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Topic: Lithium Polymer protection (Read 770 times) previous topic - next topic

Voidugu

I am planning on building a li-po protection circuit using an arduino so that i can protect my lithium polymer battery from undervoltage as it is destructive for li-pos (minimum open circuit voltage per cell ~ 3.6 volts). I need to switch the main power line going to my RC car's ESC through somekind of device that would require minimal current to operate and could handle lots of amps while being as efficient as possible. First i though bjt transistors and fets but they have that nasty voltage drop which dissipates a lot of heat under heavy loads (lets say >5 amperes), resulting in relatively low efficiency. Then i thought relays, but they require current in order to drive the electromagnet which switches the main current on or off. I would like to create a circuit that would require as less power as possible to operate and would be as efficient as possible.

My question is:
What do you guys suggest? Is there a more efficient way to switch such high currents?

{(This might sound silly)I was wandering: is there a type of "locking" relay where you provide current at the beginning only to switch it close and then after that it "locks" into position by somekind of mechanism which allows it not to drain any more current to operate the electromagnet?}

Any help and corrections are appreciated.
Thank you in advance and merry Christmas

retrolefty

Quote
{(This might sound silly)I was wandering: is there a type of "locking" relay where you provide current at the beginning only to switch it close and then after that it "locks" into position by somekind of mechanism which allows it not to drain any more current to operate the electromagnet?}


Yes, such a relay is called a 'latching relay' and they come in two coil or single coil versions. In the two coil version you pulse either the set coil or the reset coil and relay moves to that position and is magnetically retained there so no continuous coil current is required. In the single coil version you apply one polarity of voltage or the opposite to set or reset the relay and it will retain last command with no continuous coil current being required also.

On your lipo voltage levels, most recommend that +4.2 vdc is fully charged and 3.0 vdc is a commonly used cut-off 0% voltage recommendation. If you use 3.6 vdc as your cut-off value you will be leaving quite a bit of battery capacity unavailable for your use thus lowering the effective mAH rating of your battery pack.

Lefty

Voidugu

Thank you for the info

What method do you suggest i use for such a circuit?

retrolefty


Thank you for the info

What method do you suggest i use for such a circuit?


Frankly I would use either a battery pack that internal low voltage cutoff circuit built into it as many do these days. Alternately when I flew R/C aircraft all the ESCs I used had a low voltage cut-off warning mode where it would either cut off the prop motor or pulse the prop motor to let the operator know that the battery back had reached it near end of charge but retained enough to fly back home.

Lefty

Voidugu

My rc car was designed to work with Ni-Mhs. I wanted to upgrade to Li-Pos. My current lipo battery doesn't have such protective features nor does the esc-receiver module. That's why i wanted to create a "battery protector". There are some Chinese boards on ebay warning you about the voltage level but they don't cut the power, just buzz and light up. 

Anyway thank you very much for the help and have a great great day
Void

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