Hi, at present I have two, 12 V panels connected in parallel, and one victron mppt controller, which is networked with a victron smart shunt. Now, I believe I am going to exceed the current rating of the mppt in summer. Hence, can I connect two mppt controllers to the existing 12v panels keeping them connected in parallel as they are now (very simple wiring change, down in mppt/battery compartment), or do I have to separate the panels and have one mppt per panel (much mote wiring required)? Note, i would like to keep the panels in parallel for shading reasons. I apologise if this is a stupid question. Thanks.
No, this is not recommended. Unless the MPPT’s are set up as Master and slave, and networked, the MPPT units will fight each other.
Better to connect your solar panels in series - if you would exceed the max input current by having them in parallel.
If it’s just the output current that would be exceeded - not to worry too much, as this is self regulating.
If you have shading issues, then use on mppt per module, or remove the issue.
Hi Mike, thanks for your reply. Much appreciated.
The system is in an rv and i go camping all the time in the bush. Shading can’t be avoided a lot of the time, so I prefer not to go the series route. Also, running a separate set of cables through the roof and wall of the van to have an mppt unit per pv panel is not practical for me. So for me, the best two options are
- Leave it as it is and don’t worry about losing some power in the middle of summer.
- Try the master and slave option, with the networking and a smart shunt.
It does not really matter to me if it doesnt work, as i can give the second mppt unit to a mate. But I would like to try it, provided there is no chance of me releasing the dreaded smoke from any electrical components.
Can I be so bold as to assume that someone has actually tried the two mppts on the one 12 V panel?
Thanks Russell.
What I am intrigued about is how the units would attempt to share to current from the common feed in. So to finish this off, is there any chance of damaging anything with this approach, of course assuming that everything is wired correctly in the first place. Thanks again.
best option is to buy a higher power MPPT unit and sell or donate the smaller one.
Panels in series: if one is shaded, there are bypass diodes that allow the second module to carry on producing power, often there are 2 sections and diodes per module, so you get 1/2 power if it’s half shaded. this does not happen if modules are in parallel.
2 MPPT’s on a common source: If these are unsynchronised, then as one module searches for it’s max power point, it ‘upsets the other MPPT by changing the available power from the module(s). If they are synchronised as a master/slave pair (Victron units can be set up to do this) then the MPPT points track, and the units share the power equally. For 2 unsynchronised MPPT’s, it is unlikely that damage would occur IF the max voltage and current from the PV modules is within the rating of each individual mppt.
Conclusion: Series wire the PV modules, and upgrade the MPPT.
Can you clarify if you are going to exceed the input current limit or the output current limit as these can be different, also as the PV voltage is higher than the battery voltage, output current is higher than input current. Exceeding the input current limit can result in damage so check the panels short circuit current against the input current limit spec and double this for 2 panels in parallel. If the set up can exceed the output current limit that is not an issue and the unit will only pass the rated current. This is called over panelling and is often done and if you are only 30% over then there may not be much extra yield over a day with extra MPPT capacity. As you include no details we can not tell.