Solid State Relay SSR-100DD 100A DC to DC Input 3-32VDC to Output 12-220VDC Single Phase Plastic Cover https://a.co/d/gsz6NMO
is wired up with the input polarities being reversed, does the relay get activated for a split second? I have tested the continuity between the two output posts with the inputs reversed, and I can’t tell. The light on the ssr that signals it has been activate will flicker which makes me believe it may activate for a split second.
This is why I ask:
I have a project that uses two of these ssr’s. They can NEVER be activated at the same time. Even if the mcu fails and doesn’t follow the code. So, I thought I’d put both of the ssrs on the same output pin of the mcu. This way it either has to be high or low to activate one or the other. It can never do both. However, to do that, I would need to supply constant gnd to one and constant vcc to the other OR have a second output pin supply either gnd or vcc to the ssr that is being activated. This would work fine, except in order to activate one, output pin one would need to be HIGH and output pin 2 LOW. This would also be supplying a gnd and vcc BUT in reverse polarity to the other relay.
If you supply a constant vcc to one and a constant gnd to the other, it would work, but there is no way to turn both relays off.
I’m sure there is an easier way, but I can’t come up with it.
Post your sketch, well formated, with well-tempered comments and in so called code tags "< code >" and a detailed circuit diagram to see how we can help.
Sound like you need a hw gate to convert two line control where one is MotorFwd and the other is MotorRev and you must ABSOLUTELY NEVER have both on at once. We traditionally add a hardware NAND gate (74LS00) so the two lines become MotorDir and MotorEnable and no permutation will cross connect.
I can do what I want for sure with three output pins. One pin toggles and is connected to both ssrs (one ssr on the + and the other ssr on the - )
this ensures they can never be activated at the same time. The other two pins will go to one ssr individually. One to + on the ssr that receives - from the toggle pin and the other to the - that receives + from the toggle pin. This works fine. No way to ever have both on and I have the ability to turn both off if I want.
I just wasn’t sure if I could do this with only two pins, but I’m not sure I can with these relays. I think it would be possible if the relays were spdt, but these are not.
As for the code, I could supply some, but it wouldn’t work with two pins because I don’t know how to make it work with two pins.
Ultimately, I am choosing between two battery sources. Which one will be “selected” to power the device.
Is it feasible to diode-or the two +12 inputs to the board, such that it doesn't matter if you energize both? That way, regardless of design or Arduino failure, you can't mess up.
The relay specs don't specify a max reverse voltage for the input. So it would be safer to assume you can't apply a reverse voltage without damaging the relay
I considered this, but the forward voltage drop is a concern. This is a fairly high amperage circuit and I hate to loose the potential voltage. I have the three available pins, but I was hoping there was an easier way.
Then I'd suggest an SPDT relay in series with a second SPST. One selects the source, the second just enables the output. Foolproof, which is always a consideration when dealing with software.
And yes, I second what @jim-p has said. Unless you have a datasheet that indicates reverse-connection is acceptable, don't do it.
Of course, you can add your own protection - put a diode in series with each SSR's input, such that no current flows when reverse-connected; verify that the diode voltage drop isn't going to reduce your input voltage below the spec'd minimum, though.
From the relay specs:
On Voltage:≤2V. Probably means 1.9V. That's more than a diode drop.
Also if you are drawing 50A, then at 1.9V, that's 95 Watts of heat.
A mechanical relay would be best and you only need ONE SPDT or DPDT.
