Forum Discussion

brulaz's avatar
brulaz
Explorer
Feb 12, 2015

Big Solar + Tiny Solar panel in parallel

Put in 380W solar + Rogue MPPT a while ago.

With no loads, in storage, the Rogue should go through a daily cycle: Rest at night, very brief MPPT in the morning up to 14.8V, then very brief Absorb at that V until the low current limit. Rogue then turns off, lets the battery V quickly drop to Float V and then maintains that until evening and Rest. Battery V drops a bit over night. Repeat next day.

But recently noticed the Absorb V of ~14.8V was being maintained all during the day. Not dropping to Float V at all, until the sun went down, and the Rogue shut down.

Well, the trailer came with a tiny 15W panel for battery maintenance. Don't think it has a controller. And it's running in parallel to the Rogue, and apparently wired in between the battery disconnect switch and the batteries. So it's not disconnected when the batteries are disconnected from the rest of the trailer.

On sunny days that 15W panel has enough ooomph to maintain the ~14.8V Absorb V all day once the Rogue gets it up there. Surprising, to me anyway, and not what I want for storage especially in the long days of Summer. Luckily the 15W panel is easy to turn off (there's a switch on the Main panel :S). So I can still have it when there are actual loads ...

6 Replies

  • brulaz's avatar
    brulaz
    Explorer
    Feb 12, 2015
    BFL13 wrote:
    Good to see it now works right. 13.2 is sometimes the set voltage for going beck to Bulk with MPPT controllers. ISTR you said the Rogue makes that trigger to be the same as the chosen float setting?

    Some have a time in there so Vbat has to be under the trigger for a minute before it will go to Bulk/MPPT. So I suppose if your 13.2 is float and trigger it can take a spike below 13.2 and not go into bulk. Seems kind of tight.

    If the solar is still capable of doing more amps then any loads up to a point will not disturb the float, but if the loads are more than the solar can do, then with some controllers that have a separate float setting and a trigger setting less than that, what happens is the Vbat slides down to the trigger and then it goes MPPT/Bulk

    With those two settings being the same value, it would go into MPPT/Bulk a minute (if that is the time) after the solar can't meet the demand ? Could be a bit "trigger happy" if you have an intermittent load when the sun is not very high?


    With the Rogue, you set the Float voltage, and as long as that can be maintained, it stays in Float mode. But if it drops 0.5V below that (because of loads or lack of sunshine), it switches to MPPT.

    For that reason, I up the float voltage to 13.6V when boondocking and actively using the batteries. MPPT kicks in sooner that way and I end up with more charge in the batteries when the sun sets. I only set to 13.2V when in storage and the batteries disconnected from the loads.
  • BFL13's avatar
    BFL13
    Explorer II
    Feb 12, 2015
    Good to see it now works right. 13.2 is sometimes the set voltage for going beck to Bulk with MPPT controllers. ISTR you said the Rogue makes that trigger to be the same as the chosen float setting?

    Some have a time in there so Vbat has to be under the trigger for a minute before it will go to Bulk/MPPT. So I suppose if your 13.2 is float and trigger it can take a spike below 13.2 and not go into bulk. Seems kind of tight.

    If the solar is still capable of doing more amps then any loads up to a point will not disturb the float, but if the loads are more than the solar can do, then with some controllers that have a separate float setting and a trigger setting less than that, what happens is the Vbat slides down to the trigger and then it goes MPPT/Bulk

    With those two settings being the same value, it would go into MPPT/Bulk a minute (if that is the time) after the solar can't meet the demand ? Could be a bit "trigger happy" if you have an intermittent load when the sun is not very high?
  • brulaz's avatar
    brulaz
    Explorer
    Feb 12, 2015
    2oldman wrote:
    I doubt that 0.6a panel is doing much.

    From your description it doesn't sound like you're getting a full charge (ie.. Float voltage) during the day. Don't know your battery complement.


    Agree it's not doing much, but as smkettner suggests (thanks!) that's prolly because the 210AH of batts are fully charged at 14.8V by the Rogue.

    So the Tiny Panel is just keeping them at 14.8 V as long as there's sunlight. (The Tiny panel is not very powerful and really doesn't justify a better/any controller.)

    Now that I've turned off the Tiny Panel, after Absorb finished at 14.8 V, it took less than an hour for the batt V to drop to 13.2 V float, and it stayed in Float for the rest of the day (8 hours until sundown). Much more reasonable.

    The amount of time spent in Absorb under these no-load, storage conditions is less than a few minutes. I haven't been able to witness it, and the log records it as zero minutes. The Rogue does spend more time, perhaps an hour under low light conditions in the morning to raise the battery voltage from about 12.7 V up to the 14.8 V Absorb point.
  • time2roll's avatar
    time2roll
    Nomad
    Feb 12, 2015
    Goes to show the Rogue is giving a full honest 100% charge.
    Yes I would disconnect the 15w solar or move it on the other side of the cut-off switch.
    No sense in having the battery at 14.8 all day going low on water.
  • mlts22's avatar
    mlts22
    Explorer II
    Feb 12, 2015
    Can you put the panels on separate charge controllers?
  • 2oldman's avatar
    2oldman
    Explorer II
    Feb 12, 2015
    I doubt that 0.6a panel is doing much.

    From your description it doesn't sound like you're getting a full charge (ie.. Float voltage) during the day. Don't know your battery complement.

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