Can a solid state relay switch other solid state relays? Anything to watch other than to wire them up? I didn't spend a lot of time looking but didn't see an answer to this question. The solid state relays seemed like an answer to a problem I had to solve. The switching ssr needs to operate two others. One is a quarter mile away, the second is a half mile away.
Thanks, Gentlemen
Worst case maybe put a small resistive dummy load on the output of the switching ssr?
It will take some work to make one SSR to activate another SSR. The SSR depends on having a source of power on the output, usually an AC voltage. It may activate ona DC voltage on the output, but may lock up in the on state. The input depends on haveing a voltage applied to it.
Not that it can not be done, just requires more work than a simple hook the out to the in .
I have done that in my holiday light control for about 5 years. A small computer (Arduino) controls 3 small SSRs (switching 12VDC). The load on the output is a few larger SSRs that switch 120V for the lights.
BTW, "off" is not entirely off. It's close enough that incandescent lights won't light, but if the load is only small LED lights, they may no go completely off. I still have a few incandescents.
For what I have, I didn't need such a load on the first SSRs (the ones that control others), only on the second SSRs if I just want to switch LED lights.
On 8/3/17 3:38 AM, Uncle Monster wrote:
I need/want to stay under 30 volts for the control voltage. The code will let us do that without grounding and interlocks on the panels where the controlled relays are mounted. The reason for the DC is those seem to be much more common. Plan A was a master ssr at the center point of an irrigation system. It would be activated by 12vdc from an irrigation engine located in the northeast corner of a field. Eighteen hundred feet away give or take. The masters output would be supplied by 24vdc. The load was to have been the two slave solid state relays. The first slave would've been in a well panel straight north of the master about thirteen hundred feet away. The second slave would've been in a well panel about thirteen hundred feet west of the first slave. The slaves would've been switching power to a 480vac three phase motor starter. They'd have had about 240vac through them. The supply house sent zero point switching ssrs. Control voltage is 4-32vdc. Output 600 vac. I think that might have been a problem with the 3 phase. They didn't work every time, either off or on. I solved that perceived problem with a 480x120 transformer. The slave ssrs are now switching single phase 120 going to a mechanical relay. That relay runs the pump starter. The problem now is the slaves won't obey the master. My guess was they don't impose enough of a load on the master. I must be on the right track judging from the other responses. Someone else buried the pipe and wire long ago. The wire is 12 uf with ground. Our customer asked us to make the irrigation system kill the wells and any failure kill the other three parts of the group. Three wells are supplying water to one center pivot at a time. I'm used to mechanical relays, switches, and contactors. Those won't work due to the voltage drop. Any ideas?
The input to the master will be 12vdc. The power supplied to the output will be 24vdc. The slaves are supposed to work on 4-32vdc in . There's a more extensive description in my answer to the Monster. Not to be confused with a Munster.
One thought is to replace the master ssr with a 12vdc mini relay. It would be about 1800 feet from its source though.
Thanks
I use SSRs a lot. You do need a little bit of a resistive load to make them turn off reliably but 15w of incandescent light seems to work OK. Typically they look like a 1000 ohm resistor so at 5v they draw about
5ma. (maybe more like 24ma at 24v) Voltage drop should not be a problem no matter what tho since the range is so wide. Just for gee whiz info 12ga wire at 1800 feet carrying a half an amp only drops 3.6v or so. Just be sure you have clean DC (no ripple). Typical transformer wall warts suck without adding a fat filter capacitor. but a switcher is OK. If you put a lamp (or just a resistor) for a load at the first SSR and the irrigation for the load at the slaves you should be fine.
I think the lightning problem can be mitigated with some big MOVs kicking off at 30v or so. Since SSRs are, by there nature, isolation devices you do not have a direct path. I would also loop the leads through some big ferrites but other than that it is not a big worry. Lightning surges are generally common mode transients. SSRs are cheap and pretty tough. Just keep spares and worry about the lightning problem when you see it is a problem.
Why would I buy a $40 protector to protect a $10 SSR? Particularly since you are just protecting a LED If there was a CMOS front end in there I would worry about it but if the hit was strong enough to take out a LED, that protector will be smoking too.
On 8/4/17 7:27 AM, Uncle Monster wrote: Cut a bunch. There are solid state relays that have a wide voltage range to trigger them. The thing I'd be most worried about is what would happen to your control system when there is a nearby lightning strike. If you're running a very long control cable to low voltage triggered solid state relays, the induced voltage surge on the control cable could burn out your relays. If there is electrical power at your remote pumps, consider wireless control. ?(?)?
The last link in this hookup will have to be wireless due to lack of buried wires. or
A bunch cut due to aioe quotation limits.
Could I bug you for specs of a resistor that would work? Would a 24vdc flashcube relay do the job?
Thanks
or
This is a unique situation for us. Solid state stuff is a new world for me. Distances are usually short enough that we can use mechanical relays and contactors. We really don't have much problem with them. We put 480 volt 3ø lightning arrestors for the incoming power to the irrigation system sometimes. The system will have some suppressors factory installed for the 110 volt circuitry. Other than that, no.
I already said some MOVs will do the job. This is not CMOS, it is a LED
A mechanical relay would work fine.
Good deal. That relay might let me avoid the wireless pump shutdown. Cost plus terrain issues favor relays of some sort. Thanks again.
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