Potting material causing abnormal behaviour

[biswaIITH]

We are building a 750 W battery charger for EV applications. Following is the brief specification.
Input voltage :- 170 to 270 V AC
Output Voltage :- 35 to 58 Vdc
Output current :- 12.5 A

To evacuate the heat we are using a potting material the datasheet of which I have attached here. During the ambient operating (25 degree) conditions, the maximum internal ambient goes upto 110 to 115 degree. Most of the critical parts are are at this elevated temp such as capacitors ,ICs etc After doing the potting & testing we are observing some abnormal behaviour during the higher ambient conditions such as current loop going out of the control & CAN communication discontinuation etc.

Can anyone suggest the suitability of the potting material selected ?

 

[KlausST]

Hi,

there are known electrical and mechanical problems:

When curing the material shrinks. It may rip SMD parts off the PCB (soldered on pad).
Thus a potting meterial for SMD part should be not become very hard. A mit of elasitcity and softness keeps force to SMD parts low.
Mind: to keep exact mixing ratio. An often used mistake to add more hardener than specified results in much harder end material.
Also increased temperature during curing makes the end material harder.

Also the dielectric constant causes stray capacitance to increase.

From the description ... the used compound should be suitable.

I recommend a deeper investigation in electrical error reasons.

Klaus

 

[D.A.(Tony)Stewart]

Potting material is generally electrical and thermal insulators thus terrible for power loss and thermal rise.

A Silicone dip or spray with forced air is better. Ratings are usually 10~15 kV/mm