Wet Bay Heater - FIXED

[cbr046]

Ordered parts in Feb from Newark Electronics and they finally showed up, just in time for Summer 😉

The problem with the wet bay heater is a single under-spec'd thermal fuse controlling a 300W heater element.  300W/12V=25A.  Maybe the OEM fuse was 25A . . . . or 30A, but those aren't available anymore.  The largest thermal fuse available is 20A / 184C.  This value is way under-spec'd.  Still, the 20A / 184C fuse will last a little while . . . a few minutes?  an hour?  a night maybe? 

My solution was to split the top and bottom elements into 2 banks, one with 2 elements the other with 3 elements with a fuse for each bank.  The top bank will draw 120W, or 10A.  The bottom bank will draw 180W, or 15A.  This is well below the rating of the available 20A / 184C fuse. 

The top and bottom "banks" no longer have the same mechanical support.  I thought about adding a dab of epoxy to bridge the gap . . . . . but didn't. 

I crimped two 20A / 184C thermal fuses to the supply with one fuse going to the bottom bank and the other to the top bank.

BTW, the crimps are ugly because I used vice grips to clamp them on.  BIG vice grips.  The recommended terminal crimp is very heavy duty, rated for 343C. 

Here's the Newark part numbers

20A / 184C thermal fuse - https://www.newark.com/thermodisc/g5a01184c/fuse-thermal-184-c-20a-250vac/dp/39T4439 - $2.37 each

Terminal Crimp (Parallel Splice) - https://www.newark.com/amp-te-connectivity/323754/terminal-parallel-splice-crimp/dp/50F3313 - $0.875 each

By shorting the snap-disc in the wet bay I was able to test the repair and see all 5 elements glow a nice orange, but I guess I won't know how good the fix really is until December.  I am VERY optimistic!

- bob

 

[CLIFF918]

Hey Bob here is another option for the future. Amazon has an assortment of thermal fuses available:

https://www.amazon.com/Hilitchi-Circuit-Temperature-Thermal-Assortment/dp/B0719DHV9P/ref=sxin_25_ac_d_rm?ac_md=0-0-dGhlcm1hbCBmdXNl-ac_d_rm_rm_rm&crid=LWNW4GJ7XSZ&cv_ct_cx=thermal+fuse&keywords=thermal+fuse&pd_rd_i=B0719DHV9P&pd_rd_r=1ba352d1-bd63-4517-8dc0-ecabb95453d7&pd_rd_w=G3OPK&pd_rd_wg=wXj3n&pf_rd_p=7de181be-756e-4582-93e5-e9bf36281b5f&pf_rd_r=0BFXJDKTXRQJDMT40D29&psc=1&qid=1651310873&sprefix=Thermal+fuse%2Caps%2C130&sr=1-1-7d9bfb42-6e38-4445-b604-42cab39e191b

[cbr046]

2 hours ago, CLIFF918 said:

Hey Bob here is another option for the future. Amazon has an assortment of thermal fuses available:

https://www.amazon.com/Hilitchi-Circuit-Temperature-Thermal-Assortment/dp/B0719DHV9P

Those are all 10A fuses and would blow in a millisecond.  But that's the trick - gotta have current and temp ratings which I discovered very hard to find . . . . . And no, you can't put two 10A fuses in parallel! 

- bob

[jim.hamblin]

I’ve got several extras from when I repaired mine, I’d have to look to see what rating they are. I got the part no. from the original poster on doing the repair here on this site. 
If anyone need one or more and I’ll send them. 
jim

[jacwjames]

Any reason you couldn't mount a self-resetting circuit breaker on the outside. 

I installed a small 120 volt Broan heater in the master bath for my wife, I even put a timer in the circuit knowing she'd forget to turn it off.   She has a tendency to run a lot.  Last month she said "the heater quit working".  So I tore into it and found that they installed a thermo disc in the heater but it was not self resetting, you have to physically press a small button.  Not a big deal now that I know it's there.