Motorbike Lithium Battery - Why is it ok for the bike alternator to charge it?

[GT250]

Hi all,
Having recently purchased a new motorbike, I was thinking of putting in a Lithium battery. I made a post about this on the FJR forum and was told - in no uncertain terms - I had to have a dedicated Lithium charger if I ever needed to charge it.

I have two of these battery's installed on motorbikes of which I have owned for maybe 5yrs and they still work great. One of them starting a 1100cc Yamaha Virago.


Look at the weight 1KG!!!!

Never had an issue with either one after 4 years. Both have had to be charged now and again, both with the below chargers.

I have charged these by a Jaycar 4step wizzbang charger and also a good old 4amp charger. Never had an issue. The 1100cc Virago has always been on a 'tender' charge from some solar panels/10amp inverter for about 4 years, as sometimes I won't use the bike for a month or so.

NB: The battery's I have are Lith PO - I think this is Phosphate based. Which does not (AFAIK), blow up!

So the question is; what is the difference of a normal motorbike alternator charging a 'commercial' lithium battery (might not be 'PO'), as against a normal battery charger?
I understand that a normal charger might have a 'dirty' DC charge current. But what about a motorbike?

I include a section of the reply from my bike forum: I'm sure it's ok as it's available to the general public. FJR13.org

"No, you can't use a normal charger. It's not the waveform that's the problem. Batteries, lithium included, don't need a pure DC waveform which is why you only have a bridge rectifier on your alternator and no filters or zener diodes. The problem is with the rate of charge and overcharging.
When a battery discharges some material moves from one electrode to the other. When you charge a battery, it moves back again. With lithium batteries if you charge them too quickly, the material doesn't go back and cover the electrode uniformly. It forms dendrites, which are like stalactites, on the electrode. When these dendrites get to a certain size, they short out the two electrodes and an explosion occurs. This might happen after 10 recharges or it could take 100 recharges, there is no way to tell....which is why some people have been using the wrong chargers and then saying "I've never had a problem". They will have one eventually.
The big danger, with lithium, is that it stores a lot of energy. When something goes wrong, it goes VERY wrong.
I have seen a solution for this but it is still in the experimental and testing stage and a few years away from going on the market.
The only other way to be safe is to use a charger designed for lithium batteries".

I never got an answer as to why a generic motorbike alternator is ok to charge Lithium battery's?

Unfortunately, my lithium battery won't fit in the new bike

A YT post shows the battery I have:
Cold Start:


So experts: The question is: Why can a Motorbike alternator charge 'safely' a Lithium battery, but one must use a 'special' lithium charger if one wants to charge it away from the bike?

Just seems bizarre that I, personally have had two lithium battery's (of this Po4 Type), charged them left/right upside down, from flat (no lights, no nothing), to being ok from normal Jaycar and Supercheap Auto specials, to having them installed in two bikes over 4-5 years and never had a problem!

Now when I want to get a Lith for the new bike, I'm up against - "You can never charge it without a special Lithium charger..."

Yet the bikes alternator is ok, bearing in mind that as standard a SLA battery is OEM?


GT250.

[Uncle Fester]

Yes it is a LiFePO4 battery and you can charge it with a normal 12V charger.
They are not critical to over charge but charging at voltages higher than spec will reduce it's cycle life.

Unlike other Li-ion types they have no thermal runaway, they actually perform better at higher temperature even 60˚C where things would get dicey with the Cobalt types.

Dendrites occur when Li-Ion batteries are discharged below critical levels.

The worst thing that happens with a LiFePO4 is that an internal short will puff it up and it releases gas (somewhat toxic).
A fire due to overload on the wiring or terminals is still possible as with any battery including lead acid. It will be the enclosure that will catch fire rather than the components inside the battery, unlike the Lithium-Cobalt types in your phone, laptop, RC models, etc which explode with volatile flames that do not stop until the internal material has burnt out.

The rated voltage is about 3.2V per cell. Unlike other Li-ion it stays constant until it reaches around 80% depth of discharge.
The recommended charge voltage is 3.6V per cell.
You have 4 cells in a 12v LiFePO4 battery.

[ol' boy]

It is ok for a simple reason.

The battery will never be 100% charged nor does it need to be, 80% or 90% is fine.
All it has do to is start the bike, that is it!

It's not a deep cycle where you are counting every single Ah like gold.

It has to crank, start and then quickly recharge to a reasonable charge state (enough to start it again and not be too discharged).

14.4volts will do that...
The Lipo Charge Profile on my Smart Chargers is static at 14.4v

It is a fair question, but for the purposes for starting, i think a normal alt output is fine.

[hinekadon]

no meat is correct ! the section re other forum is almost a direct copy of nicad instructions re dentrites answer they have it stuffed up as they short out the battery not allowing you to charge it . lithium doesnt have this type of chemical composition lithium requires constant voltage charge so your lead acid charger will do it at the right voltage cheers

[GT250]

Many thanks for the replies people.

As I can't physically fit one of these Lipo's I have into the new bike and so if I buy a 'normal' Lithium motorbike battery like;



Then as it says in the description it's a Lithium Ion Polymer, then I will need a special charger for it? Doh! Answer below I guess...

NB: Quote from another site same battery: "This battery is not suitable for deep cycle applications and car starting – use for motorcycle starting only.
Do not use a “smart charger” or any charger with pulse charging with this battery."


But I still don't know why the motorbike alternator/charging system is ok for these types of batteries!!! Or as Oceanboy is saying when on the bike it is not ever fully charged, just to 90%?

[ol' boy]

I had a mate that kept buying the Lipo Batteries for his sons KTM250, but he kept killing them every 3 months
I thought it may have been the Bikes output but no, it was the charger he was using.

Got him the correct charger for the application, no more problems.

[hinekadon]

Do not use a “smart charger” or any charger with pulse charging with this battery."
this is the important point it has to be a constant voltage source , no modified wave forms !! As oceanboy found out .Motorcycles have an alternator which is a constant voltage source cheers

[ol' boy]

Do not use a “smart charger” or any charger with pulse charging with this battery."

Ive been using these without trouble so far

[hinekadon]

these are a switch mode charger and as such supply constant volts! yes you wont have any problems with them , they work by taking the mains to dc, then wobbling it to say 300hz and put it thru a transformer then rectify it to dc level required on the out put and smoothed by capacitors .The wrong one chop the output dc cycles and go from 0v to max v in one cycle which kills the battery , make sense ?? hope so cheers

[GT250]

Thanks for your replies guys.

I'll probably go with a standard battery - Motobatt $120 4yr warranty. They have four terminals so I can use the other half to add bits and bobs without removing the bikes supply.
The Lithium is nice but $200+ and then another $200 to charge it if ever I have to. The missus has gone crazy with me, especially since I had to get a taller windscreen at $420!!!!


Once again, many thanks people.
GT250.

[Tom Mix]

Lifepo4 can be charged at 3.5v cell CV ok. It is lipo and liion that are critical and cannot be charged over 4.2v cell.

[lsemmens]

What's this about batteries for motor bikes. ALL my bikes have had a little lever on the side that when depressed with your left leg would start the bike almost instantly. (Even my old Kwakka 1000 and Suzi Katana had one.)

[Uncle Fester]

What's this about batteries for motor bikes. ALL my bikes have had a little lever on the side that when depressed with your left leg would start the bike almost instantly. (Even my old Kwakka 1000 and Suzi Katana had one.)

Maybe we are all getting a little bit old and lazy

However I even had a 6Ah SLA on my pushbike in the late 1970s because I was annoyed how the light dynamo slowed me down at night.

[loopyloo]

Maybe we are all getting a little bit old and lazy

However I even had a 6Ah SLA on my pushbike in the late 1970s because I was annoyed how the light dynamo slowed me down at night.

Not wrong there.
When I was 8yo, I connected mine to a 6" speaker I had taped under the cross bar. lol

[SS Dave]

The mechanic next door had one of the lightweight battery's in his Subaru rally car what killed the battery was not disconnecting it when the car was in long term storage.

The battery is been sold to use in a vehicle and be charged by the vehicles charging system so no special charging is required.

SS Dave

[LeroyPatrol]

Do not use a “smart charger” or any charger with pulse charging with this battery."
this is the important point it has to be a constant voltage source , no modified wave forms !! As oceanboy found out .Motorcycles have an alternator which is a constant voltage source cheers

The alternator is not a constant voltage source. It's AC and varies with RPM. This is why there is a rectifier that then changes this to DC.

......Leroy

[Uncle Fester]

The alternator is not a constant voltage source. It's AC and varies with RPM. This is why there is a rectifier that then changes this to DC.

......Leroy

Pretty sure there is also regulator(usually built into the rectifier housing) that keeps it at a resonably constant 13.8-14.4V. Depending on the size/type of the bike it might drop below that in idle but it will never exceed 14.4V once you rev it. So for the sake of the charging function it can be considered a constant voltage.

The actual alternator internally will have a wild swinging voltage before it is regulated but the rectifier/regulator forms part of the complete system. I am not aware that you can access the AC output without dismantling it.

[LeroyPatrol]

yes rec/reg in the one box. On my Ducati's for example, to access AC from the alternator/stator you just unplug the reg and you can then measure the voltage and rev engine to see if it's working. Usually measure around 30V ac per phase.