12v Pump Installation Issue

Chris McN · Oct 12, 2023

Hi, I have very little electrical experience and would like a bit of advice. I have a kerosene pump installed in the back of my van. According to the manual, it draws 44a. It's powered by a leisure battery (split charge relay).

The issue is, the pump is meant to have a 80L/min flow rate, but it's only pumping at around 30L/min. The person who installed it has used 4mm cable, the length of the cable (one way) is about 5m. It has a 50a maxi fuse, and kill switch fitted.

The person who fitted it says he is snowed under and can't look at the issue for a couple of months. Another person I spoke to said the cable size shouldn't be an issue but from my little bit of amateur research, I think that 4mm cable may be too small and could be causing too much of a drop in voltage. It is a new pump so I'm pulling my hair out trying to figure out what the issue could be.

Is 4mm cable ok for this setup? Any advice would be appreciated.

James · Oct 12, 2023

What is the make and model of the pump?

Chris McN · Oct 12, 2023

James said:
What is the make and model of the pump?

Hi, here is the pump info

James · Oct 12, 2023

Looks like when you get to about 1.3Bar of back pressure the rate drops to about 30L per min.
80 is the maximum it can achieve with no resistance

Avo Mk8 · Oct 12, 2023

If the 4mm cable is twin conductors for the 5m (ie 10m) the max voltage drop would be 2V at 44A.
It could be worse if there are poor connections in the circuit.

I suspect James has identified the issue as above.
Bigger pipe?!

Chris McN · Oct 12, 2023

Thanks. Yeah, there really shouldn't be much back pressure though. It is pumping through 30m of 1 inch hose at a max of 2ft higher than the pump. Someone else has the exact same setup as me (although he isnt sure what cable size was fitted), and he is getting around 60L/min. It says in the manual that there shouldn't be more than a 5% voltage drop, I just assumed that might have been the issue.
Maybe it's more of a mechanical issue with the pump then, rather that electrical

Avo Mk8 · Oct 13, 2023

Chris McN said:
Thanks. Yeah, there really shouldn't be much back pressure though. It is pumping through 30m of 1 inch hose at a max of 2ft higher than the pump. Someone else has the exact same setup as me (although he isnt sure what cable size was fitted), and he is getting around 60L/min. It says in the manual that there shouldn't be more than a 5% voltage drop, I just assumed that might have been the issue.
Maybe it's more of a mechanical issue with the pump then, rather that electrical

Looking on the interweb at flow rates through hose vs pressure required, it seems to me the small size of your hose is what is restricting the flow rate, given the pump is only delivering a bit over 1 bar.