12V water pump weirdness

[loanrangie]

I bought a cheap 12V pressure pump off ebay for my caravan, rated at 6 L/M which is enough for the joolca hot tap that i'm plumbing the van for.
I plumbed it in today and did a temp wiring just to test the pump by hooking into the 3 way fridge power lead which is close to where the pump is mounted, connect the wires and nada.
Get the multimeter out and check the cables and i've got 13.79V so should be good, pump specs say it needs 9-14.4V to run.
I take it to the shed and test it on a motorbike AGM battery i have on the bench thats sitting on 13.1V and the bloody thing works !, i cant understand why it wouldnt work in the van ?
I may need to take power from somewhere else but if i plan to change to lithium the system would probably sit on higher than 13.1V meaning the pump wont work.
I told the seller it was faulty and bought another one (fittings weren't ideal) so hopefully the new one will be ok.

[loanrangie]

I think my found my problem, the wiring at the fridge that i thought was live is actually wired to the trailer plug. It had voltage but no current, the wiring i need to tap into is higher up near the top of the fridge.

[V8Ian]

I think my found my problem, the wiring at the fridge that i thought was live is actually wired to the trailer plug. It had voltage but no current, the wiring i need to tap into is higher up near the top of the fridge.
Humble apology sent to the seller? [bigwhistle]

[p38arover]

When looking for faults in 12v automotive situations, a DVM can be a bad choice. Its input impedance is too high (10Mohms/volt) and it doesn't load the circuit.

An old 1000ohms/volt analogue meter is much better but they are hard to find. They load the circuit and you can see the supply voltage drop if the connection in circuit are high resistance. Even the 55+ year old multimeter I built at tech when I was a trainee technician is 20,000 ohms/volt but its still better than a DVM for this sort of job.

(As an aside, that own-built multimeter with its taut-band suspension meter is still working and in excellent condition and I prefer it to my AVO8.)

[loanrangie]

Humble apology sent to the seller? [bigwhistle]Yes, I explained what was happening and thanked them for their support.
Still came back and asked for a video and I told them not to worry it was a wiring issue.

[loanrangie]

When looking for faults in 12v automotive situations, a DVM can be a bad choice. Its input impedance is too high (10Mohms/volt) and it doesn't load the circuit.

An old 1000ohms/volt analogue meter is much better but they are hard to find. They load the circuit and you can see the supply voltage drop if the connection in circuit are high resistance. Even the 55+ year old multimeter I built at tech when I was a trainee technician is 20,000 ohms/volt but its still better than a DVM for this sort of job.

(As an aside, that own-built multimeter with its taut-band suspension meter is still working and in excellent condition and I prefer it to my AVO8.)I don't have anything else to measure but once I found a wiring diagram for my van it was clear although still strange that I had good voltage.

[loanrangie]

I ran new power leads direct from the battery to the pump and now have water pressure at the tap, tested the joolca hot tap and it heats to 40c but not much water pressure.
They say that 6lpm is the minimum but i think i'll need something around 10-11 to get decent pressure.

[RANDLOVER]

I don't have anything else to measure but once I found a wiring diagram for my van it was clear although still strange that I had good voltage.

Could be due to a switched neutral/ground wire.