fresh water pump installation.. advice needed please!

[sparrowcycles]

Hi there and thanks to everyone that has helped me in the past (either through my posts or through gleaning much wisdom from others exploits)..

 

I am slowly working through the long list of niggles in the interior re-fit of nb Kerbau which I live aboard in Liverpools albert dock,

Im at the point of tackling the water system and have fitted a 3.5gpm shureflo pump with a 2 ltr accumulator tank right by the water tank.

 

Now im certain that the batteries (2x 110ah) are not in the best state (two new ones are on the way) but even with the charger on i notice the lighting (all led) noticeably drop whenever the pump kicks in..

 

The pump is wired via a length of 6mm twin and earth fitted by the previous owner which is far beefier than the cable used for the pump on my last boat which had no such issue.. It seems like there is too great a voltage drop over the cable run and I am wondering if it is possible to fit the pump near the stern far closer to the batteries to reduce this factor.

 

Before taking any rash steps though I thought i would ask you knowledgeable folk if theres any glaring reason why this cannot be pursued, with the boat always slightly bow up and the potential pump fitting spot literally on the base plate it should still be gravity fed to the pump which would be the only danger i can think of having the pump fitted so far away..

 

any advice greatefully received!

 

merry christmas!

[NMEA]

I would check all the connections are "bright & tight" first, also though you have 6mm2 conductors, what is that connected to and how long is the run from 12v battery terminal to 0v battery terminal? Also, have you checked the voltage at the pump as it starts up?

Edited December 22, 2014 by NMEA

[Phil Ambrose]

I'm always suspicious of household cable when used in boats, myself I would look at rewiring in multi strand conductor and beefing up the size, I always go OTT with size and have never had voltage drop issues, don't forget for the purpose of calculating voltage drop your cable run should be out and back.

Phil

[BargeeSpud]

Simple test, bypass the switch/circuit breaker if you can & if the dimming goes away when you activate the pump, you will know that that is where your voltage drop is coming from. If the lights still dim, then hang in there 'til the new batteries arrive! I had a similar drop problem with my Eberspacher, some 2v, & I had to permanently bypass the switch/fuse & hook up directly to the batteries via my isolation switch & inline fuse.

 

Good luck & I hope its as simple as fitting the new batteries.

[b0atman]

Greenie for post 3 that is way to go too many boats have under sized cable and suffer from volt drop .

There are good sites online that will give you cable sizing to get zero volt drop.

Post 4 I do not understand why should the switch/circuit breaker be the cause ?

[NMEA]

I had a similar drop problem with my Eberspacher, some 2v, & I had to permanently bypass the switch/fuse & hook up directly to the batteries via my isolation switch & inline fuse.

 

That's how they should be cabled in anyway, never via a switch or panel, either direct to the terminals or the live side of the isolator switch.

[DeanS]

My lights flicker when the pump kicks in.

It doesn't bother me much. it could just be the type of LED lighting you're using...I'm almost convinced that 12V halogen bulbs would be less sensitive.

;-)

[NMEA]

Greenie for post 3 that is way to go too many boats have under sized cable and suffer from volt drop .

There are good sites online that will give you cable sizing to get zero volt drop.

Post 4 I do not understand why should the switch/circuit breaker be the cause ?

Zero volt drop (under load) is almost unacheavable except with massive cables, the acceptable for marine electronics is 3%, for all other stuff like pumps, motors and incandecant bulbs a drop of 10% is acceptable. Even a proper marine Eber or Webo has an operating voltage level of under 11v.

[NMEA]

I always find using tables a bit ass about face, the simplest way to specify cable is to decide the voltage drop acceptable for a device and use the following simple formula to get the circular mill.

 

CM = K x I x L ÷ E

Where:

K = 10.75 (resistivity constant for copper)

I = Current (amps)

L = Round Trip Wire Distance (feet)

E = Maximum Voltage Drop Allowed (volts)

[BargeeSpud]

That's how they should be cabled in anyway, never via a switch or panel, either direct to the terminals or the live side of the isolator switch.

 

That's what happens when you rely on a boatbuilder, who ends up going bust near the end of your build, to install the damn thing! I wouldn't mind, but it worked perfectly for quite a few years.

 

BTW, my D7W installation manual makes no mention of specific wiring connections to a power source, either direct to the batteries or via fused switches/circuit breakers.

Edited December 22, 2014 by BargeeSpud

[ditchcrawler]

Bear in mind the OP is not suffering volt drop at the pump, so the cable length and size not a factor, he is suffering volt drop on the feed to his led lighting circuits when the pump cuts in, so as others have pointed out is drop in the distribution panel of the feeds from the battery to it, could be on positive or negative, In fact good size conductors to the pump could make it more noticable as if they weren't so robust there would be more volt drop along them and less on the supply.

[NMEA]

 

BTW, my D7W installation manual makes no mention of specific wiring connections to a power source, either direct to the batteries or via fused switches/circuit breakers.

Do you have a marine unit?

To quote from my factory marine installer's D7W manual.

 

"2 core harness (red and brown).

- Connect red wire to vessel battery (+), use ring

terminal provided.

- Connect brown wire to vessel battery (-), use ring

terminal provided."

[NMEA]

 

That's what happens when you rely on a boatbuilder,

Yes, NB buiders should stick to what they are good at...welding. Some of the least compliant installs I have seen have been done by builders.

Edited December 22, 2014 by NMEA

[sparrowcycles]

Thankyou all!

 

what speedy and varied replies already!

 

Thanks ditchcrawler, id not thought of it in that way.. It makes great sense when spoken by another!

I was worried by the size of the busbar on the distribution panel, it looked way too thin so i soldered a high strand wire along its length to add capacity as it were but it could still be insufficient..

 

The pump is indeed wired through the distribution panel, now i know that is not the norm i will break it out and connect straight to the switched side of the battery isolator! The pump is rated at 11a so im wondering what the best way to fit an inline fuse will be, would you recommend in a holder down by the pump itself? The 6mm connects to a thinner but higher strand cable for a few inches before the pump, a fuse could easily be fitted there.

 

 

Bear in mind the OP is not suffering volt drop at the pump, so the cable length and size not a factor, he is suffering volt drop on the feed to his led lighting circuits when the pump cuts in, so as others have pointed out is drop in the distribution panel of the feeds from the battery to it, could be on positive or negative, In fact good size conductors to the pump could make it more noticable as if they weren't so robust there would be more volt drop along them and less on the supply.

 

 

 

I will also check the voltage across the pump when actuated, if just to see some numbers regarding whats happening down there

 

 

I always find using tables a bit ass about face, the simplest way to specify cable is to decide the voltage drop acceptable for a device and use the following simple formula to get the circular mill.

 

CM = K x I x L ÷ E

Where:

K = 10.75 (resistivity constant for copper)

I = Current (amps)

L = Round Trip Wire Distance (feet)

E = Maximum Voltage Drop Allowed (volts)

 

thanks NMEA.. i shall be using this formula for a lot of my rewiring from now on!!

 

 

 

I picked up some 35mm battery flex for the new battery connections, im hoping that will make a difference too!

 

 

 

Im down south for xmas/ new year but i will be on it as soon as im back in liverpool and will keep you all posted..

 

many thanks