Using LiPO as motorbike battery

Thread Starter

janz1961

Joined May 31, 2020
4
Hello All,

I want to use a LiPO instead of an ordinary battery. "Ordinary" already is a Li-ion battery, but that is still not capable of turning the starter motor on my high compression engine. To my surprise, a 4S LiPO is easily capable of turning the engine. This cannot be cause by the 1.4V extra, so I assume the LiPO has a much lower internal resistance.

Now I could use a separate battery to run the bike and use the LiPO only for starting (and charge it only when disconnected). But it would be much nicer if I could use it like a normal battery, so charging it while the bike is running. Of course this would require a battery protection board, but ... it has to work even if the battery is used with a running engine.

When searching for LiPO protection board, I have found several, but they often mention Li-ion or LifePO4 and they don't explicitly state that it also works when the battery is part of an active circuit.

So, the million dollar question: is this possible?

If so, can someone point me to a ready board or a a design I can build myself.

Any response is appreciated.
 

Audioguru again

Joined Oct 21, 2019
5,416
You need a charger circuit designed for the spec's of the Li-PO battery.
A Li-PO is a Li-Ion battery in a poly case. A Li-Ion is in a metal case.
Most lithium batteries are 4.2V when fully charged but a LifeP04 charges to a lower voltage.

If charger circuit detects that a battery has a dangerously low voltage then it refuses to charge that might cause an explosion but a protection circuit does not detect. Some protection circuits correctly disconnect the load from the battery when the discharging voltage becomes too low.
A charger circuit detects a full charge then disconnects charging when the battery is fully charged to prevent over-charging or trickle charging that kills a Lithium battery but a protection circuit does not detect.
 

Audioguru again

Joined Oct 21, 2019
5,416
You need a charger circuit designed for the spec's of the Li-PO battery.
A Li-PO is a Li-Ion battery in a poly case. A Li-Ion is in a metal case.
Most lithium batteries are 4.2V when fully charged but a LifeP04 charges to a lower voltage.

If charger circuit detects that a battery has a dangerously low voltage then it refuses to charge that might cause an explosion but a protection circuit does not detect. Some protection circuits correctly disconnect the load from the battery when the discharging voltage becomes too low.
A charger circuit detects a full charge then disconnects charging when the battery is fully charged to prevent over-charging or trickle charging that kills a Lithium battery but a protection circuit does not detect.

Most charger circuits do not work properly when the battery has a load.
 

Thread Starter

janz1961

Joined May 31, 2020
4
Thanks for the responses. They were partly helpful too if only because I decided to read up on the differences between LiPo en Li-ion. And there are more differences than just the casing. ANd also more variants than just the two :)

But Li-ion en LiPo use a different separator and therefore a different chemistry. LiPo are Li-ion batteries using a polymer electrolyte instead of a liquid electrolyte (source: BatteryPower Tips, thanks)

As I said in my original post, I already employ a Li-ion battery in my bike. At 13.4 volts (without any load) it is 1.4V less than a 4S LiPO. But this alone cannot explain the performance difference when cranking the engine, I dare say the internal resistance of a LiPO is much lower. The Li-ion battery doesn't even manage to turn the engine, with the LiPo it is as if I removed the sparkplugs. This is why I want to try and use LiPo's.

So I return to my original question: does anyone know of balancing electronics (that may include a processor such as an Arduino) that will properly keet the LiPo balanced and protected against over and undercharging even when under load.

If not, I'll just fit two separate batteries and charge the starter LiPo when the bike is not running. The main battery can be much smaller then so in the end I won't add much weight.
 

BobTPH

Joined Jun 5, 2013
6,078
What are the rated capacities and discharge rates if the two batteries? This will tell you how much current they can supply.
 

Thread Starter

janz1961

Joined May 31, 2020
4
What are the rated capacities and discharge rates if the two batteries? This will tell you how much current they can supply.
Good questions. For de LiFePo4 I have found a value named "starting current" of 190A (Reference). The LiPo is a 6000mAh 120C. So, theoretically, could give 720A continuously and has 1.4V extra. Maybe that explains it?
 

Audioguru again

Joined Oct 21, 2019
5,416
A Li-Ion cell is fully charged at 4.2V per cell same as a Li-Po.
You are talking about a LifeP04 battery for motorcycles that charges to a lower voltage and produces less power than a Li-Ion or a Li-Po. Therefore they do not catch on fire as easily.

Your voltages are not for a fully charged battery. Your voltages are for a "storage and selling" half charged battery.
You said a LifeP04 is 13.4V (each of its 4 cells is only 3.35V) but your link to the Shido motorcycle battery says 12.8V and 3.2V per cell.
You said a 4s Li-PO is 1.4V more at 14.8V. Then each of its 4 cells is only 3.7V which is its storage and selling half-charged voltage. Each Li-PO cell should be 4.2V when fully charged and be about 3.0V to 3.2V when the load should be disconnected to avoid battery damage.

The maximum output amperes depends on the size and amount of chemical dilution of the battery. One country makes cheap batteries because they dilute the chemicals with rice flour.
 
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Thread Starter

janz1961

Joined May 31, 2020
4
For some reason, my last response was not submitted, so here it is again.

Although I'm happy with the responses because they have given me more insight in LiPO's and similar batteries, my question remains unanswered: where can I buy or how can I create a BMS for Li-PO's that works even if the battery is part of system that is being used at the same time so I can use is as a replacement motorcycle battery.

I know this is possible, at least for LiFEPO4 batteries because you can buy them (I have them) and they can be used safely in a motorbike (I use them).

I have seen carious BMS boards, but none of them explicitly state the can or cannot be used when the battery is under load at the same time. So, anyone?
 
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