SX350 Chip fuse question

[Romelee]

Hi all,

Quick question..........

I use 2 x 6A fuses parallel for a single cell 18650 battery using the DNA30 chip.

Question is  would them fuses be ok for the SX350 chip?

The reason i ask is because i noticed on a different forum somebody using 2 x 3A fuses in parallel for a single cell 18650 battery using the SX350 chip

This is the fuse i normally use when making a mod using the DNA30 Chip.

Fuse: http://uk.rs-online.com/web/p/resettable-wire-ended-fuses/5176944/



YIHI SX350 Board: http://www.supavape.com/YiHi_SX350_board/p2203934_12199390.aspx



Looking forward to your replies 

Jason

EDIT: Also forgot to ask will this switch be ok with the SX350 chip: http://www.stealthvape.co.uk/electronic-cigarette-mod-parts/ecig-mod-parts-momentary-switches/16mm-vandal-proof-switch-flat

Anything to do with specifications goes right over my head, but building something doesn't 

[CraigHB]

Any controller board like the DNA30 or the SX350 should not allow a short circuit condition to persist that could cause damage.  However, fuses can protect against installing batteries backwards and act as a backup for short circuits in the event there's a problem with the board. 

Since you're pretty much covered for short circuits by the controller board, it's more a matter of reverse polarity protection which may or may not work with fuses depending on the controller board.  Fuses do protect against reverse polarity with the DNA30, but can't say on the SX350 without risking a board to check it.

You could run without fuses and use a transistor for reverse polarity protection without a big safety issue.  The SX350 may already have reverse polarity protection or it may not.  If it does that makes fuses or any other protection redundant.

For those particular 6A fuses two in parallel requires a fault current over 20A for to trip them.  That's a lot.  Two 3A fuses in parallel would have a trip current close to 12A so they would still work, but they could possibly trip under maximal loading.

There's a range you can use between the trip and hold currents with PTC fuses.  For two 3A fuses, you're right up against the minimum.  For two 6A fuses, you're up against the maximum.  You get faster trip times with a lower hold current, but you run the risk of false trips.  With hold current at the maximal demand, you require the largest fault currents to cause a trip resulting in slower trip times and possibly failure to protect the circuit.

[BigHoffy]

Hmm I'm wondering if you even need anything with the sx350. I do know it has reverse polarity protection incorporated. So I guess my question would be if you really need them, since you probably reach greater efficiency in not using them. which will give you more vape time and lessen how often you need to recharge batteries.

[CraigHB]

You give up an amount of efficiency with fuses, but it's typically not a considerable amount. 

For example, if you're inserting 10 mOhms with your fuses and you're consuming 20 Watts at the atomizer, pretty typical, that's about 6 Amps input at a nominal 3.7V.  Power consumed by the fuses is 6 squared times 10 mOhms which is a 360 mW.  Compared to total power consumption that's not even 2%.  Not much really.  That's like an extra hit or two for every hundred.

When doing the same calculations for series cells, power loss at the fuses is quartered since current is halved. 

With high power consumption, that overhead is more considerable.  If you're pulling 20A at 3.7V, the fuses are consuming 4 Watts compared to a total 74 Watts which is over 5%.  Though nobody regularly vapes at those high outputs, at least that I know of.

It's standard practice to fuse the power supply for any device that consumes enough power to involve safety considerations.  That is the case for e-cigs.  So it's never a bad idea to add fuses, but if they present a problem, in some cases you can get away with not using them.  Most of the time the power cost is worth the extra layer of protection.

[BigHoffy]

Good to know. 2% aint much at all, and I don't plan on going past 20w myself. except maybe to chuck a fat cloud at the vape shop. but then I would probably hit bypass mode on the sx350. I gotta say I am loving this site and all you helpful guru's out there. anyone tried an arduino vape mod, or is that just not worth the code time? maybe using a 12a speed controller or something like that. modded of course.

[Romelee]

Thanks CraigHB, as always very informative 

As this mod is for my own use and i never take the battery out as i will just use the USB for charging, plus i don't vape at high watts anyway so on this occasion i am going to leave the fuses out of this mod.

Read yesterday that there is a upgrade for the chip coming out about June time that knocks it up from 35w too 50w 

[CraigHB]

I'm pretty sure that 50W upgrade requires series cells.  Using a single cell, there's a wall you hit with boost or buck-boost at about 40W that calls for components too large to fit on a small PCB.  It's possible to do it, but but you end up with a big board with big parts and you need a cell with very high drain, more specifically, very low internal impedance.  Series cells puts the board in buck mode full time which allows a higher output.  Even so, 50W is pretty impressive with a small board like that.

[Alexander Mundy]

I was informed by more than one source that for the  reverse polarity you need to attach the battery minus lead to the through hole at the side of the board marked "BAT-" otherwise if using the one at the bottom of the board it will put a direct short on the battery if inserted backwards and you will need to fuse it.

Didn't try it myself, but got 2 more coming and I will after I get them and recuperate from surgery.

[vap3on]

Apologies for hi jacking the thread, I have a few SX 350 mods one I have damaged the micro usb socket while it was charging.

The status led would be active if I pushed the cable up or down while the usb cable was inserted. The unit was a prebuilt mod with hot glue and epoxy.
I managed to get the usb board out with no visible damage, I checked under a magnifier if the usb socket soldered legs to the board had be fractured all appeared to be ok.

The board appears to be dead with no status led at all on inserting the cable.

Does anyone have any info on the board I am guessing there has been no component failure but due to the nature of my carelessness I suspect fractured joints. Given the board is not a straight usb charge board as it carries data does anyone know of a replacement or a schematic to fault find the board.

Apologies once again I have only just joined and suspect I cannot start a new topic.

I have ordered a hot air rework unit to remove the socket clean, de flux and resolder.

Cheers

[vap3on]

Thanks CraigHB, as always very informative 

As this mod is for my own use and i never take the battery out as i will just use the USB for charging, plus i don't vape at high watts anyway so on this occasion i am going to leave the fuses out of this mod.

Read yesterday that there is a upgrade for the chip coming out about June time that knocks it up from 35w too 50w 

Hi Romelee i still have one of your DNA mods:), the June 30th 50W update is stated at 25A this seems a bit of mare for all the mod makers that specced it up on YiHi previous 12.5A specs.

[Romelee]

Hi Romelee i still have one of your DNA mods:), the June 30th 50W update is stated at 25A this seems a bit of mare for all the mod makers that specced it up on YiHi previous 12.5A specs.

Hi Vap3on,  i won't even be upgrading, i only vape @ 10-12 watts 

Plus i did not put any fuses or anything special in my latest mod, just the chip and battery 

Latest piccy:



Thread of the mod here: http://breaktru.com/smf/index.php/topic,1265.0.html

p.s Sorry i can't help on the USB part of your problem.

[Drone]

I was informed by more than one source that for the  reverse polarity you need to attach the battery minus lead to the through hole at the side of the board marked "BAT-" otherwise if using the one at the bottom of the board it will put a direct short on the battery if inserted backwards and you will need to fuse it.

Didn't try it myself, but got 2 more coming and I will after I get them and recuperate from surgery.

This exactly what I have heard too. They have an alternate connection for battery negative that provides reverse protection. That means the negative wire soldered to the board as received needs to be moved. The post I saw that asked YiHi why they didn't add the wire to the protected solder pad received an answer from YiHi saying that would reduce efficiency by 1%. Well worth the efficiency loss to me, and that's the way I'm setting up my SX350 in my mod.

[CraigHB]

Yeah that's the problem with things like fuses and reverse polarity protection.  Any time you add components inline with the battery it costs efficiency.  You figure 1% works out to about 1 hit out 100 so if you get 1000 hits off a charge, you lose 10 hits for the protection.  Probably a reasonable trade-off.