Guys, I've a relay that is rated for a load of 10A 220V AC.
Can I use it for a load of 15A 12V DC?
The coil is 220V AC and I will drive it that way.
Thanks!
andrpex:
Guys, I've a relay that is rated for a load of 10A 220V AC.
Can I use it for a load of 15A 12V DC?
The coil is 220V AC and I will drive it that way.
Thanks!
The amp rating of relay contacts is basically because of the heat generated by the small resistance between the contacts. If the 15 amps is for a short time, less than 30 seconds, then is probably ok.
If you get smoke, then, no, it's not ok.
Paul
Thanks Paul.
It will be just for about 10 seconds, so there shouldn't be any problem.
If you smell burning, please come to check on me ASAP!
andrpex:
Thanks Paul.
It will be just for about 10 seconds, so there shouldn't be any problem.
If you smell burning, please come to check on me ASAP!
Who should I call?
Paul
An AC relay contacts are usually derated by approx 10x to switch DC. Ie a 240V 10A AC will be rated at 24V 10A DC. The problem is extinguishing the arc when the contact are broken. AC arcs diminish rapidly. DC tends to hang on and can weld the contacts together
--
Mark
Paul_KD7HB:
Who should I call?
Hemmm...well, maybe it's better to call first the Firefighters!
As I have said before, The current/Voltage rating of the relay is not the only thing you should consider. You need to look at the board that you're using as well. In this case how heavy are the traces, Are they on both sides of the board, and what kind of current will your connection terminals take. Normally if you are using one of the hobby relays that are available on eBay, The connection terminals will only take approximately 7A. In this case, I suggest using the automotive Bosch relay, And making a driver circuit for it.
andrpex:
Guys, I've a relay that is rated for a load of 10A 220V AC.
Can I use it for a load of 15A 12V DC?
The coil is 220V AC and I will drive it that way.
Thanks!
Unlikely. DC current ratings are lower than AC current for a mechanical switch. Switching
high current DC is difficult as there are no zero-crossings to extinguish the arc. 12V is very
low though, which helps.
Is your load inductive at all? If so then the standard ratings do not apply anyway.
promacjoe2:
As I have said before, The current/Voltage rating of the relay is not the only thing you should consider. You need to look at the board that you're using as well. In this case how heavy are the traces, Are they on both sides of the board, and what kind of current will your connection terminals take. Normally if you are using one of the hobby relays that are available on eBay, The connection terminals will only take approximately 7A. In this case, I suggest using the automotive Bosch relay, And making a driver circuit for it.
The relay is a Relpol TYPE R15 3PDT mounted on this screw terminal, so no problem for board traces.
Since the relay has 3 separate contact and I need to drive a motor inverting polarity (window opener), I was thinking of using 1 for opening the window connecting + and - of the motor to 2 contacts and using the third to connect 220V AC that power the 12V DC power supplier, so there shouldn't be arc problems. I will do the same with another of these relay with the DC polarity inverted to close the window.
What do you think?
Also, to drive the relay I may use a relay board (this one) or a SSR board (this one).
I would prefer the SSR since there is less failure possibility (no moving parts).
What would you say?
Thanks!
Well there will be arc problems, because the mains supply will have energy stored in its capacitors which
will be available for some fraction of a second after the mains power is cut. The inductance of the motor
also stores energy which will cause arcing (more serious effect - you have an inductive load, you need to
add a snubber circuit to help control that)
I you had a mains relay and a DC relay you could sequence the two relays so the DC relay is never switched
with current flowing, which would finesse the issue completely.
For 12VDC an automotive relay would be the obvious choice as they are designed for it, and many are
inductively rated too.
MarkT:
I you had a mains relay and a DC relay you could sequence the two relays so the DC relay is never switched
with current flowing, which would finesse the issue completely.
This problem should be already solved by a mechanical switch that will cut off the motor power when the window is completely open/close. The small relay/SSR controlled by Arduino will keep the power relay on for about 1 or 2 seconds more than needed to open/close the window, so when the Arduino relay/SSR is switched off, on the power relay there is non DC load, just the AC power supply load (what this relay is reted for).
For 12VDC an automotive relay would be the obvious choice as they are designed for it, and many are
inductively rated too.
I know, but I prefer to use what I have laying around, as far as it's possible!
If you're driving a 15A 12V load, a power MOSFET is the obvious choice..
Allan
TomGeorge:
Hi,
Simply look up the spec.
He he...just as simple as that!
I haven't looked at the spec because since on it it's only rated as AC, I didn't think it could be officially rated DC.
Thank!!!
Worst case, the relay doesn't last very long and you have to replace it. Is that a big deal for you?
DVDdoug:
Worst case, the relay doesn't last very long and you have to replace it. Is that a big deal for you?
No, it's not since I have those 2 relays laying around.
But it's good to know what I'm doing before actually doing it!
Thank you all!