Solar panel to charge starter and leisure battery

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  • Solar panel to charge starter and leisure battery
  • Premier Icon hellothisistom
    Subscriber

    Hi all, I wonder if anyone has a set up like this they could help with.

    Currently in my van i have my leisure battery being charged from my starter battery/alternator via a VSR to avoid draining the starter.

    I would like to install some solar panels. I’d like them to mainly charge the leisure battery, but to keep the starter battery conditioned and charger. (I use the van irregularly enough that it’s often flat when I start it)

    Has any one got thier set up doing this?

    I was thinking 200w of panels with a 20a controller. But I’m not sure which battery to charge. If I plug it straight to the leisure battery I don’t think that will send any extra to the starter, and if I plug it to the starter I’m not sure it will ever get the volts high enough to charge the leisure.

    Thanks!

    Premier Icon tillydog
    Subscriber

    At least 3 options:

    1 – Charge the vehicle battery and rely on the VSR kicking in to transfer charge to the leisure batteries.

    2 – Dual output MPPT solar controller (e.g. Votronic) which will charge the leisure batteries and at the same time, trickle charge the vehicle battery.

    3 – Charge the leisure battery from solar and use a separate gizmo to feed some charge back to the vehicle battery – e.g. CBE CSB2 or BCM12 or Votronic or Vanbitz (if you own a Rolls Royce)

    I went for 3 (using a homemade gizmo) because I hadn’t seen those dual output Votronic controllers at the time. I’d probably go for 2 if I did it again. Option 1 just doesn’t seem ‘right’ to me.

    (Incidentally, in case you’re wondering, it’s worth getting an MPPT controller over a PWM one IMHO)

    Premier Icon hellothisistom
    Subscriber

    Sweet thanks. That’s what I was thinking. My only thought was would it do something odd if the solar panel is working and charging both batteries and the starter is charging the leisure : ie when I’m driving in the sun.
    As you can tell I’m not an electrician!

    Premier Icon tillydog
    Subscriber

    My only thought was would it do something odd if the solar panel is working and charging both batteries and the starter is charging the leisure : ie when I’m driving in the sun.

    Don’t worry about it – the various chargers sort it out between themselves.

    Premier Icon spooky_b329
    Subscriber

    RE: charging from solar and alternator at the same time, it shouldn’t matter.

    Be careful with homebrew solutions, if you take the example of a flat leisure battery and then starting the van, you have a fresh starter battery that is primed to dump 80 amps or more into the leisure battery via the easiest route. If it finds an unsuitable route, at best it will pop a couple of fuses, or pop a solar controller, or at worst overload some wiring and cause a fire. I have a a vehicle and leisure feed to my dashboard so my radio and a couple of other items are powered from the leisure battery, but the ignition on/off still works and can be manually switched on when parked up…I spent some time making sure the two batteries could not accidentally connect through this wiring using relays.

    I think I have seen VSRs that can be switched by both batteries, so the alternator can charge the leisure, and a solar or hookup charge on the leisure will charge the starter.

    IHN
    Member

    While we’re talking about this kind of stuff, has anyone got one of the folding/briefcase type panels? I’m thinking of getting one for the van to keep the leisure battery topped up when we’re not on hookup. Probs a 100w one, main draw off the battery being the fridge which the manual says draws 45W (Dometic CB40).

    Premier Icon spooky_b329
    Subscriber

    IHN, I would consider a 100 or 200w semi flexible panel that can be glued or bolted to the roof. Follows the shape of the roof and very low profile, the great thing about solar is its always trickle charging when its bright weather (doesn’t need direct sun)…a briefcase one needs setting up so you are losing all the advantages of a constant charge.

    To keep up the the fridge you’d need a bit more power, I have 200w and it will keep an 80 litre Waeco fridge running all summer, but if I’m staying in the van and using the radio, charging phones etc it will keep things ok for 2-3 days before you need to think about a hookup or a drive to top up.

    100mph
    Member

    I have a 100W rigid panel on my MoHo roof and a duel controller sending 90% to 2 x 110 leisure and 10% to 2 x starter/habitat batteries, (so it’s charging 4 batteries) and none have ever gone flat in 4 years of use so far.
    I use the fridge on gas when stationary, so that load never comes from batteries.

    IHN
    Member

    I get a fixed panel is a better option, but it’s more expensive and it’s not happening. I’m looking at briefcase panels for about £120 on eBay (and missed a second hand bargain, grrr). It’ll be set up when the van’s parked, pointed south, and sit there till we leave.

    Premier Icon tillydog
    Subscriber

    Your fridge will only consume 45W while the compressor is running which might be 25-30% of the time, so its average consumption will be something like 15W (or 1.25 Amps x 24 hours = 30 amp hours per day).

    As a benchmark, we have 160W of solar and a good MPPT regulator. It keeps our CRX50 fridge running 24/7 from ~March to ~October in the UK. Our fridge is probably a bit less efficient than yours, being a front loader and probably less well insulated, and it uses ~40AH per day, so that sounds about right.

    The the only time last year that the batteries weren’t fully recharged each day was when the weather was hot, sultry and overcast in the middle of summer.

    If you’re using portable panels, you’ve got the advantage of being able to angle them towards the sun through the day which will make quite a difference. You’ve got the disadvantage that, unless you’re a very early riser, you lose a lot of charging time if you put them away at night / get them out in the morning.

    You might get away with 120W, especially if you’re angling the panels towards the sun – it will certainly help – but bigger is better.

    ETA: I would avoid semi-flexible panels, personally. They don’t have a great reputation for longevity unless you go for the *really* expensive ones.

    ETA2: Reasonably priced rigid panels here: https://lowenergysupermarket.com/product/mono-150w-solar-panel-only/

    IHN
    Member

    Your fridge will only consume 45W while the compressor is running which might be 25-30% of the time, so its average consumption will be something like 15W (or 1.25 Amps x 24 hours = 30 amp hours per day).

    The fridge goes off at night and will be on for, say, 16 hours a day, so 12ishW and 20ah using your calc. The battery generally lasts about three/four days, which would be about 60/80 ah used, on a 110ah battery, so that all seems to fit.

    So if I need 12W to cover the fridge use, why might I only ‘get away” with a 120W panel? I get I won’t get 120W from it all the time, but I only need it to be 10% efficient to get what I need, don’t I?

    Premier Icon tillydog
    Subscriber

    So if I need 12W to cover the fridge use, why might I only ‘get away” with a 120W panel?

    Based on real world experience of 160W reliably generating 40AH/day (March-October), 120W should generate 30AH/day.

    You didn’t say that you switched the fridge off at night.

    If you only need 16AH, then you could get away with a lower power panel (pro-rata).

    (The rated power of panels is what they generate under a clear sky, aligned with the sun, at noon at ~48 degrees north and 20°C. Real world output varies through the day, and with alignment, latitude, seasons, weather, etc. so will, on average, be less.)

    IHN
    Member

    You didn’t say that you switched the fridge off at night.

    Yeah, I’d forgotten myself to be honest 🙂

    Gotcha though, that’s really useful info, thanks.

    Are all the kits on, say, Amazon, much of a muchness?

    Premier Icon tillydog
    Subscriber

    What sort of thing have you been looking at?

    IHN
    Member

    This kinda thing

    DOKIO 100 Watt 12 Volt Monocrystalline Foldable Portable Solar Suitcase with Waterproof Charge Controller https://www.amazon.co.uk/dp/B07JVJJH47/ref=cm_sw_r_cp_apa_i_.RTrEb0CBN1N7

    martinb
    Member

    I have a 120w folding briefcase pair of panels coupled to a charging unit that is connected to the leisure battery in the campervan. The fridge is 12v powered when driving and 240 on hook up. The panels can put 10A into the battery on a clear sunny day, and pointing them at the sun makes a huge difference to charge. For plug and play, I sometimes run an inverter off the leisure battery and run the fridge off this, I know I’m wasting power through the inverters inefficiency. I’m not running off grid for weeks.

    teamslug
    Member

    A small point I would make is to consider the kind of leisure battery you have. If it is lead acid that needs topping up I would consider disconnecting it when not needed ie when van is storage. I have a decent sized panel on my MH and leaving it connected in summer really does put some power into the batteries. Can easily evaporate off and leave the cells exposed which will knacker them in no time. I replaced mine with some sealed ones but once they are topped up I disconnect if storing for any amount of time esp in summer.

    Premier Icon tillydog
    Subscriber

    This kinda thing

    Looking at a few similar ones, it seems they are.

    They seem to come with PWM controllers – If you can find one with a (genuine) MPPT controller it might be worth a premium (you should get ~ 20-30% more power from the same panel with MPPT rather than PWM. That 18V /100W panel will only give ~80W at 12V with a PWM controller.)

    The other thing is trying to pick a seller who will still be around in a couple of years if you need to claim on the panel guarantee.

    teamslug

    …Can easily evaporate off and leave the cells exposed … I disconnect if storing for any amount of time esp in summer.

    What controller do you have? The better ones (e.g. Victron) assess the state of the battery at dawn every day and keep the battery on float charge if it’s already fully charged.

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