12 Vdc motor blow fuse
12 Vdc motor blow fuse
(OP)
Hi,
I have a small circuit :
12Vdc--fuse--SSR---motor---gnd
The parameter of the fuse : little green lookalike resistor 5A.
relay : 3.5A, 5A peak (1sec)
motor : 3.3A, 12V. When stopped, the resistance of the motor is 1ohm.
The problem I can see:
When the motor start, it consume about 12A for a small amount of time. My fuse is 5A, so she blow. But what about my relay ?
Do you have any suggestion to help me with this issue ? I don't know much about motors and how to control them.
thank you
I have a small circuit :
12Vdc--fuse--SSR---motor---gnd
The parameter of the fuse : little green lookalike resistor 5A.
relay : 3.5A, 5A peak (1sec)
motor : 3.3A, 12V. When stopped, the resistance of the motor is 1ohm.
The problem I can see:
When the motor start, it consume about 12A for a small amount of time. My fuse is 5A, so she blow. But what about my relay ?
Do you have any suggestion to help me with this issue ? I don't know much about motors and how to control them.
thank you





RE: 12 Vdc motor blow fuse
Mike Halloran
Pembroke Pines, FL, USA
RE: 12 Vdc motor blow fuse
I'll look for the datasheets of my SSR, I'm pretty sure he's not intended for motor starting. But we have a lot of unit shipped and I did'nt get any problem with the SSR (maybe the fuse is protecting it and if I try a bigger fuse I'll get problem with the relay).
what is the correct way to size the fuse ? Do I have to use a slow blow at about 4A ? or I need a fast blow at about 20A ?
do you know any SSR I could use ?
Thank you
RE: 12 Vdc motor blow fuse
They'll probably ask you what kind of motor it is, and what load it's trying to accelerate.
Mike Halloran
Pembroke Pines, FL, USA
RE: 12 Vdc motor blow fuse
Motors generally require slow blows because they almost always look like a dreadful short when first turned on, especially if loaded some. I would get several different slow blow values that are around 4A and try them. Settle on the lowest value that won't nuisance blow in a warm temperature.
Make sure you really test your solution! Nothing is worse then sending out a "solution" to the field that causes another problem...
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: 12 Vdc motor blow fuse
I'll add some more information
The motor is in fact a piston pump. The load is always the same. There is not a big pressure and not a big flow.
Thanx
RE: 12 Vdc motor blow fuse
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: 12 Vdc motor blow fuse
A fuse that works well with a low inertia fan load may not be able to start the same motor driving a piston pump against back pressure.
Consider dual element or "Slo-Blo" fuses. Code for AC motors is 125% of motor full load current rating for time delay fuses. That's probably a good starting place for the tests recommended by itsmoked. Also, do you want to protect the motor from overloads, the relay in the event of motor failure or the just protect the circuit board in the event that either the motor or the relay short out? Your protection philosophy will influence the fuse selection.
respectfully
RE: 12 Vdc motor blow fuse
RE: 12 Vdc motor blow fuse
Do somebody could give me any part number ?
It`s for a 3.3A 12VDC motor.
Thank you
RE: 12 Vdc motor blow fuse
In my mind, I'd like to limit the current so the motor will not blow my power supply. I think the fuse I want is to protect the relay, the pump and the board.
Thank you
RE: 12 Vdc motor blow fuse
RE: 12 Vdc motor blow fuse
Most DC relays are really FETs and I'll bet the 5amp for 1 second is a thermal rating and the FET will handle 12 amps for a short period of time (clearly you have a number in the field that continue to work). When you determine a fuse that will work, stall the motor and see if the relay blows before the fuse does.