solar,amps and watts??

Try Redarc the solar calculator will assist you.

alan m6
Each fridges will use it's same amount while running. it is how much does each draw in amps and for how long does it/they run in a 24 hr period.
A freezer at -13 will use more in 24 hrs than a freezer at -7. Also the ambient temp will have a large bearing on run time of both fridge and freezer in that 24hr period.
If you put both units in a warm/hot environment.,after they stabilize/normalize, that will give you some idea of the run times for both and after close monitoring of each you will know what amp hours you have to replace with the solar.

The solar has many variable factors and my idea is to have twice the required solar ability to cater for the night time running of each unit and warm but overcast days and to keep up/replace the charge and also run the fridges during the day time.

Testing with an inline ammeter will tell you what each does draw while running.
As an example
My situation, 30 litre Waeco as freezer and 39L Engel as fridge uses more than what a 160 watt system can provide in 30 degree ambient temp with good sun each day.

Alan,

That's quite a question and to be helpful, needs a detailed answer.

Suggest you will find Electricity for Camping a useful read.

I fully support Ross's suggestions to find just what each of your fridges draws (amps) when running, and how many hours each compressor runs in a 24 hour period. This is essential data that determines much of your daily energy requirements. ( Lighting, charging torch, ipad, laptop, camera, etc etc need to be considered too, but the fridges will be the big item.)

From there the next round of questions starts - how many days do you want to be entirely dependent on solar? Do you intend also charging from the vehicle? Charging from the vehicle can substantially reduce your solar requirements, but depends on your travel patterns - stopping in the one place for more than a few days means more reliance on solar unless you run the engine just to charge the batteries.

Check out Electricity for Camping . It discusses lots of this stuff.

Cheers

John

You can use a multi meter to measure the amps. There are several videos on Youtube showing how.

What type of batteries do you have? Lead acid or LiFePo4 ?

If they are LA (AGM) then 20% of the capacity is useable. If they are LiFePo4 then 80% of the capacity is useable.

If they are AGM, then your 100ah gives you 20ah to use when not charging, ie at night. If you want to be fussy, you can use a meter and time the usage to work out exactly what your total usage is...Or you can guestimate. Look on the panels of the Evakools for the ratings. It will have 2 figures for example it might say 3.1 - 5.2 amps. Use the higher figure for your guestimate.

Say it is 5amps. Then it will use 5ah. Most fridges will run about 15 mintues per hour on average. So 5ah per 4 hours. 12 hours of night divided by 4 of use times 5ah = 15ah per fridge. So to be really safe, you need 30ah of useable battery capacity.

Remember, that is a guestimate using maximum figures...

Size of solar panels ? You want to be able to put 60ah into the battery. Again err on the side of caution...Say you get 4 hours per day of useable sun - 60ah divided by 4 hours = 15... 15 times 12 volts = 180 watts. So if you have the space to carry it a 240 watt panel would be great.

Running freezers does consume a lot of power. I run a 40ltr Engel @ approx -15 deg and it draws 4.5 amps and during the daylight hrs @ around 30deg ambient it runs all the time. When I first set up, I used a 75a/hr Thumper which I soon found it would not last during the night. I recently installed a 130a/hr agm and use a 140watt folding solar panel. This will hold the battery and freezer for a couple of days in sunny weather. I estimate the unit runs for around 20hrs a day consuming 90 a/hrs. During daylight hrs the solar panels needs to supply enough power to charge the battery and run run the freezer. Unfortunately the battery never gets full charged. So top up with the generator as required.

My advice is get the biggest panels you can carry and afford. It's a case of the bigger the better to keep your batteries fully charged before the sun goes down. I wished I'd opted for a larger panel. On e-bay you can get 240watt panels for $380-00.

Alan
Like so many before you, I think you are being optomistic in the least with your expectations.

Do not believe any of the published average demand figures for portable fridges...they are optomistic to say the least.

A 50 litre fridge is a large fridge and will draw a significant average demand due to its size.

The second fridge run as a freezer.....as soon as you say the word "freezer" the average demand increases massively.....a given fridge operated as a freezer may draw 6 times or more than the same fridge operated as a fridge....worst case the motor runs continuously 24 hours a day...with a total demand of around 150AH ish.

In both cases I believe your batteries to be grossly undersized.

I run a 100AH sealed wet cell battery with a 30 litre fridge.....run as a fridge, with good fridge discipline and with it and its contents already chilled down I can get 2 days (sometimes more) out of that battery before the low voltage cut out stops the fridge.

The 100 AH battery is barely adequate long term for a "drive every day" situation.

If I run the same fridge as a freezer, It will last overnight.....IF the vehicle has been driven right up to dusk and in fair weather.

I and others have done the calculations and run the tests.....the general agreement is.

For a 30 to 40 litre fridge, run as a fridge and with good fridge discipline.
For any sort of reliability and with no other charging source the minimum is a 100 Ah battery and 160 to 180 watts worth of panels.

less than that and all you are doing is delaying the inevitable and using the solar panels to extend the run time on the charge from another source.

for what you have and what you expect, think in terms of 200AH of batteries for each fridge MINimum.....AND a roof full of solar panels.

Now remember.
the maximum safe temperature for a fridge is +5C, but most people will tell you the beer is not cold till +2C or lower.
The maximum safe temperature for a freezer is -15C and that is a not a hard freeze most home freezers run at -18C to -20C.

Remember too many portable fridges do not hold a constant temperature and the display will not indicate that variation ..so its not wise to run close to the edge, because the actual temperature in parts of the fridge can be a couple of degrees higher than the set temperature.

cheers

Hi all

I can't see it in this thread (apologies if it's been mentioned before) - but to do the calculations, you also need to know how to calculate Watts to Amps. For example - a 120w solar panel will (at best) generate 10amps...obviously during daylight hours...the calculation is Watts / Volts = Amps (120/12=10). So you would need to know the draw from the fridge/s (use the multimeter approach) then work out what is left over - say 6amps. You would then need to know how long it will take to recharge your battery at 6amps during the daylight hours. We have one of these things attached to our deep cycle batteries...they work really well, and give you all sorts of information about charge and discharge rates.

http://www.youtube.com/watch?v=NPKh31L0I-E

Lots of marine/caravan places sell them.

Chris

try www.foldasolar.com.au they have a series of documents explaining solar and its power usage via solar cells etc. In the docos they have 1 listing a lot of common camping fridges with their draing powre and requirement under differnt conditions etc.

Just down load and have a lok it may save you some misinformation form the 'experts' on this forum

M

Quote"Member - Chris_K replied:
Hi all

I can't see it in this thread (apologies if it's been mentioned before) - but to do the calculations, you also need to know how to calculate Watts to Amps. For example - a 120w solar panel will (at best) generate 10amps...obviously during daylight hours...the calculation is Watts / Volts = Amps (120/12=10). So you would need to know the draw from the fridge/s (use the multimeter approach) then work out what is left over - say 6amps. You would then need to know how long it will take to recharge your battery at 6amps during the daylight hours. We have one of these things attached to our deep cycle batteries...they work really well, and give you all sorts of information about charge and discharge [end quote]

Sorry Chris
but as Brian has pointed out ,your calculation is based on a a misundertstandin of solar panel outputs
One would could virtually NEVER get the amps that you suggest
As it exceed a 120W panel's SHORT circuit current!!

One would be lucky at most times to get any thing near 7A.
EVEN at that,using a PWM reg ,
with a battery with 12V SOC voltage that means only 84W are actually going into the battery
Using a QUALITY MMPT reg will inprove on that

PeterQ

Hi Alan. Buy the most efficient fridge you can. I have a waceo 80 litre used as a fridge at 2 degrees and a 60 litre trailblazer used as a freezer at minus 18 degrees and regret buying the waceo. Both use on average 60 amps a day each. The trailblazer is 15 years old but still way more effecient. On top of my canopy i have 280 watts of panels run through a mppt regulator to two AGM batteries of 65 and 120 amps that are connected as one. The batteries are now in their 6th year . During reasonable weather ie fairly sunny i can get by with this setup without using a gennie and a 40 amp smart charger for backup allthough i usually carry both for extended trips just in case. Using some smarts such as filling up with beer in the morning and not at night and freezing fish in the vans gas fridge before putting in the trailblazer etc all help and keeping voltage in the batteries as high as possible will extend their lifespan.Hope this helps.
cheers graeme.