Solid State Relay for lighting system

[mrmojorising]

Has anyone had experience implementing a DC-DC solid-state relay between their 72V or higher battery and a 12V step-down converter for use with a 12V lighting system? The relay control would be linked to my bike's 12V key switch

I've come across these "fake" FOTEK SSRs, as it's been hard to find appropriate high-voltage, DC-DC SSRs at a reasonable price or that are accessible to me (in NZ). I know these knock-offs always have overrated capacities, but even if they could achieve 1/3 of their stated values, that would work fine for me. My 72V 20S4P pack peaking at 84V, and my lighting system is likely to draw less than 5 amps max

If anyone has had experience with these or similar relays or has suggestions, please let me know!

 

[fechter]

Are you wanting to use the relay between the battery and a dc-dc step down converter?

 

[mrmojorising]

Are you wanting to use the relay between the battery and a dc-dc step down converter?

Yes

 

[fechter]

Those should work, but if the dc-dc is off, what are you going to drive the relay with? Those are rated for 3-32v input, so you could find 5v somewhere coming from the controller to drive it.

 

[mrmojorising]

Those should work, but if the dc-dc is off, what are you going to drive the relay with? Those are rated for 3-32v input, so you could find 5v somewhere coming from the controller to drive it.

I mentioned the relay would be triggered by my 12v key switch, which is powered by the controller. The line to the relay would be split off the main battery line to the controller using something similar to this XT90 splitter

I know it "should" work, I wanted someone with firsthand experience to provide some feedback and whether they ran into any issues as I haven't found any threads with similar setups. Most reviews for these relays are for the AC versions which obviously break the connection a bit differently.

 

[chuyskywalker]

Yes, I've used this one in a bike build before to interrupt the batteries high voltage line elsewhere in the system:

https://www.amazon.com/dp/B00B88903G

You can kinda see it modeled here:

RadRunner Plus Rebuild

Now that I've got the nuts-and-bolts figured out on logging the PR/CA/GPS data down, I need to get it mounted. First, I've updated my wiring chart to include the rpi; a new 5v dcdc that can be shared between the pi, dashcam, and potentially other things down the line, I suppose. I also need to...

endless-sphere.com

It's also in the wiring diagram linked on that post. Mine does much the same thing -- when the controller gets turned on, it energized a 12v circuit I'm not using otherwise which opens the relay, then that powers the step down, which then powers the entire 12v system.

 

[mrmojorising]

Yes, I've used this one in a bike build before to interrupt the batteries high voltage line elsewhere in the system:

https://www.amazon.com/dp/B00B88903G

You can kinda see it modeled here:

RadRunner Plus Rebuild

Now that I've got the nuts-and-bolts figured out on logging the PR/CA/GPS data down, I need to get it mounted. First, I've updated my wiring chart to include the rpi; a new 5v dcdc that can be shared between the pi, dashcam, and potentially other things down the line, I suppose. I also need to...

endless-sphere.com

It's also in the wiring diagram linked on that post. Mine does much the same thing -- when the controller gets turned on, it energized a 12v circuit I'm not using otherwise which opens the relay, then that powers the step down, which then powers the entire 12v system.

Super clean! This is exactly the type of example I was looking for. Do either the relay or DCDC converter get very warm with your setup? It looks like you're running pretty low power electrics too so I'm guessing no. I have significantly less space available (see pic for reference), so I want to ensure I don't need extra heatsinking.

Have you also had any issues with voltage leakage or parasitic draw?

 

[chuyskywalker]

Do either the relay or DCDC converter get very warm with your setup?

Probably not, but honestly I haven't really reached in there to find out after a long ride But, yeah, I seriously doubt it.

Have you also had any issues with voltage leakage or parasitic draw?

Yes, actually, I have. I generally have to turn the batteries off (they have a switched BMS) otherwise I lose about a volt every two days. However, whether that's due to this part of the system or other aspects is kinda up in the air at the moment as I really haven't spent the time to figure out where the leakage/draw is happening, and there's a LOT of crap in this build.

 

[mrmojorising]

Yes, actually, I have. I generally have to turn the batteries off (they have a switched BMS) otherwise I lose about a volt every two days. However, whether that's due to this part of the system or other aspects is kinda up in the air at the moment as I really haven't spent the time to figure out where the leakage/draw is happening, and there's a LOT of crap in this build.

Ah yeah, that's annoying. I don't have a BMS switch, unfortunately, only app control, but that's not exactly convenient. The relay would be primarily to reduce parasitic draw from the DCDC converter, but it's not ideal if it doesn't do that job. Like you say, though, it's undetermined, so I might just have to try it myself.

I think if I really struggle to get it working this way I'll just have to resort to building a secondary 3S battery for electrics

 

[fill]

Dont know your bms app but if your carrying a phone with the app loaded ? has it got an api? if so bluetooth tags/camera buttons are cheap as chips 'If This Then That' perhaps?

 

[mrmojorising]

Dont know your bms app but if your carrying a phone with the app loaded ? has it got an api? if so bluetooth tags/camera buttons are cheap as chips 'If This Then That' perhaps?

Using ANT BMS, which has a "sleep timer" for the Bluetooth function to conserve power. It only reactivates when charging, so I can only access app controls during and shortly after charging. Probably a lot of work to attempt to get some sort of Bluetooth trigger to turn it on/off.

 

[fill]

Using ANT BMS, which has a "sleep timer" for the Bluetooth function to conserve power. It only reactivates when charging, so I can only access app controls during and shortly after charging. Probably a lot of work to attempt to get some sort of Bluetooth trigger to turn it on/off.

Fair enough..

Fwiw have been there with a cheap 36v hailong pack.
I found the labelled solderpads on bms pcb for a switch and the surrounding components seemed populated??
I tried both latching and momentary switches- Ha- No joy.
Then someone suggested inserting a latching switch into one of the balance wires to trigger bms protection.. HA- That may work with a load being drawn but not enough to stop pops bangs and sparks when slid onto the base enclosing the controller..

I only mention this just in case you get similar mid night inspiration - Chances are it will only waste your time and heatshrink supplies.

 

[mrmojorising]

I only mention this just in case you get similar mid night inspiration - Chances are it will only waste your time and heatshrink supplies.

Yeah also not possible unfortunately haha. I have a 72v fully sealed, custom built, Amorge battery with no way to open without cutting into silicone sealant. Not that I'd want to try anyway because it's already space optimized to the max

 

[Chalo]

Ah yeah, that's annoying. I don't have a BMS switch, unfortunately, only app control, but that's not exactly convenient.

Really? You need an app to interface between you and the real world?

300A Battery Disconnect Cut Off Kill Switch Power Isolator for Car Boat Van 60V | eBay

Rated Current: 300A. 1 x Battery Disconnect Selector Switch. Type: Battery Cut Off Switch. Switch Type: 2-Position(ON and OFF positions). Insulation Resistance: 100M.

www.ebay.com

Off is off.

 

[mrmojorising]

Really? You need an app to interface between you and the real world?

300A Battery Disconnect Cut Off Kill Switch Power Isolator for Car Boat Van 60V | eBay

Rated Current: 300A. 1 x Battery Disconnect Selector Switch. Type: Battery Cut Off Switch. Switch Type: 2-Position(ON and OFF positions). Insulation Resistance: 100M.

www.ebay.com

Off is off.

This is underrated for my application, and big and ugly . I can hide a relay & converter, but a big ol isolator switch is such a janky solution for my bike