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Lipo Batteries?

fatboyslim

By fatboyslim
in All things electric...

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fatboyslim Newbie Copy

fatboyslim

Posted
Posted

Any idea if there's such a thing as dummies guide to LiPo's

I'm looking at getting a couple for my Slash but haven't got a clue what to get

I understand that the S number is cell count but whats this 20c, 30c,40c

Also whats the deal with charging someone told me that LiPo's should only be charged at 1c??

94eg! Newbie Copy

94eg!

Posted
Posted

Yes only charge at 1C on an actual lipo specific charger. That means 1 x "capacity". So a 5000mah lipo should be charged at a max current of 5000mah (or 5amps). This is a great rule to follow for safety as well as longevity.

When it comes to "C" ratting on a lipo, that refers the packs maximum discharge rating. That means a 5000mah lipo with a 20C "continuous" rating can be safely discharged at a maximum rate of 100,000mah (or 100amps). There is also typically a "burst" rating accompanying that tells you the max ratting for short bursts.

When dealing with low milliamp batteries, the C rating becomes very important because a lot of brushless and brushed systems can easily overpower a small lipo. A 2400mah 20C battery can only supply 48amps before it will melt down. A lot of motor systems can pull that much which really strains the battery and shortens it's lifespan. A 5000mah battery of low C rating can easily handle almost any motor system. Nothing will draw anywhere near 100amps continuously...

Another very important part of lipo is discharge voltage. A lipo's must never be allowed to drop below 3v per cell (or 6v for a 7.4v pack). That means you can no longer run your cars till the stop. Most suggest running a low-voltage cutoff in your car to protect the lipo from over discharge. Personally I just run the for short stints or 5 minute races, and recharge them long before they get low.

If I lipo pack ever looks swollen, DON"T USE IT!!! Both charging and discharging can easily result in a nasty chemical fire. Neutralize the pack by soaking it a bucket of salt water for a few days (in a safe area), and then put it in a dumpster away from any buildings.

Lastly, don't store them in hot places (over 140f). I had a buddy that left all his lipos in the trunk of his car just over an hour during a hot day. Every pack had swelled up, and they all became landfill...

PS: Once you go lipo, you will never go back...

94eg! Newbie Copy

94eg!

Posted
Posted

Yes that would be fine. There is no chance you could pull anywere near 100amps in 1/10th scale cars.

FYI: 100amp draw means you would depelete an entire 5000mah pack in just under 5 minutes... :D

igbandy Proficient

igbandy

Posted
Posted

The new generation of lipo`s are now at least a 2c charge rating, I have some overlander packs that can be charged at upto 6c under supervision. But there is no need, I tend to stick at 1.5c or 2c.

If you can afford a higher c rated pack ie 30, 35 or even 40, then I would get them. You will notice a difference in the delivery of power.

SteelRat Veteran

SteelRat

Posted
Posted

There's only one real problem with LiPo batteries, once you use them, you'll want to convert your entire collection of cars to use them as well.

Couple of other things to bare in mind.

1 - Don't use Tamiya connectors for LiPo batteries. The current that comes from a LiPo is much larger than the connector can handle. At best you just wont get the maximum power from the battery. At worst you'll melt the connectors together. Use the hi-power Traxxas connectors, Corallys or Power Poles (you can get these rated up to well past 100 amps, so they're more than capable to handle the juice, and a favourite of TCers because you can join them to the ESC and battery leads without soldering)

2 - Make sure your ESC has a low voltage cut off if you're going to use it with LiPo. The Traxxas ESC used in the Slash has one built in. If you have a look at the manual there should be steps for putting it in LiPo "Mode", which enables the cut off protection. Most ESC's that support brushless motors will have one of these as well. However if you have a standard ESC, you can buy what's called a "BEC" which sits between the battery and ESC which will cut the power to it if the voltage falls below 3.2V, or at least slow it down and sound a warning beeper. Also the way in which the power curve for LiPos work means that when the voltage starts to fall, it falls very sharply. Some people just dont use a BEC at all, and just stop the car when it starts to slow down. It's not something I'd ever want to do though.

3 - Don't be put off by LiPo scare stories. Some of the youtube video footage I've seen of LiPo fires scared the bejesus out of me and really did make me hesitate in moving to LiPo, but it's like everything else. Make sure you take a little bit of care with them, make sure you always use the right charge profile when charging (And it's worth while investing in a decent balance charger as well) , and always make sure the old brain is engaged when you're using them, and you'll be absolutely fine.

mike_o Proficient

mike_o

Posted
Posted
There's only one real problem with LiPo batteries, once you use them, you'll want to convert your entire collection of cars to use them as well.

I have to agree! I don't own a single NiMh pack anymore.

And the power to energy ration benefit translates either into more speed, longer run time, or into substantially lower weight (which again leads to more speed and longer run time ;) )

94eg! Newbie Copy

94eg!

Posted
Posted

You can run them in any old car, you just have to be mindful of the charge status. If you normally run your car for 10 minutes on Nimh, make it 8 with lipo. Of course you also need to take the milliamp rating into account. I don't have cuttoff on any of my cars, but I do keep a multimeter handy to check pack voltage every once in a while. As long as your packs stay above 7v, your good.

PS: Don't charge packs at more than 1C. Even though they are rated at higher values, it will reduce their life expectancy...

  • 2 weeks later...
Walsall-Basher Enthusiast

Walsall-Basher

Posted
Posted

hi a lipo newbie here, i recently bought a proper charger (core uac-40) and i saw a cheap lipo pack for sale, its an overlander 3200 25C/35C burst at around £22. my main use will be some not very serious silvercan racing with a tamiya ESC, im guessing that'll all be fine. it hasnt got a low voltage cut off but i think for a 5 minute run with the 540 motor it wont get even half discharged? standard or am i being reckless? will obviously be very careful about recharging after each and every run and will build up to the 5 minutes incrementally to make sure everything is working out.

im also wondering if i can pop it into my df03 as well tho, its fitted with an EZrun 5.5t brushless motor with the Ezrun-60A-SL speedo, as i understand it the battery can deliver 3.2 * 25 = 80 amps but i noticed the esc needs 60A continuous and 380A burst. is this set-up cutting things a bit fine for the lipo?

Walsall-Basher Enthusiast

Walsall-Basher

Posted
Posted
You should be fine, it is cutting it close though...

for the ezrun set-up you mean? im thinking that too, its has got lipo protection built in but im wondering if the discharge needs might put a little bit too much strain on the battery. think i need to spend a bit more on a 5000 pack with a 40 or 50C rating. my poor old debit card!

ive been looking into the tt01 set-up and ive decided to replace the esc with an mtronics viper that ive got sat here, the tamiya TEU-101BK in there now hasnt got a BEC i've read so there might be some issues with the Rx current, have also ordered a cheapish hobbywing low voltage cut-off for the same car. i might have even wasted the money on this battery as its not a hard case and the club rules state those only. ill slap it in something i guess.

DCLXVI Experienced

DCLXVI

Posted
Posted

No, a 5000 with 20C should be enough....

hobbyking.com has lipos for as low as 25 usd, mind the size of them though, some of their hard cases are to big...

Backlash Veteran

Backlash

Posted
Posted
Couple of other things to bare in mind.

1 - Don't use Tamiya connectors for LiPo batteries. The current that comes from a LiPo is much larger than the connector can handle. At best you just wont get the maximum power from the battery. At worst you'll melt the connectors together. Use the hi-power Traxxas connectors, Corallys or Power Poles (you can get these rated up to well past 100 amps, so they're more than capable to handle the juice, and a favourite of TCers because you can join them to the ESC and battery leads without soldering)

2 - Make sure your ESC has a low voltage cut off if you're going to use it with LiPo. The Traxxas ESC used in the Slash has one built in. If you have a look at the manual there should be steps for putting it in LiPo "Mode", which enables the cut off protection. Most ESC's that support brushless motors will have one of these as well. However if you have a standard ESC, you can buy what's called a "BEC" which sits between the battery and ESC which will cut the power to it if the voltage falls below 3.2V, or at least slow it down and sound a warning beeper. Also the way in which the power curve for LiPos work means that when the voltage starts to fall, it falls very sharply. Some people just dont use a BEC at all, and just stop the car when it starts to slow down. It's not something I'd ever want to do though.

SteelRat..

Great post, but I must correct you on a few things..

1. The best possible joint, or way of connecting two wires together is by soldering.. To get the lowest possible resistance when using the "PowerPole" style connectors, I would recommend soldering the wires to the connector in lieu of just crimping them..

2. A BEC, or Battery Eliminator Circuit, is the hobby term for a voltage regulator, a device designed to reduce or regulate voltage to a certain level, and in our hobby this is typically the voltage from our 7.2V NiCd/NiMh or 7.4V LiPo to 5 or 6 Volts for the receiver and servos..

The device that you are speaking of in your point #2 is a "LiPo Cutout".. Its principal function is to stop the car from running in the event that the voltage from the LiPo gets to a certain level (often around 3V-3.2V per cell).. More info on the SmartStop can be found here.. http://www.teamnovak.com/products/lipo_cut...dule/index.html .... These devices are often mandatory when racing..

An alternative is the Low Voltage LiPo alarm that beeps whan the voltage gets too low, but these will not stop the car from running, and you could still damage the LiPo from over discharge..

Cheers

smegs Collaborator

smegs

Posted
Posted

Im finally going lipo. Got some batteries from hobbyking. So far awesome service cant wait to get them.

Also ordered a charger from hobbyproz. (Thunder A6)

smegs Collaborator

smegs

Posted
Posted
Im finally going lipo. Got some batteries from hobbyking. So far awesome service cant wait to get them.

Also ordered a charger from hobbyproz. (Thunder A6)

Here's a photo of the charger ordered.

94eg! Newbie Copy

94eg!

Posted
Posted

I've had a Thunder AC6 for some time now. It's been absolutely great. I've charged everything from AA nimh, up to 1:1 scale 12v car batteries, and it just keeps on going. Not bad for $50. Plus all the different style plugs and clamps it includes are really nice. I even decorated mine with some carbon fiber look vinyl and a large Tamiya decal... ;)

AC6package.JPG

smegs Collaborator

smegs

Posted
Posted
I've had a Thunder AC6 for some time now. It's been absolutely great. I've charged everything from AA nimh, up to 1:1 scale 12v car batteries, and it just keeps on going. Not bad for $50. Plus all the different style plugs and clamps it includes are really nice. I even decorated mine with some carbon fiber look vinyl and a large Tamiya decal... :lol:

AC6package.JPG

Can you post some pic of your charger I wanna see what it looks like.

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