Recommended C rating for LiPo Packs?

[geosped]

What's the recommended c or discharge rating that I should consider when buying new LiPo batteries. I'm considering a 20 or 25c rating battery as they seem to be quite a bit cheaper than the higher discharge batteries. I'm just trying to climb a hill not really looking for a land speed record.

 

[dogman dan]

20c is good for commuter type bikes, 20 amps controllers max if you will only carry 5 ah. But if you will carry 10 ah, then 40 amps can run fine. But best results from 15-20 ah size packs when you have a 40 amps controller. Keep discharge rates with the 20c stuff down to no more than 4c or 5c is the idea.

But if you are going to run off road, and want the bike light, get 30-40c stuff. So a 5 ah pack can really punch. with 30c packs, you can get away with 6-7 c discharge rates, and still run a fairly cool pack.

In either case, you are looking for voltage sag under max load that's not much more than 2-3v. If the pack gets too hot each ride, you'll kill em fast.

 

[wesnewell]

What you need depends heavily on the controller you have and how much you weigh when climbing hills. I'm 270lbs and I've got 13K miles and 3+ years on my 10ah 20C lipo pack with a 40A max controller. So that's a 4C max draw from the pack.

 

[neptronix]

I will only give you my special exclusive advice if you stop using that accucel charger and nearly overdischarging your batteries.. :lol:

 

[geosped]

What you need depends heavily on the controller you have and how much you weigh when climbing hills. I'm 270lbs and I've got 13K miles and 3+ years on my 10ah 20C lipo pack with a 40A max controller. So that's a 4C max draw from the pack.

That's great to know. I'm in the same boat I'm about 260. I'm not sure I understand the max draw thing though. If I have a 10ah 25C lipo with a 36A controller then how do I figure out the max draw? What's the math on this?

 

[wesnewell]

Amps divided by AH = C rate, so 36/10=3.6C discharge rate.

 

[geosped]

Ok thanks for that. Now for the next noob question. Now that we know what I shouldn't exceed 3.6c How do I apply that when riding. Does everyone have some sort of battery monitoring or computer mounted apparatus? Can I do this with a Watt meter? Just trying to figure out how to apply this new found knowledge so I don't catch fire riding down the street. On the Watt meter I can monitor volts / Amps and Watts. I also have a cell checker that I carry with me and after 10 minutes of riding I'll check some of the individual cells make sure I'm not below 3.7

 

[wesnewell]

All you really need to monitor while riding is pack voltage. Hook this up on the controller side of the battery connections and use it as a fuel gauge.
http://www.ebay.com/itm/DC-15-to-120V-Waterproof-Red-LED-Panel-Meter-DC-Digital-Voltmeter-Two-wire-NIGH/141365876290
Also, as long as you have lvc correct in the controller, it won't let you over discharge the pack. And with the volt meter you can do that manually by just watching the voltage too. A watt meter will also give you voltage, amps, watts, etc. but for me it was just worthless info and took up more space. I took mine off. Besides, if you know the max amps of your controller, you'll know the max amps and watts you can pull from the battery without any meters. Oh yeah, the only time I check individual cells is when I go to charge the pack.

 

[dogman dan]

I think his charger will work fine with packs that aren't dead.

Lets get back to basic math.

Say you have a 10 ah pack. 10 amps is 1c. 20 amps is 2c. 30 A is 3 c. 40 A is 4c. If you have a 5 ah pack, then 10 amps is 2c, and 20 amps is 4c. So for a 5 ah pack, don't use a controller stronger than 20 amps with the 20c RC packs. (to keep them below 5c which is the real, usable, c rate for those 20c packs) Or get stronger packs, for example, a 40c pack in 5 ah size works fine with a 40 amps controller. It's still 1/4 of what they claim.

Up to a 40 amps controller works fine with 10 amp hours of 20 c packs. But you will have less voltage sag under the heaviest loads with 30c packs. Bear in mind, Wes lives in Texas. He does have some hills, but never climbs a mountain for 10 miles non stop. You'd want 30c for sure, if you climb mountains. Or, a bigger pack than 10 ah. Less sag under load makes knowing when to stop easier, and less stress when you need to run them very low. So the pricy stuff can be nice, but it costs you.

You don't need to monitor your amps as long as know the amps of your controller. If you have a 40 amps controller, it will not run your packs any harder than 40 amps continuous.

A watt meter can show you what is going on as you ride, and let you know approximately when to stop. But the best bet is to just be sure you have enough c rate to handle the amps of your controller. Your controllers amps may be written on a label on it, or not. If not, running with a watt meter will tell you what amps you are pulling. If it's too much, grab less throttle on the starts.

 

[geosped]

Thanks for the math lesson.

 

[ernesttan1976]

All you really need to monitor while riding is pack voltage. Hook this up on the controller side of the battery connections and use it as a fuel gauge.
http://www.ebay.com/itm/DC-15-to-120V-Waterproof-Red-LED-Panel-Meter-DC-Digital-Voltmeter-Two-wire-NIGH/141365876290
Also, as long as you have lvc correct in the controller, it won't let you over discharge the pack. And with the volt meter you can do that manually by just watching the voltage too. A watt meter will also give you voltage, amps, watts, etc. but for me it was just worthless info and took up more space. I took mine off. Besides, if you know the max amps of your controller, you'll know the max amps and watts you can pull from the battery without any meters. Oh yeah, the only time I check individual cells is when I go to charge the pack.

Hi Wesnewell,

I think my Bafang battery has failed and I am seriously looking into a replacement using RC lipos.
I was into RC hobby in the last 5 years so I know about RC lipos.

My motor is a Bafang 500 W mid drive with 48V lion 10Ah.

I'm thinking of buying 4 pcs of 6s 4900mah 20C lipos to give me 12s2p 10 Ah.
http://www.hobbyking.com/hobbyking/store/__7300__Rhino_4900mAh_6S1P_22_2v_20C_Lipoly_Pack.html

I will get a battery monitor or a led voltmeter.
http://www.hobbyking.com/hobbyking/store/__17864__In_Line_Voltage_and_Amperage_Meter.html
Lipo 6s Balance Charger
http://www.hobbyking.com/hobbyking/store/__58187__X120_120W_Touch_Screen_Smart_6S_Balance_Charger.html

Let me know what you think ok? Thanks.

Ernest

 

[geosped]

Id be curious to hear what others say about the voltmeter you chose. It's only rated for 30a.

 

[wesnewell]

It's also limited to 30V which makes it not usable on 12s lipo which is over 50V charged. You can get by with a 6s charger if you don't mind splitting the pack to charge. But you can buy 12s chargers now, and even a bms is an option you might consider.

 

[ernesttan1976]

Hi wesnewell and geosped, thanks for replying.
I could not find a 12s charger or BMS on the hobbyking website. Can you tell me where to find those?
Thanks again guys.

 

[wesnewell]

http://www.hobbypartz.com/75p-1220-charger.html?gclid=CNa3z9_N57ICFayPPAod10MAPw
https://bmsbattery.com/bmspcm/330-smart-bms-513-cells-in-series-bms-pcm.html
There's lots of different bms's for 12s lipo. I just happen to have these links.

 

[ernesttan1976]

Thanks man