Charging Caravan 12v system from an external lithium battery

[kjpalmer100]

Hi everyone. I'm new to this forum as just buying a caravan

Previously I've camped in a tent and have a 100Ah LiFEpo4 battery which has much more available power than a lead acid battery.

I initially wondered about using the lithium battery in a caravan however I understand that I cannot swap the Lead Acid leisure battery in the caravan for a lithium battery due to the different charging voltages etc.

So, I had an idea. Would it be possible to make up a cable that would utilise the car->caravan connector and provide power to the caravan from the Lithium battery? I expect i'll need a DC-DC converter to sure that the voltage is correct for the caravan.

Has anyone tried this or does a ready made solution exist? I'm thinking this will extend the 12v power considerably when off-grid.

Thanks,
Kevin

 

[Jcloughie]

Hi kjpalmer, and welcome to the forum.

Others have put their lithium battery into the caravan. But you do need advice as to what chargers are suitable. Some caravan chargers are. There have been recent posts on here you might want to view, one member is very knowledgeable. But that is not me.

If your lithium is a nominal 12 volt battery you should be ably to connect direct with the caravan connector, either making up or buying a cable. Caravan low voltage electrics tend be happy with a range of voltages around 12v say 11-14.

John

 

[kjpalmer100]

Hi kjpalmer, and welcome to the forum.

Others have put their lithium battery into the caravan. But you do need advice as to what chargers are suitable. Some caravan chargers are. There have been recent posts on here you might want to view, one member is very knowledgeable. But that is not me.

If your lithium is a nominal 12 volt battery you should be ably to connect direct with the caravan connector, either making up or buying a cable. Caravan low voltage electrics tend be happy with a range of voltages around 12v say 11-14.

John

Ah, that's interesting. I'll see if I can find out if my Caravan can take them. It's a 2016 caravan, so maybe not.

 

[JTQ]

You could go a "hybrid" way, using the van's LA battery, and the built in distribution for the low demand applications, and for the higher demand issues, for example your TV viewing, run that totally separately off your Lithium unit.
I have done much the same having carried a second battery for the non "life support" things like TV and HiFi, where if there is not enough, it does not stop the camping trip.

I kept the two systems independent of each other, I would certainly do so in your case where LA & Li are involved.

 

[ProfJohnL]

... So, I had an idea. Would it be possible to make up a cable that would utilise the car->caravan connector and provide power to the caravan from the Lithium battery? I expect i'll need a DC-DC converter to sure that the voltage is correct for the caravan.

Unfortunately this will not work without having to make some changes to the caravan's 12V wiring as car connection only powers the fridge, and the on board caravan battery. All other circuits are normally isolated when towing.

My suggestion relies on the assumption you have a suitable LiFEpo4 charger already or could get one.
Turn off the caravans built in charger and leave it off. remove the LA caravan Battery and replace it with the LiFEpo4 into the caravan's battery space. Arrange to bring your LIFEpo4 battery chargers wires into the battery storage box from inside the caravan, so the charger is next to the battery box under the bed, and plug it into a a 230V ac socket.

Just make sure the caravans LA charger is never turned on.

 

[Jcloughie]

Unfortunately this will not work without having to make some changes to the caravan's 12V wiring as car connection only powers the fridge, and the on board caravan battery. All other circuits are normally isolated when towing.

My #2 reply assumed the OP would be utilising pins 9 (permanent live), and 13 with the van switched to ‘car’. My understanding is, that the ‘car’ switch will only allow one or the other battery to be used.

John

 

[GUMPY]

I run a Fogstar 105 battery in my van, you just need to check that the charge sources are OK for it.
I changed the solar and mains charger on mine to make it more efficient, I probably didn't have to. As for charging from the car just check the current into the battery with the engine running, mine is 5amps so no worries at all.
HTH

 

[ProfJohnL]

My #2 reply assumed the OP would be utilising pins 9 (permanent live), and 13 with the van switched to ‘car’. My understanding is, that the ‘car’ switch will only allow one or the other battery to be used.

John

We don't know if the OP is buying a new caravan or an older model, How the car/caravan battery switch functions may vary depending on make and age of the caravan, so both our assumptions could be wrong. Its really just a heads up to check.

 

[otherclive]

We don't know if the OP is buying a new caravan or an older model, How the car/caravan battery switch functions may vary depending on make and age of the caravan, so both our assumptions could be wrong. Its really just a heads up to check.

It’s a 2016 caravan model.

 

[birdman101]

I think you will find powering through the 13 pin connector may switch the habitation relay therefore 12 volt lights etc would be off.

 

[Tobes]

Depending on the battery, it may just be drop in supported.
We have a LiFePo4 battery made by Kepworth. All its power is delivered via a BMS and so is pretty much a drop in replacement for lead acid. It's been working absolutely fine using our old integrated charger (2016 Bailey) though I did update our solar controller so it would have the ability to maintain a higher charge voltage.

 

[kjpalmer100]

Thanks for all your suggestions. It looks like me idea of connecting via the 13 pin connector is a no go then as it basically sounds like it puts the caravan in 'transport' mode. I guess I could always use this to charge the LA battery if we were away from the caravan for some time but it would be no use whilst using the caravan.

I did think about replacing the LA battery with the LiFePO4 battery but I think my main concern is with the recharging and the systems ability to recognise the charge level of the battery. Is it likely to cause problems? The caravan we are buying is a 2016 model Swift Elegance if that helps. It has a factory fitted solar panel as standard so I don't know if it's replaceable.

 

[birdman101]

I presume you have the Sargent solar controller if factory fitted as our last Swift caravan. If you change the controller to a Truma as fitted in our present Swift you have dip switches on it to change to the Battery to LiFe PO4

 

[ProfJohnL]

Thanks for all your suggestions. ...

...I did think about replacing the LA battery with the LiFePO4 battery but I think my main concern is with the recharging and the systems ability to recognise the charge level of the battery. Is it likely to cause problems? The caravan we are buying is a 2016 model Swift Elegance if that helps. It has a factory fitted solar panel as standard so I don't know if it's replaceable.

Not if you use my suggestion in #5

 

[trevormonty]

I did think about replacing the LA battery with the LiFePO4 battery but I think my main concern is with the recharging and the systems ability to recognise the charge level of the battery. Is it likely to cause problems? The caravan we are buying is a 2016 model Swift Elegance if that helps. It has a factory fitted solar panel as standard so I don't know if it's replaceable.

Most solar chargers can be reconfigured to support LiFeP04. If that doesn't work replacement PWM ones are only £10. Not as efficient as MPPT but lot cheaper and worth try at £10.
As for AC charger see how solar goes before buying new charger.

 

[kjpalmer100]

Hi all, picked up the Caravan yesterday so I am going to have a play and experiment Will look into the various options mentioned here. Thank you for your advice! Will let you know how I get on!

 

[Gafferbill]

Thanks for all your suggestions. It looks like me idea of connecting via the 13 pin connector is a no go then as it basically sounds like it puts the caravan in 'transport' mode.

.....some confusion here!

Making up a bespoke lead to connect your caravan via the 13 pin connector is doable.
You need a caravan with a switch that let's you choose between car and caravan as a source of 12 volt incoming power.
You would also need to make the bespoke lead connect positive 12 volts to pin 9 and negative to pin 13.
Such a bespoke lead would not allow a connection between the caravan battery and auxiliary battery.

The habitation relay would not be triggered .....what the OP refers to as "transport mode".
This is because the refrigerator circuit would not be live and it is this circuit that triggers the habitation relay when a towing vehicle is connected.

Whilst it is possible to use an auxiliary battery in this way, it would be difficult to secure the battery against theft.

 

[kjpalmer100]

Ah, yes I think I've got it! So, you can connect a 12v supply to pin 9 but not pin 10. This will allow an external 12v battery to power the caravan's appliances - I think I can select this on the Swift Command panel (the caravan will no longer use it's internal battery).

What this does mean is that whilst I can use an external battery to power the 12v systems in the caravan (i.e. pumps, lights etc). What I can't do is use it to power the fridge because for the fridge to work pin 9 needs to be connected which affectively activates this 'habitation relay' and connects the incoming 12v to the Fridge and the Battery charger and disconnects the Battery from the rest of the caravan.

Correct me if i've misunderstood!

For now I've got a few options.
- Look at how feasible it is to replace the LA battery with the LiFePO4 directly and if I need to change any built in battery chargers, MPPT/solar chargers etc.
- Replace LA battery but maybe isolate the built in caravan charger and instead connect a separate non-integrated Lithium charger when needing to charge the caravan battery and 240v available.
- Do the Hybrid option and just use the Lithium for TV, music, charging phones etc.
- Create a 13pin adapter cable for an external LiFePO4 battery but only connect the 9 (Orange/Permanent Live) and ground without connecting the 10 (Grey/Fridge) pin. Then I can select this battery saving the LA battery for things like the motor mover etc. I think in this case I wouldn't even need to worry about battery charging voltage as it would never try and charge the LA battery anyway.

Thanks for all your help.. It's very interesting to understand how all these systems work together.

 

[Gafferbill]

.....you've got it!
Just don't connect pins 10 and 11 to anything if you make up a lead.

 

[ProfJohnL]

You don't want to power the fridge from your battery. The current draw is significant and it will flatten a battery in few hours - even 110Ah battery.

The 12V feed for the fridge is deliberately separated out so it will only use 12V for cooling when its connected to a tow vehicle and its alternator is running.

If your Off Grid, its far better to run the fridge from LPG.

 

[Dustydog]

.....some confusion here!

Making up a bespoke lead to connect your caravan via the 13 pin connector is doable.
You need a caravan with a switch that let's you choose between car and caravan as a source of 12 volt incoming power.
You would also need to make the bespoke lead connect positive 12 volts to pin 9 and negative to pin 13.
Such a bespoke lead would not allow a connection between the caravan battery and auxiliary battery.

The habitation relay would not be triggered .....what the OP refers to as "transport mode".
This is because the refrigerator circuit would not be live and it is this circuit that triggers the habitation relay when a towing vehicle is connected.

Whilst it is possible to use an auxiliary battery in this way, it would be difficult to secure the battery against theft.

Bill,
I believe pin 9 is permanently live and its earth return 13 on most cases power the ATC.

Do you think for the OP as this is a bespoke situation he could use pin 12 for a direct live feed with 13 providing the earth?
I wouldn’t like to see anything in the modification affecting the ATC performance 😉

 

[Gafferbill]

Alan ....pin 12 doesn't connect to any caravan circuit whereas 9 and 13 pins are designed to transmit 12volts to a bona-fide caravan circuit.
My Swift caravan has a switch which allows you to select 12 volts from the caravan battery or 12 volts from a towing vehicle.
Not sure if all caravans have this facility but the OP would need to operate such a switch to fit in with a bespoke connection via the 13 pin plug.
Your right such a bespoke connection would operate the Alko ATC if fitted to the caravan but it would be in standby after it's test sequence.
Alko tell us the system only uses enough power to operate the LED when it is in standby.

I was just clarifying information for the OP regarding his original question which concerned maximising and utilising his available power sources when off-grid.

 

[Dustydog]

Thanks Bill,
A good explanation👍