RC10Talk - The Net's Largest Vintage R/C Community

Jay Dub wrote:Of course they will tell you that, they sell more batteries. Plus once a week sounds shitty to tell customers. So their batteries sound better if they tell you that you can run them as much as you want. But, I can tell you as a national champion, 100% sponsored factory racer for nearly 20 years, including up and through the NiMh craze that what I wrote is what they tell the factory drivers about the batteries -NOT the general public. Believe what you want, I have noting to gain by giving out this information. This is simply what my sponsors told me during the NiMh heyday. The guy asked how to best take care of his NiMh batteries. I am giving him the best info available.

X 2 and 100%, we were given NiMh fresh off the zappers ran them 4 times and sold them to club level guys. NiMh was the least chemically stable cells period.

great info guys thanks alot..now that you say it , i do remember people saying nimh "race packs " should only be used 1 time a week..been doin this rc stuff so long i forgot more stuff then most new rcers know .. my big prob is i know i left them sit for months without a charge.. oh well ill give them 1 more cycle .. looks like some will be junked

OK then what is needed to get into lipos? I know my charger does lipo (it says on it) but what are these balancer things? Do you charge lipos like nicad or nimh? Do they need special care if you don't use them often?

I feel like batteries are getting more and more complicated... I miss the time when you could charge a pack straight from you car battery with "booster" cables.....

Maybe I should just get back to Nicad!

For those of you that are naive enough to think that NiMh cells are safer than LiPo, have a look at these pics..

These pics are what is left of a racing buddies 4200mAh NiMh batteries that were placed in his car after the days racing.. He had eight packs stored in the case, and he lost half of them, even though only one "failed".. He had used each pack only once that day.. He followed the usual discharging it before use, put it on an equalizing tray, fully charge the pack, run it in its race, discharge again, put it on the tray again, allow to cool and partial charge for storage..

This was the result..





Sadly, this was not the only NiMh failure at our track when the 4200+ NiMh batteries were being used.. When a Nimh battery such as this fails, it effectively explodes, sending the cell casing and battery bars etc off at quite a velocity in all directions.. It got that bad, that the clubs committee considered making Lipo charging sacks mandatory for all batteries being charged in fear that someone may be hurt..

There has only been one reported case of a LiPo failure at the track, and that was where an "idiot" had decided to open the hard case of his LiPo with a screwdriver, and punctured one of the cells..

Its your call, but I know what batteries I'd rather use...

AYKBOBCAT wrote:OK then what is needed to get into lipos? I know my charger does lipo (it says on it) but what are these balancer things? Do you charge lipos like nicad or nimh? Do they need special care if you don't use them often?

I feel like batteries are getting more and more complicated... I miss the time when you could charge a pack straight from you car battery with "booster" cables.....

Maybe I should just get back to Nicad!

To go to LiPo, you will need 4 things.. (I'll try to keep it simple)

1.. Some LiPo batteries, preferably with a hard case, and if you want to race, ROAR approved packs.. 2S 7.4V packs are the equivalent to the 7.2V 6 cell NiCd/NiMh packs you are using now..
A LiPo cell is 3.7Volts each, so 2S means 2 x 3.7V cells connected in Series = 7.4V.. The Capacity in mAh is the same as for NiCd/NiMh packs, the higher the capacity the longer the runtime.
The only other consideratrion is the "C" rating (eg. 20C, 30C etc), which is the maximum discharge current from the packs.. Say you have a 5000mAh (5Ah) 20C 2S lipo, then the maximum discharge current will be 5A x 20 (C) = 100A.. For most applications 5000mah 20C packs would be fine, but higher mAh and "C" ratings can give more punch if you are racing.. If you are running 4.5T BL motors in on-road, or running 1/8 EP, then you may want to consider 40+C batteries..
A fully charged 2S Lipo will have an output voltage that must not exceed 8.4 Volts (or 4.2V / cell).. A LiPo also MUST NOT be discharged lower than (typically) 6Volts (ideally, no lower that 3v/cell)..

2.. A charger that is designed to balance charge liPo's at 1C.. If you use a regular NiCd/NiMh charge profile (i.e. peak detection charge) with a LiPo you will destroy it (= LiPo Fire)..
1C means one times the capacity, so if you have 6500mAh (6.5Ah) LiPos, then your charger will need to have an output charge of at least 6.5 Amps..
Balance charging is a process whereby the charger monitors each cells voltage in the pack (via the balance lead) to ensure that the cells voltages are kept equal throughout the charge process, otherwise the individual cells in a charged Lipo (8.4V) may not each be 4.2volts as the should, one could be 4.18 and the other 4.22V..
You dont need anything overly expensive, a charger like the IMAX B6 would suffice for most people..

3.. A suitable LiPo charging sack, or other device that will contain any flame in the event of a LiPo failure during charging.. I have heard of people using Ammo boxes, metal cash boxes, even ceramic flower pots, but I prefer a LiPo Sack.. I store my LiPo's in the LiPo sack, inside an ammo box and I store them in a cool place..

4.. Some type of Low Voltage (LV) cutoff or alarm for your car... As mentioned above, liPo's dont like to be discharged below 3V/cell (6V for a 2S pack) so you need a cutoff.. some modern ESC's will have them built in, so they only need to be activated.. For older ESC's, you can fit a LiPo LV cutoff, such as the Novak Smartstop.. OR if you are bashing (i.e. not racing), you can get inexpensive alarms that connect to the balance lead of the LiPo whilst running, and will sound when the LiPo is flat.. (search LiPo Alarm on ebay)

IMO, LiPo's have been one of the greatest steps foward in RC racing.. You do not need to discharge them before recharge like you do with NiCd or NiMh.. They dont get as hot during a run, so they need very little cooling before being recharged.. They have a "flatter" discharge curve, so give the appearance of having a longer runtime that NiCd/NiMh.. They are Lighter, and generally more powerful that NiCd/NiMh..

Look, I'm not saying that they dont need to ne handled with some care and respect, but if you can overcome all of the negativity surrounding them that the are really dangerous, IMO, they are the best battery type on the market today..

AYKBOBCAT wrote:OK then what is needed to get into lipos? I know my charger does lipo (it says on it) but what are these balancer things? Do you charge lipos like nicad or nimh? Do they need special care if you don't use them often?

I feel like batteries are getting more and more complicated... I miss the time when you could charge a pack straight from you car battery with "booster" cables.....

Maybe I should just get back to Nicad!

Maybe we should all just get back to Nicad! if they still made a good 2400 nicad thats all i would buy..

I was considering buying a single 3.7v lipo pack, the shape and wiehgt fit better into a custom build i am finishing
how much run would i get out of that?

longboardnj wrote:

Maybe we should all just get back to Nicad! if they still made a good 2400 nicad thats all i would buy..

I agree... I'm not a racer... I spend most of my time in this hobby building cars... not driving them...

86NESKid wrote:I was considering buying a single 3.7v lipo pack, the shape and wiehgt fit better into a custom build i am finishing
how much run would i get out of that?

run time will vary. What you are running(motor/ESC) and how you run it will be the determining factors on how much runtime you get out of a battery...
Todd

Do u think a 3.7 v is even worth buying
Gonna run it with an older esc with lipo shutoff and 12t brushed motor
Thanks
J

If it fits and its affordable its definitely worth buying. You won't be getting 30 minute run times but it'll turn the wheels long enuf for you to do what you aimed to do

Todd

Stumpy wrote:For those of you that are naive enough to think that NiMh cells are safer than LiPo, have a look at these pics..

Here's one from my E-Savage a couple of years ago. Not sure if it was a short or damage from the 8 foot wall I was jumping it from all day.

86NESKid wrote:Do u think a 3.7 v is even worth buying
Gonna run it with an older esc with lipo shutoff and 12t brushed motor
Thanks
J

No, a single cell 3.7 is for very light cars such as pan cars ( unless that is what you are running) you want a 2s 7.4

yeah...what Reggie said. I misread what you had written there. I was thinkin 3700 mah lipo so my mistake. Sorry for the confusion

Todd

awesome
thx for the info guys