Bilge Control Via Relay

I just searched the Internet. They are flipping expensive and with a International Rectifier MOSfet type IRFP064N HEXFET® Power MOSFET (110 Ampere) you yourself can make a 2 dollar solid state relay. At 13 Ampere you don't need a heat sink. 13 x 13 x 0.008 = 1.4 watt. It get warm, but not hot. No fancy stuff, you yourself can do it. If you are brave enough, all what you need is a small tiny switch to switch + 12 volt to the one leg of the MOSfet, the plus 12 Volt to your Bilge pump and the other wire from your bilge pump to your 2nd leg of your MOSfet and than the 3rd leg of your MOSfet to the negative/earth wire. That is all. If you are concerned, put a green LED ( with a small 5000 Ohm or 10000 Ohm resistor) over the MOSfet and bring the "ON" wire in a telephone thick tiny thin copper wire back to your Cockpit. You are the able to see whether the pump is on or off. Green LED light on, the pump is off, the green light off, the pump is pumping or you have a short in the MOSfet They make 1 million per month of those devices and I have been using a couple of hundred already. If you want to be brave, give me a poste restante address to gkuijpers@telkomsa.net and I will post you one at no cost with a note and circuit diagram with copper thickness for your switching toggle switch wire (0.01 mm wire) etc and if you are concerned about the plus 12 Volt direct to your bilge pump, put a automotive 20 Ampere fuse + fuse holder in series. Good luck. All additional other MOSfets for your system, you have to purchase from International Rectifier agent in your country. Bert

 

Bert, I think you're making this question or set of questions a lot more complex than they need to be. He seems to have sufficient wire diameter for the run and load, so the only real questions are; relay type, which is clear, solid state, because vapors can collect in a bilge and corrosion is minimized and how much heat he might expect, which I don't think will be much, unless his boat is fair leaky and the pumps under sized.

 

Don't agree with you. I haven't seen a solid state relay (affordable) which can handle 12 Volt DC 13 Ampere for the bilge pump. Most solid state relays are for low voltage input and high voltage switching. A relay is out of the question for the bilge pump. the contacts want last and fumes could be a problem. Thus a simple high current solid state MOSfet which can handle up to 110 Ampere 12 Volt DC with heat sink or 13 Ampere DC without heat sink, is a simple good solid solution and even better and less inexpensive than a fancy solid state relay. At the same time the OP can learn how he can calculate his problem without future consequences. Bert

 

The pumps won't run very often at all via the circuit I'll use the relays on - its the manual circuit. Generally I would only use the manual bilge circuits momentarily as part of regular checks.

But ... if I ever really need a manual circuit to work, then it may have to run for an extended period of tiem.

The relays I'm looking at have the heat sink built in, but I want to mount them in a sealed plastic box, so that heat won't be able to easily escape. On balance it may be easier/cheaper to go with mechanical relays.

 

Mechanical relays can cause gas fume explosions in the bilge.

 

The load-cables will be quite short. About 6m from the battery in the transom to the bilge pump and back again. That's the reason for using relays.
The control cables will be longer runs. About 1om for a lead from the helm DC main to the relays. Then about 3m for negative lead back to the battery

I don't know for a fact the Hella solid state relays will produce a lot of heat. I have inferred they will because they have heat dissipation fins.

 

Yes that's true, but the relays won't be in the bilge they will be in a small sealed box mounted in an open fronted transom locker above deck level.

 

Reading further on the Hella SS relays, they have single positive input and switch this to negative to complete the control circuit.

https://www.hella.co.nz/en/products/relays-flashers/solid-state-relays/12v-4-pin-solid-state-relay-22a.html

It's a complication I don't want on my boat, where every other circuit is fused and switched on the positive side.

 

Then you could use the same type of MOSfet as used in the above Hella Solid State i.e. IRFP06N and use a 1 :1 voltage 12 V DC to 12 V DC converter and have the IRFP064N switching on the positive side. You can only do that if you make your own Solid state relay yourself up.
Bert

 

For those who has the same problem as the OP, attached a circuit diagram whereby you can switch your bilge pump on, and do the switching with a solid state circuit from the plus instead of the minus. Also you don't need to switch the bilge pump on from the same battery, it could even be a 9 volt battery you hold in your hand.
PAR, we amateurs sometimes have good idea's. It is just that we don't have the same machinery like your people have. (grin on my face if you allow me to comment)

 

I ordered two 'hockey puck' solid state relays at the weekend (DC 30v, 100A). Should be here next week. Thanks to Bert who has helped me a lot via direct message with his electronics expertise.

The set-up I will build is as follows ...

I have two 13-amp bilge pumps. For each pump: -

• The 'auto' circuit will run directly from the battery (transom) via a fuse to a float switch and onto the pump (near transom).
• The manual circuit will run from the battery to the load side of the relay and onto the pump.
• The relay will be controlled via a single pole momentary switch at the helm.
• An LEDs at the helm will indicate whether the auto circuit has power.
• An LED at the helm will indicate when the float switch is tripped.

The relays will be housed in a waterproof ABS enclosure with a clear lid and will be protected from voltage spikes by diodes.

The higher level float switch will also be connected to an audible alarm at the helm.

Because the LEDs and the relay control circuits draw very little power, I can get away with a multi-core light-gauge cable. For example, cable designed for LED trailer lights.

 

Excellent. Your problems seem to be solved. Pleased you could find the right SS relay, which allows you to switch on the plus side instead of the minus side like the Hella. Well done. Bert

 

I would expect that you need an on-off switch at the helm, you certainly do not want to have to manually hold the momentary switch on to operate the bilge? If the auto circuit does not function and floats often do not, you need to be able to
override this without your hand on the switch. You have water in the bilge, you might be in a situation where you need two hands on the wheel or one on the wheel and the other on the radio

We have installed hundreds if not thousands of automotive relays (not in the marine environment) and never put diodes in front of or parallel to the relays to inhibit the voltage spike occurrence when you turn on/off a dc switch. I assume you are referring to Zener Diode protection? We were not protecting and you are not protecting a sensitive electronic circuit.

 

Barry, he does not put the diode over the relay, but over the coil of the bilge pump, MOSfets are notorious for switching very fast on and off. The diode shortens the spike over the coil not the relay, to protect the MOSfet used in the SSrelay. Bert

 

Every bilge panel I have seen has a momentary manual switch, presumably to stop the bilge pump being accidentally activated. I don't want to depart from what appears to be a standard practice. Doing so would also make the labeling on my bilge switch panels incorrect.

I was (based on my research) referring to a flywheel diode, to absorb energy spikes from the bilge pump. I'm still learning on this subject.

The manufacturer of the solid state relays I've ordered, specifically says to use external diode protection across the load. Bert's post explains why, much better than I can.

Quite possibly the manufacturers are just covering their backsides but I can buy a relay for a few cents and install it in a tidy and protected manner. So why not? if a diode fails it won;t stop anything else from working.