BR switch as a battery disconnect

…And here’s another picture showing the relay- new users only get one pic per post.

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Jon, that looks awesome! Nice work.

Thanks! I really appreciate the ROV and components you’ve developed. They make a great toolkit to build with.

Update on the relay-as-a-power-switch plan: Found a better relay.
I cooked a few of the SSR DD100 relays. They have enough “on resistance” that they need to dissipate a lot of heat when you’re really running the thrusters hard. With only the battery in the bottle and the relay snug against it, that’s not a great situation.
I’ve switched out the boxed relays for a lower resistance switch from thornwave labs and had no problems since.


This is something I have been wanting to do this year on my re-build. Thank you for providing the update to this thread. Were you able to find a decent the ANL fuse holder shown in the pics to use with this relay? Do you have any pictures of the install?

Thanks again.

Hi Bryan,
Looking back at order history I used this fuse holder off Amazon
I think I had to shorten the screws a bit and remove the underside nut to get it into the 3" housing.
The wire routing in there is truly ugly. You can probably make it much better with a little more forethought than I applied.
Pics coming in a moment.

It looks like I used the BR switch to pull the control line on the relay directly to battery neg.
The fat red wires are soldered directly to the relay board large pads because I didn’t have the terminal lugs to fit at the moment.
The balance leads and a pair of +/- leads from the battery go out to Bluetrail Engineering bulkhead connectors on the endcap for charging.


That is super helpful. Thank you! I will plan on incorporating this setup in my next build. Working on a new 3D design and should be printing the new body to the ROV soon.


Have you had any issues with this set up? I’m going to be upgrading my battery housing with an “On” “Off” switch but very intrigued regarding charging battery while in situ.

Do you have any pictures with blanks off? And any of your topside charging configuration.


Hi Davie260563,
All has been working well with this setup for a while now. Here are a couple of pics. The top side charging is just a cable at this point.

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Thank you so much for this I really like the idea of this to minimise the amount of times we go into the battery enclosure.

Looks great and again thank you it’s much appreciated.

Davie :+1:

Just wanted to pic your brains regarding the SSR DD100 relays you used. We’re they cheap ones that cooked or good ones. I have ordered :point_down:

Certainly not the cheapest but hey ho.

Just wondering if I’d still fit this as well as fitting the charging/balance ports within the battery enclosure. Or fit the relay with the electronics pod freeing up some space.

Thanks in advance.



As this is an open forum, I’ll add what I did…

I put the SSR-100a inside the main enclosure, as I just couldn’t get it fit comfortably in the battery enclosure. I then wired the SSR trigger to a spare pair (brown pair) of the tether, and put a toggle switch in the top side tether interface box. Now I don’t have to get my butt out of the chair to turn the ROV on/off :grinning:

Even with the 300m BR tether, it works great. As the SSR draws so little current to fire, there doesn’t appear to have any impact (interference) on the data pair in the tether.

I bought one of those Thornwave relays, but haven’t replaced the SSR-100a with it yet. That’ll be for the next teardown/rebuild.


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Hi Ken

Thanks for your input and that is a fantastic idea and much more convenient in some cases.

Is there a reason your replacing it with the Thornwave considering your currently running with 100amp SSR.

Any pictures would be greatly appreciated I love seeing members set ups as we are constantly learning and wanting to improve the system for functionality and safer.


Hi All,
Sorry for the slow reply. The SSRs I used were low cost ones from amazon. (keenso brand) I never checked on resistance so I don’t know what it was. Note that I also had to shave the corners of the box to get it in the tube with the battery.

Is it just me or do Thornwave not ship outside of US and Canada ? :slightly_frowning_face:

Hello! I just saw this post in the feed!

I am actually currently working on a solid state switch dedicated for DC current and to provide the lowest resistance possible. Compared to many SSR you will see, this has lower voltage drop and thus lower power loss. We are currently in the testing stages and if it works out, we may starts selling some of them!


Let me know when they’re ready, I’m happy to be an early guinea pig :blush::+1:

For sure! :slight_smile: What’s the max current you see on your system?

It’s hard to measure the instantaneous current but I’m assuming 100A is way more than I need. I’m running SRS Fusion thrusters at 24V, so would expect 30A tops