BMS for DIY motorcycle starter battery.

[Istria]

Hello,

As my first lithium battery project, I'm going to build a LiFePO4 1P4S battery to replace the original 12V14Ah 260A CCA lead-acid motorcycle battery.

Basically, I only need to battery for starting the engine. After that, the alternator will keep it topped up and provide the power for the auxiliaries.

Since the starter motor power draw behaviour is a bit different than for solar banks, I'm not quite sure which BMS would be suitable.
The old battery had a CCA rating of 260A. If I would take that value, I would need a big beefy Daly 250A BMS for my tiny 7Ah cells, which does not make sense. But if I assume that the starter motor draws 200A for a split second on startup, will a 40A (constant current) BMS blow up? Will a 20A blow up?



Thanks in advance!

 

[snoobler]

7Ah. 1C = 7A

Assuming you actually need 260CCA, 260/7 = 37C - absurdly high for LFP and most Lithium chemistries.

IMHO, that kind of draw will cause any BMS to trip out due to voltage drop. You're pulling so hard on the cells, the voltage is likely to drop to the protection level.

BMS have an over-current tolerance that may be several times rated, BUT it can only sustain this for a very short period of time - less than starting a motorcycle. Any lower rated BMS would likely trip due to over-current.

I recommend you get a clamp DC ammeter and measure the actual starter draw from the battery.

 

[Istria]

I am indeed also a little worried about weather 1P will be enough CCA.
The annoying thing is I can almost never find ratings for CCA, like you always see in lead-acid specs.

About lithium not being capable, I have a LiPo (not LiFePO4) RC battery capable of 65C continuous discharge.
Also, I understood lithium should be superior to lead-acid in terms of almost everything. Including current capability.
If my 14Ah lead-acid can deliver 260A of CCA, why would my 32700 6,5Ah cell not be able to deliver at least +-130A?

If the power is not enough, I will order another 4 cells to make a 2P4S configuration. But that would make it a 13Ah pack. Almost the same as the old lead-acid one. And part of my goal is to make the battery more compact. And I don't need the capacity. Only the starting current.

I short. I can order an 3S 2Ah 65C LiPo from hobbyking for 30EUR that will start the bike without a sweat. But I'd prefer to have a LiFePO4 pack in between my legs while connected to the alternator for obvious reasons.

 

[snoobler]

I am indeed also a little worried about weather 1P will be enough CCA.
The annoying thing is I can almost never find ratings for CCA, like you always see in lead-acid specs.

There's a reason why. CCA is specifically for starting cars in cold weather. When you can't find that rating, that tells you something.

CCA = the number of amps it can maintain for 30 seconds at 0°F and stay above 7.2V.

Does that sound like something a 12V LFP can do? 7.2V/4 = 1.8V - well below the "don't you dare do this" threshold.

About lithium not being capable, I have a LiPo (not LiFePO4) RC battery capable of 65C continuous discharge.

Right, but your experience in this area in no way has relevance to this exercise.

Also, I understood lithium should be superior to lead-acid in terms of almost everything. Including current capability.
If my 14Ah lead-acid can deliver 260A of CCA, why would my 32700 6,5Ah cell not be able to deliver at least +-130A?

Because you're operating from incorrect assumptions. Lead-acid is extremely tolerant of high current. LFP is not. Check any cell datasheet, and you'll see what I'm talking about.

If the power is not enough, I will order another 4 cells to make a 2P4S configuration. But that would make it a 13Ah pack. Almost the same as the old lead-acid one. And part of my goal is to make the battery more compact. And I don't need the capacity. Only the starting current.

Again, flawed perspective. You're operating on "should be" based on unrelated information instead if what "is".

I short. I can order an 3S 2Ah 65C LiPo from hobbyking for 30EUR that will start the bike without a sweat. But I'd prefer to have a LiFePO4 pack in between my legs while connected to the alternator for obvious reasons.

Right. No BMS. Charged with balance chargers. Run them too low, and they puff right up on you. Designed for high current. Lightweight. Flammable, potentially explosive. Very high currents are possible. It's also economical because there's another market for it.

Most LFP current capability is dramatically lower than high discharge LiPo. There are some high drain cells, and that's where you should start.

 

[JeepDaddy]

But I'd prefer to have a LiFePO4 pack in between my legs while connected to the alternator for obvious reasons.

LiFePo4 chemistry is not well suited for engine starting applications. Please elaborate on the obvious reasons you state. I would suggest staying with an AGM battery for a motorcycle application and choose another project for your first lithium project.

 

[reg]

You might find it interesting to read about RELiON's High Performance LiFePO4 batteries. RELiON's batteries aren't cheap, but they are well-regarded.

From RELiON's website:

 

[Tiktaalik]

For all those who claim that it is impossible to make LiFePO4 starter battery, DCS makes one:

12V 80Ah Extreme battery (LITHIUM)

www.deepcyclesystems.com.au

Here is a review:

 

[snoobler]

No one is saying it's impossible. It's just challenging. Typical cells are not rated for the currents needed, and finding a BMS capable of handling those currents is yet another challenge.

Lithium starter batteries have been on the market for years. They just ain't cheap.

 

[Q-Dog]

I don't have the patience to watch a 25 minute video. I guess no one knows how to write any more?

 

[Tiktaalik]

No one is saying it's impossible. It's just challenging. Typical cells are not rated for the currents needed, and finding a BMS capable of handling those currents is yet another challenge.

Lithium starter batteries have been on the market for years. They just ain't cheap.

So who makes them besides from DCS?

 

[reg]

So who makes them besides from DCS?

Have a look at RELiON's High Performance Series.

 

[Zwy]

Anything can be done with enough money and (what you don't want to hear) space. I'll build you a battery for starting your motorcycle for $7K USD, just deposit the money in my account.

You should start shopping for some bigger saddlebags.........

 

[reg]

I'll build you a battery for starting your motorcycle for $7K USD, just deposit the money in my account.

RELiON, one of the more high-end, expensive makers, sells batteries that will almost certainly start a motorcycle (post #11) for a hell of a lot less than that.

 

[Zwy]

RELiON sells batteries (post #11) that will almost certainly start a motorcycle for a hell of a lot less than that.

My point is at what point is it economically feasible to attempt to use LFP for starting purposes? AGM would probably get him just as far year wise for life expectancy in such a situation. And be able to provide the CCA needed.

 

[reg]

My point is at what point is it economically feasible to attempt to use LFP for starting purposes? AGM would probably get him just as far year wise for life expectancy in such a situation. And be able to provide the CCA needed.

Price may be the only consideration for you, but it isn't for everyone. I'm planning another motorcycle trip in Sicily. I'm investigating RELiON's batteries, and looking into whether there's a European equivalent, for a number of reasons. These batteries are in interesting possible option for someone who's touring by bike.

 

[Tiktaalik]

No one is saying it's impossible. It's just challenging. Typical cells are not rated for the currents needed, and finding a BMS capable of handling those currents is yet another challenge.

Lithium starter batteries have been on the market for years. They just ain't cheap.

So who makes them besides from DCS

Have a look at RELiON's High Performance Series.

View attachment 45093

Interesting. I contacted them in October and they told me that they don’t have any starter batteries and that their batteries are suitable for House applications only.

 

[Zwy]

Price may be the only consideration for you, but it isn't for everyone. I'm planning another motorcycle trip in Sicily. I'm investigating RELiON's batteries, and looking into whether there's a European equivalent, for a number of reasons. These batteries are in interesting possible option for someone who's touring by bike.

I have an AGM here that is about the size of a motorcycle battery. It is at least 12 years old, still works great. I use it daily in the summer, it sits all winter unused.

I know I'd want to go to my bike when it's cold outside with a LFP battery attempting to start it and have the BMS keep tripping when I could have easily started it with an AGM.

 

[Zwy]

From Relion specs: Note 400A for less than 3 seconds.

DISCHARGE SPECIFICATIONS
Maximum Continuous Discharge Current	50 A
Peak Discharge Current	400 A (≤3 s)
BMS Discharge Current Cut-Off	550 A ±60 A (42 ±22 ms)
Recommended Low Voltage Disconnect	11V
BMS Discharge Voltage Cut-Off	8V (2.0 ±0.08 vpc) (100 ±50 ms)
Reconnect Voltage	10V (2.5 ±0.1 vpc)
Short Circuit Protection	200-800 μs

 

[Cal]

There's a reason why. CCA is specifically for starting cars in cold weather. When you can't find that rating, that tells you something.

CCA = the number of amps it can maintain for 30 seconds at 0°F and stay above 7.2V.

Does that sound like something a 12V LFP can do? 7.2V/4 = 1.8V - well below the "don't you dare do this" threshold.

Much of the voltage drop to 7.2V is due to a considerable higher internal battery resistance of a lead acid battery.

When you say "7.2V/4 = 1.8V", the battery potential is not really at 1.8V, but higher by: I * R_cell.

 

[reg]

I have an AGM here that is about the size of a motorcycle battery. It is at least 12 years old, still works great. I use it daily in the summer, it sits all winter unused.

I know I'd want to go to my bike when it's cold outside with a LFP battery attempting to start it and have the BMS keep tripping when I could have easily started it with an AGM.

I ride motorcycles, which means that for me, unlike you, this isn't a theoretical discussion. I guess you won't be buying an electric motorcycle, such as the highly regarded bikes made by Zero, one of which is in my future. Yes, temperature has to be taken into account. So? By the way, how cold do you think it gets in Sicily