Battery Condition

[Nodak7]

OK, it is a rainy day out there so I have some time to ask a question of you brainac's out there. My battery Bank has a gross 1300 AH total for the bank. In keeping with the 50% rule I understand that my usable bank is 650 AH's. So I have my Xantrex Battery Condition Monitor set to 650 AH's. Therefore, in the morning when I awake I see that I am at 79% of that available Bank. The voltage is 12.5v. I turn my inverter on so I can run the coffee maker for my morning cup of coffee. When the heating element kicks in the battery voltage drops to 11.9 volts. After coffee (5 minutes) the voltage returns to 12.5 v and the percent is 78.7%. Does it bother the battery to run it under 12 v for this short amount of time? I don't believe it is an issue but would like to hear from the experts out there and what your opinion might be on this.

 

[Rick486]

I've been doing exactly what you describe for 10 years now. No problems. I do use a small drip coffee maker....3 cups.
Are you sure it is 1300 AHs? Seems like a lot.

 

[Don S/V ILLusion]

Every time I notice the same thing it turns out to be a lossy high resistance connection somewhere. Easy to confirm by simply noting the battery bank voltage directly at the battery terminals.

 

[Nodak7]

Every time I notice the same thing it turns out to be a lossy high resistance connection somewhere. Easy to confirm by simply noting the battery bank voltage directly at the battery terminals.

Interesting thought Don. I have watched it on my Xantrex and it confirms the Voltage reading on the panel. I was under the impression that the Panel Meter and Xantrex readings were at the battery terminals.

 

[Nodak7]

I've been doing exactly what you describe for 10 years now. No problems. I do use a small drip coffee maker....3 cups.
Are you sure it is 1300 AHs? Seems like a lot.

Rick, my Battery bank is made up of 6 6v Trojan T105's 225 AH each. Three banks of 2 in series to make a 12v each bank. Three banks in Parallel total AH for all three banks is 1350 AH at 12v. That is where I got the 650 AH (50%) entered in the Xantrex.

Yup that is probably the same 3 cup maker that we use. We were using a single cup but decided to try the "bigger" one. It definitely hits the voltage harder than the small one but not for a prolonged time.

 

[Don S/V ILLusion]

Rick, my Battery bank is made up of 6 6v Trojan T105's 225 AH each. Three banks of 2 in series to make a 12v each bank. Three banks in Parallel total AH for all three banks is 1350 AH at 12v. That is where I got the 650 AH (50%) entered in the Xantrex.

Yup that is probably the same 3 cup maker that we use. We were using a single cup but decided to try the "bigger" one. It definitely hits the voltage harder than the small one but not for a prolonged time.

I may be mistaken but three 225 AH banks equals 675 AH total.

 

[Nodak7]

I may be mistaken but three 225 AH banks equals 675 AH total.

No each battery is rated for 225 AH at 20 hours. Probably not the best description.

 

[Maine Sail]

No each battery is rated for 225 AH at 20 hours. Probably not the best description.

But in series you add voltage only not Ah's.

Each pair of T105's in series, for a 12V bank, is 225Ah at 12V...

The good news is that you saved yourself by accidentally programming the battery monitor correctly for the actual bank size...

 

[Nodak7]

But in series you add voltage only not Ah's.

Each pair of T105's in series, for a 12V bank, is 225Ah at 12V...

The good news is that you saved yourself by accidentally programming the battery monitor correctly for the actual bank size...

Really!!! Thanks. Not what I was told but I definitely believe you over my source. Especially knowing your expertise in this area.

 

[Hello Below]

The good news is that you saved yourself by accidentally programming the battery monitor correctly for the actual bank size...

Not if in his way of thinking, he could take the SOC to 0% thinking it was actually only 50%.

 

[Newport Bob]

I've been doing exactly what you describe for 10 years now. No problems. I do use a small drip coffee maker....3 cups.
Are you sure it is 1300 AHs? Seems like a lot.

WAY TO GO Rick! Knew an old Ensign sailor would know how to make good morning coffee AND calculate AHs

 

[Maine Sail]

Not if in his way of thinking, he could take the SOC to 0% thinking it was actually only 50%.

But remember he accidentally programmed the monitor for half the capacity he thought he had instead of the correct 100% of the bank capacity he assumed..

In keeping with the 50% rule I understand that my usable bank is 650 AH's. So I have my Xantrex Battery Condition Monitor set to 650 AH's. Therefore, in the morning when I awake I see that I am at 79% of that available Bank.

Proper programming, based on the assumption he had a 1350 Ah bank, would have been to program it at 1350 Ah. If this had been done, when he was at 50% SOC, based on the monitor, he would have really been at 0% / 10.5V or lower.

I suspect he assumed you put in your "usable capacity" then cycled to 50% on the monitor, not 0%, but perhaps he can correct what I am assuming he meant..?

By programming his monitor incorrectly at 650 Ah, (based on what he incorrectly assumed for capacity) he actually protected his bank when compared to the assumed capacity..

Battery monitors are programmed for the banks total Ah capacity, not half of it. There were two incorrect assumptions and the second one, programming the Ah counter for half the actual capacity, actually served to protect his bank.

When the heating element kicks in the battery voltage drops to 11.9 volts.

This is normal and has to do with the Peukert effect. Under high load draw the battery voltage will sag lower than it does under lower loads. If it gets too low, your inverter will tap out on you...

 

[Hello Below]

I suspect he assumed you put in your "usable capacity" then cycled to 50% on the monitor, not 0%, but perhaps he can correct what I am assuming he meant..?

Only his hairdresser knows for sure.
Thanks Maine. I often wonder the harm being done to batteries when bringing up the anchor even with the diesel running and the Balmar putting out what it can at low RPMs to help provide the 85 A feeding the windlass.

 

[Maine Sail]

Only his hairdresser knows for sure.
Thanks Maine. I often wonder the harm being done to batteries when bringing up the anchor even with the diesel running and the Balmar putting out what it can at low RPMs to help provide the 85 A feeding the windlass.

Golf cars and EV's, on average, draw much more power per battery than we do on boats. For example a T105 GC2 6V is rated at a 75A discharge to deliver 115 minutes of power. The 75A rating is a .33C discharge rate on the 225Ah battery..

If you take a 675Ah bank of series / parallel T105s you'd need to be discharging at 223A to equal the 75A rating. While a 223A load is possible on a boat, the duration is usually measured in seconds for thruster, stater motor or heavy duty winch operation.

Large deep-cycle banks have no issues driving short term high amperage loads. Using the alt when weighing anchor is smart because it helps reduce the load the batteries see and yields better windlass performance as there will be a higher overall voltage.

 

[Nodak7]

Thanks all!!! This post taught me 2 things. First my 650AH setting, in my battery condition monitor, is good (even though it was based on misinformation) and Second, I need not be terribly concerned with my battery temporarily dipping to 11.9 volts when I make coffee in the morning!

 

[artboas]

I concur
The correct Ah is 675.
Please see my other post about Water Miser battery caps.