Design question Cerbo/SmartSolar vicinity

DIY
,
1

The SmartSolars seem to get hot. The Cerbo will be about 10-15cm below the SmartSolar 250/70.

Is it advisable to place the SmartSolar higher and accept slightly longer cables to the battery bus? Or will the heat of the SmartSolar be directed up and not really bother the Cerbo?

This is a fixed installation and in a well ventilated area with room temperatures reaching a maximum of 30 degrees C in summer.

Screenshot 2025-01-22 at 11.14.08
Screenshot 2025-01-22 at 11.14.081178×1384 119 KB

2

This…
Although an additional 5-10 cm of cables will not hurt either if the MPPT is reaching 60-70 degrees.

3

If the SmartSolar is getting hot ;

  • They are designed to be able to handle being hot, and will slow their charge rate down automatically (“derate”) if they get too hot
  • You can help the SmartSolar by mounting it the way it is in your diagram, i.e. with the rear fins vertical so that natural convection helps to cool the heat sink on the back, and with room below and above so that air flow is not impeded.
  • If you want even more cooling, you can mount a 12v fan below or behind that moves air past the heat sink faster. For fancy points, add a thermostat that turns the fan on/off.
  • You can derate the SmartSolar yourself - on a day when its cranking, measure the temperature with some kind of repeatable measuring device. Then open VictronConnect, Settings, change the Max Charge Rate from the default (70) down to something like 64, wait about 5 minutes, and check the temperature again. Then change down to say 58A and measure again, now you can graph the current vs temperature and from the resulting curve you can reduce the temperature to whatever you feel is a comfortable temp.
  • for the most amount of fake internet points, use NodeRed on the Cerbo to pull temp details from the SmartSolar, then control one of the MultiPlus relays which turns on the fan and use a voltage divider to drop the 48v battery voltage to 12v, then post pics on the “Show Us Your System” topic.
1 Like
4

I’ll follow both advices :slight_smile:
MPPT goes a little higher on the wall and I’ll derate the charging Amps to the batteries if I notice the device will get too hot for comfort. I realise they’re designed and tested to be hot, so not too worried about that. Lower Amps charging shouldn’t be a big problem as we have lots of sun here.

I’ll think about the fan. A 48V option is also available:

I could 3D print a duct to force the air to the bottom of the MPPT to help with airflow.

5

Awesome.

One thing to note about the perceived loss of energy capture when you derate a controller;

On a solar farm, selling to the grid, the goal is to capture as much energy as possible. Every watt of energy that could be captured that is not captured, such as a maintenance shutdown in the middle of the solar day, is an opportunity lost and costs you potential earnings.

On an offgrid system, the goal is not to capture as much energy as possible, but to;

  • provide for all the appliances that you might want to run
  • plus get the battery full by EOD.
  • run all night without getting too low (which would impact on long term battery life)

So offgrid, it makes no difference at all if your battery is full by 10am, or 2pm, or 1 minute before sunset. In fact, you are reducing the long term health of the battery if you choose to charge at 100A when you could easily get the battery charged at 80A or 60A.

We have a solar calculator on our website that does a bunch of fancy math, and uses about 10 years of historic actual NZ solar data collected from real solar instruments by NZ’s research agency NIWA. Its a fantastic resource for solar design and planning.
When looking at a year of this data for designing our customer’s systems, it turns out that when modelling a particular array, battery, and load, you will often find that either zero, or only a handful of days of the year, are in the category of “battery would be full by EOD if charged at X (the max for a particular MPPT), but won’t be full by EOD if we reduce the charge rate”. If you look at the next day’s data, and its a good day, that day that was a problem is no longer a problem - ie the battery started 1 night at less than 100%, but didn’t go too low overnight, and the next day got to 100%. Most days in winter, if there is going to be a problem it is that the array could not bring in enough energy due to overcast weather , NOT that the array could, but the controller couldn’t.
This pattern often stays in play all year - the controller is limited by overcast weather, and never gets near “Max Charge Rate”.

The ONE situation it can occur is a terrible day where the overcast weather limits the battery charge, but you get a very small window of clear sun for say 2h. At this point, your MPPT is “current limited” IF and ONLY IF the array is overpanelled, the sky allows the array to exceed the MPPT’s max array wattage, AND the battery is not already full.

So in almost EVERY case, reducing say a 100/30 from 30A to 26A, in an offgrid situation, will not make a difference to the number of days that the battery isn’t at 100% by EOD.

One installer compared it to boy-racers having a pissing contest about who’s car gets them to their destination faster, when they both spend 99% of their time in traffic jams, and the other 1% is driving to their court appearances.

1 Like