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Can you use two MPPT controllers with a total charging amp higher than the battery?

Riley

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Hi Folks, It turns out my RV could only fit seven panels. I am thinking about putting six panels on a 150-100A MPPT and one panel on a 100-30A MPPT, but the battery can take a maximum charging rate of 100A. Is it still OK to set up like this, and will they dynamically keep its charging rate under 100A? Or should I just get a 70A and a 30A MPPT?
 
Hi Folks, It turns out my RV could only fit seven panels. I am thinking about putting six panels on a 150-100A MPPT and one panel on a 100-30A MPPT, but the battery can take a maximum charging rate of 100A.

LFP?
Battery voltage?
Panel wattage?

Is it still OK to set up like this,

Maybe.

and will they dynamically keep its charging rate under 100A?

If I understand your question, no.

Or should I just get a 70A and a 30A MPPT?

Depends on the above answers.
 
LFP?
Battery voltage?
Panel wattage?



Maybe.



If I understand your question, no.



Depends on the above answers.
Hey, It's a 4x LFP 24v 100ah battery bank. , each panel is 445w with 50V VOC.

Battery: 4x Ampere Time 24V 100Ah LiFePO4 Deep Cycle Lithium Battery, Built-in 100A BMS.
Panel: 445W 72Split-Cell Silver Mono Solar Panel by Solarever

24v * 100A is 2400w, which is already lower than solar array 6* 445 = 2670w. If I use a lower MPPT controller such as 70+30 seems it's going to make things worse.

I didn't go 48V because I want it to charge even with low lights when the voltage is lower.
 
What does ampere time state is max charger current per battery? 1c? .5c?

If you have 4 batteries you can X4 that value, that is your max charge current (minus a small % for safety).

So let’s assume .5c charge rate, that’s 200a, or 180a with some added safety.

Sounds like only using 6 panels is the better option, in a 3s2p configuration. This will keep your current down. Can the SCC support 3 panels in series for VOC standpoint?
 
Hey, It's a 4x LFP 24v 100ah battery bank. , each panel is 445w with 50V VOC.

I just realized I responded to your other thread, and I misread it as being 48V.

Battery: 4x Ampere Time 24V 100Ah LiFePO4 Deep Cycle Lithium Battery, Built-in 100A BMS.
Panel: 445W 72Split-Cell Silver Mono Solar Panel by Solarever

24v * 100A is 2400w, which is already lower than solar array 6* 445 = 2670w. If I use a lower MPPT controller such as 70+30 seems it's going to make things worse.

Down to 6, not 8?

I didn't go 48V because I want it to charge even with low lights when the voltage is lower.

You are creating a solution for a problem that doesn't exist. Wipe this concern from your mind. It's analogous to you purchasing a vehicle based on the type of headlight bulb it uses.

80Vmp vs. 120Vmp vs. 160Vmp will not have significant charging differences in low light conditions on 24V or 48V. Any difference would be a fraction of a percent.

The big improvement is MPPT vs. PWM where PWM charge controllers just short the panel to the battery and perform fairly poorly in low light conditions.

48V solves your current problem and permits your original 8 panel array in a 2S4P configuration on a single 80A controller within the BMS charge limits.

Edit: 2S3P would only require a 60A unit.
 
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I'm not 100% following the specifics of your question and setup, lets try to clarify a few things.

First:
Is it still OK to set up like this, and will they dynamically keep its charging rate under 100A? Or should I just get a 70A and a 30A MPPT?
Your solar charge controllers will have no awareness of what is considered the maximum charging rate for your batteries. If they are Victron controllers I believe you can set a maximum output current for each charge controller manually. If you were to invest in a GX device or maybe BMV possibly you would have the ability to set a maximum combined rate, I'm not sure, but its something to look into if you go down that road (neither device is cheap).

But getting back to your broader question.
You mentioned in the OP that your 'battery' has a 100A limit, but then in your second comment, you mention 4 x 24V 100Ah batteries.
It sounds like maybe you are misunderstanding the limit. If each battery has a 100A limit and the 4 batteries will be in parallel, that means that the current from your solar charge controllers will be split between the 4 batteries (in other words its a 100A limit per battery)
If I am understanding your setup correctly, I think you do not have a problem. You could use 1 x 100A and 1x 15A or 20A controller, or 2 x 60A controllers or whatever combination you like that gets you in the ballpark of 120A ( (7 x 445) / 25.6 = 122A)
 
I'm not 100% following the specifics of your question and setup, lets try to clarify a few things.

First:

Your solar charge controllers will have no awareness of what is considered the maximum charging rate for your batteries. If they are Victron controllers I believe you can set a maximum output current for each charge controller manually.

You can.

If you were to invest in a GX device or maybe BMV possibly you would have the ability to set a maximum combined rate, I'm not sure, but its something to look into if you go down that road (neither device is cheap).

The GX permits this, and you'll need the BMV as well for the current measurement, but the BMV can't do it on its own. The maximum combined rate is also applied to any Victron VE.Bus connected Inverter/Charger.

Additionally, the Smartsolar units with bluetooth can be networked via the VE.Smart system to coordinate charging with each other. This basically means they share the charge load even during absorption as opposed to the typical behavior where the strongest charger finishes last.
 
I just realized I responded to your other thread, and I misread it as being 48V.



Down to 6, not 8?



You are creating a solution for a problem that doesn't exist. Wipe this concern from your mind. It's analogous to you purchasing a vehicle based on the type of headlight bulb it uses.

80Vmp vs. 120Vmp vs. 160Vmp will not have significant charging differences in low light conditions on 24V or 48V. Any difference would be a fraction of a percent.

The big improvement is MPPT vs. PWM where PWM charge controllers just short the panel to the battery and perform fairly poorly in low light conditions.

48V solves your current problem and permits your original 8 panel array in a 2S4P configuration on a single 80A controller within the BMS charge limits.

Edit: 2S3P would only require a 60A unit.
Got it! It seems I should just go 48V system, using 2S3P for six panels with a 150/60 AMP MPPT, and use a 10 AMP MPPT for the extra panel. ( I have to find something that supports 48V and is cheap). Can I mix different brands of MPPT?
 
Got it! It seems I should just go 48V system, using 2S3P for six panels with a 150/60 AMP MPPT, and use a 10 AMP MPPT for the extra panel. ( I have to find something that supports 48V and is cheap). Can I mix different brands of MPPT?

Where is the extra panel? Did I miss something?

No issues mixing MPPT brands. They just need to be correctly programmed to charge your battery, and their total current must not exceed that supported by the battery.

EDIT: I see it now. You're not likely to find a single panel that will support > 60Vmp. I wouldn't bother unless you truly need the additional wattage.
 
Where is the extra panel? Did I miss something?

No issues mixing MPPT brands. They just need to be correctly programmed to charge your battery, and their total current must not exceed that supported by the battery.

EDIT: I see it now. You're not likely to find a single panel that will support > 60Vmp. I wouldn't bother unless you truly need the additional wattage.

I see. That's another issue with the 48V system. my extra panel will not be helpful with its voltage.

I would have 2670w with six panels on my 27 FT RV in California. I plan to use it full-time and only one person. I need a run mini-split, laptop, microwave, fridge, cooktop, water heater, and other common living appliances. I will add some extra insulation with XPS Foam, but it's not going to be very strong insulation like a house given the thickness of the RV wall. Do you think 2670w was sufficient, or should I try to mount more panels?

The RV is 27x8FT which should fit eight panels and gives me 3560w. But my contractor does not want to mount the 8th panel to the very front because it's going beyond over-cab(it's a class C), so it blocks the running light, and there will be too much wind going under the solar panel.
 
I see. That's another issue with the 48V system. my extra panel will not be helpful with its voltage.

I would have 2670w with six panels on my 27 FT RV in California. I plan to use it full-time and only one person. I need a run mini-split, laptop, microwave, fridge, cooktop, water heater, and other common living appliances. I will add some extra insulation with XPS Foam, but it's not going to be very strong insulation like a house given the thickness of the RV wall. Do you think 2670w was sufficient, or should I try to mount more panels?

Please tell me you have a compressor fridge. If its a propane/AC absorption fridge, it will destroy you. On AC, a 7.6cu-ft typical RV fridge will eat 5-6kWh/day.

If you haven't already, you need to do an energy audit. List all your loads, their power, and how long you want to use them. There's a spreadsheet in Resources to help you with an energy audit.

Flat panels on an RV roof will only harvest about 40% in the winter compared to summer output. If you have a typical area you'll be "camped" in, you should use PVWatts or http://www.solarelectricityhandbook.com/solar-irradiance.html to see how much daily sun is available by month and plan accordingly.

Given that you're committing to full time use, you really need to do this planning. You may find that it doesn't matter how much solar you have, your winter power needs may exceed your solar, and you'll have to use propane, run a generator and/or deploy a lightweight ground array for the lean times.

The RV is 27x8FT which should fit eight panels and gives me 3560w. But my contractor does not want to mount the 8th panel to the very front because it's going beyond over-cab(it's a class C), so it blocks the running light, and there will be too much wind going under the solar panel.

Could you sprinkle 4X 100W panels in the gaps? 4S 100W would give you ~72V and would work nicely on a second controller.
 
Please tell me you have a compressor fridge. If its a propane/AC absorption fridge, it will destroy you. On AC, a 7.6cu-ft typical RV fridge will eat 5-6kWh/day.

If you haven't already, you need to do an energy audit. List all your loads, their power, and how long you want to use them. There's a spreadsheet in Resources to help you with an energy audit.

Flat panels on an RV roof will only harvest about 40% in the winter compared to summer output. If you have a typical area you'll be "camped" in, you should use PVWatts or http://www.solarelectricityhandbook.com/solar-irradiance.html to see how much daily sun is available by month and plan accordingly.

Given that you're committing to full time use, you really need to do this planning. You may find that it doesn't matter how much solar you have, your winter power needs may exceed your solar, and you'll have to use propane, run a generator and/or deploy a lightweight ground array for the lean times.



Could you sprinkle 4X 100W panels in the gaps? 4S 100W would give you ~72V and would work nicely on a second controller.
I see. It seems I barely have enough power in winter. Thank you so much!
 
You might want to have a look at the Electrodacus SBMS0.

 
You might want to have a look at the Electrodacus SBMS0.


Why are you making this recommendation? Do you actually understand the product and it's limitations and how it would eliminate his choice of panels?
 
I see. It seems I barely have enough power in winter. Thank you so much!

Dude... I gotta know... do you have an absorption fridge? If so, here's my solution:

Use a programmable wifi plug. Put the fridge in auto mode and cycle the plug on to run it for ~8 hours/day on AC when you actually have solar and then have it switch over to propane when the switch cuts off. This will cut you down to about 2kWh/day of AC. In this fashion, I've had a 30# propane bottle last about a month. Here's what mine looks like:

1638635331725.png

You can see when the fridge turns on and off and how it remains off at night. The BIG spike is the water heater. I turn it on for a couple of hours per day to make sure the tank doesn't freeze overnight.

The better solution is to replace the fridge with a 24" residential unit OR replace your absorption cooling unit with a 12V unit from https://jc-refrigeration.com/. Personally, I would prefer the residential fridge option because you gain a lot of storage volume in the back, i.e., you can typically fit a 10cu-ft residential fridge in the hole a 7.6cu-ft absorption fridge is installed.
 
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I would have 2670w with six panels on my 27 FT RV in California. I plan to use it full-time and only one person. I need a run mini-split, laptop, microwave, fridge, cooktop, water heater, and other common living appliances. I will add some extra insulation with XPS Foam, but it's not going to be very strong insulation like a house given the thickness of the RV wall. Do you think 2670w was sufficient, or should I try to mount more panels?

I have 640 watts of PV on my RV roof and 640 watts on the ground. So less than half what you have. My current inverter isn't enough to run the microwave, but otherwise my PV and 560 Ah of LiFePO4 is enough to run my trailer for a long time with no worries. But I have retained the propane appliances, which greatly reduces the electric load. The propane water heater is very efficient, it doesn't even have an AC option. If you're trying to run everything off the electric then you're going to need a very large PV and battery system. Propane is just so much more efficient. In moderate weather, I can camp for at least three weeks on two 30 lb tanks of propane. Winter is a different story and I bring extra tanks.
 
Dude... I gotta know... do you have an absorption fridge? If so, here's my solution:

Use a programmable wifi plug. Put the fridge in auto mode and cycle the plug on to run it for ~8 hours/day on AC when you actually have solar and then have it switch over to propane when the switch cuts off. This will cut you down to about 2kWh/day of AC. In this fashion, I've had a 30# propane bottle last about a month. Here's what mine looks like:

View attachment 74492

You can see when the fridge turns on and off and how it remains off at night. The BIG spike is the water heater. I turn it on for a couple of hours per day to make sure the tank doesn't freeze overnight.

The better solution is to replace the fridge with a 24" residential unit OR replace your absorption cooling unit with a 12V unit from https://jc-refrigeration.com/. Personally, I would prefer the residential fridge option because you gain a lot of storage volume in the back, i.e., you can typically fit a 10cu-ft residential fridge in the hole a 7.6cu-ft absorption fridge is installed.
Hi, I have a small residential freezer, "Whynter CUF-301SS Upright Freezer, 3 Cubic Feet, Stainless Steel", it's an energy star and rated for 79 watts running. I think the biggest factor is mini-split; this freezer is so tiny.
 
I have 640 watts of PV on my RV roof and 640 watts on the ground. So less than half what you have. My current inverter isn't enough to run the microwave, but otherwise my PV and 560 Ah of LiFePO4 is enough to run my trailer for a long time with no worries. But I have retained the propane appliances, which greatly reduces the electric load. The propane water heater is very efficient, it doesn't even have an AC option. If you're trying to run everything off the electric then you're going to need a very large PV and battery system. Propane is just so much more efficient. In moderate weather, I can camp for at least three weeks on two 30 lb tanks of propane. Winter is a different story and I bring extra tanks.
Not sure how do you keep the room cool? In South California, I would need my heater inside my house in winter, and my RV is at 100F under the sun. I felt I would need ~4kwh every day just for a mini-split.
 
Hi, I have a small residential freezer, "Whynter CUF-301SS Upright Freezer, 3 Cubic Feet, Stainless Steel", it's an energy star and rated for 79 watts running. I think the biggest factor is mini-split; this freezer is so tiny.

Okay. That probably doesn't use much compared to the RV fridge.

Mini-split for both heat and cool or just cool?
 
Okay. That probably doesn't use much compared to the RV fridge.

Mini-split for both heat and cool or just cool?

The goal is to have as little maintenance as possible, so I won't want to add propane to my RV constantly. The built-in tank only holds about 15 lb., so I would like to use a mini-split for both heat and cold.
 
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