Tiny House Build and 12v fuse block

[Sabatical]

I don't quite get how to do the math (never my strong suit) but I have 840 watts of panel and 675 amp hours of battery capacity. We have not dropped below 90% SOC in our time living with solar and have hit the full mark (theoretically) daily. I will most likely add another panel next summer. I believe that there is enough capacity in my charge controllers to handle some more wattage although it would require running them in series as opposed to parallel as i currently do.

 

[SternWake]

Yes Sabatical, If more people were to dip the hydrometer at the moment when their solar controller drops to float voltage, most will find the specific gravity reading indicates the batteries are in the 90% charged range and that the blinking green 'full 100% charge' light has been mocking them.

One needs to know the maximum specific gravity of their batteries though, and this can range from 1.270 to 1.310.

Generally an Equalization charge of upto 16V is required to see just how high the SG can go on a used battery, and the temperature of the electrolyte needs to be factored in on each Cell, as cells in the middle of the battery get hotter than the outside cells, and tightly packed battery banks can really have huge temp differences from outside to inside.
When a battery is new and fully charged, is the best time to establish what the maximum specific gravity is to compare to all future readings.

Trojan states what their maximum specific gravity is. 1.270 minimum IIRC, but many people report getting much higher readings. This can be due to the electrolyte level in the cells being lower or inaccuracy of the hydrometer. So it is important to use the same hydrometer as it is comparable to itself on future readings, but not to other hydrometers on the same batteries. Noting the electrolyte level is important too when taking readings, and note after refilling they will always read low and the voltage held under discharge will sag for a few cycles too.

The OTC4619 includes a thermometer which says how much to subtract or add to the float level reading. For a 10$ hydrometer it is a good value, but those seeking the best most accurate and precise hydrometer, google Francis Freas.

Keep in mind I often will espouse 'Ideal'. I don't expect anybody to actually go nuts trying to achieve ideal. i do not do so myself. I find an acceptable minimum/maximum through experimentation. However Knowing what Ideal is, is, in my opinion, important.

One can go well below ideal and be 'just fine' and 'good enough' and sacrifice some battery longevity, but there is also a ' head in the sand' ostrich approach and I do get a little miffed when this is recommended to somebody trying to learn.

The ostrich approach can unwittingly cost a lot of money, as one might not be able to realize how unideal their system actually is, until battery capacity has diminished to a point where it is unavoidable to know that capacity has decreased and can no longer meet one's needs. At this point, it is usually battery replacement time, which hurts financially, and then the person wants to know why they did not get the expected cycle life from the batteries. Sometimes an Aggressive equalization charge, or a series of them back to back can restore some lost capacity, but getting batteries upto 16v usually requires special chargers too. The after the fact attempts at capacity restoration usually instill the owner with the knowledge to prevent it occurring again on the next set of batteries. My goal is to help prevent it happening to the first set of batteries with people new to living on 12v lead acid batteries and who are expecting a lot from them.


Flooded batteries:
With 6v GC batteries one should expect at least 800 cycles to 50% discharge when charged properly
with 12v quality car jar deep cycle batteries one should expect at least 400 cycles to 50% discharge when charged properly. East penn/Deka, Trojan, Crown, USbattery.
with 12v standard easily obtained car jar marine batteries (walmart) ~ 250 range to 50% when recharged properly
Overall time a battery lasts when one does not know the depth of discharge or the number of total cycles, is largely irrelevant.
Those who claim years and years should also state they have very shallow infrequent cycles, but this does not make them look smarter nor does it instill bragging rights and a superior attitude.


AGM batteries have special needs and they can vary widely. Generally they want higher recharging currents, and they require actual 100% recharges to get anywhere near their expected lifespans when cycled to 50% DOD/SOC. Return an AGM to only 95% cycle after cycle and expect less than half the cycles than if it saw 100% recharge each cycle, with the occasional high amp recharge thrown in every 7 to 10 cycles.

AGM's high price tag often instills their owners with 'super battery' warm and fuzzies, but these batteriy's 'needs', to achieve super battery status, are much harder to meet, compared to flooded batteries, and they cost twice as much for the privilege of lasting half as long when their special needs are not regularly met.

Please remember claims of working "just fine' only means has not failed yet.

"Just fine" for 500 Cycles or 800 deep cycles, actually means 'just fine and totally acceptable'

Shallow cycles are pretty easy on most batteries. Claims of longevity on very shallowly cycled batteries mean very little.

My Aim on my batteries is 50% discharges often, and 100% recharges every day. I managed almost 500 cycles from my previous group31 flooded USbattery, but I did not fine tune the absorption voltages/duration for the first 100 cycles which degraded lifespan.

Right now My Northstar AGM is my only battery. 90AH total for both Engine starting and house duties. The SOB is being worked hard, but being recharged hard to 100%, and I cannot detect any capacity loss in nearly 200 deep cycles and 23 months of age.

Its all about the recharging.

 

[SternWake]

If you are actually only depleting to 90% and actually returning to 100% then your 840 solar watts to to 675 AH of capacity is actually 'just fine'

But if you were to discharge to 50% day after day and your monitor claimed 100%, then it is highly likely it is not just fine.

Really the only way to truly know is the hydrometer. The ideal absorption duration is a moving target, and no controller does this automatically perfectly. The human discharging the batteries needs to know there is a huge difference in requirements when a battery is cycled to only 90% and when it is cycled to 50%.

10% discharges are usually wasteful as the batteries at this state of charge limit the charging sources maximum ability.

Charging batteries in bulk mode, upto 80% or so is 98% efficient, but after this point the efficiency goes way down. With Solar it is no big deal as the suns output is free, but if you have 875 watts, then perhaps 400 watts could accomplish the same exact thing in the same time frame with such shallow discharges.

When you start cycling the batteries well below 80% is when the solar wattage to battery capacity should be 2 to one or higher.

If you never discharge below 80%, it could be argued you have way more battery capacity than needed.

 

[Sabatical]

You make some great points and leave me wondering if removing the two used batteries from the bank and discharging the remaining bank deeper would be a wiser way of doing business.
I have a feeling that this may have been what you were hinting at.
As always thank you for the input.
Scott

 

[Canine]

Looking good Sabbatical.I think you are going to enjoy this place.I love my traveling,but I have to admit when I get rundown,it's nice to have a homebase to rest up for a couple,three months.

 

[SternWake]

You make some great points and leave me wondering if removing the two used batteries from the bank and discharging the remaining bank deeper would be a wiser way of doing business.
I have a feeling that this may have been what you were hinting at.

I was not trying to suggest that you deliberately lower capacity now, since everything is already in place, but if you, or someone new, were to  design a new solar/battery system, from scratch, and then never went below 90% charged, well that is a huge unneeded buffer that might perform no better, and perhaps worse than a smaller capacity battery bank would, and cost more to underperform.

NOw if the nightly loads were to increase and draw the depth of discharge is lower, it is another story.

My only concern with your system in your current stated usage, is the older batteries in parallel with the new.  They might be so close to the new ones in capacity and resting voltage that all of them will get along great  have some beers, and sing kumbaya  each and every night when discharged so lightly overnight and recharged promptly by midmorning..

But the two older ones could possibly be like the bad influencers, and bring out the serious party gear, passing around hard liquor and some opium inbetween the beers, and they all sing some death metal off key together, and forever after have a bad hangover that never seems to go away. 

Determining the character of the 2 older units could determine the outcome of keeping them all together always.

Again the hydrometer is the tool to determine this.  Resting voltage is a good clue, as long as the period of rest is sufficient, but if the older batteries have SG readings 0.015 lower than the new batteries, no point in resting the batteries until they older ones are equalized, SG maxed out, and only then compare resting voltages.

Older and new batteries in parallel is not an instant death.  BUt a capacity compromised older battery in parallel with a bunch of newer batteries is a bad idea.  It is like scouting party having to shoulder and carry a member who broke a leg, and eats twice as much food as those carrying him.  One might think 8 is better than 6 no matter what, but if the extra 2 are injured and can't perform properly, then they just slow the whole group down..

You could separate the new and older with a 1/2/both/off manual switch and charge and discharge them separately if the two older ones are hiding the hard liquor and drugs and have peer pressure on their minds.

My system uses 3 manual switches to shift all stock vehicle/ ignition loads to either of two batteries, all house loads to either of 2 batteries, and the Solar or Meanwell power supply/charger to either of 2 batteries.  One of those batteries lived out its useful cycle life, and I removed it and all 3 switches are just turned to one 90AH AGM battery.  I discharge it to the 50% region 4 to 5 nights a week.  I have no real buffer, but no real concerns either.  All the fat is currently trimmed off, and it is working well.  But if I were unable to drive, and unable to plug in, the 200 watts of solar would not be able to keep the battery happy by itself unless I were to lower my overnight consumption to 20AH or less.  1/3 to 1/2 of what I currently consume nightly without worry.

This AGM battery requires high amp recharges every 5 cycles, in my experience, or it starts walking down in capacity and takes forever the Absorption  tapering amperage  threshold to be met, longer than the day is long.  By my battery monitor might still  proudly say 100% and blink the green light all afternoon, and a less observant person might not know that the voltage held for the same loads and level of depletion is falling slightly, night after night.

 

[Sabatical]

Love the analogies SternWake!

 

[ZoNiE]

Nice!

 

[MikeRuth]

LOL at myself, I totally forgot this was a tiny house. So used to thinking Van Dwelling.

Mike R

 

[akrvbob]

We've drifted a log way from Sabbaticals original thread, but if that's okay with him it's his thread. If you want us to get back to let, say so and we'll get back to it.

Here's the problem with going to 50% discharge every day by sizing a minimal system, that's fine if 1) you live in a city and drive a lot or, 2) have access to a generator or shore power. Sternwake has both of those so 50% discharge works well for him.

As a boondocker, I can easily go a week without starting my van and have no access to 110 volt. If I size my system for 50% discharge every day and I'll be buying new batteries every year.

Storms happen and winter is coming, with solar, it's better to have too much unless you drive a lot or have access to 110. I think for everyone it's better to size your system for no more than 80% discharge and have enough solar to recharge even if you go down to 50%. That way you can ride out the storms and the short winter days.

You can laugh at 3-day storms during winter knowing your batteries will be just fine.
Bob

 

[SternWake]

Poking me with that 'just fine' stick eh Bob?? What's next, a Locust gun?

My personal electrical system at this point is about pushing the limits. I do not necessarily drive every day, but I can almost always plug in and high amp recharge and hold absorption voltage as long as needed. I also am usually parked in direct sun from 9 to 5 every day in a sunny and mild climate.

So I do not really need a buffer and am currently questioning my personal need for a house battery at all, since this AGm is so damn impressive being both engine and house when it is high amp and fully recharged often. My 200 watts of solar could never keep this AGM happy on its own with 50% discharges daily, but My alternator and a minimum of 15 minutes of driving on a sunny day certainly could, easily. Add in the occasional meanwell and a full charge followed by an all night long at 13.6v, and my battery mails me thank you notes after its 'happy ending'.

I do not recommend people follow my method of 50%+ daily discharges, unless of course they can plug whenever they want and have an adjustable voltage, high amperage charging source that can hold absorption voltage, well, forever, if they decide to Make it so.

Please keep in mind My particular AGM loves high amp recharge rates. Flooded batteries can accept high charge rates but they 'prefer' a 10 to 13% rate over 7 to 10 hours, not the 38 to 70% which I deliver via Meanwell or alternator upto the 80% charged area. Some AGMS say no more than 30% and it is wise to heed these recommendations on the lesser$$ AGMS which state this.

I do want people to know that the best flooded battery maker on the planet recommends a solar off grid System that can meet a 10 to 20% rate, and 10% is more than a 2 to 1 ratio of solar wattage to battery capacity, and twice the often recommended 1 to 1 rate.

Now everything is a compromise. It is unrealistic to meet a 20% charge rate Via solar in a mobile application, and quite difficult to meet a 10% rate in one, and the more capacity one carries, the harder it becomes.

Long story short is more solar is better. More capacity is not always better. Enough capacity to have as a buffer for the bad days, then enough solar to actually get to 100% on that first sunny day, is a good plan. An alternator that can dump a lot of amperage in a short amount of time and get 50% batteries to 75% quickly has a lot of merit, but Idling a high amp alternator is hardest on the alternator due to low alternator fan speeds and low airflow through the engine compartment speeds. Driving is so much better and so much more effective than idling to recharge when the capable alternator is well wired. If one wants to carry a generator and a high amp charger, well that is great too. The small engine powering an Alternator is a good bulk charger too, but no matter whatm that last 20% of charge to reach an actual battery orgasming 100% state of charge, takes hours, about 4 of them, no matter the available strength of the charging source.

Please disregard any statement that a well depleted lead acid battery can be fully charged in less than 4 to 5 hours. 90 to 100% alone takes 2.5 hours. the higher the state of charge, the slower it recharges.

You don't want to have to have multiple sunny days in a row to overcome a bad week of weather. Employ other charging sources. The alternator can be an excellent bulk charger.

But then again they are only batteries. Spending 1000$ to make a 300$ battery last twice as long makes little financial sense.

Regarding my system, I might have found a way to trick my engine computers' voltage regulator and manually control an external voltage regulator allowing me much more precise control of the alternator's contribution to my battery.

Does somebody hear distant maniacal laughing??????

That would be me.

Now since my alternator is worked hard, I plan on making a forced cold air intake for it, to increase output and reliability and longevity, even though it has a lifetime warranty and only takes me 15 minutes to replace and the previous one lasted 8 years being worked hard often

 

[Sabatical]

Bob I don't mind going wherever the thread takes us. Also, I absolutely plan on laughing at winter storms...from AZ 😛

 

[akrvbob]

Bob I don't mind going wherever the thread takes us. Also, I absolutely plan on laughing at winter storms...from AZ ?

You've got the system for it! 
Bob

 

[WheelEstate USA]

Sabbatical... Looking forward to your arrival down here.
The house looks great. Glad you are getting comfy.
Y'all take care

 

[Sabatical]

Thanks Jay. We are counting the moments! We have started picking time off at work and hopefully everything will fall into place. We will leave 12/30 or 31 and I will go back 4/4.

 

[WheelEstate USA]

Cool...hugs for L

I have seen SternWake's system and it is quite impressive, but I'm in this for total solar and zero shore power. I need solar overkill for the same reasons Bob mentioned. Our goal is good frozen ice cream in the desert

 

[Sabatical]

Mmmmm ice cream [SMILING FACE WITH SMILING EYES]