From: localhost@127.0.0.1
"robb6435 via ElectronicsKB.com" wrote in message
news:7a0b56f579d42@uwe...
>I don't understand why you don't just pull one leg of the 240v and a
>neutral
> to get your 120v? better yet, why not just return the heaters and get
> 240v
> ones? What type of control box? I would use a 20a contactor, and run the
> control voltage through the heat control for the contactor. use 120v
> control
> or a transformer to achieve the customary 24v control voltage. if you use
> the 240v simmerstat control, make sure it is rated at least 25A. It will
> still work. You can go up involtage rating just not down. Do you know
> what
> a contactor is? I would use a contactor, one leg of the 240v hot and one
> leg
> of neutral. this will give you the 120v. hook the t stat to the magnetic
> coil connectors. this will pull in the contactor as needed based on the t
> stat. you could run two wire connectors out from the contactor to your
> outlets, and they will be hot or not based on the t stat setting. I'd
> even
> install some light switches in there for control if he wanted.
Thank you for your suggestion.
Unfortunately its not that simple.
The gear has to be constructed to meet certain standards and customer
expectations.
Here in Australia, the neutral and earth are bonded at the power supply
station and at all earth points enroute from the supply to the users outlet
meaning that the PD between line and either neutral or earth is 240VAC.
The heaters belong to a customer, not mine. He purchased them ex-USA and the
supplier only manufactures 120V units.
Yes, indeed, I do know what a contactor is. The first contactor I ever came
across was in 1963 when I was an apprentice. It was a really robust piece of
gear with built in overload that used oil in a damping mechanism (called a
dash pot) and was if I remember correctly made by GE.
I do not use contactors or relays in applications as described here as they
are a bit out-of-date as opposed to solid state devices which last much
longer.
One must also bear in mind that when making up equipment for a customer (who
is always correct!) a number of factors have to be taken into account.
Firstly final price to the customer, and of course enough profit.
Then there are the many compliance requirements to ensure the equipment
meets all local electrical laws etc.
The equipment must be professionally presented, built to meet the
expectations of the customer and to mechanically fit the industry into which
it will be used.
Taking these and a few other aspects into consideration one then sets about
designing the equipment, endeavouring to meet all requirements and deliver a
quality piece of apparatus.
I have finalized my design and run a test which works adequately for the
application and meets the customers expectations.
The design uses a simple LM555 circuit configured to provide a PWM signal of
approximately 100Hz which drive a solid state 30A relay with built in
features such as zero crossing, overload protection etc. The mechanical
loading (heatsink) provided for the heating elements by the work being
performed is more than adequate to ensure the circuit is kept busy
constantly thereby providing reasonably accurate temperature maintenance
without any closed loop configuration. Further protection is provided by a
circuit incorporated into the control that allows the device to operate for
30 minutes at a time. This means that the operator resets the control every
30 minutes - this is to prevent uneccessary use of the heating elements when
no in active use (customers request).
The operators of the equipment learn through experience the optimum setting
for the various materials they run through the machine/heating elements.
Thanks to all for their valued comments.
F.
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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