Stopping confusion with multiple charging sources onto single battery bank?

[DevoDave]

Hi guys,

In response to recent posts, my concern is that the Balmar/MC614 may stop outputting it's up to 150A (1800W) because it sees the charge voltage from the PV/Midnite (500W max) and assumes that the batteries have a higher SOC than they actually have.

This might happen at stages 4,7, and 9 below.

Regulator Operation
The MC-614 regulator’s microprocessor controlled charging system uses a sophisticated, multi-stage profile to deliver
maximum charging output, while protecting the batteries from overcharging damage. When the regulator is first turned on,
the processor performs a quick one-second self diagnostic assessment. Following that diagnostic, the MC-614 initiates a
charge program as follows:
1. Start Delay - Factory set at one second. Can be user-adjusted to a maximum of 999 seconds in the regulator’s advanced
programming mode. See Advanced Programming section for adjustment instructions.
2. Soft Ramp - Gently increases voltage to bulk preset levels based on battery program selected.
3. Bulk Charge - The most aggressive of the charging stages. Voltage is held at a pre-set level, specified by battery
program selected, for a set time period. Factory-set bulk time is 18 minutes. Adjustable in 6-minute increments.
4. Calculated Bulk Charge - Holds voltage at bulk level for six minutes, then calculates battery condition by comparing
existing voltage, time at voltage, and field percentage to target values. If values are met, the regulator advances to
the next stage. If values are not met, the regulator continues to bulk charge and compares real-time to target values.
This will re-occur until all values are met.
5. Ramps down to Absorption voltage.
6. Absorption Charge - Regulator continues to control the alternator’s output voltage for an additional 18 minutes at
approximately 2/10’s of a volt below bulk charging voltage. Adjustable in 6-minute increments.
7. Calculated Absorption Charge - Holds voltage at absorption level for six minutes, then calculates battery condition
bycomparing existing voltage, time at voltage, and field percentage to target values. If values are met, the regulator
advances to the next stage. If values are not met, the regulator extends the absorption charge and compares realtime
to target values. This will re-occur until all values are met.
8. Ramp down to Float.
9. Float Charge - Regulator continues to control the alternator’s output voltage for an additional 18 minutes, typically
at a volt less than bulk voltage (based on battery program presets). After that initial fixed time period, the regulator
can respond to increased charging demand by cycling to absorption voltage. After 12 hours of continuous operation,
the regulator will automatically revert to absorption voltage through calculated absorption and back to float charging
stage.

Am I barking up the wrong tree?

   

[dgd]

Dave,

The alternator controller appears to just go through the normal Bulk, Absorb and Float cycles. I assume you can configure  the Absorb and
Float voltage set points? I would just make these the same as those for the Classic or perhaps even set the Classic slightly higher to maximise the PV power usage while reducing diesel use (I think I have the logic the right way around )
I would not expect any issues of confusion to occur.

I was also intrigued by your making the PVs into one serial string because of shading issues. I don't know much about the effects of partial array shading but I imagine that serious shading on even one panel of the string would seriously drop the power, voltage and current.
My thinking is that the four panels set up as two strings of two (since they are nominal 12v panels and your battery is 24v) would provide more power if one string was shaded but the other was seeing full sunlight.
I may be (probably am) completely wrong with this but it may be worth trying if you can readjust the panel wiring for 2 strings of 2 panels.

dgd

[DevoDave]

dgd,

Your question prompted me to dive into the advanced options on the MC614 charging regulator.  I *HAD* thought that the only programming available was to set the chemistry of the batteries.  (I have 2x200Ah AGM's in parallel for a 12V system BTW.)

I have found that I can in fact amend the Bulk, Absortion, and Float voltages!  The options are buried behind password protection, and programming consists of using a magnet to trigger a reed switch buried inside the epoxied device observing a 3 letter 8-segment display.  May be an arduous operation.

So, (thanks to your suggestions) it looks like I just need to tweak settings between the Midnite and the MC614 to ensue that they are not fighting.  Thanks!!  That'll save me some cash.

As far as the shading issue on the PV panels goes, I can easily make the system 1 string of 4, 2 strings of 2, or 4 strings of 1 if need be.  The solar panels are all within a couple of metres of each other, and the Midnite is only 4 metres cable run from any of them. 

Considered wisdom in the boating fraternity varies widely, with the gold-standard suggestion being an MPPT for EACH panel.  Shading on a boat is not considered to be the same as shading on a rooftop.  It will vary as the boat swings with wind/water and will have solid items like the mast and boom (with sailbag/sail) casting quite dark shadows.  Another factor is that all the panels will be flat-mounted.. reducing efficiency.

With modern panels and decent MPPT's (like the Midnite) I have seen a lot of people say that series connection with a panel-bypass diode on each panel is a good solution.

I'm probably going to have to suck-it-and-see to determine the most efficient wiring configuration with my panel positioning and yacht behavior.  Very willing to hear of real-world experience if anyone has been doing a lot of marine work?