Wondering how others have wired the 12 volts on their 3 way fridge. Mine is wired by the manufacturer with the 12 v coming from the van batteries and draws approx 20 amps, I have a 20 amp DC-DC charger in the van connected to the tug via an anderson plug (standard arrangement), I was thinking of splitting this feed to supply the fridge direct and supply the charger, which would mean the fridge will take 20 amps constantly when I am driving and if the batteries are low then the charger will kick in and take another 20 amps, 40 amps in total from the tug. At the moment if I stop for lunch I just turn the fridge off or turn on the gas if I'm stopped for over an hour. I also have 540 watts of solar so if the sun is out it is putting in over 20 amps anyway. Any suggestions ? Ian
I think wiring a three way fridge to the van battery is a very bad idea. It is not practical to run a three way from a battery and by wiring it this way the van's charging circuit now needs to be able to supply 20A more than it should.
I would disconnect it from the van battery and wire it to an Anderson plug which may be mated with another Anderson plug wired to the car via an ignition controlled relay.
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Ian, What is the fridge make and model? The vans manufacturer may assist as well.
Is it an AES fridge? If so the connection the house battery is generally only to power the circuit board in the van and the 12 V element is supplied from the trailer plug. If it is not an AES fridge then I would be rewiring it to Dometic's recommendation.
Thanks Peter and Mick, it is a Thetford N3185, aren't both of you agreeing with what I propose to do. I have an anderson plug on the tug supplying my DC-DC charger, I intend to take a feed from this supply to my fridge rather than from the van batteries and put an ignition relay on on the tug. It will draw 20 amps constantly when driving for the fridge and a further 20 amps if my van batteries are low, so is a 40 amps draw normal from the tug ? Thanks Ian
Our caravan is absolutely basic - no battery, no solar panels - the 12 V power feed coming straight from the car. I have a permanent 12 v power supply on the car and leaving the van parked for a few hours could and did flatten the battery. I installed a "Fridge Switch", which is a movement activated switch on the 12 V feed to the fridge. I have never had any trouble since fitting it. This way, the 12 v lights in the van still operate whereas with a 12 V isolating system in the car, they would not. I have fitted a 12 v computer fan at the rear of the fridge to assist in airflow in hot weather. I can tell if the fridge switch is working simply by feeling the temperature of the air coming from the top vent - it is warmer than ambient when the fridge is working, but near ambient when it is not.
Single feed system
WIRE SIZE MUST BE 25mmsq / 3 b&s
If running a dc2dc the 3 way Must BE connected to the IN /car side of charger as to not interfere with house battery charge .
The fridge must use a movement RV fridge switch for fridge operation
Twin circuit to van
1 x 13mmsq cable , fridge operation via vehicle ignition switched relay
1 x house battery charge 13mmsq
Cable size
13mmsq 6b/s 18amps 9mtrs at .4volt drop
25mmsq 3b/s 36 amps 9mtrs at .4v drop
More volt drop can slow charging
I have wired mine so that it runs on 12v from the vehicle switched by a relay that operates when the car is started (ie off the accessory feed as suggested by Mike Harding). It goes thru an anderson plug on the car and terminates on another anderson plug in the van. Harding)
I can connect that plug to either the van fridge or to the van battery DC to DC charger. (I couldn't locate a suitable switch to make it easier so I made do with the anderson plug arrangement). I always choose to connect it to the fridge.
The van's solar is permanently connected to the van's DC to DC charger, so the battery is kept charged while traveling.
Unfortunately the DC to DC charger can only accept one input at a time & always chooses the input from the car.
Whenever I stop for a break or meal I always switch the fridge to gas.
Single feed system WIRE SIZE MUST BE 25mmsq / 3 b&s If running a dc2dc the 3 way Must BE connected to the IN /car side of charger as to not interfere with house battery charge . The fridge must use a movement RV fridge switch for fridge operation
Twin circuit to van 1 x 13mmsq cable , fridge operation via vehicle ignition switched relay
1 x house battery charge 13mmsq
Cable size 13mmsq 6b/s 18amps 9mtrs at .4volt drop 25mmsq 3b/s 36 amps 9mtrs at .4v drop More volt drop can slow charging
Where did you dream up that information. The information is totally incorrect in every way. Under NO circumstances should a single wire be used. The cable sizing all depends on the fridge element wattage. Without the fridge element wattage everything you posted is irrelevent.
Fridge switches are not recommended as they turn off the heating element every time the vehicle stops or even slows. VSR is all that is needed and required.
Using a straight relay on an ignition circuit is also not recommended. A VSR (Voltage Sensitive Relay) should be used to allow the vehicle electrics to stabilise prior to the fridge connecting. The larger capacity fridges take up to 25A. If the fridge has a D+ wire, using a VSR the D+ can be connected to the directly to the positive from the VSR. Same as using a DC-DC charger. No need to run a separate IGN or D+ wire.There should be no physical connection to the house batteries for the fridge element, except in the case where the the fridge needs 12V to power the electronics on the fridge if fitted.
Been working back the past months helping out auto electricians short staffed. Seeing many alterantor failures from people overloading their alternator with 3 way fridges and high capacity DC-DC chargers. These are expensive repairs. Not necessarily the cost of repairing the alternator, the time takes to remove and replace the alternator on modern vehicles.
Got sick and tired replacing the horrid 12 pin plugs. Got that many travellers wanting them replaced we couldn't handle the work and had to send them on their way. Usually was not a case of only replacing the 12 pin plug, but repair or upgrade the wiring.
Thanks twin 25 mm is a huge cable, I doubt I could get that through the crevices in my MUX, as I have plenty of solar my DC -DC charger is rarely used so might go with the 13 mm and put up with a bit more voltage drop. It has 6mm at the moment as that is what most auto elects seem to fit as standard and that charges the batteries ok though not ideal. Thanks Ian
Depends where the storage batteries are ? Being load is at least 20 amp . Btw 20 amp DC needs larger cable . You need cable size wire over distance . Due to dreaded VD . Best to have auto switches, DC to DC charger , relays and VSRs to keep barriers with charge and switch over only when being charged from vehicle. Depending on solar or other charging . Ive found trying to do manually ? It often get left or forgotten! Having flat batteries is no way of enjoying camping ! Fitting the most fail
Safe system you can !! Way less stress !!
Thanks twin 25 mm is a huge cable, I doubt I could get that through the crevices in my MUX, as I have plenty of solar my DC -DC charger is rarely used so might go with the 13 mm and put up with a bit more voltage drop. It has 6mm at the moment as that is what most auto elects seem to fit as standard and that charges the batteries ok though not ideal. Thanks Ian
25mm Square . Its not that large depending on insulation .
Yes 20 amp . What is confusing is the wire / cable size between building elect and auto elect etc ! Theres about 4 different ways of measuring wire wise .
So 20 amps, 20 metres ( total length of + & - , ie 2 x 10m).
Voltage drop 0.2092 volts.
Personally I would go for 2awg 33mm˛ cross sectional area of the actual copper wire (that's not the insulation outside diameter).
Use the 120 amp Anderson plugs, they work better than the 50 amp plugs anyway & you can fit the wire in the lug.
To solder wire, drill hole in block of wood, stand up lug, 2/3 fill with lead 40%/tin 60% solder, use a heat gun (great soldering iron for very heavy cable), unless you have two 100 watt soldering irons, then heat shrink with a couple of layers.
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hi MonicaW Fridge switches have a delay period in there ON/OFF period so false switchings can be avoided and yes they can carry high amperage . Far safer to operate fridge via ignition/engine ON power trigger , switched relay/ solenoid and not run the battery down via vsr. Operating a dc2dc of 25amp is not going to wreck an alternator period . Many alternators that are operated close to max have a shorter life .
You posted irrelevant , thats why I posted cable size , suggest u might need some glasses /read properly B4 u comment To satisfy you some people run a single circuit of 35mmsq cable
Considering 90% people have there vans wired this way [single or twin circuit ] on this forum , my suggestion works .
-- Edited by swamp on Tuesday 22nd of February 2022 12:04:02 PM
-- Edited by swamp on Tuesday 22nd of February 2022 12:04:37 PM
Hi Swamp if I run a single line with an ignition switch relay then I wont need the fridge switch ? How will a VSR flatten the battery, surely it can only operate when the vehicle is running ?
Thanks Ian
hi MonicaW Fridge switches have a delay period in there ON/OFF period so false switchings can be avoided and yes they can carry high amperage . Far safer to operate fridge via ignition/engine ON power trigger , switched relay/ solenoid and not run the battery down via vsr. Operating a dc2dc of 25amp is not going to wreck an alternator period . Many alternators that are operated close to max have a shorter life .
You posted irrelevant , thats why I posted cable size , suggest u might need some glasses /read properly B4 u comment To satisfy you some people run a single circuit of 35mmsq cable
Considering 90% people have there vans wired this way [single or twin circuit ] on this forum , my suggestion works .
-- Edited by swamp on Tuesday 22nd of February 2022 12:04:37 PM
Can see you are obviously void of competent technical knowledge. I won't waste my time confusing you with facts, as can see your mind is made up. Nobody runs a single circuit. It is truly amongst the most stupid things that can be done Have 50 years auto electrical experience, retrained qualified auto electricians in correct methods Always kept my hand in technically and just worked for the last auto electrician Never ever have seen a single circuit. Don't think you should be replying to technical posts, as clearly you are technically incapable. This comment "Far safer to operate fridge via ignition/engine ON power trigger , switched relay/ solenoid and not run the battery down via vsr." indicates not only your complete cluelessness, and your ignorance of modern electrical systems. A VSR will not run a battery down. Like the circuit diagram posted with a relay today and for a long time is technically incorrect. The other issue a VSR requires no wiring intrusion into the vehicle electrical wiring. Will go back to the international cruising forum. They prefer to learn what is right and wrong from technically qualified people, and don't make ridiculous statements
hi
If the cable size 25--35mmsq within acceptable volt drop requirements will handle the current load, why not use it . Oh yea relays and solenoids been around awhile. So perfectly suitable for automotive.
Single cables running to sub-boards has been practised alot.
Monica, I think you are getting you are getting your nickers in a twist. I think you are reading Swampie as saying he means one wire. A circuit is not one wire, it consists of two. There have been many discussions on this and other forums. Regarding one or two circuits, i.e. one for the battery and one for the fridge, there were many who had problems using only one circuit if they did not wire it in 2 gauge cable. There were many attempting to use one circuit in 6 gauge for a fridge and direct battery charging. The only ones were satisfied with one circuit were those who used 2 gauge cable.
Do a search and look at some threads on the subject where oldtrack123 was involved. He was a very experienced man in electrical matters. He was an advocator of using two circuits and gave good explanations of why the home installer should be using them. In technical knowledge and experience I would equate him to any other on this forum.
What is wrong with using high current relays or solenoids in circuits like we are discussing After there were some notable battery management systems (which are just VSRs with a bit of hysteresis built in) which had common relays in then. I see your comment "Like the circuit diagram posted with a relay today and for a long time is technically incorrect" as a business person profiting from supplying incorrect information to a customer. Something does not become "for a long time is technically incorrect" just because a new item with more profit value has come onto the market. Also, the FridgeSwitch is rated to operate with any of the small and medium size 12 V. They are rated for up to 25 A. You are leading to legal problems for denigrating them as you did. I do not use VSRs or FridgeSwitches as there is an adequate device available for a fraction of the price.
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