How do I run 12v lights from 72v and 90 v bikes?

Quokka

Quokka

1 kW
Joined
Feb 9, 2016
Messages
305
Location
Perth, Western Australia
Guys, I am sure i am not the first person to try this and have searched the threads but i have not been able to track down any fool proof methods of being able to step down from 72v or 90v. I know i need a dc dc step down transformer, switch etc- I have seen these availible on aliexpress and other locations. The part that is puzzling me is how to set up the relay. I am having trouble finding something with suitable voltage input. Most solid state relays appear to eates to 32v :(
If anyone has done this could they please through up a parts list and circuit schematic :D
Bike 1- Qulbix Q76R, adappto maxe, bms with 20s 12P Ga sanyo 18650
Bike 2- NYX, Adaptto MaxE, Bms, 22s 18P sanyo GA 18650

Both bikes are chock a block full of batteries, there is abit of room for dc converter but not much.
 
What do you need a relay for? I assume to switch power to the DC-DC converter off and on? I use one on my 52V pack to power some lights, but I just connected it to the main battery leads with a fuse and don't worry about switching it off, as it seems to draw an immeasurable amount of current when there's no load on the 12V side. It would probably take months or years to drain the pack down.
 
The greater the delta the greater the challenge.

DoctorBass recommends using an AC-DC wall wart.
See the 4th message in the thread "DC-DC Converter over 48V - Recommendations": https://endless-sphere.com/forums/viewtopic.php?f=2&t=50458
MSG Link = https://endless-sphere.com/forums/viewtopic.php?f=3&t=50458&start=3

Another thread of interest: https://endless-sphere.com/forums/viewtopic.php?f=3&t=46438
and another: https://endless-sphere.com/forums/viewtopic.php?f=3&t=65820
 
That's what I've been using, is old wallwarts that are meant for about 14-15vdc output; under load they usualy end up close to automotive "12v" that is more like 14-ish. Most of mine I get from Goodwill or stuff other people are going to toss out.

(sometimes I also use a separate lighting pack, for instance for my car horns and headlights, as they take enough current the wallwarts can't quite handle that).


But there are a lot of commercial potted vehicle type DC-DC's out there, including many that have an enable line, so you don't need a switch to carry any current.
 
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