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Solid State Relay

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Hi, can i use an SSR as an h-bridge instead of BJTs to switch a DC Motor in two directions because i want the rated current between 8-14 A
at 24 V
 

Bob Scott

New Member
Hi, can i use an SSR as an h-bridge instead of BJTs to switch a DC Motor in two directions because i want the rated current between 8-14 A
at 24 V
Any SSR I have ever heard of is for switching AC only. The actual switch inside the SSR is a triac. If you try switching DC, the triac will switch on but it will not switch off.
 

Mikebits

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mdwebster

New Member
Yep, you can get AC or DC SSR's. DC's use a FET, AC's a pair of FET's or a pair of SCR's (a triac).
As to the initial question ...
I don't see any right off that aren't fairly expensive ($65+) that hit the current requirements you're looking for. And you'd need four of 'em to switch directions since they're SPST's.

How about a real relay? You might need to hook up some drive FET's to turn it on and off using a micro (if that's what you're doing). I guess it depends on how fast you need to switch it on and off.
 
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mdwebster

New Member
14A is a lot of current. All of the H-bridge or SSR's up in that range that I could find are either obsolete or really expensive. Short of building one up from discretes, you might try running 3 of these in parallel to hit your current requirement.
 
No , sorry i mean by 14A as stall current as im scared if the robot's motors would hit a wall and then stopped suddendly , circuits would be burnt and it happend alot with the
L298 h-bridge driver ...
 

mdwebster

New Member
Again, you might just put 2 or 3 of those in parallel to increase their current tolerance.

Or you could rig up a current-sense resistor (would have to be pretty low to regularly hit 8A+, like 0.1 or 0.2 ohms or so) to kill the motor if a certain threshold were exceeded. I'm not too sure I'd like hooking up a line tied to an inductive motor straight to an ADC input though ... I'd have to think about it a while, use some kind of resistor divider to read the voltage off of the current-sense resistor maybe. I'd probably also put a low-breakdown zener or TVS on the ADC pin as well, but maybe that's just me being paranoid ... :)
 

crutschow

Well-Known Member
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Hi, can i use an SSR as an h-bridge instead of BJTs to switch a DC Motor in two directions because i want the rated current between 8-14 A
at 24 V
Solid-state relays generally have millisecond operate times so would not work for pmw unless the frequency is very low.
 
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