Relay for bildge pump

[Discovery 15797]

Originally Posted by GeneM

Quote - "Truth be told...my primary bilge pump is now directly wired w/o a switch. My secondary bilge which was automatic is now switched and safety wired to the auto position."

Question1 - I thought it was important to use a two-position switch for auto (float switch) and then manual on. I have lights that tell me when a pump is operating, so manual-on is a good test rather than lift my 5 floats and ask my wife to observe the lights. Do you have no switch?

Question2 - My pumps are direct to the battery, but each one goes through a fuse. I'm considering eliminating the fuses, because who cares if the wire burns when sinking is a concern. Do you have fuses?

Question3 - My float switches are not heavy duty. Thanks for the info on that. I have wondered why normal floats have very thin wires (maybe 20 gauge). Maybe a relay is good to lower the current through the float. Comment?

I suspect you are asking me so I'll chime in.

First, virtually all commercially made switches for bilge pumps (Johnson, Rule, Water Witch, SeaDog, Aqualarm, Blue Guard, etc) are 3 positions switches (on-off-auto). There is one company that I know that specifically makes an Auto-Manual switch.

My bilge pump is wired similar to New Wire Marine's #1 Human Error Proof wiring diagram. I use a Water Witch electronic switch to activate the pump instead of float switches (which are complete crap and prone to failure). The switch is not Auto - Manual, the switch is Manual - Off. In the off position the pump is in automatic mode. I also have a high water alarm and a bilge cycle counter.



YES...USE FUSES! Fuses are there in case the switch get stuck in the closed position and the pump runs continuously or the pump or switch develops a short. If not fused, your boat will burn and then sink. (The only thing that would cause me to abandon my boat before the water is above the top of the cabin is an uncontrollable fire onboard.)

WRT switches...I'd invest in an electronic switch. I'm familiar with Water Witch and very happy since I installed it 10 years ago. Johnson also makes something similar.

My secondary bilge pump uses a Whale electronic switch to activate the pump in automatic mode. It's never been used in the 1.5 years since it's been installed. I also had a typical 3 position switch that was installed during manufacture. It is 'safety wired' in the Auto position, but I do 'break the seal' to test the pump every 3 months.

By the way...a relay does not lower the current draw of a pump, and I would never put a relay in a bilge pump circuit...it's an unnecessary potential point of failure.

[stormalong]

Originally Posted by Discovery 15797

My bilge pump is wired similar to New Wire Marine's #1 Human Error Proof wiring diagram. I use a Water Witch electronic switch to activate the pump instead of float switches (which are complete crap and prone to failure). The switch is not Auto - Manual, the switch is Manual - Off. In the off position the pump is in automatic mode. I also have a high water alarm and a bilge cycle counter.



YES...USE FUSES! Fuses are there in case the switch get stuck in the closed position and the pump runs continuously or the pump or switch develops a short. If not fused, your boat will burn and then sink. (The only thing that would cause me to abandon my boat before the water is above the top of the cabin is an uncontrollable fire onboard.)

Wire marine's #1 (recommended way) uses an extra, unnecessary fuse. Maybe this is an attempt to have redundancy in case one fuse fails. This is poor planning, as is using a fuse instead of a circuit breaker. Why, you ask? Because if one fuse blows and you use the manual switch without clearing the problem the other fuse blows and now you have to hunt for a spare fuse and put it in and you still have not solved the problem. With a circuit breaker all you have to do is reset the circuit breaker. If it won't reset you know you have some other problem that must be resolved before you can pump the bilge. Also, you may have no idea that the fuse if blown until water starts coming over the floorboards. With a circuit breaker you have a visual indication that it has popped.

One more thing: Add a high water alarm that is independent of the circuit breaker (here a fuse is probably fine - that's how mine is). The high water alarm can use a low current magnetic reed float switch which comes in a plastic case to prevent debris from clogging the switch. Magnetic reed switches are very reliable, coupled to a solid state alarm they are virtually foolproof.

PS. The second diagram is much more complicated than it needs to be. An SPST switch across the float switch changes to manual. And again, the circuit breaker is the off switch.

[Discovery 15797]

Originally Posted by stormalong

Wire marine's #1 (recommended way) uses an extra, unnecessary fuse. Maybe this is an attempt to have redundancy in case one fuse fails. This is poor planning, as is using a fuse instead of a circuit breaker. Why, you ask? Because if one fuse blows and you use the manual switch without clearing the problem the other fuse blows and now you have to hunt for a spare fuse and put it in and you still have not solved the problem. With a circuit breaker all you have to do is reset the circuit breaker. If it won't reset you know you have some other problem that must be resolved before you can pump the bilge. Also, you may have no idea that the fuse if blown until water starts coming over the floorboards. With a circuit breaker you have a visual indication that it has popped.

One more thing: Add a high water alarm that is independent of the circuit breaker (here a fuse is probably fine - that's how mine is). The high water alarm can use a low current magnetic reed float switch which comes in a plastic case to prevent debris from clogging the switch. Magnetic reed switches are very reliable, coupled to a solid state alarm they are virtually foolproof.

The fuse in the switch side of the circuit is to protect in case the pump shorts when the switch is activated. Just as the fuse in line with the float switch/pump part of the circuit protects against a short in either the pump or the float switch. Basic electrical wiring principles...always protect the power source in case of a short.

In your scenario, if the fuse in the float switch / pump circuit is blown, either the float switch or the pump is shorted. (That will also trip the CB.) If I turn on the rocker switch in the alternate circuit and the pump runs I immediately know the float switch is shorted. If that fuse blows...the pump is shorted. Now...let's see you try that with your circuit breaker setup!


If a short occurs it doesn't really matter if you have a fuse or circuit breaker. In the case of a short if you reset a tripped CB it's gonna blow again! Shorted electrical conductors are quite simple that way. Until you fix the problem there is no difference between a fuse and a CB (other than you might expend a few fuses if you can't quickly isolate the problem).

Also, if a circuit breaker trips unexpectedly (usually when something is powered on and the surge hits) and resetting the CB works then
1. it's a faulty CB
2. it's a CB that's going bad (yes, they can go bad; esp. when used as switches)
3. There's TOO MUCH LOAD on that CB (which is often the case)
4. The CB is incorrectly sized for the load

(BTW...Fuses solve the problem of surges with slow blow fuses. I recommend fast blow for electronics, slow blow for motors.)

When I rewired my boat I changed everything to fuses. Why? Because I've seen too many rats nests on the electrical panels on boats. Circuit breakers with 6 or more wires attached. I've seen a Circuit breaker for a GPS that also had an inline fuse between the breaker and the GPS unit. I've seen people cut out the inline 1 amp fuse and wire the electronic component to a 10 amp circuit breaker.

Also, when I rewired my electrical system every unique device and system has it's own fuse (one for the cockpit chartplotter, one for the nav station chartplotter, one for the primary bilge, one for the secondary bilge...and so on). The lights are localized on fuses...if a light in the forward cabin shorts the "forward cabin light fuse" blows but all other cabins continue to work; I know immediately where the problem is and just have to identify which of the 3 lights in that cabin failed. Easy troubleshooting. BTW...in 7 years....I've never had a single fuse blow. My spare fuses are kept in the same electrical cabinet where the BlueSea fuse boxes are mounted. The old tired 'fuse' arguments are just that...old and tired.

So, since my high water alarm is on a separate circuit from the pump circuit I will know immediately if the pump fails. Even with a circuit beaker panel I would recommend putting all safety devices (CO2 detector, LP Gas detector/shutoff, bilge alarm, etc) on individual circuits). I also said I have a secondary bilge pump that is also on its own separate circuit, so water coming over the floor boards it means Moby Dick stove-in my hull, or a submarine surfaced underneath me.

I don't really want to debate the merits of fuses vs. circuit breakers. I've made my decision and I'm happy with it. I am not a zealot one way or the other. If you like looking at circuit breaker panels...great...it's your boat. For me, my circuits are simple, isolated, and quite reliable, and hidden. (And yes, I have 2 master rocker switches that activate Blue Sea Remote switches..one for starting battery, one that kills all house circuits EXCEPT the bilge pumps, and the refrigeration system.)

[stormalong]

Originally Posted by Discovery 15797

The fuse in the switch side of the circuit is to protect in case the pump shorts when the switch is activated. Just as the fuse in line with the float switch/pump part of the circuit protects against a short in either the pump or the float switch. Basic electrical wiring principles...always protect the power source in case of a short.

In your scenario, if the fuse in the float switch / pump circuit is blown, either the float switch or the pump is shorted. (That will also trip the CB.) If I turn on the rocker switch in the alternate circuit and the pump runs I immediately know the float switch is shorted. If that fuse blows...the pump is shorted. Now...let's see you try that with your circuit breaker setup!


If a short occurs it doesn't really matter if you have a fuse or circuit breaker. In the case of a short if you reset a tripped CB it's gonna blow again! Shorted electrical conductors are quite simple that way. Until you fix the problem there is no difference between a fuse and a CB (other than you might expend a few fuses if you can't quickly isolate the problem).

Also, if a circuit breaker trips unexpectedly (usually when something is powered on and the surge hits) and resetting the CB works then
1. it's a faulty CB
2. it's a CB that's going bad (yes, they can go bad; esp. when used as switches)
3. There's TOO MUCH LOAD on that CB (which is often the case)
4. The CB is incorrectly sized for the load

(BTW...Fuses solve the problem of surges with slow blow fuses. I recommend fast blow for electronics, slow blow for motors.)

When I rewired my boat I changed everything to fuses. Why? Because I've seen too many rats nests on the electrical panels on boats. Circuit breakers with 6 or more wires attached. I've seen a Circuit breaker for a GPS that also had an inline fuse between the breaker and the GPS unit. I've seen people cut out the inline 1 amp fuse and wire the electronic component to a 10 amp circuit breaker.

Also, when I rewired my electrical system every unique device and system has it's own fuse (one for the cockpit chartplotter, one for the nav station chartplotter, one for the primary bilge, one for the secondary bilge...and so on). The lights are localized on fuses...if a light in the forward cabin shorts the "forward cabin light fuse" blows but all other cabins continue to work; I know immediately where the problem is and just have to identify which of the 3 lights in that cabin failed. Easy troubleshooting. BTW...in 7 years....I've never had a single fuse blow. My spare fuses are kept in the same electrical cabinet where the BlueSea fuse boxes are mounted. The old tired 'fuse' arguments are just that...old and tired.

So, since my high water alarm is on a separate circuit from the pump circuit I will know immediately if the pump fails. Even with a circuit beaker panel I would recommend putting all safety devices (CO2 detector, LP Gas detector/shutoff, bilge alarm, etc) on individual circuits). I also said I have a secondary bilge pump that is also on its own separate circuit, so water coming over the floor boards it means Moby Dick stove-in my hull, or a submarine surfaced underneath me.

I don't really want to debate the merits of fuses vs. circuit breakers. I've made my decision and I'm happy with it. I am not a zealot one way or the other. If you like looking at circuit breaker panels...great...it's your boat. For me, my circuits are simple, isolated, and quite reliable, and hidden. (And yes, I have 2 master rocker switches that activate Blue Sea Remote switches..one for starting battery, one that kills all house circuits EXCEPT the bilge pumps, and the refrigeration system.)

NO. You only need one fused wire to the battery followed by the two switches. There is no need for two fuses. Look at the circuit again. If the float switch is shorted the pump runs continuously. There is no negative connection to the float switch so no possible direct short.

The magnetic circuit breakers used on boats are very reliable. They have their origins in the electronics and computer industry. There is a reason why fuses are not used in buildings anymore and the same logic applies even more to boats. Plain and simple circuit breakers are resetable, fuses have to be replaced. If I am in mid ocean and don't have a replacement for a blown fuse I might bypass the fuse protection. How many home fuses were bypassed with a penny and then left that way, only to have the house burn down.

[Discovery 15797]

Originally Posted by stormalong

NO. You only need one fused wire to the battery followed by the two switches. There is no need for two fuses. Look at the circuit again. If the float switch is shorted the pump runs continuously. There is no negative connection to the float switch so no possible direct short.

The magnetic circuit breakers used on boats are very reliable. They have their origins in the electronics and computer industry. There is a reason why fuses are not used in buildings anymore and the same logic applies even more to boats. Plain and simple circuit breakers are resetable, fuses have to be replaced. If I am in mid ocean and don't have a replacement for a blown fuse I might bypass the fuse protection. How many home fuses were bypassed with a penny and then left that way, only to have the house burn down.

You're correct wrt to the wiring of the pump/float switch in the example. Again, I despise those silly float switches.

I should have been clearer to indicate that the Water Witch electronic switch that I use has a ground wire from the Water Witch itself, so if in my particular case my Water Witch had an internal short for some reason, the fuse in that part of the circuit would blow. (I apologize for the confusion; I was trying to correlate how my system is actually wired using a simplistic example instead of a schematic.)

The same problems that many boats face with overloading a limited number of circuit breaker panels in stock boats were the same problems caused by fuses in homes. Most homes built using fuses had a limited number of fused circuits for the entire house. Hence circuits were overburdened, wrong size fuses were used, so standards changed to prevent stupid people from burning down their house.

I wonder how many people take time to investigate why a breaker tripped prior to resetting it, and then after resetting it never gave it an after-thought...until it tripped again?

As I said, I'm not going to debate the fuse vs. circuit breaker issue. There are positives and negatives on both sides of the argument. I made my choice, I've traveled several thousand coastal and ocean miles with fuses in my boat, I'm satisfied with the integrity and simplicity of my electrical system, and I'm not trying to convince anyone to ditch their precious circuit breaker panels.

[lonesoldier0408]

Originally Posted by slug

Read it

And yet, municipalities maintain the infrastructures to, repeatedly, have, “Accidental Discharge of Sewage, etc.....”

[GordMay]

Definition of Relay Terminology ➥ https://media.digikey.com/pdf/Other%...cal%20Info.pdf

Pickup Voltage
The pickup voltage is the minimum voltage, across the coil, needed to close the switch. For example, for one particular "12V" relay, the pickup voltage is 7.5V.
Dropout Voltage
The dropout voltage is the maximum voltage, below which, a closed switch will open. For example, for the same "12V" relay, the dropout voltage is 3.3 V.

Why are pickup and dropout voltages so different (or different at all), you might ask? The equation for the force generated on the armature is:
F = 2*pi*(N^2) / (A * (R0 + x/A)^2)
Where:
N is ampere-turns
A is area of pole piece
x is distance between pole-piece and armature
R0 is reluctance of the iron pieces
The key point, is that the force is stronger, when the distance x is smaller (when the relay is closed), so lower "ampere-turns" (current) is needed to generate the same force.

Heat
The resistance of the copper wire, used in the coil, increases with temperature, so the current through the relay will decrease, if the voltage across the coil is held constant. The magnetic field strength is directly proportional to current, so the pickup and dropout voltages do vary with temperature.
Wetting Current
Having too low a current, through the contacts, leads to reliability problems. A minimum "wetting current" is useful, to clean oxide coatings off of the contacts. Oxide can build up on contacts, to such a degree that an electrical connection is not made, even when the contacts are closed.

[gwyn]

I use the KISS and be safe principles.

Buy a 3 way bilge pump switch with alarm that has the facility for connecting two separate float switches. They are not expensive. One float at the bottom of the bilge and one float above the level at which the first one triggers. The top one stays dry nearly all the time so is very reliable as a backstop. Got mine from ASAP Supplies in the UK, part no. 710264.

[CharlieJ]

There are a lot of misconceptions about “bilge pumps” being promulgated on the docks and repeated in this thread.

Fallacy #1: “Bilge” pumps should be sized to dewater a boat should the hull be compromised; e.g., holed, dropped shaft, etc.
Fact: Using fluid dynamics, a 2 inch diameter hole 3 feet below the waterline will allow 139 gallons per minute into the boat. That is a flooding rate of 8,340 gallons per hour. Note that this is only the initial T= 0 rate of flooding as the hole will be subjected to more head as the boat sinks lower in the water. At 8.6 lb/gallon, the boat will take on 1,195 lb/minute or 71,724 lb/hour. There are no “bilge pumps” on the chandlery shelf that will meet this challenge.

Fallacy #2: Do not put over current protection in the B+ feed to a bilge pump.
Fact: Overcurrent protection is required by US and European standards to protect the circuit (wiring) and, in the case of a centrifugal pump, is to be sized IAW the pump manufacturer’s specifications to protect from the possibility of a locked rotor allowing the pump to overheat, melt and possibly cause a fire.

Fallacy #3: Relays in bilge pump B+ are unnecessary, dangerous, another point of failure, etc.
Fact: Relays are sometimes the best alternative to supplying bilge pumps with a reasonable source of power without excessive voltage drop. A single trunk line can be run directly from the house bank B+/B- buses to the compartment furthest from the battery bank. Each compartment’s bilge pump derives its power, via a relay, from the trunk lines. The bilge pump control switches at the operating stations (helm, flying bridge, etc.) send a low current signal to the relays over relatively small AWG wire to command the relays. This schema saves a huge amount of large diameter wire. And, yes, any time another component is added to a system, another point of potential failure is created. Quality components and quality workmanship can reduce the probability of failure to near zero.

Opinions:
1. Spring return bilge pump control switches should not be installed on any boat. A far better arrangement is a single pole, double throw switch with no OFF position. My reasoning is that the OFF position is dangerous as the switch can inadvertently be left in that position. Yes, there are guards.
Regarding not having the spring return (momentary) feature: As shown above, a normal “bilge” pump will not save the boat in a true flooding incident. The source of the leak must be found and mitigated. If the float (mechanical or electrical) switch has failed then the only way to keep the pump running is to activate the control switch. If it is a spring return (momentary) switch, one of the crew is going to operate the switch and will not be available to search for and mitigate the source of flooding.
2. Contura type switches should not be used to control bilge pumps. They are attractive but are very easy to bump and activate a pump as their construction provides very little tactile feedback to alert the operator that the switch position has been changed. A toggles switch takes more force to operate and provides the tactile feedback required for critical systems.
3. The WaterWitch electronic switch is superior to mechanical float switches and is preferable to the UltraSwitch because its operation can be tested without unshipping the switch.
4. Every boat of any size should have a bilge high level alarm installed.

[rslifkin]

Originally Posted by CharlieJ

Fallacy #1: “Bilge” pumps should be sized to dewater a boat should the hull be compromised; e.g., holed, dropped shaft, etc.
Fact: Using fluid dynamics, a 2 inch diameter hole 3 feet below the waterline will allow 139 gallons per minute into the boat. That is a flooding rate of 8,340 gallons per hour. Note that this is only the initial T= 0 rate of flooding as the hole will be subjected to more head as the boat sinks lower in the water. At 8.6 lb/gallon, the boat will take on 1,195 lb/minute or 71,724 lb/hour. There are no “bilge pumps” on the chandlery shelf that will meet this challenge.

This one very much depends on the boat. In my case, the biggest hull penetrations are my 1.5 inch shafts, about 1.5 feet down. Even if we call it 2 feet to account for some settling in the water, that's 62.5 gal / minute. Let's assume the maintenance pump in the bilge is good for 300 gal/hr in the real world, then we add a pair of Rule 3700s as emergency pumps, which we'll say are good for 2200 gal/hr each in real world conditions. That gives us 4700 gal/hr of pumping capacity, which is 78.3 gal/minute, more than that shaft hole will flow. It'll make a big mess until you plug the hole with something, but it won't sink the boat and you'll have plenty of time to deal with the issue.

[thereefgeek]

I don’t trust mechanical bilge switches, so we installed electronic switches, pump cycle counter, and high water alarm from https://waterwitchinc.com/
Sealed units, no moving parts. The switches turn on when water completes the circuit. We have dual pumps, and if the backup high-water pump kicks on and can’t keep up, the alarm goes off in the main cabin, and also out in the cockpit. Simple wiring and no relays needed.

https://m.youtube.com/watch?v=bmg46UVb-I8

https://m.youtube.com/watch?v=9A13D57oaQ8

We also have two independent manual bilge pumps; one under the floorboards in the main salon, and one in the cockpit that can be operated from the helm.

I’m a “Belt & Suspenders” kind of guy when it come to keeping our home and everything we own from ending up at the bottom of the ocean.

https://m.youtube.com/watch?v=Cc0P-7RWo2M

[skenn_ie]

A "freewheel" diode works wonders for reliability too.

[Bawlmer]

I don't know how adding complexity to a system can make it more reliable.

[CharlieJ]

A bit more clarification and discussion about bilge pump facts.

The Rule 3700 is rated at 3700 gph, at 0 ft of discharge head and 13.6 VDC; 2900 gph at 3.35 ft of discharge head and 13.6 VDC and 2400 gph at 6.7 ft of discharge head and 13.6 VDC. {Source: Rule (Xylem) Standard Bilge Pump Instruction Manual © 2012 Xylem, Inc. 950-0518 Rev. C 10/2012}

Discharge head has two components; the elevation change from the pump discharge port to the discharge of the piping/hose and the friction in the piping/hose. With a nominal 3' of elevation change (bilge to overboard) and clean, smooth (not corrugated) tubing, a conservative discharge head of 6 to 10 feet is not unreasonable.

The Rule family of pumps base their performance on a supply voltage at the pump of 13.6 VDC. For a 12 VDC system; this equates to a LA battery on float which means that a charging source is operating and zero voltage drop between the battery and the bilge pump!. Zero voltage drop is impossible.

With <13.6 VDC being applied to the pump, the impeller will not be rotating at the specified number of rpm and the specified quantity of water will not be pumped. Note that the spec sheet shows a load of 15.5 A @ 12.0 VDC and 20 A @ 13.6 VDC. Why? Centrifugal pumps can be characterized by pump affinity laws which state, for rotational speed of the impeller, that the flow rate is directly proportional to the impeller rotational speed; e.g., halve the rotational speed, halve the flow rate and rotational speed of the impeller is directly proportional to the voltage supplied at the pump.

So, what does this all mean? The capacity of a centrifugal bilge pump to dewater a boat is strongly dependent on the voltage supplied at the pump. My guess is that a nominal Rule 3700 with a 20 foot circuit (round trip) with 13.6 VDC (charging source operating) at the manual control switch wired with AWG 8 to the AWG 14 pump pigtails will yield 13.2 VDC at the pump. Impeller rotational speed is directly proportional to voltage and pump flow is directly proportional to impeller rotational speed therefore this system will deliver 13.6 VDC less cumulative voltage drops, (13.2/13.6) x 2400 gph = 2329 gph assuming a max. of 6.7 foot discharge head. This will keep up with a 1" diameter hole about 3.5' below the waterline.

If there is no charging source operating, and the battery bank is fully charged, than the pumping capacity becomes 12.6 VDC less cumulative voltage drops, (12.3/13.6) x 2400 gph = 2170 gph. This will keep up with a 1" diameter hole 3' below the waterline.

So, to summarize:
1. Commodity bilge pumps are not realistically rated,
2. voltage drop must be minimized to maximize pumping capacity, hence the reason to use relays in some applications,
3. discharge head must be minimized to maximize pumping capacity,
4. commodity bilge pumps will probably not keep up with a significant water in flow,
5. and, finally, for a true flooding event, a properly designed and installed bilge pump system will help mitigate the flooding and buy the crew time to find the source of the flooding and slow the inflow by any means possible.

[skenn_ie]

A relay takes the high current, and particularly, the inevitable spark when it opens, away from the relatively delicate float switch.