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Topic: Zerozone 100VA linear power supply with user-selected DC voltage with maximum amperage capacity, ranging within these seven options:1. 5VDC / 6A
2. 9VDC / 6A
3. 12VDC / 6A
4. 15VDC / 5.3A
5. 18VDC / 4.4A
6. 19VDC / 4.2A
7. 24VDC / 3.3A
I ordered the 12VDC/6A version, which operated just fine for a few months before it blew a fuse with a 3A maximum load device. There was a spare fuse in the IEC inlet with integral fuse holder, and that fuse was fine for another few month before it blew, too. The stock 5mm x 20mm slow-blow ceramic fuse value of only 1.6A 250V seemed insufficient for a 6A DC power supply, so I emailed the eBay seller about the correct fuse value and was told "Please use 1.6A --- 3A fuse".
That's the first time I've come across such wiggle room, with no indication of perhaps different fuse values based on the DC output voltage/amperage selection. So, I ordered 1.6A, 2A, and 3.15A AMR Audio silver alloy fuses that I'll work up the line with until a fuse remains stable over the test of time.
See link:
Edits: 07/21/17Follow Ups:
POST EDITED:100VA is being used as a marketing designation since it does not have an actual model number. The PSU features a 100VA toroidal transformer rather than the rated output of the PSU.
100VA transformer / 120Vac = 0.83 amps. As for the sizing of the AC line fuse protection to protect the transformer from overload multiply by, (anywhere from 110% to 250%. Depends on the designer of the piece equipment.)0.83 amps X 200% = 1.66 amps. Stock fuse ampere rating 1.6A
0.83 X 250% = 2 amps.Max FLA rating for the secondary of a 100VA transformer,
100VA / 12V = 8.3 amps. (Designer may have cut it back to 6 amp due to the full wave rectifier he used and or because of size of voltage regulator, if used).Duster,
I EDITED my post.I should have reread your original post. I misunderstood what you were saying. The pictures of the fuses in your post are 2 amp slow blow fuses.
http://www.littelfuse.com/products/fuses/cartridge-fuses/5x20mm-fuses/215/215002.aspx
If the seller said to use 1.6 amp fuse only, he must have a reason.The 1.6 amp rated fuse should not have blown with only a connected 3 amp continuous connected load.
3 amps X 12Vdc = 36 Watts.
As, I think someone said in an earlier post, place a DC ammeter in series with the connected load and watch the meter while the 3 amp connected load is fully loaded.
Edits: 07/22/17 07/23/17
Thanks for your input, jea48. The photo of the fuses shown in my first post is that of an aftermarket fuse, not the stock fuse, so don't pay attention to the 2A fuse value other than I plan to try a 2A fuse if another 1.6A fuse blows at some point.
At this time, I'm unable to wrap my head around the idea that a 6A DC power supply unit forbids no more than a 1.6A fuse at the AC line input. The notion of a 6A load not blowing a 1.6A fuse is remarkable to me, and even more so the idea of a 3A load blowing a 1.6A fuse in this case. I purposefully chose an aftermarket 6A linear power supply with twice the current capacity vs. a stock 3A switch mode power supply so I would have plenty of overhead for the application.
Since the Zerozone 100VA power supply is not intended for a specific application, I can only gather that the seller's "Please use 1.6A --- 3A fuse" recommendation is reasonable, rather than misinformation. However, it wouldn't be the first time I'd be disappointed by inaccurate information.
P = I X EP = watts, VA (Volt Amps)
I = amps
E = voltsHere we have a 100VA transformer. Manufacture spec 115Vac primary, 12Vac secondary.
Find the max available current, in amps, the secondary winding can safely deliver.
( Note: The max amp rating is determined by the wire gauge that was used to wind the secondary winding)100VA / 12Vac = 8.33 amps. So the gauge of wire used must be rated for at least 8.33 amps.
So how much current, amps, would the primary winding draw from the mains power if the secondary winding connected load is drawing 8.33 amps?
100VA / 115Vac (mains voltage) = 0.87 amps @ 115Vac. (Slightly higher due to losses)
( The wire gauge used to wind the primary winding must be rated to handle 0.87 amps minimum.If you had access to the transformer manufacture's data sheet for the transformer you would probably see Maximum Rated Primary current 0.87 amps at 115Vac. Maximum Rated Secondary current 8.33 amps at 12Vac
The manufacture supplied AC Line fuse is a 1.6 amps (slow blow) fuse. More than big enough to handle a continuous load of 0.87 amps of current the primary is drawing to supply 8.33 amps on the secondary needed for the connected load.
I am not sure why the 1.6 amp fuse is blowing with only a 3 amp connected load on the DC output of the power supply. One thing you might try is to install a temporary fuse in series with the DC connected load of say 4 or 5 amps. If the AC line 1.6 amp fuse still blows then there is something wrong with the power supply. If the fuse blows that is connected in series with the DC load then the problem is there.
By the why, what is the 3 amp connected load?
EDIT:
What is the AC mains voltage the power Supply is plugged into?Check the secondary AC winding voltage. What does it measure?
Measure with DC load connected.
Edits: 07/23/17 07/23/17
Images: Xfinity X1 DVR CATV box; Liteon PA-1360-5M01 12V 3A switch mode power supply that came with the Xfinity X1 DVR CATV box.jea48, did you notice Basslines' post about the Zerozone 100VA PSU stock fuse perhaps being intended for a 240VAC application? See link:
https://www.audioasylum.com/audio/tweaks/messages/20/204453.html
See link to data sheet for the Liteon PA-1360-5M01:
Edits: 07/23/17
Duster,The X1 DVR CATV box is drawing less than 1/2 the available power the power supply is built to supply. (12Vdc X 3 amps = 36 watts) The power supply is rated for 6 amps at 12Vdc. (6 X 12 = 72 watts)I doubt the CATV box draws 3 amps. 80% of 3 amps at best, jmo.
I personally would not increase the size of the AC line fuse from 1.6 amp.
If the 1.6 amp fuse has blown twice, and you are 100% sure it is not X1 Cable Box causing the overload,then there is a problem with the power supply.
Maybe the full wave bridge rectifier, or an electrolytic cap, or maybe a voltage regulator, or maybe an intermittent short. Something is drawing power in the power supply it normally should not. The 1.6 amp AC line fuse is doing what is is intended to do. First protect the power transformer from drawing more current than the wire of the two windings can safety handle. If the windings are overloaded beyond what the wire in the windings is rated for you will burn it up. The 1.6 amp AC line fuse is already twice the rating of the FLA rating of the transformer. (I see a label on the transformer, does it give any rating specs?)Second, if the designer of the power supply, designed the DC power supply properly, it should handle an overload caused by a connected load until the AC line blows. And hopefully if a component is the DC power supply causes an overload. Hopefully!
It still puzzles me, somewhat, why the Line fuse is sized at 200%, twice, the FLA rating of the primary of the transformer and not instead the FLA rating of the DC power supply. (The transformer will deliver more power than the DC power supply is designed to deliver)
EDIT:
Clarification.
There is nothing wrong with oversizing the power transformer.
The designer may have sized the transformer so it would not be loaded more than 80% of its' rating.
He may have, and I would not be surprised, sized the max output rating of 6 amps current, at 12Vdc, at 80% of the actually FLA continuous duty output rating.
Edits: 07/24/17 07/24/17
jea48,
I'm inclined to agree with your advice to stay on the safe side of things, and keep with a 1.6A slow blow fuse. However, isn't it possible that a 2A fuse would be safe if there is something about the design of the PSU that would allow it?
What might cause the Xfinity X1 box to be the source of the problem, in this particular case? It would be an easy thing to replace my current Xfinity X1 box with a new one free of charge from Comcast.
I assume the Xfinity X1 box has a male input power inlet connector on the back to feed the DC power to the unit. Can you buy a cheap power cable with the power ends needed to feed the Xfinity X1 box from the DC power supply?You could buy a cheap inline fuse holder and install it in series with the B+ DC power line of the cable. Install a 3 amp fuse and see if it blows after a couple months of use. If it blows then that would mean, imo, there is a problem with the Xfinity X1 box. If on the other hand the 1.6 amp AC line fuse on the power supply blows again, and not the 3 amp fuse installed on the DC power cord, the problem is with the power supply.
Food for thought. For the 1.6 amp AC line fuse to blow it takes 192 watts, VA, of power (1.6A X 120Vac = 192VA, watts), being consumed in the primary and secondary winding for a sufficient steady length of time, (see fuse manufacture's specs),for the element in the fuse to melt blowing the fuse.For a transformer, Power in = Power out, minus losses.
Edits: 07/25/17
Just installed an AMR Audio 1.6A 5mm x 20mm silver alloy slow blow ceramic fuse, and the Xfinity X1 box is up and running again, without a glitch, and without the stock switch mode AC adapter involved in the presentation:
Right off the bat, the Zerozone 100VA linear power supply vs. the stock switch mode PSU provides a somewhat greater liquidity, with a more relaxed energy flow, rather than a more forward and less subtle presentation via the swich mode PSU. To a degree, I think the most limiting aspect of the configuration is the mid-fi sound quality of the signal source rather than that of the power supply itself.
Crossing fingers that the fuse will remain stable over the test of time. If the audiophile fuse remains stable, I won't claim it's because the stock fuse was replaced with an audiophile fuse ;-)
BTW, in this thread, I mentioned a Zerozone 50VA PSU with a 3A output that features a 5A 250V 5mm x 20mm fast blow glass fuse. How do you do the math for that one, Jim?
For kicks and giggles, I tried one of the AMR Audio 1.6A 5mm x 20mm silver alloy slow blow ceramic fuses vs. the stock 5A 250V 5mm x 20mm fast blow glass fuse, and can clearly hear an obvious improvement in texture, albeit subtle in nature. What might be a safety issue if I use the 1.6A slow blow rather than the 5A fast blow fuse with the 50VA version? TIA
BTW, in this thread, I mentioned a Zerozone 50VA PSU with a 3A output that features a 5A 250V 5mm x 20mm fast blow glass fuse. How do you do the math for that one, Jim?
The wrong size fuse.
50VA / 120V = 0.42 amps.
(50VA / 115Vac = 0.43 amps)0.42 amps X 125% = 0.53 amps (Just a guess the fuse probably was supposed to a .5 amp, 1/2 amp, slow blow fuse)
0.42 amps X 150% = 0.63 amps
0.42 amps X 200% = 0.84 amps
***** 0.42 amps X 1200% = 5.04 amps YIKES! *****
120Vac X 5 amps = 600VA
> > > > > > > > > > > > > > >Secondary side of transformer,
50VA / 12Vac = 4.2 amp max output rating.A 5 amp fuse will not protect the 50VA transformer from burning up in the event of a continuous overload beyond what the winding wire in the transformer is rated for. Yes the fast blow fuse probably would blow in the event of a dead short, but not a continuous overload. A 5 amp fuse will pass 4 amps all day long without breaking a sweat.
4 amps X 120Vac = 480VA. You transformer is a 50VA..
NOTE: The 1.6 amp fuse in the 100VA power supply is supposed to be a slow blow fuse, right?
.
Edits: 07/25/17
jea48 wrote:
"NOTE: The 1.6 amp fuse in the 100VA power supply is supposed to be a slow blow fuse, right?"
That is correct. The stock fuse for the 50VA version is 5A fast blow.
The stock fuse for the 50VA version is 5A fast blow.
I forgot to mention. A 5 amp AC line fuse increases the secondary output to 40 to 50 amps.
***** 0.42 amps X 1200% = 5.04 amps YIKES! *****
120Vac X 5 amps = 600VA600 watts / 12 volts DC = 50 amps.
Jim
Edits: 07/25/17
Based on your information, I assume the Zerozone 50VA 3A PSU should have an approximate 0.8A 250V slow blow ceramic fuse. I plan to order an AMR Audio 1A 250V silver alloy slow blow ceramic fuse, which should certainly be better than the stock 5A 250V fast blow glass fuse. I simply don't know what they were thinking.
How about the slow blow vs. fast blow question, Jim?
Usually a designer of a piece of equipment will use a slow blow AC line fuse if the equipment draws high inrush current when the equipment is first powered up. Also if the equipment, under normal operation, draws short above normal durations of current. Example would be a decent size power amplifier.
In this case the 100VA/watt power supply unit. When the piece of equipment is first turned on, from a cold start, the caps in the DC power supply draw larger amount of current at first until they charge.Also, I imagine, in the case of a stand alone DC power supply unit that is built to power a remote piece of equipment inrush start up current may also be a factor for using the slow blow fuse. The lag time of a slow blow fuse passes the high inrush current for a time until the current drops, falls off, to normal current level which is within the normal part of the fuse's ampere rating.I question the designer's reasoning for using an AC line in the 100VA/watt power supply with, a 12Vdc 6 amp max output rating, choice of ampere rating of the fuse used. For the 100VA power supply unit I can understand using a slow blow fuse. What I don't understand is the designer's reasoning for using a fuse rated at almost 200% of rated 100VA/watt rating of the unit. I mean as stated above the slow blow section of the fuse allows for cold start up inrush current, as well, it will allow for short duration draws of current placed on the power supply from the connected DC load. Jmho, the slow blow AC line fuse should have been sized, for the 100VA/watt power supply unit closer to 110% to 125% of its' max output connected load rating than at 200%. A 1 amp slow blow fuse by my calculation.
Manufacture rating of the 100VA power supply in the eBay ad.
115Vac input
12Vdc output, max 6 amp connected load rating.100VA / 115Vac = 0.87 amps. (safe FLA continuous duty)
0.87 X 110% = 0.96 amps.0.87 X 125% = 1.09 amps.
Edits: 07/27/17
Protection - Table 450.3(B)
PRIMARY 1000 VOLTS & LESS
PRIMARY PROTECTION ONLY
Currents of 9 Amps or More 125%
Currents Less Than 9 Amps 167%
Currents Less Than 2 Amps 300%
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
https://www.audioasylum.com/audio/tweaks/messages/20/204476.html
But that is for transformers that fall under the jurisdiction of NEC. Not necessarily for cord and plug connected power supplies for audio and or video equipment. I think for overcuurent protection in this case it would be more under UL, NEMA, or some other safety equipment standards.
Where you see the 2 amps or less being 300% somewhere deeper in the code, that 300% figure is meant more for the overcurrent protection of control transformers not a small transformer used for power.
Control transformers are used in appliances and equipment to operate control devices that switch on and off larger power devices. Example a gas fired furnace found in a home. It will use a step down 120V to 24V control transformer to supply the power for the various control circuits. One being to start and stop the blower fan. (Note: Normally small VA rated transformers, say 25VA or so, will have built in fuse protection)
In commercial buildings and industrial facilities control transformers are found in all kinds of equipment. Example, motor control centers, Automated lighting switching equipment. Simple thing as an automatic door opener when you walk into a store.
This code also uses the no more than 300% factor on trannies under 2A. It also states that in control circuits the factor should be no more than 500%. Primary fuse. So it looks like some control circuits can use a higher amp fuse but the 300% figure for Duster's situation is correct. T456
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
UL and CSA (North American) Standards
North American standards, including UL 508, National Electric Code 450 , and the Canadian Electrical Code, Part 1, require
overcurrent protection on all control circuit transformers. There are two options for overcurrent protection.
.
Again relates to NEC. You need to find something that pertains to cord and plug connected equipment/appliances. Specifically consumer electronics.
I don't see any exclusion for our type uses anywhere I look. Here is what Cooper Bussman has to say. They state the standards discussed (300%) and then say it may not be adequate protection. I think I'm done. I getting a headache. While 300% looks to be the standard it looks like you, I and Bussmann think 300% is pushing it. They like the 125% thing. T456
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
Edits: 07/27/17
Article 450 Transformers
Step up your knowledge of NEC transformer requirements
Extracted from Mike Holt's Understanding the National Electrical Code textbook for EC&M Magazine
Article 450 begins with the terse statement:"This article covers the installation of all transformers." Then lists eight exceptions. In essence, Article 450 covers power transformers, transformer vaults, and most kinds of lighting transformers (Figure 450-1).
Note: Graphic images are not contained in this newsletter; they will be in the magazine.
Overcurrent Protection
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
Article 450 begins with the terse statement:"This article covers the installation of all transformers." Then lists eight exceptions. In essence, Article 450 covers power transformers, transformer vaults, and most kinds of lighting transformers (Figure 450-1).
Read NEC Article 90.1(A)(B)(C). Then 90.2(A)
I don't see where the NEC guidelines state that it is for control transformers only. Not saying it isn't there, I just don't see it, yet? So this looks like a control transformer would only be operating for a short time?? A transformer under 2A is by definition a fairly small transformer don't you think? I'd like to see the UL and or NEMA guidelines. I'll look for them. Maybe you have their publication. T456
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
So this looks like a control transformer would only be operating for a short time??
No not at all. A control transformer may be energized 24/7, 365 days a year.
A transformer under 2A is by definition a fairly small transformer don't you think?
Yes. Especially to the building electrical industry.
Something to remember about NEC. It is bare minimum electrical safety standards. It is not intended to be used as a design manual or a how to manual. See NEC Article 90.
If you wired a building, and say there was a fire and it turned out it was determined it was caused by faulty electrical wiring. If the customer sued you and for your defense in court you said to the judge, "judge I wired the building per City electrical code as well as the National Electrical Code". You will lose the case.
Read NEC Article 90.1 Purpose. (A) (B) & (C).
Then read 90.2 Scope. (A) Covered.
did you notice Basslines' post about the Zerozone 100VA PSU stock fuse perhaps being intended for a 240VAC application
Yes, I read it.
If the unit was made to be fed from 230Vac the max rated primary amps would be,
100VA / 230Vac = 0.43 amps.Fuse size, using the 200% for the 120Vac mains calculation,
200% X 0.43 = 0.86 amp. Just a guess the manufacture would install a 1 amp fuse or the next lower size near 0.86 amps.EDIT:
Though I would not use 200%. At most 150%. 150% X 0.43 = 0.65 amps. Fuse closest to 0.65 amps.When you get a chance measure the mains voltage at the wall outlet the power supply plugs into.
Also the secondary AC voltage of the transformer loaded with 12Vdc load connected.
And the DC out voltage with the load connected.Is the power supply left on 24/7?
Is the connected load left on 24/7?
Edits: 07/23/17
Duster, you have to understand that the primary and secondary see different current. The primary is high voltage, low current and the secondary is low voltage high current. It does seem counter intuitive but that's how it works. I just learned or relearned this myself as a result of this issue and not thinking about it for a long time. T456
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
Jim, where did you get the factor of 2.5. I've never seen that high a factor before in my readings. Seems too high?? Thanks, T456
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
I can't remember if it originated with NEMA or UL electrical safety standards for transformers of 1000Vac and less. My above post was going from memory....
But the percentage rating for overcurrent protection can be found in 2014 NEC Article 450, 450.3, Table 450.3B
Duster's power supply uses a 100Va transformer. Max FLA rating is
100VA / 120Vac = 0.83 amps
Table 450.3B Maximum Rating or Setting of Overcurrent Protection for Transformers 1000 Volts and Less (as a percentage of transformer-rated current)
Primary Protection
Primary only protection
Currents Less Than 2 amps - 300%
Not sure I would go 300% on a 100VA power supply transformer though.
Note:
Currents of 9 amps or more, 125%.
Current less than 9 amps 167%.
Currents less than 2 amps, 300%
Throw in secondary protection and the percentages are 250% across the board. (see note 3)
Awsome info jea. Thanks! This seems to somewhat contradict some of the other info I've seen and heard that is quite a bit more conservative. Never saw this before. T456
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
This seems to somewhat contradict some of the other info I've seen and heard that is quite a bit more conservative. Never saw this before. T456
Tweaker456,
I should have qualified my response, given in my previous post, is for transformers that fall under the jurisdiction of the NEC. Mains power AC line overcurrent protection of power transformers used in cord and plug connected electronic equipment may be different. Though I believe the max 250% of the manufacture's FLA ampere rating of a power transformer is probably safe. But that may not be the case.
Bottom line though, the designer, manufacture, of the equipment has the final say on what amperage fuse size and type of protection fuse he requires to be installed in his equipment. If the equipment is under warranty and the user installs a bigger fuse and or different type fuse and through an equipment internal failure, or caused by a connected overload, damage to the equipment may/will void the manufacture warranty.
In this case the 1.6 amp fuse is 200% of the 100VA rating, 0.83 amp FLA max rating,(for 120Vac mains) of the transformer used in the power supply.
NOTE: It seems the seller that sold Duster the Power Supply said he could use a fuse higher than the 1.6 amp supplied fuse up to a 3 amp fuse.
I read the eBay seller's add and he states the AC input voltage being 115Vac not 120Vac. I can only assume 115V is from that of the manufacture's spec of the power transformer.
100VA / 115Vac = 0.87 amps (max rated primary continuous duty amps)
300% X 0.87 = 2.6 amps @ 115Vac
100VA / 120Vac = 0.83 amps
300% x 0.83 amps = 2.49 amps
350% x 0.83 amps = 2.9 amps
Not sure I would use a 3 amp fuse to protect a 100VA transformer. I don't think an AC Line 3 amp fuse will protect the full wave rectifier or voltage regulator from a connected overload.
Jim
.
In this case one sure can't rely on the manufacturer or seller. I'm working on getting fire extinguishers put in audio equipment so the standard can be raised to a factor of 600% (just kidding). A factor of 300% seems to me to imply that they would believe that most faults would be above that and that there is a very low likelihood of a constant 300% current draw in a fault situation. Otherwise 300% doesn't seem like a safe recommendation. T456
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
Another stock fuse value in question; this time it's a lower-current Zerozone 50VA linear power supply.I have the 5VDC/3A version, and the 12VDC/3A version; the stock fuse of both versions is 5A 250V 5mm x 20mm glass fuse, which is a higher rated fuse for AC than I would expect for 3A maximum DC load. This is the opposite situation vs. the higher-current Zerozone 100VA linear power supply issue, with a seemingly under-valued fuse rating.
Zerozone 50VA PSU - User-selected output voltage / current options:
1. 5VDC / 3A
2. 9VDC / 3A
3. 12VDC / 3A
4. 15VDC / 2.7A
5. 8VDC / 2.5A
6. 24VDC / 2A
Since both Zerozone 50VA power supplies are used for very low-current demand components (under 1A load), I'll try a 1.6A AMR Audio silver alloy ceramic fuse with them. Unless there is substantial inrush current when the PSU is powered-on, I expect the 1.6A fuse will be very stable and perhaps sound better than the stock fuse.
See link:
Edits: 07/21/17 07/21/17
The 1.6a fuse on the 100VA is probably not underrated as per the math in my previous post. 50va/120V=.4166. .4166x 1.35=.562. The 1.35 is a "headroom" factor one reads about when looking into how to calculate a safe fuse value. They talk about going the closest next size up. Whoever is putting these things out either has their head up their you know what or my and Lew's calculation method is incorrect. I went through this with an electronics guy with my amp and this is the correct method for the ac primary fuse. My 5A peak current, 3A constant Tripp Lite came with a 5A fuse if I remember correctly,which seems incorrect also for a primary fuse. Maybe it's a secondary fuse but that would mean the Tripp Lite had no primary fuse. If it's a primary fuse that would mean it was a 360 watt to 600watt peak wattage device. No way Jose. While my calculations my be missing something,something sure is wrong with what you PS people are doing. Safety first, I always say. T456
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
It seems the issue of the 5A stock fuse for the lower-current Zerozone 50VA 3A PSU vs. the 1.5A stock fuse for the higher-current Zerozone 100VA 6A PSU indicates inappropriate fuse ratings, either overrated or underrated. A safe-bet is to try the 1.6A, 2A, and 3.15A fuses in that order, since the values are conservative enough to avoid meaningful risks, IMO. It's far better to expend a few underrated fuse values due to nuisance blows rather than what might be an overrated fuse value for any given application.
12x6= 72 watts (VA) ? Not 100. It's possible that a fuse of 6A x 1.35 is considered safe in the EE World, or the next highest if needed. In this case an 8 amp fuse might be safe from a EE point of view. Anyone out there know for sure?? T456
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
Assuming this is a voltage-regulated supply, you'd need to know the V developed before the regulators, in order to get an idea of the VA consumed and that is seen by the fuse.
It rated at 100VA. 100/12= 8.33 amps. Not 1.6A, not 3a and not even 6A. There is some wrong going on.
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
I could be wrong, but I think you are conflating two different quantities. The fuse is on the AC line going in. The size of the fuse has to be in relation to the AC power consumed, not the power that goes out to the equipment. Of this, I am sure. The fuse is seeing 120V coming in, so the divisor in your little equation is 120, not 12. Therefore also, the AC current consumed from the wall socket is way less than 8.33A, probably less than 1A. But we are still missing the bit of data that tells us what voltage is developed at the secondaries of the transformer. If the output is regulated (as I mentioned before) then the voltage at the secondaries has to be > 12V, maybe 15V or more for decent regulation. What I am not certain about is whether the 100VA rating refers to output or input power. The natural assumption is that it refers to output.
Edits: 07/19/17
Lew, wouldn't the max wattage (va) or the actual wattage be similar at the secondary and the primary?? UM's suggestion to actually measure what's going on, while it's a good suggestion, this issue should be dealt with correctly by the engineer of the product before they send these things out with fuses that don't make sense. Although fuse sizing can or maybe a bit complex in some situations it's still basically comes down to Ohm's Law with a certain amount of headroom from what I can tell. T456
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
Actually I think this is correct. Basically what you said Lew. 100VA/120v=.8333. .833x 1.35= 1.12A for a reasonable rating for a primary fuse. It looks like it would have to be 6A rated at the secondary. So the numbers being thrown out of 1.6-3A fuses do not look correct. Pretty sure we are talking about a primary fuse. 1.6 is a bit high and a 3A should be out of the question if staying within conventional safety calculations. This seems to put Duster back in the hot seat in terms of the frequent blowing.
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
Edits: 07/19/17
100VA is being used as a marketing designation since it does not have an actual model number. The PSU features a 100VA toroidal transformer rather than the rated output of the PSU.
....is probably the correct one for the 240vac model. The 120vac model should use a primary fuse twice the value of the 240vac model (remember, twice the voltage-half the current. Half the voltage-twice the current). Manufacturers in Europe and Asia make this mistake often on products shippef to North America.
I think you nailed it, Basslines. The intended fuse value for 120VAC environment is likely 3A. It's unfortunate that a sloppy job like that is involved, since sellers should be more attentive towards an important issue such as this.
What is wrong with a 6A fuse in a 6A PS?? The Tripp Lite I bought had at least the fuse rated for the current the PS was rated for. I don't understand this. It seems to me something incorrect in this scenario . Why would a 6A device have to be limited to a 3A fuse? I'm guessing it's a primary fuse?? T456
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
Edits: 07/19/17
If as you state your load is 3A max @12V that's 36W. Not counting losses that would be 0.6A @120V. A 1.6A slow blow would seem to be adequate. Could be that there is a current surge at turn on. Those caps look big.. Have you got a schematic? Is there a small value resistor between the bridge and the first cap? Then again you could do as suggested and try a larger fuse to try to lessen the number of nuisance blows.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
Good points, JKT. I think the current demand of the load might be substantially greater than 3A at times, so the best option is to simply test the fuse values between 1.6A -> 3A. It's better to blow a few fuses since I have no way of confirming the appropriate fuse rating for the application. I expect at least one of the fuse values will be sufficient, and safe for the unit to operate (knock on wood). Otherwise, it's a fine sounding linear power supply unit.
"I have no way of confirming the appropriate fuse rating for the application."
You do have the means to check the output current draw however. Since it's low voltage DC put a multi-meter, set to amps, in series with the output and turn things on. At turn-on you will probably see a momentary spike as things charge. To do a thorough check make sure all equipment downstream are discharged, letting them sit or through a bleed resistor.
The spike may not blow the supplied fuse immediately, recall you told us there were extended periods before there was trouble. it's probably at it's limit and repeated turn-on fatigues it.
I would bet a slo-blow fuse fixes your problem. I would use the fuse closest to the measured output current draw. You want to protect your audio equipment more than the power supply.
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