I recently took apart a failed baby bottle warmer to salvage parts. The bottle warmer worked by heating water and circulating it around the bottle.

Unfortunately, it wasn't designed to be easily disassembled and I broke the casing trying to get it apart. So, I didn't get a good look at the internals before they spilled out on my table.

I'm not an electronics expert, but this is a VERY simple appliance and I can explain almost all of it. A pump, a timer switch, some thermostatic switches for safety, etc.

What I haven't been able to figure out is the heating element. Possibly related to this, the only two parts I don't understand are two thin sheets of what appear to be aluminum, each with one wire attached. I'm not sure how they were set up in the casing, but when they spilled out, they weren't attached to each other. Just two aluminum (I think) sheets, each with one (blue) wire coming off it, and nothing on either of them (like thermal compound). And by thin, I mean thicker than aluminum foil and rigid, but probably under 1mm.

Is this some kind of two piece heating element? If so, what is it typically called and how does it work?

Thanks.

 

Searching "bottle warmer heating elements" I get this ....

The aluminium shell would just be to eliminate hot spots and conduct heat away from the coil(I guess) ...You can just see the heat resistant sleeve around the coil poking out ...These come in voltages from 12 to 240 so many types of different coils , the mains voltage will have very fine wire ... may not be a coil inside , could perhaps be a semiconductor ceramic?

The "Heat material " is described as a" PTC Thermistor "

PTC stands for „Positive Temperature Coefficient“. PTC thermistors are resistors with a positive temperature coefficient, which means that the resistance increases with increasing temperature. PTC thermistors are divided into two groups, based on the materials used, their structure and the manufacturing process.Feb 5, 2012

 

Hi mculik5,

Looks like it's 'Joule heating' with those aluminium strips being used as the electrodes.

https://www.allaboutcircuits.com/te...heating-producing-heat-with-electric-current/

Regards,

Nandu.

 

@oz93666 - Thanks for your reply. I found all the same stuff while Googling, and this seems like the most logical solution. Unfortunately, there's nothing I pulled out of the warmer that resembles your picture.

@vu2nan - I think you're right based on what's in the article. BUT...a few questions...

1. What is the advantage of this heating method over typical resistance heating? Cheaper parts? If so, why isn't this heating method more prevalent?

2. Would this heating method work with distilled or deionized water? I found the manual online and it didn't say anything about what kind of water to use. Maybe they just assume you'll use tap...? Although the manual was very specific about a lot of other things (for CYA/safety).

3. Isn't this dangerous? I don't know much about this stuff, but if, for example, the negative electrode were to become covered in scale and the resistance go up, wouldn't that mean the positive voltage would seek other, lower resistance paths to ground - like your finger testing the water temp? Obviously, a lot of things would have to fall into place for this to happen, but given the lengths companies go to avoid being sued this would seem like something they wouldn't want to risk. Or is my understanding wrong and the risk of shock is much lower or non-existent?

Thanks.