Hot Tub arching

[Nirodac]

I have a hot tub control that switches the heater element on and off to set
the water temperature.
The thermostat has 20 amp contacts, that tend to burn out. I replaced the
thermostat , then installed a slave mercury relay (contact rating 25A at 240
volts AC),(controlled by the thermostat) to switch the actual load of the
heater. The relay started to over heat and latched up. Replaced the merc
relay with a "BDR" contactor (big darn relay) with contacts rated at 30A 240
volt AC. Everything works fine, except the relay contacts arc when the
relay operates and releases. Question is, how do I stop the arcing. The
current measured with an amp meter at the heater is 22 amps . I was
thinking of also using a 40 amp 600 volt Triac, any opinions.

 

[petrus bitbyter]

I have a hot tub control that switches the heater element on and off to set
the water temperature.
The thermostat has 20 amp contacts, that tend to burn out. I replaced the
thermostat , then installed a slave mercury relay (contact rating 25A at 240
volts AC),(controlled by the thermostat) to switch the actual load of the
heater. The relay started to over heat and latched up. Replaced the merc
relay with a "BDR" contactor (big darn relay) with contacts rated at 30A 240
volt AC. Everything works fine, except the relay contacts arc when the
relay operates and releases. Question is, how do I stop the arcing. The
current measured with an amp meter at the heater is 22 amps . I was
thinking of also using a 40 amp 600 volt Triac, any opinions.

Nirodac,

Are you sure the control input of the mercury relay was rated for the
voltage you used to drive it? It is strange that a mercury relay is
overheated in a application that it's made for. So maybe the voltage too
high or ac/dc problem?

To prevent the arching I advise to use a solid state relay. Best you look
for a type that has a zero cross switch and that can be controlled by the
mains voltage. A 25A type should be good enough. They become hot so so will
need a heatsink.

petrus

 

[jtech]

I have a hot tub control that switches the heater element on and off to set
the water temperature.
The thermostat has 20 amp contacts, that tend to burn out. I replaced the
thermostat , then installed a slave mercury relay (contact rating 25A at 240
volts AC),(controlled by the thermostat) to switch the actual load of the
heater. The relay started to over heat and latched up. Replaced the merc
relay with a "BDR" contactor (big darn relay) with contacts rated at 30A 240
volt AC. Everything works fine, except the relay contacts arc when the
relay operates and releases. Question is, how do I stop the arcing. The
current measured with an amp meter at the heater is 22 amps . I was
thinking of also using a 40 amp 600 volt Triac, any opinions.

Perhaps you can parralel connect a .01 capacitor with the relay switch. It
will squelch most if not all of the arcing. fwiw.

 

[Robert Baer]

Perhaps you can parralel connect a .01 capacitor with the relay switch. It
will squelch most if not all of the arcing. fwiw.

Arcing would seem to indicate an inductive load.
But heaters are supposed to be resistive.
Get the eXplicit, raw facts from the hot tub makers as to *EXACTLY*
what they use and have inyour *particular* make and model.
Also get fromthem, exactly what *they* recommend for a controller.
Be sure all info comes fromthe factory and not a salesperson.
In short, get the raw oats (info from the factory) before the horse
eats them; you do not want re-processed oats from the back side of the
horse (salesperson).

 

[Nirodac]

The heater is resistive, I've had it replaced myself. The thermostat is a
bulb and capillary tube type that operates a "microswitch" rated at 20 Amps.
What I'm trying to do here is save the microswitch from constantly burning
out. The tub manufacturer is local, so up to now I was buying the parts
from them, (the complete thermostat) directly. The thermo part of the
thermo switch never failed, it was always the switch. It is possible that
they sub'd a higher wattage heater this last time, as this one physically
looks different.
Maybe I shouldn't have called it an arc, as much as just a bright spark.
The plate on the electrical box rates the heater at 4KW.

Nirodac

 

[Robert Baer]

The heater is resistive, I've had it replaced myself. The thermostat is a
bulb and capillary tube type that operates a "microswitch" rated at 20 Amps.
What I'm trying to do here is save the microswitch from constantly burning
out. The tub manufacturer is local, so up to now I was buying the parts
from them, (the complete thermostat) directly. The thermo part of the
thermo switch never failed, it was always the switch. It is possible that
they sub'd a higher wattage heater this last time, as this one physically
looks different.
Maybe I shouldn't have called it an arc, as much as just a bright spark.
The plate on the electrical box rates the heater at 4KW.

Nirodac

4KW (RMS) at 120VAC (RMS) .. P=I*E or I=P/E or I=(4000W)/(120V) or
I=33.3 Amps (RMS).
No wonder a 20A contactor does not last!
...Unless someone got wise and used 240VAC, which would make the
current 16.7 Amps (RMS), which is too close to the contact rating.
At minimum, the contact rating should be at least twice the peak
current being handled.
Perhaps a mercury plunger type of a contactor would be best; rated at
50 Amps (!!) for a 240V supply voltage.

BTW, a .01 capacitor is orders of magnitude too small to have any
effect.

 

[Nirodac]

It is 240VAC, The current relay I installed is rated at 30 amps. The
measured current (clamp on meter) is 22 Amp AC, for the heater only.

So, just how much heat would I need to dissipate, if I used a 40 amp triac.

 

[petrus bitbyter]

4KW (RMS) at 120VAC (RMS) .. P=I*E or I=P/E or I=(4000W)/(120V) or
I=33.3 Amps (RMS).
No wonder a 20A contactor does not last!
...Unless someone got wise and used 240VAC, which would make the
current 16.7 Amps (RMS), which is too close to the contact rating.
At minimum, the contact rating should be at least twice the peak
current being handled.
Perhaps a mercury plunger type of a contactor would be best; rated at
50 Amps (!!) for a 240V supply voltage.

BTW, a .01 capacitor is orders of magnitude too small to have any
effect.

Robert,

The OP told already in is his first post he's using 240Vac .

What makes me curious is your statement that "At minimum, the contact
rating should be at least twice the peak current being handled." Why should
a manufacturer specify a current rating that we have to double for practical
use?

petrus

 

[Fredric Smith]

How about a 480V 50A solid state relay?

 

[Nirodac]

Just ordered a 40 amp 800 volt triac and a zero crossing detector, will see
if this works

Nirodac

How about a 480V 50A solid state relay?