Wiring equipment direct to battery?

[Tim Good]

I am fitting a new 12v fridge and the instructions say best it is wired directly to the battery. I'm assuming to prevent voltage loss or use of old insufficient wiring.

Recently I was also advised to wire my webasto heater direct also.

1. Dos that mean I just do away with the switches for "fridge" and "heater" on my switchboard? (Note my switches are circuit breaker trip switches also)

2. Or do I rig a little 12v relay up near the unit and activate it via the switch but have the main wiring direct from battery?

 

[pvb]

The suggestion to wire direct to the battery is indeed, as you guessed, to minimise voltage loss. But if your wiring is adequate, it's much better to supply the fridge from the existing switched supply - that way you can be sure it'll switch off when the main battery switch is turned off. If you have to wire it direct to the battery, make sure you fuse the wire as close to the battery as possible.

 

[Capt. Clueless]

Funnily enough, I am carrying out a virtual re wire of our boat today....new for old. This is only personal choice, but will not be wiring up anything without an interrupter somewhere along the line. Personally, and many may disagree, but I would opt for staying with running through the circuit breakers.

 

[Minchsailor]

Certainly through the existing switch panel. If the wiring is not up to it - replace it.

On my boat the only thing that is directly connected to the battery is the bilge pump, so that it will operate (if needed) with the boat unattended and the battery switch 'off'.

 

[Plum]

Certainly through the existing switch panel. If the wiring is not up to it - replace it.

On my boat the only thing that is directly connected to the battery is the bilge pump, so that it will operate (if needed) with the boat unattended and the battery switch 'off'.

+1 but if you do decide to connect directly or via a relay straight to the battery I suggest you connect to the master switch so there is no risk of battery drain when you are away from the boat and the master switch is off.

Colin. Www.solocoastalsailing.co.uk

 

[VicS]

I am fitting a new 12v fridge and the instructions say best it is wired directly to the battery. I'm assuming to prevent voltage loss or use of old insufficient wiring.

Recently I was also advised to wire my webasto heater direct also.

1. Dos that mean I just do away with the switches for "fridge" and "heater" on my switchboard? (Note my switches are circuit breaker trip switches also)

2. Or do I rig a little 12v relay up near the unit and activate it via the switch but have the main wiring direct from battery?

I rather like that idea but it means that he power will have to be on to the main panel in order to operate them. You might prefer to have the fridge, at least, connected to an "always on" supply so that its can operate while power to the switch board is isolated.
You would have to match the wiring from panel to relays with the trip rating of the circuit breakers. ... I guess you would not want to change them.

On the downside relays are an extra complication and something that could go wrong.... unlikely though.

 

[RobbieW]

Another thought; the OP seems to be prepping a boat for extended cruising ? Knowing something about the state of the batteries is, IMO, an essential for that. Assuming that there is some sort of current measuring going on, any electrical feeds must be from the right side of the shunt to be measured. In that context, ignore the advice to wire direct and simply use big enough wires to cope.

 

[prv]

The advice is purely to reduce the number of complaints and service calls that the manufacturer receives, due to numpties hanging high-current devices off random 1mm² cabling that happens to be handy. If they tell people a cable size and that it must be wired direct to the battery, at least their equipment's performance isn't hostage to whatever crappy wiring is already on board.

Instead, you should ensure that your wiring is correctly sized and in good condition, and laid out (with respect to switches, fuses, etc) in a logical way.

One thing to be aware of is that blown-air heaters don't like having the power suddenly turned off without going through their shutdown cycle, so there's an argument for not having a panel switch for it. Even if you never do it yourself, one day someone else may "helpfully" turn the heater off at the big obvious switch labelled "heater". I have mine wired via the main fusebox, but without a panel switch.

Pete

 

[David2452]

One thing to be aware of is that blown-air heaters don't like having the power suddenly turned off without going through their shutdown cycle, so there's an argument for not having a panel switch for it. Even if you never do it yourself, one day someone else may "helpfully" turn the heater off at the big obvious switch labelled "heater". I have mine wired via the main fusebox, but without a panel switch.

Pete

Exactly so and not just blown air but even more important with wet systems. It is really important to have an uninteruptable supply as damage is easily done if power is off during burn, no worries about flattening batteries with them as they shut down if low voltage is detected. This is not hypathetical and I have had to attend to repair damage so caused on a number of occasions, usually the ECU and or sensors are. A definate warranty claim rejection issue on new units.

 

[VicMallows]

It is really important to have an uninteruptable supply as damage is easily done if power is off during burn,................... A definate warranty claim rejection issue on new units.

I don't disagree for one moment. ..... but surely this is unacceptable design?. Imagine if there is a mains power cut, and peoples domestic central heating irreversibly fails? There would be an almighty outcry.

 

[prv]

surely this is unacceptable design?

The evidence suggests otherwise - it's been accepted by thousands of people over the last few decades

No doubt David can enlighten us further, but I assume the problem is the sudden loss of cooling airflow with burning diesel still inside the combustion chamber. It's really not clear how you might solve this. An automotive unit mounted under a truck could perhaps open some sort of hatch and dump the fire onto the tarmac, but you don't want that in your cockpit locker.

Also, power-off isn't an automatic death sentence, just makes failure more likely. Ariam's heater was originally wired via a switch, with no warning notice, and she spent thirteen years as a charter boat during which I'm sure the heater was forcibly turned off on numerous occasions. I think I may well have done it myself early in our ownership before I was aware of the issue and before I rewired her. Touch wood, the heater's still ok.

Pete

 

[LadyInBed]

On my boat the only thing that is directly connected to the battery is the bilge pump, so that it will operate (if needed) with the boat unattended and the battery switch 'off'.

Same here.

 

[Caer Urfa]

I am fitting a new 12v fridge and the instructions say best it is wired directly to the battery. I'm assuming to prevent voltage loss or use of old insufficient wiring.

Recently I was also advised to wire my webasto heater direct also.

1. Dos that mean I just do away with the switches for "fridge" and "heater" on my switchboard? (Note my switches are circuit breaker trip switches also)

2. Or do I rig a little 12v relay up near the unit and activate it via the switch but have the main wiring direct from battery?

I also have my engine bay bilge pump wired direct to the domestic battery (also fused). however three years ago I also followed Waeco instructions and wired my new fridge with thick wiring direct to the 'domestic battery' (also fitted with a fuse close to it).

However I also fitted a Waeco controller which automatically switches over to mains when I plug in at the marina mains supply (via a RCD) or automatically switches over to battery power when unplugged from the mains.

Works fine for three years now plus I know there is no chance of draining my engine 'starter battery'.

When leaving the boat I switch the fridge off 'at the fridge' (don't forget to leave the fridge door slightly open for air)

 

[David2452]

The evidence suggests otherwise - it's been accepted by thousands of people over the last few decades

No doubt David can enlighten us further,
Pete

Your assumption is correct Pete, the heat exchanger gets very hot indeed during operation and carries quite a lot of latent heat if the cooling medium is suddenly removed, it has to or it will not work, it has to have a cooling medium either air or water to keep that temperature to a safe level, that medium is obviously what heats the (in our case) boat. If both are not present then it will not function so that part of the design is not really changeable. The small amount of diesel is not a real worry as it would be tiny due to the dosing pump shutting down and would instantly flash off. Customer and OE buyer pressure has lead to the things becoming smaller and smaller and easier to install over the years which can only increase the problem due to the lower volume of coolant and higher circulation speed in a wet exchanger or the higher air flow and hotter exchanger temperature of blown air heaters. Though internal changes are present in marine / R.V. heaters the primary use of the things by multiples of thousands is in vehicles so more and more KW per physical size is the way it will continue to go, we in marine are the "poor relation". It is often some time before the higher power heaters are approved for marine use so it is not taken lightly, for instance the AT2000ST was used in vehicles for around two years before we got the marine version, the Thermo top V 5kw though it has been around for years is not approved for our use and we still use the larger capacity Themo Top C. I guess one way to protect the ECU from the potential damage by latent heat would be to return to the days when it was a separate remote mounted component but the first manufacturer to do that would rapidly lose OEM sales so that is not going to happen. For those concerned about leaving the heater on accidentally and therefore routing it through a separate circuit breaker or battery switch it is easy to achieve the same result by wiring the heater as in a TRS vehicle or scholastic vehicle, using this method the main supply is still direct and uninterruptable but turning off the switch or breaker causes the heater to shut down normally and disables it until the breaker is turned on again.