Relay for 12v fridge switch

[Little Dorrit]

Thanks - I'm just trying to achieve the same outcome as you have with your setup, but without having to significantly extend the main 12V supply cabling to route it via a switch (which would increase the voltage drop).

To locate a switch on my electrics panel, wired directly in line with the supply, I'd have to add a good 3m to my 12v supply circuit..

So my idea to use a relay was to have a switch located somewhere convenient, but without a significant interruption to the supply circuit

I'm not an electrician but we're dealing with 12 Volts and whatever the set up you'll need a supply to the refrigerator so upgrading the cabling etc would be quite easy and a good quality switch rated for 10 amps should be sufficient.

 

[WindyWindyWindy]

I've always read (and definitely been advised on here before) to use solid state relays to avoid the ignition risk on a boat?

Most automotive relays are ignition protected.
Look for SAE J1171, although I really doubt it'll be a big deal next to things like the light switches and plug sockets.

 

[Refueler]

That looks very cost effective!

Here's another ....

https://www.amazon.com/Battery-Protection-Undervoltage-Controller-Under-Voltage/dp/B07H4T3LS7

But I do like Kemo items ... Maplins used to have a great line up of Kemo stuff ... now with Maplins basically gone - its eBay / Amazon / AliExpress etc.

 

[Refueler]

Further ....

I have a bunch of these - recc'd to me by an auto electrician who uses them to wire up additional devices to plug into cars ...

I cannot say good or bad as I have yet to actually fit one as already mentioned earlier ...

1.79￡ 10% OFF|12V Battery Protection Module Lead acid Battery Protection Board Over discharge Low Voltage Protection| | - AliExpress

 

[PaulRainbow]

I have installed a new Isotherm kit into my fridge, and want to avoid using the rather delicate-looking thermostat control as the primary method of turning the fridge on and off.

In order to avoid as much voltage drop as possible, I am taking a direct route from the battery isolator switch to the fridge via a fuse. The main wiring behind my DC electrics panel is not up to the job of feeding the fridge directly.

I'd quite like an easy-to-reach on/off switch for the fridge on my electrics panel, so I plan to use a solid-state relay to switch the main fridge supply on and off via a simple push button on the electrics panel.

Can anyone tell me firstly if there's a reason that this is an awful idea?

Secondly, I've found this solid state relay, which has a load current rated at 10A. The fridge shouldn't be drawing more than 5A when it's working hardest, according to the specs. Would this component be appropriate?

https://www.amazon.co.uk/gp/product/B01M075K7L

Are there any alternative 'known good' relays for use in 12V marine environment which would be better for this job?

Thank you!

Matt

10a isn't really up to the job.
No need for ignition protection.
No need to break the bank and no need to scour China to save a few pence and wait 3 weeks for delivery.

Fit a decent automotive relay along the lines of: 12 Volt Relay - make and break

 

[samfieldhouse]

I fitted an Isotherm fridge kit last summer. I actually ran it straight from my Victron solar controller as it has a battery protected output. You do need THICK cable, I used 6mm 50a cable as the run from the batter compartment to the fridge is about 4.5m.
I wired it via a mini isolated switch available on Amazon

 

[MattS]

I fitted an Isotherm fridge kit last summer. I actually ran it straight from my Victron solar controller as it has a battery protected output. You do need THICK cable, I used 6mm 50a cable as the run from the batter compartment to the fridge is about 4.5m.
I wired it via a mini isolated switch available on Amazon

Not a bad idea to make use of the Load output on the Victron MPPT controller actually!

 

[MattS]

Fit a decent automotive relay along the lines of: 12 Volt Relay - make and break

@PaulRainbow I have one of these in a box somewhere - would that do?

12V Relay 4 PIN Automotive 30AMP 30a Normally Open Contact Fused RY28 + 30a fuse | eBay

No need for ignition protection.

Is gas ignition not still a concern on boats?

 

[PaulRainbow]

@PaulRainbow I have one of these in a box somewhere - would that do?

12V Relay 4 PIN Automotive 30AMP 30a Normally Open Contact Fused RY28 + 30a fuse | eBay



Is gas ignition not still a concern on boats?

That would do nicely.

Gas ignition is obviously a concern, but there are a zillion things that could ignite gas, best keep the gas out of the bilges.

 

[Boater Sam]

Solid state relays incur a small forward voltage drop, which you do not want on a fridge supply.
Use a heavier switch/relay than 10A, the starting current of a fridge is higher and DC voltage erodes contacts worse than AC.
Automotive relays are usually spark safe, there are many other sources of sparks on a boat to concern yourself about. The actual thermostat in the fridge for one.......................................................................

 

[KompetentKrew]

My fridge is wired from the switch / distribution plate by the chart table - the connection from the battery to that is kinda a windy one too.

I think you're overestimating the significance of voltage drop.

Obviously you should use a cable that's thick enough, but the calculator at 12vPlanet says that you lose only 3% - i.e. 12.5v becomes 12.2v - on a cable run of 10 meters if you use 2.5mm² cable. This was based on my own fridge using less than 45W (4A), and it sounds like you're planning to use a cable run of much less than 10m.

 

[Boater Sam]

My fridge is wired from the switch / distribution plate by the chart table - the connection from the battery to that is kinda a windy one too.

I think you're overestimating the significance of voltage drop.

Obviously you should use a cable that's thick enough, but the calculator at 12vPlanet says that you lose only 3% - i.e. 12.5v becomes 12.2v - on a cable run of 10 meters if you use 2.5mm² cable. This was based on my own fridge using less than 45W (4A), and it sounds like you're planning to use a cable run of much less than 10m.

Its volts drop under starting current that determines cable cross sectional area not running current.
As a rule of thumb for 12v fridge, 1mm2 per meter of distance battery to fridge and you won't be wrong.

 

[WindyWindyWindy]

With this concern about ignition protection, you should consider a gas alarm.

 

[PaulRainbow]

My fridge is wired from the switch / distribution plate by the chart table - the connection from the battery to that is kinda a windy one too.

I think you're overestimating the significance of voltage drop.

Obviously you should use a cable that's thick enough, but the calculator at 12vPlanet says that you lose only 3% - i.e. 12.5v becomes 12.2v - on a cable run of 10 meters if you use 2.5mm² cable. This was based on my own fridge using less than 45W (4A), and it sounds like you're planning to use a cable run of much less than 10m.

You're not taking into account the startup current, which is typically 15a - 20a. Your 10 metres of 2.5mm cable will lose between 2.3. - 3.0v that's enough to stop it starting.

 

[PaulRainbow]

With this concern about ignition protection, you should consider a gas alarm.

You cannot safely ignition protect a boat from a gas leak and diesel boats don't need ignition protection.

a) Forget ignition protection, unless the engine is petrol.
b) If gas in onboard, fit a gas alarm.

 

[Alex_Blackwood]

I have installed a new Isotherm kit into my fridge, and want to avoid using the rather delicate-looking thermostat control as the primary method of turning the fridge on and off.

In order to avoid as much voltage drop as possible, I am taking a direct route from the battery isolator switch to the fridge via a fuse. The main wiring behind my DC electrics panel is not up to the job of feeding the fridge directly.

I'd quite like an easy-to-reach on/off switch for the fridge on my electrics panel, so I plan to use a solid-state relay to switch the main fridge supply on and off via a simple push button on the electrics panel.

Can anyone tell me firstly if there's a reason that this is an awful idea?

Secondly, I've found this solid state relay, which has a load current rated at 10A. The fridge shouldn't be drawing more than 5A when it's working hardest, according to the specs. Would this component be appropriate?

https://www.amazon.co.uk/gp/product/B01M075K7L

Are there any alternative 'known good' relays for use in 12V marine environment which would be better for this job?

Thank you!

Matt

Why not just wire a simple switch, rocker or otherwise in series with the thermostat if you only want to turn the fridge off during times you are on board. I assume you are using the battery isolator when not onboard ?
As said ignition protection is a load of round objects. If there is a risk why is all the other equipment not of a suitable standard (EX) Is your cooker ignition protected?

 

[PaulRainbow]

Why not just wire a simple switch, rocker or otherwise in series with the thermostat if you only want to turn the fridge off during times you are on board. I assume you are using the battery isolator when not onboard ?
As said ignition protection is a load of round objects. If there is a risk why is all the other equipment not of a suitable standard (EX) Is your cooker ignition protected?

Cracking point Alex

You can't fit a relay as it might cause a gas explosion, but you can light the gas hob

 

[MattS]

With this concern about ignition protection, you should consider a gas alarm.

Yes - it’s on my list to get one for next season! My concern is largely received wisdom - I don’t have any reason to suspect my current installation which I think is well maintained luckily!

 

[MattS]

Appreciate all the views - I can probably relax about ignition protection a bit!

 

[MattS]

Why not just wire a simple switch, rocker or otherwise in series with the thermostat if you only want to turn the fridge off during times you are on board. I assume you are using the battery isolator when not onboard ?
As said ignition protection is a load of round objects. If there is a risk why is all the other equipment not of a suitable standard (EX) Is your cooker ignition protected?

Yes, that’s definitely an option, and definitely a more simple option. I’ve almost lost track of why I felt I should be switching the main supply now!