From: baron.nospam@linuxmainiac.nospam.net
Farticus wrote:
>
> "Baron" wrote in message
> news:ffqh7q$tnt$1@registered.motzarella.org...
>> Ross Herbert wrote:
>>
>>> On Thu, 18 Oct 2007 23:02:34 GMT, "Farticus"
>>> wrote:
>>>
>>>>I need to control two 120VAC/5A heating elements off a 240VAC
>>>>supply. Two elements will be plugged into one control box and
>>>>ideally one "temperature control" is to be fitted to the box. The
>>>>elements can be unplugged so that only one element might be operated
>>>>at any one time.
>>> Cost
>>>>as always is a factor (as is with most customers!).
>>>>
>>>>The customer suggested a cooker type infinitely variable simerstat,
>>> as this
>>>>would be good enough for the type of temp control they require.
>>>>The only simerstats available locally are 240V and the manufacturer
>>> advises
>>>>that they will not function properly on120V. Then there would be the
>>> need
>>>>for interface relay/contactor to switch the element etc. etc....
>>>>
>>>>My first thought were to use a 240/120 transformer with a thyristor
>>> circuit
>>>>on the 120V output.
>>>>
>>>>My second thought was to use a thyristor without a transformer,
>>> restricting
>>>>the the thyristor output to a max of 120V via the thyristor control
>>> circuit.
>>>>The problem with this is that a short-circuited thyristor would
>>>>apply
>>> 240V
>>>>to the elements causing problems. A fuse in circuit yes, however
>>>>this equipment is to be used in a rough industrial environment,
>>>>meaning
>>> that the
>>>>operators WILL replace expired fuses with fencing wire!
>>>>
>>>>Any ideas, past experiences, circuit suggestions using triacs,
>>> back-to-back
>>>>SCR's or whatever would be appreciated.
>>>>
>>>
>>> It seems to me that your customer is trying to be a cheap-skate and
>>> doesn't understand that trying to do what he wants means making
>>> compromises which could drastically affect the safety of anyone
>>> using
>>> his cooker. In the end he will end up paying more for his bodged up
>>> job becaue it will either fail or electrocute someone. He would be
>>> well advised to simply spend the money and do it properly in
>>> accordance with electrical standards.
>>>
>>> Since each of the 2 elements are required to be operated separately
>>> as needed it does not make sense to try to do it with a common
>>> temerature controller. This would mean that either element would
>>> require some means of disconnection when not required. It makes more
>>> sense, and I believe that local electrical appliance standards
>>> wiring would require it, that each element be controlled from a
>>> separate temperature controller. Now that doesn't solve the problem
>>> of trying to power the two 120Vac/5A elements from a 240Vac supply
>>> and to my mind the best way to do this is to have a 240V to 120V
>>> step-down transformer. Unfortunately, this requires a 1500Va
>>> continuous transformer and that won't come cheap.
>>
>> I'm in general agreement. Why not simply use 230v elements. There
>> are
>> a few companies that will make up whatever size/shape you want. Then
>> you can use the "Simmerstat" to do the controlling of temperature.
>>
>> --
>> Best Regards:
>> Baron.
> Try to convince one of those customers that is "always right" - I
> agree with your sentiments exactly.
Yes I get them too! Wouldn't it be nice to tell them to "Sod Off" !!!
I must admit that I have pointed a couple at my competitors. One of
those is now a very good client. But he had to get burned to realise
where he was better off.
Good Luck.
--
Best Regards:
Baron.
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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