Author Topic: Circuit protection - fuse, thermal fuse, diode, MOSFET, Transistors, what?  (Read 4334 times)

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Offline akisTopic starter

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I have two Li-Ion batteries or a PSU supplying power to a portable device. As I explained in a previous post I have built a small circuit, with a relay, to disconnect if the current exceeds 2.5A and if the voltage drops below 10.5V (so as to protect the batteries). But this circuit is quite large (through hole components) and would like something smaller so as to fit inside smaller battery packs without adding too much size.  Maybe also polarity protection as a bonus.

The suggestions were:

1) use one of those Lithium-Ion battery protectors, as they are tiny. The cons are (a) they require to be placed on the battery and monitor each cell. (b) the amps are typically fixed (c) the undervoltage detection is fixed and way lower than I want. (d) I cannot apply this circuit to a normal PSU (admittedly the PSU only needs the over current protection)

2) use my own circuit : great, but it is too bulky due to the onboard relay and the other through hole components

3) use a combination of other components such as:

thermal circuit breaker: http://uk.farnell.com/eta/106-p30-3a/circuit-breaker-3a/dp/143827

MOSFETs instead of relay - there will be an inevitable voltage drop, and it does matter for batteries, 400mV at 2.5A, maybe if I place two FETs in parallel, but then we are not far off the relay size and there may be heat to deal with as well.

Transistors instead of MOSFETs - requires two transistors (space) and even larger voltage drop and heat - but we get the bonus of polarity protection.

Other components, like thyristors or whatever...

Any suggestions?
 

Offline Neilm

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Re: Circuit protection - fuse, thermal fuse, diode, MOSFET, Transistors, what?
« Reply #1 on: September 19, 2014, 05:01:15 pm »
If you are looking to sell this the battery pack would have to be approved. Using a recognised device would make the approval a lot simpler. I don't know what chips you have been looking at, but I have seen battery protection circuit chips that are programmable with a couple of resistors for both current and voltage.
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