trying to understand battery capacity terminology

[cruxarche]

Hi all,
I am trying to get a better understanding of battery capacity terminology. I currently have the Renogy 100W solar suitcase and an Interstate SRM-24 with a Reserve Capacity of 140 minutes. Not that it totally matters here, but my main lode will be an Engel fridge which draws about 2.5 amps and runs about a 33% duty cycle.

So if I multiply that by 0.4167 i get approx 58 Ah (amp hours).
I have read many times that you should only use approx 50% of your battery's rated Ah on a regular basis to avoid reducing the number of cycles on the battery.

Question #1: Does this mean that I should consider my battery ready for recharge after using 29 amp hours?

Question #2 (solar charger related) When My Renogy charge controller (Viewstar 10A) says it is delivering x.x amps to the battery, does that number include efficiency losses? or is that the actual amperage being delivered to the battery?

I hope these questions make sense. I am NOT a math guy.

Thanks.

 

[workerdrone]

Your battery looks like a marine type 'deep cycle' battery, which is not really a deep cycle, it's sort of between a normal car battery and an actual deep cycle battery (like a storage or golf cart battery).

Since these are cheap and don't last terribly long (a few years at most), personally I wouldn't worry about babying it. I'd just use it and enjoy.

What I would worry about is a completely drained battery and things melting or spoiling in my fridge. So you just need enough capacity to get through the time when the solar isn't charging it, and enough solar capacity when the sun is shining to get you through the next bit of darkness.

Looks like you would have about 75ah of capacity with that battery when it's new. This will gradually decrease as it ages and is worked. But plenty to run your fridge and get topped up again with a few hours of sun a day on that panel.

So #1 - I'd say more like (75ah @ 50%) is 37ah of use to 50% when new. Lead acid batteries will last the longest if they're kept at a steady temperature and cycled near 100% charge, but again I'd just enjoy your camping and not worry about draining it more than 50% if you do. It'll do that a bunch of times. I like to charge my batteries to 100% on solar and then maximize effiiciency after that by running as many loads as I can while the sun is shining strong (charge phones, cameras, laptops, whatever basically just on the excess sun, not battery to battery)

And #2 - Does not include efficiency losses, that's just the amps going into the battery.

 

[Stumpalump]

In very hot weather where I'm goin to exceed the capacity I run the fridge a bit colder while the sun is charging it. At night the fridge runs a lot less and the batts stay happy. Same with driving. If I'm driving I cool it down to just above where food freezes and turn the temp up when parked. It makes a huge difference and you will use much less capacity.

 

[SoCal Tom]

I use the same type of marine battery, if you keep it 100% charged and baby it, it will die in 5 years. If you just camp on weekends once a month, then don’t let it go below 20%, but always charge it when you can. The higher it’s charged the higher the capacity will stay.
2) get a monitor like this bayite DC 6.5-100V 0-100A LCD Display Digital Current Voltage Power Energy Meter Multimeter Ammeter Voltmeter with 100A Current Shunt [bayite DC 6.5-100V 0-100A LCD Disp...ficiency. Sent from my iPad using Tapatalk

 

[cruxarche]

Thanks. Workerdrone, how did you arrive at 75ah? Am I using an improper calculation?

 

[workerdrone]

That's just about average capacity for a Group 24 size marine battery IIRC. I might not be RC

 

[cruxarche]

Ok. Thanks. I was just trying to understand how they get from reserve capacity ratings to amp hours...

 

[SoCal Tom]

Ok. Thanks. I was just trying to understand how they get from reserve capacity ratings to amp hours...

The calculation is a guesstimate. I found this with a search
http://www.batterytown.com/interstate-srm-24-12v-deep-cycle-marine-rv-battery.html It says 84 amp hours. Ive got a group 24 marine/deep cycle from oriellys it claims 87 Ah. So essentially the same.

 

[jonyjoe101]

Question #2 (solar charger related) When My Renogy charge controller (Viewstar 10A) says it is delivering x.x amps to the battery, does that number include efficiency losses? or is that the actual amperage being delivered to the battery?

Myself I notice I had voltage drop (.5 volt) between my controller and battery. I would check what the voltage your controller is reading(14.4 volts) against what the voltage your battery actually reads at the terminals (it should also read 14.4 volts), if your battery reads something less then that means you have a voltage drop. With voltage drop your not giving your battery a full charge.
Amps are important but they have to be going into the battery at the correct voltage, anything below 14 volts and your only float/trickle charging the battery which is bad for lead acid. They need to be kept at 14.4 volts or higher the majority of the time to get a proper charge.
On my controller I had to raise the bulk voltage to 15 volts to compensate for the .5 volt difference, it actually increase the amps going into the battery. Now the battery actually reads 14.4 volts the way it is suppose to.
Thats what I would check on your system, you want it to be at max performance, .5 volt doesnt sound like much but its the difference between undercharging and a proper charge.

 

[workerdrone]

anything below 14 volts and your only float/trickle charging the battery which is bad for lead acid.

Not sure why you're saying this, because sulfation or something? I mean, you can charge a battery with 13v it's just going to take longer. I agree higher charging voltage is better, I set for 14.6 normal full charge on the bank on my rig. Over 15 for occasional conditioning.

 

[jonyjoe101]

Thats the recommended charge rate for most lead acid, some require even higher. The manufacture of the particular battery will have the correct charge voltage.
When a battery reaches 14.4 volts it is consider 80 percent charge then it absorbs at that voltage for several hours.
If you dont use the battery you can maintain it at 13 volts indefinitely.

 

[Ducky's Dad]

you can charge a battery with 13v it's just going to take longer.

Not true for all batteries. Some Optimas are not at full charge until resting OCV is 13.2V. Odyssey G31 requires something north of 14.7V to charge properly, but its resting OCV at 100% SOC is 12.85V. Lots of variations from manufacturer to manufacturer.

 

[SoCal Tom]

Found a nice brochure from interstate /http://interstatebatteries.ca/wp-c...w and then Sent from my iPad using Tapatalk

 

[vtsoundman]

Thats the recommended charge rate for most lead acid, some require even higher. The manufacture of the particular battery will have the correct charge voltage.
When a battery reaches 14.4 volts it is consider 80 percent charge then it absorbs at that voltage for several hours.
If you dont use the battery you can maintain it at 13 volts indefinitely.

Charging rates for batteries are based on chemistry and construction - and are a factor of 'C' C - or columb rate. Most folks thinks it stands for Capacity...and that's a reasonable substitution as the concept is the same. Basically it means how many amps can I cram into the battery - the battery's ability to accept current (charge) will depend on it's charge state and how much push(pressure/voltage) you apply to the terminals.

*C-rate*is a measure of the*rate*at which a battery is discharged relative to its maximum capacity. A 1C*rate*means that the discharge current will discharge the entire battery in 1 hour. For a battery with a capacity of 100 Amp-hrs, this equates to a discharge current of 100 Amps.

The upper charge C-rate 'limit' for most deep cycle lead acid will vary from 0.1 to 0.3 C. Any faster and outgassing will result. Check your data sheet if you're really worried about it.

I had a pair of Fall River 6V 220ah batteries in series. If I recall correctly, The recommended C-rate for optimized life was something around 0.15C...but carried a 0.3C upper charge rate limitation guideline. The PO of my van did not lower the max charge current of the inverter charger ... It was cramming 150-175A (150/220a = 0.68C)into those batteries. Long story short, they died in a hurry. If set properly, the charger should have been limited to ~66A or so...

Fastest way to kill a batter from quickest to slowest:
1) too high a C-rate (charge)
2) too high a voltage (primarily during absorption, bulk)
3) repeatedly cycling the SOC to from 0 to <50% without fully charging the battery


Depth of Discharge*(DoD) is an alternate method to indicate a battery's*state of charge(SoC). ... At least in some battery technologies such as lead-acid AGM batteries there is a correlation between theDepth of discharge*and the Cycle life of the battery.

 

[vtsoundman]

One other omment regarding letting batterirs sit on float:

A battery left only to float will eventually begin to 'sulfate' and capacity will drop with time.

Batteries have two different types of Life ratings... calendar life and cycle life. Cycle life depends upon depth discharge and rate of charge /discharge.

Batteries that are cycled from time to time will tend to last longer than batteries simply left on a float charge indefinitely.

please note... Calendar life, charge rate/discharge rate are highly dependent upon chemistry. Lead acid and lithium batteries are very different animals.