Re: Fixing a laboratory waterbath
 

Sounds good I ll do that. I might use the lamp bulb trick here because I m worried about causing a short again. Like putting a 100w bulb between the primary of the transformer and the PCB.

Re: Fixing a laboratory waterbath
 

Hey guys,

I ll be posting some pictures of what I am doing to make sure I don't make any mistakes.

First, the triac. I put thermal paste between the triac and mica and mica and heatsink. I put what I think is considered a thin layer. The triac is screwed to the heatsink with a washer so the screw doesn't touch the metal plate. I do not know the size of the screw but it is smaller than the triac hole. There is no continuity between the triac and heatsink or the screw and the triac metal plate. It all seems to be good but I d like to run it by you first.

I soldered the new capacitor. The way I understand this is there is no polarity in film capacitors, and also it's AC so I don't have to watch for polarity. The transformer is back where it was. I believe everything is set. I m going to get a 100w bulb and hook it up between the transformer and the PCB.

If you guys see anything abnormal please let me know. I m quite worried I either forgot something or did/hooked something wrong and do not want to have to go get new components once again.

Thank you!

Re: Fixing a laboratory waterbath
 

the washer is a special one with a lip that goes into the triac so the screw cant touch the sides.

Re: Fixing a laboratory waterbath
 

Yes that's what I got. It came with the TRIAC.

Re: Fixing a laboratory waterbath
 

One problem I see is that you are not getting your connection hot enough for the solder to flow and those connections are not going to be very good and you need a fuse holder ( or a fuse that has pig tail wire on the fuse ) and not solder the fuse to board like you did those are not going to be good connections

I am sorry if it sounds like I am giving you a hard time with this but it is important that your soldering joint connections are solid so you will not have issues later on with this device

When you see the strands of wire and very little solder on them this not going to be a very good connection you would be better off if used a piece of wire with the insulation still on the wire and go from point “A” to point “B” and make a good connection on point “A” to “B”

Or

You would have been better off if you had flatten the end of the wire across the the solder joint pads and solder it that way then your connection would have looked a lot better in the long run

If you can find wire wrapping wire which is one solid wire and you laid them side by side and flowed solder on that to make solder trace you would have been better off doing that

Are you using solder that has flux inside the solder if you are then the solder might not be of good quality if you are having issues with it to flow

Not all solder that has flux in it are the same in quality be aware of this back in the day when Radio Shack was every where you could find good quality solder you can still find solder on there website however I do not know if the quality is still exactly the same as it was back then

Re: Fixing a laboratory waterbath
 

look closely at these places ...

Re: Fixing a laboratory waterbath
 

This is good advice. I d rather you tell me that and I fix it rather then having to open everything back up to fix connections in a few weeks/months. This waterbath is supposed to run (if I m able to fix it for good) at temperatures from -20°C to 120°C. The connections must be good.

I ve been under-estimating the power of flux. I will reflow solder on these connections with some flux see what I could do about that fuse.

Thank you!

Re: Fixing a laboratory waterbath
 

It's not the temperature range of the bath that's the problem, the phase change motor's vibration is what kills electronics. I'd suspecting it's what killed your connectors in the first place, and perhaps if that avenue was checked first, there wouldn't be so many bodges around now...

Re: Fixing a laboratory waterbath
 

That is likely why it worked for a week. I ve been doing a lot of things wrong since I opened this thing a few weeks ago. Even with all these issues I get excited about this and look forward to working on it and understanding better how these circuits work. I think I ve found myself a new hobby. And of course, as I ve said before, I m really appreciative of you guys taking some of your time to help me even after half of these issues I ve caused myself.

Re: Fixing a laboratory waterbath
 

btw how the heck do you get a water bath to 120°C, is it pressurized water?

Re: Fixing a laboratory waterbath
 

To keep it liquid at 120°C, you must increase pressure to at least 200 kPa (so around 100 kPa gauge pressure).

Re: Fixing a laboratory waterbath
 

No pressure here. We use a mixture of water and anti-freeze. It allows us to get to temperatures below 0 and a bit higher than 100 °C. We almost never use it at such high temps anyways. If we wanted to we d have to use another mixture. We do use it at temperatures below 0 though.

Yesterday I made myself a small current limiter setup with a 100w bulb. I tried it today with the waterbath. The waterbath starts and runs but the display is dim and the pump fan turns slower than it should. Also the bulb is bright. I suppose it needs more amps to run properly.

Tomorrow I ll try with 2 bulbs or more. If I understand well, if I can get to a point where the bulbs are dim and not at full brightness, I can confidently assume that there is no short. Otherwise, if after adding a few bulbs they re still really bright there is probably a short. I don't know how many amps the load normaly takes but since there is a heating element I think it's likely at least a few amps. What do you think?

Re: Fixing a laboratory waterbath
 

Yes unless you have to many lights bulbs then would almost as though you were using a fuse

Re: Fixing a laboratory waterbath
 

I tried with 3 bulbs this morning. They all light up. I dont think they re at their full brightness but I m not 100% positive. They do get very hot.

I noticed the voltage drop across the primary of the transformer is about 65v. Is it normal for these bulbs to drop the voltage by that much?

The waterbath temperature increased by 0.5 degrees in 20 min. So it slowly heats up which would make sense with the limited amps and lower voltage.

I m not confident everything is working well enough to plug it without the bulbs.

Re: Fixing a laboratory waterbath
 

It's up to you to decide what's going on... especially when dealing with heaters and other things that draw a lot of power.

Re: Fixing a laboratory waterbath
 

I plugged waterbath straight into the wall without the bulbs in series. The TRIAC blew again. It was not grounded, I checked.

These are the observations I made:

The resistance between where MT1 and MT2 connect have a low resistance (even with no TRIAC connnected). Based on my reading, it is supposed to have a high resistance. From now on I ll refer to where MT1 and MT2 connect as MT1 and MT2 to make things easier. MT1 connects to the heating element. It's the live of that heating element and then there is a neutral wire that goes from the heating element to the PCB. MT2 connects to 120V.

I removed the heating element cable from MT1 and the resistance between MT1 and MT2 became very high, which makes sense since MT1 is only connected to that. Could a faulty heating element cause that? I don't see how but I don't know.

Any ideas?

Thank you!

Re: Fixing a laboratory waterbath
 

Or there is a very low resistance between neutral and live. I ll check that.

Re: Fixing a laboratory waterbath
 

If the heater element is like the type in a water heater then you need to check the outer case to the terminal of the heater element and you should NOT get any resistance if you do have any resistance then there is an issue with the heater element

What is the resistance of the heater element because if it is for 120 volts then the resistance can not be extremely low because if this might be your problem ( it should be around 8 to 10 ohms )

This also depends on the tirac amperage rating if it lower than 15 amps then your resistance would be higher than 10 ohms

Re: Fixing a laboratory waterbath
 

Thanks. I ll check that.

Re: Fixing a laboratory waterbath
 

I actually had already checked the heating element with ground and it was fine. All three terminals had high resistance with ground.

I m thinking of everything thats on the board. I ve already removed the capacitor. I m pretty sure it s not the transformer. I can try removing it. The rest are part of the circuit that feeds the pcb below it so not related to the actual heating.

Isn't a heating element just a thick tube of copper/alloy with a high current going through it? How could it be faulty?

Below is a photo of the board I ve posted before.

Next to the number "12" is in order

Gate
MT2
MT1

I made a mistake in my previous post. MT1 terminal is connected to the heater element and MT2 terminal to 120V. Either way, there is continuity between them where there shouldn't be.