Using a LiFePO4 battery pack as a starter battery?

[Yuri]

I'm planning on switching the regular lead acid battery in my motorcycle to a LiFePO4 pack to save weight and have a longer lifespan. I would be using 12 A123 cells, 3 packs connected in parallel with 4 batteries in series each, to give me a 13.2v voltage with a capacity of 6.9Ah
My main concerns are:

1)With a little search, it seems that the voltage used to charge a 12v lead-acid battery would be very similar to the one used to charge a 4x3.3v LiFePO4 battery pack, since the charging voltage is 3.6v per cell on the LiFePO4, which would be about 14.4v , and the charging voltage used for a 12v lead-acid battery ranges from 14.2 to 14.5v. I assume that charging wouldn't be an issue, am I wrong?

2)The full charge voltage for the LiFePO4 would be significantly higher compared to the lead-acid battery, 14.4v vs. 12.8v for the lead-acid battery pack. Would the starter motor be ok with this increase in voltage without compromising its lifespan?

 

[Grizzlybear]

I'm planning on switching the regular lead acid battery in my motorcycle to a LiFePO4 pack to save weight and have a longer lifespan. I would be using 12 A123 cells, 3 packs connected in parallel with 4 batteries in series each, to give me a 13.2v voltage with a capacity of 6.9Ah
My main concerns are:

1)With a little search, it seems that the voltage used to charge a 12v lead-acid battery would be very similar to the one used to charge a 4x3.3v LiFePO4 battery pack, since the charging voltage is 3.6v per cell on the LiFePO4, which would be about 14.4v , and the charging voltage used for a 12v lead-acid battery ranges from 14.2 to 14.5v. I assume that charging wouldn't be an issue, am I wrong?

2)The full charge voltage for the LiFePO4 would be significantly higher compared to the lead-acid battery, 14.4v vs. 12.8v for the lead-acid battery pack. Would the starter motor be ok with this increase in voltage without compromising its lifespan?

Hi Yuri
A123 cells for starting motorcycles are becoming popular now, you will however need a BMS otherwise the battery will become unbalanced. 12 volt (4s) BMS boards are available from PIng, I think you may have to wire the starter motor crcuit direct to the battery though due to the amount of amps it will draw. However Ping sells a red BMS witch doesn't limit amps, I don't know if he does a 12 volt (4s) one though.
I cannot see any problem with the slightly increased voltage.

I advise you contact him and tell him what you plan to do.

Griz

 

[mwkeefer]

Okay - now the million dollar question. How can I create a useable pack for my motorcycle of LiPo batteries?

Lipo has the needed CCA delivery ability but 3S is max of 12.45v and say LVC is 10.2 (3.3v per cell) or absolute 9v?

I suppose in theory it could work - it would turn the starter (plenty of current) but may not turn it fast enough (never saw my voltage drop when starting) then once then generator kicks in - its running what voltage to charge up the battery 14.4v or 12.8v?

I suppose if it's 12.8v (though I would need to add some real form of voltage control circuit (DC->DC inverter / regulator to ensure voltage doesn't exceed 4.2v per cell) and the maximum for LiPo perfectly balanced 3S is really 12.6 at 4.2v per cell.

12.8 would put us at 4.266666667v per cell which is surely not safe for LiPo

Next up would be the 4S pack:

Lowest voltage: 12v (ok, that's fine)
Nominal Voltage: 14.8 - above the car's charging circuit... but the car is able to run off this, I swear regulators output 13.8-14.8v to account for drop.

At best case we can only use 50% of a 4S pack and must keep it above 12v at all times!

I'm hoping to replace the SLA battery I replace each year with a LiPo pack of 10-20AH capacity (200/400 continuous and 300/600A burst for 60 seconds!).

Anyone see a method of doing this safely?

Thanks in advance and sorry to go off topic but 10AH 2.5C LiFePo4 cells I have wouldn't start a push mower

-Mike

 

[John in CR]

Lipo batts inside a hot engine compartment, no thanks.

Regarding the voltage, how much do you think lead batteries sag when cranking all those amps for starting?...Quite a lot I think, especially since you can see lights dim significantly. Voltage isn't the issue, but low voltage, high charging voltage, and temperatures probably are.

 

[Yuri]

I'm planning on switching the regular lead acid battery in my motorcycle to a LiFePO4 pack to save weight and have a longer lifespan. I would be using 12 A123 cells, 3 packs connected in parallel with 4 batteries in series each, to give me a 13.2v voltage with a capacity of 6.9Ah
My main concerns are:

1)With a little search, it seems that the voltage used to charge a 12v lead-acid battery would be very similar to the one used to charge a 4x3.3v LiFePO4 battery pack, since the charging voltage is 3.6v per cell on the LiFePO4, which would be about 14.4v , and the charging voltage used for a 12v lead-acid battery ranges from 14.2 to 14.5v. I assume that charging wouldn't be an issue, am I wrong?

2)The full charge voltage for the LiFePO4 would be significantly higher compared to the lead-acid battery, 14.4v vs. 12.8v for the lead-acid battery pack. Would the starter motor be ok with this increase in voltage without compromising its lifespan?

Hi Yuri
A123 cells for starting motorcycles are becoming popular now, you will however need a BMS otherwise the battery will become unbalanced. 12 volt (4s) BMS boards are available from PIng, I think you may have to wire the starter motor crcuit direct to the battery though due to the amount of amps it will draw. However Ping sells a red BMS witch doesn't limit amps, I don't know if he does a 12 volt (4s) one though.
I cannot see any problem with the slightly increased voltage.

I advise you contact him and tell him what you plan to do.

Griz

I'm new to this forum, is Ping an user? Does he have an website? The idea of wiring the starter motor directly to the battery should be easy, as there is already two positive wires, one for the starter motor and one for the rest of the systems, the only wire shared is the negative one.

Okay - now the million dollar question. How can I create a useable pack for my motorcycle of LiPo batteries?

Lipo has the needed CCA delivery ability but 3S is max of 12.45v and say LVC is 10.2 (3.3v per cell) or absolute 9v?

I suppose in theory it could work - it would turn the starter (plenty of current) but may not turn it fast enough (never saw my voltage drop when starting) then once then generator kicks in - its running what voltage to charge up the battery 14.4v or 12.8v?

I suppose if it's 12.8v (though I would need to add some real form of voltage control circuit (DC->DC inverter / regulator to ensure voltage doesn't exceed 4.2v per cell) and the maximum for LiPo perfectly balanced 3S is really 12.6 at 4.2v per cell.

12.8 would put us at 4.266666667v per cell which is surely not safe for LiPo

Next up would be the 4S pack:

Lowest voltage: 12v (ok, that's fine)
Nominal Voltage: 14.8 - above the car's charging circuit... but the car is able to run off this, I swear regulators output 13.8-14.8v to account for drop.

At best case we can only use 50% of a 4S pack and must keep it above 12v at all times!

I'm hoping to replace the SLA battery I replace each year with a LiPo pack of 10-20AH capacity (200/400 continuous and 300/600A burst for 60 seconds!).

Anyone see a method of doing this safely?

Thanks in advance and sorry to go off topic but 10AH 2.5C LiFePo4 cells I have wouldn't start a push mower

-Mike

Actually the charging voltage of the Lead acid battery is 14.2v to 14.5v, so a 4S pack would be just perfect. The 12.8v is the voltage that the lead-acid battery is when it's full.
About the options, with a 3S pack the voltage would just be too low(only 10.8V at top, and on average 9.9v), also the charging voltage would be WAY higher than it should(about 4.8v). Definitely the only option would be a 4S pack.
Edit: Ops, only now I saw you were talking about a Lipo pack, not a LiFePO4. I don't think Li-po would be really safe to use in a motorcycle... It should also need some kind of modification to the motorcycle charger system, since for 3S the charge would be to high(4.8v per cell) and for 4s the voltage would be too low(3.6v)...

Lipo batts inside a hot engine compartment, no thanks.

Regarding the voltage, how much do you think lead batteries sag when cranking all those amps for starting?...Quite a lot I think, especially since you can see lights dim significantly. Voltage isn't the issue, but low voltage, high charging voltage, and temperatures probably are.

My battery doesn't become at all hot, even when riding for a very long amount of time. Although the compartment looks closed, when the bike is moving there are some airflow inside the area, and it's also not that close from the engine.
The crank amperage, for at least my bike, when I measure it using an clamp meter, is about 40A. Pretty safe for a 12 battery pack.

 

[Grizzlybear]

"I'm new to this forum, is Ping an user? Does he have an website? The idea of wiring the starter motor directly to the battery should be easy, as there is already two positive wires, one for the starter motor and one for the rest of the systems, the only wire shared is the negative one."

Ping is known for his LIFEPO4 batteries for ebikes, but he does stuff he doesn't advertise as well, this is not widely known, email pingping227@hotmail.com for info.

Using A123 batteries is not a straightforward thing to do, if you flatten them just once(below 2.5 volts per cell) then you've ruined them, this is why you need a BMS(battery management system). The red BMS he sells may sort this out, but they can only work with a charging current of 5 amps, but if the charging mosfet is fixed to a heatsink 10 amps. I'm sure this sounds a bit confusing, but you need to know what you're getting into, otherwise your A123 batteries may not last very long.

Griz

 

[Yuri]

"I'm new to this forum, is Ping an user? Does he have an website? The idea of wiring the starter motor directly to the battery should be easy, as there is already two positive wires, one for the starter motor and one for the rest of the systems, the only wire shared is the negative one."

Ping is known for his LIFEPO4 batteries for ebikes, but he does stuff he doesn't advertise as well, this is not widely known, email pingping227@hotmail.com for info.

Using A123 batteries is not a straightforward thing to do, if you flatten them just once(below 2.5 volts per cell) then you've ruined them, this is why you need a BMS(battery management system). The red BMS he sells may sort this out, but they can only work with a charging current of 5 amps, but if the charging mosfet is fixed to a heatsink 10 amps. I'm sure this sounds a bit confusing, but you need to know what you're getting into, otherwise your A123 batteries may not last very long.

Griz

I'm going to e-mail him, thanks.
Although not an expert on batteries systems I'm not newbie to it, about the need to add a heatsink that makes perfect sense, I'm really used to cooling mods on PCs and Laptops, so this shouldn't be any problem. The maximum charging amperage when the engine is at a higher RPM is about 6.5A, so a heatsink will be needed.

 

[Grizzlybear]

"I'm new to this forum, is Ping an user? Does he have an website? The idea of wiring the starter motor directly to the battery should be easy, as there is already two positive wires, one for the starter motor and one for the rest of the systems, the only wire shared is the negative one."

Ping is known for his LIFEPO4 batteries for ebikes, but he does stuff he doesn't advertise as well, this is not widely known, email pingping227@hotmail.com for info.

Using A123 batteries is not a straightforward thing to do, if you flatten them just once(below 2.5 volts per cell) then you've ruined them, this is why you need a BMS(battery management system). The red BMS he sells may sort this out, but they can only work with a charging current of 5 amps, but if the charging mosfet is fixed to a heatsink 10 amps. I'm sure this sounds a bit confusing, but you need to know what you're getting into, otherwise your A123 batteries may not last very long.

Griz

I'm going to e-mail him, thanks.
Although not an expert on batteries systems I'm not newbie to it, about the need to add a heatsink that makes perfect sense, I'm really used to cooling mods on PCs and Laptops, so this shouldn't be any problem. The maximum charging amperage when the engine is at a higher RPM is about 6.5A, so a heatsink will be needed.

Ping is a good bloke(with very good english), If your discharging 40 amps to start, then the standard BMS will do, good luck with your project, PM me if you need any advice.



Griz