Due to unreliability of anti-spark switches and having gone through two failing closed in past 12 months – I have built and tried a latching relay based alternative to use in a new build I am commencing.
I want the main power switch to be 100% reliable 100% of the time.
The new build will be a 10S system using dual vescs.
Basic design concept is to use • a heavy duty latching relay as main +ve power switching from battery +ve to vescs +ve ( no BMS) • two momentary action push-buttons – one for “close” and one for “open” with leds in push buttons to indicate latching relay status • no electronics (to fail from the transient voltage spikes!) • use main +42V supply rail to power relay switching circuits Started off looking around for a heavy duty latching relay. Settled on one from china link to latching relay . This unit is quite cheap (Approx. US$6). Ordered two and shipping was approx. 2 weeks.
This beast ticked most boxes. The contacts are rated at 80A at 240Vac with no dc rating indicated. The contacts are quite beefy and they should be OK for the application for battery through current whilst closed (My board draws about 40A maximum battery current).
The relay dc breaking current will be practically zero (vescs idle current only)- the dc making current will be the vesc capacitor charging inrush current which causes the problems on electronic anti-spark switches.
As a test -I mocked the latching relay up through the XT90 main power socket on my existing board and completed 10 closes and opening onto dual vescs – took the cover off to look at the contacts and there was no visible signs at all of arcing on power contacts during both closing and opening.
This is probably due to the very positive mechanical action of contacts when making and the very low current when breaking. For the pushbuttons – using this one for “close” (it has a led built in)
And this one for “open”
Any momentary illuminated pushbutton with spdt contacts will do the job.
The latching relay has a single 12V coil and you need to reverse current direction in the coil to reverse the latched main power contact operation.
This means a bit of control circuitry to achieve this. I used two mini 24V relays (each with 2x SPDT contacts) hot-glued to back of latching relay. link to mini relay
Reaching back approx. 20 years to my past EE days – designed up a hard-wired relay circuit with a bit of electrical interlocking between the two push-buttons to avoid shorting +42V control supply if both pushbuttons are operated.
Used a 2A wire fuse from input +v for control supply.
After testing – hot glued wires and connections to avoid any future issues from vibration. Bench tested OK and put aside for new build.
Total cost around $20 - around same size as anti-spark switch and hopefully a lot more reliable.