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Breaktru Forum  |  eCigarette Forum  |  Modding  |  Topic: Reverse Polarity and Undervoltage Protection
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Author Topic: Reverse Polarity and Undervoltage Protection  (Read 5279 times)

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Offline davidlewallen

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Reverse Polarity and Undervoltage Protection
« on: March 20, 2014, 03:08:19 AM »
I am currently making a few mods for myself and am looking for a way to protect against reverse polarity and undervoltage.

I am using an OKR-t/10 with VTC3s.

Blew the caps the other day due to being stupid and putting batteries in backwards.
The chip will also drain my bats down to 2.5v which I dont like at all.

Anyone know of small footprint ways of fixing this?
Zener Diodes? P-MOSFETS?


Online Breaktru

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Re: Reverse Polarity and Undervoltage Protection
« Reply #1 on: March 20, 2014, 05:02:46 AM »
See: Drawing

Offline CraigHB

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Re: Reverse Polarity and Undervoltage Protection
« Reply #2 on: March 20, 2014, 06:46:08 PM »
Blew the caps the other day due to being stupid and putting batteries in backwards.

Lots of discussion here on reverse polarity protection as Breaktru indicated, but aside from that, one of the nice things about caps that are not polarized, no concern over reverse polarity. 

Unfortunately, there's no perfect capacitor.  If you could invent one with no polarity, small size, high value, low ESR, and no DC bias, you'd be a millionaire.  You can get four of the five with an MLCC cap, but you have to be careful with the DC bias on those.  The small high value MLCC caps can lose over half their capacitance at DC voltages as low as 3V. 

The best MLCC cap I've come across for our purposes is this one.  They hold at least 80% of their capacitance up to 8V, they have very low ESR, very small size, and a pretty high value.

If you need more capacitance, just parallel them up.  The very low ESR (10 to 20 times lower than an electrolytic cap) makes them more effective in filtering which is pretty much the point of using them.  It also improves their function as a tank capacitor in covering transients. 

Offline davidlewallen

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Re: Reverse Polarity and Undervoltage Protection
« Reply #3 on: March 20, 2014, 10:32:26 PM »
Talking about caps... I have a few questions or maybe just one.

What is the real need for them? I mean I understand, very basic I must admit, that they are used for stabilizing voltage, only know this from car audio, but is there an actual need for them?
I have used my OKR with and without caps and it performs the exact same except for the ones with caps I get my once saving grace with reverse polarity protection.

Another question I have. I have seen many different schematics drawn up with different resisters bridging pins. On mine I only use a resister on the trim pin where as I have seem 1k - 7.5k ohm resisters on pin 3 and 5. Whats the reasoning behind this?

Offline CraigHB

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Re: Reverse Polarity and Undervoltage Protection
« Reply #4 on: March 21, 2014, 11:25:37 AM »
Most generally, additional caps on the OKR regulators are used to reduce input and output ripple.  This can be a requirement when using them to power other electronics, but when powering an atomizer, there's no need to do that really.

If you're using one of these regulator modules with a build that includes a micro-controller, it can be a benefit in keeping input and output power clean for the digital circuits.

Some people believe that using additional caps improves reliability since it reduces input and output transient voltages when the regulator starts up.  There's no definitive data that I've seen indicating that one way or the other, but it can't hurt. 

Generally you don't need caps for the OKR regulators, but other regulators require them so you have to consult the data sheet for the regulator you are using.

I believe the additional resistors you are asking about are the components used on the enable pin to provide a low voltage cut-out.  A resistor and Zener diode on the enable pin can provide that function.  Also a resistor is required when using the enable pin to switch the regulator on and off.

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