It's similar to a transformer.
Peak starting current is very much higher than continuous running current.
Fusing needs to be ~ 3times more than the power would indicate if direct on-line starting is required.
Special arrangements are required for starting motors that have a heavy load during the start up.
Motors can have a soft start option just like transformers.
Peak starting current is very much higher than continuous running current.
Fusing needs to be ~ 3times more than the power would indicate if direct on-line starting is required.
Special arrangements are required for starting motors that have a heavy load during the start up.
Motors can have a soft start option just like transformers.
Hi. why on earth would anyone fit a thermal fuse that makes no contact with anything. Im guessing from the piccys you have posted the thermal fuse you talk about was in the location next to the AC input conector . The one with the american resistor symbol. It is quite normal to have a wire wound resistor in this location.
In my expirience with this type of psu if there is a short on the output the psu starts to trip and makes a quiet chirping sound at approx 0.5 second intervals. and does not blow the primary side fuse. do you have a piccy of this so called thermal fuse . I agree with the other members and very much doubt it to be a thermal fuse.
Regards Ian F
In my expirience with this type of psu if there is a short on the output the psu starts to trip and makes a quiet chirping sound at approx 0.5 second intervals. and does not blow the primary side fuse. do you have a piccy of this so called thermal fuse . I agree with the other members and very much doubt it to be a thermal fuse.
Regards Ian F
Hi. why on earth would anyone fit a thermal fuse that makes no contact with anything. Im guessing from the piccys you have posted the thermal fuse you talk about was in the location next to the AC input conector. Correct.
I had assumed initally that it was a thermal fuse from the microscopic piece that was left after it blew. This appears not to be the case. It was soldered to the board where the squiggle marking is.
Do I try a fuse? If so what rating?
The piece left after it blew was a tiny piece of glass, so it does not seem to have been a wire-wound resistor?
I had assumed initally that it was a thermal fuse from the microscopic piece that was left after it blew. This appears not to be the case. It was soldered to the board where the squiggle marking is.
Do I try a fuse? If so what rating?
The piece left after it blew was a tiny piece of glass, so it does not seem to have been a wire-wound resistor?
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It was most likely a normal wire ended glass fuse with the heatshrink round it to contain the fragments if it ruptured with a high fault current. A better PSU would be fitted with a proper HRC fuse. The rating may be on the metal ends but if not a 3.15A type T is a good bet for the apparent size of the PSU. However the fact that the original disintegrated suggests that at least the main switching transistor / IC is blown and this makes repair possibly difficult .
Try to find out the size of the motor the power supply operated. If you can't find that out find out the current ratings of the transformer and the rectifier. You can get advice on what size and type of fuse to use for a particular motor size for a given voltage from Cooper Bussman's web site. Use their recommendation or the next highest size. If you can't get that information use a fuse lower than the lowest rating between the rectifier and the output winding of the transformer. This can be calculated if necessary by its volt amps rating.
All fuses are thermal. The operate by heating a thin piece of wire or for larger fuses a piece of solder. When the temperature reaches a certain point it melts opening the circuit. The voltage rating is the highest voltage in the circuit that the fuse is operated at where arcing across the terminals won't occur when the fuse is open. For a 12 volt circuit it should usually be at least 125 volts, higher is ok. Every fuse like every circuit breaker has a time current curve. This must be coordinated with the time current curve of the load so that they never cross. That means the fuse's curve must be to the right and above that of the load but to the left and below that of the capability of the rest of the power supply. Different types of fuses with the same nominal rating have different curves. If you have a problem, consult an electrical equipment supply house or call a fuse manufacturer's technical support or applications engineering department for assistance.
All fuses are thermal. The operate by heating a thin piece of wire or for larger fuses a piece of solder. When the temperature reaches a certain point it melts opening the circuit. The voltage rating is the highest voltage in the circuit that the fuse is operated at where arcing across the terminals won't occur when the fuse is open. For a 12 volt circuit it should usually be at least 125 volts, higher is ok. Every fuse like every circuit breaker has a time current curve. This must be coordinated with the time current curve of the load so that they never cross. That means the fuse's curve must be to the right and above that of the load but to the left and below that of the capability of the rest of the power supply. Different types of fuses with the same nominal rating have different curves. If you have a problem, consult an electrical equipment supply house or call a fuse manufacturer's technical support or applications engineering department for assistance.
The fuse has already done it`s job - the rest of the PSU is blown and there was no fire.
I removed the heatsink today to get a better look at this. You can see that the cap next to the larger electrolytic (0.1uf) has smoked.
If I remove the TOP261Y what readings should I get with a DMM to see if it is dead.
If I remove the TOP261Y what readings should I get with a DMM to see if it is dead.
An externally hosted image should be here but it was not working when we last tested it.
Suggested procedure :-
Remove the blown cap.
Measure across the large cap - it will probably measure short but the fault is most probably elsewhere.
Remove the TOP 261 - short probably goes away.
Check all diodes on the mains side - this can probably be done in circuit - 0.6 volt forward drop, something more reverse, if in doubt lift one end.
Check all resistors in the area.
Check the O/P connection for a dead short
Replace any faulty components, this will almost certainly include the TOP261.
Remove the blown cap.
Measure across the large cap - it will probably measure short but the fault is most probably elsewhere.
Remove the TOP 261 - short probably goes away.
Check all diodes on the mains side - this can probably be done in circuit - 0.6 volt forward drop, something more reverse, if in doubt lift one end.
Check all resistors in the area.
Check the O/P connection for a dead short
Replace any faulty components, this will almost certainly include the TOP261.
I think Barry has put you on the right track. Just wondering if that cap failed due to a transient or defect or failed as the result of something else failing first. Be sure to replace that cap with the exact same type which I suspect is probably an X2 - hopefully it is still legibly marked on the case.
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