Reverse battery protection on a mech box.
- Thread starter robfo
- Start date
- th_trl_thread_readers 0
- Status
Just fuse each cell with a resettable fuse wired individually both batts into one for connecting at switch or if using a nfet at switch and atomizer. Very simple..
Do not bridge -- you can do eith the neg or pos if you fuse the pos bridge the neg if you do the neg bridge the pos making a Y connection.. 2 into 1
Heres a picture
Do not bridge -- you can do eith the neg or pos if you fuse the pos bridge the neg if you do the neg bridge the pos making a Y connection.. 2 into 1
Heres a picture
oh... do you mean a plain old mech with nothing but metal and a button? if so polarity does not matter... if you are using a mosfet then you may want to protect the fet from reverse voltage...
You do not have to run a MOSFET, it is best to run a MOSFET IMO
if you want a small unrated switch
the fuses will work with ohms up to their amp ratings in parallel.
So if you notice on that picture the two fuses are 15 amps, that gives that mod 30 amps 126 watt of protection down to .14Ω.. You add them together when used in parallel. If you need 60 amps 252 watts .07Ω just add 4 15 amp fuses 2 on each leg.
This method of reverse protection was shown to us by Craighb a helpful electrical engineer.. Super simple and effective..
Modder Mamu tested it and it works flawlessly for reversed batteries.
http://www.e-cigarette-forum.com/fo...fuses-choosing-appropriate-fuse-your-mod.html
Another good picture of it done..
In the left drawing above you'd only get 15A protection. If the current in either half of the circuit exceeds 15A a fuse will blow, at least on the left example.
In the right drawing it looks like two fuses have been wired in parallel with each other after the two branches of the circuit join. The weaker of the two will blow first, then the other would fail immediately after. In theory the right circuit will work, but it's not really kosher to do it that way. Variations in the resistance or load capacity of the two fuses would allow the weaker one to blow before the other. You would be better off just using a 30A fuse in that situation.
In the right drawing it looks like two fuses have been wired in parallel with each other after the two branches of the circuit join. The weaker of the two will blow first, then the other would fail immediately after. In theory the right circuit will work, but it's not really kosher to do it that way. Variations in the resistance or load capacity of the two fuses would allow the weaker one to blow before the other. You would be better off just using a 30A fuse in that situation.
Last edited:
Your right about the first circuit yes they are on their own leg and will act individually and are only 15 amps
but on the parallel circuit they will act as one 30 amp fuse.
This is what I was taught how to increase a fuse rating and lower their resistance by paralleling them..
Fuses wiki:
The use of fuses in parallel can be advantageous. • To obtain higher current ratings than existing ranges.
So if you wanted 30a you would need 4 fuses 2 each leg for 45 amps 3 fuses each leg and 60amps would be four on each leg.
I was told do not use more than four fuses in parallel for that which dave posted they will have issues..
but on the parallel circuit they will act as one 30 amp fuse.
This is what I was taught how to increase a fuse rating and lower their resistance by paralleling them..
Fuses wiki:
The use of fuses in parallel can be advantageous. • To obtain higher current ratings than existing ranges.
So if you wanted 30a you would need 4 fuses 2 each leg for 45 amps 3 fuses each leg and 60amps would be four on each leg.
I was told do not use more than four fuses in parallel for that which dave posted they will have issues..
It's always best to use a single fuse after a parallel join. You can find threads on using shunted breakers in all sorts of applications. There's talk in some circles about using two breakers to equal on of a higher rating. I guess that's what they have and want to use it instead of buying the right one. When multiple fusing is done in commercial circuits it's usually where 220VAC or 440VAC is protected by two or three breakers or fuses, one on each leg of a 3 or 4 wire circuit with out of phase hot leads.
Before sub ohm vaping got popular a 7A resettable button fuse was sufficient to protect a mech battery from melt down. Now, lots of people are doing sub ohm without protection.
Last edited:
The use is because not many resettable fuses over 20amps that are not straps. It would be best to use the appropriate fuse true indeed but I went ahead and selected resettable smd fuses for him lol..
He wants it for reverse protection mainly and enough rating for what ohms IDK..
It is funny 7A was more than sufficient now cats are vaping 200+ watts daily.. I cannot believe how it has evolved to insanity.
I myself vape at 10-15 amps frequently, but no way will I vape 30 amps lol...
Coincidentally a guy who is a modder on box modders facebook group just yesterday, his girlfriend was being sweet and put his batts in reversed in a parallel build she was so accustomed to series mods, it melted the batts, and his battery holder, he was able to pop them out but not before they did that damage in secs..
I have almost did it myself many times but on a series mod so no biggie there lol..
Carnage pictures
You may want to think about adding a protection diode. Just a thought.
http:// Learning about Electronics Articles/What-is-a-protection-diode
http:// Learning about Electronics Articles/What-is-a-protection-diode
If you reverse two batteries they just just fight to the death and injure bystanders. Fuses don't care. They just pop under load. Polarity doesn't matter.
To prevent reverse polarity errors a high amp diode is the solution. If you reverse the batteries, nothing happens. No vape, no explosion. The key is to install them forward biased in the circuit to allow current flow when the batteries are installed correctly and no current flow if they are reversed.
32CTQ030PBF: 30A 30V Silicon Rectifier Diode: International Rectifier
Last edited:
True, but diodes, by their nature, induce a fairly high voltage drop. Which is why people parallel PTC fuses; to lessen to resistance and induce less Vdrop in the circuit. For reverse batt protection in more complicated circuits, most people use a P-FET
A friend of mine decided one day to see how fast his new pickup would run. When it hit 100mph it engaged the electronic RPM limiter and just surged in and out. It's probably why he's still around today. He's the type to keep going to see how fast it would go.
Sometimes, we need devices to prevent us from self destructing.
- Status
Similar threads
