First time build.

[Kirkll]

Kirk, how do you regulate the heat? Just with the voltage and then it will only heat to X with X amount of current?

You got it bro.... The voltage regulator setting at about 42 volts produce about 160 to 170 degrees. At the 10 amp setting on the charger, i set the timer for 60 minutes. The temp comes up slowly in about 30-40 minutes to 160 and cooks for 20 minutes at that temp.   I have to wait until the temp drops below 90 degrees before i can take the limbs out and load it up again. I can easily do 3 pairs of limbs in a day if i have all the mill work and lams ready to rock..... But i don't work that hard any more. But its nice to be able to roll up my sleeves and get a bow kicked out quickly if needed. I can spend more time on the craftmanship, and finish that way.

Kirk

[Kirkll]

Kirk I jogged my memory in setting up the LVL form

I ran it through my sander on both sides to get from 1.75 to get to 1.5, in turn invading the contigious exterior laminations!

Maybe you you had no issues because as you suggested you used a router to get the width leaving the exterior intact.

I just dug out some stock i have and this was LVL material. I believe they treat this stuff to seal it. I've had this stuff for years and its still dead straight and flat.    Kirk

https://photos.app.goo.gl/W8aJL2p8VAaMuwmw7

[Flem]

I was checking out the pics, but did not see the battery charger?
So you are sending 42V AC to the charger and its trying to push out 10amps at 12V?
Are the stainless plates taco'd around the limbs?

Sorry for all the questions, but it's really interesting!

[Kirkll]

I was checking out the pics, but did not see the battery charger?
So you are sending 42V AC to the charger and its trying to push out 10amps at 12V?
Are the stainless plates taco'd around the limbs?

Sorry for all the questions, but it's really interesting!

OOOOPS!   Wrong link...  Here ya go.

https://photos.app.goo.gl/PgGXwR6Hk6mJVpt79

[Mad Max]

Kirk
What temperature are you getting on the stack?

[OldRawhide42]

I used to use a thing called hot shot to thaw frozen pipes at work. I do not know how hot it gets. And i think it costs alot.

[Flem]

I can't figure out why the battery charger is in the program. The regulator is rated for 10a, why not just rig up some contacts from it to the stainless strips?

[Appalachian Hillbilly]

DC is probably safer!

[Flem]

The voltage is not what's going to get you, its the current. You don't want to be a 10amp conductor either way.

[Kirkll]

Kirk
What temperature are you getting on the stack?

I use two 22 gage SS strips. One stays on the form and is actually glued in place. The glass is wrapped in thin painters plastic and goes right on top of the SS , and another on top. It’s held in place with zip ties. I use between 50-55# pressure in my air hose bringing the pressure up slowly to squeeze excess epoxy out uniformly. Too fast and things like to move on you.

The temp slowly rises to 160 degrees in 30-40 minutes time using the 10 amp setting on the charger. Then I let it cook for another 20 minutes. This epoxy is fully hard in 20 minutes @ 160 degrees.

To address the DC vs AC question…. Im not going to pretend to fully understand the specific details of how this works. My education as an electrician is limited to wiring houses and changing out breaker panels and installing upgraded service bases. I have no training or schooling in the electrical field.

Using DC voltage this way is basically shorting out the circuit at lower voltage and creating heat…. DC voltage is safer than AC in this regard. If you hooked up leads like this using AC voltage with no insulation on the strips you would most likely light yourself up, and pop your circuit breaker trying….., could it be done? I’m sure it can…. But I have no clue how to do it safely. An electrical engineer would need to be consulted. My knowledge of electrical theory is very limited.     Kirk

[Appalachian Hillbilly]

DC is safer. Has to do with grounding. Isolation transformer will help on the AC side.
Yes current is the killer, but with a floating secondary,  you are much safer.

By nature of the DC circuit, the negative is not tied to earth ground, so if you touch it , it has no path.  Now hold a lead in each hand and that is a different story. AC would work, but it would have to have an Isolation transformer for the grounding reason.


Now, strap that puppy to a self bow form for hickory, turn up the juice and do a "fire" hardened back on a hickory bow!

Now that's an idea! 

[mmattockx]

Now, strap that puppy to a self bow form for hickory, turn up the juice and do a "fire" hardened back on a hickory bow!

I don't know how hot Kirk's setup goes, but you need much hotter than 160F to heat treat the belly wood on a selfbow. I've done experiments with pieces of red oak in the oven and they don't even start to change colour until over 350F. I do like the idea for the temperature control and consistency, though. That should be much better than using hot coals or a heat gun.


Mark

[Flem]

Hillbilly, you still have electrocution potential from the positive side. Looking at the pictures of that set-up, disaster is about 1/2" shy of ruining someones day.

[Appalachian Hillbilly]

Just don't get crossed up in them!
Joking aside, caution must always be used around any kind of electricity.

Been in Industrial maintenance with 3 phase high wattage heaters and 500+ HP DC motors for over 30 years! Actually got a degree in the stuff. Arc flash is no joke . Not discounting the danger in any means.

But with an ungrounded neutral you could touch any leg and still be ok. DC chargers usually give you that. Household AC with no isolation transformer and you become the path from ANY touch to any thing grounded!

Either scenario, AC or DC here could hurt you if you get crossed up wrong in it.

It only takes 50mA of current across your heart to stop your heart. From one hand to the other across your chest is the most dangerous shock you can receive.

We were also taught that the rapid cycling of the AC causes  more damage to muscles and organs due to fribulation than direct current which gives one contraction for the duration of the shock.

[Kirkll]

You guys ever cock your leg and pee on an electric fence?  Now THAT.... is a eye opener.

Until someone comes up with a better idea, i plan on staying with this heat strip system. i'm going to contact a guy that has some knowledge building battery chargers that Max referred me to for suggestions on future power supply. I figure i'm good for another 70 bows on this charger before it sneezes and pukes....   

[Flem]

OK, I got straightened out on the 12V. I now know that it's not enough juice to overcome our lack of conductivity in most circumstances.
Still will be avoiding it.
I do like the heat strip idea, its appears to be really efficient. The delivery system is what seems screwy. Maybe somebody can set me straight as to why a variable output DC transformer would not work better? I guessing the actual output of the battery charger is not known, but it's got to be less that the dial indicates or the voltage regulator would be redundant. 
 

[Kirkll]

I believe that is exactly what a battery charge is bro. It transforms the AC input to DC .  The voltage regulator just regulates how much AC voltage is being transformed….   Now I could be all wet too…. My knowledge of electrical theory is zilch…. Naga…. Nine….   

[Flem]

Thanks for that clarification. No theory here, just trying to establish practical application parameters. An adjustable DC transformer would achieve the same goals. It transforms AC to DC and regulates the output, all in one package.
If the charger was putting out the correct amount of juice at the 10amps @ 12VDC setting, you would not need the AC regulator, correct? You are using two devices to achieve the same goal and apparently, regularly burning one up in the process. But unless you actually measure the output of the charger when the input volts are choked down, we will never know the actual power requirements of the heat strips to achieve the temperature goal.

[KenH]

All this AC/DC electrical heated stuff is why I will stick to open top forms with bicycle innertube bands and ambient heat.  All that other stuff is just too much to muck about with, just to force epoxy to set in something less than a day.  I've got other, better things to spend my money and time on.

You certainly don't need all that crud to build your first -- or your 50th bow.

[Stagmitis]

Boy this went down the rabbit hole warp speed! Poor Casey, I hope he still has interest in building a bow