Induction brass annealer redux

[GrocMax]

What kind of glue would you use for this?

You can buy heat sinks that already have double sided thermal tape, or there are epoxy products for this (heat transfer, non-conductive) purpose. A few pages back there should be a Mouser Electronics link to the ones I used, anything similar would work, I just picked out a model that would leave plenty of clearance to the capacitor leads and stuck 4 of them on. Pin fin doesn't care about airflow direction.

For low clearance setups you could salvage a laptop cpu heat pipe setup or two and glue it on.

Maybe I didn't post a link previously-

http://www.mouser.com/Search/Produc...35Gvirtualkey53210000virtualkey532-374124B35G

Used 4 of them. Lots of different mfg of similar sinks, many different sizes, should be able to find something similar at your favorite electronics outfit.

 

[bertn]

You can buy heat sinks that already have double sided thermal tape, or there are epoxy products for this (heat transfer, non-conductive) purpose. A few pages back there should be a Mouser Electronics link to the ones I used, anything similar would work, I just picked out a model that would leave plenty of clearance to the capacitor leads and stuck 4 of them on. Pin fin doesn't care about airflow direction.

For low clearance setups you could salvage a laptop cpu heat pipe setup or two and glue it on.

Maybe I didn't post a link previously-

http://www.mouser.com/Search/Produc...35Gvirtualkey53210000virtualkey532-374124B35G

Used 4 of them. Lots of different mfg of similar sinks, many different sizes, should be able to find something similar at your favorite electronics outfit.

I have some heatsink left over from pc's that i took apart for the fans.
already have my induction board screwed down but will see what i can do to add the heat sink.

Thanks for the advice.
Would you mind posting a pic of your glued on heat sinks?

 

[GrocMax]

You can just see the pins of the heat sink on the lower edge of the board in this pic. Board is mounted on 1" spacers. That fan and shroud were for the CPU of the original computer, just happened to work out well with some trimming for me. Temp sensor is on the lower left mount screw and measures board temp to vary the fan speed.

 

[SheepDog]

When getting capacitors for induction heaters you should use high frequency capacitors. The more available (and cheaper) capacitors will over heat with the frequencies involved in induction heaters. Your capacitors should also match as closely as possible to the listed parts because you are building an oscillator based on the values of the coil and capacitors. Using a different value will change the frequency of the unit and it will be less efficient.

 

[bertn]

When getting capacitors for induction heaters you should use high frequency capacitors. The more available (and cheaper) capacitors will over heat with the frequencies involved in induction heaters. Your capacitors should also match as closely as possible to the listed parts because you are building an oscillator based on the values of the coil and capacitors. Using a different value will change the frequency of the unit and it will be less efficient.

Hi sheepdog,
Are you talking about capacitors for the induction board?
I'm talking about capacitors that bridge the relay for protection of the relay. Do these also needed to be high frequency?
I salvaged mine from various old electronics so have no idea what type they are.

 

[SheepDog]

bertn,
I'm sorry, I thought you were talking about the induction board. I have always used diodes to protect the circuitry from relay inductance. I didn't make the connection. You can use the standard caps for protection circuits.

 

[GrocMax]

Yeah from a-studyin', the two components that set the tank circuit frequency are the coil itself and the tank capacitors. The lower the frequency the deeper the heating, and heating depth is material and material temperature dependent. The closer the workpiece is to the coil ID the more magnetic flux gets transferred. Example I did some 300WM and it took almost exactly the same current and time as 223 even though it was thicker, the OD put it closer to the coil.

Having the current limit control is handy, it keeps me from blowing the board up, can sneak up on it instead of either overloading the PS or letting angry pixie blue smoke out of the board, I'll also be using this thing to braze/solder fittings onto tubes.

 

[Jose_Luis_G]

Hi Jose,
Could you (or someone else of course) give me some advice?
I don't have a 1000uf @63v capacitor so I am going to substitute it with 2 470uf @ 63v capacitors parallel for a total of 940uf. Hope this works.
My power supply to induction board is 40v switched by a 12vdc single pole automotive relay (40a)
Your drawing shows the relay switching the negative (black) wire, but I have my relay wired up to switch the positive (red) wire.
Will this also work with the capacitor(s) or do I need to re-wire the relay to the negative wire?
Many thanks!

It will work in both ways, i.e. connected to positive or negative. Simply make sure you make the right connection to what polarity is concerned.
Anyway, take a look to the gap between contacts in the relay in N.O. position. It has to be at least of 2mm for a proper function.

 

[bertn]

It will work in both ways, i.e. connected to positive or negative. Simply make sure you make the right connection to what polarity is concerned.
Anyway, take a look to the gap between contacts in the relay in N.O. position. It has to be at least of 2mm for a proper function.

Thanks Jose.
I don't know the gap between contact points since it is a closed unit.
it's a 12vdc automotive relay that has a 40a rating printed on it.

Just checking,
As for the polarity when capacitor is wired in the positive wire;
Do i need to have the capacitors negative side facing the induction board and the capacitors positive side towards the power supply?

 

[Jose_Luis_G]

Thanks Jose.
I don't know the gap between contact points since it is a closed unit.
it's a 12vdc automotive relay that has a 40a rating printed on it.

Just checking,
As for the polarity when capacitor is wired in the positive wire;
Do i need to have the capacitors negative side facing the induction board and the capacitors positive side towards the power supply?

Yes, that's the way.
The relay you've got is a relative closed unit. You can open it easily and make sure about the contact gap.
More I can say, keep the unit open for the tests and you will be able to see if it is a big spark in the contacts or everything goes fine.
Also you will be able to make sure that the contacts do not get welded at opening, keeping the circuit closed all the time.

 

[bertn]

Yes, that's the way.
The relay you've got is a relative closed unit. You can open it easily and make sure about the contact gap.
More I can say, keep the unit open for the tests and you will be able to see if it is a big spark in the contacts or everything goes fine.
Also you will be able to make sure that the contacts do not get welded at opening, keeping the circuit closed all the time.

Good idea, I'll crack it open and see what's going on when i fire her up.
Might take another little while but I'm getting closer to completion. Still need to plumb in the rad and pump and figure out a shelf and trap door.

 

[normmatzen]

Above there are comments about using 1000 uF capacitors.
Be very careful!!

If you put a capacitor accross relay contacts, you may be hastening the arcing problem. When the contacts are open, the capacitor will charge to the voltage across the contacts. When the contacts close, you are putting a dead short (the relay closed contacts) and a very large current will flow thru the contacts to dis-charge the capacitor!
Another pit fall is putting a large capacitor across your DC power supply. This supply probably has a current limit built in. If you put a big capacitor across this supply, say 1000 uF, when a fault occurs, the current will NOT be limited till the 1000 uF capacitor discharges! If your supply is limited at 20 Amps as an example and puts out 60 volts, if a fault occurs such as the oscillator not starting up correctly, a huge current spike may flow in one or both transistors instantly vaporizing them. A well designed power supply needs no capacitor on its output as the supply will have excellent regulation negating the need for external capacitors.
A properly selected relay is designed to switch a rated load current at its rated voltage. This current should be greater than the power supply current rating. Putting a capacitor across the relay contacts can exceed the rated current by an order of magnitude at least! As can placing a capacitor from either relay contact to ground!

 

[GrocMax]

Found an issue going from alpha/boilerplate/spaghettiwire so it can get changed easy to the finished product- lost current control, acted goofy.

The RSP-750-48 PS manual wants you to reference (provide a 0v) the control voltage to pin 11 (gnd), this results in no workee correctly. With the 0v removed it works exactly as it should. So, control voltage to pin 5 and/or 7 only, no 0v ref on pin 10 or 11. I will change the diagram a few pages back and put a big note in. Sorta weird as I thought I had a solid 0v ref on pin 11, but I guess not. Now its back to absolute rock solid current control. Maybe this weekend I'll do a video and show control input voltage, what PS current and voltage that results in without a case, and with a case. Current stays where you set it, voltage varies.

Well doesn't look like I am allowed to edit the post a page back with the wiring diagrams, the 'bad' one has been deleted, here's the corrected one-

 

[GrocMax]

Bertn-

If the relay you have won't cut the mustard, you'll know about it real quick, within a few cycles it will weld the contacts and stay on. Be prepared to unplug something if it does. The Tyco 24v rated one I listed a couple pages back now has about 3000 cycles on it, its working fine on the 750w PS.

 

[normmatzen]

GrocMax,

I think what the manual for the power supply means is that the reference voltage is referenced to pin 11 (ground), not that you should connect the reference to ground! Many power supplies have a couple grounds, one a high quality ground for (for example) referencing the reference voltage for the highly accurate and low current circuitry. There is also probably a separate high current ground that is usually connected by a strap to the high quality ground. This is to keep the high current being controlled by the supply from developing a voltage through relatively small wires and printed board traces which will really screw up output voltage accuracy as well as load regulation.
I would bet that if you put a volt meter across REF to GND it would read 1.25V, 2.5V or 5.0V and it will be a very precise value. Most modern control loops are referenced to a Band Gap reference which is based on the energy gap potential of silicon, the Band Gap voltage is very close to 1.2V or so.

 

[GrocMax]

Thanks Norm, here's the skinny-

As shipped there is a 2 row 14 pin connector with 5 loops between pins 1-2, 3-4, 5-6, 7-8, and 13-14. 1-2 and 3-4 are remote (voltage drop) sense, up to 0.5v compensation for wiring losses between PS and load source, when looped it sees output at the V+/V- terminals on the PS. 5-6 is voltage control, 7-8 is current control, 13-14 is remote switch on. Pin 6 is a 5.75v ref, pin 8 is 5.33v. I assume from working with it the actual voltage ceiling is via the potentiometer adjuster, once this is set it won't go above it, thus the 5.75v ref.

The manual clearly shows to enable the current or voltage control function to remove the loop then apply a variable voltage signal up to 5.5v (5.0v =100% rated capacity) between the pin and pin 11 (gnd).
The symbol they used is potential or battery cell connected from pin 5 or 7 to pin 11. If there is no voltage, you get no output.

Started poking around, then put the Extech process calibrator voltage supply on it and voila, it works. Hrmm. Ground loop? Disconnected the 0v ref, then its OK.

So apparently, "Instructions unclear, lower body parts caught in ceiling fan."

 

[bertn]

Bertn-

If the relay you have won't cut the mustard, you'll know about it real quick, within a few cycles it will weld the contacts and stay on. Be prepared to unplug something if it does. The Tyco 24v rated one I listed a couple pages back now has about 3000 cycles on it, its working fine on the 750w PS.

Ah... that's too bad.
I actually ordered 3 relays 12v 80a from ebay but they never arrived....Seller refunded me the money but after waiting 7 weeks it sucks...
Since it is already in I might as well give it a try. Was only about 3 bucks so that's not too painfull
If relay goes bad and it stays on I can just flip the main switch.

 

[GrocMax]

Current limiting demo, big 1/2" diameter steel rod and a screwdriver. Starts at Switch position 7 (15.7A) and drops down to position 1 (9.5A) in more or less 1A steps. Note current is limited by switch, voltage is capped by pot on the PS to like 48.3v. If the current limit is reached, voltage drops to maintain current. Voltage got low on last position so swapped over to a screwdriver.

Makes it easy to set up for different cases or operations like brazing tubing, and difficult to damage either the induction board or PS, regardless of what goes inside the coil while its operating.

 

[Gina1]

Current limiting demo, big 1/2" diameter steel rod and a screwdriver. Starts at Switch position 7 (15.7A) and drops down to position 1 (9.5A) in more or less 1A steps. Note current is limited by switch, voltage is capped by pot on the PS to like 48.3v. If the current limit is reached, voltage drops to maintain current. Voltage got low on last position so swapped over to a screwdriver.

Makes it easy to set up for different cases or operations like brazing tubing, and difficult to damage either the induction board or PS, regardless of what goes inside the coil while its operating.

MOST excellent

 

[normmatzen]

GrocMax,

I am familiar with that fan! Welcome to the club!