Supplemental MPPT Sizing Question

[Swamplizard]

Conversion Van project has 3x100Watt in series on drivers side and identical setup on passenger side (separate series for when I have a kayak on one side of the roof).

Having a LOT of MPPT reliability issues with LV2424 and it eats a lot at idle so looking for a supplemental MPPT to feed the 24-volt 280AH LIFEPO4 bank for when I have the LV2424 turned off (Like when Van is being stored outside but not being used).

Question #1: Can I simply add an MPPT and move the solar inputs over when needed?
Question #2: If I have a Positive and Negative Bus to which I would connect the MPPT PV inputs AND the LV2424 PV inputs can both the LV2424 and an MPPT be active at the same time or will it fry something? (There is a 100Amp breaker on each solar positive cable which can be easily flipped manually). I keep reading that the MPPT controls the PV and two cooks in one kitchen doesnt sound like it would work....then again, this is not what I do.
Question #3: On a sunny Florida day I see nearly 60 volts from a single side (3x100Watt solar panels in series) but of course the Amps are less than 6Amps. Would a 100/40 MPPT handle this?

Thanks for the inputs Guys/Gals, I don't do this for a living so the documentation isnt make it clear enough for me.

Cheers!

Swampy

 

[FilterGuy]

Question #1: Can I simply add an MPPT and move the solar inputs over when needed?

Yes

Question #2: If I have a Positive and Negative Bus to which I would connect the MPPT PV inputs AND the LV2424 PV inputs can both the LV2424 and an MPPT be active at the same time or will it fry something? (There is a 100Amp breaker on each solar positive cable which can be easily flipped manually). I keep reading that the MPPT controls the PV and two cooks in one kitchen doesnt sound like it would work....then again, this is not what I do.

If I understand the question, you want to hook the same panels to two different controllers. NO this will not work well.
If you are asking if you could have some panels on the LV2424 and some panels on a separate charger then yes, it will work.
Note: If you have two different controllers, I like to get the charge profile for each as close to the same as possible.

Question #3: On a sunny Florida day I see nearly 60 volts from a single side (3x100Watt solar panels in series) but of course the Amps are less than 6Amps. Would a 100/40 MPPT handle this?

Two things to check:
Voltage: You need to check the Voc specification of the solar panels. You then need to adjust the Voc for cold temperatures. This process is explained here:

Adjusting Solar Panel Voc for temperature

When designing you solar panel system, it is important to adjust you solar panel Voc for temperature in order to ensure you do not over-voltage the PV inputs of your solar charge controller. This paper shows how to calculate the Temperature...

diysolarforum.com

Once you have the cold-adjusted Voc, multiply it by 3 and that must be lower than the Max Voltage of the MPPT. (in your case 100V)


Wattage:
The wattage of a 40A MPPT on a 24V system is 40A x 24V = 960W. That is well above the 300W of the string of panels so that is fine.

 

[Swamplizard]

Thanks FilterGuy - just wat I needed! Appreciate the time and effort.
The 100W panels are semiflexible low profile panels in series - both sides will be configured identically so I guess I could run one side to LV2424 and the other to the extra MPPT. If I combine them into MPPT only I will probably see peaks over 100v but amperage should be 2x5.95 correct?

Voltage at Pmax (Vmp)	16.80V
Current at Pmax (Imp)	5.95A
Open-circuit voltage (Voc)	20.10V

 

[FilterGuy]

Thanks FilterGuy - just wat I needed! Appreciate the time and effort.
The 100W panels are semiflexible low profile panels in series - both sides will be configured identically so I guess I could run one side to LV2424 and the other to the extra MPPT. If I combine them into MPPT only I will probably see peaks over 100v but amperage should be 2x5.95 correct?

Voltage at Pmax (Vmp)	16.80V
Current at Pmax (Imp)	5.95A
Open-circuit voltage (Voc)	20.10V

The most important parameter on almost all MPPT controllers is the input voltage. If your panel has 20.1V Voc, then 3 in series would give you 60.3V string Voc. If your controller has a max of 100V, then you would have 66% margin on the voltage. That is more than enough to cover the most extreme cold conditions.

If you want to combine all 6 panels to a single MPPT controller, you would *not* want to put them all in series. Instead, you would want to put the 2 strings of 3 series panels in parallel. This would keep the voltage to 60.3V. Since we are talking about 300W total, a single 100/40 MPPT controller should work well. In fact, even a 100/30 would handle the 600W of panels without problem.

Note: In the 100/40 designation, the 100 is PV input Voltage and the max 40 is the output current to the battery. Therefore a 100/40 controller on a 24V battery can handle 24V x 40A = 960W.

With a single string the current would be nomanally 5.95A, but the way the NEC code calculates the max you would multiply by 1.55. Therefore your wiring should assume 5.99A x 1.55 = 9.28A. With two parallel strings you would use 18.57A.

With just one or two strings in parallel, there is no need for fuses/breakers, but you should still have a disconnect and some people use breakers for a disconnect. If you use a breaker for disconnect, make it a 20A (or more) DC breaker, that way it works for either one or two strings.

 

[rmaddy]

To add more about the disconnect breaker you also need to make sure it is rated for the full Voc that it will see. I’m this case 60.3V. Many DC breakers can’t handle that much voltage. So verify the voltage and amperage of the breaker you choose.

 

[Swamplizard]

Thanks for the inputs folks - truly appreciated. Looks like a 100/30 would be ideal. It is a conversion van so I don't have room to have more than the six 100watt semi-flexibles so don't need to build for much more. They look to be about $100 but I have spent that is shipping warranty parts for my LV2424 POS already ... might be a better over-all solution to my MPP Solar tech support woes ;-)

 

[Swamplizard]

Update - found a new MPPT epever 100/30 nearby and installed it. Downloaded the software to LIFEPO4 tune it but not working. Also have the handy dandy remote screen/configuration option. On an average florida sunny day I am seeing 31-36 volts and anywhere from 1-4.5 Amps from three 100watt series panels. Does this seem about right? The panels are on a van so there is no angle and the A/C roof mounted unit can shade them a bit depending on how the van is parked relative to the sun.

Still working with MPP LV2424 tech support and trading emails with them once a week on average.....been 3.5 months without resolution!

 

[Swamplizard]

On an average florida sunny day I am seeing 31-36 volts and anywhere from 1-4.5 Amps from three 100watt series panels. Does this seem about right?

 

[Swamplizard]

Beuler? ;-)

 

[Swamplizard]

Have to vent a bit - the reason I need a "supplemental" MPPT is because my LV2424 solar has never worked....it simply doesnt see the PV inputs. Since July 12th folks in China have sent me boards to swap out and asked me to test various things. Each time I have to remove the unit from my conversion van, put it on my bench and try something....with some of their requests being as ridiculous as suggesting I move 4 pin plug cable to a 3 pin plug. This week I got this from MPP Solar Support: "Do you have another 2424LV-MSD inverter? If yes, could you separately install these boards to this unit? If this problem occurs again, it means that the board needs to be replaced." WOW! I have repeatedly asked them to send a new system and I will return ALL the parts they have sent me....do not buy from non-USA folks. Feel like I threw $700 in the trash.

 

[FilterGuy]

On an average florida sunny day I am seeing 31-36 volts and anywhere from 1-4.5 Amps from three 100watt series panels. Does this seem about right?

4.5A x 36V = 162W... roughly half the rated amount. That seems low but with the flex panels directly on the roof in the hot sun, there will definitely be a reduction in the output of the panels.

 

[12VoltInstalls]

looking for a supplemental MPPT to feed the 24-volt 280AH LIFEPO4 bank for when I have the LV2424 turned off

It sounds like it’s turned off all the time!?

I’d initiate the return ASAP and/or do whatever it takes to get your money back.
Not asking you to throw away money but order an epever post haste and report back. You’ve been chasing your tail by the sounds

 

[Swamplizard]

I picked up an Epever and works like a champ. Got this from MPP support “
We don't have this option "send a new inverter" for our warranty.

You can consider returning this unit then we repair it but you need to pay the postage twice (send it to us and we return to you).

Or we provide you a new MPPT board, PV board and control board (free) to replace and you just only pay the postage. However, these parts are out of stock, so the lead time will be at the middle of Nov”

Buy local guys ... this is a joke. FWIW we have tried all the above parts and still no joy.

 

[12VoltInstalls]

do whatever it takes to get your money back.

Credit card consumer protection

 

[Swamplizard]

MPP Support last email this week:
"Hi

We already sent two new MPPT board and a new control board. You also confirmed that the PV board was ok. We already exclude all possible cause of this issue but this issue still persists. This means that the problem doesn't result from hardware of this unit.

Please confirm whether you turned on this unit with battery before connection solar to the unit. In addition, please use a meter to measure the PV input +/- terminal voltage on the PV side."

FWIW I told them I plug the PV inputs into an epever and it works just fine....so it is NOT the solar panels or wiring. I suggested the motherboard is the next logical thing to replace....and getting no responses to emails again.....UGH!!

 

[Swamplizard]

Going to take it out - reseat everything for the 5th time, reconnect to battery, connect PV and use a meter to see where the PV power stops. Apparently I need to be an electrician to own this LV2424 LOL

 

[chrisski]

If your 2424 is goof, I think: 1) Panel input voltage is too low -or- 2) Charge settings could be off.
==================
What is the input voltage spec for the 2424? 31 volts may be too low. THis is the way many victron is worded:

“1b) The PV voltage must exceed Vbat + 5V for the controller to start.
Thereafter the minimum PV voltage is Vbat + 1V.“

If by battery voltage they mean my 24 volt battery is at 27 volts, the SCC may need 32 volts. You may need more panels in series.

I don’t run voltage that low, but depending on shade, my three 100 watt panels in series that should produce 18 -22 volts each (51 volts to 66 volts) off the sticker, read between 42 volts and 60 volts depending on the amount of sunshine and shade. One panel shaded plunges both the wattage and total voltage of the string.
===================
For your earlier question about how much energy is pulled from the panels, I set my 50 ah bank to 27.4 charge and 26.7 float. When I do that, I have found that once the bulk and absorption phase is done, if I set my float lower, the SCC won‘t keep up with power out.

What are your charge settings.

 

[Swamplizard]

Thanks Chris - my LV24 is set at 28 v charge and 27v float. I routinely see above 35v even when cloudy or morning with low sun. At noon I see over 50v. Input voltage spec for theLV2424 is up to 100v and 50Amps (I think) not sure what else it needs. So if battery hovers around 27v and I add 5 I would need 32.

Out of sheer frustration I picked up a 100v/50A Epever and it works like a champ charging batteries with 100watts on average at noon (more soon when I unshade a part of one of the panels in the string).

 

[Swamplizard]

Update - fifth try is a winner! They sent me a third MPPT board and finally the solar works on my LV2424. Took six months and five daughter boards but we are back in business!