How to choose MPPT size

[noelex 77]

Originally Posted by Canibul

So, I got two 65's and a 120 watt for a total of 250 watts on one controller, which can be some quality PWM for more than 16 amps, and four times 120 for a total of 480 watts on the other controller, which needs to be a high end MPPT that can handle something greater than 20 amps. Correct?

No the controllers are normally rated by the maximium current they can input, or output (whichever is greater). So the 480w will be converted to the battery voltage by the MPPT controller. At a nominal 12v this is 40A.

The maximium input voltage is also important. If you have installed thick enough wiring this only needs to be 30v (For parallel connection). If your wiring is thin and you need to minimise the power loss in the wiring 4x30= 120v for series, (or 60 v for series/parallel). It is important to have some leeway with the voltage as the controllers will often be instantly damaged by slight over voltage, so make sure the controller is rated above these voltages by a reasonable safety margin (at least 10%). (Please remember high voltage AC, or DC voltages can kill especially in a wet environment. Parallel connection keeps the voltage below the lethal level)

The PWM controller is unlikely to see over 15A. The controllers normally self protect(check) if over current so a 15 A model is OK and is often cheaper than a 20A version.

Consider possible future expansion of more panels when buying the regulators.

[steelwrk1]

Hello All,

I too wish to know what size MPPT controller I can use and what you would recomend. I am awaiting a quote from a local professional but the boat applications here are almost nil.

Please see below and tell me what you would do.

I am able to trade off stuff I have for the wire I will need so for my purpose the cost of the wire is nil. At this time I can run as much wire as I need and want to keep the Mppt controllers identical .

Thank you for your time, I will be more educated when I am presented with options from the local vender/professional.

Best Regards,
Pete

some of the below I have copied from other posts and emails to put it all in one place



Had a solar professional visit the boat morning before shrink wrap and am waiting for wire sizing recomendations as well as MPPT controllers recomendation and I will post these here( 3 recomended due to different shading and locations). When measured my runs are 57 feet from the 3 tiltable Set # 1 ,215 watt set and 52 feet from the two sets , # 3 & 4, of 245 watt pannels to the Mppt controllers ....then a max of 13 feet with a heavy wire from the MPPT controllers to the 84 only 60 amp 12 volt , total 1260 amp LiFePO4 house battery bank .
-----------------------------------------------------------------------------------

MPPT # 1

3 SOLAR PANELS

3 ONLY KYOCERA 215 watt model # KD215GX-LFBS... LOCATED AFT AT LOWER DECK LEVEL...59" X 39"
VPMAX= 26.6 VOLTS...IPMAX=8.09.....VOC= 33.2 VOLTS.......ISC=8.78....SERIAL # 122SKMO753
NOTE; ONE I HAVE ALREADY BOUGHT.... 2 MORE I HAVE TO BUY

CABLE RUN FROM PANELS TO MPPT CONTROLLER MAX ,INCL EXTRA, IS 57 FEET

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

MPPT # 2 ( # 3 identical but shaded differently)

2 SOLAR PANELS
2 ONLY KYOCERA 245 watt model # KD245GX-LFB2...LOCATED UPPER RADAR LEVEL AFT 65.43" X 38.98" ( 65.5" X 39")
VPMAX= 29.8 VOLTS...IPMAX=8.23.....VOC= 36.9 VOLTS.......ISC=8.91....SERIAL # ??????????
NOTE; I HAVE TO BUY THESE
CABLE RUN FROM PANELS TO MPPT CONTROLLER MAX ,INCL EXTRA, IS 55 FEET

------------------------------------------
MPPT # 3


2 SOLAR PANELS
2 ONLY KYOCERA 245 watt model # KD245GX-LFB2...LOCATED UPPER RADAR LEVEL AFT 65.43" X 38.98" ( 65.5" X 39")
VPMAX= 29.8 VOLTS...IPMAX=8.23.....VOC= 36.9 VOLTS.......ISC=8.91....SERIAL # ??????????
NOTE; I HAVE TO BUY THESE
CABLE RUN FROM PANELS TO MPPT CONTROLLER MAX ,INCL EXTRA, IS 55 FEET
---------------------------------------------------------------------------------------
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXX
SOLAR PANNEL SYSTEM SUMMARY;
Set # 1 ...3 X 215 watt ...aft (tiltable) lower
and
Set # 2 ...2 x 245 watt...radar arch level (fixed flat) forward
and
Set # 3 ...2 X 245 watt radar arch level ( fixed flat) aft .

Set # 1 will be tiltable if required for performance.

TOTAL 3 PANELS 215 WATT ( 645 WATTS )
TOTAL 4 PANELS 245 WATT ( 980 WATTS)
...........................TOTAL SYSTEM 1625 WATTS

[Canibul]

Originally Posted by noelex 77

No the controllers are normally rated by the maximium current they can input, or output (whichever is greater). So the 480w will be converted to the battery voltage by the MPPT controller. At a nominal 12v this is 40A.

The maximium input voltage is also important. If you have installed thick enough wiring this only needs to be 30v (For parallel connection). If your wiring is thin and you need to minimise the power loss in the wiring 4x30= 120v for series, (or 60 v for series/parallel). It is important to have some leeway with the voltage as the controllers will often be instantly damaged by slight over voltage, so make sure the controller is rated above these voltages by a reasonable safety margin (at least 10%). (Please remember high voltage AC, or DC voltages can kill especially in a wet environment. Parallel connection keeps the voltage below the lethal level)

The PWM controller is unlikely to see over 15A. The controllers normally self protect(check) if over current so a 15 A model is OK and is often cheaper than a 20A version.

Consider possible future expansion of more panels when buying the regulators.

So, a Morningstar Tristar TS-MPPT-45 and one of their Sunsaver 20-L PWMs would take care of everything I need to do, if I understand this right. The MPPT's 45 amp capability would allow me to put one more panel in that blank spot on my hard top if I ever want to buy another panel. And the PWM can handle what I have now and also accommodate my thoughts on adding a battery to the bow of my boat to eventually run an electric windlass. It seems to me that putting a battery up there near the windlass in the anchor locker and charging it from the other battery bank makes a lot more sense than running windlass battery leads the length of the boat.

[Canibul]

Based upon what I learned here, I've now removed the six amorphous Harbor Freight panels, and installed a new Outback FM60 MPPT for the decent panels. They were installed wired in parallel and I decided to leave it that way for now. I didn't really want to cut into the splices etc.

I installed a new Morningstar 25 amp PWM for the mismatched solar panels.

I'm amazed to watch the numbers on the display of the FM60. There's a world of stuff going on in there. I switched on the freezer mongo-compressor today, it draws 30 amps , and watched the Outback putting 20.8 back into the battery pack by itself. I wasn't monitoring the PWM or the wind, but I think it would have kept up with the compressor load all together. Normally I wouldn't do that. I would only run the big compressor when both engines were on and both 80 amp alternators on line.

Anyhow, I just wanted to say thanks to everyone who took the time to answer my newbie questions. The education I got on this forum gave me the confidence to order and import, sight unseen, a thousand bucks worth of controllers, wires, switches, circuit breakers etc. and install them myself.

I shut the shore power battery charger off two days ago.