Does my inverter have impure thoughts?

[Efskeff]

Hi all,

I recently bought a "pure" sine wave inverter to try to set up backup
electric power for my gas-fired central heating boiler, in the event of
an electrical blackout.

Boiler normally uses about 60W electric power for air fan (induction
motor), two solenoid-operated gas valves (pilot and main) and a spark
igniter. Inverter is 150W, supposed to supply surge to 450W.

It runs the ignition sequence perfectly - air fan starts, pilot gas
valve opens, spark ignites pilot flame - then stops; main gas valve
fails to open, no ignition of main burner.

Digital multimeter reads no great voltage drop as main valve "tries" to
open, slight current surge to about 300mA before settling back to 240mA,
as it does on mains supply.

Does anybody know if "pure" sine wave inverters are really pure, or do
some of them have impure thoughts, i.e. harmonics that might interfere
with the operation of the main valve solenoid?

Or is some other reason likely to be the cause of the trouble? I'm
unfamiliar with the quirks and foibles of inverters, so I hope there's
someone out there who is more experienced in them than I am.

Thanks!

Efskeff

 

[zeromedic]

Hi all,

I recently bought a "pure" sine wave inverter to try to set up backup
electric power for my gas-fired central heating boiler, in the event of
an electrical blackout.

Boiler normally uses about 60W electric power for air fan (induction
motor), two solenoid-operated gas valves (pilot and main) and a spark
igniter. Inverter is 150W, supposed to supply surge to 450W.

It runs the ignition sequence perfectly - air fan starts, pilot gas
valve opens, spark ignites pilot flame - then stops; main gas valve
fails to open, no ignition of main burner.

Digital multimeter reads no great voltage drop as main valve "tries" to
open, slight current surge to about 300mA before settling back to 240mA,
as it does on mains supply.

Does anybody know if "pure" sine wave inverters are really pure, or do
some of them have impure thoughts, i.e. harmonics that might interfere
with the operation of the main valve solenoid?

Or is some other reason likely to be the cause of the trouble? I'm
unfamiliar with the quirks and foibles of inverters, so I hope there's
someone out there who is more experienced in them than I am.

Thanks!

Efskeff

Any chance the main valve is triggered on by a wall thermostat?

And the wall thermostat is powered by a remote 24v transformer
somewhere that isn't getting inverter power?

zero

 

[clare @ snyder.on .ca]

Any chance the main valve is triggered on by a wall thermostat?

And the wall thermostat is powered by a remote 24v transformer
somewhere that isn't getting inverter power?

zero

Not too much chance of that, as the thermostat is what triggers the
ignition event to start with - and that apparently works. I'd say
there is a "gremlin" loose in there somewhere. I went through the
same kind of hassle getting my furnace to run off my old (pre recoil
start) Onan genset. The processor in the furnace got confused -
because the governor was set high and the power was closer to 70hz
than 60. I cranked the governor down from 3950 to 3600, and the
furnace fired right up. I'd be inclined to suspect harmonics or
overtones, and suggest you may just be better off with a modified
square wave inverter. Real easy way to check - just borrow a UPS - a
cheap old APC or MinuteMan would do fine - and see if THAT works.

 

[SQLit]

Hi all,

I recently bought a "pure" sine wave inverter to try to set up backup
electric power for my gas-fired central heating boiler, in the event of
an electrical blackout.

Boiler normally uses about 60W electric power for air fan (induction
motor), two solenoid-operated gas valves (pilot and main) and a spark
igniter. Inverter is 150W, supposed to supply surge to 450W.

It runs the ignition sequence perfectly - air fan starts, pilot gas
valve opens, spark ignites pilot flame - then stops; main gas valve
fails to open, no ignition of main burner.

Digital multimeter reads no great voltage drop as main valve "tries" to
open, slight current surge to about 300mA before settling back to 240mA,
as it does on mains supply.

Does anybody know if "pure" sine wave inverters are really pure, or do
some of them have impure thoughts, i.e. harmonics that might interfere
with the operation of the main valve solenoid?

Or is some other reason likely to be the cause of the trouble? I'm
unfamiliar with the quirks and foibles of inverters, so I hope there's
someone out there who is more experienced in them than I am.

Thanks!

Efskeff

Pure sine waves are really not pure, most that I have seen are really
pulsed. A lot of pulses mind you but pulsed all the same. Have you tried
measuring the cycles? plug your vom in to the output of the inverter and set
it to hz. Something close to 60 is good, above 65 or below 55 and you may
have problems.
Is the inverter grounded to the frame of the furnace? You could have an
difference in ground potential that could be driving the power transformer
for the valve nuts.

WAGs all. I hope our answers lead you to the solution.

 

[Efskeff]

Thanks for all the suggestions, everyone! I think a ripple on the sine
wave is the most likely explanation, but I don't have the equipment to
prove it - nor do I know anyone with a UPS that I could borrow!

I wonder do *all* inverters have the same amount of ripple, or would it
be worth trying another model until I find one that works? (my
supplier has a very understanding returns policy!)

Efskeff

 

[Vaughn]

Thanks for all the suggestions, everyone! I think a ripple on the sine
wave is the most likely explanation, but I don't have the equipment to
prove it - nor do I know anyone with a UPS that I could borrow!

I wonder do *all* inverters have the same amount of ripple, or would it
be worth trying another model until I find one that works? (my
supplier has a very understanding returns policy!)

Efskeff

1) I love your title for this thread!
2) Your idea of trying other inverters makes sense, but also a plain
isolation transformer may clean up your waveform enough to help. You could
theoretically use a Sola-type transformer if your inverter truly outputs a
sine wave, but I have found out the hard way that inverters and resonant
transformers really don't like each other.

Vaughn

 

[clare @ snyder.on .ca]

Thanks for all the suggestions, everyone! I think a ripple on the sine
wave is the most likely explanation, but I don't have the equipment to
prove it - nor do I know anyone with a UPS that I could borrow!

I wonder do *all* inverters have the same amount of ripple, or would it
be worth trying another model until I find one that works? (my
supplier has a very understanding returns policy!)

Definitely a WIDE variation in power quality from one brand/model to
another.

 

[clare @ snyder.on .ca]

Is this perhaps like my Honeywell valve which uses the rectifying power of
the flame to sense its presence? Instead of having a traditional heat-to-
millivolt generator sitting in the pilot flame, there is only the spark
electrode and a grounded "flag" in the pilot flame?

No, the furnace uses a hot plate ignitor / sensor with 3 wires . No
spark electrode.

If so, the problem may be that your different power sources provide
different amounts of airflow from your combustion fan, and thereby change
the shape of the ionized cloud around the flame.

I rather doubt that is the case on this furnace, as both the inductor
fan and the blower are DC fans with closed loop speed controls.

When your genset was
running too fast, its voltage was probably too high as well, and your fan
was probably overactive. Unlike a heat operated sensor, the rectification
sensor responds instantly - if the airflow past the pilot flame is right on
the edge, the gust of air out of the main burner as the valve opens can be
enough to turn off the sensor - and the main valve - instantly.

The voltage regulated to a maximum of 127 volts with the furnace
connected. Less than 130 open circuit. With the governor cranked down
the voltage didn't change 2 volts IIRC.

 

[William Mcfadden]

2) Your idea of trying other inverters makes sense, but also a plain
isolation transformer may clean up your waveform enough to help. You could
theoretically use a Sola-type transformer if your inverter truly outputs a
sine wave, but I have found out the hard way that inverters and resonant
transformers really don't like each other.

Could you elaborate? I thought I'd read in Sola's literature that you could
feed their constant voltage transformers with square waves and get
low-distortion sine waves at the output. That was for the
harmonically-neutralized type, of course. I was tempted to try it until I
read your posting.

 

[Vaughn]

Could you elaborate?

The problem I had was just weeks ago and involved a CVT, but not one
made by Sola. (don't know about the harmonically-neutralized thing, that is
a new concept to me) We installed a new commercial quality 1500 Watt UPS
with perhaps a 500-watt load, which included a CVT. It immediately smoked!
Without thinking about the CVT, we replaced the UPS with a 3 KW unit of
another make. On battery, it grunted and was obviously not happy with the
load. We eliminated the CVT and solved the problem.

Vaughn



I thought I'd read in Sola's literature that you could

 

[clare @ snyder.on .ca]

Could you elaborate? I thought I'd read in Sola's literature that you could
feed their constant voltage transformers with square waves and get
low-distortion sine waves at the output. That was for the
harmonically-neutralized type, of course. I was tempted to try it until I
read your posting.

It will work, but you get about half the power out you put in. The
rest turns to HEAT.
Some inverters just shut off when the sola resonates.

 

[Steve Spence]

What model do you have?


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