Definition of mA

Users who are viewing this thread

Giles

Retired tool & Die and Mechanic
Messages
110
Reaction score
0
Points
16
Location
N.W. Alabama--Florence--
I have a PowerMax+ Security system that has a maximum output of 550mA at 12dc volts for a remote siren. I have a large 6v bell that requires .5 A.dc
I hooked the bell up and tried it for about 5 seconds and it is really loud.
I am conserned that damage may be done to either the bell or the security system, main consern is security system.
I guess what I am asking is 550mA considerably less then .5 amp. I am also aware that I am using a 6volt bell with a 12volt source.
 

CarlH

Member
Messages
179
Reaction score
1
Points
16
Location
Northern VA
Hooking up that 6V bell to a 12V power supply will roughly double the current draw (Amps) of the bell. That would be about 1000 mA or 1 A for the bell running off of the 12V supply. I would not hook that bell up to that system or you may either blow any over current protection on the power supply or damage the power supply.
 

Giles

Retired tool & Die and Mechanic
Messages
110
Reaction score
0
Points
16
Location
N.W. Alabama--Florence--
Hooking up that 6V bell to a 12V power supply will roughly double the current draw (Amps) of the bell. That would be about 1000 mA or 1 A for the bell running off of the 12V supply. I would not hook that bell up to that system or you may either blow any over current protection on the power supply or damage the power supply.

THANKS to both of you for the quick answers. I felt that this was the situation and that is why I only ran the bell for 4 or 5 seconds. Even that could have caused problems! I guess I could use a relay and separate power source but that is a thought for later. I have a 12v external siren but the bell is, of course, much louder.
 

Thatguy

Homeowner
Messages
1,454
Reaction score
3
Points
0
Location
MD
I have a PowerMax+ Security system that has a maximum output of 550mA at 12dc volts for a remote siren. I have a large 6v bell that requires .5 A.dc
I hooked the bell up and tried it for about 5 seconds and it is really loud.
I am conserned that damage may be done to either the bell or the security system, main consern is security system.
I guess what I am asking is 550mA considerably less then .5 amp. I am also aware that I am using a 6volt bell with a 12volt source.

Assume the 12v supply goes to 14v with no load. This gives an internal impedance of (14-12)/0.55 = 3.6 Ω.

Your load is 6/0.5 = 12 Ω at 6(0.5) = 3W, rated power.

Your bell saw 14(12)/(12+3.6)= 11v @ 14/(12+3.6) = 0.9A for a power of ~10W.
You might have shortened the life of your bell.

Use a series dropping resistor.
You want a half amp, so 14/R = 0.5, so R = 28 Ω; the bell uses 12 Ω so you need another 28-12=16 Ω, with a power rating of 2x(16(0.5²))= 8w.
Believe it or not, a 75w incand. household lamp will do pretty well for this resistor. It won't light and probably won't be warm. If the measured bell voltage is less than 6 then use a larger bulb.
 
Last edited:
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks