switching appliance with low voltage switch?

J

james

Guest
I bought a bare bones dehumidifier. However I need to add a condensate pump
to it to pump the water to a sink. There are many brands/models of
condensate pump, I'm interested in the ones with an overflow safety switch
so I can turn off the dehumidifier in case the pump fails.

These safety switches are float-activated micro switches and are not rated
to switch a dehumidifier (120V 7A).

I would have to add a switching relay like this:
http://www.functionaldevices.com/building-automation/display.php?model=RIB01BDC
Costs $20.

Since this is a mechanical device (relay), it is bound to generate arc and
the contacts are bound to fail. More so if the load is inductive.

Also, the dehumidifier along with this device is placed in a sealed
crawlspace with natural gas pipe running though. In the unlikely case event
of a gas leak, I prefer there be no arc generating switches

Would it be better to use a TRIAC to switch this appliance? Something like
this:
http://www.sullivan-county.com/ele/pics/tr2.gif
The S1 would be the safety switch (normally closed)

The triac is even cheaper than the relay module. Are there reasons not to
use the triac? I understand the triac would have a voltage drop of about 1
volt, in this case amounts to 7W, which is no big deal and probably needs a
small heat sink.

And if I do use triac, what rating should I get? It's not just 120V 7A. If
the load is inductive, I would need a higher rating, but not sure how high.
 
"james" <nospam@nospam.com> wrote in news:i9fcm5$5pu$1@speranza.aioe.org:

I bought a bare bones dehumidifier. However I need to add a condensate
pump to it to pump the water to a sink. There are many brands/models of
condensate pump, I'm interested in the ones with an overflow safety
switch so I can turn off the dehumidifier in case the pump fails.

These safety switches are float-activated micro switches and are not
rated to switch a dehumidifier (120V 7A).

I would have to add a switching relay like this:
http://www.functionaldevices.com/building-automation/display.php?model=RI
B01BDC Costs $20.

Since this is a mechanical device (relay), it is bound to generate arc
and the contacts are bound to fail. More so if the load is inductive.

Also, the dehumidifier along with this device is placed in a sealed
crawlspace with natural gas pipe running though. In the unlikely case
event of a gas leak, I prefer there be no arc generating switches

Would it be better to use a TRIAC to switch this appliance? Something
like this:
http://www.sullivan-county.com/ele/pics/tr2.gif
The S1 would be the safety switch (normally closed)

The triac is even cheaper than the relay module. Are there reasons not
to use the triac? I understand the triac would have a voltage drop of
about 1 volt, in this case amounts to 7W, which is no big deal and
probably needs a small heat sink.

And if I do use triac, what rating should I get? It's not just 120V 7A.
If the load is inductive, I would need a higher rating, but not sure how
high.
A triac should be fine, but because it's switching an inductive load you can
easily do worse than start with this LT (Linear Technology) document on triac
switching..
http://www.st.com/stonline/books/pdf/docs/3566.pdf

It might also be possible to use a switching MOSFET but I'm not at all sure
they deal with mains voltages. Usually high current, low voltage, from what
I've seen. They'd be useful if they did though, bidirectional main channel,
on resistance of a few milliohms.. But I'd stay with a triac for mains
switching, I think.
 
Lostgallifreyan <no-one@nowhere.net> wrote in
news:Xns9E1525EA1D43Bzoodlewurdle@216.196.109.145:

LT (Linear Technology)
ST. Not LT. But this file is a keeper, for certain.
 
On Sun, 17 Oct 2010 21:55:06 -0500, Lostgallifreyan <no-one@nowhere.net>
wrote:

Lostgallifreyan <no-one@nowhere.net> wrote in
news:Xns9E1525EA1D43Bzoodlewurdle@216.196.109.145:

LT (Linear Technology)

ST. Not LT. But this file is a keeper, for certain.
Fortunately, neither ST or LT have Apple's business model, else they
would have trademarked the use of "T" in naming device manufacturers.

;-)

--
Rich Webb Norfolk, VA
 
Rich Webb <bbew.ar@mapson.nozirev.ten> wrote in
news:t0eob6tn1mal21km7qhr6jsanfd40gpish@4ax.com:

On Sun, 17 Oct 2010 21:55:06 -0500, Lostgallifreyan <no-one@nowhere.net
wrote:

Lostgallifreyan <no-one@nowhere.net> wrote in
news:Xns9E1525EA1D43Bzoodlewurdle@216.196.109.145:

LT (Linear Technology)

ST. Not LT. But this file is a keeper, for certain.

Fortunately, neither ST or LT have Apple's business model, else they
would have trademarked the use of "T" in naming device manufacturers.

;-)
I ought to trademark the fact that I exist, and charge everyone royalties for
the fact thay they also exist. It could even work, some of those no-win-no-
fee lawyers will try anything. >:)
 

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