Why can't you plug Proportional thermostats into UPS's or generators?

I was wondering why you couldn't plug a Proportional thermostat into a uninterruptible power supply so I emailed Helix and Jeff Washburn was cool enough to write me back and explain. Just thought I'd share with everyone.

This is the email I sent him:
I was just wondering, would it be ok if I plugged my DBS-1000's into
uninterruptible power supplies? Would there be any problems doing
this?

Quote:

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Hello, yes you will not be happy using any signal conditioner, UPS, even some older or sloppy power generators, ahead of digital equipment that
electronically controls output power. The Sign-wave that these products
produce is "square-ish" and not acceptable for use with triac driven
devices. ( Including Helix DBS-1000 and any truely Proportional
thermostat.) . This Square sign-wave tends to turn on the power at a low
level when the system wants the power OFF.
On/Off thermostats ( at least most of them) should not have this
problem.

If your looking for back up incase of power outage...

You can set up a Ranco (On/Off) thermostat, 1-2 degrees lower
setpoint, and separate small fan and heat element.
Basically the Ranco is never putting out any heat , unless the
temperature drops to the lower (secondary system) set point. This saves the relay inside and makes the Ranco system last a 1000 x's longer

It could also speed "temperature" recovery after opening the incubator,
and closing it.
Thanks for thinking Helix, Jeff Washburn, Helix Controls, Inc.

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I've thought about power backups quite a bit as well. In looking into it, it seems that virtually every backup generator creates a type of power which is not well suited to thermostats.

I think one of the best responses to heat a snake room in case of an emergency is an oil-filled radiator set in the mid 80's, plugged into a generator. Just heat the whole room and forgo the heat tape during the emergency.

For an incubator, you would have to use the on/off method as described in the post above and have a good amount of air circulation to (hopefully) even out the temp.

Jon

Yeah I ran my helix tstats off of my generator not too long ago and they were resetting themselves every few minutes. Definitely not ideal, and I'm sure that it wasn't too good for the lifespan of the tstats.

very interesting, thanks for this info

That is the same reason that a UPS shortens the life of a PC power supply, especially a high end model. The square sign wave tries to pass through the power supply which is expecting a round sine wave. This causes the 'corners' to be cut off the square resulting in a phenomenon known as clipping. It seems that the effects on a thermostat is much more dramatic, but the idea seems similar.

I don't know if they make em affordable for home use, we install UPS systems at work that run a dc motor that spins a generator so you have the proper sine wave. You lose efficiency but If your really need to make sure stuff doesn't screw up, its the way to go. I've only seen it in data centers for hospitals and banks.

That's exactly the problem, the ones for home/office use are just big battery packs, that concert DC power from their batteries to AC power for the computer, because when you use one, your computer runs off the batteries, even when the power is on. That's why you get the square sign wave, or "dirty" power.

Most usp are modified sine wave, there are a few very few that are pure (what is needed for a triac) there are a few old threads on this same issue. Dion Brewington and I corrisponded a number of times about a power back up. More generators are not pure sine wave either (the notable exception are Honda they are pure sine wave)

UPS even with the correct inverter are not designed to run heaters and a normal personal use one would not run very long at all. (many only run computers for 20-40 min so figure less than half that time)

The solution I came up with is a 3 cell bank of deep cycle marine batteries with a pure sine wave inverter, a Ranco t-stat (80º set point) on a separate heat system all together (heat cable on the backs and side of enclosures) installed with a transfer switch. If the power fails the transfer switch kicks over and the ranco takes over from the primary. The problem is cost, I have not set it up as it is well over 2500$ to install. A honda gen is cheaper.

Ive ran my herpstat off my 2000watt generator to run incubator and no problems at all. Generator is only 8 months old.

IF your using older style geenrators or any generator for that matter, you must be sure your grounding the generator to the ground.

Quote:

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Originally Posted by kitedemon

More generators are not pure sine wave either (the notable exception are Honda they are pure sine wave)

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I'm not saying anyone is wrong, I just don't understand, Something physically rotating is the only way to create a real sine wave, how does a generator not produce a "pure" sine wave? I could see when people say older or cheap generator don't because if they have a hard time keeping constant rpm, they could be throwing the sine wave all over the place. but any descent generator... how?

I also didn't understand how DC circuit could produce a pure sine wave, but after a little googling, apparently they got a couple different bridges and filters you can run it through to mimic a real sine wave pretty close, still not a real sine wave though, but the electronics can't tell the difference. So thanks I learned something new.

It is the inverter that generates pure over modified what you are speaking of is a modified wave not pure. Why a Triac does not do well with modified I don't know I have been told by those that do know.

"Modified sign wave input will not damage the system. Rather it tricks the system and keeps the power ON at a low level, when the system intends the power to be off.
The problem with modified sinewave and Square-ish wave power is that the electronic switching devices, will trigger with semi-sharp changes to the sinewave, and turn on at a low level. This condition in effect causes the heater power to remain on at a small level when the system thinks it's turned the output power OFF.
So, with electronically switched proportional systems, temperature creep occurs while under Inverted DC supply power.

On-Off thermostats that use relays, usually work fine on inverted power. The control is bit sloppier, but, adequate for emergencys. Ideally Both would be nice, Tight control 99.9% of the time, sloppier On/Off control when the house power is Out."
Jeff Washburn Helix controls

From Spyder Robotics web site,

"Question: Are the Herpstat's compatibile with UPS units or 12vdc to 120vac power inverters?

The short answer:
Most computer UPS backup systems and 12vdc to 120vac inverters output a modified sine wave. This will not work with any proportional thermostat. They will work with relay based non-proportional thermostats. In order to work with a proportional thermostat the backup system must produce a "True" or "Pure" sine wave. These systems are usually double the price of a standard UPS or power inverter.

The long answer:
Most proportional thermsotats use a Triac to control the AC output. This component gets triggered and turns off on its own once the AC voltage reachs zero volts. Common UPS systems or power inverters using "modified" sinewaves do not recreate the smooth curve sinewave that comes from your home outlet. Instead they spike the voltage 120vac positive, then drop to zero, then spike to 120vac negative. Because of this there is no way to dim the power. Also in my testing the triac typically will not turn off properly and stays stuck ON once its triggered. In order to have a proportional thermostat work properly off a battery powered (or gas generator for that matter) device it has to output a "True" or "Pure" sine wave. These systems recreate the correct smooth arced sinewave just like your home power. Because of the extra components and technology they are usually double the price.

Dion Brewington
Owner, Spyder Robotics "

I can't speak to other generators but I know that as of 2 years ago all Hondas were Pure sine wave inverted. The cost of a modified 100 watt inverter is under 50$ a pure sine wave inverter is over 300$ that is why cheap gas generators usually don't have them.