Battery Ah size recommendations

[tolbot boulton]

Hi, i am thinking of putting a Dometic CRX50 compressor fridge into the van, but not sure about what size lithium battery to go for.
I have a 100w solar panel but will be getting a better solar charger (maybe victron) to charge the battery as well as adding a smart alternator charger.

We want to go off grid for up to 5 days at a time. Running the fridge and internal lights + phones charges.

Any recommendations for battery size would be greatly appreciated

 

[Dellmassive]

Two 100ah lithiums.

Maybe look at the 230ah Roamer seat base.

Beef up the solar 200-400w

And get a dc-dc charger.


More info.....

Dellmassive’s "How I Done It" blogs.

-- Dellmassive`s -- "How I Done It" -- thread -- ************************************************** Dellmassive`s -- "how I Done It" -- Thread ************************************************** Kit List And Stuff -- How I Done It & What I Use --...

www.t6forum.com

.

 

[tolbot boulton]

That's great, cheers.

 

[Eggster79]

Hi i am looking to switch from a 105ah lead acid to a Lithium leisure battery. I’m looking at the ones linked below and wondered if anyone has any experience of using one to help me decided.

I’m also thinking about getting a 150w solar panel or if i got a 230ah lithium would that negate the need for solar?

Any help would be much appreciated.

Xplorer Polarmax 100AH Low Temperature Lithium Battery with Bluetooth - Alpha Batteries



Lithium Leisure Battery - Fogstar Drift 12v 105Ah



Roamer 100SMART3 - 12V 105Ah LiFePO4 Lithium Leisure Battery

 

[roadtripper]

The other important part of the system will need to be a DC-DC charger, you can't just straight swap.

Choose the right one of those and it will have a solar input as well.

 

[Oceanis]

Hi, it really depends on how you use your van .... do you need Li or just want it? Do you know your power budget?

If you rarely stay parked up on a camp site for longer than a weekend, or regularly use an electrical hook up, or drive your van every other day, then solar is not really necessary.

If you want to park up indefinitely (during summer) without running the engine or using an electrical hook-up then solar is essential and you need to work out your power budget.

You need to cover 2 things .... first, your batteries need enough capacity to cover your needs for 24hrs plus a contingency for the odd bad weather day, and secondly, the solar system needs to reliably replace that power (plus a bit more) every day when the sun shines.

If you want Li then just go ahead and buy it - but you will need a few extra bits to get it to work properly - particularly if you want to charge the Li battery from the engine alternator. Lithium batteries can draw massive currents from an alternator if they are discharged, so a good DC-DC charger with a Li charge profile is necessary to protect the alternator from overheating and the battery from sub-optimal charge voltages.

But on to power budgets ...

Your 105Ah lead acid battery only has a max of 50% of it's capacity available before you will seriously start reducing its service life - that's about 50Ah, which multiplied by 12V gives you around around 0.6 kWh. To put that into perspective a typical compressor fridge fitted to a VW California Ocean will need around 0.35-0.45 kWh per day dependent on settings and ambient temperature.

My power budget for my Cali Ocean looks like this ...



So I need about 0.8 kWh per day from my solar system to remain off-grid and avoid running the engine.

There is a solar estimator on the Victron web-site where you can enter your location and solar config to see if you cover your power budget.

MPPT Calculator - Victron Energy

MPPT Calculator - Victron Energy

www.victronenergy.com

Sorry I can't give you any info on the Li batteries you mentioned but there is also loads of Li info on this site in the "How I done it" section.

 

[DXX]

Plus ensure the cables and fusing are the correct cross section / rating, lithium batteries can charge at a much higher current.

 

[Eggster79]

Thanks for your help, I currently have a ctek D250SE which can do lithium & solar but i’m not sure if i will also need to change all the fusing & wires though. My current leisure battery is dead so it’s either replace like for like and get a 140w solar panel fitted for £850 or go lithium and maybe solar later if i really need to.

 

[Eggster79]

Thanks for your help, I currently have a ctek D250SE which can do lithium & solar but i’m not sure if i will also need to change all the fusing & wires though. My current leisure battery is dead so it’s either replace like for like and get a 140w solar panel fitted for £850 or go lithium and maybe solar later if i really need to.

And a sargent ec160

 

[roadtripper]

Your CTEK is likely fine for what you want to do, just double check the cabling and you might need appropriate new final battery tails making up to fit the new terminal types and location.

Your issue is going to the be the Sargent EC160 as the charger in that is not going to be appropriate for anything other than a lead acid leisure battery. Unfortunately as it is both the charger and the distribution/switch board you can't simply not connect.

 

[Dellmassive]

The three lifepo4 battery you listed above are known brands...

As is Renogy 100ah.

All will work with your d250se ctek.

You can add solar to your d250se, though you might want to look at adding a stand alone mppt for any solar, fitted or mobile.

 

[Eggster79]

Ah ok so no more charging the leisure battery from the electric hook up/house the way i can now.

 

[Oceanis]

Your CTEK is likely fine for what you want to do, just double check the cabling and you might need appropriate new final battery tails making up to fit the new terminal types and location.

Your issue is going to the be the Sargent EC160 as the charger in that is not going to be appropriate for anything other than a lead acid leisure battery. Unfortunately as it is both the charger and the distribution/switch board you can't simply not connect.

You could hard-wire the Sargent to only charge the starter battery (it has a switch on the front which could be modified). If the Sargent is also then connected to the split charge relay/diode/FET like the alternator, then when the Sargent charger is active, the CTEK would see the charge output of the Sargent (like the alternator) and provide charge for the Li leisure battery with the right profile. (I'm assuming there is a battery isolator for the alternator somewhere).

The Sargent would then charge the starter (Lead Acid), via the split charge relay (or FET, or Diode), while providing power for the CTEK to charge the LI properly. So long as the Sargent never connects it's charger directly to the Leisure battery it should be all good.

.... I think.

 

[roadtripper]

Ah ok so no more charging the leisure battery from the electric hook up/house the way i can now.

Well it might be a bit more complicated than that.

If you use your Sargent to feed your camper 12v electrics (and I assume you do) then you would need to find a way of disabling the charger - trying to remember to not turn it on isn't going to be reliable enough. That might mean opening the unit up and removing and making safe one of the charger switch connections.

 

[Dellmassive]

With EHU most people fit a smart charger.... say a Victron 15A for example for mains EHU connection.

This will run stand alone,

You may need to disable the the Sargent 12v charge circuit.

 

[roadtripper]

You could hard-wire the Sargent to only charge the starter battery (it has a switch on the front which could be modified). If the Sargent is also then connected to the split charge relay/diode/FET like the alternator, then when the Sargent charger is active, the CTEK would see the charge output of the Sargent (like the alternator) and provide charge for the Li leisure battery with the right profile. (I'm assuming there is a battery isolator for the alternator somewhere).

The Sargent would then charge the starter (Lead Acid), via the split charge relay (or FET, or Diode), while providing power for the CTEK to charge the LI properly. So long as the Sargent never connects it's charger directly to the Leisure battery it should be all good.

.... I think.

I did consider this but I strongly suspect that the charger is just connected to the 12v bus inside the unit as the manual states that it will charge whichever battery is selected on the front.

 

[Dellmassive]

Some one on here done it before,...

Disabled the Sargent internal mains 12v PSU, and retrofitted a Victron smart charger.

Haven't had a Sargent to play with myself ..... yet......

But it can be done.

...

I also seen to remember seeing something from Sargent about update to enable lifepo4 to be added as the leisure battery.

 

[slybacon67]

Ah ok so no more charging the leisure battery from the electric hook up/house the way i can now.

Will your system not simply charge the battery whilst driving then keep a float charge when on hook up. if Your battery arrives on site with say 50% charge then the Sargent will simply supply the 12 v system and not effect the battery. I have a similar set up in my van and want to fit lithium also with a dc to dc charger so I am curious if my theory will work.

 

[slybacon67]

With EHU most people fit a smart charger.... say a Victron 15A for example for mains EHU connection.

This will run stand alone,

You may need to disable the the Sargent 12v charge circuit.

Does the victory charge and power equipment at the same time whilst on hookup.

 

[Dellmassive]

Yes.

You can set two modes, charger or PSU. (Victron smart charger ip22 or ip65)

But for lithium id leave the charger set to charge mode to keep the battery topped up.

Then the 12v system will look after itself.