Amp hours needed

[Gvannin]

Hey all. Im going to be running a blue sea 7622 into a 100 ah battery. Ill be running a dometic cfx50w fridge and some lights. Want to be able to camp for 2-3 days at a time. Is 100 ah. Battery Enough? Let me know!

 

[Almost There]

How are you planning on charging that battery while you're out there?

A 100 amp hour battery only gives you 50 amp hours of usable power. IF the battery is fully charged to start with and it's not too hot out you might make it through day 2. Day 3 unless it's a drive home day morning) and you've got a continuous duty solenoid installed, well you're pushing your luck a bit.

 

[Ticklebellly]

What voltage is the fridge's low voltage cut out set to? Any idea of the ambient temperate where you intend to camp?

 

[highdesertranger]

yep, the big question is how will you recharge your battery while sitting?

I hope the plan isn't to idle the vehicle engine, because that's very, very inefficient and usually doesn't work.

highdesertranger

 

[RogerD]

I would suspect that it is going to use around 50 ah per day.

So you would want around 300 ah / 150 ah (50%) usable in batteries to last 3 days without charging.

 

[future_vandweller]

Hey all. Im going to be running a blue sea 7622 into a 100 ah battery. Ill be running a dometic cfx50w fridge and some lights. Want to be able to camp for 2-3 days at a time. Is 100 ah. Battery Enough? Let me know!

The cfx50w fridge is likely to consume between 35-50 Ah/day.  It alone will deplete your 100 Ah battery in about 1.5 days.  If you have a means to *promptly* recharge the battery *every* day, then you may safely discharge it by 90% (to 10% remaining charge).  However, if you're not planning on recharging daily, then go for 300 Ah of capacity.  By adding 100-200 Watts of portable solar power, you can stay out indefinitely.

 

[abnorm]

^^^^^^^""then you may safely discharge it by 90% (to 10% remaining charge).""


Now that's really BAD advice...……………………..

 

[B and C]

^^^What Abnorm said unless it's a lithium battery.

 

[future_vandweller]

^^^^^^^""then you may safely discharge it by 90% (to 10% remaining charge).""


Now that's really BAD advice...……………………..

It is *not* bad advice.  I have significant experience in battery chemistry (lead acid, lithium Ni-Fe, etc).  What kills lead acid batteries is not deep discharge, but staying discharged.  I have no idea how this 'don't discharge below 50%' myth got started.  It is possible to deeply discharge these batteries and get as much or more than their rated life by *promptly* and *properly* charging them.  Most commercial chargers do not charge them properly, nor do most users.

 

[highdesertranger]

"then you may safely discharge it by 90% (to 10% remaining charge)."

if that is not bad advice then you need to add caveats to it. you post that then you say it's not bad advice and in the same paragraph you add,

"Most commercial chargers do not charge them properly, nor do most users."

which makes taking them down to 90% very bad advice. that's were the 50% comes into play. I hope you understand all this. you need to explain better, that when taking them that low what you need to do.

frankly on mine I would never take them that low if I could avoid it.

highdesertranger

 

[future_vandweller]

"then you may safely discharge it by 90% (to 10% remaining charge)."

if that is not bad advice then you need to add caveats to it.  you post that then you say it's not bad advice and in the same paragraph you add,

"Most commercial chargers do not charge them properly, nor do most users."

which makes taking them down to 90% very bad advice.  that's were the 50% comes into play.  I hope you understand all this.  you need to explain better,  that when taking them that low what you need to do.

frankly on mine I would never take them that low if I could avoid it.

highdesertranger

I did add the caveat in my initial post by emphasizing the word 'promptly'.  What kills lead acid batteries is the deposition of lead sulfate on to the two plates - higher the concentration of PbSO4 & longer the discharged state, higher the deposition.  There's not much PbSO4 deposition on the plates during the discharge process as the discharge reaction brings fresh H2SO4 to the plates.  Once the discharge stops, PbSO4 begins to deposit.  By promptly charging it to 14.X Volts & until the current drops 1-2% of capacity, you're converting PbSo4 in to Pb PbO, and also removing some of the sulfate deposit.

Many battery manufacturers recommend an additional 5-15% over & above the previous discharge to fully remove the sulfate deposits.  If this is done *every* charge cycle, one can easily get as many or more cycles the manufacturer specifies.  In a flooded cell type battery, it quite possible to get 450 or more 90% discharge/charge cycles.

 

[highdesertranger]

much better. always remember the newbies. thanks.

also we should add that leaving them at 90% discharge for even a day lessons the overall capacity and lifespan.

highdesertranger

 

[Ticklebellly]

I have no idea how this 'don't discharge below 50%' myth got started.

I don't know either but constantly reinforced by amateur experts who have little idea of the nuance needed in discussing cycle life.   Your explanation of the chemistry at the plates may help.

I have stopped going to a particular mobile living site where the consensus is that 'No Effect' on cycle life happens above 50% discharge and some magical "massive damage" occurs below 50% discharge.    This consensus exists without any acknowledgement of an accompanying lack of consensus on how to establish a global measurement method to find out the SOC of the battery in front of them.

 

[Spaceman Spiff]

 . . . I have no idea how this 'don't discharge below 50%' myth got started . . . Most commercial chargers do not charge them properly, nor do most users.

The 50% 'myth' came from when solar panels were expensive.  It was recommended that you have a minimum of 2W of solar for every 1AH of battery storage.  Under ideal conditions you cannot get your batteries close to full if you discharged more than 50%.  So you give a simple rule-of-thumb for folks whose eyes glaze over when you talk about watts and amp-hours.  Your final sentence should tell you why the rule is still useful.