SSR question - Page 1
Forum section: electronics / beginners

author: Lucky-Luka
author_rank: Unknown
timestamp: May 04, 2022, 07:46:22 am
content: Hi allCan anyone tell me how can this relay be ok with such a broad input voltage?I haven't found a schematic for this kind of relay module.Thankshttps://www.ebay.it/itm/322209858572

author: wraper
author_rank: Unknown
timestamp: May 04, 2022, 08:02:35 am
content: It's not a mechanical relay but SSR (solid state relay). It has a circuit that limits the current flowing through LED emitter of optocoupler. 3-32V input voltage range is the most common for SSR. Older types often had around 5V minimum voltage.

author: Lucky-Luka
author_rank: Unknown
timestamp: May 04, 2022, 11:45:32 am
content: GTD-W-5AI haven't found a datasheet to understand the current needed for the control input

author: wraper
author_rank: Unknown
timestamp: May 04, 2022, 11:55:30 am
content: It self limits the current. If source is capable to supply at least 20-30mA, generally you should be fine.

author: Lucky-Luka
author_rank: Unknown
timestamp: May 04, 2022, 12:59:50 pm
content: So I cannot drive it using a GPIO pin of an Arduino...I need a bjt or a mos with that relay, right?

author: Terry Bites
author_rank: Super Contributor
timestamp: May 04, 2022, 01:06:34 pm
content: The description says the relay will be on when the control input excedes 3V and off when the control volage is less than 0.5V.It also says that the relay state for control voltages between 0.5-2.5 is not defined, it might be on or off or random.The maximum control voltage is 32V.They say it can be driven from an Arduino. This is cause for concern, the worst case output voltages may be out of specification for this relay.You do need to add a a driver to the GPIO. eg

author: Lucky-Luka
author_rank: Unknown
timestamp: May 04, 2022, 02:01:27 pm
content: then couldn't I just use a power mosfet instead of a relay and that bjt?

author: CaptDon
author_rank: Super Contributor
timestamp: May 04, 2022, 02:09:17 pm
content: That depends somewhat on what load you intend to drive and if that load is inductive and may sens inductive kick-back spikes into your digital world. The SSR gives you the benefit of superb isolation between the driving signal and the load. It also allows for loads connected to other voltage sources, in some cases (the usual use) even the A.C. mains.

author: Lucky-Luka
author_rank: Unknown
timestamp: May 04, 2022, 02:52:12 pm
content: Quote from: Terry Bites on May 04, 2022, 01:06:34 pmWhy?

author: wraper
author_rank: Unknown
timestamp: May 04, 2022, 04:00:11 pm
content: Quote from: Lucky-Luka on May 04, 2022, 12:59:50 pmWhy? Atmega328 is allowed to supply 40mA per pin (with limitation on overall current thru multiple pins).

author: Lucky-Luka
author_rank: Unknown
timestamp: May 04, 2022, 04:13:04 pm
content: Post #5

author: Zero999
author_rank: Super Contributor
timestamp: May 04, 2022, 04:40:53 pm
content: Quote from: wraper on May 04, 2022, 04:00:11 pmWhat's the supply voltage? If it's 3V, the output voltage will be too low.

author: wraper
author_rank: Unknown
timestamp: May 04, 2022, 04:42:28 pm
content: Arduino uses 5V.

author: Zero999
author_rank: Super Contributor
timestamp: May 04, 2022, 04:44:25 pm
content: Quote from: wraper on May 04, 2022, 04:42:28 pmIt should be fine, if it doesn't push the total current draw above 200mA.

author: james_s
author_rank: Super Contributor
timestamp: May 04, 2022, 05:24:13 pm
content: I have driven SSRs directly from Arduinos (and other AVRs) without any issues, it will be fine.

author: BeBuLamar
author_rank: Super Contributor
timestamp: May 04, 2022, 08:14:57 pm
content: Quote from: Lucky-Luka on May 04, 2022, 11:45:32 amMost SSR only needs about 10mA.

author: Lucky-Luka
author_rank: Unknown
timestamp: May 07, 2022, 08:54:13 am
content: Quote from: wraper on May 04, 2022, 04:42:28 pmI am using an Arduino that runs at 3.3V

author: Lucky-Luka
author_rank: Unknown
timestamp: May 07, 2022, 08:54:48 am
content: Quote from: Zero999 on May 04, 2022, 04:44:25 pmI use a 3.3V Arduino

author: Zero999
author_rank: Super Contributor
timestamp: May 07, 2022, 12:22:29 pm
content: Quote from: Lucky-Luka on May 07, 2022, 08:54:48 amThen use the circuit posted by Terry Bytes.https://www.eevblog.com/forum/beginners/ssr-question/msg4154950/#msg4154950

author: Lucky-Luka
author_rank: Unknown
timestamp: May 07, 2022, 03:41:21 pm
content: That works if I don't have an octocoupler on the module