External fuse for both overcurrent and reverse polarity protection with the DNA...

[mamu]

ok... I worked up the nerve to test reverse polarity with the dna using just an external fuse without a FET in line. It took me a while thinking about if I really wanted to try this though. I was thinking 40 bucks down the clinker for a dna if it doesn't work out.

Adding an external fuse prevents overcurrent and reverse polarity damage for the OKR and Naos Raptor boards, but those are buck modules using batts in series while the dna is a boost module using either a single batt or batts in parallel. Didn't know if that made a difference, just wasn't sure, so I've been using a fuse/FET combo with the DNA for my mods that have removable batts to protect from overcurrent as well as reverse polarity.

So... here goes...I used the Efest 30A batts for testing - I didn't care if I blow those pos.

Both batts inserted correctly...

Both batts inserted backwards... both red LEDs are lit indicating both batts are inserted backwards...

One batt inserted backwards, the other batt inserted correctly...red LED is lit indicating which batt is inserted backwards... the problem with this set up, other than a batt is inserted backwards is that without the red LED indicator there's no system warning and the DNA works fine.

Many many thanks to CraigHB for giving me the incentive to test this.

Note1: for this to work correctly, you need a fuse on each batt if you're running batts in parallel - you can't use a common fuse for both batts else you'll get a batt meltdown from the short when inserting one batt backwards and one correctly.

Note2: these are the fuses (wired 2x in parallel) I tested overcurrent and reverse polarity with the DNA20D - 16R300GU and MINISMDC260F/16-2

 

[shortyjacobs]

Very cool.....but how does this work? I understand the PTCs tripping when you have one batt backwards and one batt forwards, but why are they tripping with both batts reversed? And if you just insert one batt backwards, (before inserting the second one correctly), how is the system protected? And how are they tripping fast enough to prevent damage to the DNA, (I thought a few ms of reverse polarity was enough to fry it?? These don't trip that fast).

Ugh, that's a lot of questions....I'm really interested, I'm just confused how/why this works.

 

[Visus]

Best test ever thats really cool

Those fuses are really that dang cool

Craig probably wrote 100 paragraphs had diagrams and offered to send me his new build when its done
one can hope

 

[mamu]

Very cool.....but how does this work? I understand the PTCs tripping when you have one batt backwards and one batt forwards, but why are they tripping with both batts reversed? And if you just insert one batt backwards, (before inserting the second one correctly), how is the system protected? And how are they tripping fast enough to prevent damage to the DNA, (I thought a few ms of reverse polarity was enough to fry it?? These don't trip that fast).

Ugh, that's a lot of questions....I'm really interested, I'm just confused how/why this works.

but why are they tripping with both batts reversed?

The fuse isn't monitoring anything other than the current coming from the batt it's connected to. The fuse connected to that batt will trip when it sees a huge current dump from that batt... which is the case when you put the batt in backwards - you've created reverse polarity which causes a huge current dump from the batt.

And if you just insert one batt backwards, (before inserting the second one correctly), how is the system protected?

This particular situation where one batt is backwards and the other batt is correct is why each batt needs its own fuse. With one common fuse shared between the two batts, you'd have a meltdown if you put one batt in backwards and one in correctly. I tested this and that is exactly what happens.

So when each batt has its own fuse, it doesn't matter if it's one batt put in backwards or both batts put in backwards. The fuse connected to a batt will protect its batt from a meltdown as well as the circuit from an overcurrent condition.

And how are they tripping fast enough to prevent damage to the DNA, (I thought a few ms of reverse polarity was enough to fry it?? These don't trip that fast.

If you don't have a fuse in line and you put the batt in backwards, the DNA does not immediately fry. It starts heating up right away, but if you remove the batt right off, little to no damage occurs.

When selecting a fuse, keep 3 things in mind (there's more things to consider, but these 3 are the most important):

Hold current - this will be a value at which you want the fuse to allow current to pass without a hiccup. For the DNA20 with a 6A limit, a fuse with a 6A hold current is appropriate.

Resistance - the lower the fuse's internal resistance the least affect it has on the total resistance of the circuit. This is the primary reason why we parallel 2 fuses as it will decrease the fuse's internal resistance by half. We also choose, for the DNA20, a fuse with a 3A hold current. While the resistance is cut in half with parallel fuses, the current value doubles. So if I choose a 3A fuse and put 2x in parallel I have a 6A fuse, plus I get the benefit of lower resistance.

Trip time - Ideally, as small as possible so the response to an overcurrent condition is fast. The fuses I use for the DNA20 have a trip time of 1 second (16R300GU) and 5 seconds (MINISMDC260F/16-2).

The thing is with an overcurrent condition, the fuse's resistance immediately increases, so even before it trips it helps to protect.

 

[mamu]

...and offered to send me his new build when its done one can hope

haha... right.

 

[WarHawk-AVG]

Sweet...guess what

They are currently beta testing a new Vape Safe called "The Extreme". This vapesafe has been made for the sub-ohm community and can handle up to 17 amps before tripping. I do know people have safely used .3 ohm builds with this. Nothing wrong with a little extra protection. Right now I don't have a price point.

What is a vape safe?

The VapeSafe is a mechanical fuse that trips if it senses a short in the mod by shutting down the battery. The VapeSafe can also help protect variable voltage circuitry, hot springs and other circuitry that you would not want to be damaged because of a hard short.

http://.........blogspot.com/2014/01/rollout-vapesafe-extreme.html

 

[mamu]

I have an 18A fuse in Raptor - much much more than I would ever need as I don't do sub sub ohm. I occasionally do 0.8 ohm @ 4v and that's a measly 5A. I reckon that would be classified as a weany when it comes sub ohms.

 

[Littlefeather]

Mamu
You ask great questions & Craig comes up with great answers! I've had the same question bouncing around between my ears but haven't asked. DUMB ME! Only dumb question? The one you don't ask! Sooo, I'm asking! I can see where your application would be a hazard with only the fuses employed and no FET in this scenario.
You said you use fuses & FET on your removable batt mods. What I'm unsure of and I didn't see, is if the application you're using with removable batts in parallel with FET & fuses gives you the protection you're looking for? Looking to reassure myself so I don't have to put 2 more boxes in the "Rethink, Recycle, Reuse" bin.

Here are a few pics of some of my WIP I'm trying to protect against. Thanks again for your help!

ok... I worked up the nerve to test reverse polarity with the DNA using just an external fuse without a FET in line. It took me a while thinking about if I really wanted to try this though. I was thinking 40 bucks down the clinker for a DNA if it doesn't work out.

Adding an external fuse prevents overcurrent and reverse polarity damage for the OKR and Naos Raptor boards, but those are buck modules using batts in series while the DNA is a boost module using either a single batt or batts in parallel. Didn't know if that made a difference, just wasn't sure, so I've been using a fuse/FET combo with the DNA for my mods that have removable batts to protect from overcurrent as well as reverse polarity.

So... here goes...I used the Efest 30A batts for testing - I didn't care if I blow those pos.

Both batts inserted correctly...

Both batts inserted backwards... both red LEDs are lit indicating both batts are inserted backwards...

One batt inserted backwards, the other batt inserted correctly...red LED is lit indicating which batt is inserted backwards... the problem with this set up, other than a batt is inserted backwards is that without the red LED indicator there's no system warning and the DNA works fine.

Many many thanks to CraigHB for giving me the incentive to test this.

Note1: for this to work correctly, you need a fuse on each batt if you're running batts in parallel - you can't use a common fuse for both batts else you'll get a batt meltdown from the short when inserting one batt backwards and one correctly.



Note2: these are the fuses (wired 2x in parallel) I tested overcurrent and reverse polarity with the DNA20D - 16R300GU and MINISMDC260F/16-2

FYI--Thought I'd mention the attached pictures are showing my WRONG way of fusing 2 batteries in parallel. So, don't us that as a guide! Thanks again to Mamu & CraigHB for the good info and explanation.

 

[mamu]

Craig is awesome!!

Regarding the fuse/FET combo I was using, Craig said that it was doing double duty as the fuse could do the FET's job for reverse polarity protection. He said the problem with reverse polarity when a batt is put in backwards is not the reverse voltage (which the FET protects), but rather the huge current (which the fuse protects). The fuse protects components from damage by limiting the current.

He also said it's not a bad idea to use a fuse/FET combo, but using just a fuse would be ok.

And the thing is now that I've thought about it and sorted it out, with the fuse/FET combo I placed the fuse at the batt +, then the FET after the fuse, so the fuse is 1st in line to protect anyway and based on my testing the fuse alone does a good job of it.

BUT then if using a fuse/FET combo if the fuse should fail, the FET would kick in to protect. I've not tested that by not putting a fuse in line to simulate a failed fuse to see if the FET alone would completely protect both the batt from meltdown and the circuit like the fuse does. The FET is working by voltage and not necessarily by current so I'm not sure there. I've always tested with the fuse in line. And as Craig said - it's the current that is the major concern.

With this testing I've done, I have a high regard for fuses and their ability to protect us, the batt, and the circuit.

 

[bapgood]

lol....I had to think twice the first time I read your OP.....I was thinking this won't work because the fuse doesn't care about polarity and etc....then I realized what was confusing me was that there is no way to really test it without hooking it to a DNA.....Bravo to you for that!!!

 

[mamu]

LOL - thanks, bap.

yeah, I was nervous about possibly frying the DNA20.

I had lost a dual parallel DNA12 from reverse polarity. *poof* went 70 bucks. Wish I knew then what I know now.

 

[Littlefeather]

Not sure I asked my question correctly and want to make sure I understand.
To keep DNA20 protected from reverse polarity & overcurrent protection when using two batteries in parallel the following should be employed. Regardless if you’re using fuses(2X)/FET combo or just fuses(2X), each battery in parallel must have separate inline fuse set on the positive lead before any FET(backup protection for fuse failure).
As outlined in scenario: 2 batteries in parallel, separately fused inline with no FET present.
Scenario #1: 2 batteries installed correctly. Voltage and current allowed to flow as no are faults detected, DNA20 operates as designed.
Scenario #2: 2 batteries installed incorrectly. Inline Fuses detect current dump and each fuse trips. Current and voltage are blocked to DNA20 and therefore it doesn’t operate and is protected.
Scenario #3: 1 battery installed correctly & second battery installed incorrectly. Second battery installed incorrectly, fuses detect current dump and fuse trips. No current or voltage allowed to pass to DNA20 from second battery. 1st battery installed correctly, fuses allow voltage & current to pass to DNA20 and therefore DNA20 operates as designed even with one battery installed incorrectly.
Conclusion: Fuse both batteries in parallel, inline, independent of each other. Use of a FET as secondary backup but may not be needed.
Am I missing anything? If not it would appear a few more modifications are in order! My Rethink, Recycle, Reuse box is getting fuller. They say you learn the most from your mistakes. From the looks of my box, I’m should be close to being a genius! LOL! Now I just have to wrap my head around the wiring layout in my box design and figure how to pack it in. SMD sound good to me! I think I hurt my brain today.
Would be nice if evolv incorporated these ideas in their new products. Hey there's an idea! Bueller? Bueller?

 

[mamu]

No lol you didn't miss anything.

I'll lay you odds my Rethink, Recycle, Reuse box is a LOT fuller than yours.

 

[Littlefeather]

LOL, No worries here. That box of mine fosters more ideas than I'm sure I'll ever be able to complete. But, I'll give it a try and see what turns out.

 

[kurtus]

BADA$$$, thanks for posting this mamu, very cool

 

[ZeD828]

I've been reading the mod threads for a while now and wanted to say thanks to all of the modders on here for all the usefull information. I have yet to build a mod, but I plan to very soon. I just have a question about the protection circuit u guys are discussing. In the fuse/FET senario, are u using a P-channel FET? How are u wiring it in? It seems to me that u would wire it in series with the fuses and use the voltage from a reversed battery to trigger the gate and close the channel. Effectively stopping the current dump. Do I have this right or am I missing something?

 

[shortyjacobs]

I've been reading the mod threads for a while now and wanted to say thanks to all of the modders on here for all the usefull information. I have yet to build a mod, but I plan to very soon. I just have a question about the protection circuit u guys are discussing. In the fuse/FET senario, are u using a P-channel FET? How are u wiring it in? It seems to me that u would wire it in series with the fuses and use the voltage from a reversed battery to trigger the gate and close the channel. Effectively stopping the current dump. Do I have this right or am I missing something?

This should answer your questions:
http://www.e-cigarette-forum.com/forum/battery-mods/424173-reverse-polarity-protection-dna20d.html

 

[ZeD828]

Thanks shorty for the link. It was very helpful.

 

[DrMA]

Nicely done, mamu! And definitely courageous of you to test on a live, working DNA module without knowing its PIV rating, i.e. whether or not it is capable of surviving this test.

 

[kurtus]

Has this actually been tested with 6amp fuses like the te connectivity rgef600 fuses. I just fried a board testing this theory out, I used 4x fuses with 2 legs paralleled on to each battery and the othersides 4 legs joined to the positive on the dna board. That works out to a 12amp hold current on each battery and should provide reverse polarity protection but the second I flipped the battery to test it it fried instantly. Thoughts on why this happened, is it the 3.3 trip time?? Thx

RGEF600 Specs
Voltage - Max 16V
Current - Max 100A
Current - Hold (Ih) (Max)6A
Current - Trip (It) 10.2A
R Min/Max 0.010 ~ 0.019 Ohm
Time to Trip 3.3s