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BR switch as a battery disconnect

Wonderful work @xavier-surkus, thank you for sharing.

Hi Chengchang,

Yea we’ve been using these relays on our ROVs for well over 100hrs of operation with no problem at all.
We’re very wary of heat, and have had no adverse effects thus far.

This link here shows the relay I’ve been using.

Have upgraded to using a reed switch this week (instead of the Blue Robotics vent plug switch) because we ran out of penetrator holes on the back of the 4" plate when upgrading to the BlueRov Heavy (lol!). After lots of testing in our tank over a range of different situaions, it’s now the permanent solution on our Heavy. If you do implement a reed switch in your design, make sure to include a flyback diode to protect the switch - more information can be found here

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Hi Jordan, thanks for the reply. I am going to try your way.

Would it be a good idea to replace the battery-cable-penetrator on the battery enclosure by a connector (see Tether Quick Disconnect)?

The connector would act as a switch?

I am not familiar with a micro subconn connector or other small connectors that are capable of handling the max current peaks that we can expect from the battery.
When that said i think it will work, just know that the connector are not made for this and might fail. It is rated to max 20A pr. Connector regardless of how many pins there is in the connector.

Subcon power series has a 200A rated connector. 4 Pin with 50A for each pin, they also have single pin connector which can work at even higher loads.

So indeed its possible to achive a battery switch by using the connector as a disconnection, however it might come at a premium price.

Anyone who has used a relay, did you have any heating issues? All the relays I’ve looked at are rated for 5-10A load currents and suggest using a heat sink if the current is higher. Since the rov can pull upto 90-100A, I’m paranoid about heating issues

I have used a reley, 80A with great sucess.
I also implemented a reed switch so I can turn on and off using a magnet from the outside.
Jan R

I use an automotive 80A relay along with the BR switch. The relay is in the 3 in battery enclosure, with the switch on the back of it. Working for over a year now. No issues.

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If I use a SS relay with a reed switch or the blue robotics switch, I wouldn’t need a flyback diode on the control or the output side, would I? I’m a little confused as to why in one of the answers above by abyss solutions it was advised that I use a flyback diode if I use a reed switch.

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The Thruster motors appear as both a capacitive and inductive load to the power supply

When power is removed from the Thruster motor there will be an inductive reverse voltage generated that can arc across the reed switch contacts or punch though the junctions in a solid state switch. Therefore the the need for a flyback diode to prevent such an occurrence.


@tciii Does the circuitry on the ESC not prevent this somehow?


Might not. Safe is better than sorry!


This thread may have gone a bit cold, but Here’s another slight variation on the relay setup. I used an SSR DD100 with the BR endcap penetrator switch. I downgraded to a prismatic lipo battery (after flooding my battery housing, which caused me to rethink opening the battery housing every time to turn the robot on). It’s now a 10Ah 14.8v battery with the relay in the battery bottle with it. Pretty convenient. I added two ports with Bluetrail Engineering cables for charging. One for main power (4 pin, sharing 2 pins for+ and 2 for -) and one for the balance lines. The ports normally have dummy plugs, then get cables attached for charging (vent plug open so as to avoid making a bomb)

…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.