What is "dead shorting" your packs and why and how?

[old phart]

I have heard reference to doing this after a pack has been discharged. What is the purpose for it; how is it done? Thanks!

[Spinner]

connecting your pack to itself, pos to negative, to short out all of the cells

[Railman]

Old Phart, Weve been dead shorting for about 4 years or so. It does the following: equalizes so you get a maximum capacity charge, reduces cell resistance for more punch, raises average discharge voltage, stops deterioration of the battery while not in use for long periods, reduces or eliminates memory, causes false peaks when 1st charged after shorting. The false peaks are kind of scary at 1st, but you just need to add up the mah that goes in each time. Thats why the pros are so hot on the CE Turbo 35's. They have a full false peak lockout option thats just the thing for dead shorted batts. There are some who argue about some of the benifits, but an awfull lot of serious racers dead short their NiCads, & some evn do their NMH's, but I don't have any of them to vouch for what happens to them. We have had good luck with our NiCad packs. What you need to do is to bring the packs voltage down to a reading of 0 volts, & then solder a wire across the cells = & - to short them. The voltage must be all the way down 1st though. The best way to do it is with a dead short battery tray (0 volt), & then short with a wire. You can also bring the pack down to about 4 volts at a high (20-30amp) discharge rate, & then do a discharge at a low rate of say 2amps to a 1 volt cutoff. Then you can put a resistor across the batt for a few hrs until you get a 0 volt reading across EACH CELL (all 6 individually). Then it's safe to dead short them. I know it sounds confusing, & you do need to be carefull about when you do the final short, but it does make batts perform to their full potential for a long, long time. If you have questions, ask away & maybe I can help. Joe ;)

[SirSpeedy]

Well said.

And don't do it to Nimh. You just lose a TON of runtime for minimal voltage gain, and the IR remains nearly the same.

[Railman]

Thank you Sir, that means a lot to me. :cool:

[old phart]

Thanks for the info!

So, soldering a wire sounds more like a long term storage deal? What if you just want to keep them in-between weekly runs? Wouldn't a jumper made with a connector do the same?

Also, when you mentioned get a "0" reading across "EACH" cell, that can only be done with saddle packs, no?

What rating resistor do you use to bring it down to 0?

I have noticed when watching my pack discharge with a headlight (gonna make a 10 bulb discharger soon) it rapidly falls off when it gets around 4 volts, and I have pulled off the connector sometimes when it was reading between 1 and 2 volts. But, it recovers "really" fast and almost instantly gets back up to 4+ volts. Wouldn't that cause a wire or resistor to burn? How long must you leave a load on the battery to truly have it to 0 volts? I have never done this, fearing I would damage a NiCd. But the info I am learning seems to indicate otherwise. ;)

I don't have any expensive "matched" packs, I just have everyday sport packs. Is that a concern when talking about dead shorting?

Thanks again guys! :D

[ammoace]

Good questions OP, I was wondering the same thing.
Jerry

[JP]

Be careful when doing that. Somehow dead-shorting went wrong with me once and i got battery acid on me. I guess it wasnt discharged all the way. It burns, goes through your clothes. I think I still got a small scar from it...

[Railman]

Old Phart, Dead shorting is normaly done with side by side packs, but I've heard of people doing it with end to end packs with resistors as described above. The only thing I would question is what brand of batts you have. It use to be that some brands did not like their cells put into a reverse charge condition, & ended up doing permanent damage. That's why they have discharge cuttoff ratings on batteries, normally around .85 volts. When you discharge a pack, some cells have more of a charge left than others. The ones with the least charge will actually go into a revese polarity while discharging. The Sanyo RC batts (the ones that say RC1700 etc. right on them) do not have a problem with being reversed though. The others I couldn't take a guess. You will need to do your dischrge in three stages as I explained above. Then use a resistor somewhere around 50 ohms or so. We use as little as 10 ohms, but thats a little too quick to be safe. They do get hot but we've never burned one up. In answer to your other question, most do this to gain performance, but it's fairly well documented that cells will last a lot longer in storage if you get all the juice out of them. I have talked to guys that used to do this way before the newer type batts came out, & they told me that they had batts in storage for years, & they charged back up to their old numbers & performance. We have routinely done this for 6 month intervals with excellent results. Do keep in mind that it is critical that you need a 0 volt reading before you dead short. If you have enough jumper wires, go ahead & use them, they work fine. We would need 16 to 20 jumpers to do ours though, so we solder a wire instead. How long you need to leave the resistor on the pack depends on when it reaches 0 volts. Overnight woud be safe, but a couple of hours may be enough. Too long is better than not long enough though, since you can't check the voltage of each individual cell. If you have any more questions, ask again. Joe

[old phart]

Railman: thanks again for the very detailed and informative repsonses.