How to convert amps to other voltages?

[jim4065]

Side note: Got my 30 amp GFCI breaker installed today - Onward and Upward! Bought a case and a half of Noble Pils to celebrate.

Now to my question. I'm wanting to have the Auber PID control one leg of the 220 volt power going to two different heater elements. I'll take the output from the 40 amp SSR and run it to the center pole of an "ON_OFF_ON" switch which is rated for 50 amps at 12 volts, then by simply throwing this switch one way or the other I'll select which of the two dual pole switches now can be thrown to turn on an element (BK or HLT). The thing is: Will that switch be strong enough to handle the amperage at 120 volts (half of 240, right?) Right?

C'mon guys, I'm WAY out of my depth here; and I kicked my electrician nephew off the job 'cause he said I didn't need a GFCI.

 

[pompeiisneaks]

(I'm no electrician so don't guarantee this is fact) I believe the ssr should state on it its operating range, i.e. if its only good around 220 v, it will say that if not it should say either on it or w/ accompanying documents 120-220v. amps are nothing to do w/ volts. two different things w/ respect to electronics. I'm not an expert but the best way I can explain it, is that the voltage won't kill you as easily as the amperage. if a 220v circuit is pushing 1 amp, its not going to be as bad as a 120v circuit pushing 50 amps... but I may be way off, hopefully a real electrical expert can weigh in. Be very careful you don't over or under power a circuit as both can be dangerous.

 

[kezgin]

if it's really only rated for 12 volts and that wasn't a typo, don't use it

 

[ndsgr]

I would probably re-hire your nephew. Also, maybe electricians don't mind, but a little piece of an EE dies every time you say the word "amperage".

Also, voltage and current are related. Voltage=current*impedance (or resistance, similar concepts, AC vs DC). If a source will not drop voltage once connected to load (meaning there is enough charge to back the current flow) then danger is there regardless. A million volt touchable source isn't a million volts once you touch it. A 220V household source can stay pretty close to 220V once you (the load) is attached.

Back to the OP, please clarify if the switch is rated 12VDC or 120VAC. There are always work-arounds anyway, but you really need to know what you are doing.

 

[Fletch]

If you're running a 240 volt element on a 120 volt circuit, the current will be 1/4 the rated DRAW (notice - the connected load DRAWS the current, the circuit doesn't "push" it).

Also, if you do wire this thing up the way you plan, make sure you do not switch between elements without opening the circuit BEFORE the SSR. In other words, unplug it. But it's not a good design - you should two circuits for the two elements, with an SSR for each.

 

[willynilly]

He clearly states this is a 220VAC circuit.

Why are you using a 12V rated switch? These switches are sometimes used to switch the CONTROL signal from one SSR to another. I have yet to see anyone use them to switch the current going to the element. Id hold off on that.

 

[Fletch]

You're right Willy. Jim, NO, you will NOT have 120 volts going through that switch. If you meter the terminals with the switch open, then yes, each will read 120 volts. But once the circuit is completed it will be 220 volts.

You really should get some help, before you hurt yourself.

 

[P-J]

... I'm wanting to have the Auber PID control one leg of the 220 volt power going to two different heater elements.

I'll take the output from the 40 amp SSR and run it to the center pole of an "ON_OFF_ON" switch which is rated for 50 amps at 12 volts, then by simply throwing this switch one way or the other I'll select which of the two dual pole switches now can be thrown to turn on an element (BK or HLT). ...

IMHO? Wrong! {Seriously} Invest in a second SSR and use the switch you reference to switch the input to the SSRs. Check this diagram to visualize it:
Click the image for a larger pix.

 

[jim4065]

OK - I can't use that switch then. It's not marked in any way, but the seller was "Something" Vehicle Systems, which sounds like 12 volts to me. So let's say I trash the switch and get a bigger one. Is there anything wrong with having one leg of the 220 go thru the SSR and just switching it from one element to the other? If each element has a dual pole switch which is turned off between itself and the PID/SSR then even if the PID is still on the power can't go through to the element, right? Then if I turn select either AUTO for the HLT or MANUAL for the BK, and throw the ON-OFF-ON switch to select the proper element, I still have to throw the dual pole switch to power up the element, and the other element gets Zero power. Why do this? It lets me use a single Auber SYL2362 PID to control both elements (one at a time). On the HLT it works with the temp sensor to allow very precise HERMS control of the MLT, wheras with the BK it is switched to Manual to let me lower the percentage of power sent through to the element after I reach a boil. In other words, I can have a gentle boil or anything up to a "raging" boil - with no sensor input required. The SSR has 4 connections - 2 of which go to the PID and the other two are "line in" and "line out". I'm really ignorant of this stuff - how does the SSR "switch" more than one leg at a time? There's no place to connect the other line.

Edit: AHA! I see that the solution was posted before I posted. So this avoids having too much amperage going through the switch? Gotta study this a bit.

 

[kezgin]

yeah in p-j's schematic you're switching which ssr the pid is controlling. you'd be using low voltage and much lower amps

 

[Marsdude]

I like p-j's solution.

Here is a link to some selector switches just in case:

http://www.grainger.com/Grainger/wwg/viewCatalogPDF.shtml?browserCompatable=true&adobeCompatable=true&toolbar=false&CatPage=305

 

[CorgiBrew]

yeah in p-j's schematic you're switching which ssr the pid is controlling. you'd be using low voltage and much lower amps

I am going to go with p-j's approach, but am still curious why you couldn't use a selector switch after the SSR instead of having two SSR's with a selector switch before them (assuming, of course, that you had a properly rated switch). Can anyone shed some light on this?

 

[P-J]

I am going to go with p-j's approach, but am still curious why you couldn't use a selector switch after the SSR instead of having two SSR's with a selector switch before them (assuming, of course, that you had a properly rated switch). Can anyone shed some light on this?

In my humble opinion you put your SSR at risk by switching the power side live. I know you intend to power off before switching - but in the heat of the moment and a couple of beers? The risk (It could be a slight one) is dependent on the load cycle. Breaking a loaded circuit can introduce a back emf that can damage either the switch or the SSR.

I took some time to make this image so that there can be a better understanding of the amount of potential power that is involved:

On a 240 volt circuit we are really messing with about 340 volts.

Please exercise due care.

Edit: I just realized that I labeled the image incorrectly on the left. I fixed the chart.

 

[Fletch]

Corgi, SSRs are pretty cheap, just buy another one and hook it up as in PJs drawing. Also, don't use ANY component in your system that is not marked with it's rated voltage and current capacity. A 12 volt automotive switch is likely to have insufficient internal isolation (no, not iNsulation, isolation) for line voltage and heavy current. It might work a few times, just enough to make you complacent. But Murphy's Law says it'll leak the one and only time you touch it with a wet hand, standing in a puddle of water.

PJ, IIRC the backlash risk you're talking about only occurs with inductive loads, and a heating element is of course a resistive load. But I totally agree with you that switching downstream of the SSR is wrong, I just can't remember why. I believe it's in the nature of the triac circuit that comprises the SSR, seem to remember that it's not recommended, and will lead to early failure.

 

[CorgiBrew]

Like I said, I'm going the 2 SSR route, so no worries. Just asked about the other approach because I like to understand why things are done a certain way.

 

[jim4065]

I just ordered a second SSR and Heat Sink from Auber and thanks for correcting me. Bought a 12 volt double pole ON-OFF-ON switch from Radio Shack for switching SSR's. I'm wondering if it will hurt to use the 240 volt double pole switches downstream from the SSR (before the heating elements). I'd sure like to know that there's an "absolute" shut-off to the BK, which may get a little wet at times. The 240 volt 3 wire circuit now has a GFCI, same as the separate 110 volt circuit.

 

[P-J]

... PJ, IIRC the backlash risk you're talking about only occurs with inductive loads, and a heating element is of course a resistive load. But I totally agree with you that switching downstream of the SSR is wrong, I just can't remember why. I believe it's in the nature of the triac circuit that comprises the SSR, seem to remember that it's not recommended, and will lead to early failure.

You are absolutely correct about inductive loads (anything with a coil where the collapsing magnetic field induces a back EMF). The SSR is basically a transistor circuit (to put it into very simple terms) and can be rather sensitive to 'happenstance'.

It's sort of like when one figures a 25 amp SSR is good enough for a 5500 watt element. It will only draw 22.9 amps at full power so should be good to go. NOT! Even with a good heat sink it is at risk at that power level due to the amount of heat within the SSR.

Another one is the flat blanket statement that I see all the time that a circuit cannot be run to its full circuit breaker value. i.e. - Draw 20 amps on a 20 amp breaker or 15 amps on a 15 amp breaker. For the most part it's true - however - not always. There is a specific circumstance where it IS allowed and that is in accordance with the current NEC (National Electrical Code).

I guess I'm old and really set in my ways. I have tons of opinions and am just trying to spread some safety info. I initially studied and worked to be a licensed electrician in NYC. Bummer.!! Their "Local 3" is a closed "father/son" organization. I still keep very current on the whole thing as it is of intense interest to me. I ended up joining IBM Corp back in the late 50's. I'm now a retired IBM technical manager with many, many years of experience. I'd like to believe that I know how things work. If not? I dig like hell to just know for myself.

Please - Please, do not think I'm commenting or coming down on you. I'm agreeing with you and just thinking out loud.

Thanks...

 

[P-J]

I just ordered a second SSR and Heat Sink from Auber and thanks for correcting me. Bought a 12 volt double pole ON-OFF-ON switch from Radio Shack for switching SSR's. I'm wondering if it will hurt to use the 240 volt double pole switches downstream from the SSR (before the heating elements). I'd sure like to know that there's an "absolute" shut-off to the BK, which may get a little wet at times. The 240 volt 3 wire circuit now has a GFCI, same as the separate 110 volt circuit.

You will be absolutely fine, IMHO, with the double pole switch. Consider it a "Kill" switch. It will not be used in the norm of a brew day so it's a Emergency Power Off. No worries, no problem.

 

[RichBenn]

I just rapidly scanned this thread, but I gotta tell you, as an electronics engineer with 30 plus years experience, I'm concerned for your safety, Jim. Please have a competent electrician review your wiring in person before plugging it in. I say this because the questions you ask indicate a huge knowledge gap. You may get right answers here, but you may not ask all the right questions either, or you could make a wiring mistake. And a mistake could be serious. 230 volts is a significant potential.

There is a reason wiring is inspected by a separate party on houses, even though the electrician doing the job is qualified. There is a reason UL, FM or CSA approves electrical designs even though the engineer designing it is qualified. It's safety.

OK, off the soapbox now. I need a homebrew!

 

[pompeiisneaks]

I would probably re-hire your nephew. Also, maybe electricians don't mind, but a little piece of an EE dies every time you say the word "amperage".

Also, voltage and current are related. Voltage=current*impedance (or resistance, similar concepts, AC vs DC). If a source will not drop voltage once connected to load (meaning there is enough charge to back the current flow) then danger is there regardless. A million volt touchable source isn't a million volts once you touch it. A 220V household source can stay pretty close to 220V once you (the load) is attached.

Back to the OP, please clarify if the switch is rated 12VDC or 120VAC. There are always work-arounds anyway, but you really need to know what you are doing.

I really appreciate this condescending response when I qualified clearly that I'm no expert and that I hoped someone would respond and help, but I didn't mean "respond telling me how stupid I am, and then help"

 

[Special Hops]

voltage and amps are to separate things.

Think of volts being the pressure in a pipe, while amps is the flow rate through the pipe. . you cannot convert one to the other.

 

[jkarp]

voltage and amps are to separate things.

Think of volts being the pressure in a pipe, while amps is the flow rate through the pipe. . you cannot convert one to the other.

Sure you can, just need a transformer (for electricity) or a nozzle (for water).

Sorry, couldn't resist!