MPPT regulators will get you a lot more power for your panel too.
solarboy,
Jan 20, 9:29am
Read this thread last nightthen just happened to pick up a Renew magazine this morning which has a story about an Aussie couple who seem to use their caravan for a fair amount of touring and they use a 130 A/Hr deep cycle battery and calculated that they used about 30 A/Hrs per day. They fitted an 80 watt panel ( about 5 amps output ) which covers their usage well as their back-up charge powered from the tow vehicle has only been needed 4 times in nearly 200 nights of bush camping.They run LED lights, TV, DVD player, water pump, laptop and even an electric blanket ! So you'll need a fraction of their panel size to just maintain your battery during the week. Don't forget to use a regulator, a simple cheapie on/off type as adv. on Trademe from $30 or so will suffice. I use a couple of 10 watt panels ( 0.6 amps each ) to maintain and top-up several car little used car batteries, A few hours a few times a week suffices. I fitted a couple of 60 watt panels to a camper for a relative and they were way more than enough for his use - a few LEDs and many hours a day of tv use. LCD tv plus sat dish and top box.
mechnificent,
Jan 20, 10:09am
That aussie couple must be calculating their usage wrong. Thirty amp/hours a day won't cover what they are using.
solarboy,
Jan 20, 9:49pm
It actually added up to 29 Ah. They'd metered everything to get the current draw for each appliance and multiplied that by hrs/day usage to get the Ah for it before they bought their panel.Highest use was tv and tv/dvd player at 7.5 and 6.6 for 2.5 and 2 hrs respectively. The article has a chart showing all the details. Was working OK as evidenced by the fact they'd only needed the back-up charger 4 times in the nearly 200 nights camping.
mechnificent,
Jan 21, 11:49am
Well 7.5 X 2.5 =18.5, and 6.6 X 2 = 13.2, which add up to 31 A/H for a start, and an electric blanket is going to use a bit, laptops power converters are around 75 watts, water pumps will draw 10 amps. it all adds up. You really don't want to trust an aussie's maths Solar. nice people and all that but.
thejazzpianoma,
Jan 21, 12:41pm
Muzz, I recently setup a campervan with very similar requirements. I setup a spreadsheet and did all the math properly so it would "just" keep pace during cloudy winter days in the South Island. Practice seems to have confirmed the theory to be spot on. I can share my thoughts and spec if you like but you seem to have lots of reply's (which I don't have time/energy to read at the moment) so just let me know if you still need advice.
smac,
Jan 21, 1:57pm
Was looking into solar myself to be able to keep a beer fridge power neutral. Finding a DC fridge is next to impossible, they are all 3 way and therefore expensive. Think I'd have to run it for about 25 years on one set of batteries for it to make sense $$-wise.
mechnificent,
Jan 21, 5:07pm
Pfff. since when have beer fridges had to comply to a budget!
smac,
Jan 21, 5:17pm
Since it comes out of the same hole as parts for the toy.
mechnificent,
Jan 21, 5:20pm
Whow. that's a dilemma then alright.
mechnificent,
Jan 21, 5:26pm
Where did you get your figures for substandard sunlight panel output! Or did you calculate it!
thejazzpianoma,
Jan 21, 6:30pm
I calculated it, would have to dig out the spreadsheet to tell you what I used (not a good brain day today) but everything behaves pretty much exactly as I expected. I had to build a bit larger system than the OP may need due to running a DC refrigerator but I was really pleased with how cost effectively it all worked out.
I get the impression the OP doesn't really have a grasp of the fundamentals (truck battery, trying to have the system catch up over a week etc) but I wasn't going to go into it all if its already been covered or they have gone away.
mechnificent,
Jan 21, 6:36pm
Yeah it's all a bit of a guess really given all the variables, so I was wondering how you chose what figures to use. Best plan is to have plenty of batteries, and then get enough panels to supply what you need over an averaged period of time of sun. If you try to guarantee that the panels will always supply enough, even on a cloudy day, then you end up buying six times as many panels as you really need on a sunny day.
muzz67,
Jan 21, 6:52pm
.[/quote] I get the impression the OP doesn't really have a grasp of the fundamentals (truck battery, trying to have the system catch up over a week etc) but I wasn't going to go into it all if its already been covered or they have gone away.[/quote]
HaHa, nope , electronics still a foreigh language at the moment. I figure if the battery can give us 6 days over Xmas without any charging at all, I'm guessing our consumption isn't very high therefore it surely only needs a gentle charge over the 5 days to be fully erged up for the weekend! I'd rather not spend heaps on a single project among dozens of other things equelly important. Cheers!
thejazzpianoma,
Jan 21, 6:54pm
HaHa, nope , electronics still a foreigh language at the moment. I figure if the battery can give us 6 days over Xmas without any charging at all, I'm guessing our consumption isn't very high therefore it surely only needs a gentle charge over the 5 days to be fully erged up for the weekend! I'd rather not spend heaps on a single project among dozens of other things equelly important. Cheers![/quote] Its a good sounding theory but sadly you are wrong for several reasons. Do you want the long post telling you why and how to do it properly!
muzz67,
Jan 21, 6:56pm
To be honest,, not really. I want simplicity. Thanks anyway.
thejazzpianoma,
Jan 21, 6:57pm
I did a LOT of research to get my figures. I disagree about "a lot of batteries", its not cost effective to start with and batteries don't like being treated that way. I was amazed when I got into it how many motorhome setups were expensive inefficient messes,because no one bothered to keep up with pricing and technology.
thejazzpianoma,
Jan 21, 6:58pm
Cool, happy bodging!
solarboy,
Jan 21, 10:51pm
I abbreviated my post a bit too much, so blame me, not the Aussie maths. lol.The 7.5 A/h (tv) and 6.6 A/h (tv/dvd) are the totals that they used over the 2.5 and 2 hr periods so 14.1 A/h for that. Their pump draws 5 amps but only runs about 0.3 hrs daily so 1.5 A/h there and elec. blanket 5.8 amps for half an hour so only 2.9 A/h for it .Came to 29 A/h for the day alright, I just checked their maths lol.
solarboy,
Jan 21, 11:24pm
I get the impression the OP doesn't really have a grasp of the fundamentals (truck battery, trying to have the system catch up over a week etc) but I wasn't going to go into it all if its already been covered or they have gone away.[/quote]
HaHa, nope , electronics still a foreigh language at the moment. I figure if the battery can give us 6 days over Xmas without any charging at all, I'm guessing our consumption isn't very high therefore it surely only needs a gentle charge over the 5 days to be fully erged up for the weekend! I'd rather not spend heaps on a single project among dozens of other things equelly important. Cheers![/quote]
Far better for your battery if you have the panel on the roof putting some charge in each day while it's in use rather than running it way down then re-charging it over 5 days. ( I think I misunderstood your post 1). The less depth of discharge it has the longer it'll last ( ie 20% is way kinder than 50% ) and prompt recharging is important too.I mentioned using 10 watt panels myself to maintain a few car batteries but that's only to keep them up against self discharge and the odd phantom load. If you tell us what appliances you're running, their wattage (off the label on them), and roughly how many hours a day usage each device will get we'll know what size panel to recommend . Panels have plummeted in price lately and a bit bigger is better as it makes the most of the sun while it's visable on cloudy days but I'm picking 80 watts would do you like it does the Aussie guyin my post - he only needed an average of 5 decent sun hours daily.
mechnificent,
Jan 22, 5:50am
Cheers Solar.
mechnificent,
Jan 22, 5:58am
How long have you been on solar, Solar!
I've been living the dream for about twenty five years now. I trouble shoot multi thousand dollar set-ups for people. There is some terrible things going on with the so called experts selling huge banks of panels in an attempt to supposedly ensure they never run out of power even on the cloudiest few days. and they barely have enough batteries. It's jusy a money making scam and covering the suppliers arse. except it doesn't work anyway and then they deny any responsibility. sounds just like some workshop practice.
It's the way that the power output varies so much with cloud and angle that catches people out. You need enough batteries to not run them very low even after a few poor days, and enough panels to supply what you need on an averaged cloudy and hours basis, with a lttle to spare. Having enough panels to supply you needs even on a cloudy day is a ridiculous over supply on a good day.
thejazzpianoma,
Jan 22, 6:50am
This sounds good in theory but the economics, physics and practicality's of it just don't add up in a campervan/caravan type situation.
To go from say a 95Watt panel to a 160Watt panel will cost you only approx $210 extra. Going this way you also have less weight to haul around (important in a camper) and your expensive battery will tend to last longer as well. Speaking of which, your extra investment in the solar panel is going to last 2 - 3 times longer than your alternative investment in more battery's. (just the last point alone makes it a better option).
That same $210 will only buy you around an extra 100AH (be it an extra battery or extra capacity on your existing battery), given you only regularly want to cycle that to at most 50% (50AH) its not going to give you enough cover on a run of cloudy days in winter. In fact after 3 days or so you are likely going to be toast.
It doesn't matter in the least that you have a huge over supply on a sunny day, ALL that matters is the economics, and practicalities of the situation. You won't get fined for wasting sunlight.
With respect, I hope you do the math properly when you are advising other people, I see so many "over batteried" campervans without enough panels where people not only have to muck about hoping for sun and watching their meters but have also wasted even more money on backup 240V chargers and alternator hookups. None of which are required on a good solar setup.
thejazzpianoma,
Jan 22, 7:08am
BTW, in case someone gets nit picky. The above is just intended as a back of an envelope type comparison between extra panels vs extra batteries. I am not saying the OP needs 160W of panels etc as I have not considered the math of their situation. I simply haven't bothered as they are not interested in doing things properly anyway. (not having a go at them, they were honest and didn't waste my time which is great).
mechnificent,
Jan 22, 9:14am
I was talking to Solar and about home set ups Jazz.
Campers are a different situation for sure. The point about cloud and angle are still true though, there is no way to calculate just exactly how much panel you need. not even with a spreadsheet.
I'm happy to leave it to you to advise people though, it sounds like you've had heaps of experience.
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