isolator question

[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.

[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.

[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

[Sunking]

ohh, i see, so you are saying i could tie the solar panels at the pavilion into the cabin if i upped the voltage and got an mppt... nahh... its about 300' away. after paying for a mppt, we could just get a couple extra panels at the cabin.

No I do no think you understand. No controller is going to overcome 300 feet distance. Perhaps thi smight click. It takes a 300 watt system to equal a 200 watt MPPT system. A real MPPT 15 amp controller like a Morningstar SunSaver 15 amp model is around $200 and at 12 volt battery can input 200 watts, and 400 watts at 24 volt battery. Cheaper than a another over priced battery panel. The advantage of MPPT allows you to use much higher voltage grid tied panels which cost 1/2 of what low voltage battery panels cost. A 300 Watt PWM system will cost you around $600 to $700. A 200 watt MPPT system only needs a single 200 watt panel, or as many battery panels as you want wired in series. Use a GT panel cost $400 to $500. PWM is just antiquated and to expensive for anything less than 200 watts.

[idiggplants]

Like the Power Co, you will find transmission over any distance is far easier at higher voltages. Just
take the resistance of the wire you hoped to use, use ohms law at 12V and 36V, and you will see about
a 9:1 difference in loss. That difference will be even bigger including the change to MPPT.

As others have said, the extra battery isn't going to work out if you don't have the extra power to
maintain the increased load. And you can have isolated or not isolated, but not at the same time.
Bruce Roe

ohh, i see, so you are saying i could tie the solar panels at the pavilion into the cabin if i upped the voltage and got an mppt... nahh... its about 300' away. after paying for a mppt, we could just get a couple extra panels at the cabin.

[bcroe]

Like the Power Co, you will find transmission over any distance is far easier at higher voltages. Just
take the resistance of the wire you hoped to use, use ohms law at 12V and 36V, and you will see about
a 9:1 difference in loss. That difference will be even bigger including the change to MPPT.

As others have said, the extra battery isn't going to work out if you don't have the extra power to
maintain the increased load. And you can have isolated or not isolated, but not at the same time.
Bruce Roe

[idiggplants]

Leaving the pavilion panels in place would result in big loss in the wiring out to them.

could you expand on that?

ok, so lets assume we go with 4 panels in the cabin. we only really need those extra 2 in the winter time. but they will be there all the time. the battery, however, can be moved back and fourth pretty easily. it would be really nice to not have a 3rd battery... considering we dont need one at all out there during the winter. and we dont need one at all in the cabin during the summer. so... completely ignoring the panels, and if we have enough... lets completely forget about that.

is there ANY way to isolate the batteries, but charge them with the same charge controller?

[bcroe]

If you move the battery, the pavilion panels are still needed to keep it up. With the whole system moved to
the cabin, you could split your loads into the 2 systems. Or you could even use a diode from each battery
to feed all the loads if they will tolerate another 3/4V loss; the diodes would be reversed from the type isolator
used to charge 2 batteries.

Leaving the pavilion panels in place would result in big loss in the wiring out to them. You could beat that
by having say 3 panels in series out there to get the V up and the I down; then use a good MPPT controller
for this system.

I see the step after that is adding panels, with some facing east or west to in effect lengthen your day, and
to collect more under clouds (like here). Bruce Roe

[Mike90250]

Ok, so now the battery is toast
Future, you need to plan for the winter days, and need more PV panels, Shade will completely shut down a panel, so make sure there is no shade on the panel, even the shadow of a small twig is enough to halt output.
Sounds like you are using a Group 27 size battery (about as large as you can lift and about 100ah) Group 24 are about 80ah.
If you add more battery, you have to add more PV to recharge it, thinking that 4 idle days will recharge it, just walks the capacity slowly down as it sulfates a little bit each day it's below 80%.
And likely there's a few more cell phones and such, loads always seem to expand!
But the solution is more solar, either remove shade, or add more panels. Or can you haul it to the car and run the engine to recharge it a bit ?

[idiggplants]

Battery Isolators are used in RV's and Trucks that use a Starter battery (SLI) and House battery (Deep Cycle) charged from a alternator. They use different charge voltages because a deep cycle battery voltage is lower than a SLI starter battery. The Isolator takes the voltage regulator control out of the alternator and uses the Isolator regulator to control the alternator voltage output. Not compatible with a Solar Charge Controller.

You can charge two parallel batteries with a Solar Charge controller. But to do so both batteries must be the same make, model, age, and work together so they are always at the same State of charge sharing a common load so they charge and discharge at the same rate or identical twins. Otherwise they just fight each other and the stronger battery is weakened by the weaker battery. You can get away with it for a while, but soon you will notice each battery declines and significantly shorter battery life if you are OK with that. Instead if 3 to 4 years service, 1 or 2 years.

i guess my term of "isolator" was more of a generic term... a way for me to isolate 2 batteries from one another... with some device... .not necessarily an "isolator" in the official sense.

what about one of 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

which seems to do what im looking to do... and charge 2 batteries separately... i would think it wouldnt be impossible to have a charge "manager" that would direct the charge input to 2 different batteries based off of what the 2 batteries voltages were. but i guess they dont make anything like that... so i guess im a t a dead end.

[Sunking]

Battery Isolators are used in RV's and Trucks that use a Starter battery (SLI) and House battery (Deep Cycle) charged from a alternator. They use different charge voltages because a deep cycle battery voltage is lower than a SLI starter battery. The Isolator takes the voltage regulator control out of the alternator and uses the Isolator regulator to control the alternator voltage output. Not compatible with a Solar Charge Controller.

You can charge two parallel batteries with a Solar Charge controller. But to do so both batteries must be the same make, model, age, and work together so they are always at the same State of charge sharing a common load so they charge and discharge at the same rate or identical twins. Otherwise they just fight each other and the stronger battery is weakened by the weaker battery. You can get away with it for a while, but soon you will notice each battery declines and significantly shorter battery life if you are OK with that. Instead if 3 to 4 years service, 1 or 2 years.

[idiggplants]

Last thing you want to do is mix batteries, use a common solar charger on site, and then split them up to use.

i mean... thats why i asked about an isolator of sorts.

[idiggplants]

Another thing to consider is that connecting two batteries with different usage patterns together will cause the "weaker" battery to hurt the "stronger" one. Battery systems should be all the same age and get all the same charging/discharging cycles or they deteriorate at different time lines.

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!

[Sunking]

you misread. 40ah in a 4 day weekend.

according to our meter we are hitting 12v after much less than 50ah of draw. the battery is on its way out... but regardless. we arent using nearly half the battery's capacity in 2 days, let alone 1.

idk. my numbers arent exactly accurate. id just like my actual question answered... how can i add that second battery to the charge controller while keeping the batteries separated, but the controller charging both.

Does not change the answer. If the battery is shot, you do not have the capacity you think you have. You cannot mix batteries, and you must meet minimum charging requirements of the battery.

For a 12 volt battery system for every 100 AH of battery capacity on a PWM system you must use 170 watts of panels and 10 amps of controller rating to meet the minimum charge requirements. You claim to have a 200 watt panel of unknown type being battery or GT with a PWM controller and unspecified battery capacity that is shot. You say the battery is a 12 volt Marine Battery. What size in AH. Not likely even 100 AH as that would be a huge battery.

If it were me, I would buy new batteries, and a good charger 20 to 40 amp Float Charger. Take the batteries home with me, charge them up, take them with me and use whatever two solar chargers you have to supplement while at the camp. Last thing you want to do is mix batteries, use a common solar charger on site, and then split them up to use.

[SunEagle]

ok so a quick background...

we have an off grid cabin... we use very very little electricity there. we currently have 200w of panels through a pwm controller charging a traditional 12v marine deep cycle battery. it meets our needs 9 months out of the year. during the summer that sucker is topped off by 9am. we typically use 40ah in a 4 day weekend between our led lights, cell phone chargers, radio, and our 12v pump. about 100 yards away i have a pavilion with 100w of panels and another deep cycle battery that runs led lights and car radio. again... plenty of power to get that thing topped off within an hour of sunrise.

now, i mentioned the 9 months.... well the other 3 months, we have a trifecta of things that stress the cabin's system... 1, shorter daylight, so less charging, 2 its cold out so we arent hanging at the pavilion, so we are in the cabin the whole time, and 3. we are using a lot more lights in the cabin...

so in the winter during hunting season we end up dropping the voltage down to 12v and we get nervous and start using propane lanterns. not ideal.

but... we dont use the pavilion at all in the winter. so i was thinking i could move the battery up from there to cover our extra needs during those 3 winter weekends we go up there. we have figured out that a water pump and one other circuit is almost always close to half of our load. so we could easily move a pair of leads to the other battery on the "load" end of things... but for charging... how could we wire it so it kept the batteries isolated so they dont kill each other, but still both get the same amount of charge from the panels?

we also plan on adding a 3rd 100w panel at the cabin. our controller can handle 4.

thanks a lot for your advice!

What you did not mention is the Ah rating of that marine deep cycle battery or the one out at the pavilion.

With those 200 watts of panels and a PWM CC you are probably getting a maximum of 11 amps of charging which is good for a 100Ah to 150Ah battery.

Now the problem I see is that you may not have enough charging amps from that 200 watts of panels to add the second battery. Also having longer leads on that second battery will only hurt you more and make the charging very unequal. (different charging paths with different resistance values is no good). Once those batteries are wired together to be charged you have no easy way of isolating them so one does not affect the other.

Another thing to consider is that connecting two batteries with different usage patterns together will cause the "weaker" battery to hurt the "stronger" one. Battery systems should be all the same age and get all the same charging/discharging cycles or they deteriorate at different time lines.

So if you want more power at the cabin then get a bigger Ah battery and increase your panel wattage so that it provide at least 1/10th the Ah rating for charing.