Temperature Monitoring Hot and Cold

Monitoring our Boat's Fridge/Freezer and Hot Water tanks.

Our Fridge/Freezer has an adjustable Thermostat but no temperature indicator and there's no temperature indication for the Hot Water Tank. The fridge/freezer temp is important, we don't want our frozen food (think Klondike Bars) to defrost and don't want to waste fresh water running it until hot water (if there is any) to find out if it's hot enough for a shower.

Solution: Install a Dual Temperature display.

This one is from Amazon, $15

"WIDE TEMP RANGE - Temperature Range -58 ℉ ~ +257℉(Fahrenheit); Temperature measurement accuracy: ±1℉ (±0.1℉ when temperature within -9.9~99.9F). It can be not only used in water but also used to measure the air temperature. But the water temperature will be more accurate than that of air."

It's a small display, Size: 48*29*22mm. The probe wires are just 3' long, but some of the reviewers modified them to extend further.

Plan is to mount one Probe on the side of the Freezer box in the Fridge/Freezer and the other inside the thermal jacket of the Hot water tank.

As often is the case, determining where to locate the display is the challenge. The preference is somewhere that is visible without having to move anything or crawl/stoop down to some awkward position, but also away from any moisture, so not by the counter top.

I'll drill a small hole in the side of the Fridge walls and lead the wire for the probe outside of the insulation. The hot water probe will simply slide between the internal hot water tank and the fiber insulation between the tank (round) and the outer casing (rectangular). I think that the whole tank will need to be removed in order to insert the probe. There is a small area by each of the pipe attachments that I could possibly use, I'll make the decision when I get down to the boat and start on this project.

The unit has 3 connections on the back, one for each probe, the 3rd is for the power supply.

It draws about 8-9mAmps at 4v approximately 0.32Watts.

With a voltage range of 4v to 28v, the voltage drop over the power cables should not be an issue, I'll run power cables from Connection to the Compressor with an inline fuse. I'll use 16awg cable as that is the minimum size recommended by the ABYC.

This does mean that the Hot Water temperature will only be displayed if the Fridge/Freezer is powered on, but if we're on the boat and thinking about taking a shower, then the fridge/freezer will definitely be turned  on.

Back to the issue of where to mount the Display. There's a wooden panel that covers the midships water tank vent pipe on the forward side of the Galley  storage shelf. It would be easy to remove that panel, mount the display, connect the probes and power supply, replace the panel and we should be in business.

(The red arrow points to the planned display location)

Got down to the boat today and viewed the Probe location options.

Seems like the probe for the Hot Water Tank will fit by one of the 4 cutouts in the outer case of the Hot water tank. I should be able to slip a probe in touching the surface of the tank and use a couple of cable ties to secure the wire to the hose. I'll add a piece of tubing to insulate the wire and then feed it into the loom that goes up behind the sink area.

Just another fun piece of technology, an easy project. 

It turned out removing that wooden panel was easy, not sure if it is original boat woodwork though.

Easy cut out, drilled each corner than used a Fret Saw to cut out between them. 

Fits like a glove, the side 'Buckles' actually reach to the back of the panel, so it snaps in very securely.

Now to make the extension leads for the Power supply. I made the decision to get the supply from the Refrigeration Unit just forward of the Midships Water tank on the Starboard side. That's about 10'.

Next job is to extend the power cables and the cables on one of the Probes as it is too short to reach the Hot water Tank.

I'll do that at the boat. The wires will be Butt Connected and waterproofed with Sealed Heat Shrink tubing. I have not seen the power connection at the Fridge Compressor unit, need to take photos of that. 

The Fridge compressor unit is located just forward of the Midships water tank, getting to it will require some boat yoga effort.

Display Test

Here's the display setup on my workbench. I have an old 12v Power adapter (6amps) that I use to test gear at home.

The hot probe is in a cup of hot water, the cold probe in is air, the cold temp is actually my garage temperature, I'm wearing a sweatshirt, this is South Florida on January 29th 2022 !!

The temperature change reading is quite slow, it takes a while to register the increase although it does display the change about every 1 seconds. 

After sanding the panel and a couple of coats of varnish, it looks a whole lot better.

Our long term plans include lightening up the cabin by refinishing the wooden surfaces, there's a lot of wood, some of it will get painted. 

The ideas is that if the surface is smoother they will require cleaning less often due to mold growth which really is a problem here in South Florida.

I'm pretty sure this wood is Teak, it's much prettier without the darker varnish and years of exposure, most of the boat woodwork is that original dark finish, lightening up to match this finish will make a big difference.

This is the 'varnish' that I have used on the Companionway Steps which look great, it looks great on this display panel too.

Minwax Water Based Polycrylic Clear Satin

Day 1 of the installation.

Saturday January 5th 2022

The panel fit just fine, that was easy :) 

First wire to run was for the Hot Water Probe, I cut the Probe cable, it has two black wires, one was printed with white text. I connected the Red side of Black and Red Tinned Copper wire 16awg with Butt joints and then fed the other end of the twin wires along an existing loom under the sink over to the Stbd side below the Fridge/Freezer and up where the Water Fill Hose and the Tank Vent pipes ran and out to where the display is fitted. That took about an hour and a half and a lot of boat yoga.

To connect the Cold probe, I'm going to drill from the fridge forward wall, through the inch or two of insulation and then through the stringer which is outboard of the galley forward bulkhead. The probe wire is only 30inches long, so I'll probably have to extend it the same method as the hot probe.

The power to the Refrigeration Unit is connected via a screw down wire clamps, not really suited to adding two additional wires, so I'm rethinking the power supply. There's a Lighting power cable just above the Display housing, so I'll use that for the power supply just using a pair of electric cable connectors.

Looks like it will take a couple more hours to complete.

Moving ahead. I snipped one of the Probe cables and used Butt joints to connect it to a length of Twin 18AWG wire. Fed the wire from the Hot water tank end along the existing loom to the Stbd side just aft of the midships water tank, then up using a fish tape to through the existing wire holes just forward of the galley fridge/freezer and then aft to the Display unit. That took about an hour but looks neat and is supported every 6-8" 

Next I drilled a hole in the forward bulkhead of the fridge freezer near the top and as far outboard as I could get my cordless drill, it was only about 3" from the inside of the fridge  freezer to the forward bulkhead (Hull Rib). I fed the wire my from the inside the fridge and was surprised that it went straight through first time! Sweet. Then I followed the existing loom which included the probe wire from the hot tank, up to the display unit.

Last part is to hook up the power. The lighting circuit in that area has a lot of connections, sadly, some that I have added. So I'm going to rework all of those and put them to a small terminal block mounted on the upper side of the cabinets. Those wires provide power to the LED light over the aft salon table seat, the two LED lights over the Galley and the Fan over the galley. My plan is to move all of the Fans to a separate circuit (we have 4 Fans and a 5th to install in the aft berth). Meanwhile, I'll just connect the Temperature Display unit to the Cabin light circuit. I have much bigger fish to fry. (stay tuned for an upcoming intro to that upgrade)

Ok. Here's a pic of the probe mount inside of the Fridge.

That pic shows the metal temperature probe secured to the outside of the freezer box using a cable tie hold down clip that is mounted on the separation ferrules. It's really difficult to see from looking down into the fridge/freezer but it's very secure. I added a strain relieving cable tie to secure the wire to that ferrule too.

That method alleviated the need to drill a mounting hole in the surface of the fridge/freezer box itself.

All done!

The final wiring was pretty straight forward, it is connected to the Lighting circuit.

Right now the Cabin temp is 81º F so the hot water tank is actually cooler! 

The Fridge/Freezer (blue) temperature is set for max cooling, and the display varies from 31.3 (as shown) to 8ºF when the Compressor is running.

We'll see how the hot water temp shows when we next run the engine.

Ok, sign off on this one.

Oh, the lighter finish of the woodwork is appreciated by the Admiral. It's a winner.

See you on the water (we are right now, rafted up with 4 other boats from the HISC in Lake Boca)