9-36v BMS Upgrade to 400a Relay+Fuse Kit

This kit includes a 500a relay and a 400a fuse.

These were recovered from industrial battery modules. These are normally VERY EXPENSIVE online. If you have any project that needs a high current relay this is your chance to save some money.

Make a cheap 30a BMS into a 400a BMS. This will work for batteries in the 9-36v range so perfect for Lifepo4 and Lithium Ion 4s-8s. Wire your BMS like normal except the C- that goes to your charge and discharge will go to the black wire on this relay. The red wire on this relay will go to the positive of the battery.

To be clear, you will need to buy a lower amp BMS like the 30a BMS units we have that are not expensive. You will wire the BMS like normal. You will have a positive and negative wire that you normally would charge and discharge through. Instead of charging and discharging through those wires you will connect them to the thin red (+) and black (-) wires of the relay.

When the BMS is on it will trigger this relay on. When it detects a problem the BMS will shut off and trigger the relay to shut off.

Now your main thicker positive wire for charge and discharge that will handle up to 400a will go right to the battery positive and the relay with fuse will go in line with your main thick negative wire. You will want to add the fuse in line like the 1st photo shows to protect from an external short or fault that is not battery related. Let's say a charge controller breaks and causes a short, you need a fuse to protect your battery from that. Do not use this with a BMS without adding the fuse because you never know what equipment could fail. Chargers, charge controllers, and inverters can fail and you need to protect the battery against that. Since you are using the relay to handle higher amps the BMS will monitor the voltages of the cells but it will not protect against a short or over current. That is why you need the fuse on the relay.

The relay can handle up to 500 amps and works up to 900vdc but the trigger wires work between 9-36v which is perfect for all 12v and 24v systems.

There are many reasons and applications for using these relays and there is no need to spend hundreds of dollars on them when we have them here for a small fraction of the price.

If you just want the relay and have your own fuse we have them for sale in our accessories area for a few dollars less.