purple_car

Quick newb question that I couldn't find an answer for:

How do I discharge my NIMH packs after the c/10 form charge? My charger doesn't have a discharge function. Would it be ok to put them in my car and just run it at slow speed until they're low (but not totally dead)?

Thanks!

discgolfer72

here u go cheap and works great and will explain how its done

http://www.rccaraction.com/rc/articl...scharger_1.asp

JNorton

My Feedback: (2)

If you want to form your packs in my opinion don't use a lamp discharger. The current draw is way too much. Just run your car at slow speed. The other thing I have against bulb discharger's is that because they don't stop discharging it is a great way to discharge a single cell in a pack too far. Then that cell if you continue to discharge it using a bulb discharger becomes reversed. Now sometimes you can do a C/10 charge and try to equalize the pack and it will work. But of course if you keep using the bulb discharger it will happen again. All in all it is a great device to make sure you buy more packs. If I was a manufacture I'd love these things. Please be sure to keep on using them you'll keep our economy going.
John

PS You really don't want to know what I really think of these things. If you want to know how rechargeable batteries actually perform rather than someones opinion read RC Battery Clinc by "Red" Scholefield. He developed these things called NiCads. He knows what he is talking about. If you just want to keep abusing packs listen to the site you quoted.
www.rcbatteryclinic.com

Basic NiCd stuff
http://www.rcbatteryclinic.com/seminar.htm

JNorton

My Feedback: (2)

Purplecar,
Run the car slow spped until it starts to slow on it's own. Recharge and it should be close enough. Try to save up for a decent charger. It will pay you back by not overcharging your packs and being able to do a decent capacity check. In my opinion currently it is hard to beat the Multiplex LN5014 from a price and performance standpoint. You'll need a power supply to use it at home. Check with the PC repair centers in your town. Often they give you a used ATX power supply. Look at Red's site above to find directions on how to convert it. It's on the menu at the left all the way down
http://www2.towerhobbies.com/cgi-bin...&I=LXKSY1&P=ML

There are many other good chargers if you don't like the Multiplex just select one that also discharges.

John

discgolfer72

i use the bulb discharger with no problems tho i do use my multi meter to keep an eye on voltage
never had any problems and i use a 15 bulb one for raceing i have a few 2000nicds that ive had for years with no loss in power

JNorton

My Feedback: (2)

I can't seem to leave well enough alone quote from the Light Bulb discharger site. "It’s the tool you’ll use to drain your packs before recharging them, to train them to run at race pace and to monitor their capacity." Way well way back in the stone ages when chargers were run by timers this was true. You need the pack fully discharged so you wouldn't over charge it. Nowadays there's delta peak detection chargers that charge packs without overcharging them. If you consider that battery packs are electro-chemical devices with only a limited number of charges I'll use my charge racing instead of doing useless discharge cycles that aren't limited to .9 volts per cell.

discgolfer72 this in no way shape or form should be considered a rant against you. It is a rant on the stone age practices still being put forth as preferred methods of battery maintenance by some of the car community who should know better. End of rant.

John

purple_car

Thanks for the good information!

I just got some new 3300 mah NIMH packs so now I'll form charge them!

James

purple_car

Two more newb questions:

1. The wall wart charger I have kicking around charges at 150 mah, not the 300 mah that I need for C/10. Is this ok to use for the form charge, if I leave it for something like 30 hours instead of 14-16?

2. The wall wart charger I have is a nicad charger. Is this ok for NIMH?

THanks!

JNorton

My Feedback: (2)

A .05 charge rate is right on the border line, on Red's site under Basic NiCd stuff he says that the .05 rate is the minimum used for commercial practices. I'm calculating the charge rate by dividing the charge from the charger by the packs rated capacity. 150 mA/3300 mAh = .045 So I'd say charge it for 30 hours and you should be okay. Try to get a better charger.

You can slow charge either NiMh or Nicd. The biggest difference between the two is that NiMh does not like to be left on a C/10 charge.
John

Dawman

My Feedback: (33)

if you use expensive batts , I`d invest in a discharge tray that discharges the cells indiviually. This one works great , but you can get some cheaper one on the market. http://www.shopatron.com/product/pro....0.235.0.0.0.0

JNorton

My Feedback: (2)

The point is what use is it? If I want to equalize cells just charge them at a C/10 rate.
John

JNorton

My Feedback: (2)

If I was racing cars the first thing I'd look at is the power to weight ratio. The second is the gearing and wheel alignment. The third is lowering the measured losses in the wiring from the pack to the motor. Fourth the timing of the motor and the making the most efficient ESC using the latest low resistance FET I could find to make sure all the power I can use goes to the motor. What purpose does discharging batteries have in all this?
John

purple_car

Thanks for the great information JNorton. I'm giving them a good form charge now and I think I'll invest in a better charger in the future.

James

Dawman

My Feedback: (33)

Well , you seem to know more than the battery manufactures . So maybe you should tell them and all the car racers that they are doing everything wrong. The only way to accurately equalize cells is to charge and discharge them individually. Like a dischagre tray to dicharge them . If you can argue with that , you should take over the battery industry and be a millionare.

JNorton

My Feedback: (2)

What battery manufacture recommends using a discharge tray. Sanyo? Panasonic? Give me a name brand manufacture not a distributor and a good URL as proof and I'll eat my words plus you'll have a $20.00 bill winging it's way to you.

Please read Red's Battery Clinic. www.rcbatteryclinic .com

That said you are absolutely right some car racers are doing many things in the stone age. If I can equalize a pack without a battery tray and it's easier on the pack why do it? You still haven't answered my question?

John

JNorton

My Feedback: (2)

Dawman,
Sometimes I tend to state my position too forcefully. If I've offended you that was not my intention. I just get nuts reading about archaic practices that seem to have no bearing with todays technology. 10 to 15 years ago it might have made sense, I don't see where it does today.
John

Dawman

My Feedback: (33)

http://www.teamnovak.com/products/ba...tery_care.html , http://www.smc-racing.com/ , for starters .

Dawman

My Feedback: (33)

well , then Novak , SMC , and others must be in the "stone age" . They match the packs and know the best way to care for them . They all seem to have different ways , but I`ve had great succes following these guidlines.

JNorton

My Feedback: (2)

I think we are just going to have to agree to disagree.

You showed manufactures of the trays Novak who obviously have a vested interest in selling trays. Where are the major battery manufactures? SMC claim to fame is their matching process which sounds very good. However SMC says that using a battery tray will actually improve run time by a few seconds while using a dead short (after discharging to .9 volts) will drop run time by 20 to 25 seconds. I don't see this a something to get excited over nor do I see it as an advantage over equalizing with a C/10 charge.

I've read your sites have you read Red's?

John

Dawman

My Feedback: (33)

yes , I have . Both have intersting points . Like I said everyone has different views on battery care. I don`t dead short my batts unless they are really bad condition and end up as practice packs . But from 17 years of car racing I have found the described methods to work the best. The major battery manufactures don`t give any deailed care. The companies that get the bulk of cells from Sanyo , Panasonic , GP , and etc. match them into "different" matched sets. They have specific detailed care from the way they are matched. one care method can not work for all matched sets. Like my Novak GP 3300 sets recommend a charge rate of 6amps. My integy IB3600 sets recommend a 5 amp charge , SMC 3300 reccommend 5.5 amp charge . These companies all recommend kepping them discharged at .9v/cell when used weekly and some charge when stored longer . The Trinity Panasonic 3000 pack reccommend a 4 amp rate and always keeping a charge left in them . So , I think we both have good ideas it just depends who we listen to.

JNorton

My Feedback: (2)

Wish I had the reflexes to race cars. I know with the background I have in electronics and mechanical systems I could be extremely competitive. And if I wasn't well it wouldn't be the first time I've had my tail kicked.

Logically speaking (I know there I go again) if a pack is matched as well as SMC does theirs and you have huge buss bars like I saw on their site for the lowest resistance between cells how does a pack go out of balance so quick as to require being balanced between races? The packs are in series so each cell sees the same amount of current through it - the exact same amount - Kirkoff's law. Do you run the cars until the batteries are totally exhausted and you're experiencing cell reversal?

The guys that also abuse their packs flying planes don't use trays and their discharge rates are comparable. They don't keep their packs discharged between uses either. It just seems to be a car thing.

Well if there is one thing I've learned in life it's that some things just can't be explained. I'm sure not going to change your mind about something that you've had good experience with for 17 years.

May you win at least a couple of heats per race and have as much fun doing it as I have flying my planes.

John

Rodney

No offense intended but a lot of what Dawson says is contrary to what I have found to be true about batteries and their care and upkeep. I tend to agree with JNorton and Red as their inputs and advise has been right on and jibes with my considerable experience and activity in instrumentaion, electronic design and general aerospace experience. To accurately make any conclusions, one must have an adequate number of samples and very controlled testing over an extended period of time. Most of us have not had the luxury of being able to take at least a 100 samples and test under laboratory conditions over a many month period. Our experience with just a few samples under uncontrolled conditions can lead to some very bad or inadequate results. That is why it is best to first get the info from the manufacturers and heed it until proven otherwise.

Dawman

My Feedback: (33)

Well you guys do whatever you want. I`ll continue listening to the people that I get the batteries and coninue my racing . I never had any problems in the past 17 years , why would I stop listening to them and listen to you . If what you say is the case then why isn`t there any car guys that are using that method . It seems to me that just you plane guys are argueing about this. I have brought this up on some other forums where car racing people seem to agree with me , Novak , SMC , Integy , Trinity , and others. Any way I`m done debating about this.

JNorton

My Feedback: (2)

Dawman,
I haven't been looking at it from a airplane verse car thing, only from an engineering standpoint. Personally if I was building a car I'd be looking at 4 brushless motors with a 40 - 60% split with bias toward the rear and 4 individual MOSFET ESC being controlled via an onboard PIC looking to keep traction. I'd power it by a LiPo pack. And I still wouldn't use a tray.
John

PS I don't believe Rodney was looking at it from anything but an engineering viewpoint either.

Dawman

My Feedback: (33)

Thats good since you can`t put a lipo pack on a tray.
That is a good point , but in my line of work I know that an engineers calculations and examples are totally different than what actually happens in the field.