solar power help

[DRUT]

I run a 60l trailblazer(draws about 4ah) 24/7 in the back of my fender (just to keep a few ales on hand). My battery system consists of a Century cranking batt linked to 4 x 38ah sonenshine gel cells. This is the secondary battery setup which is seperated by an IBS management system. This is in addition to the unknown standard battery to kick the truck over. What I have found is if I leave the truck for 2-3 days without starting the fridge runs the batt flat. I want to install a solar panel over the cab to keep up with the fridge 24/7 and if possible a 40l engel I run on longer trips. Mostly for the trailblaza as when I run 2 the truck is running long hours itself with just overnight stays. I was thinking of an 80w or 125w BP solar. Your thoughts???????:D

[waynep]

I'm gonna be shot down in flames by by Drivesafe and others on here are some thoughts to start off with....
If we work using watts : Power ( watts) = voltage X current.
Assuming 13.5 volts is the minimum you want at the battery terminals to charge it. So an 80 watt solar panel can theoretically deliver around 5.9 amps max to charge the battery ( 80Watts/13.5V ). However the solar panel will only deliver that in optimum conditions ( full sun, angled correctly etc. )
So let say on average you are going to only get half that - say 2.5 amps -and then only during the day.
You say your fridge is rated at "4 amp/hours" . Are you sure that it is not just "4 amps" ? So your fridge draws 4 amps when the compressor is going ? The compressor doesn't work all the time of course - it depends on what you have the the temp set to, the ambient temp etc etc.
I think the short answer is that there are too many variables. You'd probably need to fit the biggest solar panel you can and then see if it works for your needs. If not you'd need to add more panels, more batteries, or have another method of supplementary charging.
Drivesafe, p38rover and others can your correct this if I am way off track here ?

[Michael2]

Why not wire in a small 240V battery charger with an external plug (like a caravan). When parked in a driveway / gargae / caravan park, you can keep your batteries charged up. When you're on a trip and driving everyday it doesn't matter, as you said. You will probably need a switching relay that disconnects the power supply when the battery is fully charged. This may be a more robust and much cheaper alternative.

[Rosco]

I have an 80W BP panel mounted over the sloping front section on differing height racks so it's more or less parallel with the hood. Connected via a regulator direct to the aux batt. Runs the 60l Waeco very well when stopped at the one spot for a few days. I reckon it only puts in about 80-90% of what the fridge pulls out, so slowly flattens the batt, but it would take quite a few days stationary for this to happen. On an average sunny day the voltmeter reads about 13.5-14V. Works well for me. Weeds has a similar setup and AFAIK he's also happy.
Cheers

[isuzu110]

My 2c

I have a 60L evakool with a freezer compartment, 2 x 40w of solar and a stecca solar regulator. My 80w will only keep that setup going for about 2.5 days in summer in SEQ. I therefore run my vehicle (rotronics dual battery system) for 30 mins each day to keep on top of it.

I would expect your trailblaza to draw less current per day as they have better insulation.

I'd be aiming for 100W - 120W of solar to be self sufficient indefinitely.

[weeds]

go the solar powered defenders

i reckon go the biggest solar panel you can afford, you can never have to much

i have a 65w panel as a wind deflector for the roof rack. the rig is fitted with three batteries, 1 x start and 2 x deep cycles (1 x 80amp/h and 1 x 120 amp/h), they are isolated by a manual marine style battery isolater (idiot switch) which is mounted on the console along with the regulator and amp meter.

i have always been meaning to document the figures but i reckon on a nice sunny day with the car and solar panel facing to the north i reckon the solar panel would put somewhere around 25-30 amps back into the batteries.

my engle has a max current draw of 2.5amps/h and cycles around 50% of the time so lets say it uses 1.5amps/h which = 36amp per 24hrs. i also run at least one fluro light fora few hours so there another 3-4amps that makes me approx 10amps short for the day

but having the solar panel and good storage capacity i never have to worry about power for a long weekends, i can just park the rig (facing the north) and not worry about having to go for a drive to top batteries up.

now there is a lot of science with solar and batteries and somebody will be able to explain it better than me

i normally check the voltage before turning the fridge on when going away, resting voltage across the three batteries is normally around 12.7/8 volts which makes me think i have not got 100% storage amp/h available. when i'm keen i put the battery charger on to top up a bit more the day before, i shoud get on of the multi stage ones.

when i'm touring or want icecream for weekend trips i run two engles with the second one the older style that uses more amps. i have not runned out of power yet. not sure if its a good thing or a bad thing but the engles do nothave low voltage cutout so they will still run the compressor at 10v and provide some cooling, not very healthy for the batteries, i must look into a low voltage cut out

[drivesafe]

i normally check the voltage before turning the fridge on when going away, resting voltage across the three batteries is normally around 12.7/8 volts which makes me think i have not got 100% storage amp/h available. when i'm keen i put the battery charger on to top up a bit more the day before, i shoud get on of the multi stage ones.

Hi weeds, at 12.7/8, your batteries are that close to fully charged it wouldn’t matter if you didn’t put the battery charger on.

[drivesafe]

So let say on average you are going to only get half that - say 2.5 amps -and then only during the day.

Hi waynep, that’s actually a pretty good explanation of how solar panels work.

Most people think they are going to get the 80w out of an 80w panel but as you posted, 2.5 amps is more likely to be the real output.

This may sound strange but with most solar panels, the brighter the sun light, the less power you are going to get and the reason is that as a solar panel gets hot, it’s current producing capacity decreases.

So in the middle of the day, you will be lucky to get more than 2.5 amps going to your batteries.

Cheers

[drivesafe]

Hi DRUT, this is just a suggestion and if you want to go solar, go solar but if you consider the cost of an 80w panel and a solar regulator, I personally think you would be better off putting in an additional battery ( or 2 ) and for a lot less start up cost. Solar, over a long period may eventually workout cheaper but this is only if you use your system frequently

You say the truck is running long hours. If you do 4 or more hours driving, no matter how low the batteries are when you start, you will put the bulk of the charge back into all the batteries.

Note, you need to drive for around 7 to 8 hours to fully charge low batteries but if you just put the bulk of the charge back, with an extra battery, you should be able to stop for a few days at a time without any dramas

Cheers

[waynep]

Hi waynep, that’s actually a pretty good explanation of how solar panels work.

Most people think they are going to get the 80w out of an 80w panel but as you posted, 2.5 amps is more likely to be the real output.

This may sound strange but with most solar panels, the brighter the sun light, the less power you are going to get and the reason is that as a solar panel gets hot, it’s current producing capacity decreases.

So in the middle of the day, you will be lucky to get more than 2.5 amps going to your batteries.

Cheers

I saw an analogy once that makes it easy for dumbies like me to understand.

Think of the solar panels as simliar to a house roof feeding a water storage tank. The tank is equivalent to the battery. A tap and hose at the bottom of the tank, feeding a garden is like the feed to your fridge and other accessories.
So the variables are the amount of rain going onto the roof ( = sunlight), the size of the roof ( = size of your solar panels ), size of the tank ( =size of your battery ), and the watering needs of your garden. ( the fridge)
So as long as the input from the roof equals or exceeds the water going out through the hose at the bottom, your tank will remain full. If you don't have a big enough roof, or enough rainfall, you need a bigger tank( battery) to store the water/electrical energy.
A solar regulator is like a diverter for the water coming off the roof, when the tank is full the diverter (regulator) puts the water down the drain.
The size of the hose is like the size of your cables feeding the fridge. If the hose ( cable) is too small, it will constrict the flow and your fridge won't get the power it needs.

Course this anlaogy falls down when you think of rain going directly on to the garden ....hmmmmmmm :( :confused:

[weeds]

Most people think they are going to get the 80w out of an 80w panel but as you posted, 2.5 amps is more likely to be the real output.

:o geez Tim are you sure, i have an amp gauge fitted in line with my 65w solar panal, in the middle of the day i easy get 4 and a bit amps/hr, i have also checked this with a tong multimeter thingy and get the same reading

my mate has a BP 80W panel, i will do some test on it

i do agree that solar is a big capital outlay but they say they are good for 20 years + i have been told that having a solar panel connect all the time with a regulator that switches to float charge conditions the batteries that will extend the life of the batteries, not sure how correct this is

[Robbo]

You either do this properly or don't do it. For starters the Sonnenschein batteries you have should most likely be charged at a higher voltage than your car battery. These batteries are designed to be charged to 14.1 volts which is slighlty higher than your car battery. This in itself is not a problem but if you hook up a solar panel to it the most important part is your regulator that go's inline. This regulator has to be designed to match these batteries. Then you have your solar panels. Most panels have a higher voltage of around the 18-22v output. This is one reason you require a regulator. Then there are different types of Solar panels. To keep it simple There is really two types you need to know about. The first type like the "Canon Unisolar" will work in partial shade. Panels like the Kyocera's will put out more power than the equivalent Uninsolar in full Sun but will not perform as well in shady areas as the Unisolars. You need to think long and hard on how and where you are going to use your solar panels before you purchase them. The Batteries you have are among the best for Solar applications but you need to get the other two links correct.
Cheers Robbo