Electronics > Beginners

simple controller problem

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tpowell1830:

--- Quote from: kafor1 on December 17, 2018, 02:15:26 am ---

aah yes the purpose of D1 is to show that it is OFF since it is red, D2 is green it would indicate that its ON, and your opinion is verry goood i didnt think of that, i guess if i didnt add that i would put my hole in my picket since ill be buying lots of 9v bat hahah. ill add that to my circuit. and so can my relay handle 10.5A ? since the rating is just 10A

edit.. and also if its not a hassle can u explain me the term load, and provide example is its ok with you  :) :)

--- End quote ---

Your relay is rated at 10 amps, but could handle 10.5 amps for a short period of time. My rule of thumb on relay contact parameters is to make them 20% higher current carrying than rated load. So, in this case, 20% of 10.5 amps is approximately 12 amps, so I would pick the closest or higher current rating to 12 amps, which the standard is probably 15 amps for most relays.

Load, when mentioned in this context, is current in amps. Your inductive motor has a load of 10.5 amps for the contacts to "carry" (like a truck carries a load).

Hope this helps...

wraper:

--- Quote from: tpowell1830 on December 17, 2018, 02:56:39 am ---
--- Quote from: kafor1 on December 17, 2018, 02:15:26 am ---

aah yes the purpose of D1 is to show that it is OFF since it is red, D2 is green it would indicate that its ON, and your opinion is verry goood i didnt think of that, i guess if i didnt add that i would put my hole in my picket since ill be buying lots of 9v bat hahah. ill add that to my circuit. and so can my relay handle 10.5A ? since the rating is just 10A

edit.. and also if its not a hassle can u explain me the term load, and provide example is its ok with you  :) :)

--- End quote ---

Your relay is rated at 10 amps, but could handle 10.5 amps for a short period of time. My rule of thumb on relay contact parameters is to make them 20% higher current carrying than rated load. So, in this case, 20% of 10.5 amps is approximately 12 amps, so I would pick the closest or higher current rating to 12 amps, which the standard is probably 15 amps for most relays.

Load, when mentioned in this context, is current in amps. Your inductive motor has a load of 10.5 amps for the contacts.

--- End quote ---
With inductive load you should derate relay like 2-3 times. Often you can find about this in datasheets. Snubber should be used as well. Also don't forget about inrush current.

tpowell1830:

--- Quote from: wraper on December 17, 2018, 03:02:22 am ---
--- Quote from: tpowell1830 on December 17, 2018, 02:56:39 am ---
--- Quote from: kafor1 on December 17, 2018, 02:15:26 am ---

aah yes the purpose of D1 is to show that it is OFF since it is red, D2 is green it would indicate that its ON, and your opinion is verry goood i didnt think of that, i guess if i didnt add that i would put my hole in my picket since ill be buying lots of 9v bat hahah. ill add that to my circuit. and so can my relay handle 10.5A ? since the rating is just 10A

edit.. and also if its not a hassle can u explain me the term load, and provide example is its ok with you  :) :)

--- End quote ---

Your relay is rated at 10 amps, but could handle 10.5 amps for a short period of time. My rule of thumb on relay contact parameters is to make them 20% higher current carrying than rated load. So, in this case, 20% of 10.5 amps is approximately 12 amps, so I would pick the closest or higher current rating to 12 amps, which the standard is probably 15 amps for most relays.

Load, when mentioned in this context, is current in amps. Your inductive motor has a load of 10.5 amps for the contacts.

--- End quote ---
With inductive load you should derate relay like 2-3 times. Often you can find about this in datasheets. Snubber should be used as well. Also don't forget about inrush current.

--- End quote ---

Thanks Wraper, I agree completely, my mind was derailed when I mentioned this. But it is often derailed these days....

Inductive motor load switches should use a much higher current rating and, I would say (normally, if my head was screwed on right), get a proper motor starter relay with built in thermal overload protection.

kafor1:

--- Quote from: tpowell1830 on December 17, 2018, 03:10:46 am ---
--- Quote from: wraper on December 17, 2018, 03:02:22 am ---
--- Quote from: tpowell1830 on December 17, 2018, 02:56:39 am ---
--- Quote from: kafor1 on December 17, 2018, 02:15:26 am ---

aah yes the purpose of D1 is to show that it is OFF since it is red, D2 is green it would indicate that its ON, and your opinion is verry goood i didnt think of that, i guess if i didnt add that i would put my hole in my picket since ill be buying lots of 9v bat hahah. ill add that to my circuit. and so can my relay handle 10.5A ? since the rating is just 10A

edit.. and also if its not a hassle can u explain me the term load, and provide example is its ok with you  :) :)

--- End quote ---

Your relay is rated at 10 amps, but could handle 10.5 amps for a short period of time. My rule of thumb on relay contact parameters is to make them 20% higher current carrying than rated load. So, in this case, 20% of 10.5 amps is approximately 12 amps, so I would pick the closest or higher current rating to 12 amps, which the standard is probably 15 amps for most relays.

Load, when mentioned in this context, is current in amps. Your inductive motor has a load of 10.5 amps for the contacts.

--- End quote ---
With inductive load you should derate relay like 2-3 times. Often you can find about this in datasheets. Snubber should be used as well. Also don't forget about inrush current.

--- End quote ---

Thanks Wraper, I agree completely, my mind was derailed when I mentioned this. But it is often derailed these days....

Inductive motor load switches should use a much higher current rating and, I would say (normally, if my head was screwed on right), get a proper motor starter relay with built in thermal overload protection.

--- End quote ---

so am i doing something dangerous, not using any motor load switches, ,motor starter relay,, just plugging the cord to 15A extension wire to energize and unplugging the cord to deenergize the motor? since i dont have any switches

Edit: also i dont know what is the rating of snubber should i buy,or where i should connect it in my circuit

spec:
Hi kafor1

Bad news. The current rating for a relay is defined with a resistive load. The relay current rating is much reduced for an inductive load like a motor. Without seeing the data sheet for your relay or motor, I would guess that you would need a relay with a resistive load rating of around 25A at least for switching the motor. You would also need snubbing/catching circuits as already described.

But in any case, there is little danger, all that would happen is that the relay contacts would burn out or weld together and keep the motor permanently on. So you can carry on using the relay, but don't be surprised if it does not last too long. :)

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