Storing MH with Solar System

Pre-Solar I always just hit the factory battery disconnect switches when putting the MH in the storage lot.

It is rare if the coach sets 30 days without use.

I have 2 DC260-12 AGM batteries, Morningstar 45 MPPT solar controller, 680 watts of solar panels, and a Xantrex Freedom XC Inverter all connected with appropriate disconnects, breakers, and fuses. This system feeds the coach 12v power circuit control box.

I'm wondering what, if anything, should be shut off when I put in storage now?

Thanks,
Tom

Hi Tom. I don't know that you'd actually "need" to turn anything off, but I've always thought that if I were going to store our motorhome for an extended period of time, away from where I could regularly check on it, I'd turn off the disconnect switches between the panels and the controller, and the controller and the batteries - just to be on the safe side.

Having said that, I'll note that when we're not using our coach, it's in our garage, which is attached to our house, and it's always plugged in to shore-power. I don't turn the solar disconnect switches off, and I've never had any problems at all. FWIW

Kev

With the Outback fm80 controller that I use, it goes into sleep mode at night, and then starts a cycle fresh the next morning. That cycle includes the absorb stage, which on my unit is close to 15 volts, and it holds it there for 2 hours whether the batteries need it or not. That causes the electrolyte to bubble. I would not leave my system in the Sun for an extended period unless I was drawing the batteries down somewhat every day.


I leave our unit on shore power beside the house the rest of the year, with the solar panel disconnect switch flipped. This separates the array from the controller.


Our Progressive Dynamics converter does not restart a cycle when the sun goes down. Once it has charged the batteries and put them through one absorb cycle, it stays in float indefinitely, never putting the batteries through another absorb cycle until we take the trailer out and actually use it again.


On our unit, at least, I think the solar controller would boil the batteries dry in a relatively short period of time if I left the solar connected while it was in storage beside the house.

Heli_av8tor said:

Pre-Solar I always just hit the factory battery disconnect switches when putting the MH in the storage lot.

It is rare if the coach sets 30 days without use.

I have 2 DC260-12 AGM batteries, Morningstar 45 MPPT solar controller, 680 watts of solar panels, and a Xantrex Freedom XC Inverter all connected with appropriate disconnects, breakers, and fuses. This system feeds the coach 12v power circuit control box.

I'm wondering what, if anything, should be shut off when I put in storage now?

Thanks,
Tom

Click to expand...

If your storage is outside and has sunlight then let the solar do it's job.
if you are covered or inside a garage/shop then use the disconnects.

solarman said:

If your storage is outside and has sunlight then let the solar do it's job.
if you are covered or inside a garage/shop then use the disconnects.

Click to expand...

Solarman:


Then I guess I need some training here. I would have thought that as well, but the way my solar system is set up at the moment, the Outback fm80 restarts a cycle every time the sun goes down. The absorb stage is on a simple timer that is currently set for 2 hours. During absorb, the solar will cause the electrolyte to bubble. So, I have a few questions...


1) is it alright to let the batteries go through a two-hour absorb cycle every day when in storage?


2) if not, then should I be using the function that ends the absorb cycle when the charge current gets below a certain point?


3) if I should be using a charge current trigger to end the absorb cycle, how would I calculate what that current should be? I have 6 gc-2 s.


4) if none of the above are correct, then what would you suggest?


Thanks.


Frank.

Frank B said:

Solarman:


Then I guess I need some training here. I would have thought that as well, but the way my solar system is set up at the moment, the Outback fm80 restarts a cycle every time the sun goes down. The absorb stage is on a simple timer that is currently set for 2 hours. During absorb, the solar will cause the electrolyte to bubble. So, I have a few questions...


1) is it alright to let the batteries go through a two-hour absorb cycle every day when in storage?


2) if not, then should I be using the function that ends the absorb cycle when the charge current gets below a certain point?


3) if I should be using a charge current trigger to end the absorb cycle, how would I calculate what that current should be? I have 6 gc-2 s.


4) if none of the above are correct, then what would you suggest?


Thanks.


Frank.

Click to expand...

1. Absorb is not a timed event so no !

2. Absorb should be applied until the charge current tapers down to between one and three percent of C.
two percent is a good number. so set your controller to end absorb and go to float at the 2% point.

3. 2% of battery C ( eg: 400 Ah battery * 2% = 8 A )
  The above is correct if you are on shore power long enough to complete a possible 4 to 8 hour absorb cycle.
  the absorb time is variable and depends on the previous days DOD. on solar you might not be able to complete absorb
  depending on conditions so I have a different way.

4.  Some battery manufacturers are now moving away from 3 stage charging for solar applications and
just specifying a bulk charge of 2.47 V per cell, then go to float at 2.25 V per cell.

you can do this "fast charging" method by setting your bulk/absorb voltage to 2.45 per cell to begin with and at the end of each day
measure the SG with a good hydrometer or refractometer, if the SG is low then increase the voltage up by 0.2 V, if the SG is high then reduce
the voltage by 0.2 V . do this until you find the ideal voltage. after this you go to float at 2.25 V per cell.
there is a chance you will overcharge your batteries a little and use more water, but this is better than undercharging and sulfation.

Solarman:

2. Absorb should be applied until the charge current tapers down to between one and three percent of C.two percent is a good number. so set your controller to end absorb and go to float at the 2% point.

Click to expand...

Please remind me again of what C stands for. It looks from your response that this would be the capacity of the battery Bank in amp hours, is that correct?

Frank B said:

Solarman:




Please remind me again of what C stands for. It looks from your response that this would be the capacity of the battery Bank in amp hours, is that correct?

Click to expand...

yes, C is the 20 hour rated capacity in Amp/hrs

To add to the discussion...

My controller has two settings.  I think of them as bulk and float.  For extended dry camping I want to get as many amp hours in as possible.  For storage I don't want to boil the batteries.

I have a Progressive Dynamics Converter which uses 13.2 volts for float, so that seems good.

My settings are:
Camping 14.8 - 14.4
Storage 13.8 - 13.2

This has worked well for me for several years.

joelmyer said:

To add to the discussion...

My controller has two settings.  I think of them as bulk and float.  For extended dry camping I want to get as many amp hours in as possible.  For storage I don't want to boil the batteries.

I have a Progressive Dynamics Converter which uses 13.2 volts for float, so that seems good.

My settings are:
Camping 14.8 - 14.4
Storage 13.8 - 13.2

This has worked well for me for several years.

Click to expand...

The OP doesn't have the luxury of shore power when stored, so his converter is obviously not powered.
he has a choice of solar or nothing.  Frank on the other hand has a timed absorb which should not be used.

what solar controller do you have ?
most have adjustments for bulk/absorb/float

batteries in storage will or should be on float..

Solarman,

I was less than clear again.

I used the PD voltage as a guide to determine what setting to use for my solar controller when the 5er was sitting at home.  The PD converter has the reputation of being kind and gentle to batteries, so I set the the solar storage float voltage to the same as the PD (13.2).

My Controller is the ECO-WORTHY 20A MPPT Solar Charge Controller 12V/24V.

Joel

joelmyer said:

Solarman,

I was less than clear again.

I used the PD voltage as a guide to determine what setting to use for my solar controller when the 5er was sitting at home.  The PD converter has the reputation of being kind and gentle to batteries, so I set the the solar storage float voltage to the same as the PD (13.2).

My Controller is the ECO-WORTHY 20A MPPT Solar Charge Controller 12V/24V.

Joel

Click to expand...

just a little.. LOL

most flooded lead acid have a float voltage of 2.25 V per cell.
so that's 13.5 for a 12 V system.

solarman said:

just a little.. LOL

most flooded lead acid have a float voltage of 2.25 V per cell.
so that's 13.5 for a 12 V system.

Click to expand...

I think 13.5 volts on that battery would tell me that 12V battery is under charge or just removed from charging. A full charged  battery should be 12.6V or so with no charging system functioning. But... I could be wrong on that.

Alfa38User said:

I think 13.5 volts on that battery would tell me that 12V battery is under charge or just removed from charging. A full charged  battery should be 12.6V or so with no charging system functioning. But... I could be wrong on that.

Click to expand...

Correct, a typical FLA at 100% SOC left idle for at least an hour will read 12.6 Volts.

to maintain batteries in good health for periods of time such as storage, the applied voltage should be 13.5 Volts, this is the float condition.

I've been leaving all on. Looks like my Morningstar does start the morning with an Absorb charge rate even though the Trimetric is showing 100%. Don't know if this is at all harmful to the batteries. I'd think it would be better to just resume the Float rate.

Thanks for everyone's input.

Tom

Yeah, that is something that I am going to have to get at. I need to program the absorb cutoff amperage on my Outback controller. I would expect it to start the absorb stage daily, as it goes through all three stages every time the sun comes up However, if the current limit is set, it should drop out of absorb very shortly after it begins. That should allow the batteries to just sit there at float the rest of the day.

Solarman:


Okay, I finally got a chance to reprogram my outback fm80 solar controller according to what you suggested. I increased the absorb time from 2 to 6 hours, and set the end of absorb current to 12 amps. The end current should therefore be the limiting factor on the absorb cycle. That should be about right. You suggested 8 amps for a 400 amp hour battery bank, and mine is very close to six hundred amp hours (630).


I also increased the absorb voltage from 15 volts, to 15.2.. The specifications on my interstate batteries say 15.4 volts, but that is very close to the maximum voltage that the electronics in my refrigerator will take. I just don't want to go quite that high.

I realized the need for these changes today. we had rain and cloud all day yesterday, which brought my state of charge to about 50%. today we had bright Sunshine, but it dropped into absorb very close to noon, and was still putting in over 20 amps. no way it would have charged that depleted battery Bank in 2 hours.

Thank you for your help!

Frank B said:

Solarman:

I realized the need for these changes today. we had rain and cloud all day yesterday, which brought my state of charge to about 50%. today we had bright Sunshine, but it dropped into absorb very close to noon, and was still putting in over 20 amps. no way it would have charged that depleted battery Bank in 2 hours.

Thank you for your help!

Click to expand...

It may seem odd to dismiss these automatic 3 stage algorithms, but 3 stage is of no use to to an off grid RV unless you have 24 hrs of sunshine..!

here's another tip..

Towards summer when you have much more sun, you will need to reduce the voltage a little to avoid overcharging the batteries.
you will know if your water consumption increases somewhat..

also if you can smell that "rotten egg" smell then you are overcharging a little, so back off the voltage by 0.2 or so Volts
and check the batteries a week later.

Solarman:


I hate to admit it, but I am basically lazy.   I just want to be able to set it and forget it.


I only run my solar when I am actually using the trailer. When the unit is at home, I plug it in and let the progressive dynamics charger keep the batteries up. As someone else has already mentioned, the PD charger is generally easy on batteries.


At the moment, we are in Southern Arizona and/or Southern California, so I am using the solar charging regularly. Having a 15.2 volt threshold to go to absorb does not seem to be working the batteries too heavily (Interstate actually recommends 15.4!). There is no sulfur smell, and no excessive gassing that I am able to detect. I'll check the water again in a few weeks. At the moment, there is no appreciable consumption.


I am glad that I did as you suggested and adjusted my Outback controller to switch from absorb to float based on the current draw of the battery bank. As you state, this is not a timed event, but depends on the state of the batteries themselves. The only reason that I ever set it up as a timed event to begin with is because some of the information on the Interstate batteries suggested a time window for the absorb cycle, and I did not know that I could adjust the switch from absorb to float based on current.


In any case, my solar installation continues to please me greatly! It does all I wanted, and more.


I popped four batches of popcorn in our 1kw hot air corn popper today. Two batches for me (the first batch blew off the picnic table because it is windy here today), and two batches for the ducks here on the lake.   My wife also ran the microwave for well over 15 minutes to cook a squash. Neither event bothered the system in the least bit. I'm still going to have a full charge before 3 pm.


The only downside is the people beside us at various locations that do not have solar, and instead use those noisy, stinkin' generators! LOL!

Solarman:


I did a visual check on the water levels in the batteries a few days ago. Levels seem to be pretty much where they were when I topped the batteries off last summer.  So, I guess I'm good.