Battery Bank Configuration

[ChrisOlson]

I feel you have answered my questions and I don't want to make it sound like I was arguing or didn't believe you.  I do, believe me, believe you and appreciate your experience.  I do have my reservations regarding a big battery in parallel with a little battery but I will overcome that once I just do it and see what my results are. 

Oh, not at all.  I had reservations about putting the boat batteries in series and parallel connecting them to the bank.  I know I read someplace, but don't remember where I seen it, that you just "can't do that".  But when it says, "WARNING - do not push any buttons - especially the last one" I will typically push them anyway, and start out with the last one, to see what happens   
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Chris

[Watt]

" But when it says, "WARNING - do not push any buttons - especially the last one" I will typically push them anyway, and start out with the last one, to see what happens    "

I do believe this fits you well....   

Thanks again Chris.

[Cornelius]

To see what happens with a small battery and a larger battery in parallel; why not connect them together with an amp meter between each, and load/charge/equalize them? An easy enough test, and it will put many of our minds to rest...

[Watt]

To see what happens with a small battery and a larger battery in parallel; why not connect them together with an amp meter between each, and load/charge/equalize them? An easy enough test, and it will put many of our minds to rest...

I think I was more concerned with heating the little battery too long.  But, I guess my IR heat gun would answer my question easier than anything. 

[Wolvenar]

I was also interested in the amp draw. I always put my boat batteries in parallel with my bank also. I have never seen a problem yet,and they are going on thier 9th year .. I'm rather amazed at how long they have lasted given the abuse I put them through. But these are golf cart batteries also ..
I have never monitored them myself, never even thought about it. I figured it HAS to be better than letting them go dead, or worse.. freeze.

[ChrisOlson]

They should never freeze if they're charged until it gets down to -70.  Of course, if you're anywhere close to International Falls that could happen   
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Chris

[Cornelius]

The lowest temp last night here in Norway was -44deg C...

[Wolvenar]

@ Chris. exactly my point. If I don't keep them on something to keep them charged they lose charge on their own, and will freeze in Minnesota temps.

[ChrisOlson]

I put a little 19 watt Coleman solar panel on the roof of our 5th wheel RV a couple years ago and that works pretty good to keep the battery up in that.  I got the picnic table sitting by the camper so I can reach the roof and sweep the snow off that little solar panel.

I was in the camper the other day to grab a stainless frying pan out of it that my wife wanted.  So I pressed the "test" button on the "Command Center" in the camper and it showed the battery at 12.62 volts.  The last time we used it was in September when we took it to Canada.  That little solar panel only puts out about a 1/4 amp most days in the winter, but it's enough to keep the battery up.
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Chris

[tomw]

Back when I was starting this journey through the wastelands of RE, I studied up on batteries and read anything I could find on them. Most helpful (then) was RV and boating crowds. Solar and wind were kind of fringe stuff then. Mostly folks "selling" and not much historical data on the RE installations and long term battery health.

I got a lot of my battery "attitude" from the Blue water sailors. Their stuff has to work. Period. Can't pull over at the roadside battery mart any time you want on the high seas for a replacement.

A lot of what they did was not according to manufacturer specifications. Things like a bit higher voltage for float charging and numerous other little bits that I follow yet today but will not get into lest I set off a battery abuse intervention by some user(s).

I have routinely mixed sizes in parallel but would NOT do so in series. I figure they are both a source and a load and simple DC electric theory 101 tells me they will see exactly the same voltages (discounting cabling losses) and will draw or deliver the amperage it is capable of into or from it as if it were in the same situation alone if the load is X volts and Y ohms you get Z amps. The confusing bit is the big boy bank holds the voltage up and this seems to just put the baby battery into a form of stasis where it does not have to provide any current because the big boy is pushing the amps into the load until a point where the voltage is low enough that the little one can shove some amps and so on and so forth. They just act like any source or load in parallel because, ultimately that is what they are. Curiously enough at the same time sometimes.

Hope that was as clear as the mud spattered rear window on the Dakota!

Some of the seemingly complex puzzles are just as simple as this.

No quantum physics.

Loads and sources.

Thevenin would be proud of me ;=>

Or say **Cough**BULLSHIP**Cough**

That is my take on morphodite battery combinations.

There you have it so have a blast showing me I am full of it.

Same voltage batteries, obviously.

Tom

[rossw]

I'm not even convinced that the same solution works the same in different environments.

[Wolvenar]

I am mostly with Tom on this.
However Ross  brings an interesting aspect to the mix. Environment, in my area could be interpreted as temperature of the bank.
Here if say its that batteries are in a colder area, or if or all are in a cold area, it may be that smaller batteries would be colder not having the mass and not have a normal internal resistance if under light use. Under heavy use they may be the warmer of the bunch This would make a big difference on its draw and capacity, but would it make a difference on its overall voltages?? It is not anything I would worry about, but it becomes an interesting exercise trying to calculate the variables.
 I have no idea..

[rossw]

I am mostly with Tom on this.
However Ross  brings an interesting aspect to the mix. Environment, in my area could be interpreted as temperature of the bank.

I meant "environment" in the fullest extent of the word.

How hot or cold it is. How far down it gets drawn, and how quickly. How long it remains discharged. How quickly and how hard it gets recharged. If it's a pulse charge or a heavily smoothed and filtered charge. How much rest they get along the way.

For example: I know my batteries behave differently when being charged from the hyper-smooth DC from the PV compared to the "ripply" charge from my turbine. I know they behave differently over winter to summer - even though their temperature remains only a few degrees different (being burried 15' underground sees to that). But in summer they spent far more time in float, get discharged less overnight, get recharged earlier the next day. However in winter they get a much faster charge (from the genset) - put puts the same amphours back in, but they don't seem to "hold" the charge as well as if they get it more slowly and can "digest" it better.

Nothing I've measured and/or tried to quantify, just what I've observed.

[ChrisOlson]

However in winter they get a much faster charge (from the genset) - put puts the same amphours back in, but they don't seem to "hold" the charge as well as if they get it more slowly and can "digest" it better.

I've noticed the same thing.  A genset charge don't last near as good as a long "soak" with the turbines and solar panels.  I don't know how yours works, but mine bulk charges and absorbs, then the inverter shuts the generator off.  I have the absorb "done point" set at 2% of ah capacity of the bank, which is what the manual recommended.  But I don't think the batteries are "quite there" yet at that setting and they require several hours at float to really get fully charged up.
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Chris

[rossw]

I've noticed the same thing.  A genset charge don't last near as good as a long "soak" with the turbines and solar panels.  I don't know how yours works, but mine bulk charges and absorbs, then the inverter shuts the generator off.  I have the absorb "done point" set at 2% of ah capacity of the bank, which is what the manual recommended.  But I don't think the batteries are "quite there" yet at that setting and they require several hours at float to really get fully charged up.

Years since I set mine, so I'm working from a combination of memory of the original setup, plus the odd tweek since.

The inverter will call for the generator to run in a multitude of events. The only relevant at the moment are:
    (a) if the voltage falls below (x)
or (b) if the amphours discharge is more than (x)
or (c) it's within (y) hours of the generator going into "night lock" and the batteries are discharged more than (z) AH
or (d) the generator is in "night lock" but the volts dropped below (z)
or (e) the generator is in "night lock" but the amphours are more than (y)

Once it's started, it will run for a minimum of 1 hour. If there's no other reason for it to turn off, and assuming there isn't more renewable comming in than some set limit, and assuming the total load is less than some other set limit (sounding like a nightmare to document already!), then it will continue to run until the voltage reaches the "absorb" setpoint, at which stage it goes into the absorb charge stage, which it will do until it gets to the "float" threshold. Then it goes into the "float" charge mode and will hold there for a set time before it turns the generator off.

It's very inefficient to run the generator just to hold the cells in float for 2 or 3 hours, so it usually drops the generator fairly quickly - I think I have it at 30 mins of float.

Even so, I think that 100 amphours of generator charge "holds" the batteries for less time than 100 amphours of solar charge does, assuming neither of them actually gets the batteries to float.