Solid state relay is turning very hot. - Page 1
Forum section: electronics / beginners

author: stdcall
author_rank: Newbie
timestamp: November 26, 2017, 08:13:57 am
content: Hi.I recently purchased a solid state relay rated 25A to control high current (220V) water heater. it's controlled by 3V GPIO connected to Raspberry Pi.The relay arrived with a heat sink, and although connected to it, it's turning super hot when active. not touchable by hand.Is it normal ? what are my options to reduce the heat ? choose a higher rating (40A) ? replace to electro-mechanic relay ?Links to the relay and heat sink.https://www.ebay.com/itm/MGR-1-D4825-Single-Phase-Solid-State-Relay-SSR-25A-DC-3-32V-AC-24-480V/231308265775?epid=1038702603&hash=item35db0c092f:g:8eQAAOSwR21Z0e3Khttps://www.ebay.com/itm/311293100616

author: ez24
author_rank: Super Contributor
timestamp: November 26, 2017, 08:45:58 am
content: How many amps does your heater use? Also I assume the relay works as intended (minus the heat).I would use a relay rated at least twice the load. Lets see what the experts say. One thing for sure, a Chinese 25 amp relay cannot switch 25 amps.

author: jeroen79
author_rank: Frequent Contributor
timestamp: November 26, 2017, 08:49:10 am
content: How much current are you running through it?It will drop some voltage and thus dissipate heat.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: November 26, 2017, 08:56:53 am
content: You mention the current rating of the SSR, but you don't mention the current that you are controlling. You do not say how your PI is controlling the SSR (are you using a derivative method, for instance?) or just on when it needs to be on and off when it is hot enough?The heating elements in water heaters are typically made from a ni-chrome material and can pull large currents when powered, depending on the wattage rating of the heating element. Do you know the wattage rating of the heating element?Some SSRs from China have visual ratings that are much higher than they can actually handle, is this a cheap Chinese Ebay SSR?I have many more questions, but you could simply show what you have done and how you have done it in schematic and explain the theory of operation of your PI controller.Also, there is the danger aspect of what you are doing. I have seen SSRs explode once they reach a point, so touching the SSR while operating is not a good idea, on many levels.

author: stdcall
author_rank: Newbie
timestamp: November 26, 2017, 09:20:29 am
content: The Wattage rating of the heating element is around 2500.The Raspberry Pi is controlling ti SSR using GPIO, so basically I'm controlling the SSR using 3.3V source.I posted the link to the exact SSR in ebay in the post, do you consider it cheap Chinese ?

author: nali
author_rank: Frequent Contributor
timestamp: November 26, 2017, 09:22:14 am
content: Looking at the datasheet for a real D4825 it shows a voltage drop of 1.15V at full load. So you have up to 1.15 x 25 = 28.75W of heat to deal with. That's quite significant, so you'll need some way of getting rid of it i.e. airflow or conduction.Of course as it's a cheap clone that value could be higher... measuring the actual volt drop and current will give you a real value.

author: capt bullshot
author_rank: Super Contributor
timestamp: November 26, 2017, 09:23:09 am
content: Depending on your load, that's quite normal. If you look at this datasheet of a randomly chosen triac:http://www.st.com/content/ccc/resource/technical/document/datasheet/bc/c6/38/ee/88/59/49/0d/CD00002263.pdf/files/CD00002263.pdf/jcr:content/translations/en.CD00002263.pdfand find the power dissipation vs. load current curve, e.g. there's about 16W power loss at 16A load current. You'd also want to mount the heatsink vertically so air can ventilate through the fins.This datasheet is a 40A triac, for a smaller current rated one (we don't know what's inside the module), the power dissipation might be somewhat higher.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: November 26, 2017, 09:46:01 am
content: Quote from: stdcall on November 26, 2017, 09:20:29 amThere is no way to tell if it is for sure an over rated clone, but the fact that you bought it from Ebay and not a reputable dealer, I would say that you probably have a cheap Chinese clone that is over rating the SSRs capability.The wattage that you state for your heating element is 2500 watts/ 230 Volts = ~ 11 amps. As nali stated, you already have a high wattage to dissipate, even if you had a genuine SSR. I would not trust this device (or any Ebay devices) with my home electrical controls. Pay the extra money and get the real deal from a reputable dealer.Using nali's formula (ohm's law) the dissipation of your SSR is 11 A X 1.15 V (if it is the real deal) = ~12.7 watts to dissipate. now you need a formula for figuring out the size of the heatsink that you will need in calm air (unless you have a fan blowing over the heatsink). There are many online hits for this, here is one:http://www.designworldonline.com/how-to-select-a-suitable-heat-sink/#_With that said, an electro-mechanical device, such as a relay would work much better for an on/off control, where the cycle is long (>1 minute), but I still do not know your mode of control.

author: stdcall
author_rank: Newbie
timestamp: November 26, 2017, 10:08:35 am
content: The usage is turn on/off for around 45 minutes 2-3 times a day.If you can point a good electro-mechanical alternative that can be switched on/off using low voltage DC I would be grateful.Thanks.Ramon.

author: babysitter
author_rank: Frequent Contributor
timestamp: November 26, 2017, 10:50:01 am
content: Just recently my coworker made a test setup with a chinese solid state DC relay. At 12A the relay had over 1.1V voltage drop and heated up a lot even bolted to a metal plate.When i finished the PCB with IRLR8743 that small (not tiny) MOSFET barely heated up.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: November 26, 2017, 01:59:28 pm
content: Quote from: stdcall on November 26, 2017, 10:08:35 amPanasonic SP2-DC3V; 3VDC coil, DPDT, Contact Rating 15 A @ 250 VACAvailable at Mouser:https://www.mouser.com/ProductDetail/Panasonic/SP2-DC3V/?qs=%2fha2pyFaduivEe%252bpfSIeUP17VwMRR%2ftbetEfI0UTZSQ%3d

author: ez24
author_rank: Super Contributor
timestamp: November 26, 2017, 06:28:12 pm
content: You can learn a lot by reading a datasheetFor example:http://www.mouser.com/ds/2/418/NG_DS_1308242_T92_0517-712775.pdf

author: tecman
author_rank: Frequent Contributor
timestamp: November 26, 2017, 06:37:52 pm
content: Bigger heatsinkpaul

author: vk6zgo
author_rank: Super Contributor
timestamp: November 26, 2017, 10:43:51 pm
content: Quote from: stdcall on November 26, 2017, 10:08:35 amUse your SSD to switch a proper AC contactor .Such devices last for decades.

author: Bootalito
author_rank: Unknown
timestamp: November 29, 2017, 03:18:55 am
content: Quote from: vk6zgo on November 26, 2017, 10:43:51 pmThis.As an automation engineer I can say for sure that using a ssr is not the correct choice for this application. But as you already bought it, buy a contactor with a 220v coil:https://www.automationdirect.com/adc/Shopping/Catalog/Motor_Controls/WEG_Electric_Miniature_Contactors_(3-Pole)/16_Amp_(AC3)/CWC016-10-30V24

author: ez24
author_rank: Super Contributor
timestamp: November 29, 2017, 04:13:17 am
content: Quote from: Bootalito on November 29, 2017, 03:18:55 amIf starting from scratch would you use a power relay? I have a planned project that will run 18w 120v LED lights triggered by a 12 volt alarm. The limit on the number of lights is determined by the current capacity of the wires which will be 15 amps.I bought a 12v - 120v 40a SSR with a heat sink but I did not calculate the heat loss. Now I do not like the idea of the power loss in the SSR so I am looking at power relays. TIA

author: Bootalito
author_rank: Unknown
timestamp: November 29, 2017, 11:25:18 am
content: Quote from: ez24 on November 29, 2017, 04:13:17 amA contactor is an appropriate choice for this too. You may not find many 12v coils with industrial contractors like those from Automationdirect. But it's easy enough to use another relay with a 12v coil to switch 120v,then get a 120v coil contactor to switch the high amps 120v.I'd be more concerned about stringing enough 18w led lights together in series in order to get anywhere near 15amps. That's a TON of lighting. Like... Whole house christmas lighting amount. Which if that's what you are doing just remember a contactor is mechanical, so it doesn't want to be turned on and off real fast.

author: james_s
author_rank: Super Contributor
timestamp: December 01, 2017, 06:03:36 pm
content: Those Chinese SSRs are almost all completely bogus in terms of ratings. A quick check you can do without opening it up is look at the metal back, if there's a threaded hole with something screwed into it, that's the screw holding down the ordinary TO-220 triac inside. Real SSD's are built differently. I've used a few of those Chinese ones and they work ok for switching low currents but they're not capable of anywhere near their nameplate rating.

author: ez24
author_rank: Super Contributor
timestamp: December 01, 2017, 07:44:22 pm
content: Quote from: james_s on December 01, 2017, 06:03:36 pmMy Chinese 60A SSR has this hole, so how many amps can it control? I want to control this with 12vdc from an alarm and turn on some 110v LED lights. So I wonder if the relay can control 5 amps at 110v? Thanks

author: perieanuo
author_rank: Frequent Contributor
timestamp: December 01, 2017, 07:48:08 pm
content: Quote from: james_s on December 01, 2017, 06:03:36 pmI had a machine with 2x2.2 KW heating resistors with ssd, who worked at 180 degrees C 16 hours a day, now I have a 600W heating plate with s202s12 that I use 1-2 hours a day. All passive cooling. The Chinese ssd is sh...t I recommend to disassemble and remake the ssd with good MOC-s and triac.Envoyé de mon HUAWEI NXT-L29 en utilisant Tapatalk

author: james_s
author_rank: Super Contributor
timestamp: December 01, 2017, 10:06:29 pm
content: Quote from: ez24 on December 01, 2017, 07:44:22 pmIt's impossible to say without looking inside to see what type of triac it uses, but it's certainly not capable of 60A. I suspect 5A will be no problem though.