tonigau
Member
Looking for a clarification of the output switching device in these Fotek DC SSR's - Should be BJT?
A colleague got a bunch of these to control water heaters from a 48V Battery but none? are working (still waiting to clarify any failure mode(s)-smoke, excess heat etc...). Each heater is 30A so well within the current spec. They are 60V rated so not enough safe operating margin for a full charging LA battery & cable inductance (long wires out to tanks). They are mounted on heatsinks.
Ignoring for now the volt margin, he did an autopsy & the switching transistor is a P140NF75, 120A 75V N-ch MOSFET.
I have used FOTEC SSR-40DD devices before & they were BJT switching device.
Unfortunately the device is mostly potted so can't confirm ATM if there is some charge transfer circuit over the isolation barrier for the Gate.
I am suspecting factory loaded MOSFET's by mistake ? more investigation is ongoing...
Here is some photo sent to me...
![SSR-100DD.jpg SSR-100DD.jpg](https://www.electro-tech-online.com/data/attachments/121/121410-96ae8df8740cee6e48cba5101df57efd.jpg)
![OutDevice.jpg OutDevice.jpg](https://www.electro-tech-online.com/data/attachments/121/121409-8b65b360652fb5d767fdd8ca4abbc0b7.jpg)
A colleague got a bunch of these to control water heaters from a 48V Battery but none? are working (still waiting to clarify any failure mode(s)-smoke, excess heat etc...). Each heater is 30A so well within the current spec. They are 60V rated so not enough safe operating margin for a full charging LA battery & cable inductance (long wires out to tanks). They are mounted on heatsinks.
Ignoring for now the volt margin, he did an autopsy & the switching transistor is a P140NF75, 120A 75V N-ch MOSFET.
I have used FOTEC SSR-40DD devices before & they were BJT switching device.
Unfortunately the device is mostly potted so can't confirm ATM if there is some charge transfer circuit over the isolation barrier for the Gate.
I am suspecting factory loaded MOSFET's by mistake ? more investigation is ongoing...
Here is some photo sent to me...
![SSR-100DD.jpg SSR-100DD.jpg](https://www.electro-tech-online.com/data/attachments/121/121410-96ae8df8740cee6e48cba5101df57efd.jpg)
![OutDevice.jpg OutDevice.jpg](https://www.electro-tech-online.com/data/attachments/121/121409-8b65b360652fb5d767fdd8ca4abbc0b7.jpg)