Deep Cycle Capacity Battery Question - Not doing what i expect

Nomad_Nev · Veteran Member

Deep Cycle Capacity Battery Question - Not doing what i expect

Peter_n_Margaret · Guru

1. Your voltage checks are not a remotely reliable method of determining state of charge.
2. Your fridge draws a lot more than 0.7A average.

3. 12.0V is quite low, but they won't be damaged by taking them lower.

Cheers,
Peter

-- Edited by Peter_n_Margaret on Monday 21st of December 2015 11:05:56 AM

Nomad_Nev · Veteran Member

Thanks for the reply,

I hear you on the voltage, will need to figure something else out to measure the usage, perhaps an inline current meter with a total and just keep track of the consumption after a full charge, i have one but it doent have very very thick leads, so i wouldnt want to put too much load on it, can use it to test though

Why would you think that the fridge uses a lot more than 0.7? My calcs have actually worked it out to 0.66 based on a 2.2 Amp load and 30% run time, the 0.75 is what the manual says so i went with the higher number to be safe.

Perhaps damage is the wrong word, i'm concerned about significantly reducing the number of charge cycles on the battery by over discharging them, from what i have read under 20% discharges (Some even say under 30%) will reduce the number of charge cycles and therefore the lifespan of the batteries, hence me wanting to figure out the usage and get an idea where the batteries are at.

As a side, i am going to skip putting out the solar panels today, then i can do another check after 24 hours of drain on the batteries and see if that tells me something new

Peter_n_Margaret · Guru

Nomad_Nev wrote:
Perhaps damage is the wrong word, i'm concerned about significantly reducing the number of charge cycles on the battery by over discharging them, from what i have read under 20% discharges (Some even say under 30%) will reduce the number of charge cycles and therefore the lifespan of the batteries, hence me wanting to figure out the usage and get an idea where the batteries are at.

Deeper cycling provides more power from the battery each cycle compared with a greater number of shallower cycles, so yes the battery will have less total cycles over its lifetime, but that is not what battery life is about.

Battery life is about the total power supplied over its lifetime and deeper cycles will reduce that, but not by a great deal.

Shallower cycles also means that you will require more batteries (more $s invested and more weight) to be carried to get you from one charge cycle to the next.

Always charge them when you can.

Cheers,

Peter

woofta and precious · Senior Member

Hi Nev,
Try disconnecting the older 100ah battery and just leave the newer one connected.
You don't say how old the 100ah battery is, but it is my understanding you should have batteries of the same age and capacity connected together for the best results.

Brian

Peter_n_Margaret · Guru

Nomad_Nev wrote:
Why would you think that the fridge uses a lot more than 0.7? My calcs have actually worked it out to 0.66 based on a 2.2 Amp load and 30% run time, the 0.75 is what the manual says so i went with the higher number to be safe.

2.2A seems very low to me, but maybe it is correct.

The duty cycle will vary dramatically depending on the temperature difference between the inside of the fridge and the outside of the fridge.

5c inside and 15c outside is 10c difference.

-10c inside and 40c outside is 50c difference and will require the compressor to do 5 times the work to keep up. It will probably be running at 100% duty cycle and not maintain the set temperature at 50c difference. Insulation quality is the key.

None of the above includes opening losses or adding warm stuff.

Cheers,

Peter

Peter_n_Margaret · Guru

woofta and precious wrote:
Hi Nev,
Try disconnecting the older 100ah battery and just leave the newer one connected.
You don't say how old the 100ah battery is, but it is my understanding you should have batteries of the same age and capacity connected together for the best results.

Brian

Age and capacity are unimportant, but they should both be in good condition and the same chemistry otherwise the poor one will reduce the performance of the good one. Older may suggest the performance may be down though?

Cheers,

Peter

Izabarack · Guru

Peter_n_Margaret wrote:
1. Your voltage checks are not a remotely reliable method of determining state of charge.

Totally agree with that statement. Plus, 60 seconds is not nearly enough to let surface charge to dissipate leading to misleading readings on which to base estimates of state of charge.

Second thing is that every 40 Litre Engel I have ever measured drew 2.45 to 2.5 Amps when running. At around 18 Degree C ambient, I would expect a duty cycle close to 35% or 40% with good ventilation.

Full charge voltage for deep cycle batteries is not the same across specific batteries and across brands. I once had a deep cycle FLA battery that would not charge past 12.51 volts. It got flogged and still lasted 7 years. In your case the charged voltage number is likely distorted by reading things so soon after charge and the morning reading may have been pulled down by a battery that normally reads a bit lower.

I suggest you try using one battery alone, leave the battery for at least an hour after removing from charge, and do some duty cycle measurements. You would then have some reasonably accurate figures to make some estimates on. Might be good to get some understanding of the difference between Amps and Amp/hours as metrics. Your story about drop off of charging current late in the day and the capacity in your battery bank does not suggest any problems with the setup.

Overdischarge and damage - Only 500 cycles out of a battery lets you flog a battery once a month for a long time more than expected time-of-life.

Iza

Nomad_Nev · Veteran Member

Thanks for the comments, the older battery is less than 6 months old and almost never used until a month ago, i hear you on the number of cycles, I should do a full cycle every 4 days and that is only about 90 a year, I wont really need them to last that many cycles before they get replaced with bigger/better. Still going to hook up the inline watt meter and get a better feel for the usage, but will be less concerned about exact ending voltage

Jaahn · Guru

Hi Nev,

Some good info so far.

Just to reinforce a suggestion given, you must get to understand AMPS and AMP/HOURS before you can make some sense of it. The fridge etc use X amps when running but over an hour then it becomes X amp/hours. Over more Y hours then the same amps become XY amp/hours. The batteries hold amp/hours so that is why you must understand the concepts to judge what is happening.

And as has been said Volts are unreliable for indicating battery state, certainly you must leave then rest for an hour, but the only reliable measure is one which measures the power in and the power out to tell you how much is there.

Jaahn

Dav4Cris · Senior Member

I note that you increased the battery capacity from 105 to 205 but you did not increase the solar at all. I would be getting another 200watts of solar to recharge the batteries. 200 watts is not enough to recharge 205Ah of battery, need at least 400w.

exa41 · Guru

the best way to check your batteries is to do a full load test . charge the batteries until they are full ,separate and attach a globe , say 100 watts to each battery and tabulate voltage drop over 8 hour period , the battery voltages should be pretty close at end of test , if not you may have a bad cell or even a bad connection .

Nomad_Nev · Veteran Member

cool, so i have attached a watt meter to both the solar and the battery load, so i can now tell exactly how many amps hours are going in and coming out of the battery, 24 hours on a really hot day and night used 23 amp hours, Going to recharge all the devices and spend the day working on the laptop and will see what that uses, which should give me a worst case scenario, and between these i should get a good feel for the days i can expect out of the batteries and how much charge to expect to put back to get em to full. I think i should be ok with the 200w of panels, on a good day i can get 70-80 Amp Hours back into the battery, also with us full time on the road with a wife and little one, we just dont have the space for more panels, will have to make these work :P

Gundog · Guru

I to have a question about batteries, I have a 100ah which is the main house battery, it is maintained by the setec II. According to the setec manual it is not recommended to fit a battery greater than 100ah. I also have a 97ah battery which I want to included in the circuit, considering the limitations of the setec, I have a 16amp 8 stage battery charger which I will be connected to the 2nd battery and the 2nd battery will be connected to the 1st battery. We are in the process of swapping out our 90ltr 3 way fridge with a 228ltr Samsung digital inverter fridge, which will run on 240v shore power when 240v is available and when we are mobile it will run on 12v via a victron 350va 300w inverter connected to battery 1 The next part of the new circuit will have 240w solar panel connected to a Morningstar Duo which is set up to connect to 2 batteries. Is my thinking correct.

Nomad_Nev · Veteran Member

So couple of bits,
seatec is a company that makes a lot of different stuff, not sure what product you have when you talk about the seatec, see:
www.setec.com.au/

Your setup sponds simular to mine just with a lot more fridge, we had a 100amp battery, and just added a second to give 200amps, it is recharged off 200 watts of solar, and runs the camper fridge, (12 volt fridge) lights and a 300w inverter for recharging 220v stuff occationally

The process is Solar Panels -> Regulator -> Batteries

The regulator needs to be big enough to handle the amount of solar, my 200w panels work fine through a 20Amp (I havent seen them go over 14 Amps)

Not sure what item would reccomend that you dont use more than 100amps of batteries becuase the above bits dont care, just takes longer to recharge more batteries, and with the fridges you mention, you are going to need a lot of power,

For me basic LED lights, and a 40L fridge use 24 Amp Hours out of my batteries a day, call it 30 to be safe and i get 5 days out of my 2x100Amp batteries (You dont want to run them flat)

The 200w of solar panels (Good quality ones) get me about 60-80 Amp Hours back into the batteries if i have good sun, so 2 days of recharged power (And the days use) for a day in the sun.

-- Edited by Nomad_Nev on Saturday 26th of December 2015 10:41:25 AM

-- Edited by Nomad_Nev on Saturday 26th of December 2015 11:32:24 AM

PeterD · Guru

Nomad_Nev wrote:
So couple of bits,
seatec is a company that makes a lot of different stuff, not sure what product you have when you talk about the seatec, see:
www.setec.com.au/

No the link you should have given is - Jayco Customers - Gundog did say "setec II," you will be able to download the literature from my link and put yourself in the picture. If you hang around for long enough you will be able to educate yourself in these matters.

These are good power supplies to run your house 12 V from the mains but are not particularly good battery chargers. Gundog, I would prefer a larger battery charger than 16 A. Your proposed charger will be a little light for quick recovery if you need to recharge from a generator. However give it a try and see how you cope, if it does then look for one with at least 35 A output. You can just connect it across your battery bank and leave everything else in place. When you recharge from the mains the Setec will provide the house power and the charger will not have to provide any of that.