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Low voltage relay question

J

John Popelish

Jan 1, 1970
0
AB said:
Still a newbie so please bear with me....

I have this 12VDC alarm panel that limits the siren output draw to
110mA. As this is not adequate for me, I replaced the siren with a
beefier model that draws 750mA and added a small strobe light that
draws 150 mA...so 900mA total draw.

I rigged a small relay to separate the alarm circuit from the new
siren/strobe...this one here:

http://www.radioshack.com/product/i...=12vdc+relay&kw=12vdc+relay&parentPage=search

I also got a 1000mA rated wall wart to power the new setup. My
question is that since I'm pretty close to the maximum draw rating of
both the power supply and the relay...will the relay get hot and burn?
The circuit will only be in use for 12 minutes maximum and then the
alarm panel resets, but I really can't run the siren for 12 minutes to
test it.

What do you all think, should I be OK with this setup for intermittant
use?

If your current values for your loads includes the initial
inrush, then I think you'll be fine. But I am worried that
the strobe light includes a big capacitor that will suck
lots of current for a few milliseconds, right while those
contacts are bouncing to a stop, and that will eat the
contacts. I think I would look for a 3 to 5 amp contact
rated relay. That are pretty common. Or drive two of these
in parallel and use one for the horn and one for the strobe.
 
A

AB

Jan 1, 1970
0
Still a newbie so please bear with me....

I have this 12VDC alarm panel that limits the siren output draw to
110mA. As this is not adequate for me, I replaced the siren with a
beefier model that draws 750mA and added a small strobe light that
draws 150 mA...so 900mA total draw.

I rigged a small relay to separate the alarm circuit from the new
siren/strobe...this one here:

http://www.radioshack.com/product/i...=12vdc+relay&kw=12vdc+relay&parentPage=search

I also got a 1000mA rated wall wart to power the new setup. My
question is that since I'm pretty close to the maximum draw rating of
both the power supply and the relay...will the relay get hot and burn?
The circuit will only be in use for 12 minutes maximum and then the
alarm panel resets, but I really can't run the siren for 12 minutes to
test it.

What do you all think, should I be OK with this setup for intermittant
use?
 
A

AB

Jan 1, 1970
0
If your current values for your loads includes the initial
inrush, then I think you'll be fine. But I am worried that
the strobe light includes a big capacitor that will suck
lots of current for a few milliseconds, right while those
contacts are bouncing to a stop, and that will eat the
contacts. <snip>

Are we talking just a ruined relay here or a possible fire risk?
 
J

John Popelish

Jan 1, 1970
0
AB said:
Are we talking just a ruined relay here or a possible fire risk?

No fire. Just the possibility of a welded contact that
won't release.
 
C

Chris

Jan 1, 1970
0
Still a newbie so please bear with me....

I have this 12VDC alarm panel that limits the siren output draw to
110mA. As this is not adequate for me, I replaced the siren with a
beefier model that draws 750mA and added a small strobe light that
draws 150 mA...so 900mA total draw.

I rigged a small relay to separate the alarm circuit from the new
siren/strobe...this one here:

http://www.radioshack.com/product/index.jsp?productId=2062481&cp=&sr=...

I also got a 1000mA rated wall wart to power the new setup. My
question is that since I'm pretty close to the maximum draw rating of
both the power supply and the relay...will the relay get hot and burn?
The circuit will only be in use for 12 minutes maximum and then the
alarm panel resets, but I really can't run the siren for 12 minutes to
test it.

What do you all think, should I be OK with this setup for intermittant
use?

Mr. Popelish has been steering you in the right direction. Since
you're at Radio Shack, try their 12VDC 10A DPDT relay Model: 275-217
with socket Model: 275-220. This will do the job -- it will reliably
work for you.

Good luck
Chris
 
J

John Popelish

Jan 1, 1970
0
Chris said:
Mr. Popelish has been steering you in the right direction. Since
you're at Radio Shack, try their 12VDC 10A DPDT relay Model: 275-217
with socket Model: 275-220. This will do the job -- it will reliably
work for you.
I think that is the part number for a relay socket. I think
the 10 amp relay with 30 mA coil current is 275-248.
 
E

ehsjr

Jan 1, 1970
0
John said:
I think that is the part number for a relay socket. I think the 10 amp
relay with 30 mA coil current is 275-248.

You're right 275-248 is the relay he should use.

Ed
 
A

AB

Jan 1, 1970
0
Thank everyone for (once again) great advice. I couldn't have done any
of this before hanging out here.
Bob
 
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