Power connector overfused

[torch]

@sovol: My SV08 Max died today.

It had successfully completed a print overnight. I removed the print, changed the filament and started pre-heating the bed. While I was preparing to upload the next file, the fans quit spinning, LEDs went dark, the screen went blank and it dropped off the local network. DED dead. Joined the Choir Eternal. It was no more, had ceased to be, was bereft of life, it rested in peace. This was now an ex-printer.

I won’t bore you with the ensuing diagnostic investigation, suffice it to say I tracked it down to a defective power socket. One of the conductor’s rivets was now loose and the connection intermittent. Fortunately I had a spare from another project that would fit.

But during the investigation, I discovered the installed fuse is rated 15 amps. The power switch is only rated 10 amps (at 125VAC – I’m in North America). This should not be! For safety, the fuse should be equal to or lower than the rating of any other component! I’m pretty sure this violates any electrical safety certification.

I know from past curiosity that the SV08 Max (120VAC version) draws just under 10 amps when pre-heating the bed and typically draws about half that when printing PLA.

I installed a 10 amp slow-blow ceramic fireproof fuse. I’ve run several pre-heat (65°C) and printing cycles now without blowing it, but haven’t tried any high temp prints with ABS, etc. as yet. If it needs a 15 amp fuse to meet the published specifications then it needs a 15 amp switch and socket as well! I am now suspecting repeated heat/cool cycles drawing current at the limit may be what caused the rivet to loosen in the first place.

This should either trigger a recall or you should provide owners with the correctly rated parts for retrofit.

[sovol3d]

This fuse is located on the motherboard. The motherboard can operate at up to 15A, and this fuse protects it. The motherboard was designed for 15A. The power supply’s wattage and current were determined based on the actual functions used (some functions were not used or were not fully utilized), which is why the power supply current is slightly lower. The power supply also has short-circuit and overcurrent protection functions, not just the fuse on the motherboard. The entire system also has an AC fuse to protect the entire machine.

If you have any questions, please send the email to info@sovol3d.com The after-sales staff will help you to solve it.

[torch]

@Sovol

To your list above, I would add the machine came with a heavy duty power cord – heavier gauge than most. It was one of the things that impressed me when I first got the machine.

There may well be a fuse on the motherboard too – I wouldn’t know, it’s irrelevant. A chain is only as strong as the weakest link. Besides, a fuse on the motherboard (which is after the power supply) is probably protecting low power 24VDC circuits and in any case does nothing to protect the wiring to the bed heater. The bed heater is claimed to be 1300 watts. I suspect that may be the 250VAC version since it would require 10A @ 125VAC. My own measurements suggest the current draw of the bed is closer to 5A @ 125VAC.

The fuse I am referring to is inside the power inlet module, before everything (but the cord).

If you will kindly observe, the power enters the machine through the power inlet module. The wiring then bifurcates, feeding both the power supply AND the bed heater module:

Please look closely at the female spade wire connector on the red wire in the centre of the power inlet module. Notice how it is discoloured? That brown suggests the insulation around the connector has been overheated. That’s on the terminal that is loose and failed.

The fuse and switch to which I refer are located inside that power inlet module, protecting BOTH the power supply and the bed heater:

Again, look closely at the upper fuse contact in the module’s base. See the brown discolouration? This is the other side of that loose connector.

Let us now proceed to look at the switch rating:

5A @ 250VAC
10A @ 125VAC

OK, what about the power inlet module itself then, what are those contacts rated for?

It doesn’t give a value at 125VAC, but 10A @ 250VAC means it can handle 2500V-A so we’ll give it the benefit of the doubt and say it could be good for as much as 20A @125VAC125VAC. The loose connection may have been due to manufacturing error rather than overloading. Hopefully mine is an isolated case.

To sum up then:

Power cord: 15A
Fuse: 15A
Switch: 10A
Module base: <20A (?)

See the weak link in the chain? The fuse should never be sized for a higher current than the lowest rated component can handle.

QED: Sovol either needs to install 10A fuses or 15A switches.

[Lion]

These switch are always the weakest link in a printer.
I’ve replaced 2 of mine so far & will expect to replace others in the future.
I hope that since you see the discoloration, that you have found a suitable replacement switch on Amazon.
Most of what you will find will be the same switch, 10amp or 15 amp glass fuse, maybe an extra prong & some with a little pre-wiring.
Myself, I never use the wires because they are usually a smaller gauge.

You seem smart enough to know what your doing…
so please post back with what kinda of switch you used for the MAX.

@torch

I installed a 10 amp slow-blow ceramic fireproof fuse.

[torch]

For now, I used a 10A power input module with a 10A ceramic slow-blow fuse because that’s what I had on hand. It seems to be up to the task printing PLA – but it’s right on the edge of 10A while pre-heating. Current draw drops to around 5-6A when printing. The bed heater requirements are probably higher when printing something like ABS so I don’t know where that will land yet.

It’s a snap fit, but it fits the hole and got me printing again:

I haven’t yet found a SPST switch of this size and shape rated higher than 10A @ 125VAC – but I do have a DPST switch rated 10A @ 125VAC per pole. I could either parallel the poles or use one pole to power the bed heater and the other the printer power supply. It doesn’t have an illuminated rocker, but I can live with that.

Fuses on the left, DPDT switch in the centre, Sovol’s switch on the right:

[fmstrat]

Replying to follow this. This seems like a big deal, and would like to know more details from @sovol3d . A 15 amp fuse behind a 10 amp switch to a bed heater of this size seems like a really bad idea, especially for something commonly left unattended.

[torch]

I printed several hours of PCTG (80°C bed temp) today without blowing the 10A fuse. I still have yet to try my luck maxing out the bed heater printing ABS.

While Sovol does need to address this, fuses are cheap and I suggest owners be proactive: check the fuse for the proper rating – 10A for those with 125VAC mains and 6A for those with 250VAC.

[fmstrat]

Yea, ABS is my main concern. It would be good to hear once you’ve tried. Thanks for doing all this investigating!

Given:

The bed heater is claimed to be 1300 watts. I suspect that may be the 250VAC version since it would require 10A @ 125VAC. My own measurements suggest the current draw of the bed is closer to 5A @ 125VAC.

I would bet a 10A fuse will handle 100C fine, but would love some real-world confirmation once you do get to it since you seem more knowledable.

I’m also curious about if 10A is appropriate vs 15, as to your point in North America 10A would be shy of a 1300W system. If thats the case the max they should be advertising is 1200ish W, but it seems like your measurements show it as way less, already (basically half).

[torch]

Bear in mind that in AC circuits Watts are only approximately equal to Volts x Amps. Frequency and phase also play a role. I didn’t bother getting that deep into the math.

[scharkalvin]

AFAIK switches are rated in AMPS, and power, but neither rating should be over stepped. So a switch rated 10A at 250V can handle ONLY 10A at 125V safely. Yes, the heating will be less at a lower voltage, and Arcing on make and break is also less at lower voltage. Devices that can operate on dual voltage levels with a selector switch should come with a fuse rated at the level safe for the highest voltage input, even if that limits the power available at the lower voltage setting (or switch fuses along with voltage setting).

[cardoc]

@scharkalvin

Yes, the heating will be less at a lower voltage

You’ve got it entirely backwards…

Assuming the power requirement is the same (1200W for example) the higher the voltage the LOWER the current. The heat generated at the switch contacts is a function of the current SQUARED (P=I^2R)

For example assume a 1200W heater and 0.1 ohms at the switch:

24V @ 50A would generate 250W at the contacts

120V @ 10A would generate 10W at the contacts

240V @ 5A would generate 2.5W at the contacts.

This entire thread is meaningless as the OP’s failure was a rivet joint between 2 connectors. That is a manufacturing defect NOT a systematic rating failure. The single rating on the switch is for 100% duty cycle over infinite time. If we had access to ALL the specifications you would find an maximum instantaneous rating (probably around 25A), a 60 second rating (20A?), a 5 minute rating (15A?).

Until someone can show you a SWITCH that failed in service stop second guessing the fuse choice.

[torch]

You are correct that the switch did not fail – the arcing was in the connector due to the loose rivet on the mains connector. I don’t know if the rivet was loose from overheating due to exceeding the current rating or it was overheating because it was loose and arcing. The mains connector itself does not show a 125V current rating.However, as you correctly say, for the same power, 250V requires roughly half the current so it is likely the mains connector (rated 10A @ 250VAC) can handle well in excess of 10A @ 125VAC without overheating.

However, I dispute your assertion that “this entire thread is meaningless”. I put it to you that a switch is not a fuse; some theoretical capacity to handle short-term instantaneous current spikes is unsubstantiated and in any case: irrelevant. Particularly in the case of such a large-volume printer where it may be running for days at a time to produce a single print. Heck, it often takes more than 5 minutes just to heat the massive build plate before the print even starts!

The point of this thread was not to debate the switch itself per se, but rather the unacceptable installation of a fuse that is rated for a higher current than the switch (or any other component in the printer).

Sovol has responded that the fuse was sized to 15A because the motherboard may draw up to 15A. I doubt very much that this is true – it may draw 15A @ 24V, but that won’t draw 15A from the 125VAC mains. The only two components that draw mains current are the power supply and the bed heater. But the comment was not written by an engineer – more likely a CS agent or AI.

So long as the bed heater and the power supply are not capable of drawing a cumulative total of more than 10A @ 125VAC (or 6A @ 250VAC in those markets) then the switch is fine. But the installed fuse should – nay, MUST - be rated accordingly. This is electrical safety certification 101. We don’t need to wait for a switch on this particular product to fail, the standards are there for long and well established reasons.

Conversely, if the printer is capable of drawing more than 10A@125VAC in normal operation and therefore requires a 15A fuse, then the switch is inadequate. I have been using the printer with a 10A fuse installed for a week now without issue but I do not claim to have tested all possible scenarios during that week. Sovol’s engineers should have compiled that data during the design and certification phase.

[torch]

I finally had the opportunity to print a number of parts in ASA (similar temps to ABS) the past two days.

I have had complete success and no blown 10A fuses. The draw is greatest during the initial warm-up phase, bumping up hard against 10A (@ 110VAC today) for about 15 minutes until the bed temp is reached. However, maintaining the bed temp (inside the enclosure) for the ensuing heat soak only draws between 6 and 7 amps with Mainsail reporting 40 to 60% duty cycle.

By the time it’s actually printing at speed (300mm/s), the bed heater duty cycle is down to 20 to 40% and the current draw drops further. The highest I observed was 6.25A – although it’s entirely possible that could be exceeded for a moment at some point.

So, @sovol3d: Cheap fix. Don’t risk violating electrical safety certification; stop overfusing. Ship the 125V version with 10A fuses!