first time racing electric

[HPI_freak]

i am going to race my HPI Micro RS4 at the HPI challenge in Dayton, Ohio and i have a Peak Performance Boost 7.2V 1200mAh NiMH Micro Pack and i was wondering how, and when to charge it for the race? i have an adapter that plugs into my car that i can plug my charger into so i can charge my batteries at the track. should i charge my batts between each heat or should i discharge and recharge between each heat, or just charge em once for the whole day of racing (about 3-4 6 min. heats)?

[HPI_freak]

any help would be awsome

[SteveK]

NiMH cells do not have to be discharged before being recharged, but I would re-peak them between runs. Before to let them cool before charging them.

[gizmoguy303]

You also might want to pick up an extra pack or two to simplify the process and make it easier on your batteries.

[highroller]

You'll find you will get slightly better results by discharging the pack after each use. The problem you may run into is having adaquate time for the pack to cool properly before it can be charged. That was again misinformation concerning NIMh cells of not needing to be discharged, depending on the amount of inactivity the pack will see certain companies recommend storing packs with different charge amounts. But before using most advise discharging the packs before using and allowing sufficient time for cells to cool at room temperature before charging. I agree having a couple of extra packs is adviceable, you'll see some racers (big events) having packs for each race heat plus a pack or two for practice.
Most racers will be using chargers that are compatible with the type of cell they are using and using something to discharge the pack after use from a string of lightbulbs to chargers equipped with a discharge function. Take into consideration the length of time it takes for your pack to fast charge and determine the number of heats and when you heat will be up. Start charging the pack so it peaks prior to your heat race. Also consider the time it will take the pack to discharge and cool properly, and whether one pack with be sufficient or a couple extra packs is going to be needed.

[SteveK]

I'm about to make the jump to NiMH this summer probably, what IS the current 'guideline' for handling them properly?

[highroller]

It varies with the type of racing, and lately what type of cell is it. If you remember the Panasonics (most of the information concerning NiMh was found not to be completely true concerning their characteristics). Although it is chemically different from a Nicad it produces voltage the same way. To see good results for each the voltage much be reduced - each type of NiMh responds differently to how low each cell can be discharged. But discharging the remaining voltage down to a .90 volts cell level is the norm for any battery used to power a car. This just allows the cell to charge better the next time-this is still considered a memory though not a strong - the problem some people encounter is not allowing the cells to cool which leads to damage or premature failure. Each type responds differently to how low you can deep discharge a cell but it should be done at a lower amperage rate usually no higher than 2amps (however some manufacturers of equalizing trays use a 20 -30amp rate which is suppose to yield higher voltage output). After discharging the pack after use at whatever load the pack is normally subjected to in use 10,15, 20 or even 35 or 40amp to a .90 volt per cell limit(multiply .90 by number of cell to determine what the package voltage should be and remove the load). Depending on type of NiMh some should only be discharged/equalized to a certain level: Panasonics .25 to .15 volts, Sanyo .05 -.02, GP3300 .05 - .00 (some racers dead short them to increase voltage - this generally decreases runtime and not used for modified use), the newer version of GP3700 and IB3600 or IB3800 kinda varies and nothing is specific as least in my case - I haven't dead shorted the new GP3700 most matchers suggest not to dead short including Danny at SMC . It doesn't hurt either talking with the people where you purchase your battery packs to find out what they suggest. Try varying the technique a little to see what works best for you or the type of racing you do. At first I would recommend charging Micro packs above 1 to 1.5amp but after visiting and try Micro vehicles it doesn't hurt them to charge at 3amps, 4amp won't hurt too much probably cut the life down a little, plus some companies are zapping them with a few talking of matching them for Micro racing.

Normally I buy cells for a specific type or class of RC racing with GP3300 being the primary cell right now due to ROAR and track rules. Or use the packs that have lost too much runtime in modified as stock packs.
Stock offroad/Touring car pack is charge at 5-6 amps 6.50 is traction is very good, .05 - .07 (50 -70mv) depending on ambient temperature, discharging at 24 (12 lightbulbs) amps. Packs are discharged down to .90volt per cell (5.40 volts per pack) and stored.
Stock oval and 19turn (4cells) charged rate is general 7amps with a .03 (30mv) detect setting, discharged to .90 volts (3.60 volts), pack is placed in an equalizing tray (Trinity Real Time 2 or Integy Octane 2) until pack has cooled, if I intend to use it a second time if not once voltage is low enough (.05 or less) a jumper wire is soldered to pos and neg to dead short.
Modified Packs - offroad and TC charged at 5volts, with a .05 cutoff, discharge at 30amp (15 bulbs) to .90volts and stored, mod oval charge at 5.50 to 6.50 (varies with runtime I need) with .03 (30mv) detect setting, discharging at 36amp (19bulbs) to a .90 volts (3.60 pack voltage) pack is stored. I never charge the packs for storage no matter how long they may go inactive or unused. But packs are placed in an equalizing tray before charging the next time for use, just to make sure each cell is as low as possible and all cells are close to the same voltage levels. Cells (packs) that have gone through long periods of inactivity behaved just like Nicads packs that went through long periods of now use. The first time they get charged they may false peak, the mah rate - peak voltage may seem adnormally low and in racing conditions it may seem sluggish or have no punch it once did. After a couple of frequent uses the cells generally stablize and act normal.
Some racers will cycle a pack a couple of times before the actual day of the race - allowing pack to rest a day or two, or you just use the pack for practice discharge it and cool then run it in the qualifing and main races but that may not be sufficient sometimes even new packs may not show good results the first couple of cycles, like the 2400 Nicads you start seeing an improvement between the second to third cycle. Cycling them or using a CE unit doesn't seem to help, better results seem to happen by actually using it in race conditions. I found over time that even matched cells will begin to discharge to different voltage levels, it you normally stored the packs partially charged or didn't equalize the cells some why this was one cause for false peaking problems, even with some stick packs if you used one 1157 bulb and placed on pack until it dims pack did not false peak as much, you still may encounter some false peaking but generally it because of a cell or two starting to degrade.

For Micro Packs some of the Techniques we used with regular sub C cells can provide the same results depending again on what type of NiMh cell it is. GP cells still seem to be very durable and available to be subjected to more abuse. Most suggest charging at 3amp with a 10amp discharge with a .01 detect setting. However you limit the cells life and depending on how tight the rules are that club uses rebuilding packs into side by side or hump configuration elimanates the problem with heat and resistance, this may allow you to charge and discharge at higher rates thereby getting cells to produce more voltage. Also the plug and stuff may have to be replaced (if rules allow) with plugs that allow for higher rates. Even then you may want to only experiement with one pack vs all your packs just in case it doesn't work. Also you may be more concerned about getting more life out of pack vs performance so it may be necessary to change the way you charge and store them. Nothing is 100% right or wrong just what each person finds works for them.

Once the method we used early in RC was to charge a pack up (don't try this now under any circumstances) then hook the positive and negative connectors together then drop it cool water until pack discharged. The idea was to get pack (1200) to produce good voltage, in most cases it worked but shortened the life of the cells and if done incorrectly destroyed a perfectly good pack. Also those that remember the Sanyo 1700SCE where they suggested or recommended charging them no higher than 3.50 volts and only at a linear rate, well again we found that wrong some if not most of them I used were pulsed charged at 5-6amps and still have some that are used up 3 years ago for breaking in motors although most are going bad now.