using relays to control high amp components???

[centerline]

i have owned many boats in my lifetime but nothing newer than a 1990 model, or larger than what I have now.... and I have never seen a relay being used on any of them, other than a start relay (solenoid).
relays ARE used on all the tug boats/fishing boats I have worked on, but ive never seen them used on smaller pleasure craft...

my question is,.. on a boat, why would it not be acceptable to use a regular SPDT Bosch Relay to operate the heavier amp load devices, such as bilge pumps and radios?....

it takes about .01 of an amp to operate the relay, and by getting the relay closer to the device, the load carrying wire run could be at least 10 times shorter, and in turn, have less voltage loss, and a more efficient and longer lasting device

it wouldnt be practical or necessary for all electrical needs, but why dont we see these being used more on boats?... especially where they could make a BIG difference.

its possible that relays ARE being used on newer boats, but I dont know these things... all I know is what I have seen and experienced, and I have never seen relays on any of the sport boats I have ever owned.

on the Cal that I bought, the batteries and buss panel is on the port side near the aft end of the engine. the electrical panel is at the nav station on the starboard side just forward of the engine... the wire run to the panel from the batteries is (routed as it is) about 12ft....

so almost all the circuits that go elsewhere in the boat, other than near the nav station, has at least twice that amount of wiring to get to it( from the batts to the switches at nav station, then from the switches to component), and then the return to ground.... all of this wiring must carry full current demand when the devices are operating.

by using a relay in the bilge pump system, I could shorten the actual load carrying wire to 5ft, without making any changes to the switch panel, AND it would reduce the load on the float switch to a very minimum "signal" amount of current, which is about 1/100th of an amp... yet still deliver a stronger current to the device itself...

even on our simple little sailboats, I see advantages in using relays in the circuits for bilge pumps, large freshwater pumps and vhf and ssb radios.... because they can all demand a high amp load at times.

I suppose one way to help the system without the use of relays, would be to put a heavy buss panel at the nav station near the switches... with 2 or 4 gauge wire going to it... this would allow a better power draw to the switch... which may be the best way to do it since it seems to have been working reasonably acceptable as it is for the last 37 years...

 

[Jackdaw]

There are hi-amp relays all over my 2006 First 36.7...

Electric Winch, windlass, AirCon, etc. The downside is each must be separately fused, away from the DC panel.

Most are SPST; there is no need to break the ground.

Bilge pumps and radios are not hi-amp devices... those should be wired to the panel.

 

[Don S/V ILLusion]

My only comment is that I would be concerned with pitting and arching of contacts in a marine environment and would suggest you also consider PIN diodes for switching.

 

[Pilgrimtex]

The way I see it and I'm not an electrician is that you still need the load carrying wire from battery source to the high amp device. The relay is just a switch. You can run a BUS the length of the boat and branch off of it but it has to be sized at least 125% higher than your maximum load with everything starting at the same moment. Relays fail as well which means stocking spares etc. My windlass has a relay by the windlass due to it's load. So you're not really saving on the wiring unless you run a BUS to shorten overall runs. In fact you have now got control wiring running all over your boat as well.
We used control wiring and relays when I was designing manufacturing machines. That was replaced by the programmable logic controllers. If you really want to go sophisticated you can get a PLC to control all your systems like the Mega Boys do.

 

[Jackdaw]

My only comment is that I would be concerned with pitting and arching of contacts in a marine environment and would suggest you also consider PIN diodes for switching.

This is the harken solenoid control box for the winches. Its encased in epoxy. Runs about US$250.

 

[Ken Cross]

Relays are useful and work well. The issue is to get ones that are sealed for a marine environment. That should take away many of the reliability issues on a boat. I absolutely agree that it can save wire length at a cost of complexity and cost. Due to the coil current, I think one would only want to use the relays on equipment that has an intermittent use (as opposed to your VHF). My boat doesn't really have any big current users except the starter. The potable water pump would be next but it's only a couple of feet from the electrical panel.

 

[Stu Jackson]

Conceptually, yes. Realistically, just more potential points of failure in simple circuits.

In addition to our starter solenoid, I added a glow plug solenoid which helps a lot. I can't think of any other high amp draw motor on our boat, other than the macerator pump which on my boat is adjacent to the electrical panel.

 

[walt]

it takes about .01 of an amp to operate the relay

Do you have an example link? This sounds about a factor of 10 too low but maybe its some sort of "latching" relay..

The power to keep the relay on for longer periods would be one issue.

 

[centerline]

Do you have an example link? This sounds about a factor of 10 too low but maybe its some sort of "latching" relay..

The power to keep the relay on for longer periods would be one issue.

im getting my numbers from one of the many websites available...

see the bottom of page 3 here...

I deal with these type of relays daily, and they make higher amperage ones and sealed ones of this size... but the 30
Im no stranger to relays as I also deal with 24, 36 and 48 volt systems that all operate thru relays... but its relays on boats that I had a question about

and I suppose my question has been answered already, in that it is impractical because the simplicity of the system with its big wires running all over the boat where necessary, is easier to understand for most people when there are electrical troubles...

and I KNOW a 20 to 30 amp draw is not HIGH amperage considering what a windless could draw, but it is higher than a fan or normal lighting, and higher than what normal 16ga wire should be carrying for 25-30 feet.... and, even though my diaphragm bilge pumps may draw less then an impeller pump, i still dont like seeing much of a voltage drop on the line when it gets to pumping....

so.... using a much heavier wire to move the buss closer to the switch panels for its supply will more than likely solve any problems I think I may encounter.... and clean up a lot of unnecessary wire running across the boat....

my whole thought process stemmed from looking at float switches... a 15amp float switch is $30... with higher amp switches on up to $115....(at the local marine store) i was thinking a person could run as big of draw as their big pump required with the little float switch if they used a relay....

 

[Maine Sail]

im getting my numbers from one of the many websites available...

see the bottom of page 3 here...

I think what Walt was saying is that you simply misstated the coil load.

It is approx 150mA (0.15A) not the 10mA (0.01A) that you suggested it was...

A 0.15A load for an "always on" device like a bilge pump is 3.6Ah's ever 24 hours. A week of sitting on a mooring and you are down 25Ah's for just one circuit..

If it was 0.01A/10mA then you would use just 1.7 Ah's per week...

it takes about .01 of an amp to operate the relay

BTW there are lots of relays used in marine applications.... Every combiner or ACR is a relay, every glow plug solenoid is a relay, almost every windlass uses one, bow thrusters, autopilots, electronic battery switches etc. etc..

 

[Don S/V ILLusion]

This is the harken solenoid control box for the winches. Its encased in epoxy. Runs about US$250.

I have a few myself. My only point was that the OP seemed concerned about failure and wanted to give him a non-mechanical alternative capable of carrying virtually any size load.

 

[northptsailor]

My Tartan came from the factory wired for a windlass, heavy amperage wire from the battery to the anchor locker. I didn't like the idea of a high amperage - always on- wire running the lenghth of the boat, so I installed a relay near the battery controlled by a panel breaker. Now the windlass wires are only hot when I am using it. I discovered after the first solenoid failed that there are two different high amp relays for marine use, instantaneous and continuous duty. The starter might use the former and the windlass the latter.

 

[mitiempo]

I have a few myself. My only point was that the OP seemed concerned about failure and wanted to give him a non-mechanical alternative capable of carrying virtually any size load.

That is mechanical - it contains 2 solenoids.

 

[mitiempo]

My Tartan came from the factory wired for a windlass, heavy amperage wire from the battery to the anchor locker. I didn't like the idea of a high amperage - always on- wire running the lenghth of the boat, so I installed a relay near the battery controlled by a panel breaker. Now the windlass wires are only hot when I am using it. I discovered after the first solenoid failed that there are two different high amp relays for marine use, instantaneous and continuous duty. The starter might use the former and the windlass the latter.

A simple on/off battery switch aft accomplishes the same thing.

 

[Ralph Johnstone]

Relays are also the lazy man's way of tapping into your water hi temp. alarm circuit or your low oil press. alarm wiring if you can't run a wire from your ignition switch down to your engine. I did this recently to activate a cooling fan for the engine compartment but ONLY when the engine was running. Near impossible to run a new wire down to the engine.

The relay to use is a solid state one as it uses only 2 mA and won't activate your alarm relay.

 

[Bill Roosa]

if you control the relay with a switch/CB then the current needed when off is 0.00

 

[LakeOntario270]

I am an electrical engineer. A relay for heavy current is an excellent idea. Switches are usually good for only a couple of amps. Yes, you can get heavy duty switches but you pay a lot for them.

 

[Don S/V ILLusion]

That is mechanical - it contains 2 solenoids.

I know. I am referring to PIN diode switches which are not mechanical and therefore not subject to common breakdowns

 

[mitiempo]

On many boats you will find 3 or 4 solenoids and if kept dry they have a very long service life. The windlass has one (2 if powered down as well), the propane solenoid, and the starter solenoid.