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Old 07-25-2012, 07:41 PM   #11
mendesm
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Originally Posted by wilserbrewer View Post
While I agree it is not good practice to run things beyond their rated potential, why do you percieve nearly 100% chance of failure? These things must be slightly overdesigned, no?

How about 4500w?

Sorry for the noobish question, is something like this ready to use, or are more components needed to control an element...

It's designed to source a max of 3800w. 3800w at 220v eats 17.3 amps and 34.5 amps at 110v. For your 4500w, that's 20.5 amps @ 220v or 41 amps @ 110v.

If you run it at 110, you'll first have to ensure your wiring can handle that. Most house circuits today cry uncle at 20 amps. 2000w/110v = 18.2amps, so even that is pretty close.

But going back to over loading the thing...

Electronic circuits are not designed to handle abuse. Some more complicated designs may have fault tolerance/protections designed into them, but from the pictures in that item on ebay, it's clearly not the case here. It's only a potentiometer, an SCR, 2 resistors, 1 capacitor and 1 coil (the yellow component, which might be another capacitor, I can't tell from the markings on it). Just enough parts to make that SCR work to control power.

That heat sink mounted to the SCR is there because that component clearly needs it at the stated power rating. Even if you mount a much bigger heat sink to it, you're likely to short/blow it's junctions from the over current/heat, because the heat has to radiate out from the the junction inside the SRC before it can be dissipated by the heat sink. The resistors have the same implications, but they're not heatsinked.

A quick google search found this 5000w dimmer, and by the looks of it, it's from the same manufacturer http://www.aliexpress.com/store/prod...557766931.html
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Old 07-26-2012, 02:48 PM   #12
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A quick google search found this 5000w dimmer, and by the looks of it, it's from the same manufacturer http://www.aliexpress.com/store/prod...557766931.html
So rather than building some elaborate control box with PIDs and SSRs, I could use this "dimmer" on the hot lines (it appears to have 2 ins and 2 outs) of a 4500W/240VAC heating element and have the ability to dial down the heat once I've reached a rolling boil?
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Old 07-26-2012, 06:27 PM   #13
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Yes. The reason people like the PIDs is because they can be used to automate things. You can set the timer and the temperature and it goes off and regulates accordingly, applying more/less power as needed etc.

With these you set them manually and they stay until you turn it up or down, just like an electric stove.

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Old 08-16-2012, 01:30 AM   #14
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The 3800w dimmer would work if you use a SSR also, right?

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Old 08-16-2012, 03:01 PM   #15
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The 3800w dimmer would work if you use a SSR also, right?
You lost me.
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Old 08-17-2012, 03:31 PM   #16
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Quote:
Originally Posted by wilserbrewer View Post
While I agree it is not good practice to run things beyond their rated potential, why do you percieve nearly 100% chance of failure? These things must be slightly overdesigned, no?

How about 4500w?
cheap products from china are never over designed. more often they are under designed, and often, a product that should really only be rated at 3500w they slap a 3800w sticker on. dont expect miracles out of bare-bottom cost chineese made products.

that being said (and ignoring possible inflated ratings from the manufacturer because theres no way to easily know), you always need to assume 3800w max means exactly that. 3800w does not mean 4500w, nor 5000w. if it did, then they would rate it higher because higher specs sell better. do not ever expect to be able to go over somethings rated max without issue. doing so is entirely at your own risk (risk of money loss, personal injury, or property damage).


when it comes to semiconductors, like these, or SSRs or any type of mosfet, the closer you get to the rated maximum, the exponentially more heat they produce (its not linear). so if you have a 1000w load to switch, buying a 1000w max rated SSR will run very hot. buying a 2000w max rated SSR will run much cooler, and will last that much longer. if you put a 1500w load on a 1000w max SSR, its going to burn up very shortly, if not instantly.

Quote:
The 3800w dimmer would work if you use a SSR also, right?
thats like saying "this light switch would work if you use a light switch also, right?"
what do you mean?


Quote:
Originally Posted by TheGrouch View Post
So rather than building some elaborate control box with PIDs and SSRs, I could use this "dimmer" on the hot lines (it appears to have 2 ins and 2 outs) of a 4500W/240VAC heating element and have the ability to dial down the heat once I've reached a rolling boil?
if you want to do this you would only use one dimmer rated for the full load of the element, and it would be on either of the hot legs; not one on each side, if thats what you meant. but yes, that would work.
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Old 08-17-2012, 03:40 PM   #17
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Quote:
Originally Posted by mendesm View Post
It should work with 120v and a 2000w element.

EDIT: looking at the pictured item again, it has only 2 screw connectors, one for the input, the other for the output, so it looks like this has to be connected in series with the load on the neutral wire. It's the only way I see this working with a 220v setup, which normally has 2 hots and 1 neutral and I don't like that. In a 110v set up, you can connect it between the on/off switch and the load in the hot wire.
the dimmer would be connected in series to either of the HOT sides of the incoming line. neutral is essentially just a ground in 240v, and none of the power flows thru neutral (unlike in 120v where neutral is the return path).
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Old 11-15-2012, 06:15 PM   #18
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After reading this thread I feel like I have a fairly clear idea of how I want to control my heat.

Now I just want to be sure that the parts I've picked out will work well together and how I go about wiring them up

I want to use a camco 5500w 240v low density element, and this http://www.ebay.com/itm/180816240982 for control

Assuming these parts are ok, how do I wire all this up? And do I need any thing else?

Thanks, any input would be greatly appreciated, I'm a noob at this.

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Old 11-15-2012, 08:22 PM   #19
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What about something like this?

http://www.aliexpress.com/item/Free-...582778743.html

To use with a 2000W 120V element.

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Old 11-15-2012, 08:52 PM   #20
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Search for voltage resistance SSR on ebay or amazon.
It is a phase angle control that uses a potentiometer to control the power delivered to the load. Buy one rated for 25amps or 40amps. A PWM control can be used with a regular ON/OFF SSR with similar results.

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