Trying to make an auto-stop dis-charger

[Al P]

If I can't fly the packs that are charged for a few days, I prefer to dis-charge them until the next flying opportunity. However, my Orbit can only discharge up to 2.3 Amps on my 8 cell packs. That is a long time on 3300 and 2600 packs.

I've read of several folks who use light bars or automotive headlights to discharge packs at higher rates. This would be fine, but would seem to require constant attention to prevent too deep of a discharge. Is there an electronic component that is readily available to install in the discharge circuit to stop the discharge at a pre-set voltage ? Thanks,

Al

[steve lewin]

I don't discharge my batteries in those circumstances because I reckon it wastes the cycle life but it's your choice ;).

Probably the easiest way to do what you want is to connect the load through a relay. By choosing a resistor to put in series with the coil you can fix the voltage at which it drops out and disconnects the load.

It's not super accurate but it is dead simple. :).

Steve

[Christer Lagerstedt]

Go to www.gerd-by-air.de and you will find under Technik schematics for a add-on discharger. It has to be conected to a Schultze or other automatic charger. It uses two headlamps to discharge the battery. More lamps could be added if one needs a higher discarge current.

I could do a translation from German if someone asks nicely.

Christer

[Never Enough]

I know that I am going to take some ribbing at my high tec suggestion...

Waaaaay back in the 80's when I used to run 10'th scale Ecars (RC-10's) we used to use auto lights as talked about here hooked up to a $6 timer switch (the kind that are used for the fan in your bathroom) they are a spring loaded and run from 5 min to 60 mins (some go to 90).

I know, cheesy but it worked....

[jrb]

This link should help: http://www.marcee.org/Articles/BatteyPackDischarger.htm

[Speed E Freak]

hi,
a simple way with equipment that all e-flyers have!

connect up your pack to a speed controller as normal, but instead of output going to a motor+prop, connect it to a bank of car headlight bulbs. speed controller will auto cut off at low voltage as it does in flight, without discharging pack completely.

speed

[Tom Melvin]

That, my friend Speed E Freak, is positively brilliant. Thank you.

[Stickman]

Al,

On the other hand, you could build a dedicated circuit for automatic battery discharge using only a PnP power transistor, two to three resistors and a zener diode. Throw in a junk of metal to heatsink the transistor and a fan, driven off the load- side, and thats it. The simplicity is nice, but the real advantage, at least IMHO, is that it's linear operation eliminates some of the negative characteristics of digital high-rate dischargers--at least
the ones of my own previous design.

Anyway, Just another thought to throw into the pot.

Mark

[Al P]

Thanks for all the replies and great ideas ! :)

Al