electronicsfreak
Member
Howdy folks, looking for your opinion here!
So a bit of background before diving into my question, another hobby of mine is airsoft. A few years ago I had built a PIC based trigger switch for one of my AEG's (basically an electric rifle that shoots small plastic BB's) to help the gearbox cycle more consistently than it had previously. Worked like a charm for a few years now with a couple of 9.6V NiMH battery packs.
Welp, those old NiMH cells are beginning to show their age, and I'm looking to upgrade to a newer battery. I'm looking for something able to handle a wee bit more current such as a LiPo pack. The more I look into it, I believe an 11.1V, 3cell pack may be a bit more than is really needed for this AEG motor, however that leaves a 7.4V, or a 2cell battery.
Here's where I'm looking for your opinion or experience. At continuous, the motor draw settles to something close to 20-22A on a 9.6V pack, with a much much larger spike at startup. I know for a fact that initial spike and following continuous load sags the batteries output voltage to a much lower voltage than the nominal or open measurement significantly (gotta love ESR, heh).
Unfortunately, to power the logic in this switch, It's using an old LM7805 regulator to generate a 5V line, which according to the datasheet, will only function when a minimum of 7.5V is applied to the input. This is where my concern for using a 2 cell LiPO comes in to play.
I'm looking for your opinion or experience. Do you think this is too close of a margin for using a 7.4V LiPO in this condition? The circuit is in a state that I cannot make any changes (sealed and secure in the rifle's stock from the elements)
I think I could push using a 3cell pack, but this will potentially introduce more mechanical wear than was needed before. The system works as it is, but I would much rather make the switch to a LiPO pack instead of building another NiMH pack.
Thanks in advance for your input fellas!
--EF
So a bit of background before diving into my question, another hobby of mine is airsoft. A few years ago I had built a PIC based trigger switch for one of my AEG's (basically an electric rifle that shoots small plastic BB's) to help the gearbox cycle more consistently than it had previously. Worked like a charm for a few years now with a couple of 9.6V NiMH battery packs.
Welp, those old NiMH cells are beginning to show their age, and I'm looking to upgrade to a newer battery. I'm looking for something able to handle a wee bit more current such as a LiPo pack. The more I look into it, I believe an 11.1V, 3cell pack may be a bit more than is really needed for this AEG motor, however that leaves a 7.4V, or a 2cell battery.
Here's where I'm looking for your opinion or experience. At continuous, the motor draw settles to something close to 20-22A on a 9.6V pack, with a much much larger spike at startup. I know for a fact that initial spike and following continuous load sags the batteries output voltage to a much lower voltage than the nominal or open measurement significantly (gotta love ESR, heh).
Unfortunately, to power the logic in this switch, It's using an old LM7805 regulator to generate a 5V line, which according to the datasheet, will only function when a minimum of 7.5V is applied to the input. This is where my concern for using a 2 cell LiPO comes in to play.
I'm looking for your opinion or experience. Do you think this is too close of a margin for using a 7.4V LiPO in this condition? The circuit is in a state that I cannot make any changes (sealed and secure in the rifle's stock from the elements)
I think I could push using a 3cell pack, but this will potentially introduce more mechanical wear than was needed before. The system works as it is, but I would much rather make the switch to a LiPO pack instead of building another NiMH pack.
Thanks in advance for your input fellas!
--EF