Relay Tips for >300 amp 48v battery systems

[thefutureisbright]

I have a question and then the real question....

I bought a JBD - JK-B2A25S-60P BMS for my battery bank (300 A-H, 48v 16s1p) and I have struggled to select the right relay for it. I've come down to these general guidelines for selecting a relay contact for operating the system. I would like feedback if I'm missing anything on the list:

So overall the list of things you want in a relay is:

• Adequate continuous amperage rating for your continuous use purpose
• Adequate surge amperage allowance
• Adequate amperage for the max current of your wire/fuse
• Dual coil ( or low maintenance wattage <5 watts)
• Adequate voltage rating for your battery… 60v rating for 48v battery
• Low enough trigger in rush current that your battery management system can handle it some are 4 amps for a 12v BMS) Note: May need to have a separate relay to switch on trigger…a relay to a relay.
• EMF protection for trigger release voltage spikes to protect your BMS components (called coil suppression)
• The relay needs to be rated for both polarities to handle by directional current (some only handle one direction)

What's missing from this list?

So question #2. On the JK-B2A25S-60P BMS it has 3 spots for relays listed in the manual (see diagram).

What is the voltage of the relay switch circuits O2, O1, DC+, DC-, C+ and C- and what is the maximum amps they can supply (some relays need up to 4 amps on a 12v supply but I don't know if my BMS can supply that)? JBD documentation is kinda sparse. So I'm reaching out to y'all.


So

 

[Hedges]

#1 for longevity, use precharge circuit so capacitor inrush doesn't weld the points on closing.

You can add snubber for the coil. Diode alone could make it slow to open, so maybe diode & resistor.

Not sure if snubber for contacts is effective at those currents. Capacitor and resistor?

 

[bluenomads]

Have a look here - https://diysolarforum.com/threads/j...-how-to-connect-to-battery-power-leads.44494/
Has some English diagrams that may help.

 

[thefutureisbright]

Yea I saw that thread and it was extremely helpful but I couldn’t find the max amperage off the coil circuit. Some relays require up to 4 amps to close the switch.

It may be that I should just grab myself a relay with a 3-4 amp coil surge current when closing and see if the BMS can handle it, but I get nervous as I don’t want to burn it out.

I saw that some other people had been recommending some relays with similar coil closing currents like this one:

https://www.aliexpress.us/item/3256803396525959.html?spm=a2g0o.detail.0.0.fd5961fa3xMJEt&gps-id=pcDetailBottomMoreThisSeller&scm=1007.13339.274681.0&scm_id=1007.13339.274681.0&scm-url=1007.13339.274681.0&pvid=24a1fd42-8026-41c8-b6d1-25b91e1b2440&_t=gps-id%3ApcDetailBottomMoreThisSeller%2Cscm-url%3A1007.13339.274681.0%2Cpvid%3A24a1fd42-8026-41c8-b6d1-25b91e1b2440%2Ctpp_buckets%3A668%232846%238109%231935&pdp_ext_f=%7B%22sku_id%22%3A%2212000026372170978%22%2C%22sceneId%22%3A%223339%22%7D&pdp_npi=2%40dis%21USD%2124.0%2124.0%21%21%21%21%21%402101c84d16594559079623209e19c4%2112000026372170978%21rec&gatewayAdapt=glo2usa

 

[bluenomads]

Ah yes, I didn't catch that missing bit. I'm not quite as far along although I've bought the same unit but not connected anything.
If I get to it sooner, I'd attach the contactors without load and measure the current through to them from the BMS.

I saw that there are 3 contactors, with the "charge" obviously needing to be very big (400-500a), and the "pre-charge" could presumably be pretty small (5a would probably be enough), but the "discharge" I'm unsure about - my naïve assumption is another 5-10a unit would do...?