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Author Topic: Electrical Heating  (Read 1375 times)
BlueBee
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« on: February 27, 2014, 01:47:15 PM »

Iíve had a couple of PMs from a member about my bee hive heaters.  I figured after typing all this up, I should just post it on a new thread for all to see.

The basic question was why am I using multiple cement potted heaters in a hive instead of just 1 big heater and isnít 15 watts the electrical heat what most beeks recommend?

My Answer:

How much wattage one Ďneedsí in a bee hive heater(s) depends upon:

1.)  How cold it gets in your area
2.)  How well insulated your hive is.  Wood is a bad thermal insulator.
3.)  How many bees you have in the hive.  Mites really knock down numbers in winter.
4.)  Your philosophy on what temperature you believe is best for the bees. 

Most beeks have the philosophy that the bees know best and 0 watts of electricity is the best solution.  I respect that philosophy and adding electricity to a bee hive is certainly not natural.  However, I do have a different philosophy about this.  I try to maximize yields and I think electricity is a tool that can be used effectively to that end.
 
So how many watts does one Ďneedí?  We hear a lot about 15 watts?  Well, 15 watts in TN is going to keep a hive a lot warmer than 15 watts in MN or the Dakota's  since heat loss is a function of delta temperature (inside to outside).  How many watts you Ďneedí depends on how cold you get and how well insulated your hive is.  Ironically the old 3 deep ďwinter solutionĒ increases the surface area of a hive and results in MORE heat loss.  Heat loss is proportional to surface area.

In an early photo I was using 4 of my cement bee heaters inside a WOOD hive in Michigan.  Each cement resistor can generate up to 10 watts of heat.  So I was pumping up to 40 watts of heat into a wood bee hive (3 mediums tall at the time).  The problem was wood has almost no insulation value (R1) and the heat flows out of the wood about as fast as new heat is generated.  Hence the heat never builds up much inside a wood hive unless youíre pumping in some significant heat.  Just like an old house with no insulation in these bitter temps; it gets REAL cold real fast unless youíre dumping in a TON of heat.  $$$$  That is why I went to insulated hives.

The more insulation you have the less watts you need to keep a bee hive from getting bitter cold.  As Iíve said before, my latest hives are built from 1.5Ē thick (38mm) polystyrene (the pink stuff) and I havenít been using any heaters in them when they are packed with bees since the bees appear to generate about 15 to 20 watts on their own.   15 watts of heat (from bees or electricity) trapped inside a well insulated box was keeping my hives between 45 and 60F all last winter.   

My electrical goals are focused on wintering 5 to 6 frame nucs at this time; single story.  An insulated big hive can take a lot of cold, the small nucs cannot.  I only use 1 of my cement resistors in each nuc.  Itís the below 0F temps that REALLY knock out the small colonies.  If you can just get them through those nights, the small guys can make it.  As long as the mites are under control, a well insulated big hive stays warm all by itself in my area.  If I was in MN or the Dekotaís with weeks below 0F, I would be adding electricity to the big hives too.  We donít get weeks below 0F in MI.

As for why I donít just use one cement bee heater instead of four?  Well, I do just use ONE for my nucs.  It kind of depends upon what you buy for resistors and what voltage youíre working with.  There are some electrical constraints you have to work with if any one variable is fixed (ie voltage, resistance, resistor wattage).  Personally I would rather have 1 heater than 4.  Less parts to fail.  The downside with using higher wattage resistors (mine were 2 watts a piece), is the bigger ones get REAL hot.  REAL real high surface temps.  You can easily burn a finger on an un-potted power resistor.  You donít want something above the kindling temperature of wax hydrocarbons in a box filled with wood, foam, and hydrocarbons.  The bees generate a lot of wax capping debris all winter long.  That falls right on top of my bottom heaters.

By putting the raw resistors in a potting material (I used cement, it is cheap), you lower the surface temperature of the part that is exposed to wax debris and reduce the chance of fire IMO.  My cement potted heaters never get hotter than about 100F at the surface.  With some mechanical ingenuity, you might be able to build an effective shield over top of some raw power resistors and solve the flammability concern.  However itís also important to keep in mind that the leads of exposed parts have voltage on them and that can be deadly if youíre not careful.  Ie.  Exposed lead + wet bee keeper + wet ground = dead bee keeper. 
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Bush_84
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« Reply #1 on: February 27, 2014, 02:45:02 PM »

Thanks for this!  I think I have a few things to tinker with from now until the thaw.  Most of what I plan to do with these is to assist with wintering nucs.  Right now my full hives are all wood.  Heating those may just be like pissing in the wind but maybe one day.  Getting the resistors won't be an issue.  Connecting the resistors won't be an issue.  Getting some speaker wire.  Getting a cheap computer power supply also won't be a huge issue.  Is there a trick with connecting the power supply to the speaker wire?  Maybe it'll be apparent once I get the power supply.

Looking at some of your stuff, do you run some sort of thermostat on your hives or just let them run all the time?  It looks like you have some sort of board on your photobucket account.  Maybe it's not necessary...I don't know.
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BlueBee
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« Reply #2 on: February 27, 2014, 06:30:32 PM »

I agree with your philosophy with regards to Nucs.  I think that is where you can really make a big difference in yields.  I did get a number of 4 frame medium nucs through winter last year with good insulation.  That isnít bad for Michigan.  Iíve got a number of 4 frame mediums out there right now, but this has been a much colder winter.  Without electric heat Iím expecting a near 100% loss of those small nucs.  I would have to trek a mile through knee high snow to check on them so I donít know how theyíre really doing at this point.  If I was a betting man, I would bet on 100% losses.  Weíve had so many nights below 0F this winter, itís ridiculous.

With regard to the computer power supply, they are a good low cost source for 12volts DC and a lot of amps (20+).  You can buy them cheaply from most online computer retailers (under $40).  However there are some complications (of course!).  Computer power supplies arenít designed to run in sub zero (0F) weather!   They use electrolytic capacitors to filter the output voltage.  The dielectric in those capacitors are water based and water freezes at 32F.  The caps donít actually freeze at low temps, but their ESR goes up and that causes all sorts of potential problems.  Hence, if youíre going to heat your nucs from a computer power supply (sitting outside), youíre probably going to have to put the power supply inside an insulted box too.  Thatís what I did. 

A power supply is never 100% efficient and the energy that is lost shows up as heat.  If you put an insulted box over a computer power supply in your bee yard (assuming weíre talking outside here), that waste heat from the electronics can keep the power supply from freezing.  That is what I did.  There are photos of that somewhere on my photobucket page. 

If your nucs are close to a building with 120VAC power, then it might be feasible to run the power supply inside your building and use heavy gauge landscape wiring (10 gauge) out to your nucs.  However, that is going to start causing new problems if your nucs are more than about 50 feet from your power supply.  Any current flowing over any wire drops voltage.  Speaker wire is way too thin to use in most cases.  I used 100 feet of 10 gauge landscape wire in my first attempt and only had 10 volts by the time the power got to the nucs.  A loss of 2 measly volts might not seem like much until you look at the bee heating power you lose.

A 2volt drop over your supply wire is a 16% loss in voltage, but that generates a 30% drop in the power (heat) available for your bees.  For example, assume you build your resistors to generate 12 watts of heat from a 12volt supply.  That would require a 12 Ohm resistor.  (Power = Voltage x Voltage / Resistance.  12watts = 12v x 12v/12r ).  Now if you lose 2 volts in your supply wires (speaker, landscaping, whatever), your power available at the bee heater drops to 10vx10v/12r = 8.33 watts.  A whopping 30% less than you expected. 

Lesson is, a voltage drop in a low voltage system is a real power/heat killer!  This whole voltage drop over a wire problem is why Tesla won and Edison lost in the AC vs DC power wars a century ago.  How do you get around this problem?  You really canít, you just have to compromise your layout around the laws of physics.  If you go with a low voltage DC power supply, youíre going to want to keep the lines between it and the nucs from getting very long.  That might require moving the power supply outside.

Yeah, there are some Ďtricksí you need to apply to a computer power supply as well.  Theyíre designed to run inside computers, not bee hives.  First trick is you need to jumper the motherboard connector on the power supply to power up.  Just plugging in a computer power supply doesnít turn it on.  Iíve got a photo of the jumper somewhere in my photobucket library; you could also search the internet.  I donít remember the pin #s as Iím typing right now.  Next, many modern power supplies require a minimum load to run.  You may need to connect up an extra 12VDC computer cooling fan to draw enough load; a few hundred milliamps is usually enough.  I did have to connect a fan to keep my supply running.

Once you have the supply working, youíll need to tap into the 12volt line and ground to connect your speaker wire/landscape wire to.  I soldered my wire directly to the power supply to reduce the voltage drop at the junction.  Remember any voltage losses in a low voltage system really wrecks your bee heat.  I did use wire nuts at the other end of the hookup wire to connect the bee heaters up.  I didnít solder everything because you donít want to make the system too hard to repair if something fails at -10F. 

Ideally you would regulate the amount of heat you give each nuc with a small controller of some sort.  I used a custom built 8bit microcontroller and a thermistor for that.  I can program in a hive temperature and the controller will modulate the wattage output until that temperature is met.  You can buy various prebuilt controllers for probably $50+.  I happened to build mine from scratch for about $5 in parts.  The controller is probably the biggest problem for the average beek.  Theyíre really pretty simple things, but it does require a little experience to be competent working with them.  Again, find some 16 year old neighborhood computer geek and he could set you up with no problem.
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Bush_84
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« Reply #3 on: February 27, 2014, 09:26:44 PM »

I'll be moving this spring.  So I don't really know what my apiary is going to look like.  I don't suspect that my main apiary will be next to a power outlet, but I could easily move nucs to a location where there is one.  I'll just have to see how it goes, but for now I'll likely have to plan on an insulated power supply box with a extension cord out to it. 
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BlueBee
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« Reply #4 on: February 27, 2014, 10:11:01 PM »

Spring huh  You think weíre going to have one this year. laugh  Good luck with the move.

I also believe putting the power supply outside, close to the nucs, is the better design.  Thatís what Iíve done.  The safety purists will argue that using a 120VAC extension cord is more dangerous than a 12VDC cable and against codes, and theyíre probably right.  However how many billions of strands of 120VAC Christmas lights have folks strung outside in the rain and snow for the past 100 years?  Without even GFCI outlets? 

Yes electricity can kill, but stupidity is way more deadly.

Iím putting my power supplies at the end of 120VAC runs too, but Iím building out 100+ nucs so Iíve gone to 24VAC power supplies for cost reasons.  A 24VAC power supply is basically just a step down transformer that can be bought for under $10.     
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loumaro
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« Reply #5 on: March 01, 2014, 04:13:30 PM »

Why don't you just use a 12 volt transformers instead of a computer power supplies. Those resistors will get hot with AC power just like DC, plus you don't have to worry about temp on capacitors and etc. And I think I would forget using speaker wire, it needs to be heaver than that.



Louie
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Louie
Bush_84
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« Reply #6 on: March 01, 2014, 05:24:19 PM »

Whatever works.  I don't know much about this stuff so I am at the mercy of you guys.  I'd use a transformer if you guys thought it'd work.  I'd prefer an autobot over a decepticon, but maybe beggars can't be choosers.  Care to share a link of a proper transformer?  I have some leftover wire from some previous indoor lighting projects.  I also have speaker wire.  How do I know what is ok and what isn't?
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BlueBee
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« Reply #7 on: March 02, 2014, 06:45:51 PM »

Lou, I am using transformers; 24VAC, 40VA output.  

24VAC is still within what the NEC calls ďlow voltageĒ and presumably a little safer than operating at higher voltage.

The only problem with going with an AC transformer vs a DC computer power supply is your controller.  Most controllers only run on DC so if you go with AC power you're going to need to know a little more about electronic design to be successful.  Controllers of this vintage typically run on 5volts or 3.3volts DC.  Yes you can add a bridge rectifier after the xformer to generate the DC voltage to drive a microcontroller but that still needs filtered and regulated for a micro.  Just donít use an electrolytic there  Smiley  Many circuits do use them.  

Then there is the issue of controlling power to the resistors.  How do you do that with an AC supply?  You canít use FETs (theyíre DC devices).  You have to use either relays or traics to turn on or off power to the heating resistors.  Relays are mechanical and not a great idea when itís -20F outside.  Mechanical things have a tendency to freeze up when itís really cold.  Relays also require a descent holding current from your improvised voltage regulator which means youíll need bigger filter capsÖwhich usually means electrolytic!

I would go with traics to control the power resistors in most cases.  However they do drop about 1 volt across them when running and hence I would move up to 24VAC transformers so the nuc heaters donít take as much of a power hit as with 12VAC.  24VAC also delivers more power for less current (P=VI) and you can use smaller wires to the load.  I did use speaker wire myself Smiley

Bush, maybe you need to get one of those geeks from that Radio Shack commercial to lend a hand.
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Bush_84
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« Reply #8 on: March 02, 2014, 09:29:48 PM »

Lol ya maybe.  I have some relatives who may know something about this.  I'll have to see.
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loumaro
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« Reply #9 on: March 03, 2014, 02:00:59 PM »

To control the voltage out of the transformer you could use cheap speed control for router or sander. They cost about $20.00. Or even a Light dimmer for incandescent lights.
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Louie
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« Reply #10 on: March 04, 2014, 12:06:18 PM »

Those are devices (triacs) that chop off each AC cycle before it completes which reduces the power delivered to the load (light bulb, motor, etc).  If the load is a motor, then yes the voltage drops too as the motor speed and the back EMF drops.  However the voltage is still AC, not DC.  To get DC you have to rectify the AC wave with a bridge rectifier (diodes).  Microcontrollers/processors for controlling the hive heaters will not run on chopped up AC voltage, they require clean, smooth, DC voltage.

Getting DC out of an AC transformer is pretty basic knowledge for those with a little experience.  Again find a high school electronics geek, or a book, if needed.  The best solution will depend upon the voltage and currents you are working with and hence I canít give yíall a universal circuit for all cases. 

The simplest, lowest cost solution is a bridge rectifier, some filter caps, and a 75 cent voltage regulator chip (LDO type).  That can give you a clean DC voltage to run your microcontroller off of.  In volumes those parts only costs pennies on the dollar.

However things can get more complicated if your system design requires more DC current or you start from too high of a rectified voltage.  In those cases, you might have to switch to a switching type voltage regulator chip/circuit which is a more complicated design and costs a few dollars.  Computer power supplies are ďswitchingĒ type supplies.
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loumaro
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« Reply #11 on: March 05, 2014, 05:07:41 PM »

Why do you need DC? ALL you want to do is power a resistor for some heat, who cares if it is AC or DC.
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Louie
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« Reply #12 on: March 05, 2014, 06:53:06 PM »

Seems very complicated. I just bought some of that heat wire that you use to melt Ice dams off of your roof. I run it along the hives and shove a coil of it under each hive. When it gets real cold I plug it in.

Alfred
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BlueBee
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« Reply #13 on: March 05, 2014, 07:50:24 PM »

Bee keepers are very good at making simple things complicated  laugh

If all you want to do is make heat, it IS very simple, just plug in something that generates heat.  What I think I was discussing huh in the past few posts was a desire to control the amount of heat generated.  That requires a thermostat of some sort; either a controller with two legs, or some form of electronics.  Most all electronic logic requires DC voltage to function; hence the slight complications. 

There is a reason why most people have thermostats in their homes.  Iím suggesting if one wishes to add a furnace to a bee hive, it would also be a good idea to install a thermostat there too.  IMO, you don't want a hive/nuc to get too hot or too cold.  I have seen nucs get up to 90F in the middle of a Michigan winter and it was not a pretty sight.   

My goals with electricity is to simply (ha!) prevent nucs from croaking when it gets really cold outside (<10F).  My use of electricity is to emulate the temperatures in the basements of the old timers 100 years ago (CC Miller etc), or the modern beeks in Canada that winter indoors.  In both cases, the goal seems to be to keep the bees from getting too hot or too cold.  With some wire, electronics, and heaters, I donít have too fool with building a pole barn, moving hives, worrying about warm winter days, keeping out all light, missing cleansing flights, etc.

BTW. I donít have a problem with heat tape solutions.  I own quite a bit of the stuff but I use it for plumbing purposes. applause
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ScituateMA
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« Reply #14 on: March 23, 2014, 01:38:27 AM »

i recently made 5 heating pad from nickel chrome wire. i paid 6 dollars for 100 feet and i made 5 and  I still have some more wire to make another 3 pads. I used two vinyl flooring tiles ( 1 feet by 1 feet) and applied silicone and embedded wires in between them. each is 840 ohm which is 17.14 watts.My power supply is 120 volts.
 You can easily put the heating pad on the bottom board ,it is thin enough to slide the pad in the hive.
my hives are made of wood and not insulated and don't know if 17 watts is enough for cold New England climate in spring. Should I make the heating pads stronger until at least i switch to Styrofoam brood boxes?
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BlueBee
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« Reply #15 on: March 23, 2014, 01:51:16 PM »

The best solution to your dilemma is use a thermostat to control your heat source(s).  Simply set it to turn off when the hive is at 85F in the spring.  That way you never have to worry about cooking your bees.  A complication with wood hives is solar gain on sunny spring days.  The solar gains can be quite substantial and if you also add in too much electrical heat (without a thermostat) you could overheat the bees during the day.  

The spring buildup is probably the most thermally stressing period for the bees since they need to keep large swaths of brood at about 95F while it can still get way below freezing at night.  Heat loss is a function of temperature differences.  The bigger differential the bees have to control, the more heat energy they have to generate.   In the spring that could be 95F brood Ė 25F at night = 70F delta.

In the dead of winter the bees arenít raising much, if any, brood and hence they donít need a hot hive.  Like I said, my goals are just to keep a nuc above freezing in the winter.  Say I set a controller to maintain 40F inside a nuc.  In a typical winter we donít have too many days below 0F here (this winter wasnít typical).  So youíre looking more like a delta temperature of 40F in the winter on cold nights.

That means a spring hive is actually going to need to expend about twice as much energy (watts) as a winter hive.  A wood hive will get an assist from solar gains (during the day), but you might find something more than 17 watts is optimal.  I canít say for sure because I donít use wood hives.  I dunno    
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