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Old 19-08-2019, 16:46   #1
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12v raw water pump ideas

I want to pick the brains of some creative folks around here. I need to come up with a cheap, simple , and reliable solution for engaging a 12v centrifugal pump only when the engine is running. So it can be activated by either oil pressure or alternator.

I have a basic low oil alarm that is ground activated , meaning it isolates the ground once oil pressure has been achieved. Ideas for a solenoid that can be activated when the ground is removed ?

I have (2) 1 wire 100 alternators that are hooked directly to my batteries so the alternator output is hot all the time. Not sure how I could use this to activate a solenoid.

Let's hear your solutions.

I am trying replace my belt driven water pump">raw water pump with a 12 v one to make some room on the engine for another alternator (yes I want 3 alternators!) I have nothing but problems with my belt driven jabsco pump and this seems like a good solution .
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Old 19-08-2019, 16:50   #2
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Re: 12v raw water pump ideas

If it was my boat I would get a NO oil pressure switch, thus it would close when pressure is above a preset value something like 5 or 10 psi. This NO switch would activate a relay that powers the centrifugal pump. Good luck
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Old 19-08-2019, 16:58   #3
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Re: 12v raw water pump ideas

That is what I have installed now and would like to use. what I'm not familiar with is the relay or solenoid and could use some suggestions or examples of such things
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Old 19-08-2019, 17:00   #4
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Re: 12v raw water pump ideas

The question is really help me find a relay that will be activated when a circuit is disconnected. Then the pump circuit will be on my ignition circuit
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Old 19-08-2019, 17:04   #5
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Re: 12v raw water pump ideas

You should use a positive displacement pump for raw water cooling.

A centrifugal will probably not work well.
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Old 19-08-2019, 17:05   #6
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Re: 12v raw water pump ideas

So what you are looking for is a 12v nc (normally closed) relay. When the relay is not activated (current through the coil) the contacts are closed. There are tons out there.
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Old 19-08-2019, 17:20   #7
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Re: 12v raw water pump ideas

I have both types of pumps to try. I just thought the centrifugal style was more reliable for continuous duty, it's not uncommon for me to motor for days at time
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Old 19-08-2019, 17:24   #8
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Re: 12v raw water pump ideas

I am not very familiar with the difference between relay and solenoid. Would this relay activate a solenoid or can the relay supply 10-20 amps continuous
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Old 19-08-2019, 17:34   #9
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Re: 12v raw water pump ideas

A centrifugal pump will not prime if above the waterline, positive displacement pumps like the rotary vane will pump water or air equally well so are self priming. The belt driven pumps are also a simple method of matching the flow to engine speed.
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Old 19-08-2019, 17:42   #10
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Re: 12v raw water pump ideas

A solenoid is a very heavy duty relay. A common relay found on eBay or Amazon. The one shown says 80 amp, but I doubt it. $7 on eBay:
https://www.ebay.com/itm/12V-80A-5-P...wAAOSwdC5ceEl5
Search for 12v relay. Also at any auto parts store.



Your centrifugal pump will only self prime when below the water line and no loops in the plumbing. Otherwise you have to prime it every time. (Unless it has a rubber impeller that makes contact with the housing).





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Old 19-08-2019, 17:54   #11
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12v raw water pump ideas

A Centrifugal pump will work fine, but as has been noted it has to be below waterline, I use one for my generator and it works fine.
However my generator is a fixed RPM device, itís very likely that at idle there would be too much water flow.
Iíve considered this myself and I believe the answer is to use a ball valve connected to the throttle so that at idle the valve is pretty much closed off but wide open at 3/4 throttle or so.
I decided that the complexity wasnít worth it, but Iím pretty sure that you will need to turn down the water flow at idle.

I believe a solenoid is an electromagnet that moves a mechanical device, where a relay is an electromagnet that closes an electric circuit.
There are now relays available that are solid state and donít use electromagnets but thatís beside the point.
I think relay / solenoid is like engine / motor. Engine is supposedly an internal combustion machine, and a motor is electric.
But why is Detroit Motor City, and not Engine City then? In other words they are often used interchangeably.
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Old 19-08-2019, 17:54   #12
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Re: 12v raw water pump ideas

I am pleased that you have brought up this subject.
Without wishing to hijack your question, I have often wondered about the relative issues such as reliability, space availability, ease of access, belt maintenance, impeller maintenance, efficiency/performance and costs of the common belt-driven impeller systems to a 12v pump.

Regarding your actual question... You might already have a 12v fuel pump, lifting the diesel to a header tank, or priming the fuel system. This is probably already driven by a relay, and activated ON when the ignition key is turned...

Tim
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Old 19-08-2019, 17:59   #13
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12v raw water pump ideas

Quote:
Originally Posted by Karanga View Post
I am pleased that you have brought up this subject.
Without wishing to hijack your question, I have often wondered about the relative issues such as reliability, space availability, ease of access, belt maintenance, impeller maintenance, efficiency/performance and costs of the common belt-driven impeller systems to a 12v pump.

Regarding your actual question... You might already have a 12v fuel pump, lifting the diesel to a header tank, or priming the fuel system. This is probably already driven by a relay, and activated ON when the ignition key is turned...

Tim


Yes, but ideally you donít want water to flow until the engine is running, you donít want water flow to begin when the key is turned on.
On my generator the pump is connected to the generator output, so itís not turned on until the generator is up to RPM and the electric generator is online, so for a few seconds it runs with no water, which hurts nothing.

For a main engine the oil pressure switch is the easiest and most reliable way in my opinion, Hobbs meters have been run through oil pressure switches for Iíd guess almost a Century now. Itís a well proven method.
You may not even need a relay, but the very common automobile relays are 30 amp, and I doubt your pump is going to pull 30 amps, thatís quite a large pump. So a NO oil pressure switch and an automotive relay and your in business, but I still think your going to have to modulate flow with RPM.
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Old 19-08-2019, 18:11   #14
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Re: 12v raw water pump ideas

I presumed that the raw water is provided "in excess" through the heat exchanger. Temperature control is then carried out by the thermostat, regulating the flow of coolant water through the exchanger.

Does the raw water flow rate need to match the RPM of the engine?
And does it matter if there is raw water flowing from the time the key is turned on until the engine is running (and indeed reaches a temperature where there becomes a requirement of cooling)?
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Yes, but ideally you donít want water to flow until the engine is running, you donít want water flow to begin when the key is turned on.
On my generator the pump is connected to the generator output, so itís not turned on until the generator is up to RPM and the electric generator is online, so for a few seconds it runs with no water, which hurts nothing.

For a main engine the oil pressure switch is the easiest and most reliable way in my opinion, Hobbs meters have been run through oil pressure switches for Iíd guess almost a Century now. Itís a well proven method.
You may not even need a relay, but the very common automobile relays are 30 amp, and I doubt your pump is going to pull 30 amps, thatís quite a large pump. So a NO oil pressure switch and an automotive relay and your in business, but I still think your going to have to modulate flow with RPM.
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Old 19-08-2019, 18:19   #15
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Re: 12v raw water pump ideas

I'd hesitate to regulate flow by restricting intake with a valve due to the risk of inducing cavitation in the pump, might be safer to regulate the output.
Quote:
Does the raw water flow rate need to match the RPM of the engine?
And does it matter if there is raw water flowing from the time the key is turned on until the engine is running (and indeed reaches a temperature where there becomes a requirement of cooling)?
The flow must not flood the water muffler and possibly even up the exhaust to the engine, not a cooling issue. The raw water flow thru Hx is excessive to the needs engine cooling such that a thermostat is required on coolant to maintain temp of the block.
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