Forum Discussion

full_mosey's avatar
full_mosey
Explorer
Jan 11, 2018

Automatic, smart battery charger?

I would like to hear some comments and suggestions.

In July 2017, I made some progress on understanding the settings in the MS SS MPPT 15L solar controller. I then modified several settings which move towards a more automatic charging approach. I use two overnight low Voltages(OLV), 12.6 and 12.4, as triggers . These two OLVs drive three charging profiles for the day.

Each AM, the controller executes a start up process(charge_state=4) when the charge_state switches from Disconnected(3) to Bulk(5). This seems to be driven by the appearance of Array Volts. At this time, the day's profile is established.

I set up three profiles.

1. Storage - there is a one hour timed ABS stage before float because the OLV was 12.6 or above.

2. Extended Abs - there is a two hour timed ABS stage before float because the OLV was between 12.6 and 12.4.

3. Cancelled Float - there is unlimited ABS because the OVL was below 12.4.

Now we can see this working in a graph.



This covers 7 days; Jan 5 - 10 in full and Jan 11 up to 9:40AM.

Jan 5,6 - this is a perfect definition of Storage in good solar; One hour of timed ABS. :)

Jan 7 - Bad solar day! The controller was stuck in Bulk and never made it to ABS.

Jan 8 - Good solar. The controller AUTOMATICALLY adjusted ABS to 2 hours because OLV dropped below 12.6(not shown).

Jan 9,10 - AUTOMATICALLY Adjusted back to Storage with good solar.

Jan 11 9:40 - I am looking out at the bad weather and predicting a repeat of Jan 7. Tomorrow's forcast is Sunny and the controller will AUTO-correct the same as it did on Jan 8.

Here is a summary of possible profiles since I started logging in May 2017.

Count Profile Avg Min Volts
---------- ------------ -------------
14 Cancel Float 12.26
105 Extend Abs 12.53
99 Storage 12.68

I switched to the SSMPPT15L because the programming features greatly exceed the TRISTAR 45 PWM.

I must shout out to MS for patiently answering many questions, thanks guys!

HTH;
John
  • pianotuna's avatar
    pianotuna
    Nomad III
    Feb 24, 2018
    Hi John,

    Thanks for providing data that demonstrates what I've suspected for years--that higher voltage panels deal with poor solar harvest conditions better than lower voltage nominally 12 volt panels in parallel.

    My own system input voltage to the controller is 33. I get some charging even in rain.
  • full_mosey's avatar
    full_mosey
    Explorer
    Feb 24, 2018
    Here are an interesting two graphs that show a difference between parallel and series connected 12V panels with MPPT. I have a TT and a van in the driveway. Both have their own panel arrays and they have been subjected to the same weather.

    This morning, I was greeted with the fifth consecutive day of inclement weather. It was dense fog followed by rain and then complete overcast. We had freezing rain for 3 days beforehand and the panels were covered with ice until yesterday with about half covered overnight.

    First, the series graph of the van.


    You see V-Array, or solar Volts, beginning at 13V and the controller in Bulk. Next V-Array rises until the sky darkens and the rain begins where the V-Array drops back to 13V. After the rain passes, the V-Array rises to 32V where we see some more Amps.

    Second, the parallel graph of the TT.



    Here you see what happens when the V-Array Volts are cut in half due to the parallel setup. Charging starts out as above, but when the rain began the V-Array dropped low enough that the controller went into NIGHT/DISCONNECTED mode. Once the V-Array rose back to 13V the controller reverted to Bulk mode.

    Comments?

    HTH;
    John
  • full_mosey's avatar
    full_mosey
    Explorer
    Feb 20, 2018
    Why is an adjustable, temperature compensating charger important? We all should know that a battery at 25C is usually charged at 14.4V. We know we can set most chargers to 14.4V But, how often is your battery actually at 25C? Plus how often is 14.4V the correct charging Volts? The answers to both are "Not often".




    This is a graph of the bank in my van covering ~260 days. It includes the extremes of Summer and Winter.

    The V_Target is the regulated Absorption Voltage as calculated based on the battery temperature. I capped this at 15V.

    The plots are of the first minute of the day when the Morningstar SS MPPT 15L wakes up and switches from night to Bulk stage. These are the starting bank temps and charge Volts. Normally the bank temp rises and Volts are reduced during the day. The 15L automatically monitors temps and adjusts Volts throughout the day. Even Float volts are regulated by battery temperature.

    Summer is not too bad.

    In Winter the constant 14.4V is way too low. With a constant 14.2, 14.4, 14.6, 14.8 setting type of charger, it never is right most of the time. Some chargers have an extra-time override, but then again, it may still not be enough Volts to top-off/finish the charge.

    Comments?

    HTH;
    John
  • full_mosey's avatar
    full_mosey
    Explorer
    Feb 07, 2018
    I am working with the definition of a topped-off battery is "...when a low point of Amps is reached and held for 15 minutes during Abs.". I became weary while waiting for days to see the charge Amps flatten out at a low Amps. Weather was not cooperating.

    Last night I used garage/shore power to run the 50A Magnum inverter/charger. I wanted the next day to begin with a fully floated bank.



    It is a clear sunny day. In this graph you see the Magnum maintaining 14V Float Voltage until sunrise. Did I say I use temp-comp chargers? I ran the Magnum from 4PM to 8AM. By 9 the MPPT was holding the V-batt at 15V and Amps were steady at ~1.68A. The Target Volts smothers the V-batt.

    This exceeds the top-off rule of thumb, and we are ready for the MPPT to Float.

    Parasitic draws are:
    Magnum on standby
    2 x Dometic 12V CF-35 fridges
    12V to USB adapter
    Raspberry Pi 3 B

    HTH;
    John
  • full_mosey's avatar
    full_mosey
    Explorer
    Feb 05, 2018
    Here is the Amps graph for today 4 Feb:

    Amps:


    What is interesting/alarming to me is that the Amps went lower and never leveled out as I expected. Abs lasted nearly 6hrs, somewhat less than 2Feb. The late afternoon switch to Bulk=5 is due to waning V-array. The controller is trying to hold the V-batt to Target Volts.

    Where is the bottom? Was the bank badly sulphated?

    I will keep Float cancelled and wait and watch for a leveling out.

    Maybe the race to Float is a fool's errand!

    HTH;
    John
  • full_mosey's avatar
    full_mosey
    Explorer
    Feb 04, 2018
    pianotuna wrote:
    Hi John,

    Thanks for taking the time to present the data.

    I'd add another 200 watts of solar myself. Or is there no room?


    Thanks.

    This is on my Savana van where I have a 10' x 5' area on the roof rack. I could fit two more 12V 58"x26" panels. I am already maxed out on the 15A MPPT controller which is rated for 200W but tolerates the present 280W.

    Right now I want to make sure I am fully using the existing system. I am running driveway tests.

    When camping/traveling, I do have the 6Ga charge line from the OEM 105A alternator to assist. I wont be driving any until March. I guess I could use a 10A portable charger to simulate morning Bulk charging, or any driving for that matter.

    HTH;
    John
  • pianotuna's avatar
    pianotuna
    Nomad III
    Feb 04, 2018
    Hi John,

    Thanks for taking the time to present the data.

    I'd add another 200 watts of solar myself. Or is there no room?
  • full_mosey's avatar
    full_mosey
    Explorer
    Feb 04, 2018
    With the suggestion from MEXICOWANDERER, I analyzed my collected data and decided that the Abs times have been too short and need to be lengthened because the switch to float was too far above 0.5% = 1.35A on average. The bank is 270Ah and 0.5% is 1.35V. Having too short Abs times can result in slowly sulphating the battery over time. I do load capacity tests that seem to show the bank is in good health.

    On 2 Feb 18, I began charging without float which leaves only Bulk and Abs. I have been observing how long in Abs it takes for the Amps to stay low. Next, I can make timer settings to the MPPT.

    A Raspberry Pi 3 B(RPi) computer collects data from the Morningstar Sunsaver MPPT 15L(MPPT) 24/7/365 at one minute intervals. The Rpi is used to analyze the data and it could be used to make immediate adjustments to the MMPT. I am hoping I can find MPPT settings that can be more permanent without relying on the RPi to make ad-hoc changes. The RPi runs a web server and I can examine the data and change MPPT settings remotely as well.

    With this analysis I hope to know what MPPT settings are needed to regularly top-up the bank and when the genny is needed to catch up. The main charging goal of the genny is to speed up the Bulk charge in the morning and let the MPPT finish the Abs and Float charging.

    Below are two graphs which show the MPPT charging on 2 Feb:

    Volts:


    This shows the MPPT has no problem holding the battery at the Target Volts for 6 hours. Surely that is enough time to call the battery charged, or is it?

    Amps:

    Now we see the Amps in play. What I want to see is a flattening of the Amps which should indicate the appropriate time to switch to Float. This graph suggests that 2A and 4 hours Abs would be reasonable. You can see that morning is the best economic and strategic time to run a genny or use shore power to shorten the Bulk time.

    HTH;
    John
  • full_mosey's avatar
    full_mosey
    Explorer
    Jan 28, 2018
    I ran a little test today to see what would be the maximum solar Amps as the sun is low. I am prepping for an Alaska drive-about.


    Here you see the daytime process as read from the controller each minute. During bulk the battery Volts slowly rise to the Abs setpoint, then Volts hold for one hour, then switch to the float setpoint. Just before Noon I switch on a 500W inverter load. The battery Volts drop immediately and the controller switches back to bulk.


    Here you see the same time frame with attention given to Amps. The controller transitions from bulk to abs at 5.5A to float at 3A. As soon as the 500W load is invoked, the controller collects the maximum Amps commensurate with the insolation. It is a clear day. At 12:30 solar Noon, the Amps top out at 10.5 and begin to decline.

    HTH;
    John

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