ESC question

[punkin438]

I am looking for an esc to rebuild my Aerobird Xtreme with.The cutoff voltage on some esc's say 4.2 Volts.Does that mean i will only use less than half of my 7.2V battery?Any recommendations on a less expensive esc for this project.I believe the stock motor draws about 20 amps.Thanks.

[Gary Warner]

I am looking for an esc to rebuild my Aerobird Xtreme with.The cutoff voltage on some esc's say 4.2 Volts.Does that mean i will only use less than half of my 7.2V battery?Any recommendations on a less expensive esc for this project.I believe the stock motor draws about 20 amps.Thanks.
Battery voltage falls off very slowly for most of the discharge and then very fast at the end of the discharge. At 4.2 volts 99% of the charge has been used. It would be considered a full capacity discharge at 4.2 volts.

Gary
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[punkin438]

So you are saying that is a suitable cut off voltage.I have seen other esc's that cut off at lots less than 4.2 V.

[jeffs555]

There are two reasons for a cutoff on an ESC. The first and oldest reason is so that the motor will quit before the receiver and servos stop operating. Most receivers and servos will start to screw up below 4 volts, and that is the reason for a 4.2 volt cutoff. When the battery is drained to this voltage, you will have a glider, but at least it will be a controllable glider.

The second reason for a cutoff applies to lithium polymer batteries. These batteries are destroyed if they are discharged below a certain voltage. ESC's for lithium batteries are usually programmable for the number of cells, or else automatically detect the number of cells.

If your batteries are NiCAD or NIMH, then you don't have to worry about overdischarging them, but you do need the 4.2 volt cutoff to make sure the motor quits before the receiver and servos do.

[punkin438]

Thanks very much.Thats what i needed to know.I am new at rc stuff and am amazed at the generosity of people on this site to help people like me.Very much appreciated.