Multiple MPPTS on same solar array?

[justinm001]

How exactly do MPPTs work?

So I have an enclosed trailer I sometimes take behind my RV and other times its just sitting around my house. I added 1000w solar to its roof and likely will put another 600-1000 more. Inside the trailer is just a SLA 100ah battery for lights and tongue jack but will be adding a 1000w little inverter to charge drill batteries and other small devices. Ideally I'd have 2 MPPTs on the solar array where one converts the solar to 12V for the trailer and the other converts it to 48v to charge the RV huge system when attached. Is this at all possible?

The option I'm planning on now is just to have 2 separate MPPTS and move the solar from one to the other but that means when attached and parked the solar would be going to the RV.

 

[robby]

No, two MPPTs will not work on one Solar array.
The simplest option is to use one MPPT for the 48V system and then convert some of the 48V using a DC-DC converter to 12V for the other system.

 

[sunshine_eggo]

MPPTS on the same array will fight each other continually trying to find the maximum power point.

 

[justinm001]

MPPTS on the same array will fight each other continually trying to find the maximum power point.

wouldn't they find the same max power point or at least very similar? What about a mppt and a pwm? any other way I can pull some power sometimes from the solar while giving the rest to a main mppt?

 

[justinm001]

No, two MPPTs will not work on one Solar array.
The simplest option is to use one MPPT for the 48V system and then convert some of the 48V using a DC-DC converter to 12V for the other system.

Yeah but that means a wire from trailer to RV then a 2nd pair from RV to trailer. Also when the RV isn't connected then there's no 48v system

 

[LakeHouse]

wouldn't they find the same max power point or at least very similar?

No, they don't find any sort of stable equilibrium. They both constantly try to adjust until one ends up in an error state and disconnects itself (or maybe releases the magic smoke).

What about a mppt and a pwm?

I can't say for sure that this wouldn't work, but I suspect it would still be problematic. Others may have better insight on this. One potential problem is that the PWM has to be sized for the power of the entire array because you can't overpanel a PWM, and you can't rely on the MPPT drawing any power if, for example, the battery is full.

Yeah but that means a wire from trailer to RV then a 2nd pair from RV to trailer.

The wires don't care what direction power is flowing. So if you had a single MPPT in the trailer with wiring to the 48V system, you could connect your DC-DC charger to that same wiring in the trailer.

Also when the RV isn't connected then there's no 48v system

Maybe I'm misunderstanding what you're trying to do, but it seems like this is the case either way.

 

[sunshine_eggo]

wouldn't they find the same max power point or at least very similar? What about a mppt and a pwm? any other way I can pull some power sometimes from the solar while giving the rest to a main mppt?

No and no.

PWM requires the array be same as battery, 12V, 24V or 48V on the PV side and works by shorting the array to the battery.

The action of one MPPT throws off the other. They're not holding hands and skipping along. They're independent of each even if in a VE.Smart network.

 

[justinm001]

The wires don't care what direction power is flowing. So if you had a single MPPT in the trailer with wiring to the 48V system, you could connect your DC-DC charger to that same wiring in the trailer.

Maybe I'm misunderstanding what you're trying to do, but it seems like this is the case either way.

Solar and 12v battery on trailer. RV has 48v system so if I connected the MPPT to the 48v array in the RV I'd need to run a 2nd line to the dc-dc back to the trailer to charge the trailer battery.

Unless you're saying run the solar to mppt to 48/12DC-DC to the 12V battery then have a 2nd cable from mppt to the RV battery bank. Idk if I can have an mppt set to 48v then use a 48-12v dc-dc converter without any 48v system.

I guess I could go the other way and solar to MPPT to the 12V battery then have a 12/48 DC-DC to connect that to the RV. Seems expensive when working with 1500w+ taking from 150v to 12v to 48v.

 

[justinm001]

No and no.

PWM requires the array be same as battery, 12V, 24V or 48V on the PV side and works by shorting the array to the battery.

The action of one MPPT throws off the other. They're not holding hands and skipping along. They're independent of each even if in a VE.Smart network.

gotcha. seems like no good way to connect systems together without major losses.

 

[LakeHouse]

RV has 48v system so if I connected the MPPT to the 48v array in the RV I'd need to run a 2nd line to the dc-dc back to the trailer to charge the trailer battery.

Where do you intend to physically locate the MPPT? If it's in the trailer then you only need one set of wires to go to the RV... That wiring charges the 48V battery in the RV when the sun is shining, and can also be used to charge the 12V battery in the trailer via a DC-DC charger when the RV is connected, but regardless of the sun shining. The DC-DC charger should be in the trailer anyway, since you'll want it close to the 12V battery.

 

[justinm001]

Where do you intend to physically locate the MPPT? If it's in the trailer then you only need one set of wires to go to the RV... That wiring charges the 48V battery in the RV when the sun is shining, and can also be used to charge the 12V battery in the trailer via a DC-DC charger when the RV is connected, but regardless of the sun shining. The DC-DC charger should be in the trailer anyway, since you'll want it close to the 12V battery.

The location of the MPPT and anything else doesn't matter. But when the RV isn't connected you're saying the MPPT will go to the DC-DC 48/12 then to the trailer battery? No 48V battery at all when disconnected? This would work especially considering I think I have a 30a limit for charge rate on 12V

 

[marionw]

Just a thought...
Use a 12 vdc MPPT charge controller with a min PV input less than 48 VOC and a max PV input greater than 48 VOC. Use the 48 Volt battery as the PV input to the charge controller. Don't know what idle power draw of the charge controller would be once the 12vdc battery is fully charged, it would I expect continue to float charge the battery

 

[LakeHouse]

The location of the MPPT and anything else doesn't matter.

It does for the question of whether you need two sets of wires from the trailer to the RV. If the MPPT is in the RV you need to run PV array wire to the MPPT, and then to the RV battery, AND 48V wire from the RV back to the trailer to feed the DC-DC charger.
If the MPPT is in the RV, you run PV wire to the MPPT, then 48V wire from there to both the RV (this is the only RV connection) and to the DC-DC charger.

But when the RV isn't connected you're saying the MPPT will go to the DC-DC 48/12 then to the trailer battery? No 48V battery at all when disconnected?

This won't work without the RV connected. Your MPPT set for a 48V system probably won't function without the battery connection. It needs to see the 48V battery.

 

[LakeHouse]

Use a 12 vdc MPPT charge controller with a min PV input less than 48 VOC and a max PV input greater than 48 VOC. Use the 48 Volt battery as the PV input to the charge controller. Don't know what idle power draw of the charge controller would be once the 12vdc battery is fully charged, it would I expect continue to float charge the battery

This would work, but only when the trailer was connected to the RV. It's just using an MPPT to take the place of a DC-DC charger, which isn't a bad idea. Idle power draw for MPPT controllers is very small.

 

[justinm001]

It does for the question of whether you need two sets of wires from the trailer to the RV. If the MPPT is in the RV you need to run PV array wire to the MPPT, and then to the RV battery, AND 48V wire from the RV back to the trailer to feed the DC-DC charger.
If the MPPT is in the RV, you run PV wire to the MPPT, then 48V wire from there to both the RV (this is the only RV connection) and to the DC-DC charger.

This won't work without the RV connected. Your MPPT set for a 48V system probably won't function without the battery connection. It needs to see the 48V battery.

I mean idc where the MPPT is at can be either or both.
This is what I'm saying, the DC-DC doesn't fix my need to charge the trailer without the RV and it'll require 2 pairs of cables.

It seems only/best option is to have 2 mppts, one for the 12v and one for the RV, have an anderson plug and swap from 12V to 48V mppt if connected to RV or not.

 

[wme]

If you unplug the 48v battery from the SSC you will need to unplug the solar panels from the SSC. Remember the drill is to hook up the SSC to the batteries BEFORE you hook up the solar.
Put the solar panels on the RV with the 48v MPPT. Put a 100w panel on the trailer with a 12v 10 amp MPPT.

 

[justinm001]

If you unplug the 48v battery from the SSC you will need to unplug the solar panels from the SSC. Remember the drill is to hook up the SSC to the batteries BEFORE you hook up the solar.
Put the solar panels on the RV with the 48v MPPT. Put a 100w panel on the trailer with a 12v 10 amp MPPT.

Plan is to cover both the RV and trailer in panels. I was thinking the same with a 100w panel but doesn't make much sense as the trailer will rarely need power and thats a 100w panel wasted if the trailer battery is full and I'm boondocking.