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Old 12-08-2014, 05:37   #1
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MPPT (Maximum Power Point Tracking) On or Off for Storage?

I'm planning to haul the boat out next week for two months. We've got a bunch of solar, a new Outback MPPT, and four new GC batteries. I'm wondering what the "conventional wisdom" is on leaving it all unattended. Do you shut down the MPPTs and, disconnect the batteries and then sort it all out when you relaunch, or do you leave it all connected and trust the MPPT to keep the batteries in good shape?
Do you leave any 12 volt devices running, like lights or fans, to put a load on the batteries?
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Old 13-08-2014, 09:48   #2
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Re: MPPTs on or off for storage?

We leave our reefer/freezer running and set the solar controller for 14V absorption and leave it all running when gone. The lower absorption voltage decreases the battery water loss and keeps the batteries charged from the small overnight draw down.

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Old 13-08-2014, 11:48   #3
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Re: MPPTs on or off for storage?

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Originally Posted by colemj View Post
We leave our reefer/freezer running and set the solar controller for 14V absorption and leave it all running when gone. The lower absorption voltage decreases the battery water loss and keeps the batteries charged from the small overnight draw down.

Mark
+1

But for this you might need a controller with a 'custom' setting.

There might be dip switches you can set to change the voltage to GELs at 14.1v.
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Old 14-08-2014, 09:20   #4
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Re: MPPTs on or off for storage?

I've got lead acid 6 volt golf cart batteries, all new. And an Outback FlexMax 60 mppt.
I don't know about changing things on it, I read that it was set up for lead acids from the factory and didn't get into making changes.
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Old 14-08-2014, 10:20   #5
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Re: MPPTs on or off for storage?

If there is no load on the batteries I would suggest an absorption voltage of 14.1v. An absorption time of 10 mins and a float voltage of 13.2v as appropriate for long term storage.


Have a read of the manual and if you don't understand it I can talk you through making the changes.
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Old 14-08-2014, 12:26   #6
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Re: MPPTs on or off for storage?

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....I don't know about changing things on it, I read that it was set up for lead acids from the factory and didn't get into making changes.
You asked the original question ......"do you leave it all connected and trust the MPPT to keep the batteries in good shape?"....

The answer is NO!

The point that is being made here is that "Smart" controllers, even the Outback, aren't that smart and if left for 6 months to charge the batteries up each day when they don't need charging may dry them out.

A simple explanation is that the charger will raise the voltage to 14.4v and hold it there for maybe 3 hours - thats how most chargers work. So charging the battery each day to 14.4v will cause the battery to gas slightly, which is fine, but if the battery is already fully charged and held at this voltage for 3 hours it will gas too much and lose water.

A few chargers, like the Outback, can measure the charge actually going into the battery, and can be programmed to drop to Float at a set "end amps" charging current. This needs advanced knowledge of battery charging!

Reducing the absorption voltage to 14.1v for 10 minutes as nolex 77 suggests will be much easier and keep charge in the battery and stop water loss, because 14.1v is below the gassing voltage.
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Old 14-08-2014, 13:05   #7
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Re: MPPTs on or off for storage?

Hell you can program a FlexMax 60 to never go into float if you want just by changing the settings. The menus are pretty easy to understand and you probably could do even without the directions.

I would leave mine on I think. But I would turn the settings way down as all I would looking to do is make up for the self discharge

I also think this would be a good time to wire the Aux output to run a couple of fans (would need to install a relay)
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Old 14-08-2014, 15:41   #8
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Re: MPPTs on or off for storage?

Why run fans? Is it specifically to put a load on the mppt or did you mean use the free solar for ventilation?

We've got six solar vent fans on it already. But they exhaust out the top, they don't circulate inside air.
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Old 14-08-2014, 16:04   #9
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Re: MPPTs on or off for storage?

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Why run fans? Is it specifically to put a load on the mppt or did you mean use the free solar for ventilation?

We've got six solar vent fans on it already. But they exhaust out the top, they don't circulate inside air.
Just for ventilation since you have the available power anyway. You can program the Aux output to only run when voltage is high, meaning it is free power so may as well use it for something. I would think a shut up boat in the tropics could never have too much air flow.
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Old 14-08-2014, 16:05   #10
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Re: MPPTs on or off for storage?

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Hell you can program a FlexMax 60 to never go into float
That was suppose to be absorption, not float. You turn the absorption setpoint way down and it will just be a float charger.
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Old 20-08-2014, 10:29   #11
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Re: MPPTs on or off for storage?

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Originally Posted by noelex 77 View Post
If there is no load on the batteries I would suggest an absorption voltage of 14.1v. An absorption time of 10 mins and a float voltage of 13.2v as appropriate for long term storage.


Have a read of the manual and if you don't understand it I can talk you through making the changes.
Thanks. I'm having the boat hauled in the morning and will be spending the next day or so buttoning her up for the rest of storm season.

In addition to the MPPT, I have some other solar on a MorningStar PWM. I was thinking of just shutting that off entirely, and letting the Outback MPPT be the only charge and battery monitor source. Does that make sense?
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Old 23-08-2014, 00:24   #12
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Re: MPPTs on or off for storage?

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Does that make sense?
Yes if you do not have any loads on the system you need very little solar. However, the voltages are still going to rise to the absorption set point, so adjusting these values down to an ideal level is still beneficial.
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Old 23-08-2014, 04:01   #13
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Re: MPPTs on or off for storage?

We hauled the boat out yesterday. After thinking about it, I decided I felt best with all the power off. MPPT and pwm off, battery switches off. only thing running on the boat for the next two months are the solar powered vent fans.

This way I won't be asking myself, "but what if that flaky looking doo dad shorted and the crummy wiring got hot and discharged four golf cart batteries into that other thing that may or may not be fused .....". Just the kind of thing I worry about when I am too far away to check.

I'll check the levels in the batteries and turn the solar back on the day before we launch it and I would expect it to be back to fully charged within hours. Fully charged, disconnected batteries should do okay just sitting for two months. I'm sure they sat on NAPA's shelves a lot longer than that.
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Old 23-08-2014, 04:12   #14
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Re: MPPTs on or off for storage?

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After thinking about it, I decided I felt best with all the power off.
That is quite a reasonable option, for two months, especially if the temperatures are not high. (Self discharge goes up with temp)

Just be careful that everything is off. The best way is to actually disconnect the leads off the battery posts.
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Old 23-08-2014, 04:21   #15
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Re: MPPTs on or off for storage?

The only things directly wired are two big bilge pumps on mercury switches. I feel confident that they won't be draining the battery. It will be warm, of course, it's high summer here and Sept. is typically one of the hottest months with temps hitting around 90 deg F.
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