Right now I'm using a 4 relay module 5v and the problem I'm having it the contact inside the relay welding closed. I'm only powering a 300watt 120v device. When it kicks on the arc welds the contacts shut. I need a fast solution to prevent this.
Can someone give me some ideas. Maybe a 120v compatable mosfet or transistor? Please help!
Thanks
What is the load ?
Add arc suppression to the contacts.
Always show us a schematic of your cct.
larryd:
What is the load ?Add arc suppression to the contacts.
Always show us a schematic of your cct.
It is sort of an inductive load. The relay powers a 15 amp dc power supply and the dc power supply powers a 12v solenoid to turn on a 60 amp load. Switching the dc power supply on with a load on it causes the relays to weld.
It been a while since I've torn into this module.
I have some 130v mov on the circuit and it helped but now it dont like this new load.
The relay module says good for 15 amps at 120v. I need to be very sure this wont happen anymore. I am willing to buy some new parts but I would like opinions from people that know more than me.
For my testing I shorted the ends of the 15 amp power supply together and switch the relay. Wheb I do that the relay welds Only when there is a load on the dc power supply. It didnt do this with 100watt pumps. Are these relays just crap? What other ones can I use that wont let this happen so easily? Or what else can I use?
MOVs and or kickback diodes across DC inductive loads is almost always needed to snub out spikes.
Show a schematic of the load side cct.
“15 amps at 120v” is AC volts ‘not DC’, and yes those relays are poor quality.
larryd:
MOVs and or kickback diodes across DC inductive loads is almost always needed to snub out spikes.Show a schematic of the load side cct.
“15 amps at 120v” is AC volts ‘not DC’, and yes those relays are poor quality.
I'm not actually sure how to draw a schematic for you. I can say tho it's really simple. The 5vdc relay powers a 15amp 120vac power brick. The power brick is connected directly to a 12vdc lawnmower start solenoid. A 12v battery connectors to the load input on the solenoid and then the load output of the solenoid is connected directly to a 60 amp 12vdc motor.
What do you mean by cct? Can you reccomend some relays to use? Would it make more sense to use a mosfet type switch for ac power?
cct. = circuit
Sounds like you need a heavy duty ‘contactor’ to make and break that DC inductive load.
Cannot recommend a MOSFET as a 60amp 12v inductive load is huge.
Perhaps others here have had experience with driving that large of an inductive load.
Edit
Are you saying the Power supply INPUT is 120VAC @ 15 AMPS ?
notsolowki:
I'm not actually sure how to draw a schematic for you. I can say tho it's really simple. The 5vdc relay powers a 15amp 120vac power brick. The power brick is connected directly to a 12vdc lawnmower start solenoid. A 12v battery connectors to the load input on the solenoid and then the load output of the solenoid is connected directly to a 60 amp 12vdc motor.
What do you mean by cct? Can you reccomend some relays to use? Would it make more sense to use a mosfet type switch for ac power?
You get a piece of paper and a pencil. Draw a block for each component- label it. Show how the components are wired. Label each wire. Scan or photograph this and post it.
I think cct is meant as ckt, or circuit. Since this is an international site, acronyms should be spelled out at least the first time they are used.
I assume a 5vDC relay does not take much torque to close and open. Would a 24v or 12v dc/ac relay be a better solution? It dont take much to unweld the relay contact just a slight tap. I use commercial products every day that use relays to switch 10/20amp inductive loads and they seem to last atleast a few years of heavy use. They also use relays that take high voltage to operate.
What is a good quality name relay to choose from?
Also all I use for protection on the ac side is a 130vac mov and some chokes and the chockes are not helping anything on the relay side . I dont understand a lot about the smoothing and filtering circuitry. Will a snubber circuit actually dramatically help the welding of the relays due to initial inrush current?
What I did to temporarily use the device is I lowered the size of the dc power supply. The solenoid runs good on 800ma and the relay dont weld anymore
Without important details (actual power supply, load, duty cycle) we can only guess which evaluates to “use a bigger relay”. The Songle parts are okay if derated by at least 50%, I’ve had good reliability with the 30 amp parts used at 240vac and 10 amps for motor loads.
That's actually OK as a schematic.
(Better then Fritzing)
We really need the specs of the 12V PSU.
You might consider an SSR (Solid State Relay). There are models that only switch on zero crossing. (Zero crossing is when the AC sine wave crosses zero). This way there's practically no load on the control switch or relay.
i bought a couple of these omron relays do you think these will work better?
not sure which relay to use. 120vac 10a is enough per relay but im not considering the current thats drawn when the power bricks caps charge up.
if anyone has any link to some parts to consider that would be great too
what do i need to make a snubber circuit for these relays. one designed to help prevent contact weld? if someone could help explain to me what to do. the relay would never have more that 120vac 10amp max rms but more like 5amp rms.
I believe what's happening is the caps in the switching 12vdc power supply are causing a large inrush current and it welding the contacts on the relay.
would something like a ntc thermistor help this situation? how do i choose the right one?
Not related, but I am impressed with your keeping the wiring to the logic parts tidily twisted together. This (bundling, not necessarily twisting) is an important discipline in preventing malfunctions (crashes) due to impulse pickup.
How much current does the solenoid coil require?
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