Wanting to replace mechanical relays with some form of solid state device (SPDT mechanical replacement)

Thread Starter

david78641

Joined Jan 28, 2021
2
Hello,
I have a small PMG that outputs 56Vac (per the label 6.2A, 600W). Currently it uses three SPDT NC mechanical relays as a braking device when power is removed. One of the relays has failed and while I could probably unsolder it from the board and a replacement for it, I would prefer to go solid state for longevity....if possible.

The VCC shown in the attached file is controlled by a "power good" signal (not shown in the diagram) that when high applies 12vdc to the solenoid of the relays. This flips the relays to the NO position which then, because the way it is wired, allows the PMG to spin. If the power good signal is removed or lost (due to low battery voltage or purposely turned off) then the solenoids loose power and the relays revert back to the NC position. When in the NC position, the legs of the PMG are all connected together which applies a braking action to the PMG.

I have looked for SPDT SSR (DC-AC) relays and have not found any. I have searched for SPDT MOSFET-TRIAC circuits and found numerous questions about using MOSFETs or TRIAC to make SPDT circuits and even some circuit ideas, but nothing that I think I can use to replay the circuit that is attached.

I am just looking for some ideas because I have hit a roadblock mentally. I think I have become focused on doing/seeing it one way and that way I haven't been able to make work (using complimentary N-channel and P-channel MOSFETs, using two back-to-back N-channel MOSFETs, TRIACs in a SPDT configuration - never even really found a way to do that). I know I am mentioning MOSFETs and TRIACs and from what I always understood MOSFETS were for DC and TRIACs for AC, but I have read where back-to-back MOSFETs will handle AC and also because there is a mix of DC and AC (DC control signal if you will and the low voltage AC from the PMG). thought maybe a MOSFET or NPN could handle the DC side and a TRIAC the AC side or all MOSFET or ....... ???

Any direction or ideas would be appreciated it.
 

Attachments

jpanhalt

Joined Jan 18, 2008
11,088
Permanent Magnet Generator based on the context.

Apparently, the braking is by shorting the coils. Would be nice to have the whole circuit. This site may be helpful: http://www.4qdtec.com/pwm-01.html

The originator, 4QD TEC, was bought our several years ago; however, that legacy site has a lot of useful information. Search on brake or braking.
 

Thread Starter

david78641

Joined Jan 28, 2021
2
Sorry.... yes, PMG = Permanent Magnet Generator as jpanhalt stated.
I have not traced out the whole board, but will try to and post it when I am able.
Appreciate the 4QD TEC website. It does have some good info.
 
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