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16-10-2016, 12:08
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#1
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Registered User
Join Date: Mar 2013
Location: Live in Waikoloa Hawaii, boat in Southern France
Boat: Nicols 1150 38ft long
Posts: 6
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Latching relay
Hi, I want to install a switch on the panel at my boat's helm to control a relay to switch on/off the 12v fresh water pump. To cut down on current draw I want to use a latching relay. I understand I will need to use a momentary switch. The question is what amp size relay to use. The pump is rated for a 10 amp fuse. Also any suggestions for a reliable relay brand?
Thanks, Rains808
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16-10-2016, 13:10
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#2
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Registered User
Join Date: Feb 2008
Location: North Charleston, SC
Boat: Camano Troll
Posts: 4,669
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Re: Latching relay
Wouldn't it be easier to just switch the power to the pump directly? A simple toggle or rocker switch is all you would need.
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Ron
HIGH COTTON
Sent from my laptop using Windows 7
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16-10-2016, 13:29
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#3
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Registered User
Join Date: Mar 2013
Location: Live in Waikoloa Hawaii, boat in Southern France
Boat: Nicols 1150 38ft long
Posts: 6
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Re: Latching relay
Thanks rwidman, wouldn't I have to run a heavy gauge wire back to the pump rather than a light one to handle the power requirements of the pump? If so what gauge should I use for the pump?
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16-10-2016, 14:17
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#4
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Registered User
Join Date: Feb 2008
Location: North Charleston, SC
Boat: Camano Troll
Posts: 4,669
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Re: Latching relay
Quote:
Originally Posted by rains808
Thanks rwidman, wouldn't I have to run a heavy gauge wire back to the pump rather than a light one to handle the power requirements of the pump? If so what gauge should I use for the pump?
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#12 unless it's a really long run. There are tables in the West Marine catalog to calculate wire size vs. voltage drop.
Without seeing your actual boat, I can't say for sure but you probably don't have to run a pair of wires from the vicinity of the pump to the helm. You can interrupt the circuit anywhere it's convenient.
__________________
Ron
HIGH COTTON
Sent from my laptop using Windows 7
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16-10-2016, 18:41
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#5
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Registered User
Join Date: Mar 2013
Location: Live in Waikoloa Hawaii, boat in Southern France
Boat: Nicols 1150 38ft long
Posts: 6
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Re: Latching relay
Thanks for the ideas. She's winterized now, so time to considered all this in the next months.
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16-10-2016, 20:01
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#6
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Registered User
Join Date: Sep 2008
Location: Adelaide, South Australia
Boat: Swanson 42
Posts: 7,316
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Re: Latching relay
Adding a relay is adding another point of failure. Not to mention a handful of extra connectors. For the cost savings involved(after paying for the relay and the connectors, and a spare relay to be safe) it hardly seems worth the added risk of failure of such a critical piece of equipment.
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Launch delayed.
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16-10-2016, 20:46
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#7
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Registered User
Join Date: May 2009
Location: Brisbane, Queensland
Boat: None
Posts: 46
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Re: Latching relay
Not to mention, that the current to latch the relay will be a constant drain on the batteries. It may be small but it must be taken into account.
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"You do not ask a tame seagull why it needs to disappear from time to time toward the open sea. It goes, that's all." Bernard Moitessier
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16-10-2016, 21:37
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#8
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Moderator
Join Date: Feb 2010
Location: La Ciudad de la Misión Didacus de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 12,530
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Re: Latching relay
Quote:
Originally Posted by pdbms
Not to mention, that the current to latch the relay will be a constant drain on the batteries. It may be small but it must be taken into account.
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I thought the whole point of a special latching relay was they took a momentary current to open or close the relay but otherwise weren't drawing anything.
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Num Me Vexo?
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
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17-10-2016, 04:00
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#9
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Senior Cruiser

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 39,845
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Re: Latching relay
Quote:
Originally Posted by Adelie
I thought the whole point of a special latching relay was they took a momentary current to open or close the relay but otherwise weren't drawing anything.
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You thought correctly.
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Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"
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17-10-2016, 04:14
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#10
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Moderator Emeritus

Join Date: May 2008
Location: North Mississippi
Boat: 48 Wauquiez Pilot Saloon-C22 Chrysler Sunpiper- 19 Potter-Preparing to cruise w/my girl
Posts: 5,975
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Re: Latching relay
Quote:
Originally Posted by GordMay
You thought correctly.
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^^^  THIS  ^^^
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In the harsh marine environment, something is always in need of repair...
Mai Tai's fix everything...
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17-10-2016, 04:16
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#11
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Moderator Emeritus

Join Date: May 2008
Location: North Mississippi
Boat: 48 Wauquiez Pilot Saloon-C22 Chrysler Sunpiper- 19 Potter-Preparing to cruise w/my girl
Posts: 5,975
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Re: Latching relay
Curiosity kills me as to why you want a FW pump switch on the "helm" ???
EDIT - ALSO ... with a latching/momentary, you'll never be sure whether the pump is on or off at the helm... Unless of course you install an indicator... Which is really starting to complicate a simple system...
__________________
In the harsh marine environment, something is always in need of repair...
Mai Tai's fix everything...
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17-10-2016, 13:56
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#12
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Registered User
Join Date: Mar 2013
Location: Live in Waikoloa Hawaii, boat in Southern France
Boat: Nicols 1150 38ft long
Posts: 6
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Re: Latching relay
Thanks Adelie for clearing up the latching relay issue.
Here's the whole story: when we bought the boat 4 years ago it did not have a fresh water pump on/off switch, but the wiring was there from the past. The switch had obviously been bypassed. A mechanic installed a relay controlled by an existing control panel switch at the helm (nav lights, wiper, etc. located there also). All worked well so we could switch off the pump when we were away from the boat until the coil on the simple relay (automobile type) burnt out this year. So, not having a spare I bypassed the relay. My idea now is that at the start of next cruising season to install a latching relay so the relay would not need to be energized constantly. In terms of the wiring the batteries are located in a hatch in the stern. The pump is in a hatch just forward of that. So the wiring would have to run from the stern to the helm (about midship) and back to the pump. I want the pump on its own wiring circuit to hopefully avoid the lights flickering as the pump cycles when it's on. No indicator for the pump needed since the kitchen sink is near the helm so it's easy to tell if the pump's on or not. To me a relay makes sense rather than running heavy gauge cable from the batts to the switch to the pump.
So...right now I'm shopping for a proper relay to install next year.
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18-10-2016, 06:07
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#13
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Moderator Emeritus

Join Date: May 2008
Location: North Mississippi
Boat: 48 Wauquiez Pilot Saloon-C22 Chrysler Sunpiper- 19 Potter-Preparing to cruise w/my girl
Posts: 5,975
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Re: Latching relay
All righty...
This is starting to make a little more sense now given your layout! I would still say a proper breaker panel is the way to go, but your control wire is already there... It probably BTW is large enough for a 5A pump, but your latching idea is fine...
Latching relays are obviously a bit harder to find when simple SPST 12v relays are practically laying in the street for the taking... $5 at an auto store, a 5 pack with harnesses from Amazon for $14... They take something like 20ma to energize, so literally nothing
Trying to stay on the low $$ side for a Latching Relay, you'll need a short piece of DIN rail
https://www.amazon.com/20-21-9-012-0...latching+relay
McMaster
$45 with socket
McMaster-Carr
__________________
In the harsh marine environment, something is always in need of repair...
Mai Tai's fix everything...
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18-10-2016, 06:08
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#14
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Moderator Emeritus

Join Date: May 2008
Location: North Mississippi
Boat: 48 Wauquiez Pilot Saloon-C22 Chrysler Sunpiper- 19 Potter-Preparing to cruise w/my girl
Posts: 5,975
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Re: Latching relay
A handy wire size chart for you to bookmark or print...
http://assets.bluesea.com/files/reso...on_chartlg.jpg
__________________
In the harsh marine environment, something is always in need of repair...
Mai Tai's fix everything...
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