DIY Drysuit Heated Vest

I finally got around to “finishing” my DIY drysuit heated vest project. While I have been using a Thermalution heated vest for the past two seasons I wanted something with a little longer runtime that heated over a larger area. I also wanted the ability to isolate the battery in the event of failure.  I really can’t take credit for this design as I pretty much copied the parts list from my friends Matt and Lea who designed their vests before me.  I waited for them to be guinea pigs until I built my own version of their vests.

Having said that, with the number of commercial heated vests on the market now there is really very little reason to build your own vest if you don’t like to tinker. If you want something ready-made I suggest the Thermalution, Light Monkey heated base layer, Santi heated vest or Golem gear vest.  There are others too but these ones all seem to be the most popular.

Heated Vest Version 0.9 (prototype/beta)

The first version of their vests worked very well but in the end they found the heating pads they used not to be very reliable.  The were warm but they were not very flexible and would develop shorts overtime that could burn you.  Not something you really want in a heated vest!

Matt is also an electrical engineer and had designed a small circuit/controller that went inline between the vest and the battery which would regulate output and allow you to adjust the vest to high and low settings by toggling the power off and on.    His circuit was very similar to the Pitkin controller that Light Monkey sells but installed inside the suit between the waterproof bulkhead and heated vest.

Heated Vest Version 1.0b or something like that..

It was around this time that Light Monkey announced their new heated vest base layer. Unlike traditional heated vests, the thermal pads used by Light Monkey use a silicone-insulated, carbon fiber heating element instead of wire, so they won’t bend and short out over time.   Light Monkey also sells these pads separately so you can make your own DIY solution.    They cost $35 each and you can buy them from any Light Monkey dealer.

We opted to switch to using these pads as opposed to the old rubber heating pads that Matt/Lea used in their original design.   Each thermal pad draws approximately 20W of power so if you wire them in parallel you’re looking at 40W.   Since they are effectively self-regulating and only draw 40W of power there was no need to install a controller.  You can simply hook them directly up to a 12V battery source.

E/O Connectors

E/O connectors are a ubiquitous 2-pole wetmate electrical connector used in the dive industry. They are most commonly used by scuba divers to connect heated vests and light heads to battery canisters.  They are sold by many different manufacturers including Halycon, Light Monkey, DiveRite, etc.   They were originally made by a company called Electro/Oceanic hence the name E/O.    While they are not the most resilient connector we opted to use these as they are compatible with most every other commercially sold battery system on market that has wetmate connectors.

You can buy them from wet-connect.com (Dive Xtras). They can be a little pricey when you add everything up but it’s nice to have a connector that’s compatible with what everyone else is using.   If I didnt care about that you can probably find a better waterproof connector (I’ve heard Impulse and Marshall connectors mentioned but I have no experience with either one of them)

Assembling the Heated Vest

I went super ghetto and bought the cheapest black zippered fleece vest on Amazon I could find for $11.67.   As a bonus this will function as an additional layer of insulation even if I wasn’t using the heat.  The vest is actually pretty nice though in the future I would try to find one without a neck collar.

From here I had my girlfriend sew the two heating pads into the sides of the fleece vest.  You could get really creative here and make a zippered pocket or even velcro them into a base layer or another undergarment but I figured sewing them in would be a little easier.  The downside is you’ll have to carefully hand wash the undergarments.  If I build a second revision I will probably make the pads removable so I can wash the vest separately.

Once the heating pads are placed in the location you desire and sewn into the vest you wire the two heating pads in parallel and add an appropriate connector of your choosing on the end.

Since I fully admit my wiring skills are pretty poor I had Matt finish the wiring.  He used waterproof heat shrink solder butt connectors that you melt with heatgun in order to make an effective and secure connection.  From here he covered everything in additional heat shrink tubing which provided an additional protection and  insulation layer. It also looks a lot more professional 🙂

From trial and error Matt / Lea also discovered that you really want some sort of locking connector otherwise you risk the heated vest coming unplugged if your wires don’t have enough slack.  This happened to them a couple times before they replaced them more secure connectors.

They found some generic “waterproof” screw-on locking connectors on Amazon.  I was going to just use some basic Molex connectors but I decided to order the same connectors that they did so that everything would be compatible.

BYOB (Bring Your Own Battery)

The easiest and cheapest solution here is try to re-purpose an existing battery from an old canister light of desired capacity.  I suggest using the largest battery you can find. I had an old Hollis can light battery with a busted lighthead so I decided to use an existing battery I already owned.  I simply installed an E/O connector onto the battery.  This was simple. It seals with a PG7 gland into the canister.

Unfortunately the battery I used is a pretty small one.  The Hollis battery is 5A/h 11.1V Lithium-ion Polymer (LiPo). So it’s only 54Wh.  Since my vest draws 40W this will only in theory give me a runtime 1 hours, 21 minutes (54Wh/40W=1.35hours).  Really not enough runtime for two long dives for me.

Luckily a few of mine gifted me an old Sartek canister with a 13.2V 4.5Ah NiMH battery.  While the NiMH battery is shot, the canister proved to be a drop-in replacement for 11.1V 10.4Ah (115.Wh) Li-Ion 18650 ( 3S4P) battery.  Awesome! One less thing I need to build!

With the battery rated at 115.44Wh hours and a 40W draw on the vest this should give me a runtime of almost 3 hours (~2 hours 52 minutes)

Drysuit Heater Bulkhead / Adapter

So once you have this fancy vest built you need a way of powering it by the battery outside your drysuit.  There are a few different options here.  Most people use a dual outlet heater valve that installs where your drysuit inflator is.    Light Monkey, SiTech and DUI all make suitable bulkheads that install through your inflator.  The DUI one in particular is pretty bulky but the benefit of using a bulkhead that installs through your drysuit inflator is that you dont need to add another hole to your drysuit.

I opted to use a separate stand-alone Drysuit Heater Adapter sold by Light Monkey. It’s very low profile and you could theoretically install it somewhere hidden like in near a pocket or in the telescoping torso of the drysuit or any custom location you want.

Arguably the hardest and most nerve-wracking part of this entire process for me was using a 7/8″ hole punch to install the bulkhead in my drysuit.  It’s the same concept for anyone who has installed a pee-valve in their drysuit. Once you add a hole to your drysuit you are permanently committed to that location.  I spent a little extra thinking about where I wanted the bulkhead installed before I added the hole.

From here I used RTV silicone around the edges of the hole to make a “hopefully” watertight gasket on the outer fabric of the suit.    I then screwed the bulkhead down allowing the RTV silicone to be sandwiched between the suit and valve to creative an effective seal.

I didn’t screw it down completely so that the gasket would have room to form.  After 24 hours curing time, I tightened the bulkhead down completely and did a leak test on my drysuit. SUCCESS!   If there are any leaks then they’re not coming from the newly installed bulkhead,.

Total Estimated Cost / Parts List

I’ve attached a list of parts and their estimated costs.  Note: This obviously doesn’t include stuff you might need for the project like a hole punch tool to install bulkhead or a sewing machine or any of the heatshrink tubing for the wiring.

You can also save a lot of money if you have an existing battery you want to re-use.  The battery and heater bulkhead make up the bulk of the costs.

Results

It works! Seriously… I’ve successfully completed 3 dives without flooding, any leaks or electrocuting myself so I would consider that a success.  I still need to do a little more testing, change some of the wire lengths on my E/O cords but overall everything seems to be working as expected.

I’m still not sure I consider this any warmer than my Thermalution vest yet.  To be honest I need to do more real world testing.  It’s a different kind of heat so it’s hard to tell.  The Thermalution vest uses wires to heat up a large area on your back. When it is on medium/high you can really feel it.  The heating pads from Light Monkey I am using cover a larger and more distributed area on my sides and back but they don’t feel as hot.   The good thing is it’s a more uniform heat and I’ll have a much longer runtime depending on if I remember to charge the battery.