Reducing starting current of semi conductor heat tape?

icarus · March 2018

Hey folks,

Long time off line.

I have an interesting problem that perhaps the electrical genius’s can solve for me.

I have a year round water system that pumps directly from the lake into a pressure tank, and then self drains back into he lake to prevent freezing. I have heat line heat tape on the line from the building into the water to a depth below the ice, so that when I leave for a while I can quickly thaw the pex pipe. It takes about 15 minutes of genny time to thaw after being in the ice for days or months.

A problem has developed that the water line will freeze on occasion, probably due to the build up of rime ice not he inside of the pipe with only occasional use. This is really no problem, except I have to run the genny for a few minutes every few days if the over night temps drop below about -25C (-10f). I would like to be able to run the tape off the inverter instead of having to lug the genny out to thaw.

The tape draws ~5-800 watts while running, but draws ~1500+- while starting. I have a 1 kw psw standby inverter that I use to run a coffee maker (got so much excess solar now, I can use an electric coffeemaker!). It is a cheapy from Canadian Tire, but it will put out 2 kw surge, and I have run a 1500 watt hair dryer on it to do some heat shrinking. The heat tape will not start on the inverter, going to overload cut out. A kill-o-watt confirms the starting wattage is ~1500 watts, and after 30 seconds or so it drops to 6-800 watts.

My question is...is there someway I can ease the starting current somehow,using a capacitor or something?

As always, thanks for any help and suggestions.

Tony

PS Still quite cold for this time of year. The past few nights have been close to -30, 35” of ice under ~15” of snow.

Dave Angelini · March 2018

A variac or similar could be used to test bringing up the AC voltage slowly. Glad that you are still around Tony! Miss your dulcinous tones

mike95490 · March 2018

What you want is a DIY electricians "Fuse Saver".

It's a Quad box (you are going to need something a bit larger) that has a couple light bulb sockets on it. Wire the light socket in series with the AC line and outlet, so all AC amps has to go through the light bulb. Maybe you want to modify it so a couple of 500W halagon bulbs (in parallel, gives you 1kw) work lamps are in series, which will limit amps to a bit under 1kw .

After your 4 minute warmup, use the switch to bypass the lamps and get full power to the protected outlet. A mod sine inverter should be fine.

Image: https://us.v-cdn.net/6024911/uploads/editor/v1/pv8if0ejxohn.jpg

icarus · March 2018

Thanks gentlemen. So what you are suggesting is load the inverter to full or a bit over full capacity, let it run for a few, then simultaneously unload the dummy load and load the heat tape? Do I have that correct? So the issue is the inverter no being able to “spool up” fast enough. Perhaps I will try it with my coffee maker as a dummy load.

All is well here. Just a bit older, not really any wiser. Life has taken it’s turns and we spend a fair bit of time on the road between coastsas family has scattered. I keep trying to keep in touch here, but as everybody knows, life gets in the way.

Once again it is great to see the forum still running and familiar voices still opining.

Tony

icarus · March 2018

Dave,

If I were to use a Variac, I assume that you would plug the variac in with the voltage lower and slowly dial it up? The heat tape has a built in GFCI device on the cord end. How would that play with the lower voltage? I don’t think the heat tape would care about the lower voltage.

Tony

icarus · March 2018

Mike,

I tired your idea, using a coffee maker ~500 watts no go. Then I used a hair dryer at 350 watts, and then again a 1 kw. Once again no go. My guess is the inrush current need is just to big.

Tony

Dave Angelini · March 2018

We had variacs for all kinds of issues like this Tony. If the GFCI acts funny disable it but I don't think it will. Did you find one for reasonable dollars?

Just reading your thread made me cold....Maybe some Canadian whiskey at happy hour

icarus · March 2018

Dave,

Funny you should mention that... I just poured a shot of good Canadian (Gibson’s) over icicle in a glass. I don’t generally drink much but ever now and again a shot over icicle is just what the doctor ordered.

Back tothe subject...I find Vaiacs for ~$60 on amazon. The other item is a triac put I don’t think that would fit he bill.

All that said, I don’t really need to spend the money for a problem that doesn’t really exist, but as m

Tony

icarus · March 2018

Touched the post button, must be the Whisky! To finish that thought, my wife suggests that it just bugs me that the water system just doesn’t work 100% as well as it should , and the genny is a pain.

Cheers,

T

Dave Angelini · March 2018

I hope it is a blended whiskey, I will be right over....

icarus · March 2018

Not enough “O”s in smooth!

t

mike95490 · March 2018

a 1K load in series with your 1Kw heat tape, will be less than 1Kw, closer to 500w

icarus · March 2018

I see...I think, load the heat tape load and the bulb load in series, then disconnect the bulb load with the by pass switch. What I don’t understand is why a 500 watt bulb load and a 1kw heat tape load will only draw ~500 watts but Ill give it a shot tomorrow. T

Vic · March 2018

Hi Tony,

Often these types of situations can be handled with an NTC Power Thermistor: Some examples here:
http://www.farnell.com/datasheets/85914.pdf

The exact Thermistor needed, is a bit experimental.

Another approach is a Step-Start, or Soft-Start relay. This often uses an RC time constant. When the circuit is initially powered-up, a resistor reduces the inrush current for a period of time. After this period of time a relay pulls-in, shorting the current-limiting resistor and allowing full voltage to be applied to the load. And after warm-up that heat tape load would probably need less current.

FWIW, Vic

icarus · March 2018

Can I just wire in a motor starting capacitor? (If so, how?)

Tony

mike95490 · March 2018

a motor start cap is not the answer.

With a motor, the cap works with a special internal motor winding to shift the Volt/Amp phase relationship to assist the motor to begin rotation. Sometimes, fine-tuning the size of the cap, helps optimize the minimum starting current allowed by the LC network of the motor / cap combination.

Estragon · March 2018

I think this is the type of self-regulating heat tape that can be field cut to length. How about segmenting it into two or more sections, and turn on each segment at intervals long enough for the inrush current for that segment to diminish?

My drainback system, which is also occasional use, includes an air pressure tank. Water in the line above ice level drains back by gravity, and the air pressure forces the water between top of ice and pump out. I have heat tape on the line from top of ice to liquid water level in case something goes wrong, but rarely use it.

icarus · March 2018

^. That is exactly my situation. I have an automatic (mechanical) drain valve at the pump under water that opens at 5 psi and closes at 8 psi ( a sprinkler drain valve) and a solenoid valve at the P tank to let air in to allow it to drain. Freezing up is simply a matter of residual water plugging some portion of the line. I could (have) done it in two lengths of heat tape, but it is (currently) frozen in under 30” of ice, and regardless, it is incased in 6” of foam inside a 6” drain tile liner, buried under a ton (or three) of rocks under 3-5’ of water...so I am not going to change it. As I said, I only use the genny on initial start up, and then on the occasional freeze. Last night, for example, I pumped water at 10pm just to run some water through, temps dropped to -25c (~-15f) with no wind, and at 8 am I pumped again with no problem. Like my wife says, this is a solution in search of a problem. For the few times a winter I need to do it, running the genny for a few minutes is no big deal, as I keep the Eu2000 inside so it is always warm in an emergency.

All that said, I’m building Mike’s magic box as we speak. I’ll let all know if it works.

Tony

icarus · March 2018

So Mike wins the prize of the day! I build a “fuse saver” as directed. At first, with a nominal 750 watt coffee maker it wouldn’t switch over. Changing to a 1500 watt hair dryer, waiting a few minutes and BINGO! It works great. Both the coffee maker and the hair dryer drew ~1/2 thier named wattage. I confess, that I don’t have a clue electrically why this works, which is only a measure of my ignorance, but clearly smarter folks than I exist on this forum, and I thank you all for that.

I will now build this into a real box and use it in the future. Once again thanks to all, and thanks NAWS for a great forum!

Tony

Estragon · March 2018

I was thinking part of the tape was above ice level. 800w seemed like a fairly long length. IIRC, mine is ~50' at 5w/ft running. It's just needed for where the pipe is in ice. Above that gravity drains, and below the ice is above freezing (absent current) liquid water.

Obviously, if the tape is mostly below ice level, splitting it won't work.

My system is similar to yours, but with the addition of ~5psi of air pressure from a tank to displace the water in the line the rest of the way to the pump. Air in the line repressurizes the air tank when the pump starts.

icarus · March 2018

The tape runs from the building, ~10’ From the lakeshore, into the water to below the bottom of the lowest expected ice, perhaps 10’ vertically below the building and ~60’ horizontally. The idea was (is) to only have to thaw the part that is in the ice when the place has been vacant for a while after freeze up. To this end it has worked flawlessly.

I am curios to know how you introduce air to force drain your system, and how you allow it to drain back through the pump. (I am assuming you have some sort of submersible pump?). Mine just drains via gravity and works well. As I said, the only issue is what I belive to be rime ice building up in the pump when it is only used occasionally. We only pump a few gallons of water per day, maybe 15 total. I typically pump in the morning when I have full sun, but nowadays with excess PV I don’t really need to load shift the way I once did.

Tony

Estragon · March 2018

The drainback is a simple ball valve. Opening it allows water in the line to fall by gravity to the waterline (top of ice) and for the line to fill with air at ambient pressure. After a few minutes, the ball valve is closed, and the pump started. The air in the line is pumped into the air tank. When water gets to cabin level and all the air in the line is in the air tank, an air valve closes, and water goes into water pressure tanks through a check valve. Open the ball valve again to let the line fill with air, then open an air tank valve to force water down to submersible pump level.

Once done in the fall, it mostly recharges the air tank and keeps water at pump level without further intervention. Air saturation into pressurized water and/or minor air leaks can make it necessary to recharge occasionally, but it mostly works well.

The heat tape is backup for when, for example, a hose connection got loose and let water rise when I wasn't there. Like yours, it thawed in under 1/2hr. I fixed the loose connection and all was well again.

I got most of the parts from a place in Toronto that specializes in cottage water systems.

icarus · March 2018

So you have to manually open and close your ball valve?
What I did, was use a normally open solenoid valve (12vdc) that closes when the p switch calls for water. The pump is 12 vdc. After the p switch shuts the pump off, the solenoid valve opens and lets air in, in essence taking the finger off the straw. As I mentioned, I have a irrigation drain valve that opens at 3-5 psi (when the pump is off, the static pressure from the house to lake level is only ~3’) it closes when the pump comes on at ~10psi. With a larger, more powerful pump it was suggested that I could simply drill a small hole in the pex tubing near the pump and allow it to pump most of it’s capacity to the tank, while bleeding a bit, but allowing it to self drain. My little pump probably would never get to pressure with such a “leak”.

What I am curious about in your application is what kind of pump you I are using, and will the pump back drain through itself without any calving. What I don’t know about my shuflo submersible diaphragm pump is whether or not it would drain with out the drain valve. A conventional positive displacement submersible probably will drain.

Tony

PS. Where are you located?

mike95490 · March 2018

icarus said:

So Mike wins the prize of the day! I build a “fuse saver” as directed.

It's an easy build, and once you learn the timing 4 min or 6 min to get it working, it's all sorts of useful. And you don't have to wait a week to order a time delay relay, just manually throw the switch.

You are adding resistors in series with this. The more resistance, the lower the amps. I guess the coffee pot was too low - glad you got something working instead of having to fire up the gennie

icarus · March 2018

The price was right too! Next time I go to town, I’ll get a four square box, clip the ears on the receptacle and it will be a nice simple device. Right now I have a line cord female to the load (as you drew) but a clipped duplex outlet will serve both functions in one easy box.

Once again, thanks Mike for the idea.

Tony

Estragon · March 2018

The ball valve is just used for charging with air. The pump is a regular submersible capable of filling 2x30gal pressure tanks in < 5 mins with a rise of ~30'. There's a valve just above the pump to allow for drainback, so no spinning the pump backwards.

A diagram of the setup...

https://www.cottagewatersupply.com/winter-water-systems/self-draining-winter-water-system-b/

Mine is essentially that, with the addition of backup heat tape.

Putting a small hole might work, but I'd be concerned it would be so slow to drain the water could freeze while draining. The valve setup drains ~100' of 1" pipe in about 3-4 minutes.

I'm in NW Ontario near Kenora. Water freezes pretty fast on a breezy night at -40.

The fuse saver idea sound like a much cheaper and faster solution though

icarus · March 2018

We are nearly neighbors!

The only real difference is the diverter valve and the introduction of air in your system. I use a simple boiler float vent valve to vent the air from the line to atmosphere. I went to to the cottage water supply site, and I would like to see some detail on the diverter valve for future reference.

When I designed and built my system, there was virtually no system components out there except heat tape. In my case, back then the real issue was the pump strength. The little Shurflo is reliable, and runs just fine on a small battery bank. Originally I had it running on 12 vdc from a pair of T105s, now I have 4 t 105s and use a voltage doubler to run the pump on 24vdc from the 12 vdc battery bank. It fills a normal pressure tank from 30-60 psi in about 5 minutes.

If you have some more detail on your diverter valve I would love to see it.

Tony

Estragon · March 2018

I also have a 12v pump, which I use mainly to run a bit of antifreeze into the lines. If I have to get water old school for any reason (haul from a hole in the ice), it will also fill pressure tank. Nice little pump.

I don't have much more info on the diverter valve. It's been a few years since I installed it. I found the guy in Toronto quite forthcoming answering my questions though, so you might want to email or call him for more details.

icarus · March 2018

All my domestic lines are pex and self draining. If I have to leave for more than a day or two, I simply open the outside hose bib, dropping the pressure to 0 psi which opens a number of installed low point drains, using the same sprinkler valves. These are great inventions, cost a few bucks and seem very relaible. https://www.homedepot.com/p/1-2-in-Brass-Auto-Drain-Valve-51039/100196222n. The filter simply keeps dirt out in a underground application, pulls right off.

The nice thing about PEX is the way it will handle repeated freeze thaw cycles without damage.

Tony

Estragon · March 2018

I like the idea of those drains. Replumbed everything with pex, but fittings are still a problem. Changing a 90 at the bottom of each supply manifold (or making new manifolds) to drain directly might make sense.

icarus · March 2018

All my plumbing is in the building envelope and is exposed, nothing behind the wall. The P tank, shower and demand water heater all share the same space, and there are just a hot and cold to the kitchen sink. (No toilet, still use an outhouse). The nice thing with PEX is you can plumb with few fittings and gently angle your pipes so that there are no low points except where you design them, I use those little valves under each fixture. Dropping the pressure to 0 and leaving the shower and sink valves open and they drain, water heater as well, although there is a built in low point drain in the water heater, the only thing I have to open when I leave, save the hose bib.

tony

PS. I thought I mentioned it, but guess not. We are between Ignace, Uppsala and Atikokan, sort of out in the middle of the bush.

Reducing starting current of semi conductor heat tape?

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