additional 12v circuit for non-essential loads

[frater secessus]

Maybe everyone has already considered this and I am the last one to arrive at the party, but....

I've been thinking about how to maximize the usable capacity of small solar setups when folks are limited in physical space or funds.  The MPPT controller is capturing a ton of power from the panels during Bulk but we are "wasting sunlight" in Acceptance and Float.  What if we could shift some of the overall load to the Acceptance/Float stages to recapture some of that capacity?

Proposed method:  power discretionary (non-essential or at least not time-sensitive) loads off the charge controller's LOAD output*, with the LOAD low voltage disconnect set to float voltage.  Examples of discretionary loads:  phone/tablet/laptop/drill charging, entertainment, etc.  
Essential loads would come off the battery through a ~12.1v LVD setup as usual.

I drew on one of Chargetek's graphics:

I think this would:

1. energize the discretionary circuit only when the battery is charging, and likely in absorption or float since most systems spend the majority of their time there.  Bonus:  plenty of untapped current available in these phases.
2. let normal, essential circuits cycle the bank down to 50% DoD.
3. increase battery health by allowing a more rapid recharge in the morning; reduced load on the system until the system hits Vfloat.  Reduces battery murder.
4. reduce the time spent at 50% DoD;  the bank hits 50% later at night due to reduced load.  This also reduces battery murder.
5. reduces human errors like "I'll turn off that load when the sun goes down"
6. reduces the need to add more batteries, which also reduces the time spent at 50% DoD, saves money, weight and space

Activation of the discretionary circuit during bulk (in that little shoulder area just before Absorption) is not optimal but I don't see a way around it that doesn't kill the circuit in Float.  According to Trojan's graph of battery voltage while charging, the battery passing through Vfloat during bulk phase puts the batteries 75% SoC when charging at C/10. 

I would like opinions on this.  It would be really cheap to implement, particularly during the build.  A few extra bus bars and at least one parallel run of wire to the far side of the camper. 




* or a standalone LVD with a high setpoint, but I am having trouble finding those

 

[GotSmart]

I am confused.  (lately, quite a lot.)  

Why not just increase the battery bank so you do not drain the unit? 

Perhaps I  just am the type that over engineers everything.  

Small solar set ups do not "waste" a lot of power.  They do not generate a lot of power. 

Either you have enough battery, or you do not.  Charge up the gadgets in the afternoon to collect the excess power being generated. (If you do not have enough battery storage.) 

The more parts that are put in a system, the greater the chance of failure.

 

[John61CT]

Why not just increase the battery bank so you do not drain the unit?

premise was limited funds and/or physical capacity to carry big banks

worthy of discussion within that context?

 

[Optimistic Paranoid]

Assuming you are able to do everything you want to do, daily, and the solar panels return your battery back to 100% soc, daily; then worrying about "unused" energy that is being "wasted" strikes me as being a little OCD.

 

[frater secessus]

Assuming you are able to do everything you want to do, daily, and the solar panels return your battery back to 100% soc, daily; then worrying about "unused" energy that is being "wasted" strikes me as being a little OCD.

I'm not particularly interested in the unused power on a capable system.  I am more interested in scavengeable power for folks with marginal, battery-killing systems.

 

[frater secessus]

Charge up the gadgets in the afternoon to collect the excess power being generated. (If you do not have enough battery storage.) 

The more parts that are put in a system, the greater the chance of failure.

This would automate that system at no (or little) extra cost, removing human error and lowering the amount of battery that is "enough".  

There are no electrical parts added to this system; the previously-unused LOAD connection is put to use.  Additional minimum components would be one strand of wire and one bus bar.

 

[MrNoodly]

If you panel is small, you might be using all of your daylight hours just getting your primary battery/batteries through the absorption phase and to the float stage.

 

[frater secessus]

If you panel is small, you might be using all of your daylight hours just getting your primary battery/batteries through the absorption phase and to the float stage.

The circuit comes online at >= float voltage, not just during float stage proper.  Since Vabs > Vfloat it's also running in Absorption where there is current to spare.  There is also, unfortunately, a shoulder during late Bulk stage when bank voltage is greater than Vfloat but less than Vabs (see the graphic).

 

[frater secessus]

Thanks for all the comments so far!  I've corrected the original graphic to be more accurate (if my cartoonish attempt at photoshop can be described as "accurate"):

 

[SternWake]

In early absorption via solar, there is little current to spare, Only after some time when amps taper to less than the battery needs, and can also power the load, will there be benefit.

If some load gets triggered at absorption voltage, then voltage will fall below  absorption, then the load gets triggered off, then voltage rises, then load gets turned on, then voltage drops because of load.  On and on until the load decides to release the blue smoke, or the amperage the battery requires to be held at Vabs has lowered to the point where it and the load are below the level of the panels output at that point. 

if the idea is to not prematurely murder a battery, One would be better off actually ensuring the absorption voltage is high enough, gets there early enough, and lasts long enough.

Far too many people see their solar controller has dropped to float and claim their batteries are full, when it could be that 2 more hours were required.

So few actually dip a hydrometer on their flooded batteries when their solar controller quits and drops to float voltage, and so few with AGM batteries actually see the amperage flowing at absorption voltage to know if it was held for long enough( it was not).

So the issue causing premature  battery failure is not wasted solar power during later absorption and float voltage, it is the premature triggering of float voltage and the astounding ignorance of putting one's faith in a flashing green light.

In a daily usage scenario, unless one has excessive solar capacity and battery capacity, those with marginal systems should program their float voltage up in the 14's, and only lower it if they stop cycling the batteries nightly.  Yes some solar juice will be wasted.  

Could this be employed elsewhere? of course, but do it so that it does not affect the ability of the solar system to hold the battery at absorption voltage as long as is required.  This would likely require some sort of time delay on the triggered load after Vabs has been reached, and how long depends on the size of the load, and battery.

An ammeter and or a hydrometer will prove than 95% of charging sources quit the absorption phase too early on a regularly deeply cycled battery.

It is a shame that it is so easy to determine when a battery is indeed full, with a hydrometer and or ammeter and voltmeter, and ensure their solar or other charging source are holding Vabs for long enough, but almost nobody ever does.

Because of that flashing green light and the hugely mistaken  belief that float voltage means the batteries are full.

 

[frater secessus]

In early absorption via solar, there is little current to spare, Only after some time when amps taper to less than the battery needs, and can also power the load, will there be benefit.

Agreed.  The question in my mind is how to maximize that benefit at minimal cost.

Thanks for stopping in, BTW.  I sacrificed a chicken, danced in the moonlight, and invoked your name thrice hoping you would appear.  

If some load gets triggered at absorption voltage, then voltage will fall below  absorption, then the load gets triggered off, then voltage rises, then load gets turned on, then voltage drops because of load.  On and on until the load decides to release the blue smoke, or the amperage the battery requires to be held at Vabs has lowered to the point where it and the load are below the level of the panels output at that point. 

In this model the non-essential loads are triggered at the Vfloat setpoint as voltage rises through Bulk stage.  I think the ideal time to bring it online would be just before the system hits Vabs.  This would delay the non-essential loads as late as possible while preventing hunting between Bulk and Absorption.  But doing this would knock the circuit offline if/when the controller went to Float, so the model triggers it at Vfloat instead.

Consider this scenario, highly reductive with steady loads to benefit my lizard brain.

• 200Ah FLA battery bank
• essential load LVD disconnects at 12.1v.  and reconnects at 12.7v, as with any other setup.
• non-essential LVD disconnects at [a little below, 13.0v?] Vfloat and reconnects at Vfloat 13.5v
• charge controller can put out a 20A
• non-essential load is 10A (a laptop with low battery, smartphone with low battery)
• essential load is 5A (compressor fridge, etc), but is not considered since it is always there acting as steady background workload

Here is the order of events this model attempts to exploit:

1. Night:  Battery voltage drops below Vfloat, disconnecting non-essential load circuit.
2. Later that night:  Battery drops to 50% DoD, normal house LVD disconnects essential load at 12.1v. (Vlvd?)
3. Dawn:  Bulk stage commences, bank voltage starts rising.
4. Bank voltage hits 12.7v  and LVD reconnects essential load as with any other setup.  Voltage sags, charger stays in Bulk.
5. Bank voltage hits 13.5v (Vfloat).  Non-essential circuit LVD reconnects non-essential load. Voltage sags, charger stays in Bulk.
6. Bank voltage hits 14.7v (Vabs).  Absorption stage commences.  By definition we know the controller can hold Vabs with both load circuits running; it is already doing so.   If it couldn't hold Vabs it would have not entered Absorption.  Correllary:  any system that can hold Vabs under a given load can also hold Vfloat under that load.
7. after this the controller either
         
   1. stays in Absorption until sundown; or
   2. "finishes" Absorption and starts Float; or
   3. "finishes" Absorption and starts "Float" at a modified voltage (Vfloat == Vabs) as described further down the post.

In a standard setup the batteries would be receiving a max of:
20A from 12.1v to 12.7v
 5A from 12.7v to 14.7v when both essential and non-essential loads are online

In this bifurcated setup the batteries would be receiving a max of:
20A from 12.1v to 12.7v
15A from 12.7 to 13.5v when essential loads are online
 5A from 13.5v to to 14.7v  when both essential and non-essential loads are online

if the idea is to not prematurely murder a battery, One would be better off actually ensuring the absorption voltage is high enough, gets there early enough, and lasts long enough.

Agreed.  And this model doesn't change Absv or keep it in there much longer.  It does get the battery from 50% to, say, 75% faster by delaying some of the load until Bulk passes Vfloat.  I think it would also get into Absorption sooner.  

So the issue causing premature  battery failure is not wasted solar power during later absorption and float voltage, it is the premature triggering of float voltage and the astounding ignorance of putting one's faith in a flashing green light.

I am not suggesting that unused power in Absorption or Float is killing batteries.  I am suggesting that delaying non-essential loads until the battery hits stages with underutilized current is preferable, and there is an easy/cheap way to make that happen.  It would be especially preferable for those with marginal systems that struggle to charge the banks fully.

In a daily usage scenario, unless one has excessive solar capacity and battery capacity, those with marginal systems should program their float voltage up in the 14's, and only lower it if they stop cycling the batteries nightly.  Yes some solar juice will be wasted.  

Agreed.  I don't care about wasted juice in latter stages, per se.  I would like to shift non-essential load from Bulk to those latter stages.

Could this be employed elsewhere? of course, but do it so that it does not affect the ability of the solar system to hold the battery at absorption voltage as long as is required.  This would likely require some sort of time delay on the triggered load after Vabs has been reached, and how long depends on the size of the load, and battery.

I don't understand.

If the system is able to reach Vabs with the steady state load described above it should be able to hold Vabs.  Sure, adding additional loads outside our model could cause sag below Vabs but that would happen in a non-bifurcated system.

An ammeter and or a hydrometer will prove than 95% of charging sources quit the absorption phase too early on a regularly deeply cycled battery.

It is a shame that it is so easy to determine when a battery is indeed full, with a hydrometer and or ammeter and voltmeter, and ensure their solar or other charging source are holding Vabs for long enough, but almost nobody ever does.

Because of that flashing green light and the hugely mistaken  belief that float voltage means the batteries are full.

I agree with all of that.  

I am using Vfloat as a setpoint for an LVD to turn on the non-essential circuit because it allows the circuit to stay on when/if the charger drops to the (default) Float stage.  I'm making no claim that dropping to Float stage is an indication of SoC.

 

[GotSmart]

OK.  To get specifics here, I need brand, model, and size of all solar components.  


Not all 100W panels deliver the same output in differing conditions. (100w at 75* is 82w at 110*)  The same with controllers and converters.  (12v is realy 17 v or more)

Not all similar items draw the same amperage, or have identical cycles.  

Utilizing the "load" connection on a controller is still pulling power from a system.  Weather this is "excess" or "wasted" power is anybody's guess.  Drawing down batteries to 50% every night is a sure way to murder them.  

Building a solid system that does not kill batteries is much better than building something that just barely squeaks by and destroys your batteries in 18 months.

Going cheap is a sure way to get expensive.

 

[SternWake]

Sacrifice no chickens in my Name.  Dancing in the moonlight  and thrice invoking my screen name might have the guys in white suits and carrying the straight jacket, cart you off.



Are you wanting to remove loads so that the battery bank can get to Absorption voltage quicker?  Then once there is a surplus amperage to turn them on again?


Price out these low voltage disconnects.  There might be some return on investment issues where the return might take years and years, and more benefits realized elsewhere.  Best return on investment for ultimately getting the most from lead acid house batteries is usually thicker copper between alternator and house battery, and the programmable Vabs solar controller, then more solar, then a better plug in charging source.

The Cycling of a compresssor fridge on and off during bulk/absorption will likely havoc with voltage based load switching.  It can play havoc with Amperage based egg timers if the solar has no idea what the battery is accepting vs what the DC loads are at that time.

If the fridge can maintain sub 40f reliably during bulk and early absorption then i'd consider turning off the fridge at sunup to get to Vabs sooner.

The earlier in the day Vabs can be reached by all charging sources, then held via only solar,  the better.  Achieving that goal alone ensures good system performance.

As far as switched loads when there is solar surplus, well if that can be done automatically, easily without much effort or cost, more power to you.

I've not really researched LVD and HVD's as much as I should have.  I don't much stress going below 12.0v occasionally, but i would freak out if I were not be able to get it above there during daylight and have it hover in the 40 to 60% range for days.

My solar controller(sb2512i)  has no load function, and if it had it I would not utilize it, but I might have put some thought into how I would do so, and I did so,........... then decided I would not use it.  My regret is not buying the better model for 35$ more which would allow for a battery temp sensor.  It would have allowed the load function too.

Adjustable Vabs and its duration is Key.  If I could do one or the other, Adjust Vabs or have a load switched on or off when there is solar surplus, it would be adjustable Vabs 99 times out of 99.1 times. 

The Smartgage, I have only read about.  I reset my IPN pro remote( battery monitor) regularly when i know the battery is full, or If I notice it reading out of whack.

What i love about the AGM, is amps to hold absorption voltage can be used to determine 100% charged.  Still require more than 0.5% of the 20hour rate capacity at Vabs,..... keep holding Vabs.

A 100% charged starting point achieved regularly, gives one a good basis for comparison.

When charging sources do not allow one to hold Vabs as long as required or force it easily, that's where I have drawn a line in the sand.  Its one thing is if the sun  or lack there of can't do it, but when a smart charger or the solar controller decides '2 hours at Vabs is just fine thank you.......'  Sledgehammer time.

I bent my alternator to my will too. I use an adjustable voltage regulator whose voltage dial is on my dashboard.

Nothing worse Than driving at 65mph with a well depleted house battery and seeing only 13.7v and few recharging amps flowing.

 

[John61CT]

Please specify controllers that would survive your sledgehammer?

 

[SternWake]

No
Automatic Voltage controllers need to keep and eye out for a looneytics carrying sledgehammers.
Keeps them on their toes.

 

[frater secessus]

[dangit, was trying to no-quote reply to GotSmart here. I took too long and other posts came in.]

/squinting

I am familiar with the concepts you mention.  

The assertion that 50% DoD every night is a sure way to murder them may not be supportable.   It's probably the most common rule of thumb about using FLA deep cycle batteries.  Even Trojan says:  

For optimum life and performance, we generally recommend a discharge of 20 to 50% of the batteries rated capacity...

 

[frater secessus]

Are you wanting to remove loads so that the battery bank can get to Absorption voltage quicker?  Then once there is a surplus amperage to turn them on again?

Yes, that is the general outcome.

Price out these low voltage disconnects.  There might be some return on investment issues where the return might take years and years, and more benefits realized elsewhere.  Best return on investment for ultimately getting the most from lead acid house batteries is usually thicker copper between alternator and house battery, and the programmable Vabs solar controller, then more solar, then a better plug in charging source.

The LVD is already built into all the controllers I've seen that have a LOAD output.  There would already presumably be one on the battery side for normal house use, so no extra LVDs would be required.

The Cycling of a compresssor fridge on and off during bulk/absorption will likely havoc with voltage based load switching.  It can play havoc with Amperage based egg timers if the solar has no idea what the battery is accepting vs what the DC loads are at that time.

I  used the fridge as an off-the-cuff example of a load one might consider essential.  Even if we do use this item as an example the compressor fridge would be on the essential side and therefore not eligible to kick the charger out of Absorption.  It might trigger the 12.1v main LVD unless there was a delay on it.

I agree with letting the fridge coast at night if it can.  Although if it is insulated well enough to do that it might not come on anyhow.

As far as switched loads when there is solar surplus, well if that can be done automatically, easily without much effort or cost, more power to you.

That's the idea, although there is some slop because the switched load comes on just before the surplus is available. 

Adjustable Vabs and its duration is Key.  If I could do one or the other, Adjust Vabs or have a load switched on or off when there is solar surplus, it would be adjustable Vabs 99 times out of 99.1 times. 

Both are free to implement on halfway-decent controllers, even the Chinese Tracer line.  So I'll take both.

Thanks again for cutting into your surfing time to share your knowledge.  

 

[GotSmart]

[dangit, was trying to no-quote reply to GotSmart here.  I took too long and other posts came in.]

/squinting

I am familiar with the concepts you mention.  

The assertion that 50% DoD every night is a sure way to murder them may not be supportable.   It's probably the most common rule of thumb about using FLA deep cycle batteries.  Even Trojan says:  

[font=Verdana, Arial, sans-serif]For optimum life and performance, we generally recommend a discharge of 20 to 50% of the batteries rated capacity...[/font]

Here is the complete quote in context.

http://www.trojanbattery.com/tech-support/faq/

Lead acid batteries do not develop any type of memory. This means that you do not have to deep discharge or completely discharge a battery before recharging it. For optimum life and performance, we generally recommend a discharge of 20 to 50% of the batteries rated capacity even though the battery is capable of being cycled to 80%.

[font=Arial, Helvetica, sans-serif]Also this applies.[/font]

[font=Arial, Helvetica, sans-serif]1. What are common mistakes made by flooded battery owners?[/font]

[font=Arial, Helvetica, sans-serif]Undercharging: Continually operating the battery in a partial state of charge, or storing the battery in a discharged state results in the formation of lead sulfate compounds on the plates. This condition is known as sulfation. Both of these conditions reduce the battery’s performance and may cause premature battery failure. Undercharging will also cause stratification[/font]

[font=Arial, Helvetica, sans-serif][font=Arial, Helvetica, sans-serif]When using solar, it is critical to remember that just because today was 75* and sunny, and the batteries got a full charge, (because everything was working at 100% capacity)  the next week might be overcast, 100*, and the panels are producing 25% less per day.  This is when squeezing the nickle to get fertilizer from the buffalo just kills the buffalo. Always plan for the worst case.  [/font][/font]

[font=Arial, Helvetica, sans-serif][font=Arial, Helvetica, sans-serif]One does not have a solar powered pacemaker in Seattle, (58 clear days a year)  only Arizona.(211 clear days a year)  [/font][/font]

[font=Arial, Helvetica, sans-serif][font=Arial, Helvetica, sans-serif]Location plays the main part in engineering/sizing a system.  [/font][/font]

https://energy.gov/maps/solar-energy-potential

 

[frater secessus]

I got changed to night shift earlier this week and am sleep deprived.  Here is my attempt to distill the approach:

#1.  Delay non-essential loads until Absorption or Float.
#2.  Automate #1, using stuff one probably already has.

It is likely you are making solid points and I am too fatigued to follow.  In my current condition I am not seeing how brand names and model numbers, PV efficiency at differing temps, actual output voltage of nominal 12v panels, similar items pulling different amps, where LOAD current comes from, sulfation, insolation due to latitude or weather,  etc has any special applicability to the approach I put forward.  I will get some sleep and try to regroup.

 

[GotSmart]

You can give it a try.  

Just saying that in dealer training, it was proven to me that identical systems will produce different amounts of power depending on location alone.  The same system in Seattle will produce X power.  In Quartzsite it produces 2X power.  Exact system.  

Without specifics on components, a system is just put together, not designed to work at full potential.  

Think of it as a water supply system.  One is generic just thrown together from 1/2 inch galvanized pipe.  It delivers water.  One is designed by an expert.  It has 1 inch pipe as a feed, air gaps, diminishing sizes to make sure pressure is maintained while being used by multiple people. It can keep your shower water unchanged if someone flushes a toilet.