Deciphering my remotes display (MT50)

Aguarancher

The whole series, parallel issue has to do with shading as littleharbor2 pointed out earlier.

 “When series wired, any shadow will substantially affect the panels output as they are essentially one panel. Do whatever necessary, including relocating them to avoid shadows”

 You have enough panel voltage you can hook the panels in parallel and help reduce the potential effects of shading.

update..thought you had panels with approx. 40ocv each. upon further re-reading the posts, they seem to be 18.5 ocv. As stated with wiring losses that puts you on the edge of under charging, but the part stated by littleharbor2 still explains the reasoning between hooking up your panels series or parallel.

Estragon

With an mppt controller, there are two numbers for amps; one for input to the controller at panel voltage, and another for controller output to the batteries and loads at battery charging voltage. The total wattage (volts times amps) should be close for both input and output.

Putting 10a into the controller at (eg) 18v isn't necessarily better than putting 5a in at 36v. The wattage is the same in either case, but if the panels are hot the voltage will be lower than rated, and may get too low for an mppt to charge properly. If the controller was a pwm type, the higher voltage is sort of wasted, but am mppt type uses it.

My boat reefer is likely not well insulated, but it's built into galley cabinetry and I would have to rip it all out too add more. I may drill a small hole to get an inspection camera in, and add spray foam insulation if that looks possible.

I built a 12v fridge/freezer box in the cabin that's well insulated but uses the same danfoss type compressor/evaporator set used on boats, and it only uses ~25-30ah/day as a freezer.

BB.

More or less, if your battery is at 80% or less state of charge, it is hungering for charging current and your charger should be outputting 100% of the available current to the battery bank. This is the "bulk mode" of the charge controller--The controller is in "maximum" output current mode (charging voltage is less than 14.4 volts) and is simply outputting to the battery bank the maximum available solar power.

Over ~90% state of charge, the batteries are near full, the charger is in "absorb" mode--Or constant voltage charging (14.4 volts or whatever you have set) and the batteries will accept whatever current they "want".

Once the battery is at ~14.4 volts for 2-4-6 hours (whatever the hold time programmed is), the controller will enter "float" mode. At this time the controller will hold ~13.6 volts and the battery bank will be drawing much less than 1% rate of charge.

Note that in Absorb or Float mode, the charge controller will "do what it takes" to hold the set point voltage (14.4 or 13.6 volts). If your refrigerator is running, the charge controller will output more current to hold the set point voltage--Until the point where the voltage starts to sag because the solar array has no more Wattage to output to the battery bank.

Once the battery bank falls below 12.7 volts or so for a (not too long) period of time, the controller will drop out of float mode and transition to bulk mode and start the process over again.

You have an MPPT type charge controller. The Vmp of the array should be somewhere Vmp of your panels (if your panels are Vmp~38 volts, then Voltage of the array will be around 38 volts (cold array) to around 0.8*38= 30.4 volts (full current from very hot array). If the array is not supplying less current to no current, the array voltage will rise to Voc (voltage open circuit).

The way a MPPT works is it tries to run the array at Vmp and Imp (Vmp*Imp=Pmp). And the output current/voltage is set to what the battery needs. For example:

• 37.2 volts * 1.1 Amps = 40.9 Watts from solar array

And to the battery bank:

• 40.9 Watts / 14.4 volt battery bank = 2.84 amps to battery bank

The charge controller numbers are close (there should be ~3-5% losses), and many times, they simply use the math to figure out the other numbers (i.e., Vbatt*Ibatt*1/Vpanel=Ipanel).

Anyway, more or less,   if your battery bank voltage is at 14.4 volts, it should be charging. If the battery voltage is >12.8 volts, it is not discharging.

If the battery bank is less than 12.8 volts it is being discharged (or "resting" if there are no load currents).

Solar panels rarely output their rated voltage (panels are cold, full sun pointed at sun for STD ratings). Vmp (and Voc) of the array is temperature sensitive (as temperature of the panel rises, Vmp-array falls). More or less, the typical maximum output of a solar array is ~77% of the STD rating of the panels. For example:

• 200 Watts * 0.77 panel+controller deratings = 154 Watts typical maximum power available to charge battery bank on a warm to hot day
  
• 154 Watts typical maximum / 12.8 volts battery = 12.0 amps (discharged battery bank with full available solar power, contoller in bulk mode)
  
• 154 Watts typical maximum / 14.4 volts battery = 10.7 amps (battery >80%-90% state of charge, controller in absorb mode, maximum available charging current).

Assuming warm to hot panels, pointing within ~10 degrees of sun (Cosine 10 degrees = 0.98 ~ 98% of available solar energy).

Note that electrical loads should draw energy directly from the charge controller... I.e., if you have 10.7 amps available and an 8 amp load, that leaves 2.7 amps available to charge the battery bank.

200 Watts is not a lot of energy to run a refrigerator... For example, say your fridge runs at 8 amps @ 12 volts and 50% duty cycle. Then the load would be:

• 8 amps * 12 volts * 0.50 duty cycle * 24 hours per day = 1,152 Watt*Hours per day
• 1,152 WH per day * 1/0.61 typical off grid DC system eff * 1/200 Watts STD of panels = 9.4 hours of Sun needed per day...

For many areas, ~5-6 hours per day is doing very well. Your solar array is probably not enough to carry the Refer load by itself. Add any shading (lines, sails, masts, the panels are not facing the sun directly, etc.) that shade the array (even a little shading can cut the array output by 50% or more), and it becomes even more difficult.

-Bill

littleharbor2

  Your MT50 has 3 sets of numbers on the main screen. The one on the left is what's coming in from your panels, volts and amps. The center is what's going into your batteries after your MPPT controller does its thing. If you have series wired your panels the voltage into the controller should be in the 35 to 36 volt range at whatever the amperage the panels are rated at.  The voltage out will be whatever the battery will accept when bulk charging and the amperage will be whatever the wattage available is divided by the voltage it is charging at, roughly double the input in this case.. You should see higher amperage and lower voltage in the center set of numbers. The exception here is when your battery is nearly full the amperage accepted by the battery will be minimal.
 I hope this makes sense to you. I may have, not so eloquently,  added too many words in my attempt to describe this.

Estragon

Assuming panels are mounted flat over the bimini with no shadows from backstay etc., using pvwatts.nrel.gov comes up with about 5 1/2 hours of full sun equivalent. With wire and controller losses, that would be something like 1kw of average daily production.

Using the generator may be unavoidable. An efficient way to do so would be to run it for an hour or two in the morning to get the bank up to about 75% full (~14.4V), then let the solar finish charging while carrying the fridge load.

redunculous

littleharbor2 said:

  Your MT50 has 3 sets of numbers on the main screen. The one on the left is what's coming in from your panels, volts and amps. The center is what's going into your batteries after your MPPT controller does its thing. If you have series wired your panels the voltage into the controller should be in the 35 to 36 volt range at whatever the amperage the panels are rated at.  The voltage out will be whatever the battery will accept when bulk charging and the amperage will be whatever the wattage available is divided by the voltage it is charging at, roughly double the input in this case.. You should see higher amperage and lower voltage in the center set of numbers. The exception here is when your battery is nearly full the amperage accepted by the battery will be minimal.
 I hope this makes sense to you. I may have, not so eloquently,  added too many words in my attempt to describe this.

Ok, now this makes sense. I have been stumped on the output as it didn't seem right (I always thought the left was the total amps to the batteries) and I didn't get an answer to my initial question (unless I missed it). So that info regarding the main screen makes me feel better, we just kicked off our battery charger and adjusted the thermostats on our fridge and freezer to get them working. The remote now shows us

34.8v and 2.9 amps on the left
13.8v and 7.1 amps in the centre
Far right 13.8v and 0.1amps to the right (we have nothing attached to the load part of the MPPT)

It did bump up to over 10amps in the center at one point when the thermostats initially kicked in.

So I would hazard a guess and say we have a pretty efficient system (or am I a complete idiot) considering we are able to get over 10amps on occasion to our batteries at 13.8v - we have seen it over 10amps pretty regularly when we were anchored. 

Estragon, I think if we can increase the insulation to stop them kicking in so often as well as educating ourselves that we should really only open them when we know what we want rather than staring inside the fridge we may get down to running it once a day - currently we run it in the morning then in the night before bed. Luckily we only have a little Honda EU2000 on board and it seems to sip gas.

Estragon

I have the same honda at the cabin, and for the boat. As well as being easy on gas, I also like that it's relatively quiet as generators go.

Another thing that helps is if you're putting warm stuff in the fridge, do it while the genny is charging so it cools down and the fridge runs before running off batteries.

eugenesan

> @redunculous said:
> I cannot seem to find this in the remote Manual but can anyone tell me what the reading is below the battery image? I have an MT50 and it's showing 1.1 under solar panels, 2.9 under battery?
>
> On that note, if 1.1 is my current amp input from the panels it seems quite low for 2 x 100 watt wired in series? Suns out in force here in Florida right now - have I done something wrong?

I've browsed through the thread but could not find a link to the manual, so here is it: http://www.epsolarpv.com/en/index.php/Product/pro_content/id/484/am_id/139

littleharbor2

 A picture would help. When your battery is above about 80% charged and at the preset absorb voltage, your controller should transition into a  absorb charging mode, the amperage being accepted by the battery will slowly decrease until full at which time your controller goes into float charging mode. If you were to put a load onto the system your incoming amperage from your array should rise.