Fuse between battery and UBEC

Hi! I put a fuse on the HV side of the UBEC (Yep 20 HV). On the low voltage side of the ubec I have the receiver and water pump. For the water pump i use a Step-up DC/DC converter. This enables my to set the pump voltage higher in order to get a better water flow. I use the small water pump rated to 5-12V and I run it on 8 volts now.

I started of with a 3A fuse but that one blew early, not because the load from the pump and receiver but because my prop was to “long” and pushed against the pod when power was applied in water.

I changed to a 5A fuse for my second try and I could ride for apprx 5 minutes. At the second start I lost balance and had to release throttle and then reaply it, this caused to fuse to pop.

Im trying to figure out why the fuse is blowing under motor load. Ive monitored battery voltage and the drop is only 1-2 volts during acceleration.

Could it be that the ubec cap is drained during acceleration and that the inrush current to recharge it is higher than the rating on the fuse? I guess a diod could help stop the inrush current?

I use a seaking 130hv in my new build.

Any ideas?

step-up waterpump