12v supply

[martinriches]

I have just replaced the fuel pump that tops up the day tank.According to the instructions it should not be used when the engine is running as the voltage may be to high.How can I get a 12v supply from the battery's when the engine is running? [It is 4.5 amp]
The pump is Rule iL280P

Martin

 

[FWB]

How about a stabilised 12V supply like this perhaps..
http://www.boatlamps.co.uk/contents/en-uk/d148.html

 

[pvb]

How big's the day tank? As the pump is capable of around 1000 litres an hour, can't you fill the day tank quickly when the engine's not running?

 

[lw395]

Can you run it from a battery that is easily taken off charge, e.g. a house battery that can be disconnected?

If the day tank is good for a whole day or so, some people adopt the discipline of pumping it when the engine is shut down for daily oil check etc.

Alternatively, a regulator will do the job. If the motor draws 4.5A continuous, you will want a peak rating of rather more than that, say 10A to cope with starting?

 

[sarabande]

.According to the instructions it should not be used when the engine is running as the voltage may be to high.How can I get a 12v supply from the battery's when the engine is running? [It is 4.5 amp]
The pump is Rule iL280P

Martin

There will be some voltage drop from the distribution system to the pump when the engine is running, so even if the battery is at a nominal 14v or so, the pump will not suffer. It is more important to make sure it does not run dry, as it will then overheat from turning too fast.

Perhaps check the battery voltage when the engine is running. Likely to be highest V when charging starts, but this should quickly settle down. If over 14.5 when the engine has been running for a while then there are other issues you need to consider than one small pump.

 

[prv]

I have just replaced the fuel pump that tops up the day tank.According to the instructions it should not be used when the engine is running as the voltage may be to high.

Sounds like it's not fit for purpose to me :nonchalance:

Pete

 

[pvb]

Perhaps check the battery voltage when the engine is running. Likely to be highest V when charging starts, but this should quickly settle down.

Rather the other way around! Battery voltage is lower when charging of a depleted battery starts, and climbs as the charging progresses.

 

[martinriches]

How big's the day tank? As the pump is capable of around 1000 litres an hour, can't you fill the day tank quickly when the engine's not running?

I get about 4 hours running from the day tank so occasionally I might need to use when the engine running. I will look into fitting a regulator. Whare might I find a suitable one?

Martin

 

[sarabande]

Interesting. Mine seems to produce a high voltage to start, and decline quite quickly. Perhaps it has to do with the state of a battery's charge ?

 

[sarabande]

I agree with prv; if it can't work on a normal "12v" system, with its normal variations higher and lower, then the pump is NFP.
Having used the LVP model of that pump for years on the farm to transfer diesel from a big tank to tractors, all I can say is that it works with whatever voltage the tractor throws at it.

I really don't think you need a regulator. Check the system voltages at the various stages of stationary and running, then come back with data.

 

[pvb]

Interesting. Mine seems to produce a high voltage to start, and decline quite quickly. Perhaps it has to do with the state of a battery's charge ?

Yours sounds unique! Does your alternator have an external regulator capable of dropping to a float voltage?

 

[pvb]

I get about 4 hours running from the day tank so occasionally I might need to use when the engine running. I will look into fitting a regulator. Whare might I find a suitable one?

Rather than a regulator, perhaps just putting a diode in the supply would drop the voltage enough for it not to be a problem. If sarabande's experience with a similar pump is anything to go by, the voltage may not be a problem anyway, especially for shortish periods of operation.

 

[[3889]]

Sorry for drift but what's the idea behind a day tank? Is it to facilitate gravity feeding?

 

[martinriches]

Sounds like it's not fit for purpose to me :nonchalance:

Pete

prv

You might be right but it is a direct replacement [same model no.]the original is about 10-15 years old.It has been blowing fuses .[ now drawing about 12a when it should be 4.5a] could be the over voltage has damaged it though.

Am I right in thinking a 6o watt regulator would give me 5a ?

Martin

 

[lw395]

prv

You might be right but it is a direct replacement [same model no.]the original is about 10-15 years old.It has been blowing fuses .[ now drawing about 12a when it should be 4.5a] could be the over voltage has damaged it though.

Am I right in thinking a 6o watt regulator would give me 5a ?

Martin

If it's drawing a lot of current, is that because it's a high capacity pump with restrictive pipe work?
Is it trying to shove fuel through a filter quickly by any chance?

 

[rogerthebodger]

I have one of those pumps that I use for pumping out my dingy after rain. It is only a simple 12vdc motor so should not be damaged running up to 14volts for a short time (20 mins or so)

 

[martinriches]

Sorry for drift but what's the idea behind a day tank? Is it to facilitate gravity feeding?

Not sure as it came with the boat but don't think it was original equipment. When I replaced the pump I found that the fuel line to it was partially blocked I managed to clear it by blowing it through. Perhaps that's why it was fitted.

Martin

 

[martinriches]

It was still drawing 12a when I disconnected it though I found the pipe nearly blocked so it may have damaged it.

Martin

 

[sarabande]

something wrong somewhere, with a 50W motor drawing nearly 150W. Did it have a line fuse, or through the normal power distribution ?

 

[Jabs]

prv

You might be right but it is a direct replacement [same model no.]the original is about 10-15 years old.It has been blowing fuses .[ now drawing about 12a when it should be 4.5a] could be the over voltage has damaged it though.

Am I right in thinking a 6o watt regulator would give me 5a ?

Martin

Yes. BUT a 60w regulated supply will blow because the start up current will be much higher.

Tony.