Watts needed for charger

Re: Watts needed for charger

Just buy an automotive type battery charger (soon) and charge it. One of the 10 amp, cheapo chargers is all you need for your battery but if you don't do it very soon it will be ruined and you'll have to replace it.

Re: Watts needed for charger

You should find out how much power the bar fridge is using.

The two batteries you bought are probably 125 AH Everstart MAXX marine.

You should not discharge these more then about 50% of their rated capacity if you want them to last several years. Always keep them charged. They will degrade if left in a partial charge state for a month or so.

For two batteries in parallel with 50% discharge that gives you 125 A-H. At 12vdc this would be about 1500 watt hours.

A regular 15-17 cu ft. refrig less then a few years old will average about 1500 watt hrs per 24 hours period. There will be peak power draw of close to 1000 watts for compressor startup surges and defrost heaters.

I would assume your bar fridge has 1/3 to 1/2 the consumption of a full sized fridge but any fridge consumption depends on how much the door is open, allowing heat in that must then be cooled.

The inverter internal power consumption should also be taken into account. Assuming it is a 1500 watt modified sinewave inverter it it probably about 5-7 watts for its no-load consumption.

As to charging from a car, the biggest risk is damage to your car's battery. The car alternator is self limiting and will not put out more then its design limit but if a discharged battery is put in parallel with a charged battery the charged battery (your car's battery) can deliver some very high discharge current for a long enough time period to damage it. Using the car for charging is a large waste of gas as the efficiency will be very poor.

Re: Watts needed for charger

blackmagic wrote: »

I tough that a deep cycle battery would last better if discharge fully than recharge, like a lithnium battery.
.

Not true for either. You are thinking of NiCad battery. LiIon battery will be damaged if taken below about 2.2 vdc. There is actually a circuit in your cellphone battery that 'pulls the plug' if battery drops below about 2.3 vdc)

For Lead Acid, of the Marine type you purchased, the deeper you discharge it, the shorter the longevity. These 'Marine' batteries are not true deep discharge batteries. Everybody here targets about 50% DOD even for true deep discharge to get good longevity.

Google 'State of Charge for Lead Acid battery'

A lead acid battery that has rested with no load or charging for 2-3 hrs should be at 12.7 vdc if fully charged. 50% state of charge will be at about 12.2 vdc.

Charger should hold battery at 13.2-13.4 vdc in 'float charge condition.

Initial charge voltage can go to 14.5 vdc but should drop back to the lower voltage after a period of time. This can be when charge current has dropped to about 3% of AH rating or just a timer timeout after a few hours.

Re: Watts needed for charger

blackmagic wrote: »

Forgive me for not being clear la night It was late and not thinking straight.

First I do a lot of camping and before , I always camped with full hookup.
This year I decided to setup my camper with 2 batteries and an inverter since I do most of my camping during the weekend I tough that 2 batteries would be enough. The fridge is a 3 cubic foot size of a tent trailer ice box.

[EDIT: Fixed brain fart decimal point misplaced math.]

You said it's a bar fridge? Last time I looked at bar fridges (demos on the shelf at Fry's), the lowest electrical draw I saw was 1.1 amps.

I'm going to guess yours at 1 amps just to make the rough math easy.

Say you have 2 batteries, and each is 125ah (amp*hours) @12v capacity. They are wired in parallel to give 250ah@12v capacity.

Also, say the fridge draws 1a@120v - that converts to 10a@12v. So, your 250ah of battery could supply that fridge for 25 hours of running the compressor. If the compressor runs at say a 25% duty cycle (only running 15 minutes out of every hour) then you could run it for 100 hours.

That's the basics on how it works. So...take a look at the sticker on your fridge and see how much it draws and take a look at your batteries to see what their actual capacity is.

You can't escape the math, and you can't do the math without the numbers.

(((((When I get home from the weekend I charge my batteries using a 2 amp charger witch takes about 8 hours each.))))

[EDIT: Nevermind; this was just all wrong.]

((((so I bought a 18 watt coleman solar panel along with a controler witch gives me about 1.2 amp charge witch is not enough for more than a 3 day camping trip{{{1.2 amps of charge in full sun , but not much in shady days.}}}))))

These batteries can last aproximate 1 week without charge but they would not last long . That much I know .

Again, it comes back to the math. Say you have a 125ah battery and you draw it down 50%. You now need to replace 62.5ah of juice. How many hours will that take with a 1.2a charge?

Or, if your loads suck out say 120ah per day and you put back 1.2ah with the solar panel, then it will take the solar 100 hours to replace what the fridge took out - or 10 hours with 12a worth of solar panels.

Say you get 5 hours of good sun a day on the panels and you have 12a worth of panels. You put back 60ah per day, but if you are taking out 120ah per day, then each day your batteries are at 60ah less than they were the day before.


This is all just rough math, but you get the idea.


As for batteries - lead-acid battery lifespan is rated by "X number of cycles at Y discharge". So say you draw them down 10% and recharge them, their rated life might be 5,000 cycles. At 25% regular discharge they might be rated at 3,000 cycles. At 50% discharge, maybe 1,000 cycles. At 80% discharge, they might last 150 cycles.

You'd have to check with whoever made your batteries to find out what their cycle ratings are.

I'm looking for alternatives so I can stay on longer camping trips. Without putting my batteries at risk .
I am very interested in solar energy , have been for over 15 years .

You have to do the math to figure out what you need - there's no other way.

To run a bar fridge for boondocking I would guess you would need at a minimum a panel of say....I dunno...135w maybe. Two would be better.

My camper has a Norcold 323 and runs on propane for 3 weeks on high, or 4 weeks on low from a single 5g tank (my camper has a horizontal frame-mounted 5g tank). I filled that tank up a couple weeks ago and the propane was $1.88/gallon. The 323 has no thermostat, but it doesn't really need it - it's "close enough for government work". (And no thermostat control board to burn out and have to be replaced (common RV fridge problem).)

http://www.thetford.com/Home/Products/NorcoldRefrigeratorsHome/323T/tabid/209/Default.aspx

(there's a typo on that page - they show the AC load as 12V, but it's really 120V)

I looked very hard at replacing that with an electric unit, but it's bulletproof and I need to haul propane for cooking anyway...it just doesn't make sense to switch to electric and try to run it off solar. I do have a house battery, and I'll add a solar panel and charger to keep it charged, but I won't even begin to try putting in enough solar to run an electric fridge.

As for running my little Norcold from electric - yikes. It draws 11.7a@12v (and since it is constantly heating the ammonia absorption, that is constant - no cycling on and off), which would take my 100ah house battery down to 50% in about 5 hours.

And running it through an inverter would draw 1.4a of 120v, but that's no different since the inverter would draw 11.4a of 12v in order to create 1.4a of 120v.

To run it 24/7 would draw 281ah per day out of the batteries (if I even HAD that much battery). And there's that pesky math again...I would need about 600ah of battery to feed that fridge and still keep the battery depth of discharge at 50% or less (to get many cycles of life out of them), and I'd need to feed the batteries 300ah of power a day to replace what the fridge took out.

If I used the 135w panels, that's about 7.5ah each. So I'd need 40 hours of sunlight to replace 300ah with one 7.5ah panel, or 20 hours with 2 panels, or 10 hours with 4 panels or 5 hours with 8 135w solar panels. I put that in bold because 5 hours per day of good full sunlight is about what one can reasonably expect the average solar setup to harvest.

So, running my (dinky, smallest they make) ammonia absorption fridge on solar would be a horror - I'd need 8 135w solar panels and 600ah of batteries - I'll just stick to propane for that little bad boy.


Your bar fridge wouldn't be as bad since it must cycle on and off, but I have a very hard time believing that it'll run for a week from a pair of 125ah batteries.

Have been looking for alternatives to harvest my home from the sun and wind But nun of them seem to be feesable at the present time , even built a small wind generator a wile back .

So if you have an alternative I'm all ears.

P.S. If these questions are not valid in this forum or upsets other people like Kamala then forgive me, and delete this post , I do not wish to make anyone uncomfortable .

Nah, don't sweat it - Kamala was just being grouchy. All us old fuddy-duddys reserve the right be grouchy and snap at people now and again.