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View Full Version : Just had a idea. Would running a PC power supply into a SSR work to get DC voltage??



fathead45
01-22-2010, 10:20 AM
Well i was looking at DCSSR boards and i have Reg AC SSR's. Well what would be the outcome if i was to input 12 or 24 volts of DC voltage into a reg ssr and use it for my led strips? i know it prob wont work but the reason i was thinking this is i have some 12 ch SSR boards and i could in theory if i had the right components i could just input 12 volts dc off a power supply i could run 4 strips off that board instead of more DCSSR. maybe it wont work but just thinking allowed.

dslynx
01-22-2010, 12:03 PM
It would latch on, and stay on till the power was removed. These SSRs require an AC signal.

fathead45
01-22-2010, 12:08 PM
ok, that is what i figured. i know it might be reengineering the wheel but i wonder how hard it would be to adapt something like this or just tell me to buck up and just buy DC SSR, lols

djulien
01-22-2010, 12:18 PM
It would latch on, and stay on till the power was removed. These SSRs require an AC signal.

When used with incandescent lights, the load on the SSRs is typically high enough to latch the SSRs. However, an LED string connected to an AC SSR often does not drain enough power to latch the SSR (which is why the Renard PWM firmware is usually needed). In that case, you *might* be able to use DC with the AC SSRs and the Renard PWM firmware. The lower voltage might affect the ability of the SSRs to turn on, though. If you have a spare SSR that you don't mind potentially damaging, you could try it - if it stays lit and dims okay and nothing overheats, then you're all set.

don

dslynx
01-22-2010, 12:23 PM
But, the triac requires the voltage to drop below a threshold to turn off, no? So, once the triac is latched by the gate, it will stay on till the threshold voltage is met even without a gate voltage, which is why it works for AC.

I could have sworn I tried this back in my early days of playing with triacs and SCRs. It would light an LED, but stay on till the LED's supply was removed.

g2ktcf
01-22-2010, 06:14 PM
But, the triac requires the voltage to drop below a threshold to turn off, no? So, once the triac is latched by the gate, it will stay on till the threshold voltage is met even without a gate voltage, which is why it works for AC.

I could have sworn I tried this back in my early days of playing with triacs and SCRs. It would light an LED, but stay on till the LED's supply was removed.


Yep, this is how it works except the latch is the incoming power. The gate is the switch that allows the "latch" to function. Then the gate power can be removed but as long as there is voltage to the input, it will stay on.

djulien
01-23-2010, 12:56 AM
But, the triac requires the voltage to drop below a threshold to turn off, no? So, once the triac is latched by the gate, it will stay on till the threshold voltage is met even without a gate voltage, which is why it works for AC.

That is correct. However, the point that I was trying to make was that if the Triac *does not* latch (because the load is too light, as with an LED string), then it would turn off at the end of the AC half-cycle because the PWM firmware stops sending the signal until it is time to turn on again in the next AC half-cycle. The part I was unsure about was whether there would even be enough voltage for the Triac to turn on.

don

P. Short
01-24-2010, 07:01 PM
Generally if the Triac is 'on' it is also latched (in fact, it never ocurred to me that it could be ON without being latched). It's probably not possible to _reliably_ control this.

djulien
01-24-2010, 09:39 PM
Generally if the Triac is 'on' it is also latched (in fact, it never ocurred to me that it could be ON without being latched).

I'm confused - why is the Renard PWM firmware needed for light loads such as relays or LED strings? I thought it was because the Triac does not latch. under those conditions.

don

P. Short
01-24-2010, 10:16 PM
I think that it doesn't turn on nor latch under those loads...especially since the LEDs don't pass any current at the beginning or end of the cycle.

P. Short
01-24-2010, 10:21 PM
Come to think of it, the triac probably is turned on under the extremely light loads, even if it is only passing a few micro-amps of current. But definitely not latched.

P. Short
01-24-2010, 10:29 PM
Anyway, back to the original question...

You cannot just send a DC voltage to the conventional AC coop SSRs to control DC. Both the optos and the triacs will latch when they turn on the first time, and you won't be able to turn them off.

Another question that people have been asking for a long time is whether or not you can put different components on the coop SSR boards to have them control DC. The problem here is that the pinouts of the optos that you need to use here are not compatible with the pinouts of the triac-output optos, and the pinout of a transistor (BJT or MOSFET) is not compatible with the pinout of the triacs. People have re-worked the AC coop SSR boards for DC use, but it is a painful process and difficult to describe.

Cheater
01-24-2010, 10:34 PM
I'm going full DC and wjohn has DC SSR boards which do the trick.
Just grab some of them.

fathead45
01-24-2010, 11:00 PM
yea im going to get some dcssr's.

thanks for all the info guys.