Amp hour question for boat sparky

[klee wyck]

Attached are pictures of the battery spec labels and the wiring diagram for how these 12 batteries are connected. You will see immediately in the diagram that I missed drawing in one connection on the bottom row but I assure you it is there.
I have been told I am sure, but today I am scratching my head for how many amp hours I have stored at 100% of capacity on these pretty new industrial (<2 yrs) cells. I have a Victron Energy battery monitor and cannot pull it down below the mid 90s when I am cruising with no generator or away from power for short lengths of time. I have not put it to the test with days away from power or cruising. I had thought this came out to about 1400 amp hours of a twelve volt bank equivalent but it is acting like more than that it appears to me. Admittedly we do not run much AC on this boat as we are not in AC country. Still, frig, freezer coffee, convection microwave.

Help from the guru gallery please....

 

[O C Diver]

If each of the cells are 2 volts, you have 720 AH at 24 volts. You have 12 cells wired in series, so AH don't multiply.

Ted

 

[BobH]

Label on the batteries is 24VDC. That would make the bank 288VDC.

 

[O C Diver]

Rereading your post, it would be the equivalent of 1440 AH at 12 volts. I have around 900 AH at 12 volts. A night on the hook rarely brings the bank below 90%. The one exception to that is heavy microwave use.

Ted

 

[Insequent]

You are showing all 12 batteries connected in series, allowing for the drawing error you noted. The label shows a 24V system. So each battery is 2V. Each battery will be 720 Ah at 2V. Series connected batteries keep the Ah designation, so your system is 720Ah at 24V.

If you had 2 sets of 6 of these batteries in series, and then paralleled those two sets you would have 1440Ah at 12V.

It is a reasonably large capacity. But your loads, fridge and freezer in particular, must be quite efficient units given you stay at 90% or above. The convection microwave won't draw much when nuking (short run times) but if used as an oven for a roast it would draw down your bank quite a bit.

You might want to check in the Victron setup parameters that the bank capacity is correctly set at 720Ah. It is possible that whoever programmed that might have mistakenly entered 1440Ah, which would then not seem to get drawn down much. Unlikely, but mistakes can happen!

I have 1284Ah (at 12V) and end up down to 60% capacity overnight. That is running a Norcold reefer and 2 Waeco freezers, plus leaving the TV/sat dish in standby overnight (often recording stuff to watch later).

 

[High Wire]

12 x 2 volt cells in series is 24 volts IF they are 2 volt cells. Amp hours is what the label says 720. It would be nice to see the whole package.
But if you split it into 2 banks of 6 series cells and wire those two banks in parallel, then you get 1440Ah at 12 volts.
Voltages add in series.
AmpHours add in parallel.

 

[klee wyck]

Thanks to all with the quick replies. It seems it is as I think I was advised. It is indeed wired in series all the way thru the 12 cells.
Is it also true then when I think of the power consumption in a 12 volt system, this 24 volt system will consume energy for a given purpose at half the rate of a 12 volt set up? In other words, this 720 amp hour 24 volt set holds the equivalent of 1440 amp hours at 12 volts in terms of the energy I am consuming, right?
Then this seems about right and I should have expected what I am seeing.

 

[Rossland]

Sounds like you need to calibrate your battery monitor.

https://marinehowto.com/programming-a-battery-monitor/

To be accurate, you will need the following:
- AH capacity, which is not necessarily what is marked on the label
-Perkut number because batteries will supply more amps if discharged slowly
- Charge Efficiency. Because you always have to put more amps into a battery than you can get out.

The last two numbers can be supplied by the battery manufacturer. The link gives much more detail and explains how to conduct a battery capacity test.

 

[klee wyck]

You are showing all 12 batteries connected in series, allowing for the drawing error you noted. The label shows a 24V system. So each battery is 2V. Each battery will be 720 Ah at 2V. Series connected batteries keep the Ah designation, so your system is 720Ah at 24V.

If you had 2 sets of 6 of these batteries in series, and then paralleled those two sets you would have 1440Ah at 12V.

It is a reasonably large capacity. But your loads, fridge and freezer in particular, must be quite efficient units given you stay at 90% or above. The convection microwave won't draw much when nuking (short run times) but if used as an oven for a roast it would draw down your bank quite a bit.

You might want to check in the Victron setup parameters that the bank capacity is correctly set at 720Ah. It is possible that whoever programmed that might have mistakenly entered 1440Ah, which would then not seem to get drawn down much. Unlikely, but mistakes can happen!

I have 1284Ah (at 12V) and end up down to 60% capacity overnight. That is running a Norcold reefer and 2 Waeco freezers, plus leaving the TV/sat dish in standby overnight (often recording stuff to watch later).

I think the Victron monitor may be ok. If I look at amp draw at no load and then start adding loads, the draws make sense to me. I suppose it had to be told what total beginning supply it was drawing from to get SOC readout subsequent to that so I will check on that and appreciate this line of questioning. I will pursue that for sure.

 

[dhays]

I think the Victron monitor may be ok. If I look at amp draw at no load and then start adding loads, the draws make sense to me. I suppose it had to be told what total beginning supply it was drawing from to get SOC readout subsequent to that so I will check on that and appreciate this line of questioning. I will pursue that for sure.

It would be worth reading through one of CMS’s articles on battery monitors on his website. Not that you will be able to be terribly accurate with setting up the monitor, but at least you will start to understand the variables.

 

[DDW]

I have 1284Ah (at 12V) and end up down to 60% capacity overnight. That is running a Norcold reefer and 2 Waeco freezers, plus leaving the TV/sat dish in standby overnight (often recording stuff to watch later).

How big are those reefers? That is one heckofalotta energy overnight. 6KW or so. My sailboat can run about 5-6 days on that (with the reefer and freezer on). But one thing I am quickly learning in the trawler world is that not much attention is paid to efficiency in their DC systems.

The overnight amp-hr use of the OP shown by the Victron will not be far off, even if not well calibrated. The amps drawn are measured by shunt, which needs no calibration. The SOC could be affected by calibration or settings.

 

[caltexflanc]

Looking at the website for Midac, that battery bundle is 720 AH at a c5 rate, so will be less at the more standard c20 rate used for deep cycles.
Battery info down towards the end with a picture of what these bundles look like.

http://www.midacbatteries.com/brochures/MIDAC_Catalogo_CHARGERS.pdf

http://www.midacbatteries.com/brochures/oldMIDAC_CatalogoMOTIVEPOWER.pdf

 

[Lou_tribal]

Looking at the website for Midac, that battery bundle is 720 AH at a c5 rate, so will be less at the more standard c20 rate used for deep cycles.
Battery info down towards the end with a picture of what these bundles look like.

http://www.midacbatteries.com/brochures/MIDAC_Catalogo_CHARGERS.pdf

http://www.midacbatteries.com/brochures/oldMIDAC_CatalogoMOTIVEPOWER.pdf

Less or more?

L

 

[dhays]

Less or more?

L

C20 will give a much higher AmpHr value than the C5 rating. The slower the discharge, the more energy you can get out of a battery bank. So if the 720Ah value is a C5 value, the C20 value would tend to be MUCH higher for most batteries.

Again, C5 measures the amount of energy taken from a battery when it is fully discharged over 5 hours. C20 is the amount of energy taken when it is fully discharged over 20 hours.

 

[caltexflanc]

Here's a good explanation; sorry, lost the internet there fo awhile.

Why Does a Battery Have a C5, C20 and C100 AH Rating? Can't They Make Up Their Mind?

Advise calling the battery mfr.

 

[Insequent]

How big are those reefers? That is one heckofalotta energy overnight. 6KW or so. My sailboat can run about 5-6 days on that (with the reefer and freezer on). But one thing I am quickly learning in the trawler world is that not much attention is paid to efficiency in their DC systems.

The overnight amp-hr use of the OP shown by the Victron will not be far off, even if not well calibrated. The amps drawn are measured by shunt, which needs no calibration. The SOC could be affected by calibration or settings.

The Norcold is the DE 0061. The freezers are Waeco CF110, so 110 litres each. Running them as freezers uses a lot of energy.