About fuses and choosing the appropriate fuse for your mod

[mamu]

A common fuse wired either to the positive or negative, or a common fuse wired to both positive and negative like you have, does not protect the voltage source from reverse polarity damage when paralleling batts - you'll have batt meltdown and fried wiring if you put one batt in backwards.

For reverse polarity protection, you need to fuse individually to each batt when using dual parallel batts. Positive or negative side doesn't matter though as the fuse responds to excessive current, not voltage or polarity. You'll have full reverse polarity protection as long as each batt has its own fuse.

And fusing individually to each batt, you only need 1x 6A fuse per batt, for a total of 2x fuses. In your set up, you're using 4x 6A fuses and still don't have full reverse polarity protection.

 

[Doug_xx2]

A common fuse wired either to the positive or negative, or a common fuse wired to both positive and negative like you have, does not protect the voltage source from reverse polarity damage when paralleling batts - you'll have batt meltdown and fried wiring if you put one batt in backwards.

For reverse polarity protection, you need to fuse individually to each batt when using dual parallel batts. Positive or negative side doesn't matter though as the fuse responds to excessive current, not voltage or polarity. You'll have full reverse polarity protection as long as each batt has its own fuse.

And fusing individually to each batt, you only need 1x 6A fuse per batt, for a total of 2x fuses. In your set up, you're using 4x 6A fuses and still don't have full reverse polarity protection.

Is that because the voltage forces itself to circulate around the jumper wires on the end of the battery holder and through the batteries ignoring the fact that they are connected on one end or the other because of the fact that there is going to be less resistance between the point where the wire connects to the jumper between the two batteries than the other? So rather than the pressure from one battery canceling out the pressure from the other battery it just circulates around the battery box turning it into what effectively is a series setup rather than the intended and wired parallel setup? Where if all things were perfect (which they never ever will be in the real world) and there was 0 difference in resistance between the common hookup to the jumpers on both ends of the battery box and each battery then they would cancel each other out?

I'm sorry I am just trying to learn something of the theory here so I can gain understanding of what you are telling me instead of just knowing that mamu says it is bad. LOL which in and of it self is probably good reason to not do it but I like to know why. You know like when your kids turn two or three and everything you tell them is "why, why? but why?" LOL

Oh and another thought:
If I only put one 6A fuse on either end of each battery then because it is impossible to get equal draw between the two batteries because of the difference in resistance between the two circuits is it ever going to be possible to get the full draw from the batteries to the device? Or is the difference between the draw on the two batteries ultimately so small that it will even out when it comes close to the pop point for the fuses? Or is the 12A that the DNA can tolerate high enough above the required maximum draw of the DNA when pushed to say 30 watts on a .5 ohm coil that 6A plus whatever it can draw from the battery with the higher resistance between it and the device will be enough to run it?


LOL and edited to include one more does that protect just the batteries or the board as well?

 

[mamu]

For the simple side of the answer, look at the wiring in your pic between the parallel batts - there is nothing preventing or inhibiting a huge amount of current flow between the + of each batt and the - of each batt and the wiring between the batts if a batt should be placed in backwards.

We are using safe chemistry batts, but they are unprotected batts so these batts have nothing to shut them down from the kind of current as you see with reverse polarity - they'll be destroyed as well as destroying anything in that area that will melt or burn.

With reverse polarity, there is a huge amount of current (with extreme heat) coming from the batts and nothing to shut it down unless you pull the batts or have a fuse wired to each batt (or a MOSFET wired to each batt).

A common fuse (or even a common MOSFET) will not protect the voltage source when using dual parallel batts, but will protect the DNA from excessive current (but not from heat/melting if it gets that far if the heat radiates out from the batt area). If you put one or both batts in backwards, you're creating extreme current between the batts and batt wiring - the wiring in that area and batts themselves will get hot hot hot and melt or catch on fire.

A fuse individual to each batt when using dual parallel batts will protect the voltage source and the DNA. If you put one or both batts in backwards nothing will happen - both batts and entire circuit are safe.

Go ahead and test it and maybe that will be the best explanation and learning experience for you to see for yourself exactly what happens with a common fuse and dual parallel batts with reverse polarity - what exactly is going on with the batts and the wiring in that area. I did and it wasn't pretty.

So I tested some more with individual fuses wired to each batt to see what would happen.

http://www.e-cigarette-forum.com/forum/battery-mods/510487-external-fuse-both-overcurrent-reverse-polarity-protection-dna.html

ETA: as a side note, if the DNA itself did have reverse polarity protection you'd still have to individually fuse each batt if using dual parallel batts to protect each batt from excess current conditions or from one batt being unstable in order to protect the other batt.

 

[Doug_xx2]

For the simple side of the answer, look at the wiring in your pic between the parallel batts - there is nothing preventing or inhibiting a huge amount of current flow between the + of each batt and the - of each batt and the wiring between the batts if a batt should be placed in backwards.

We are using safe chemistry batts, but they are unprotected batts so these batts have nothing to shut them down from the kind of current as you see with reverse polarity - they'll be destroyed as well as destroying anything in that area that will melt or burn.

With reverse polarity, there is a huge amount of current (with extreme heat) coming from the batts and nothing to shut it down unless you pull the batts or have a fuse wired to each batt (or a MOSFET wired to each batt).

A common fuse (or even a common MOSFET) will not protect the voltage source when using dual parallel batts, but will protect the DNA from excessive current (but not from heat/melting if it gets that far if the heat radiates out from the batt area). If you put one or both batts in backwards, you're creating extreme current between the batts and batt wiring - the wiring in that area and batts themselves will get hot hot hot and melt or catch on fire.

A fuse individual to each batt when using dual parallel batts will protect the voltage source and the DNA. If you put one or both batts in backwards nothing will happen - both batts and entire circuit are safe.

Go ahead and test it and maybe that will be the best explanation and learning experience for you to see for yourself exactly what happens with a common fuse and dual parallel batts with reverse polarity - what exactly is going on with the batts and the wiring in that area. I did and it wasn't pretty.

So I tested some more with individual fuses wired to each batt to see what would happen.

http://www.e-cigarette-forum.com/fo...rcurrent-reverse-polarity-protection-dna.html

ETA: as a side note, if the DNA itself did have reverse polarity protection you'd still have to individually fuse each batt if using dual parallel batts to protect each batt from excess current conditions or from one batt being unstable in order to protect the other batt.

I afraid to try flipping one around fuses or not I think I will take your word on it. I was trying to understand why the two batteries didn't cancel each other out. I guess I was thinking that it would be like one tank of water pushing water through the pipe and the other sucking water out of the pipe with equal force and when I thought about it I thought I had the answer so I was trying to get you to confirm my understanding of the theory behind it. I am trying to learn electronics not just how to build a DNA. I suppose that makes me kinda off topic with my question but only kind of. I wish I had an amp meter that went above 10 amps so I could test the fusing without taking the chance of cooking my DNA but I don't . Well thanks for your help I am positive you are correct and was just asking you to spoon feed me theory on top of your answer because I wanted to understand how it worked.

I will definitely check out the link.
Thanks

 

[etchie]

I don't think you will find em local but maybe. I don't know if these will be apropriate for you but I used two on the positive side and two on the negative in parallel. 16R600GU Littelfuse | Mouser They are in stock

They are a little on the big side though.

Hope this helps

you might also try this site http://www.digikey.com/

This can be used for a 30? I hope so, I already ordered them. Haha!


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[Doug_xx2]

This can be used for a 30? I hope so, I already ordered them. Haha!


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well what mamu is saying is if you want any sort of reverse polarity protection (because the DNA itself has none and it will fry if you accidentally reverse a battery in the setup I depicted) you need to: (quote from mamu a few posts ago) "For the DNA30, you would use 1x 6A fuse, or 2x 3A fuses, on each positive when using dual parallel batts."

I have kind of muddied the water here by asking questions about why. I personally think it is best to go with what she says

so does that mean you don't have to put any on the negative side then mamu?

 

[etchie]

well what mamu is saying is if you want any sort of reverse polarity protection (because the DNA itself has none and it will fry if you accidentally reverse a battery in the setup I depicted) you need to: (quote from mamu a few posts ago) "For the DNA30, you would use 1x 6A fuse, or 2x 3A fuses, on each positive when using dual parallel batts."

I have kind of muddied the water here by asking questions about why. I personally think it is best to go with what she says

so does that mean you don't have to put any on the negative side then mamu?

We'll also, I'm not using 18550's. I'm using the rechargeable......bricks? You know. So I won't be moving anything.


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[Doug_xx2]

We'll also, I'm not using 18550's. I'm using the rechargeable......bricks? You know. So I won't be moving anything.


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Well it might be a good thing to prepare for the future. Someday those batteries will need to be changed.

 

[etchie]

Well it might be a good thing to prepare for the future. Someday those batteries will need to be changed.

Yeah. I definitely plan on it. As soon as batteries are able to hold more, I will change them. I really wanted more mah them I'm going to get.


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[foggdawg]

We got 9a and 5a fuses from Tibs and Mike's DNA30 CoOp. Guessing that just one 9a would do for a single 18650 batt. setup on the DNA30.

 

[etchie]

We got 9a and 5a fuses from Tibs and Mike's DNA30 CoOp. Guessing that just one 9a would do for a single 18650 batt. setup on the DNA30.

What about for 2 batteries? I ended up going dual lipo.


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[foggdawg]

I used 2 9a fuses in parallel for my single battery mode. I vape sub ohm so I'm thinking 2 9a would be safer. If I were using 2 battery mode I'd use 2 9a in parallel connected to each battery.

 

[etchie]

I used 2 9a fuses in parallel for my single battery mode. I vape sub ohm so I'm thinking 2 9a would be safer. If I were using 2 battery mode I'd use 2 9a in parallel connected to each battery.

Still unsure of parallel and series. What do they look like when set up? Also parallel is when both batteries are draining at the same time, right? I was going to go with that. Never really heard any advantage of series. Thanks!


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[foggdawg]

A paralel connection is when 2 or more (batteries of the same voltage and mah) are connected at the same point(positive or negative) to make one point. So when connecting 2 batteries together you connect both +ends. Then you connect both negative ends. Thus you now have a battery with the same voltage but double mah. So, a pair of 3.7v 1200mah batteries connected in parallel will remain 3.7v but mah will double to 2400mah. If connecting batteries in series you would connect the positive end of one battery to the negative end of the next battery. Batteries connected in series will double in voltage but mah will remain the same. So, a pair of 3.7 1200mah batteries connected in series will have an output voltage of 7.4v. These examples were with two batteries of the same voltage and mah. The more batteries you add the the string be it parallel or series will increase voltage or mah accordingly. So to sum it up: parallel connection voltage stays the same mah increases. In a series connection voltage increases and mah stays the same. I'm sure Bap or Mamu could of explained this better than I did.

 

[etchie]

A paralel connection is when 2 or more (batteries of the same voltage and mah) are connected at the same point(positive or negative) to make one point. So when connecting 2 batteries together you connect both +ends. Then you connect both negative ends. Thus you now have a battery with the same voltage but double mah. So, a pair of 3.7v 1200mah batteries connected in parallel will remain 3.7v but mah will double to 2400mah. If connecting batteries in series you would connect the positive end of one battery to the negative end of the next battery. Batteries connected in series will double in voltage but mah will remain the same. So, a pair of 3.7 1200mah batteries connected in series will have an output voltage of 7.4v. These examples were with two batteries of the same voltage and mah. The more batteries you add the the string be it parallel or series will increase voltage or mah accordingly. So to sum it up: parallel connection voltage stays the same mah increases. In a series connection voltage increases and mah stays the same. I'm sure Bap or Mamu could of explained this better than I did.

No, you explained it perfectly. Thank you!


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[EDog13]

I've been following and understanding the thread so far. i'm going to be building my own dna30 box mod and I would use 2 3a fuses for each of the 2 parallel 18650's. Hypothetically, what would be your fuse recommendation if I was to go with 4 18650's in parallel?

 

[sphongled1990]

Okay so im nit getting this..im new to modding and basically trying to avoid math..I know thats wreckless and is half the fun for you folks but I hastily ordered a lot of stuff to build my first mod including chip . I have plans for a dual 18650 sx350 box mod using mamus arlo tutorial. . Same box..im wondering if I need different fuses or will those same fuses cut the mustard? Please point me towards the right ones if those 3a paralleled fuses will not work thanks

 

[StereoDreamer]

Not trying to hi-jack the thread, but I have a question about parallel batteries with the DNA-30.

I'm building a mod that is going to be relatively small based on the DNA-30, and the case is spherical in shape, because I want it to look like a potporri pomander. I do medieval historical reenactment, and don't want to carry around an obviously modern PV at events, so I thought I'd pick up a couple silver-plated potporri balls I found on EBAY and turn them into mods.

Anyway, they are 3" diameter on the outside, which makes it a little tricky to fit an 18650 sled in them.

Since I'm a relatively low-power vaper (rarely do I go above 15 watts, and my "sweet spot" for most juices is more like 7-9 watts), I wondered if I could get away with using a pair of 18350s in parallel to power the DNA-30. In this application, I'll be using mostly cartos, or attys built at around 1.8-2 ohms, so the load the DNA needs to drive won't be too demanding. I figured a pair of paralleled 18350s would give enough amperage to drive the sort of toppers I plan to use, at the power levels I usually vape at, but I'm not an expert, so I thought I'd ask for opinions.

This question is mainly pointed to Mamu, since she is a DNA goddess, and an authority on this sort of creative mod-hacking... ;-)

But I appreciate responses from anyone.

Thanks in advance folks!

 

[mamu]

@ EDog13 - the DNA30 has max input current 12A. If using 4x 18650 batts in parallel, you would use 1x 3A fuse per batt (12A / 4 batts = 3A).


@ sphongled1990 - the SX350 has max input current of 12A (actually 12.5A, but close enough to round it down to 12A). For 2x 18650 batts in parallel, you would need 1x 6A fuse on each batt, or 2x 3A fuse on each batt - your option to choose 6A fuse or 3A fuse.


@ StereoDreamer - the DNA30 requires a batt that has a minimum of 12 amps continuous discharge current to operate effectively.

The purple Efest IMR 18350 batts (I have no idea how good they are as I haven't used or tested them) are rated at 10.5A 700mAh.

Using 2x in parallel gives you 21A 1400mAh. So these batts would be suitable for your vaping needs with the DNA. At 1400mAh, you will be getting very short vape time between charges though.

Alternately, you could use 1 Sony VTC5 18650 batt and have 30A 2500mAh for your vaping needs - larger current cushion and longer vape time between charges.

 

[TomGeorge]

Do you need fuses if you are not using a chip? Just batteries in parallel, 510 connector and a switch?

Would I just use the battery specifications as the converter specifications?