Author Topic: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"  (Read 78496 times)

Offline petespaco

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Quote
The copper tubing is less prone to temperature degradation but resistive heating will lead to higher resistance and more loss, and eventually power limiting, depending a bit on the actual design. Contacting the tubing is probably the limit here. Or what is the general opinion?

In my opinion, you should always be water cooling the  copper tubing, so "resistive heating" should not become an issue, since the tubing never even gets close to 100°C (in my experience).

Regarding capacitors:
The zvs induction heaters that I have all use this capacitor:

BM brand.
0.33 mfd  630VAC, ((1200VDC)
Type MKP

The 1000 watt units have 6 of them in parallel
The 1800 watt units have 9 of them in parallel
The 2500 watt units have 12 of them in parallel
So far, I have never had one of them fail.

I always force air-cool the induction heater boards, pushing the air downwards towards the circuit components.


Offline T3sl4co1l

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Incidentally, one could even operate with no resonant capacitors at all, just brute force inverter capacity.  This maximizes transistor use, putting all reactive power through them -- but if they're cheap, maybe that's not such a big deal.  The catch is, you still need to handle that current somewhere, somehow; in this case it comes back to the DC link / inverter bypass caps, which need to handle all that ripple current.  The only consolation is that the ripple voltage is small, so much lossier, bulkier types can be used -- DC link film, "filmlytic", the kind with the bolt studs, and even polyester (MKS) and electrolytic are suitable, as long as you have enough of them.  I think it's a poor tradeoff overall, that you'll end up spending more here (in cost or size) than the resonant version.

The one upside is that frequency can be freely controlled, which makes for interesting possibilities in special applications (like variable depth case hardening).  Of course, this requires industrial scale machines to be practical (100s kW, to heat up the surface fast enough while the core of the part remains cool).

Tim

Offline petespaco

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If you do decide to use the same capacitor that is on the units that I have, they cost about USD$1.00 each.  Here's one example:
Ebay Item  174496593032


Offline rikkitikkitavi

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Those I recocgnise, they are typically used in a half bridge simple induction cooking stove plate. Due to that topology they are subjected to high voltage stresses. 

Considering that only a few , 2-4 or so is used in each cooking plate with a output of 1+kW parallelling a bunch explains why they can take a lot of power.
Normally it is not thte caps that fail in those cooking tops, but the IGBTs.
Have become hero of the neighbourhood  as I fix expensive  4 plate stoves for a handful of dollars , compared  to  what the dealers charge for a replacement module (no warranty give n though as other parts might have taken a beating, but I always rely on the circuit breakers for that...)

I have seen these black boxes, a  grey box and some round white caps with axial leads (probably more inductive )

Unfortunately no datasheet with specs easiliy avialable but your  table is good data to be used as an indication

Thanks for the input!
« Last Edit: April 11, 2021, 09:27:57 PM by rikkitikkitavi »
A man can not have too many variacs

Offline petespaco

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New work coil related video----
 Finally trying to actually forge and then harden something using the 2500 watt ZVS induction heater as the sole heat source.
-I went through a LENGTHY process of (mostly) empirical coil "design" that may be of interest to some:

/>
  You WILL need to have a fresh cup of coffee or your favorite beer to watch this one.

Pete Stanaitis
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Offline hightemp1

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Cold quart of milk is my perferred poison. 

That is a great way to heat those strikers. 
Maybe even cover with a nice warm kaowool blanket.

Offline hightemp1

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This blacksmith architect toasts three ZVS 2500W heaters before learning about AC initial voltage surges from transformers. 
At 6:35 in video - reminds me of superman bending steel - very cool  8) 
/>Now, the powerful small coil may be ramping up the amps above 2.5kw?  Judging by time it took bend metal rod -maybe running at or near 3kw - doubt if over 3kw, else PS's over-current of approx. 60 amps would have kicked in?
Pete and company enlighten him on the finer points of induction heating. Maybe a FAQ page at the start of this thread would be a good idea, esp. since I have diluted much of the meat so badly.

« Last Edit: April 24, 2021, 04:31:14 PM by hightemp1 »

Offline petespaco

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I finally watched the video suggested by hightemp1 and I did make a comment.  I also emailed him directly with a link to some of my pages, etc..

TOPIC of this post:
Attempting to protect my DC to DC SSR's from unintentional overcurrent induction heater events
------------------------------------------------------------------------------------------------------------
I thought I might be able to put a fast acting automotive or electronics type of fuse in series with the DC power to protect the SSR.  So far I have learned that simple cartridge and blade type fuses aren't all that simple after all.
Terms like "standard", "fast acting", "ultra fast acting", and "slo-blow", etc. get in the way.
My first test was to insert a 40 automotive type blade fuse in DC circuit.  It didn't blow at 50 amps, at least not in the several minutes that I tested it.
After reading some more, it APPEARS that many fuses of these types don't blow QUICKLY until, maybe twice their rating.
I just tested a 15 amp fuse that blew at 30 amps and
a 20 amp fuse that blew at about 45 amps.
Who knows if that's even fast enough to save a Mosfet (or whatever) inside a DC-DC SSR!
I will do some more testing, but I doubt that I will be able to arrive at a fuse size or type that will be able to withstand 50 amps for at least 20 minutes a time and still be able to blow at, let's say, 55 amps, reliably.  And, even then, will it blow fast enough to save the SSR?
Plan "B"  will be to read the voltage drop across the current shunt that powers my analog ammeter with an Arduino  and simply shut off the SSR in case of a current surge beyond a programmed value.  I'd require a manual reset of the Arduino after such an event.
"Beats sitting in a bar", says I.

Offline T3sl4co1l

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Or rather, they are exactly as simple as they are, nothing more -- a coupon of metal that heats up under load, and maybe melts at some point.  The breaking current varies with time delay (and construction, hence the various types) and can easily be double the rating.

Fuses only protect the wiring, and function best when large fault currents are available to clear them -- a lead-acid battery or a mains circuit, for example.  A switching power supply with current limiting, might happily sit there simmering into a short circuit, until it blows up (maybe a good reason to choose "hiccup" type overcurrent limiting supplies -- the hiccup should be pretty safe over the long term).

Fuses are especially poorly suited to protecting semiconductors.  A "semiconductor" fuse is so named because it is just capable of protecting the most robust kinds of semiconductors -- diodes and SCRs.  All other types (MOSFETs, IGBTs, etc.) will have long since failed and turned to plasma, by the time the fuse opens.  (Which can still be of some value, for example reducing the hazard of shrapnel and arc flash emitted from an industrial IGBT module.)

For that, one needs a current limiting or protected switch -- using semiconductors to protect semiconductors, with some clever circuitry to protect itself in the process.

I've made a few such units myself, though nothing rated for quite this current.  One is unidirectional 40V 8A and extremely fast (so fast it's difficult to use!), another is unidirectional 40V 10-12A and fast (limiting current within 20us and faulting in 0.3 to 7ms), and the last is bidirectional +/-30V 20A and slow (permitting a fault condition for up to 150ms; it has a special design to deal with the heat dissipation).

I have made a prototype scaled-up version good for +/-30V 100A, but it's not behaving quite how I expected, and I don't currently have plans to make a proper PCB version.  If there's enough interest, I could develop it further.  (e.g., how many people would be willing to pool funding for that; or what kind of unit cost would you be willing to pay for such a device.)

BTW since these are electronic fuses, they also have on-off buttons and can be interfaced to controls, so they can replace the SSR too.

As for the proposed method, that can work -- don't even need an Arduino, just a logic gate or two and comparator.  The trick is in the details, turning on and off.

Tim

Offline petespaco

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Subject:  Protecting DC-DC SSR's from operator error when inserting work piece too far.

I am now working on  an Arduino  controlled device to sense current from the DC power supply and shutting off the power if I see a potential overcurrent (which I write into the Arduino code.

Progress report #1,  can I get enough voltage across the existing 75 mv shunt to do what I need to do?
/>Answer: No, but---


Progress report #2.  What if I add a single rail opamp?
/>Answer: I think so, but not quite there yet.

Offline petespaco

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Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
« Reply #410 on: September 13, 2021, 01:10:07 AM »
DC-DC SSR Protection Device finally working correctly!!!
  Well, it has been a long time in getting there, but I think I finally have a working device.

See:
/>
For those of you who might be looking at my solution through a microscope <G>,  I could still shorten the Arduino sketch significantly by eliminating all LCD code  if I need the system to act even faster.

Pete Stanaitis
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Offline petespaco

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Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
« Reply #411 on: September 15, 2021, 12:10:23 AM »
Here' a "follow-on video to the one I published yesterday.
I am simply catching up and cleaning up after all the time I spent making my SSR protection device work correctly.
In this one I tackle 3 subjects:
- A block diagram of my heavily expanded 2500 ZVS heater "system", with pictures to match the diagram,
-A simple spreadsheet that details current draw for a number of non ferrous materials.
-and, a little bit about repairing one of my recently failed DC to DC SSR:
/>
You guys should feel lucky that I won't bother you with ANY of several videos that I made DURING the process; those that were so boring and mistake-ridden that I'd be embarrassed if the ever saw the light of day.

Pete Stanaitis
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Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
« Reply #411 on: September 15, 2021, 12:10:23 AM »

 


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