fatdoggy

I recieved a ceramic(spelling?) discharger when I first got into the hobby when I bought a pair of maxx packs. My Q is, is it possible for these dischargers to send your cells into cell reversal? And also at how many amps would one ceramic discharger discharge at?

Thanks.

fatdoggy

Nobody has any idea? C'mon chuck me a bone here.

newracer

yes it can reverse a cell unless it also has the correct diodes to prevent it.

the amps depends on the specs of the resistor

fatdoggy

Thanks, if I ran a doide from the pos to neg would I be able to stop it from reversing? Thanks.

patcollins

The only two ways to prevent cell reversal is to not discharge deep enough that one cell becomes completely discharged while the others still have charge in them. If this happens the ones that still have charge in them must still send their charge through the dead cell (because the cells are in series) and the dead cell receives a negative voltage from the ones that still have a charge. The voltage of the pack itself will still be positive so putting a diode here will do nothing. The second way to prevent cell reversal is to isolate each cell electrically like a discharge tray does.

As far as ceramic discharger, I guess you mean a ceramic resistor. The rate at which it discharges will depend on its resistance and the voltage in the pack, its not a constant discharge rate.

For example the resistance is 7.2 ohms and lets say you pack puts out 7.2 volts when connected to it because of ohms law V=IR we can get I=V/R so it will be discharging at 1 amp. Now as a pack discharges its voltage drops so the discharge rate will decrease.

Diodes in discharge trays don't have anything to do with cell reversal. Because in a try the cells are electrically isolated from each other the max any tray can do to a battery is bring it to zero. The diodes prevent this because they have a forward voltage drop of arround 0.7 volts. This mean for any current to flow there must be 0.7 volts or more applied. Diodes were added to discharge trays a few years back because dischargeing batteries to 0 volts can sometimes lead to a pack that likes to false peak early in its charge cycle. Now with NiMH cells they also benefit your cells because if you take a NiMH cell to zero it may never take a charge again, but it has nothing to do with cell reversal.


Hope I helped out.

Pat

fatdoggy

Thanks mate you helped out a heap, cheers.

Ian

if i'm building my own tray...which diode should i use??i could think of 1N4001 and 1N5404...what the cutoff of these 2 diode..anyone got ideas??

JesseT

The cut-off depends on the material used only. All silicon diodes have a cut-off of 0.7 V, which will be just fine. It seams that the 1N5404 has a slightly lower internal resistance and can handle more current. Of these two it would be my choise.

http://www.fairchildsemi.com/ds/1N/1N4001.pdf
http://www.fairchildsemi.com/ds/1N/1N5404.pdf

Ian

JesseT
thanks mate