Maximum distance between the fuse and the batteries

Q&A and troubleshooting
, , ,
1

I am planning to replace my 14-year-old gel batteries with two Victron 25,6/200 NG batteries, connected in parallel. For the connections to the MPPTs and the MultiPlus I am considering the following Lynx components:

- 1 Lynx Class-T Power In

- 1 Lynx Smart BMS 500

- 1 Lynx Distributor

The cable length between the batteries will be approximately 60 cm. My question is whether I need to install additional MRBF fuses on the batteries or whether the fuses in the Lynx Class-T Power In are sufficient?

2

I always put an MRBF on the battery. If there is a short from the battery to the bus, there is no protection without it.

3

Thank you very much for your answer. I was thinking the same. In this case is the additional use of Class-T fuses recommend?

4

At 24V, I would put the cables on the BMS bus input. Put one lug underneath and one on top with a M8 bolt through them. You can also buy some M8 bolts and mod the Lynx power-in to add mega fuses. You dont need the Lynx Distributor.

image
image1126×748 175 KB

This is a power in. You undo the screws and pull out the plastic holder and put some M8 bolts then you can ad fuses. Much cheaper that the distributer if you dont need the leds.

image
image1920×1116 437 KB

5

This is a good idea, even though the AIC capacity of the MRBF fuse at 24V is somewhere between 5kA-10kA.

If it were my boat, I would use the Class T fuses in addition to the MRBF since the Class T fuses have an interrupt current rating of 200kA. I have three Victron NG 24V 300Ah batteries in my personal RV and I have MRBF fuses at the terminals and about 1.5m of cables to a Lynx Class T PowerIn with Class T fuses.

If we were building this system for a customer we would definitely use both fuses.

6

Thanks again for sharing your experience. I will set up my system (a stand-alone PV system) accordingly.

7

Side note, make sure when ordering your products that you select the Lynx Smart BMS NG 500, not the regular Lynx Smart BMS 500. The very minimal difference in naming convention is very important and very easily missed!

8

Some codes require the fuses to be very near the batteries. In my case, I use fuse holders with Class T fuses about 10cm away from the battery terminals . I don’t use the Class T Power-In. Instead I use the Lynx Distributor with a Mega fuse. Batteries are double-fused.

9

Thanks for the important note. I was aware of the difference, but I was wrong in the of components I mentioned here.