sportpak

iTrader: (26)

I'm not the type to just go and blow stuff up. I'm not sweating the 40mv either, it's just interesting.

Rick Hohwart

We have found lots of things. We will eventually post results (hopefully on a new and improved website) so that users can get the most performance from their Reedy batteries.

It is a function on the charger. This procedure is described in the charger's instructions.


It is 80mV if you are comparing it against the maximum allowed voltage of 8.44. It won't make a difference. The fact is that the charger is not working properly if it is not charging the battery completely.

linger

iTrader: (1)

Hi Rick,
Thanks for the good info. The intent of the the 8.440V limit was to prevent people from intentionally overcharging a lipo to get an advantage. If the 8.440 limit is not realistic, then I'll campaign to change the limit. Lipo batteries normally drop back 10-20mV after a charge so a charger needs to be at least 50-60mV over 8.400 to be over the ROAR limit.

I dug though a stockpile of data to see what I can come up with. Out of a batch of 25 or so Hobby Quality chargers (made by Bantam), I picked out the worst offender which charged to almost 4.270V (single cell) - about 70mV out of spec. Immediately after charge, it the battery would drop down to 4.240 - pretty darn close to the ROAR limit.

The tolerance of using the same charger was extremely close from charge to charge. I plotted out 10 consecutive charges (see attachement). The total tolerance is less than +/- 10mV from charge to charge.

I did some spot checking on a bank of about 6 Duratrax Ice chargers and none charge above 4.200V/cell. They seem be be calibrated very well.

sportpak

iTrader: (26)

If 80mv isn't an issue, then why do so many people sit around and bench race the stickers on their nimh batteries?

Seriously, if you had two batteries sitting on your bench and you were up to run, which one would you choose, A @ 8.37v or B @ 8.42v? We all know which battery we'd choose...

BURATIS-SPP

guys sorry to divert you discussion. I have a silent charger (much more). I just want to get info on how to charge my rec pack with 1100 mah; 7.2 volts.
What can you guys recommend on the charge rate amp. and best discharge rate amp. wise? I know i should set it a 2cell or 7.4 volts but I dond know what the best amp to use for the receiver pack? Is 1.0 amp good enough for charging and 1.0 amp. for discharging? ty guys

sportpak

iTrader: (26)

Find out first what kind of battery you have, that's VERY important.
If your pack is nimh, be in nimh mode. For charging, I would charge at 1a. If you wanted to dischage, I would set it at .5a.

If it's lipo, you charge it in lipo mode at 1.1a. I would not discharge it if it were lipo.

Ben

kufman

iTrader: (6)

There is an easy way to trick the charger, but I probably shouldn't mention it

oXYnary

iTrader: (4)

I guess my questions is, why wouldn't they be used in the first place? If a charger is using lower quality components to make a price point, and fails the charging cutoff. Should ROAR have to change the rules just for that or group of chargers cheap ICs?

Rick Hohwart

ROAR's only rule is that the battery be no more than 8.44V. There is no reason for ROAR to regulate chargers. The user must be aware that actual voltage can vary from voltmeter to voltmeter (whether it is a stand alone unit or integrated into a charger) and this can affect the legality of their car.

And the post prior to yours illustrates how any charger with voltage calibration can be tricked into charging to higher voltages.

Francis M.

iTrader: (2)

One more thing, I know NIMH has a higher peak voltage but drops off within a few laps vs lipo. I guess I want to know How long the lipos stay at peak voltage during the run or at least close to peak voltage?

oXYnary

iTrader: (4)

Gotcha, though I think its a matter of prespective. Though, I know a charger can be tricked with longer leads (in example) thats the users ignorance or cheating. The cutoff has to be set at some point by ROAR. While continually increasing it slowly just to accommodate some poorly designed chargers seems to invalidate ROAR.

I'm saying... If the charger fails because it naturally overpeaks via poor circuitry versus specific manipulation by the end user. Should ROAR be bending rules for all those drivers who use it?

I'm not saying ban chargers, I'm saying to keep a cutoff, and don't continually revise it if lower quality chargers can't make the grade. If a charger fails to be precise, and it DQs the user for at least that round. Is it then the Charger, ROARs, or users fault? From your viewpoint, it sounds as your saying its ROARS, from my viewpoint, its the chargers for being inprecise.

Linger showed the ICE keeping a pretty consistent tolerance cutoff between each unit.

Francis M.

iTrader: (2)

It's always the racer's responsiblity to pass tech.... Roar has set guidelines with room for a small tollerance discrepancy for practicality purposes in regards to different chargers....

Francis M.

iTrader: (2)

It's always the racer's responsiblity to pass tech.... Roar has set guidelines with room for a small tollerance discrepancy for practicality purposes in regards to different chargers....

Rick Hohwart

I am sure the 8.44V limit will not be modified by ROAR. The .04V tolerance is in place for just this sort of thing. ROAR, or tracks, should never bend the rules. This limit is the absolute limit and it should always be enforced.

It is not that hard to be legal. As an example, I had a battery at the Nationals that was 8.44V but intermittently flashed to 8.50V. They would not let me run it so I wnet back to my pit and discharged it for a few seconds at 1 amp and it was now legal. I don't think anyone would even need to be disqualified because teching voltage has to be done before the race starts.

oXYnary

iTrader: (4)

Rick, your such a good spokesman. You said it perfectly.