Solar Power and Battery Capacity

Travelling Oma · Newbie

Solar Power and Battery Capacity

Mike Harding · Guru

Are you intending to use the unit as:

1 - a fridge

2 - a freezer

3- both

Freezers use considerably more energy than fridges.

vince56 · Senior Member

Hi T.O.,
Unless I am camping in hot overnight temperatures I normally turn my 50 litre fridge off most nights the fridge doesn't get opened during the night and holds temp pretty well without power.
When travelling in the car I turn the fridge much colder (to near freezing) to use the available power from the alternator whilst the motor is running.
I use a Waeco insulated cover and protect the fridge from direct sunlight (a real killer for portable fridges), sometimes when stationary I cover the fridge with towels to further protect from outside heat (dont cover the vents though)
Your 120W panel should run the 35 litre quite well (on fridge temps not freezing as Mike says above) if there is a bit of sunlight around.
Using the above methods I can keep my fridge in good nick with only an 80W panel during the day with a 110 Ah battery.
I suggest using the biggest Deep Cycle battery you can handle.
Cheers Vince

Aus-Kiwi · Guru

Many ways and options ? One simple method is using existing battery . With voltage sensitive relay . With good sized wire to fridge depending on length or distance away . Yes turning fridge off as you go to bed is an option . If fridge is full it keeps cool temps well if cold in the first place . If your traveling every day this is fine . A solar system helps big time when camped . The voltage sensitive relay will prevent fridge flattening battery to the point you can not start your engine . Personally I would have another deep cycle 100 AH battery . Yes more weight . But have you ever been out bush with flat battery ?? Atleast have one of those emergency jumper style CHARGED !! But the weight, $$$ May as well carry another battery ??

Izabarack · Guru

Travelling Oma wrote:
I don't want to really carry a large full-size car battery, due to the weight

A Fifty Ah Lithium battery weighs about 6.5 Kg and is about 145mm cube in size. Will run a Forty Litre Engel for a couple of days. Bit of a cost overhead if you cannot DIY.

Iza

Warren-Pat_01 · Guru

Hello Maria, welcome to the forum.

Like Vince & Aus-Kiwi, when I carry our car fridge, I generally crank it up (the thermostat) for the last couple of hours of driving & then turn it off. We've found frozen stuff in the bottom stays frozen. We took King George whiting fillets from our previous homeplace of Ceduna to Townsville using this method. We had a 24v Nissan Patrol with no spare aux battery.

However, I would suggest a heavier cable feed to the location of your fridge than running it off the cigarette lighter socket - often these use light wiring & you can get voltage drops on them. Preferably, I'd suggest an alternative aux battery but in a small car, there isn't much room for "luxuries". An alternative would be to increase the size of your battery - if that's possible BUT DO NOT RUN THE BATTERY DOWN BELOW 12v! You do need to start your car the next morning.

All the best!

Eaglemax · Guru

Hi Losts of good advice here. We toured oz with a waeco cf18 small chest fridge used as a fridge with 120w of solar thinking they'd be so much sunshine! The trouble was, the fridge works so much harder in hot humid weather. We have a cover and away from sunlight. So at Mt Isa we purchased a portable 90w panel but as we travelled 4 hours a day it missed out on that sun. We mounted it on the drawbar to remain connected...still not enough. When we arrived at Albany I gave the battery to an electrical shop and they gave it a good charge and gave me some education! He advised I stayed in a caravan park once a week for a good charge up. Since returning home I've added thick cables from the car battery to the caravan then to an inverter (12v to 240v)and on to a smart charger. In effect everytime I drive I'm charging the van battery as if I'm in a caravan park or at home. This also means if its overcast for 4 days in one place you can idle your engine to give some charge to your van battery. Its an insurance policy. Lithium batteries are expensive but really light but are more potentially dangerous so charging demands a proper lithium capable charger. If you can afford a yamaha 1kw generator at 12kg its another way. So solar is good but the forum pages are full of advice to mix up your ways of keeping your deep cycle battery charged...the more ways the merrier, dont just rely on solar. Some even have a wind turbine .

Jaahn · Guru

Hi Oma smile

Some good advice give already. Just another couple of points.

The battery must be a deep cycle type, not a car battery type as they will fail fast with this usage. Lithium batteries are the best but very expensive and must be set up correctly or will fail badly. furious

A sealed AGM battery might be suitable and the bigger the better for a long life. You could work out the minimum AHr required or people may like to recommend a size. I would say bigger is better though and may last for years, whereas a minimum size may not last so long as it is 'working" harder. You should not use more than 50% for good life. hmm

The best battery charger will be your engine alternator and if you drive every day may be all you need. Certainly as said it can be an excellent backup for solar when the sun goes away. Depends on your car type but it may be sufficient to fit a heavy duty pair of cables to the second battery and a Voltage Sensitive Relay (VSR) to control the charging and some terminals for the fridge connections. The fridge should have a low voltage cutoff to switch it off also, in case the battery gets too low, to protect your battery.

Cheers Jaahn

Warren-Pat_01 · Guru

Have a look at www.portablefridgesonline.com.au/fridge-accessories/fridge-electrical-accessories/battery-packs.html - battery power packs re available for Engel & Waeco but they aren't cheap & some are very small in capacity.

If you do decide to use the one & only battery - change it for the largest "Marine" battery that you can fit - they have both "cranking" power & "deep cycle" power & it might be the cheapest way out of the problem. Just don't flatten it over night!

I found my Trailblazer fridge had a voltage cut out set to 10.5v - way, way too low to crank my diesel engine!

What sort of car do you have, Oma?

Izabarack · Guru

Initial costs of installing a Lithium battery system can be quite high when compared to a Lead Acid battery based system. Costs over the life of a Lithium system result in equations the show Lithium is arguably cheaper. Size and weight advantages are considerable, especially if included in cost over life calculations.

A DC to DC charger that handles LiFePo4 can be had from Jaycar, for example, for under $150. The same charger/regulator could also be recommended a AGM based system being charged from the alternator. So, no cost advantage there for not going LiFePo4, especially is installing from scratch. An Off-The-Shelf low voltage cutoff is about $45, again a Jaycar price, and would be useful safety in any Aux Battery system. Because I have some DIY skills, I recently build a LiFePo4 battery for under $320. An equivalent usable capacity AGM battery is being sold at Jaycar, again, for example, for $299.

I have replaced an AGM battery in my Aux battery system with my LiFePo4 and saved 31.5 Kg. I keep the new battery in a hard side six pack esky. I also have a 120 Watt semi flex panel that weighs 2.1 Kg.

An Off-the-shelf LiFePo4 brand name battery will always be up against the RRP disadvantage over AGM. The storage device is only one item in an Aux battery system. How do you price the weight, size, and flexibility advantages that come with the technology?

Iza

Mike Harding · Guru

I think lithium batteries are the way of the future but I'm not convinced that future is yet here.

Powersonic (I have three of their AGMs) offer a three year warranty but it only covers the battery to 60% of its rated capacity so if your 100Ah battery has deteriorated to a 60Ah battery after a few months you don't have a warranty claim.

http://www.power-sonic.com/images/powersonic/LithiumIron/PSLWarranty.pdf

If the battery freezes the warranty is void and the storage temperature is specified as > +4C, I have camped in -6C here in Victoria.

https://www.rfiwireless.com.au/media/downloads/pdfs/PSL-12450-AUS15.pdf

The price needs to drop or the warranty needs to improve significantly before I'll buy one over an AGM.