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Tp4056 reverse voltage protection
#21
Good find on stackexchange. That was one of the styles I've seen before, just couldn't remember where. There's also plenty on Youtube that show reverse polarity protection.

Now that we have the info here, it can be found by many on powerwalls Wink
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#22
Hi Guys
Thanks for that advice I will use it on my BFC rig I'm just building.

But are we still using a MOSFET and a Schottky Diode in this circuit. Where does the resettable poly fuse go?

Can anyone do a circuit diagram for my reference

thanks
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#23
Here's a circuit diagram for ya. The fuse would/could be used in the same location, between cell and board, or could be between board and main rail. You could really put the fuse anywhere. I personally dont see need for a fuse in "this" particular application as the TP's will shut off and don't allow power to flow "out" of them at all

Quote:
Quote:When initially given power, R1 pulls the gate of the MOSFET close to the source, keeping the mosfet from turning on. Once a lithium cell to be charged is added, current from the cell flows trough R2 to the base of Q1, turning it on. Q1 then pulls the gate of the MOSFET low turning it on. If the battery is connected backwards Q1 never turns on and the MOSFET never conducts. D1 is there to protect the base of Q1 from the negative voltage of the battery.
The problem is that even after removing the cell the MOSFET stays on, allowing Q1 to stay on and keep pulling the gate low in a positive feedback loop.
Now that I think of it, the latching circuit would work after all: If the MOSFET is on when adding a cell the wrong way, the charger IC goes into short circuit protection which causes the charger output voltage to fall below the threshold voltage of the MOSFET switching it off, and interrupting current flow.

Quote:To the OP: This is probably your best bet. You can probably find a PTC to use instead of a fuse. There is probably a way to get a MOSFET to do the job, but it will not be easy. I think if you draw it out with the MOSFET, and showing the body diode, you will see why.
Quote:I tested it with a 30V/1.1A RUEF110 (thanks mkeith) PTC fuse, and it does the trick, the tp4056 does not even get hot. By the way im using a random diode i found. Sometimes the cheapest and the most simple solution is the best! Only drawback - it will take a few seconds after the short for the ptc to recover though.

Thank you for the simple solution, i have worked a lot with tp4056 and have blown my diy tp4056 parralel 10A chargers with reverse polarity on the battery ends. I thought of using a mosfet but my solution came to same problems as jms-s. So forget the mosfet idea.

And a link from Afrotechmods reverse polarity protection video

 

[video=youtube]https://youtu.be/IrB-FPcv1Dc[/video]
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#24


Where you see the fuse symbol, you can put the PTC there. 

In fact, there is another device called a PPTC that does the same thing.

I ordered a hundred of them on Ebay.  it was a JinKe Polymer PPTC PTC DIP Resettable fuse 16V 2A.

When I get them in a couple weeks, I am going to test one first before rolling them out on my chargers.
I am concerned about the resistance of this particular part that I ordered because it did not actually list the resistance. but similar parts from other sources had a resistance of 0.047 ohms.  Thats acceptable toward the end of the charging cycle when the charge current drops below 100 mA.  At 100 mA the drop across the fuse is just .0047 volts which is not noticeable. So instead of getting 4.11 volts on the battery, you get 4.105 volts.

I ordered a bunch of 1/2 watt diodes a few weeks ago, and I plan to test those as well.
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#25
@egam

This schematic is not correct, you know that right?
1N4148 diode is way too small for this application.
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#26
What makes it not correct?

VRRM = 75-100 V — maximum repetitive reverse voltage
IO = 75-200 mA — average rectified forward current
IF = 200-300 mA — maximum direct forward current
VF = 1.0 V at 10 mA.[13]
IFSM = 1.0 A (pulse width = 1 s), 4.0 A (pulse width = 1 µs) — non-repetitive peak forward surge current
PD = 500 mW — power dissipation
TRR < 4 ns — reverse-recovery time


Is it the IF of 200 -300mA you are referring to?
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#27
(06-13-2017, 10:50 PM)FERCSA Wrote: @egam

This schematic is not correct, you know that right?
1N4148 diode is way too small for this application.

I copied the schematic from one of the links I listed, and that is not the diode Im using. But I suspect it would work in this application anyway.

it only has to work until the fuse pops.  So if the battery is installed upside down, the current flows through the diode and across the fuse (ptc)  The one I chose to test is a 2 amp that pops at around 4 amps.  The PTC open circuits until the battery is removed.

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#28
LOL
"I guess the biggest takeaway is I am going to protect a cheap circuit with cheap components to come up with a more reliable system that is dummy proof to my inability to put the cells in correctly every time."

I love that Tongue I think that about sums it up for all of us at some point or another Wink

Good work on the problem solving.
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#29
(06-13-2017, 11:44 PM)Korishan Wrote: What makes it not correct?

The author states that it is too small in the video.

-John-
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#30
Forward voltage of 1v @ 1A = 1 Watt of power loss. I know that adds up over several units, but it's still small. It's small than the example in the video. And, in the video he's using a 1N5400.

However, i would recommend a schottky over this one, though.
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