UPS on boiler Flame Safe Guard

[spector]

Who here has experience with sizing/installing UPS on boiler FSG (flame safe guard) circuit?

Our boiler controls cabinet has 2 circuits. One for the burner/level controls, and one for FSG.

We recently added UPS to our boiler Honeywell digital control circuit to provide stable power. It now prevents outages on the control due to spikes and lightning strike, but the FSG still drops out from same.

The FSG circuit is 110 VAC and pulls 3.5 amps while in normal operation, but pulls 6 amps momentary during boiler light off.

We would like to add UPS to this circuit, but need a little help selecting the correct one.

Thanks

 

[jbartos]

Suggestion: Check with the UPS manufacturer for the proper UPS size and characteristics matching nature of the load.

 

[spector]

Thanks....been there, done that just yesterday. They lie.

We are using APS UPS 650 VA 400 watt units now on our Honeywells-one for each control. Their telephone tech reps all give differing answers. One would say it is rated for 5.4 VA, the next would say 3.3 VA, and a third claimed 4.5 VA. None would/could offer any certain sizing specs.

Admittedly, these devices are intended for PC equipment. They were never intended to be hardwired. Our control contractor installed them recently to solve problems with his digital controls. He discovered our plant electrical systems are dirty, spikey and not stable enough for the Honeywells. The little UPS's fixed that problem.

Now we would like to add them to our FSG to prevent outage from spikes and momentary voltage drops we experience due to frequent storms. We are also considering them for our chiller plant controls. All they need do is hold in a series of relays like you find in a typical FSG ladder. There are no motor loads.

Can you suggest a manufacturer of a hardwired device that can properly spec it out? And do you have experience with same?

 

[jbartos]

Suggestion: The UPS spec is supposed to be based on "The FSG circuit is 110 VAC and pulls 3.5 amps while in normal operation, but pulls 6 amps momentary during boiler light off."
The UPS should withstand 6A momentarily. If you spec the UPS for 6A to be 125% of the UPS rated value, then the UPS rated value will be 6A x 100%/125% = 4.8A, which will correspond to 110V x 4.8A = 528VA, assuming 1-phase 110V 60Hz power supply. If the 6A current is longer "momentary" then specify 110V x 6A = 600VA UPS or contact a different UPS manufacturer for the UPS sizing.

 

[dpc]

You might ask the flame safety manufacturer for recommendations. They may have been through this before. I agree with you that the APC UPS systems are probably not a good solution. You also have to be sure that these UPS can transfer quickly enough to prevent the flame system from shutting down.

Also, having individual UPS on each systems creates a lot of additional failure modes, especially as the UPS batteries give out.

If you have a station battery system, you might consider a pair of inverters to provide the 120V ac you need for critical loads. Or use dc power for critical loads whenever possible.

 

[busbar]

As agonizing as power interruptions and subsequent controls malfunctions may be, the matter needs extremely careful study. Insurance carriers and occupational-safety folks can come unglued at discovery of the described arrangement.

Production losses and maintenance-department overtime could not likely justify the current solution. Resolution may need to be elevated to the highest levels of your management and that of the controls and boiler manufacturers.

What ever you do, keep careful documentation of all of your work, because you may someday be asked to very formally recount your work {under oath.}

 

[spector]

(You might ask the flame safety manufacturer for recommendations. They may have been through this before.)

That was my first stop....Turns out my ladder was site built using various maker's components. None of them know enough about the other to volunteer anything, and that's understandable. It's not a system like you would find on a package boiler where the maker assembled it all and could provide such info.

The program timers are the durable old style mechanical Honeywells with Fireye flame amps using Mercoid and MacDonnel Miller controls. This is a Federal utilities site, not your typical commercial plant where the bottom line or profit margin drives everything. So, the ladder is very well designed, speced and maintained using quality components and assembly. It meets or exceeds all code requirements. I know that because I still hold my NB boiler inspector's commission.

As a boiler inspector, I inspected many a FSG IAW code requirements. And our's is top notch. I also served as an insurance co. loss prevention expert, so the other poster's comments and cautions in that regard are unnecessary.

(I agree with you that the APC UPS systems are probably not a good solution. You also have to be sure that these UPS can transfer quickly enough to prevent the flame system from shutting down.)

Actually the APC UPS devices our contractor installed work very well. They have an almost instant transfer rate, but seem slightly undersized when connected to both the new controls and the FSG. I experimented yesterday by attaching the FSG circ (thru a pigtail) to a parallel outlet on the UPS. It held up the FSG and Honeywell when I disconnected it from the 110 VAC line. After 30 seconds tho, the UPS signaled the battery was discharging at it's upper limits. So I need to increase it's capacity. Also, I'd prefer that the unit be hardwired industrial grade vice the consumer desktop PC stuff.

(Also, having individual UPS on each system creates a lot of additional failure modes, especially as the UPS batteries give out.)

Exactly why I'm here asking this question. Thank you for being the only one to actually understand and respond properly. The reason I'm shopping additional UPS's for the FSG instead of just one for both circuits, is because no one here wants to 'interfere' with the new digital controls while they are under warranty. It's my intention that the UPS I decide on will be able to support the whole cabinet, tho. I will disconnect and scrap the originals once the warranty period has expired.

(If you have a station battery system, you might consider a pair of inverters to provide the 120V ac you need for critical loads. Or use dc power for critical loads whenever possible.)

We have mo-better. Our plant has a dedicated diesel generator set that supports the complete plant. It has a bank of automotive batteries and inverters that provide interrupt and diesel starting power. However, it's that instant before it loads or unloads when our FSGs tend to drop out. Even during the weekly generator op test, the FSG's usually fail open. All I need the UPS for is to span that few seconds of loss before the generator takes the load and during severe storms.

Thanks for your answers. I'll continue to research and contact industrial UPS makers. Maybe one of them will decide to conduct a site visit and assist me.

 

[Macbeth]

The size of the UPS should be simple a min size can be figured as.
110vac * 3.5a = 385va
110vac * 6.0a = 660va

Since the 6a is only a short spike that does not really need to be factored to much. I would recommend a 500va unit. That should yield about 20min runtime. Many manufactures will add more battery if longer run times are needed.

I would stay away from APC they often have bad switch over times and relays can't handle that well. Sola or best are the only trouble free unit I have used.

Also some UPS have a either net or an RS232 port, Since these are tied to such a device as your boiler i would recommend setting up some type of monitoring system. Excessive inverter switching can lead to failure.

Well just my thought.....

 

[spector]

Thank you most tragic Sir,

Hey, I couldn't resist...Is that your real name, or are you also a fan?

I agree with your math. A 660VA unit should do the trick. But in talking with the various makers, I've discovered they lie. Almost every 650-700 VA model I've investigated actually works out to a little better than half that once you pin them down. Must be because they are consumer market oriented for PC use that they feel they have to exagerate.

I've narrowed the field to several 1000-1200 watt models that don't incorporate cooling fans and can survive in a non-airconditioned environ. These are going to be installed inside a spider-tite boiler control cabinet, not under a skirt's desk. So they need to be able to handle 'industrial' conditions.

Thanks. Still waiting to hear from one who has been there.

 

[jbartos]

Suggestion: Magnetek recommends the elevator VFD size in HP matching the elevator motor in HP exactly since they design VFDs somewhat bigger under their nominal HP ratings. However, this can be considered a unique match.

 

[EEAutomEng]

Spector...We have been using UPS's manufactured by Sola for some time now and they hold up very well in the harsh environment we use them in. Some of their models feature self monitoring functions via serial data or contact closure. We have tried using APC units but have had two of them fail in the last year. We use the Sola S41000 mini-tower units in our machines to provide stable and clean power to an industrial PC control scheme.

http://www.sola-hevi-duty.com/

 

[Shortstub]

Is the ignition transformer supplied power via the FSG?

 

[Shortstub]

Further to my earlier post.. two additional comments:

1) FSG design.
At one time the (oil) company I was with tested all commercially available FSG components for response to momentary power. If AC supplied, then, without exceptiion they could not tolerate an interruption greater than 1 cycle. Some tripped if the interruption was less than 1/2 cycle. Of course, the flame-loss circuitry was often blamed.

Tests showed, however, that because the circuitry was analog, i.e., supplied internally by rectified DC, they were unaffected by momentary interruptions. And, in some cases, they easily rode thru interruptions lasting as long as 2 seconds.

The eventual culprit was... the output relay. Typically, they were suppied from half-wave (1 diode) rectifier supplies. The load capacitors were too small. The solution was to add additional caps. Here's the rub... manufacturer's ignored our findings, so we modified them ourselves.

2) UPS performance,
Secondly, most UPS' take a finite time to switch to a backup sorce. Many, especially AC powered relays will drop-out if the changeover time is in the order of 1/2 cycle. All instrument's powered from by UPS had their internal AC/DC power supplies "beefed-uop" to yplerate a 2 second interruption.

An aside! This will explain why unwarranted trips occur on uninvolved branch circuits, when electrical faults occur on others!

I never did understand why instruments are powered by AC, when virtually all have internal circuits that are DC?? But, that's fodder for (pls excuse the pun) additional food for thought!

 

[jbartos]

Suggestion: There are various principles of UPSs. Some produce short transitional disturbance on their output, others are actually without any noticeable disturbance on their output since they produce their AC output over the DC source. The conversion is in a form of AC-DC-AC.