isolator question

[bcroe]

Ok Sunking is right, that distance is going to make adequate wire more expensive than
adding panels. Systems that big need to run over 200V. Bruce Roe

[idiggplants]

except i already have 200w of panels and a pwm controller. im not adding an mppt, im not adding 300' of wire. all i need is maybe 200w more of panels and we will have way more than enough.

all i did was come here and ask for advice on a way to keep the batteries separate. which apparently isnt possible. idk how we are suddenly talking about mppt controllers.

[SunEagle]

yeah, thats generally why we want them isolated. but it sounds like that isnt really an option.
ive seen charge controllers such as these:

https://www.amazon.com/RENOGY-Dual-Battery-Charge-Controller/dp/B00KI5J5W6/ref=sr_1_1?s=lawn-garden&ie=UTF8&qid=1485455056&sr=1-1&keywords=dual+battery+charge+controller

that are made for 2 batteries. i wasnt sure if there was something we could add to our charge controller that would do something similar.

i think the batteries are 100ah. they are the typical deep cycle batteries that people get for their rv's and boats. the biggest ones readily available. id have to make a few phone calls to find out any more info.

we are at the cabin 3 times a year for the weekends we have trouble with.

my issue with the advice of needing more panels that is always the advice i get from solar forums... more panels... more panels... that that was the advice we got before we did anything. people were saying... ohh, you need 1000w of panels and 3 batteries, all this nonsense... and our 200w + single battery setup is pretty much enough. our battery has lasted 4 years on this setup? and probably another 2 years previous to that of use as a carry in- use for 3 days... take home and charge on the trickle charger. so im a bit suspicious when i get recommendations to add more panels.

all we are looking to do is add a slight bit more capacity with a battery that we have that isnt being used., not reinvent the wheel. i figure if the panels have to charge 10ah? from one battery vs 5ah from 1 battery +5ah from another battery, it shouldnt matter too much. it just lets us drain each battery a bit less. and again... this is 3 times a year. actually more than likely, 2 times a year. rifle season and muzzleloader season.

anyways. sorry if i sound rude or unappreciative. i just feel like i know that we arent that far away from a completely sustainable setup. buying a simple isolator is one thing... but adding $200 in panels and another $120 battery to the setup... ill just stick with propane lights!

Well if your battery is about 100Ah and you have 200 watts of panels then you have a balanced system so you don't need to add any panels to it.

Also it seems that if you only use about 10Ah a day (40Ah for 4 days) your battery is barely being used around 10 to 15% DOD. That is why you can put back what you take out by 9 AM.

So I do not see any reason to mess with your cabin system. But the problem still remains that you do not have enough for those 3 months.

Since it is only a short time of a power deficit maybe adding another small system that has separate panels, battery , CC and inverter. (Maybe even move the one at your pavilion if possible) You could split up your loads so you don't over tax either system which should help get you through the night without dropping the battery voltage too low.

Now another option would be to get a small inverter style generator that can allow you run more load in the winter time and help recharge the battery since you have less then adequate sunshine. It may be even cheaper for that 1000 watt generator then to purchase more panels, battery, CC and inverter for the few time you need it.

I believe you have a few choices but connecting the two existing batteries is not a good one. You would be better to build a larger system from scratch but that may be overkill since you don't need a larger system for most of the year.

[Sunking]

except i already have 200w of panels and a pwm controller. im not adding an mppt, im not adding 300' of wire. all i need is maybe 200w more of panels and we will have way more than enough..

OK you are still not understanding. Your PWM controller is your bottleneck, or cement swimming shoes. What size are the 2 PWM controllers you have now?. You must have two controllers because you said you have another 100 watt system in the pavilion.

If they are 15 amps or less, you cannot add any panels because they are already maxed out. So to add panels requires new controllers unless they are 20 amps or more. That would be silly to buy panels or more PWM controllers.

Your first thing to do is buy new batteries. Yours are toast. For the 100 watt panel system with PWM can only support a 30 to 50 AH battery, and the 200 watt panel can only support a 75 to 100 AH battery with PWM. Most likely that will fix you up. If not, the solution is not to buy more god awful expensive battery panels. That would cost you $400. If you buy 200 watts more for a total of 500 watts using 2 PWM controllers gets you a 330 watts from 500 watts. Replace the two antiquated PWM controllers with two 15 amp MPPT Controllers means you get the full 300 watts from 300 watts of panels.

1. By two new batteries, a 50 AH for the Pavilion, and 100 AH for the cabin.

2. Answer the questions. What size are your two current PWM controllers?

3. Do not buy any more panels. If replacing the batteries does not get you back to where you want to be, and assuming the controllers can actually handle the panels you got to step 4.

4 Replace the two controllers with 15 amp Morningstar SunSaver MPPT controllers. It will be less expensive than buying two more expensive battery panels and two larger PWM controllers for the same amount of power. You do not need panels.

With MPPT your 100 watt system can support up to 100 AH battery vs your PWM maximum of 50 AH. For the 200 watt system can support up to a 200 AH battery vs 100 AH with PWM.

It takes a 300 watt PWM system to equal a 200 watt MPPT system. You need to understand that. Once you do then you can understand our advice. Start by replacing your batteries, they are Boat Anchors. Do not buy panels. To expand it takes a 500 watt PWM system to equal a 330 watt MPPT system. Say that over and over again until you understand. You already have 300 watts now reduced to 200 watts using PWM.

[idiggplants]

ok, ill see if i can address everything i one post...

our charge controllers are both 30a.

we have thought about the generator addition, and it hasnt been dismissed, but for $900 that a reliable(honda/yamaha) one would cost, we figure we could beef up our setup to where a generator wouldnt be necessary. of course, having a generator gives you all sorts of other advantages... 110v, power tools, coffee maker, toaster, even a small ac... but honestly we kind of like the "roughing it" atmosphere up there, and what we would gain in convenience, we would loose in experience.

ill have to get our real usage numbers. they are written on a notepad in the battery closet up there(4 hours away), so im kind of guessing..

with a fresh battery in the cabin i think we would be ok. we would be pushing it a bit, but ok. a 3rd or 4th panel(or an mppt controler?) and a second 100ah battery would have us sitting pretty, but i really dont like the idea of 2 batteries. unfortunately the local battery plant(deka) only has blemished batteries in the size we have. so we are stuck with 100ah per battery.

question... are 2x 100ah batteries any different from 1x 200ah battery? in my head ive been thinking that 2x batteries will tend to kill each other faster? i understand that you would have to get identical batteries at the same time and keep them connected always on the same load, etc.

next question...
assuming the same usage.... 1 100w panel on a 50ah battery...vs 1 100w panel on a 300ah battery...
now, i know it is silly to do the second... but if you are only using 5ah a day, the 100w panel wont really care if it is replenishing 5ah on a 300ah battery, or 5ah on a 50ah battery, right? or is there more at play here?

the reason i ask, is because at the pavilion, we really use almost no power. before we put in the solar, we would use the old, shot 100ah battery that we used to use in the cabin, to power the radio and lights in the pavilion... we will probably continue that tradition... when we replace the cabin battery, the shot one will go to the pavilion. and we will use it till it is completely dead there. running out of power mid weekend there isnt a big deal. no radio means we have to play music on our phones. ohh well.

[idiggplants]

Your first thing to do is buy new batteries. Yours are toast. For the 100 watt panel system with PWM can only support a 30 to 50 AH battery, and the 200 watt panel can only support a 75 to 100 AH battery with PWM. Most likely that will fix you up. If not, the solution is not to buy more god awful expensive battery panels. That would cost you $400. If you buy 200 watts more for a total of 500 watts using 2 PWM controllers gets you a 330 watts from 500 watts. Replace the two antiquated PWM controllers with two 15 amp MPPT Controllers means you get the full 300 watts from 300 watts of panels.

hmm. almost missed this...

i hadnt realized mppt controllers are that much more efficient. i knew they were a bit more efficient, but i thought the big advantage was with the high voltage applications.

so adding an mppt charge controller at the cabin might be our way to go. we could get one for essentially the same price as a 100w panel. and instead of 2 runs of wires from the panels, we could run them in series, right? to get 24v? and less line loss?

as for the pavilion, we honestly dont need to mess with that. i could have gotten away with a 50w panel. the pwm controller doesnt need to be upgraded down there.

[Sunking]

hmm. almost missed this...

i hadnt realized mppt controllers are that much more efficient. i knew they were a bit more efficient, but i thought the big advantage was with the high voltage applications.

Yes using higher voltages is a big advantage of MPPT, but only half the picture.

PWM Output Current = Input Current. At first that may not mean anything to you. But the numbers speak for themselves. So what is the Input Current? Real simple it is the current the panels are supplying. So you have 12 volt 100 watt battery panels I assume. Look at the specs and take note of two numbers. Vmp (voltage maximum power), and Imp (current maximum power). On your typical 100 watt battery panel you will see somethin glike Vmp = 18 volts and Imp = 5.55 amps. [18 volts x 5.55 amps = 100 watts] With me so far? So what is the output assuming your battery is discharged and demanding full power from the panel. Again simple if we input 5.55 amps, we have 5.55 amps output into a 12 volt battery. Do the math. 12 volts x 5.55 amps = 67 watts.

Add another kink, say you did not know better and you wired those two panels in series to get the voltage higher. Or say we used a 200 waty GT panel with a Vmp = 36 volts and Imp = 5.55 amps. What do you get out of the PWM controller? The same 5.55 amps or 67 watts with 200 watts of panel. Understand what is going on?

MPPT Output Current = Panel Wattage / Battery Voltage. That is completely different. We now have a Power Converter, not an antiquated Series Regulator. So now take that same 100 wat panel and see what you get. 100 watts / 12 volts = 8.33 amps or 100 watts. Realistically there are conversion losses in both controllers because they do use some power. So in the end at very best a PWM controller is around 62 to 64% efficient, and good quality MPPT are 96%+.

so adding an mppt charge controller at the cabin might be our way to go. we could get one for essentially the same price as a 100w panel. and instead of 2 runs of wires from the panels, we could run them in series, right? to get 24v? and less line loss?

Correct.However not yet. From your statements I do not think at this time you have a panel wattage issue. and switching to a MPPT is not going to buy you anything or solve your problem. At least not yet.

Everything you have said so far screams your batteries are Boat Anchors and must be replaced. It makes no difference how much panel wattage you have if your batteries are shot. They cannot hold a charge. Your first step is to replace your batteries. With 30 amp PWM controllers you can input up to 500 watts of panels. So if you use your two 100 panels in parallel gives you 11 amps of charge current and that can support a battery as small as 80 AH and up to 130 AH.

He is my recommendation for you and why:

1. Replace your batteries. On the 200 watt system opt for a pair of Golf Cart batteries. GC batteries are 6 volts so you wire them in series. Capacity ranges from 190 to 250 AH. Somewhat larger than 200 watt panels can support kind of. By support I mean for a battery that is cycled every day of the week and discharged 20 to 30% every stinking day of the week year round. By you rown statements you indicate 10 to 20 AH per day which is not even a full 10% on the most common 225 AH GC battery. 225 AH is going to be more than you need, but GC batteries are much better than a Marine Battery you are using now. They will last longer. By using say a Trojan T105 or less expensive US Battery US 2000 XC2 opens the door to step 2 if needed. Hell if you really want to pinch penny's go to Wally World, Sam's, Costco and buy the house brand GC batteries. All of them are made by Interstate, a decent low end entry level battery

2. If then you find out the 200 watt panels are not enough power, unlikely, then upgrade to a MPPT Controller. 200 watt panels with a 15 Amp MPPT controller is just about a perfect match for a smaller GC battery. There is one catch. Maximum input power on a 15 amp MPPT controller is 200 watts @ 12 volt battery, and 400 watts @ 24 volt battery. So if you do go with MPPT you might consider 30 amps which wil allow you to grow a 12 volt system to 400 wats which is a match made in heaven for a 250 AH 12 volt GC battery.

OK that is my Smart Money recommendation with no traps or nasty surprises. A entry pair of small GC batteries will run right around $200 and last at least 2 years. A pair of Trojan T-105s are 225 AH and wil run you $300 and last 3 years and maybe 4 if you take care of them. Equivalent US Battery of US 2000 XC2 are 230 AH and just under $300 for a pair and should last 2 to 3 years.

Damn almost forgot. Get yourself a simple 20 to 25 amp Marine Charger for the house. All batteries need to be equalized from time to time, and to bail you out of jail. If for some reason say your Controller fails, or you and the budies get to drunk and over discharge your batteries, you can take them home and give them a good saturated charge to save them and do periodic maintenance. In your application no reason for a generator on top of the charger. Trust me it wil be the best $60 to $90 you will ever spend and can be used on all your 12 volt batteries at home like your vehicles, boats, or whatever.

Good Luck

SK

[idiggplants]

sorry double post

[idiggplants]

thanks for the reply. im not sure how i missed it a while back.

i will definitely be replacing the battery before we do anything else.

the batteries we currently get are blemished batteries from deka for $100. and they last us 5+ years on our current setup... granted it seems like we are squeezing an extra year(or 2) out of them... but regardless, its hard to justify changing too much there, but if we can get similar life out of a battery that costs us nearly the same amount, then im open to changing it up.

a friend of mine in the industry just told me he can find me these:

https://www.civicsolar.com/product/canadian-solar-maxpower-cs6x-305p-305w-poly-slvwht-solar-panel

for 100 bucks a pop. which is an insane price, but would require a lot of retrofitting. different mount, wiring?, and id need an mppt controller on top of that. so im not sure that i can take advantage of the offer.

we have the need for another charge controller and another panel for a remote shed. something similar to what our pavilion uses... so we have to get another charge controller... im thinking about getting an mppt controller, and swapping it into the cabin, and using the pwm for the new project...

how many amp mppt would i need for 200w that we currently have, but would like the freedom to up that to 400w in the future.

currently everything we have is renogy brand.... crappy generic stuff, i know, but it has worked for us quite well. this is the controller i was planning on using..

https://smile.amazon.com/Renogy-MPPT-Solar-Charge-Controller/dp/B00G3XTWTS/ref=sr_1_1?ie=UTF8&qid=1486492412&sr=8-1&keywords=20a+mppt+renogy+controller

unfortunately i dont think ill be able to afford too much more $ on anything more name brand.

[idiggplants]

hmm. no further advice? would i be better off starting a new thread?

[Mike90250]

hmm. no further advice? would i be better off starting a new thread?

Do you have another question, or a better way to ask the same question ?

question... are 2x 100ah batteries any different from 1x 200ah battery?

two 6V 100ah batteries in series. Golf Cart batteries are cheap, and easier to carry than a single 12V 200ah 130lb battery !

next question...
assuming the same usage.... 1 100w panel on a 50ah battery...vs 1 100w panel on a 300ah battery...
now, i know it is silly to do the second... but if you are only using 5ah a day, the 100w panel wont really care if it is replenishing 5ah on a 300ah battery, or 5ah on a 50ah battery, right? or is there more at play here?

100w on a 300ah battery will eventually destroy the battery, unless it has the lightest of loads, in which case, it's way too large.
This was common in the 70's when PV was expensive, but after 1 or 2 years, folks massive battery banks were dead from sulfation, the battery would sit for days at mid-charge, slowly charging, but the sulfate crystals were hardening up, the next week, a bit more capacity locked up in crystals. and eventually, the battery is gone.
But doable with a LiFePo4 battery, because they don't degrade sitting at half charge. Lead acid, below 80%, crystals start to form & harden, While soft, they can be re-dissolved, but once hardened, that portion of capacity (acid) is lost forever.

[SunEagle]

Do you have another question, or a better way to ask the same question ?


two 6V 100ah batteries in series. Golf Cart batteries are cheap, and easier to carry than a single 12V 200ah 130lb battery !



100w on a 300ah battery will eventually destroy the battery, unless it has the lightest of loads, in which case, it's way too large.
This was common in the 70's when PV was expensive, but after 1 or 2 years, folks massive battery banks were dead from sulfation, the battery would sit for days at mid-charge, slowly charging, but the sulfate crystals were hardening up, the next week, a bit more capacity locked up in crystals. and eventually, the battery is gone.
But doable with a LiFePo4 battery, because they don't degrade sitting at half charge. Lead acid, below 80%, crystals start to form & harden, While soft, they can be re-dissolved, but once hardened, that portion of capacity (acid) is lost forever.

I think another problem with not having enough charging amps to keep the sulfation from occurring is a long term issue and not quickly noticed by most people that have an off grid system.

Since it may take a while for the batteries to "lose" their ability to get back to their nameplate 100% SOC rating and along with having a small load it seems that the battery is working just fine and lasting a long time but in reality the battery is "getting smaller" and will never produce it's full potential when put to the test.

On top of that even though a battery is "past it's life" according to the manufacturer, if it still provides enough power to "keep the lights on" then the user believes all is well and that the batteries are getting a long life but they are really closer to their "death" and past the point of needing to be replaced. That usually ends up with a disappointed user because the batteries will fail when they really need them to perform.

[idiggplants]

Do you have another question, or a better way to ask the same question ?

my post number 24 seemed to bring a few new questions to the table. perhaps i should start a new thread.

two 6V 100ah batteries in series. Golf Cart batteries are cheap, and easier to carry than a single 12V 200ah 130lb battery !

price and size are moot points in this question.
my point was more along the lines of electrical question. are 2 100ah married batteries any different than 1 single 200ah battery? do i have to treat them differently. do the 2 separate batteries wear each other out faster?

100w on a 300ah battery will eventually destroy the battery, unless it has the lightest of loads, in which case, it's way too large.
This was common in the 70's when PV was expensive, but after 1 or 2 years, folks massive battery banks were dead from sulfation, the battery would sit for days at mid-charge, slowly charging, but the sulfate crystals were hardening up, the next week, a bit more capacity locked up in crystals. and eventually, the battery is gone.
But doable with a LiFePo4 battery, because they don't degrade sitting at half charge. Lead acid, below 80%, crystals start to form & harden, While soft, they can be re-dissolved, but once hardened, that portion of capacity (acid) is lost forever.

please reread my question.

assuming the same usage.... 1 100w panel on a 50ah battery...vs 1 100w panel on a 300ah battery...
now, i know it is silly to do the second... but if you are only using 5ah a day, the 100w panel wont really care if it is replenishing 5ah on a 300ah battery, or 5ah on a 50ah battery, right? or is there more at play here?

i specifically said the same exact usage. does it matter if there is a bigger battery? if im using 10ah per day... does it matter what size the battery is? im failing to see why having a bigger battery bank, actually matters, but you are seemingly saying that it does? same load... same panels, upping the size of the battery suddenly causes sulfation etc etc? could you explain that to me? i would assume, 200ah bank... if i use 10ah, and the panels can replace that in a day, thats the same, if not better, than a 100ah battery doing the same thing. batteries replenished in a day, with less % of the battery used.

[SunEagle]

my post number 24 seemed to bring a few new questions to the table. perhaps i should start a new thread.


price and size are moot points in this question.
my point was more along the lines of electrical question. are 2 100ah married batteries any different than 1 single 200ah battery? do i have to treat them differently. do the 2 separate batteries wear each other out faster?



please reread my question.


i specifically said the same exact usage. does it matter if there is a bigger battery? if im using 10ah per day... does it matter what size the battery is? im failing to see why having a bigger battery bank, actually matters, but you are seemingly saying that it does? same load... same panels, upping the size of the battery suddenly causes sulfation etc etc? could you explain that to me? i would assume, 200ah bank... if i use 10ah, and the panels can replace that in a day, thats the same, if not better, than a 100ah battery doing the same thing. batteries replenished in a day, with less % of the battery used.

The problem with using too little charging amps is that it will not disrupt the sulfation action happening to the battery plates. If the charging is not aggressive enough (having a charging rate between C/8 and C/12) then the battery will slowly go bad and not produce it's nameplate 20hour output if called on.

I guess the question comes down to, is it worth the cost of getting a battery much bigger then I need and have it last X years compared to one that provides enough power without discharging more than 25% and have it last Y years.

IMO you will pay more for that larger battery and never get it to last the lifetime it was supposed to but depending on what you pay for it the larger battery may be cheaper then the "right sized" one.

[Mike90250]

2 paralleled 100ah batteries are worse than a single 200ah battery, Parallel batteries are never "equal" and leapfrog each other to the death, the single battery should last longer than the pair.