Battery Capacity

[delmarrey]

Here are some specs. You really don't want to let the batteries get below 50% and 75% is the safest for longevity.


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[mcarling]

Originally Posted by Bill Balme

they are Rolls 8D batteries (4).

Looks like you've got just about 312 kg (686 lbs) of batteries. If you decide to replace them, I would suggest considering lithium phosphate. Something like this would give you about double the useable capacity (admittedly a bit less nominal capacity), weigh only 187 kg (412 lbs), last a lot longer, and would be safer:
Balqon (Winston) 1000AH 4x3.2V Lithium Phosphate Battery Pack

Posters here have had mixed experiences with this supplier, though they seem all to have worked out ok in the end. Even the smaller 700AH version would have more useable capacity than an 1100AH lead acid battery pack.

[Bill Balme]

Post 16 by Delmarrey shows SG's that are much lower than those I measured today. However, today I measured while the batteries are being charged - does that have an effect. I was getting readings up in the 1.26 - 1.3 range mostly with just a couple of cells low at 1.15 and 1.2. Charging was still going on (I'd left the boat for a few days and the voltage had dropped to 12.4V.)

Tomorrow, when fully charged, I plan to equalize the batteries again.

I'm concerned that I've got quite a lot of variation in SG in each of the 24 cells - hopefully some of that will even out by the time everything is fully charged?

[Bill Balme]

Anecdotally, it appears that batteris 1 & 2 get harder use than batteries 3 & 4. Is there a reason for that or am I misinterpreting?

Is there any justification for moving batteries around in the bank - other than trying to get a severe workout!!! (I can't believe these things weigh over 175# each!)

[delmarrey]

Not all cells will be perfectly the same, especially over time. The plates may vary in thickness, or may have crud lodged between the plates, causing one to drop lower then another.

[btrayfors]

Bill,

It's very important to connect multiple batteries comprising a single battery bank in a manner which distributes the load (and the charging) as equitably as possible.

SmartGuage Electronics did a nice piece a few years back, with explanations and diagrams: SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

Look particularly at the contributions of each battery to a nominal 100A load in, e.g., the first method and the second one.

As the author says, there's simply no reason for connecting batteries as in the first method. Any of the other three are much better.

That said, charging voltages are extremely important as well. Be sure your flooded or AGM 8-Ds are getting at least 14.6-14.8VDC during the absorption phase (measured at the battery terminals).

Bill

[goboatingnow]

Originally Posted by btrayfors

Bill,

It's very important to connect multiple batteries comprising a single battery bank in a manner which distributes the load (and the charging) as equitably as possible.

SmartGuage Electronics did a nice piece a few years back, with explanations and diagrams: SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

Look particularly at the contributions of each battery to a nominal 100A load in, e.g., the first method and the second one.

As the author says, there's simply no reason for connecting batteries as in the first method. Any of the other three are much better.

That said, charging voltages are extremely important as well. Be sure your flooded or AGM 8-Ds are getting at least 14.6-14.8VDC during the absorption phase (measured at the battery terminals).

Bill

I wouldn't attribute much to that article. The differences in impedance in the short distances typical of interconnects compared to the internal impedance of the batteries is negligible

Dave

[DeepFrz]

I wouldn't attribute much to that article.

Interesting that Trojan Battery Co. agrees with the information in the above link.

[Maine Sail]

Originally Posted by DeepFrz

Interesting that Trojan Battery Co. agrees with the information in the above link.

& Rolls, Lifeline, Enersys/Odyssey, Deka/East Penn and my Midtronics and Argus analyzers..... I regularly & routinely measure banks that are wired against manufacturer suggestions to be regularly out of balance compared to banks that are wired per the battery manufacturers instructions.

I think Odyssey/EnerSys does the best job at clearly spelling this out in their Technical Manual on page 19.


From the Odyssey Battery Technical Manual
"PARALLEL CONNECTIONS
It is common to have batteries connected in parallel to achieve a desired amp-hour capacity. This is done by connecting all the positives to each other and all the negatives to each other.

Typically the positive and negative leads to the load are taken from the same battery; usually the leads from the first battery are used. This is not a good practice. Instead, a better technique to connect the load is to take the positive lead from one end of the pack (the first or last battery) and the negative lead from the other end of the pack. The two methods are illustrated above. Solid lines and arrows indicate positive terminals and leads; broken lines and arrows indicate negative terminals and leads.
In both illustrations, the positive leads are connected to each other; similarly the negative leads are connected to each other. The only difference is that in the first illustration the positive and negative leads to the load come from the first and last batteries. In the second case, both leads to the load are tapped from the same battery.

The first schematic is recommended whenever batteries are hooked up in parallel to increase battery capacity. With this wiring, all batteries are forced to share both charge and discharge currents. In contrast, a closer inspection of the second schematic shows that it is possible for only the battery whose terminals are tapped to support the load. Implementing the first schematic eliminates this possibility and is therefore a better one."


For now I will stick with what the battery manufacturers say is correct and what my very expensive analyzers repeatedly tell me works and what does not to help keep banks in balance..

[goboatingnow]

Originally Posted by DeepFrz

Interesting that Trojan Battery Co. agrees with the information in the above link.

Its one of those great in theory ideas. Theoretically they are correct. In practice the difference in resistance in the wires is way less them other variables like the terminal connections or differences in the batteries themselves. It's a bit of a " good practice " thing that's all.

I personally have never seen from specific gravity tests any variance due to different parallel connection strategies in a typical boat battery box. There is far more variability due to different ageing ,partial sulphation and other variables, resulting in strong/weak cells then is attributable to the parallel wiring strategy

I've done a lot of design work on battery charging in the past

But hey knock yourself out.

Dave

[mcarling]

Originally Posted by goboatingnow

Its one of those great in theory ideas. Theoretically they are correct. In practice the difference in resistance in the wires is way less them other variables like the terminal connections or differences in the batteries themselves. It's a bit of a " good practice " thing that's all.

I personally have never seen from specific gravity tests any variance due to different parallel connection strategies in a typical boat battery box. There is far more variability due to different ageing ,partial sulphation and other variables, resulting in strong/weak cells then is attributable to the parallel wiring strategy

I agree with all of this, but I still wouldn't use the (slightly inferior) first example in the article -- unless the boat were already set up that way and changing to any (slightly) superior arrangement would require replacing a (difficult to install) battery cable with a longer one.

[noelex 77]

The importance of wiring the batteries correctly is very dependent on the charging currents , number of batteries and to lower extent the discharging currents.

With boats that accomplish most of their charging for high power devices such as generators and battery chargers the voltage drop in the wiring and connectors becomes far more significant and to compound the problem this sort of boat tends to have a large battery bank and run high power devices, such as microwaves.
With this sort of boat the correct wiring is quite important.

If most of the charging is much lower current devices such as solar, the voltage drop will be lower and incorrectly wired batteries won't do much harm.

If wiring a boat from scratch the correct practices are just as easy and cheap as wiring the batteries incorrectly, but if deciding if your existing set up needs changing the above concepts may help you decide.

[Surfer Girl]

Originally Posted by Maine Sail

Wea should also not forget that while cruisng you will rarely get a bank back much above 85% SOC unless you pull into a marina or turn off loads and let the solar or wind work at it for 10-15+ hours.

So a 1000Ah bank is really a 500Ah bank at 100% SOC but at 85% SOC that 1000Ah bank really only has a usable capacity of 350Ah's before you hit 50% SOC..........

Originally Posted by CharlieJ

...and to continue Maine Sail's post:
If you do not frequently fully charge a lead acid battery, the battery's cycle life will be dramatically shortened as it will be chronically undercharged leading to sulfation and electrolyte stratification.

In general: Batteries on boats do not die. They are murdered.

So what's the best strategy on longer passages? Say 4 days plus, or 8 days (St Martin direct to Colon, Panama which we will be doing next year).
Assuming you are running the auto pilot, chart plotter and fridge/freezer more or less 24/7, cabin lighting in the evenings, nav lights all night, the odd bit of watermaking, charging laptops via inverter, etc.... (about 100 amps/day?) and assuming your solar panel bank (4 x 225w = 900w) is keeping up and/or even topping up - the battery bank will not get better than 85% SOC.
Can the battery bank handle this for 8 days or longer (and I don't even want to mention the 21 or 22 day passage from Panama Canal to Hiva Oa, but I just did ) without significant reduction of life?

Or would it be good practise to turn everything off for about 3 hours during the day (hand steer, steer by compass and the freezer plates will stay frozen for this short period) and run the engine for 3 hours to achieve a full charge? I know we cruisers don't do long passages very often but I really would like to not use the engine for charging on a long passage, if possible without shortening the life of the expensive battery bank!

[mcarling]

Originally Posted by Surfer Girl

So what's the best strategy on longer passages?

The best strategy for longer passages is to replace lead acid batteries with lithium phosphate batteries. I know that's not what you wanted to hear.

Obtaining a full charge does not require turning everything off. It's only necessary that the charging current exceed the load current by a sufficient margin and for a sufficient duration. What is sufficient will depend on many factors, which have already been well covered in this thread.

[noelex 77]

Originally Posted by Surfer Girl

So what's the best strategy on longer passages? Say 4 days plus, or 8 days (St Martin direct to Colon, Panama which we will be doing next year).

Charging the batteries up to 100% regularly is helpful for battery life. It's more important for some types of batteries such AGM.
There is no need to be obsessive, however. A 100% charge every few weeks will still give a very good battery life.

For best battery life reducing the depth of discharge is the most important factor.

The best way to charge them up to a 100% is with a slow charging method like solar. If you are using less than you can produce your batteries are likely to get to get up to 100% often enough.