Battery lifetime/cost vs. state of charge

[kmacdonald]

From the graph on post #13 we see that the total lifetime amp hours available are close to equal. Only about 6% difference between 50 and 80% DOD. Not enough difference to justify a larger bank and the associated weight penalty IMO. It should be noted that different batteries will have slightly different graphs.
If you want to take your argument a little further maybe you need 8 - 6V golf cart batteries to gain a larger 13% total energy difference between 20 and 50% DOD. It certainly wouldn't be worth it to me but it fits your argument.

[kmacdonald]

Originally Posted by valhalla360

If you get to the point where you can't fit in the battery bank at 50% DOD, you probably need to either reduce consumption or switch to a generator as you probably don't have room for the solar array needed to support it.

I think the logical choice would be to go to a 80% DOD use before considering a generator. YMMV

[chala]

Originally Posted by kmacdonald

Just out of curiosity, where do you draw the line on battery bank size?

Originally Posted by valhalla360

As far as your curiosity, I size the battery bank based on needs. Haven't had to mess with it on the new boat but the last boat, I swapped out 4 - 6v golf cart batteries for a single 12v. Of course, the fridge ran on propane when away from the dock, so 12v use was negligible for lights, water pump and occasionally some fans.. Never dropped below 75% with just the solar panels and you could pull start the motor easily, so no worries about having significant battery reserves.

Propane when sailing?
I think he meant Capacity for bank size?

[kmacdonald]

Originally Posted by chala

Propane when sailing?
I think he meant Capacity for bank size?

Thanks for your technical editing, this thread could use more of it. To be clearer, I meant physical size, capacity, and weight.

[a64pilot]

One thing we are missing is that it's virtually impossible to recharge to 100% with Solar if you discharge to 50%.
If you discharge to 20% it will be impossible and each charge cycle will walk down to lower PSOC cycle.
Only way I can see the deep discharge work is if you had a generator and used it pretty much daily or of course shore power.

[chala]

Originally Posted by a64pilot

One thing we are missing is that it's virtually impossible to recharge to 100% with Solar if you discharge to 50%.
If you discharge to 20% it will be impossible and each charge cycle will walk down to lower PSOC cycle.

Why that?

[mitiempo]

Originally Posted by a64pilot

One thing we are missing is that it's virtually impossible to recharge to 100% with Solar if you discharge to 50%.
If you discharge to 20% it will be impossible and each charge cycle will walk down to lower PSOC cycle.
Only way I can see the deep discharge work is if you had a generator and used it pretty much daily or of course shore power.

That depends on bank size and size of solar array.

[Lamb Chops]

Hi, I very much appreciated the tutorial in this thread about SOC and learned a great deal. I laughed at myself that I was willing/interested enough to actually sit for hours reading these threads! I currently have 3 different charging sources (1 -charger/inverter, 2 - Solar, 3-Alternater with 3 stage controller). The battery monitor is an old Link 2000.

I have several questions... In several threads I have read the idea that a temperature sensor is a good idea on the inverter/charger and also on the panels to make sure that you don't over charge based on battery temperature. I am now of the opinion that this is not in fact what these remote temperature sensors are for. My understanding is that in fact the purpose of a temperature sensor is to help the charger understand the environment the batteries are in to determine optimal voltage while charging. Am I correct? if this is true there really is no value in a remote sensor as long as your batteries are not in an environment that is substantially different than where the inverter/charger is located.

The reason I am asking is that my Heart 25 inverter/charger did not come with a remote temperature sensor and I was wondering whether I should swap it out but I am now of the opinion that I am fine. Similarity some solar controllers also have remote temperature sensing but most don't. The ones I have actually have the temp sensor built onto the controller motherboard. So, again as long as the batteries and the controller are environmentally in similar locations all is fine (the factory rep seemed to dissuade me from the idea that the temperature sensor also had any role in backing off if the batteries got too hot.

So.... thoughts? Thanks!

[a64pilot]

Originally Posted by mitiempo

That depends on bank size and size of solar array.

No it doesn't. It a how long does it take to charge a bank as opposed to how many Solar hours there are in an average day.
Best way to overcome this is to start a generator early in the morning when the bank can accept lots of amps and shut it down when the panels can take over

[Cadence]

Originally Posted by chala

Propane when sailing?
I think he meant Capacity for bank size?

I think his reef is an absorption unit. If done right the propane is no problem and highly efficient

[valhalla360]

Originally Posted by Cadence

I think his reef is an absorption unit. If done right the propane is no problem and highly efficient

Exactly but apparently, they didn't bother to read the full post which clearly indicated it ran on propane. Since the fridge is the main draw for most boats, using a propane fridge really cuts down on the battery bank needed.

Of course, it's interesting how a certain poster was adamant that there was no difference in lift time amp-hrs but suddenly when the numbers are provided that clearly debunk that, the story changes to it's not enough difference...all while ignoring the fact the graphs provided by the manufacturers are for full charges between cycles ignoring the impacts of leaving the bank at a low state of charge.

[kmacdonald]

If the battery bank is not fully charged after use it makes even more sense to discharge to 80 percent DOD and size the bank accordingly.

[mitiempo]

Originally Posted by a64pilot

No it doesn't. It a how long does it take to charge a bank as opposed to how many Solar hours there are in an average day.
Best way to overcome this is to start a generator early in the morning when the bank can accept lots of amps and shut it down when the panels can take over

True, but it also depends on solar array size, bank size, and how much it is down. With too little solar you may not get out of bulk, although the absorption point will likely occur at a higher percentage of charge.

[kmacdonald]

I recently reviewed some articles on marine batteries and charging systems by one of the best authorities on the subject. One thing that stood out in the articles was the lack of knowledge and understanding some of his clients had. This thread has confirmed his observations and then some.

[mitiempo]

Originally Posted by kmacdonald

I recently reviewed some articles on marine batteries and charging systems by one of the best authorities on the subject. One thing that stood out in the articles was the lack of knowledge and understanding some of his clients had. This thread has confirmed his observations and then some.

What article, what author?