Customer: Tellus
Project name: MPPT – Street lamp with Solar tracker to charge batteries
QTTY: 10k pieces / year (ramp up)
SOP: 2Q2107
The design is based on the SM3320-BATT-EV: http://www.ti.com/tool/SM3320-BATT-EV
At the moment we are facing 3 problems:
- Panel mode problem
PV panel voltage Vmpp is 30V and Impp is 8.5A. Battery voltage is 24V. It means there are times when the SM72442 enters in Panel-Mode, which means it turns off the H bridge. In this case, our design will stop charging because there is no circuit for Panel-Mode charging.
Is there a way to avoid this?
I’ve noticed that the controller SM72445 has the option to use the H-bridge in Panel-Mode. What are the changes I have to do in order to replace the SM72442 by the SM72445?
- H-bridge Mosfets problem
Too many times there have been units with defective H-bridge Mosfets. Sometimes they are totally short-circuited and other times they have just low resistance between Gate and Source.
We are using isolated Mosfest, so we changed the original part number to PSMN9R5-100XS.
Mosfets are usually damaged in pairs: buck-side pair, boost-side pair or both pairs.
Sometimes the D200 diode in parallel with the low-side buck Mosfet blows with smoke.
What is the cause of these problems?
- High current problem
We have added a fuse on the battery side to avoid reverse polarity connections. Its value is 15A.
Sometimes, when the PV panel is charging the batteries, there is a high-pitch noise for a second and the 15A fuse blows. The fuse is replaced and the Batteries and PV panel are connected again and the system starts working again, so I assume the Mosfets are not damaged.
What could be the cause of this problem?
They are using the following batteries and battery configuration:
2*VRLA 12V in series (V = 24V)
Panasonic LC-XB12100P (12V, 100Ah, 20HR).
could you help on this? I'm not very familiar with these 2 parts.
schematic and report in attachment
thanks a lot in advance
KR
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