Ranco etc burned out?

[spyderrobotics]

Here is my 2 cents:

There is some confusion about ranco or any relay thermostat. I myself had to do quite a bit of research as we have some products entering this field. Here is a manual for the Ranco I found on line:

http://controltrends.org/wp-content/.../Ranco-ETC.pdf

The heating used with reptiles is resistive heating. That is what the oil filled heater is as well. You can see from this manual that the relay used is rated at 9.8 amps resistive which is 1176 watts (9.8 amps x 120 volts). So in this case a oil filled heater on high is more than the spec of the device. Medium should be fine as most of those heaters draw about 900 watts on medium.

Now the bigger story:
When the relay disengages it makes a huge arc across the contacts. I have run tests with relays doing this and each cycle you are wearing a little of the relay at a time and building up carbon on the contacts which increases resistance inline. Many of these relays are only rated at 30-50K operations resistive. So lets say your heating situation turns on the heater for 5 minutes and then cools for 5 minutes. Your cycle time is ten minutes. That is 144 cycles a day or 52,560 cycles per year. So in one years time you have used up rated life of those relays. High endurance relays last 100K cycles. So maybe 2 years life. Unfortunately relay based control is the best value for controlling oil filled heaters but you have to consider your control device as a consumable. BTW relays have two failure states. The relay can fail off (as in too high resistance due to carbon build up on the contacts) or it can fail on (high current welding of contacts together).

Solid state control is possible instead of relay control which does have the advantage of proportional control and no contacts to wear out but the problem is it generates alot of heat in the parts. I experimented with a couple of designs with aluminum enclosures using the whole enclosure as the heat sink and 1500 watts still got the enclosure up to a uncomfortable to the touch temp. Plus when all was said and done it would have been in the $250ish range for a single high output proportional thermostat which didn't seem sellable considering oil filled heater control isn't a big part of the market.

You can do some things to help prolong the life of a relay base thermostat. If the room is cold and you have excessive cycling consider using another oil filled heater on low as supplimental full time heat. Then the thermostat controlled one would be adding the final bump to your target temp. Or leave a few lights on in the room. You get the idea. The longer the periods are of on/off times the longer your relay thermostat life will be.

The power module we just came out with is also a consumable. The big advantage with it over a ranco is the ability to use the week scheduling for different temps and also because people can connect it to a internet based home thermostat so they can checkup on room temps.

We do have another full fledged thermostat coming out later this year for this purpose. This model has active line sensing and attempts to break the connection when the voltage in the ac sine wave is low which minimizes the arc. In my testing this took endurance relays that were shot at 100K and pushed them well above 300K+ and they were still in great condition. So the life will be much longer. We are also backing it with a second safety relay like in our other products plus many of the other advanced features of Herpstats. We are waiting for our parts supplies to catch up with the Herpstat 6 demand and then we will be working on the launch of that product.

So that is the skinny on relay based control. Hope that helps some.

Dion Brewington
Owner, Spyder Robotics

[highqualityballz]

Here is my 2 cents:

There is some confusion about ranco or any relay thermostat. I myself had to do quite a bit of research as we have some products entering this field. Here is a manual for the Ranco I found on line:

http://controltrends.org/wp-content/.../Ranco-ETC.pdf

The heating used with reptiles is resistive heating. That is what the oil filled heater is as well. You can see from this manual that the relay used is rated at 9.8 amps resistive which is 1176 watts (9.8 amps x 120 volts). So in this case a oil filled heater on high is more than the spec of the device. Medium should be fine as most of those heaters draw about 900 watts on medium.

Now the bigger story:
When the relay disengages it makes a huge arc across the contacts. I have run tests with relays doing this and each cycle you are wearing a little of the relay at a time and building up carbon on the contacts which increases resistance inline. Many of these relays are only rated at 30-50K operations resistive. So lets say your heating situation turns on the heater for 5 minutes and then cools for 5 minutes. Your cycle time is ten minutes. That is 144 cycles a day or 52,560 cycles per year. So in one years time you have used up rated life of those relays. High endurance relays last 100K cycles. So maybe 2 years life. Unfortunately relay based control is the best value for controlling oil filled heaters but you have to consider your control device as a consumable. BTW relays have two failure states. The relay can fail off (as in too high resistance due to carbon build up on the contacts) or it can fail on (high current welding of contacts together).

Solid state control is possible instead of relay control which does have the advantage of proportional control and no contacts to wear out but the problem is it generates alot of heat in the parts. I experimented with a couple of designs with aluminum enclosures using the whole enclosure as the heat sink and 1500 watts still got the enclosure up to a uncomfortable to the touch temp. Plus when all was said and done it would have been in the $250ish range for a single high output proportional thermostat which didn't seem sellable considering oil filled heater control isn't a big part of the market.

You can do some things to help prolong the life of a relay base thermostat. If the room is cold and you have excessive cycling consider using another oil filled heater on low as supplimental full time heat. Then the thermostat controlled one would be adding the final bump to your target temp. Or leave a few lights on in the room. You get the idea. The longer the periods are of on/off times the longer your relay thermostat life will be.

The power module we just came out with is also a consumable. The big advantage with it over a ranco is the ability to use the week scheduling for different temps and also because people can connect it to a internet based home thermostat so they can checkup on room temps.

We do have another full fledged thermostat coming out later this year for this purpose. This model has active line sensing and attempts to break the connection when the voltage in the ac sine wave is low which minimizes the arc. In my testing this took endurance relays that were shot at 100K and pushed them well above 300K+ and they were still in great condition. So the life will be much longer. We are also backing it with a second safety relay like in our other products plus many of the other advanced features of Herpstats. We are waiting for our parts supplies to catch up with the Herpstat 6 demand and then we will be working on the launch of that product.

So that is the skinny on relay based control. Hope that helps some.

Dion Brewington
Owner, Spyder Robotics

Until your new thermostat launches will the power module fit my needs?

[spyderrobotics]

Until your new thermostat launches will the power module fit my needs?

The power module will run a oil filled heater and was designed for that purpose. You will need to purchase a standard home thermostat and thermostat wire to connect the two from a local home improvement store. The wiring is fairly easy and the wiring instructions will be included with the home thermostat.

[MarkS]

Here is my 2 cents:


Now the bigger story:
When the relay disengages it makes a huge arc across the contacts. I have run tests with relays doing this and each cycle you are wearing a little of the relay at a time and building up carbon on the contacts which increases resistance inline.

Is this why it kept tripping my GFI? Would a proportional thermostat work with a GFI outlet?

[spyderrobotics]

Is this why it kept tripping my GFI? Would a proportional thermostat work with a GFI outlet?

This very well could be. Proportional thermostats usually work fine with GFI's. I've only come across one or two cases where there was an issue. If I remember right the person replaced the GFI with a new one of the same model and then it was fine. So there may be some tolerance differences. If you weren't already I would use a surge protector with a 2000+ joule rating in between the thermostat and wall outlet. The protectors have a mov cap that I suspect works both ways and may keep the relay arc from tripping the GFI.

[MarkS]

This very well could be. Proportional thermostats usually work fine with GFI's. I've only come across one or two cases where there was an issue. If I remember right the person replaced the GFI with a new one of the same model and then it was fine. So there may be some tolerance differences. If you weren't already I would use a surge protector with a 2000+ joule rating in between the thermostat and wall outlet. The protectors have a mov cap that I suspect works both ways and may keep the relay arc from tripping the GFI.

Thanks, I didn't even think of a surge protector. That's a good idea.

[westom]

Thanks, I didn't even think of a surge protector.

Some Circuit Interrupters completely ignore arcing. Others are for detecting arcs - interrupting power if an arc is detected. No valid recommendation can exist without first defining what type breaker exists.

Same applies to a surge protector. It does nothing for that anomaly - does not even claim to. But many only know all good things solve all bad problems. Junk science reasoning. Most buy power strip protectors that are so tiny as to not even protect from near zero surges only because others say it is in the list of good things.

Start with that circuit breaker. Is it a GFCI or an AFCI? Arcing in a switch is often averted with a snubber. Did they include a snubber inside that design? Line filter would go a long way into averting intermittent AFCI trips. Numerous options exist AFTER the anomaly is first defined. That protector is not one. It does nothing until 120 volts well exceeds 330 volts. A 330+ volt transient anomaly does not trip breakers.

[spyderrobotics]

Some Circuit Interrupters completely ignore arcing. Others are for detecting arcs - interrupting power if an arc is detected. No valid recommendation can exist without first defining what type breaker exists.

Same applies to a surge protector. It does nothing for that anomaly - does not even claim to. But many only know all good things solve all bad problems. Junk science reasoning. Most buy power strip protectors that are so tiny as to not even protect from near zero surges only because others say it is in the list of good things.

Start with that circuit breaker. Is it a GFCI or an AFCI? Arcing in a switch is often averted with a snubber. Did they include a snubber inside that design? Line filter would go a long way into averting intermittent AFCI trips. Numerous options exist AFTER the anomaly is first defined. That protector is not one. It does nothing until 120 volts well exceeds 330 volts. A 330+ volt transient anomaly does not trip breakers.

From the thermostats circuits I have seen a snubber is not used. I experimented with many snubber designs to minimize relay arc and few showed any promise. From what I read the GFCI's work by sensing a imbalance between hot and neutral. I wonder if the relay arc is enough to upset that. The surge protector may not be the answer but something easy enough to test. I am not sure if it would provide any filtering or not. Line filter is a good solution but will also be costly. Zero crossing has worked the best in my testing and while a mechanical relay timing is not perfect you can still greatly minimize spark and I suspect much less likely to trip the gfci.

[westom]

From what I read the GFCI's work by sensing a imbalance between hot and neutral. I wonder if the relay arc is enough to upset that.

Arcing does not create an imbalance. But again, is it a GFCI or an AFCI? AFCI would assume arcing is a failed extension cord - cut off power.

Semiconductor switching would eliminate arcing using techniques such as switching on zero crossing (so as to not create excessive heat). Also necessary are numbers for that heater and for switch rating. Switches that cut off more than 1 amp will arc. But a switch is designed to minimize that arc and to not cause contact damage. Snubbing will not eliminate the arc - but will significantly reduce destructive effects.

If a GFCI trips simultaneously with arcing, then current is going somewhere else - where it should not be going. GFCI would be tripping as designed; reporting a potential human safety issue.

Line filters are expensive? What is expensive - a number required?

https://www.google.com/url?sa=t&rct=...68rtmX327KQOjg