SSR from Auber is less than $20 and the heatsink is about another $20. You only need 1 ssr. And you could do with a single outlet for the element. Just unplug the element from the HLT and plug in the element from the boil kettle, this would save you the cost of the switch too (which isn't too bad anyhow).

For your prosed 120v setup, the two gfci outlets you'll need to buy along with the 3 breakers will probably equal the expense of the HD spa box ($50 if I remember correctly) and the single double pole 30 or 50amp breaker (~$10) needed for the 240v system. Plus you have the added expense of the additional element, nut to secure it (from bargain fittings) and time to drill the extra hole.

It looks to me like a more complicated system that isn't any better and isn't going to be any cheaper. I don't see what you save by going with 120v. That said, I will agree the expense of an electric system is hidden. It doesn't look pricey until you start adding up all the little things (outlets, wires, switches, heatsink, fuses, fuse holders, etc.). I speak from experience.

You could use the mechanical relay but I sure wouldn't expect it to last long. There are some around here who have or are toying with the idea of a PWM to control the element. It would be like adjusting the heat on a stovetop element - you turn it up and down until the temp is where you like it. There's no setting it for 150F and leaving it, you would have to monitor it constantly and 'learn' your system (i.e. how far to turn the dial to maintain the temp you seek).

I think the PWM is cheaper but I'm not positive about this, it's worth looking into though. I would consider a PWM if I wasn't doing HERMS, with HERMS I really need to set the HLT at a specific temp and maintain it there. If I were just heating the strike and sparge water and boiling the wort then I would definitely consider a PWM if it were cheaper and it may be.

Anyhow, food for thought.

I agree... 3 120V Breakers seems like it would be more annoying and more expensive. You would also be using much more current to get the same wattage. I'd go with 240V
 
Yeah you may be right. I need to really get it all in an excel doc and crunch the numbers. The money I'd save though, is more from the parts I already have. If I reduced the system to two outlets then made one for the lower element in the kettle then switched the hlt and upper bk element at the other outlet, I'm pretty much already wired past the outlets. I just need to add some code to the arduino. I'd need two more 2000w elements, nuts from bargain fittings, and the extension cords to them, one breaker, one gfi outlet, etc. Like I said though, I've still got numbers to crunch. I'll let you know what I come up with.

As far as pwm, that's all pids do already. Pulse width modulation is just turning the load on and off for a percentage of the latch time. Generally latch times are pretty fast, in the kHz, but even 2 seconds is still technically pwm. What makes it cheaper is that you could put together a pwm circuit for about 10 bucks using a 555 chip and a pot. Anything large is run this way. 240 volt 30 amp rheostats are fairly non existent.
 
As far as pwm, that's all pids do already. Pulse width modulation is just turning the load on and off for a percentage of the latch time. Generally latch times are pretty fast, in the kHz, but even 2 seconds is still technically pwm. What makes it cheaper is that you could put together a pwm circuit for about 10 bucks using a 555 chip and a pot. Anything large is run this way. 240 volt 30 amp rheostats are fairly non existent.

That is pretty much my understanding as well. The pid, though, incorporates a temp sensor and intelligently adjusts the pulse width to obtain and maintain the set temp.
 
Lost said:
That is pretty much my understanding as well. The pid, though, incorporates a temp sensor and intelligently adjusts the pulse width to obtain and maintain the set temp.

Actually depends on the pid output. Output styles include relays, pwm for a ssr, voltage, and current. They do this so you can use them for many applications. The major use around here is to drive a relay or ssr, thus the pwm output is used.
 
As far as pwm, that's all pids do already. Pulse width modulation is just turning the load on and off for a percentage of the latch time. Generally latch times are pretty fast, in the kHz, but even 2 seconds is still technically pwm. What makes it cheaper is that you could put together a pwm circuit for about 10 bucks using a 555 chip and a pot. Anything large is run this way. 240 volt 30 amp rheostats are fairly non existent.
It is hard to tell what your knowledge level is, but building your own PWM circuit, especially if your own custom spec'd waveform deviates drastically from common parameters, is a little sketchy. I am only mentioning this since you had to had to ask about 240v flavors, but even with some EE knowledge, the US electrical system and codes are a little mysterious.

You say you are already using an Arduino and want to use an SSR (eventually). The PID routines and designs for PWM boards/outputs to use with an SSR are already available for Arduino, as well as manual control modes. Why not use one of those, and the available support on the Arduino (Brewtroller) forums?
 
1: Building the controller myself I can use just about any cycle length I want. I think most PID's use a 60hz cycle but I don't see that being necessary and rough on the SSR. I was thinking more like a second or so. So 50% would be .5sec on .5sec off.

I thought I had responded to this in my earlier post, but apparently I didn't.

Most PIDs actually only use an 0.5 Hz cycle. 1 timing cycle ever 2 seconds. Not 60 cycles every second.
 
It is hard to tell what your knowledge level is, but building your own PWM circuit, especially if your own custom spec'd waveform deviates drastically from common parameters, is a little sketchy. I am only mentioning this since you had to had to ask about 240v flavors, but even with some EE knowledge, the US electrical system and codes are a little mysterious.

My knowledge of anything 12volts dc and lower is pretty high. Anything in that range is a simple hot/gnd setup so having 4 wires, two of which being hot is a little new. Plus we're talking about pretty major amounts of current. I'm just making sure I'm within code. I have an Arduino in a telescope mount that runs a self built circuit to control stepper motors and point to precise points in the sky and follow them. That controlled by a lcd, pot, and PS2 joystick. I think I can handle a 555 circuit especially if all it's doing it turning a relay/SSR on and off. I don't see a self assembled PWM circuit being sketchy unless you don't know what you're doing or are too lazy to do any sort of testing on it. We're talking on and off, nothing more complicated than that for what we're using here. I don't really see PWM having common parameters per say unless you're syncing it to some sort of clock for sending data places. That or you get into the 60hz range, then you're fighting against the frequency that the AC is cycling at. I'm certainly not pushing into those ranges at all.

You say you are already using an Arduino and want to use an SSR (eventually). The PID routines and designs for PWM boards/outputs to use with an SSR are already available for Arduino, as well as manual control modes. Why not use one of those, and the available support on the Arduino (Brewtroller) forums?

I program for a living. I'd rather write it myself and solder it myself.
 
I think I can handle a 555 circuit especially if all it's doing it turning a relay/SSR on and off. I don't see a self assembled PWM circuit being sketchy unless you don't know what you're doing or are too lazy to do any sort of testing on it. We're talking on and off, nothing more complicated than that for what we're using here.
30 amps is good bit of current, and 240v is nothing to sneeze at. I was just giving a warning about using switching rates and waveforms far outside what tried and true PIDs/PWMs use for this type of system. Your wording about doubting existing waveforms as being suitable was concerning. There are numerous effects when dealing with that much current/voltage/power that prevent nice, pretty, digital behavior.

I program for a living. I'd rather write it myself and solder it myself.
I never said you shouldn't, or couldn't, build it yourself, and even referenced that the designs were available. Even if you want to design or code it yourself, there is no shame in reviewing prior art. After all, I assume you will be using Ohm's law without deriving the effects and equations yourself. Standing on the shoulders of giants, and all that, you know.
 
I thought I had responded to this in my earlier post, but apparently I didn't.

Most PIDs actually only use an 0.5 Hz cycle. 1 timing cycle ever 2 seconds. Not 60 cycles every second.
This is why reviewing and verifying known applications of what you are trying to design is important. Getting the facts from a known source, or several, is critical if you are going to build your own PWM driver to mimic a PID. There are all kinds of PWM out there, from DC with <.1 Hz to HF AC with > 20Khz. The information that is important is that which applies to the situation at hand.
 
I think most PID's use a 60hz cycle but I don't see that being necessary and rough on the SSR. I was thinking more like a second or so. So 50% would be .5sec on .5sec off.

My own gut instinct and design was pretty close to what they actually use. I was thinking more of the art a DC motor PWM might use in my assumption.

I don't intend on reinventing the wheel, just making my own version, with a few tweaks to make it more round than round:D
 
My own gut instinct and design was pretty close to what they actually use. I was thinking more of the art a DC motor PWM might use in my assumption.

I don't intend on reinventing the wheel, just making my own version, with a few tweaks to make it more round than round:D
It is a whole lot easier have seen a few good wheels first, and improve on those. That is all I was saying. Relying on your gut for high power electronics has greater consequences than a few laps around the block on a square wheel.
 
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