fuse question
Mar 5, 2006 at 3:02 PM Thread Starter Post #1 of 5

americandreaming

100+ Head-Fier
Joined
Jan 1, 2005
Posts
224
Likes
10
i went back and added a .25 amp fuse to my tread and it worked fine. however when i powered up my millett a second time it stopped working. i replaced the fuse but it happened again. is the 250 mA too small a value? what should i use?

while on the topic, what value should i use for a charlize amp? i'd rather not go through the process of uncasing and replacing fuses again.
mad.gif


thanks!
 
Mar 5, 2006 at 7:19 PM Post #2 of 5

mono

1000+ Head-Fier
Joined
Jan 10, 2005
Posts
1,412
Likes
11
Added a fuse where, exactly?


Any amp with a lot of capacitance and a PSu with a transformer capable of suppling a high current (relative to the fuse chosen) is expected to strain if not immediately blow the fuse.

A fuse is not a current limiting device, don't select a size barely bigger than the expected surge currents.

Given than the supply itself is capable of (arguably, depending on perspective such as amount of capacitance) at least 1A, it would seem unreasonable to choose a fuse on the output that is lower than 1.5A, or even larger if your transformer is capable of more.
 
Mar 5, 2006 at 9:33 PM Post #3 of 5

NeilR

500+ Head-Fier
Joined
Dec 2, 2005
Posts
929
Likes
12
My Millet ran 220ma, I think before I added discrete buffers. I watched the current once while it fired up and it was in the 300's, as I recall. Your fuse needs to survive the inrush current at start up when your caps charge up.

The tube heaters alone draw 160ma, I think- going by memory.

You also might want to use a slow blow, which I believe Tangent spec's for the Steps, for example. If it were me I would go with a half amp sloblo fuse, mainly because that is what I have in my Steps and it is surviving the Millet and an M3 drawing up to 350ma.

If something really goes wrong with your PSU (like a short across the output) , such that you need the fuse, I would guess that in many cases the precise value is irrelevent- it's going to blow
etysmile.gif
 
Mar 6, 2006 at 2:38 PM Post #4 of 5

americandreaming

100+ Head-Fier
Joined
Jan 1, 2005
Posts
224
Likes
10
thanks neilr and mono. the fuse was added between the dc input jack and the switch on the tread. i chose 250 mA because i remembered reading that value on tangent's tread parts lists. i guess it is an acceptable value for pimetas but too low for the millett. i will go with 800 mA or 1 amp.

not sure though with the charlize amp and haven't figured out how to measure current draw. you can't measure it in parallel like voltage, correct?
 
Mar 6, 2006 at 2:49 PM Post #5 of 5

NeilR

500+ Head-Fier
Joined
Dec 2, 2005
Posts
929
Likes
12
You have to put the meter in line with the DC power input....

I use a simple test cord to measure current into an amp from a plugged stand alone PSU. I used a panel mounted jack I had laying around, and a Kobiconn plug with attached cord. I cut the cord down to about 8 inches, soldered the ends to the jack, and added some heat shrink to prevent shorts if it touched a case. I cut the positive lead in the middle, and cut about two inches out of that lead, and tinned the ends. I attach my meter's grabber ends to the tinned leads. The reason I cut two inches or so from the lead in the middle is to try to prevent the two tinned wires from touching, which would not actually hurt anything but would take the meter out of the circuit.

Something like this:

(Tinned) (Tinned)
PLUG + ------------------- (2 inches removed)--------------- JACK +
PLug - ----------------------------------------------------- Jack -


I can use this cord to add current metering to anything that has a dc input jack without screwing around with the circuit.

My meter uses a cheap standard 5x20 250ma fast blo fuse. My tread "brick" is not fused (unless the wart is) so I use this for initial startups to add a fuse in line. I should add a fuse to the tread but never got around to it.
 

Users who are viewing this thread

Top