Our leisure battery is 70 ah AGM and is struggling to power Dometic CR50 compressor fridge overnight when off grid. Apart from interior led lights and occasional use of diesel heater no other major load on LB. We have a choice to make and need some advice: do we install a 150w (say) flexible solar panel on our pop-top to top up AGM or instead just beef up battery and upgrade to a 100 ah (say) Lifep04 ? Not much price diff between the two as I would be getting someone to fit the solar panel. Frequently go off grid for 2 or 3 days when away.
Solar panel or upgrade to Lithium battery?
- Thread starter Carhoona
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Regardless of whether you go for solar I would say you need a bigger battery even if that’s just a 100ah AGM (probably the cheapest option to give you a bit longer run time). We have a 95ah battery and 150w solar and it’s a stretch to get more than a day or two with the fridge running in the height of summer.
If your charger etc can take a lithium battery then I’d go for that first, then you could always add solar later. This would give you more than twice the juice of your current setup for starters on a cloudy day whereas solar would at best top the current battery up and at worst struggle to maintain it.
If your charger etc can take a lithium battery then I’d go for that first, then you could always add solar later. This would give you more than twice the juice of your current setup for starters on a cloudy day whereas solar would at best top the current battery up and at worst struggle to maintain it.
Thanks for comprehensive reply and very good advice. I will definitely go down the Lithium route. One final question: we currently have a Victron blue smart charger 12v/10a fitted which does have a “Li-ion” setting. What is the max ah Lithium I could go for which I could simply swap for the AGM without running into other concerns? I am proposing 100 ah but could I easily go higher?
you can go to any size you like.
the only difference will be the time it takes to charge from the charger. . .
you would need to make sure your dc-dc charger had a lithium profile.
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I have the 12/7 blue smart and 100ah lithium which works fine. As above it just takes a little longer to charge.
Our 70Ah AGM easily powers our very similar fridge overnight so I would guess your battery is either knackered or not charged properly. Understanding which is the issue is critical to deciding what the fix is. If the battery is knackered to the extent that it won’t keep a fridge going overnight, then a solar panel won’t help much, whereas if it’s not getting charged properly then a whizzy new lithium battery might not help as much as you think if that doesn’t get charged properly either.
Design your energy system to do what YOU need because there are a number of factors that influence how much battery capacity and solar generation to fit.
Lithium has major advantages over AGMs because it will have many more charge cycles and can be discharged much lower than an AGM with no detrimental effects, and it is lighter - Lithium is a no-brainer IMO, the only disadvantage is that the alternator charging system is designed to charge AGM batteries so a DC-DC converter with a lithium charging profile needs to be connected between the 12v AGM system and the 12v Lithium battery system - you end up with the vehicle electrical system (engine etc.) running off the AGM engine battery and all the domestic 12V loads running of the Lithium system. If you have an aftermarket conversion then this should be relatively straightforward, if you have an Ocean or equivalent with a charge-relay, camper unit, and AGM leisure batteries, then a fully integrated lithium conversion is much, much, more complicated (and expensive).
If your usage pattern is to stay somewhere, off-grid, for a long weekend and then drive a reasonable distance before camping again, then maybe just a switch to Lithium will be enough. The use case would be to arrive with the lithium battery fully charged, and leave with it almost empty - charging it fully again using the alternator while moving to the next site.
To decide what capacity you need, you need to do a power budget - and the biggest consumer (assuming you don't have an inverter with lots of 240V devices) will be the fridge. Compressor fridges can use anything from around 0,3kWh to around 0,8kWh dependent on ambient temperature, insulation, contents and size. It is worth getting a watt-meter (https://www.amazon.co.uk/Diymore-Analyzer-Detectorm-Consumption-systems/dp/B0B96F6RH8) and wiring it in series with your fridge to find out how much it uses over a typical weekend away. Whatever it uses needs to be available, in Ah from the lithium battery you choose - with a bit of extra capacity for all the other 12V loads you have.
If you want to extend the amount of time you can remain off-grid then think about solar as a means of providing additional power ... again, do a power budget and look at how much energy a solar setup will typically produce in the area where you usually camp. You can estimate it here ... MPPT Calculator - Victron Energy ... the calculator enables you to enter the parameters of the solar system you are thinking of installing and you can get an estimate of the yield by entering the location where you normally use your van.
My energy budget for my van looks like this ....
... and as I decided to stick with the AGM leisure batteries fitted to my Ocean, I ended up with 310W of solar on the roof. I am in central/southern Europe so it more than covers my energy usage between April and September when I use the van most.
Lithium has major advantages over AGMs because it will have many more charge cycles and can be discharged much lower than an AGM with no detrimental effects, and it is lighter - Lithium is a no-brainer IMO, the only disadvantage is that the alternator charging system is designed to charge AGM batteries so a DC-DC converter with a lithium charging profile needs to be connected between the 12v AGM system and the 12v Lithium battery system - you end up with the vehicle electrical system (engine etc.) running off the AGM engine battery and all the domestic 12V loads running of the Lithium system. If you have an aftermarket conversion then this should be relatively straightforward, if you have an Ocean or equivalent with a charge-relay, camper unit, and AGM leisure batteries, then a fully integrated lithium conversion is much, much, more complicated (and expensive).
If your usage pattern is to stay somewhere, off-grid, for a long weekend and then drive a reasonable distance before camping again, then maybe just a switch to Lithium will be enough. The use case would be to arrive with the lithium battery fully charged, and leave with it almost empty - charging it fully again using the alternator while moving to the next site.
To decide what capacity you need, you need to do a power budget - and the biggest consumer (assuming you don't have an inverter with lots of 240V devices) will be the fridge. Compressor fridges can use anything from around 0,3kWh to around 0,8kWh dependent on ambient temperature, insulation, contents and size. It is worth getting a watt-meter (https://www.amazon.co.uk/Diymore-Analyzer-Detectorm-Consumption-systems/dp/B0B96F6RH8) and wiring it in series with your fridge to find out how much it uses over a typical weekend away. Whatever it uses needs to be available, in Ah from the lithium battery you choose - with a bit of extra capacity for all the other 12V loads you have.
If you want to extend the amount of time you can remain off-grid then think about solar as a means of providing additional power ... again, do a power budget and look at how much energy a solar setup will typically produce in the area where you usually camp. You can estimate it here ... MPPT Calculator - Victron Energy ... the calculator enables you to enter the parameters of the solar system you are thinking of installing and you can get an estimate of the yield by entering the location where you normally use your van.
My energy budget for my van looks like this ....
... and as I decided to stick with the AGM leisure batteries fitted to my Ocean, I ended up with 310W of solar on the roof. I am in central/southern Europe so it more than covers my energy usage between April and September when I use the van most.
Our T6.1 was ordered from new as a panel van with factory fitted 2 captain seats and leisure battery under the passenger seat - van was then converted to camper with Victron Blue Smart charger 12v/10a added as part of the electrics. So where does that leave me regarding a DC to DC charger if I’m now changing LB to Lithium- is that now more complex?? Apologies if that sounds like a stupid question
If you’re running a factory leisure battery then it’ll likely be hooked up via a simple relay - you should be able to verify this if you look under the passenger seat. If so, it’ll be charging to no more than 80% full so you might want to consider a DC-DC charger. You’ll need one of these anyway if you install a lithium battery, you can’t connect these with a relay.
I don't have access to a schematic showing a panel van with leisure battery, but as already mentioned, it will almost certainly be connected to the engine battery via a relay operated by VWs Special Vehicle Control Unit (SVCU) - maybe it's a Battery Control Unit in your van, I don't know. This second battery will also very likely have a shunt attached to the negative terminal which allows the SVCU/BCU to estimate the charge level - which it tries to hold at around 80-90%.
The batteries and smart alternator are part of the emissions control system on modern cars (and vans). What this does is when you accelerate, the smart alternator stops producing power, and the vehicle electrical system is run from the batteries. This removes alternator load from the engine and saves fuel during an acceleration. When you decelerate, the smart alternator dumps power into the batteries to give additional engine braking and to recover energy - storing it in the batteries. In order for this to work, the system tries to keep the batteries around 80-90% charged to allow for recuperation. The other action of the smart relay is to disconnect the leisure battery during an engine start so only the starter battery and wiring have to deliver the load required to start the engine.
Obviously, for a camper van, 80-90% charge is not what you want which VW recognised and in the versions with a Camper Unit (display above the rear-view mirror) there is a Max Charge option which you can switch on - this changes the behaviour of the engine, the idle speed is raised, start-stop is disabled - and the batteries are charged to 100% ... normally switch this mode on about an hour before arriving at a camp site.
My wiring looks like this ... your van is probably the same minus the Battery Charger and 3rd battery.
If I were you, I would look through the posts from @Dellmassive for an appropriate diagram and explanation relevant to your setup. Basically you isolate the Lithium leisure part from the AGM based engine part with a DC-DC charger running a Lithium charging profile. This will charge the Lithium batteries with the right charge profile but using the alternator as the power source.
Here looks like a good place to start ... @Dellmassive`s T6 T32 Sportline 204 LWB DSG PV MY18 - Van Adventure
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