Fixing a laboratory waterbath

[sam_sam_sam]

Re: Fixing a laboratory waterbath

You need to use a scotch-brite-heavy-duty-scour-pad pad that you can find in the grocery store it one that is green in color do not use sand paper ( unless you use a block of wood that has a very flat surface and it must be very fine grade ) it will make it uneven and you will not have the heat transfer

https://www.zoro.com/scotch-brite-he...28/i/G4676353/

They also make polish pad that you can put on your drill or die grinder

https://www.harborfreight.com/pack-o...scs-99985.html

You must make sure that you have NO connection to the heat sink from the device pins or the mounting tab this a must or you keep burning up triacs

Just in case you are not sure how to do this the correct way I am not trying to be an a** about this

When you put the plastic spacer to the triac it is the smaller end that goes through the metal tab of triac the head of the screw must be on the plastic flat part of the spacer you must use the nonconducting thermo pad under the triac metal tab and you put thermal heat sink compound on the thermal pad to the triac and you put on the heat sink as well one note you only need a small amount of heat sink compound on the metal tab to the thermal pad only you do not need to smear it on the thermal pad on the side of the triac the side that is the heat sink side needs to cover the thermal pad completely

[vrasp]

Re: Fixing a laboratory waterbath

What if I clean off the surface and sand it with some 3000 grit sandpaper? I d like to avoid drilling a new hole.

[sam_sam_sam]

Re: Fixing a laboratory waterbath

I have found that some plastic spacer have an issue with the way you install them the plastic is very thin and if you use the wrong type of screw then you can cut the plastic and short out to the heat sink and like what was mentioned earlier about the heat sink compound you have to use the right type and if you only paid $4.00 for it and it more than a couple of ounces then you got some real crap compound because when I buy heat sink compound I pay about $20.00 for a tube

Here is the one I use

https://www.mpja.com/Heatsink-Compou...info/30389+MG/

I have use this product for years and not had an issue with it

[eccerr0r]

Re: Fixing a laboratory waterbath

If you perhaps created some shrapnel that could have pierced through the insulator, but I've never had this happen. Never had a TO220 short with the heatsink when I have all the correct hardware installed.

As petehall347, you might have to end up selecting a new, clean site. But try with no heatsink compound unless it's known to be insulating (like "White" ZnO) first. Use the sharp probes to scratch into the paint and oxide coatings on metals to ensure you get a good contact.

[vrasp]

Re: Fixing a laboratory waterbath

That transparent mica that comes with the TRIAC is not enough, or no good. I ll try with just the other mica that I bought separately instead of both.

I didn't check the tube but I m pretty sure it's the regular kind. It was $4. The metal based ones are more expensive I believe. I ll have to double check the label.

Like I said in a previous post, even putting both probes on the heatsink gives me no continuity. But everything else gives me proper measurements. That's what I find confusing.

I didn't realize it could fry with so little. I guess if I had tried with the heating element right away I would ve fried it.

[eccerr0r]

Re: Fixing a laboratory waterbath

Sigh...so it turns out something silly... If we can't trust measurements, what can we trust...

dirty probes? Probes have sharp points for a reason - to dig through thin oxide layers.

Using two insulators, though better electrically, is significantly worse thermally. Usually TO-220s can handle at most about 2W without a heatsink. For TRIACs this means you can pass about 2A before you fry it when not attached to a heatsink.

Also are you using conductive thermal paste? Don't, or don't bother with thermal paste at all. Wish I could trade you this ZnO heatsink compound I have, I'm still waiting for "gray" heatsink compound to see if it's better for my CPUs...

[petehall347]

Re: Fixing a laboratory waterbath

obviously it was shorting to the heat sink by the way its burned the aluminium check the earth connection as it looks burned . i would drill and tap a new screw hole and move the triac to a flat bit .

[vrasp]

Re: Fixing a laboratory waterbath

I think I finally got to the bottom of this.

I plugged the waterbath to the wall (no bulb in series) and got a short on MT1. The 15A fuse didn't even blow but the circuit breaker of the laboratory did. I thought the fuse would blow before the circuit breaker. I don't know why that was not the case. Anyways, I decided to remove the TRIAC from the heatsink and left it hanging without touching anything. Then I turned the waterbath on and this time there was no short and the lamp in place of the heating element turned on.

I then put the TRIAC back on the heatsink, this time with two mica. Now everything seems to be working fine (lamp turns on). I have no tried it with the heating element yet.

I had measured the resistance of TRIAC with the heatsink and screw and got max values even at 2000k Ohms. Obviously the TRIACs that blew must have had some continuity with ground. This surprises me. How do I know I can trust the measurements? My leads are clean and I was careful when taking those measurements.

Next step is to connect the heating element and make sure the water heats up.

[vrasp]

Re: Fixing a laboratory waterbath

Like I said earlier in a post you need to know if you are getting a signal from the controller to the triac and it is controlling the triac if it not then you need to figure out what is not working

Or get something like this

https://www.ebay.com/itm/22210532801...53.m1438.l2649

And manually control the temperature and simplifies this setup if you can not figure out how to fix it

Or get a temperature sensor controller and control the temperature that way

Also you can do the compressor controller the same way use a temperature controller for this part as well and do way with the controller it has now but it going to take some work on your part and Google for the different controller that you need for this project

If I can help you figure out what might work for you I would gladly help you as much as I can

I haven't worked on it since last time. I ll check tomorrow or Friday if there is a signal from the controller. I do like the SCR voltage regulator idea. I might do that if I really cant figure it out. There is already a temperature sensor that works so I just need to control the heating.

Thanks for the help! It's greatly appreciated.

[sam_sam_sam]

Re: Fixing a laboratory waterbath

Like I said earlier in a post you need to know if you are getting a signal from the controller to the triac and it is controlling the triac if it not then you need to figure out what is not working

Or get something like this

https://www.ebay.com/itm/22210532801...53.m1438.l2649

And manually control the temperature and simplifies this setup if you can not figure out how to fix it

Or get a temperature sensor controller and control the temperature that way

Also you can do the compressor controller the same way use a temperature controller for this part as well and do way with the controller it has now but it going to take some work on your part and Google for the different controller that you need for this project

If I can help you figure out what might work for you I would gladly help you as much as I can

[vrasp]

Re: Fixing a laboratory waterbath

Well you're right it is MT1 MT2 Gate, but sorry, no additional clues why it's frying. You're on your own.

That's ok. You ve already helped a lot!

[eccerr0r]

Re: Fixing a laboratory waterbath

Well you're right it is MT1 MT2 Gate, but sorry, no additional clues why it's frying. You're on your own.

[vrasp]

Re: Fixing a laboratory waterbath

And that's why I'd suspect that the TRIAC should be fine as is controlling a shorted heating element, even... and it should end up throwing a breaker before it "instantly fries the TRIAC". With the past history of this thread, I'd highly consider the possibility of the miswiring of the TRIAC when soldering it, causing it to blow. Again connecting the gate terminal and MT1 (the diode drop) across mains voltage will instantly fry the TRIAC. Other miswirings would just cause issues in it turning on or it being always turned on.

Seems as typical for all these three terminal devices that aren't high powered RF devices, when facing the TO-220/TO-247 the left pin is the high impedance input (gate for TRIAC, base for BJT, gate for MOSFET), center pin (and thus metal tab) is the "output" (MT2 for TRIAC, collector for BJT, drain for MOSFET) and the right pin the low impedance common input (MT1 for TRIAC, emitter for BJT, source for MOSFET).

Oddly enough SCRs seems to not follow this pattern - more like diodes ... and again RF transistors where the center pin is typically emitter/source...

I was rereading all the answers to make sure I hadn't forgotten anything. Just realized you said left pin is GATE, middle is MT2 and right is MT1. Are you sure about this? The datasheet (attached below) seems to indicate the GATE is right, MT2 middle and MT1 left. The diagram in the datasheet is showing the TRIAC from the front correct? If it's actually from the back I ve been wiring it wrong this whole time...Could you check my photos with the wiring above and tell me if it's correct?

It goes
Purple - GATE
Black - MT2
White - MT1

Thank you!

[vrasp]

Re: Fixing a laboratory waterbath

I could be wrong but I would concern that it seems like you do not have a control signal to the transformer but the question is why

Because if your light is not lighting up this not making any cents to how it blowing up the triac

I dont think there is a control signal like you said, but it could be because the waterbath is only getting 77v instead of 120v. I guess I ll have to just plug it into the wall to find out.

If there is 77v on the primary of the toroidal transformer (for the control PCB and display) then the secondary voltages must be much lower than supposed to be. That could be insufficient. The display LCD does works though.

I wonder why a 100w bulb drops the voltage by that much. Its resistance must be high but why...

[sam_sam_sam]

Re: Fixing a laboratory waterbath

I could be wrong but I would concern that it seems like you do not have a control signal to the transformer but the question is why

Because if your light is not lighting up this not making any cents to how it blowing up the triac

[vrasp]

Re: Fixing a laboratory waterbath

The reason I said it could still blow is that the max GATE current is below 0.1A so I m worried about that. Or thats what I understood from the datasheet. Also maybe I should get a 10A fuse instead. I dont know how fast a fuse blows but what if a current just over 15A has time to blow the TRIAC before the fuse blows. I have no idea if this is possible. Do you think there is a risk?

I ve gone through enough TRIACs already.

[eccerr0r]

Re: Fixing a laboratory waterbath

Proverb: "The fast acting transistor always blows first to protect the fuse." -- unknown

[vrasp]

Re: Fixing a laboratory waterbath

I have installed the new TRIAC. A NTE56010. Same as before.

I added 15A fuses on MT1 and MT2 and a 0.1A fuse on GATE. I did not solder the fuses. I did a quick job. The wire is just twisted in the fuse holder's holes. This will be done properly after it's fixed.

I replaced the wires from the PCB to the TRIAC so there is no splice or colour changes. It's now easier to follow.

I plugged the waterbath in series with a 100w bulb and made the following measurements. First, the bulb in series drops the voltage to 77v between live and neutral. I don't know if this is normal.

I also removed the heating element live wire and put a 100w bulb instead.

Resistance is max between any TRIAC pins and ground with my multimeter at the max Ohm setting. Putting both multimeter leads on the heatsink also gives me a max resistance. It should give me continuity or at least some resistance. It is connected to ground. There is no continuity between heatsink and ground either. The heatsink must have a very high resistance. Why is this the case? It makes me doubt that the TRIAC is not shorted. My multimeter works fine and the leads are clean, so are the surfaces I m measurement on.

There are the measurements:

GATE - MT1 : 30 Ohms
GATE - MT2 : 47 Ohms
MT1 - MT2 : 17 Ohms
GATE - Neutral : 35 Ohms
Bulb (so MT2-Neutral): 12.1 Ohms

Of course these measurements were done when the waterbath is off so the TRIAC is not activated.

I then turned on the waterbath with the bulb in series and measured this:

GATE - MT2: 77v
GATE - MT1: 0.1v
GATE - Neutral: 77v
MT1 - MT2: 77.1v
Bulb (so MT2 - Neutral): 0v

At this point I haven't tried plugging the water bath staight into the wall. I think the TRIAC is OFF because it's at the same potential then live and neutral, hence why the bulb in place of the heating element does not turn on.

I believe this could also be due to the fact that only 77v is supplied to the waterbath. This might not be enough to power the whole thing and turn on the TRIAC. I m not sure. I m not confident enough at this point to plug it into the wall. I have fuses on each TRIAC wire but they are 15A and 0.1A so I think the TRIAC could still blow.

This is where I need your help figuring out what to do now. Anything else I can do before plugging it into the wall?

Thank you!

[vrasp]

Re: Fixing a laboratory waterbath

This is an old picture but the best one I have. It s the first TRIAC.

Blue: GATE
Black: MT2
Orange: MT1


. I wired the subsequent ones similarly.

[eccerr0r]

Re: Fixing a laboratory waterbath

what i'd like to see is how the wires connect from the PCB to the TRIAC... the wire colors don't seem to make sense from the limited photos of the wires in the existing pictures, alas it looks like a lot of splices are in place so things may not be as they seem.