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Old 20-04-2020, 14:59   #1
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Relay for bildge pump

I've heard people here talk about using a relay with their float-switch controlled bilge pumps to improve overall reliability. In such a system, as I understand at least, the float switch feeds a relay and the relay energizes or de-energizes the pump instead of the pump being powered directly through the float switch.

I presume it's a smaller current flowing through the float switch that improves overall reliability but haven't seen any discussion, only statements by some that they use a relay in this manner.

I'm curious to hear thoughts about this.

I'm also interested in seeing what relays are being used for this application. A quick search of a couple of marine suppliers didn't turn up anything. I also tried to search this site for threads with pump "pump relay" in the title without success.

Thanks
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Old 20-04-2020, 15:54   #2
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Re: Relay for bildge pump

I wouldn’t put a relay in my bilge pump, the reason is it’s another point of failure, I would however install a very high quality float switch, one that has a design cycle life of in the millions at least, the Ultra float switch due largely to it having a reed switch meets this requirement.

I had a relay in the starting circuit of my starter, and I have one in the circuit of my fresh water pump, the reason is that the fresh water pump uses a small micro switch, the high current causes the switch to fail pretty quickly, replacing the switch is a lot of work.
The relay is designed to handle far more current than the pump pulls, and relay replacement is simply a plug in affair
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Old 20-04-2020, 15:57   #3
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Re: Relay for bildge pump

I'll be interested to see responses. I don't see how adding a relay in the middle could improve reliability. It seems like just one more thing to fail. Perhaps I don't know what the usual failure mode is for float switches. I have only seen mine fail mechanically, by the bearing becoming sticky. Lower current will not help with that.
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Old 20-04-2020, 16:42   #4
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Re: Relay for bildge pump

Quote:
Originally Posted by Nord Sal View Post
I've heard people here talk about using a relay with their float-switch controlled bilge pumps to improve overall reliability. In such a system, as I understand at least, the float switch feeds a relay and the relay energizes or de-energizes the pump instead of the pump being powered directly through the float switch.

I presume it's a smaller current flowing through the float switch that improves overall reliability but haven't seen any discussion, only statements by some that they use a relay in this manner.

I'm curious to hear thoughts about this.

I'm also interested in seeing what relays are being used for this application. A quick search of a couple of marine suppliers didn't turn up anything. I also tried to search this site for threads with pump "pump relay" in the title without success.

Thanks
A common continuous duty Pump relay

https://theelectricaldepot.com/relay...amps-br-1-each

Amp rating depends on the pump you wish to energize
These relays can be purchased at auto supply shops

20/30 amp is good for normal yacht size pumps

Typically a bilge pump is wired to a two position rotary switch

Position one .....manual pump on

Position two ... level sensor control auto pump function


full automatic pump functions are against the law

Hence two positions
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Old 20-04-2020, 17:02   #5
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Re: Relay for bildge pump

That's just a common Bosch style automotive relay, find at any auto parts store.
Or just lift the hood on your buddies car and swipe one from rhe fuse box.
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Old 20-04-2020, 19:36   #6
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Re: Relay for bildge pump

The bilge switch is the weakest link on the bilge pump system. Using a relay is not a bad idea in itself but the relay have to be protected from voltage surge with a MOV ( Metal oxyde varistor).
When a relay or a switch is used to control an inductive device ( ex: bilge pump motor), the energy stored in the inductance in the device will subject the switch contacts to a high voltage when the switch opens. When the switch contacts open, the contact gap is initially small. Arcing across this contact gap can occur immediately after the switch opens. This can happen in resistive as well as inductive loads, but inductive loads generate a higher voltage and this causes increased arcing. Increased arcing decreases switch and relay life.

Additional information on the subject:https://library.automationdirect.com...issue-18-2010/
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Old 20-04-2020, 21:07   #7
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Re: Relay for bildge pump

Quote:
Originally Posted by slug View Post

Typically a bilge pump is wired to a two position rotary switch

Position one .....manual pump on

Position two ... level sensor control auto pump function


full automatic pump functions are against the law

Hence two positions
If you are going to state 'it's the law' or 'it's against the law,' please reference (link) the specific law and to which country it is applicable.

An outdated method was typically to include a 3 position switch inline with the bilge pump. (auto - off - manual), and some manufacturers such as SeaDog, Johnson, & Rule still make such switches.

However, according to the most recent ABYC standard ABYC H-22 the automatic bilge pump must be operable when ALL panel switches and battery selectors are to the OFF position. Here is an example.

I verified this with 2 different surveyors after 1 told me I had to remove my switch and wire directly to the battery. The insurance co. also confirmed as a condition for insurability.

(The reason for the change was that too many chuckleheads either rewired their boats with the bilge circuit connected to the main battery switch, and/or the 3 position switch was inadvertently switched to the off position when the owners left the boats and the boats flooded/sank.)

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.
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Old 20-04-2020, 21:32   #8
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Re: Relay for bildge pump

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Originally Posted by Discovery 15797 View Post
If you are going to state 'it's the law' or 'it's against the law,' please reference (link) the specific law and to which country it is applicable.

An outdated method was typically to include a 3 position switch inline with the bilge pump. (auto - off - manual), and some manufacturers such as SeaDog, Johnson, & Rule still make such switches.

However, according to the most recent ABYC standard ABYC H-22 the automatic bilge pump must be operable when ALL panel switches and battery selectors are to the OFF position. Here is an example.

I verified this with 2 different surveyors after 1 told me I had to remove my switch and wire directly to the battery. The insurance co. also confirmed as a condition for insurability.

(The reason for the change was that too many chuckleheads either rewired their boats with the bilge circuit connected to the main battery switch, and/or the 3 position switch was inadvertently switched to the off position when the owners left the boats and the boats flooded/sank.)

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.


Read it
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Old 20-04-2020, 23:00   #9
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Re: Relay for bildge pump

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Originally Posted by slug View Post
Read it
Hmm...I read it...I've re-read it...and I even referred to the real law (not an image of the placard) and electronically scanned for the word "automatic."

Guess what...that word is not in the laws. Even the Federal Water Pollution Control Act (regulation) does not contain the word "automatic," and only 1 instance of the word "bilge."

BTW...the specific US Federal Law is 33 CFR Section 151.10 and 33 CFR Section 155. (33 CFR Section 155.450 is the specific section of the law that requires all boats over 26 feet to display a placard of at least 5x8 inches of the image you shared.) Some states have additional laws.

The law prevents discharging oil, oily mixtures, and residues.

The law also includes subsections on oily-water separation equipment.

The law has nothing to do with the ABYC standards for electrical wiring of a bilge pump.

I hope in the future if you suggest something is the law or against the law that you read and cite the specific law so as not to mislead forum members, or confuse them with opinion vs. actual law. It helps us all learn.

For the OP, if you are confused or concerned I recommend you ask a current and licensed marine surveyor. I have relayed what was told to me by 3 surveyors (one a personal friend when I belly-ached about it), what was written in my survey in April 2019, and confirmed by the ins. co. underwriter.

As for me...I'm pretty religious about preventing oil in my bilge to begin with...it's nasty and makes the boat smell bad.
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Old 21-04-2020, 05:23   #10
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Re: Relay for bildge pump

What kind of monster bilge pumps are you all running! Mine use less than 4 amps, I think you'd be hard pressed to find one on a pleasure boat that was much over 5. Add to that the fact that the thing hardly ever runs, and I don't think a relay is even remotely necessary.
As an aside, it turns out bilge pumps and sensors are remarkably robust. I had a broken discharge hose on my cabin cruiser back in the day (so the pump just continuously ran pumping water back to the bilge) that meant my pump circuit was on potentially for over a week. It wasn't even warm, and continued a long and healthy life. On the other hand, I'm in the middle of a warranty fight with Johnson for a failed solid state switch that as far as I know was never triggered in anger in the year between installation and failure in a dry bilge. All anecdotal, but I don't think current in the switch is the issue.
Aside aside, turns out if you buy a Johnson pump product at Amazon and you need warranty work they insist you contact Amazon to get it. Which of course leads to a predictable ignore. Then after a bunch of threats they finally "do you a favor" and send you a replacement. Horrid company.
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Old 21-04-2020, 05:30   #11
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Re: Relay for bildge pump

I'll agree that using a good switch should be adequate. If you have a truly massive pump (something drawing 20+ amps), then a relay might make sense.

As far as wiring, I disagree with the idea of bypassing the battery switches and personally won't do that on my boat unless an insurance survey forces me to. In an emergency, turning power off should mean off. For everything.

My 3 small maintenance pumps (forward, engine room and aft) have breakers on the main panel and man-off-auto switches at the helm (with auto being the normal/down position). I've got a Rule 3700 in the engine room as a backup. That one is wired only to the float switch next to it, no cut-out switch or manual override on it. But the float for it is easy to reach, so I make a point to test it frequently and don't worry about it. I do intend to add an alarm to it at some point this season though. By the time water reaches that pump, I've got a decent bit down in the narrow part of the bilge and the engine room and aft pumps will have been pumping for a few minutes.

As far as power draw, my maintenance pumps draw about 4 amps. But the big backup is rated to pull 15 - 20 depending on input voltage.
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Old 21-04-2020, 07:03   #12
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Re: Relay for bildge pump

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Originally Posted by redneckrob View Post
What kind of monster bilge pumps are you all running! Mine use less than 4 amps, I think you'd be hard pressed to find one on a pleasure boat that was much over 5. Add to that the fact that the thing hardly ever runs, and I don't think a relay is even remotely necessary.
As an aside, it turns out bilge pumps and sensors are remarkably robust. I had a broken discharge hose on my cabin cruiser back in the day (so the pump just continuously ran pumping water back to the bilge) that meant my pump circuit was on potentially for over a week. It wasn't even warm, and continued a long and healthy life. On the other hand, I'm in the middle of a warranty fight with Johnson for a failed solid state switch that as far as I know was never triggered in anger in the year between installation and failure in a dry bilge. All anecdotal, but I don't think current in the switch is the issue.
Aside aside, turns out if you buy a Johnson pump product at Amazon and you need warranty work they insist you contact Amazon to get it. Which of course leads to a predictable ignore. Then after a bunch of threats they finally "do you a favor" and send you a replacement. Horrid company.
Anything over 1000gph (which is not a large pump) uses 5 amps or more. The Rule 1500 requires a 10amp fuse (typically is a 5amp draw) my johnson 4000gph pump (back up) requires a 25amp fuse so its on a relay as finding a good float switch that can handle 25 amps is difficult without spending a fortune!
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Old 21-04-2020, 07:13   #13
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Re: Relay for bildge pump

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Originally Posted by pcmm View Post
Anything over 1000gph (which is not a large pump) uses 5 amps or more. The Rule 1500 requires a 10amp fuse (typically is a 5amp draw) my johnson 4000gph pump (back up) requires a 25amp fuse so its on a relay as finding a good float switch that can handle 25 amps is difficult without spending a fortune!
And remember to add in the current draw from the .. pump on light, horn alert circuit

Also remember that amps goes up when Volts goes down .....a possible scenario with a full on bilge pump run In Anger

A big relay is worthwhile
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Old 21-04-2020, 07:17   #14
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Re: Relay for bildge pump

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Originally Posted by slug View Post
Also remember that amps goes up when Volts goes down .....a possible scenario with a full on bilge pump run In Anger

A centrifugal bilge pump will typically do the opposite. They're not a constant-power device where that will happen. Lower voltage will cause the pump to run slower, which means less load and less power draw. For example, my big Rule 3700 is rated to draw 20 amps at 13.6 volts, but only 15.5 amps at 12 volts. It also moves less water at 12 volts.
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Old 21-04-2020, 07:34   #15
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Re: Relay for bildge pump

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A centrifugal bilge pump will typically do the opposite. They're not a constant-power device where that will happen. Lower voltage will cause the pump to run slower, which means less load and less power draw. For example, my big Rule 3700 is rated to draw 20 amps at 13.6 volts, but only 15.5 amps at 12 volts. It also moves less water at 12 volts.

Low volts burns relays

Slow motor speed overheats and burns up air cooled motors
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