I’ve got two Smart Solar MPPT 75/15 chargers. Both PV inputs are connected to the same power source, which is a large 60V battery bank – yes, I know that’s not how it’s supposed to be done.
The battery outputs of both chargers are connected to the same small 24V (8S) 25Ah LFP battery.
My question is: can I also connect the load outputs of these chargers in parallel, so they can share the load current between them?
I realize an SCC isn’t really designed to work like this, but I’m using single Smart Solars like this in several locations and they’ve been working great. Basically, I’m using them as buffered power supplies for monitoring systems.
Normally, I had a 12V battery behind the Smart Solar and powered the monitoring gear directly from the load output at 12V.
This particular case is a bit different because I need additional operating voltages besides the main battery voltage. So behind the Smart Solars there will be Orion-Tr DC-DC converters generating the required voltages — in this case 12V for the recorder and 48V for powering cameras over PoE.
Without having it tried myself, i would be surprised if putting the load output in parallel would be an issue in of itself, when the battery outputs of the MPPTs are connected to the same battery bank.
However, i guess you want to put them in parallel to increase the switching current? I doubt this will work as expected. First, one of the two load output will always switch first, theres no way to synchronize them. So one will have to provide the inrush current.
Which is a seperate issue. Despite the load outputs being rated at 15A, depending on the load you wont be able to switch it on. My 75/15 failed to start a 4A compressor fridge.
Then theres also current distribution. If both load outputs are on its not guranteed that the load current will split 50/50. Most likely it will not.
What about using Orions instead of MPPTs? The 48/12 and 48/48 have an input voltage range of up to 70V. Use one of each to provide the necessary 12V and 48V without the need of an additional buffer battery or 24V stage
I’d like to use the MPPT because I can basically make it work as a buffered power supply. What do I mean by that?
Under normal conditions, when the big 60V battery is available, the MPPT will power the loads connected to its load output — let’s ignore for a moment what exactly those loads are; I’m talking about the general operating principle.
When running like this, a SmartSolar MPPT is electrically much more efficient than a regular Orion-Tr, reaching efficiencies above 98%, while the Orion is somewhere around 80%.
An additional bonus is easy load power monitoring in VictronConnect. A simple Orion-Tr won’t give me that.
On top of that, the basic SmartSolar units are dirt cheap and I always have a few on hand. An Orion with comparable power output would be much, much more expensive.
If the 60V battery supply disappears, the SmartSolar will automatically start powering the loads from the 24V battery connected to it, keeping the attached equipment running from that small battery.
Now, back to the loads. On the SmartSolar load output I’ll have Orion-Tr converters, because I need different voltages in this system than the main battery voltage — in this case 12V and 48V.
So the simplified diagram would look like this:
60V battery → SmartSolar PV in → 24V battery → SmartSolar load out → Orion-Tr 24/12-9 → DC loads
Im probably the last one to tell you that feeding a battery voltage into an MPPT doesnt work, because ive been there and done that as well.
If its important to run the 12V and 48V loads while the 60V input is not available, then i agree with your solution. Using the MPPTs gives you more insight into power and energy usage compared to simple DC/DC converters.
If thats not important, then going through a single conversion, even if only 87% efficient, will always be more efficient than going through a 97% and an 87% conversions plus charging/discharging another battery. Whatever energy you use, will come directly from the 60V battery, so you only need to worry about a single battery and its SOC
