 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Electronics : SSR’s on DC
| Author | Message | ||||
| Phil23 Guru  Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
I do understand that commonly available SSR's are not suitable for switching DC, like solar arrays.  Can someone explain a bit more clearly why, and also why a similar simple DC device is not readily available. OR am I just demonstrating my total ignorance of which is the correct item for the purpose. Phil. |
||||
Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Here is a DC -DC version. Or you can build your own as shown here. this one is isolated for use with a GTI. There are only 10 types of people in the world: those who understand binary, and those who don't. |
||||
| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
These (ac type) solid state relays all use either a triac or sometimes a pair of back to back silicon controlled rectifiers. (SCRs) These types of device are triggered "on" usually with a short pulse, and then through internal feedback lock themselves permanently on. Once switched on the only way to turn the thing off is to either remove all power from the device, or reverse the polarity of the applied power. If you use one with a main dc supply, you can switch it on fine, but there is then no way to turn it off. On ac, the polarity of the power reverses 50 times per second. So you can switch it on, and then unless you keep repetitively switching it on, it will turn itself off during the next half mains cycle. So on ac, it acts much like a mechanical relay, it can be turned both on and off. On dc it turns on then locks up permanently, which is pretty useless for most things. You can get solid state dc relays which are basically a big mosfet or big transistor that can be switced both on and off, but they are very different to the ac types. [url]https://www.ebay.com/itm/SSR-100-DD-Solid-State-Module-Solid-state-Relay-DC-DC-100A-3-32V-DC-5-60V-DC-/312100885769[url] Cheers, Tony. |
||||
| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Yes following that thread & that's probably the way I will go. Out of curiosity, why is the -ve leg switched as opposed to the positive? Just time poor in getting things done in the appropriate order. The link you posted lists it as 5-80VDC. Why are we not seeing say 600-1000V devices? Phil. |
||||
| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Because NPN transistors and N channel mosfets are much more efficient devices. Very high voltage transistors and mosfets, while possible, would greatly limit the maximum rated current. Apart from high voltage solar, most switched dc applications involve a battery and operate at relatively low voltages. An 80 volt 100amp device would have far more useful applications than an 800 volt 5 amp device. Cheers, Tony. |
||||
| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
What is the outcome you are wanting to achieve Phil? There are only 10 types of people in the world: those who understand binary, and those who don't. |
||||
| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Outcome will be to simply switch my 3 strings to the 2 PV inputs I have. Only using 2 out of 3 at any given time. String 1 (NE) will probably always stay on PV1, but PV2 would switch between Strings 2 & 3. Phil. |
||||
| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
The Isolated MOSFET circuit would do it, if you are feeding into a GTI you could use PWM with it and current sensing to limit the output of the GTI. There are only 10 types of people in the world: those who understand binary, and those who don't. |
||||
 Print this page |
