My Lipo trials

[Deleted member 4366]

I bought 4 of these packs and wired them up two pairs in parallel in series to make a 10.4ah 37v pack:
18.5v 5200mAh 20C LiPo 5S 18.5 Volt RC Akku Battery WF | eBay UK
To wire them up I needed a pair of parallel Y leads and a single series delta power lead, and to make charging and balance easier I made two 2 into 1 balance leads. I used Taylors connectors throughout.Before connecting up, I made sure all cells were at the same voltage. I charge them using one of these and a 5amp 12v power supply from Maplin:
B6 7.4v 11.1v 18.5v LiPo RC Battery Balance Charger Ro | eBay UK

I was able to connect directly to my normal battery connection with spade connectors, with the battery in one of my panniers.

The first time out, I used only throttle and went up and down local hills to flatten them as quick as I could. I was surprised that they gave noticeably more power than my lifepo. My meter showed 5.7ah when the voltage started to rapidly drop from 36v, so I called it a day and went home to re-charge.

Next day, I set off for Ellesmere (a 70 mile round trip from Telford) using the pedal assist only. Again, I noticed the increased power and speed, and I arrived in just over 2hours at an average speed of 17mph (a record for me!) After a 90 minute break, I started home, and now, with the battery half flat, the speed and power was about the same as my lifepo. At 65 miles the voltage started to drop rapidly again and was showing 31v up a hill, so I swapped over to my lifepo. The meter was showing 5.7ah again. I normally see 6.5ah to flatten my 9ah Lifepo. When I got home, the residual voltage was 37v. I guess they had recovered a bit. I checked the charge when re-charging after that and the meter showed about 11.5aH to charge, so it looks like the meter on my bike is reading a bit low, but I don't care because at least I now when the batteries will go flat.

My conclusion is that this is a viable way of getting a cheap battery, provided that you can solder well, and that you're very careful to lay the wires neatly and that they're well protected. The balance lead wires are quite thin and could easily be damaged, which would result in an instant fire.

4 battery packs £104.40
Charger £20
Power supply £14
Connectors and leads £20
Total = £158

I've now ordered a set of the 6-cell 22v packs to make a 44v 10.4ah pack for £112. I have enough spare leads now, so that's the total cost for the pack. I hope my controller can take it!
5200mAh 22.2v 20C LiPo 6-Cell 22.2 RC Akku Battery WF | eBay UK

I think that a pair of 18.5v packs in series for 37v 5.2ah would make a very good solution for a lightweight stealthy bike because of their light weight (less than 1.5kg) and high power (100amps) - might just fit in a water bottle!

 

[HittheroadJ]

Great job.

Would this trick be possible for 24V?
I see the 22.2V 14.8V and 7.4V (multiples of 7.4) and the 18.5V.
If I mix the 18.5+7.4=25.9 would that be too much?
Otherwise I'd love to try two each 10.4Ah at 25.9 V c would be a good deal.

If this is not possible any other combinations that would work?
I know some have taken the currie motors up to 36V but that is with extra cooling on old controllers that tolerated 36V.
What if the controller cuts out?

Hm. Any engineers can advise?

thanks.

 

[Scottyf]

Excellent stuff. Like you've said would make a good stealth option or for those who want to push alot of power at a limited range for an ebike. These things have a great c rating an even if you do pull alot of amp's and reduce the life there pretty cheap to replace.

 

[Deleted member 4366]

Using a 22.3v and a 7.4 pack would work as long as they have exactly the same type of cells. Two 14.8 packs would probably be better for 29.6v. it should be alright for your motor and controller, but I can't be certain. Whatever you use, it's very important to have an onboard meter so that you can see the voltage at all times. You shouldn't let the voltage drop much below 36v. Some say 3,2v per cell is the minimum, but I found that they went down to that within a mile of 36v, so better to keep it higher.

 

[NRG]

Voltage drop depends on the quality of the cells. I use the Turnigy packs from HobbyKing and the voltage holds well after 3.6v it's a progressive drop to 3.2v where the cell is just about flat and on the 'cliff edge'

I would also strongly advise some sort of cell LVC monitoring as pack voltage could mask a failing cell in use. Celllogs for instance, they are cheap enough and add an extra layer of security.



-------------------------------------------------------
Posting from my iPhone using Tapatalk

 

[Deleted member 4366]

I would also strongly advise some sort of cell LVC monitoring as pack voltage could mask a failing cell in use. Celllogs for instance, they are cheap enough and add an extra layer of security.

If using cells only in series, I agree with you that these or similar devices are essential.
Lipo Battery Voltage Tester 1S-8S link Low Buzzer Alarm | eBay UK They need to be checked for accuracy first, as I've heard that some don't trigger until too low.
I monitored the cells whilst discharging before fitting to the bike and found a tendency to go a little out of balance at lower voltages, but, after I paralleled the packs, they stayed in balance much better, so the errors must tend to cancel each other out (I guess), so in the end I decided not to fit the alarms but keep to an average of 3.6v per cell instead. I think this is safe enough. I'll keep checking before charging each time to see if they now stay in balance.

 

[rooel]

It is not clear if these packs come with a battery management system wired in, but if not, would it be possible to wire in one of these:

PCM with Equilibrium Function for 29.6V Battery Pack at 30A limit

assuming two 14.8 volt packs were wired together to give approximately 29 volts.

Also, does the ebike controller itself not deal with the over-discharge cut-off, and the battery charger with the over-charge question?

 

[MalcolmW]

my Lipo

As a new member I am concerned not to try to pontificate, but there is an issue here that needs clarification.
Cell voltage.
In general LIPO open circuit voltages gives a good indication of the remaining capacity. It is not worth allowing cells to drop below 3.66v/cell as they are then below 10% of capacity.
At the other end, at 4v/cell the cells are at 90% capacity. Lipos are very sensitive to overcharging or discharging.Because these cells are of low internal resistance voltage under load should not be that much different but to be safe we should use no-load voltage as an indicator of state of charge remaining.

I think that using rc packs will become a real option when LIPOFE really gets going.

regards,

Malcolm

 

[MalcolmW]

My Lipo

As a new member I am concerned not to try to pontificate, but there is an issue here that needs clarification.
Cell voltage.
In general LIPO open circuit voltages gives a good indication of the remaining capacity. It is not worth allowing cells to drop below 3.66v/cell as they are then below 10% of capacity.
At the other end, at 4v/cell the cells are at 90% capacity. Lipos are very sensitive to overcharging or discharging.Because these cells are of low internal resistance voltage under load should not be that much different but to be safe we should use no-load voltage as an indicator of state of charge remaining.

I think that using rc packs will become a real option when LIPOFE really gets going.

regards,

Malcolm

 

[NRG]

As a new member I am concerned not to try to pontificate, but there is an issue here that needs clarification.
Cell voltage.
In general LIPO open circuit voltages gives a good indication of the remaining capacity. It is not worth allowing cells to drop below 3.66v/cell as they are then below 10% of capacity.
At the other end, at 4v/cell the cells are at 90% capacity. Lipos are very sensitive to overcharging or discharging.Because these cells are of low internal resistance voltage under load should not be that much different but to be safe we should use no-load voltage as an indicator of state of charge remaining.

I think that using rc packs will become a real option when LIPOFE really gets going.

regards,

Malcolm

I'm sorry but that is complete nonsense, at 3.66v / cell you are just below the nominal 3.7v rating with 50% capacity sill remaining. At 3.2v you have about 10% capacity remaining.

 

[NRG]

If using cells only in series, I agree with you that these or similar devices are essential.

A weak cell is a weak cell is a weak cell. Does not matter if it's wired in series or parallel. To ignore LVC at the cell level is asking for trouble no matter how diligent you may be. There are enough horror stories on ES past and present to be a warning to all that using RC Lipos require a number of safety measures one of which includes cell LVC monitoring.

I'll also add that in my own experience I've been lucky so far but on two occasions I've nearly been caught out and had to replace packs before they caused an issue due to not monitoring cell voltage under. It's your choice...

 

[Deleted member 4366]

A weak cell is a weak cell is a weak cell. .

Some cells might be very weak, but, luckily, I don't have any at the moment. I always check cell voltage before and after charging and they seem to be behaving as they should. I'll let you know if any become weak. What makes a cell become weak?

 

[NRG]

Overcharging and discharging, temperature, momentary shorts, poor storage, manufacturing defects, phyisical damage, luck....cells that are seemingly OK to start with can go weak for no obvious reason. I've got one at the moment in my Peugeot pack, the only one out of 24...its the always the first to hit LVC and the last to fully charge.

 

[MalcolmW]

Could be you are discharging your pack too low........

 

[NRG]

No.

 

[alexk-il]

I've now ordered a set of the 6-cell 22v packs to make a 44v 10.4ah pack for £112. I have enough spare leads now, so that's the total cost for the pack. I hope my controller can take it!
5200mAh 22.2v 20C LiPo 6-Cell 22.2 RC Akku Battery WF | eBay UK

Great info, thanks for sharing!!

I guess you will be required to use this charger to charge 22V cells, right?

By the way, how do you charge your set of 18.5V batteries? Do you charge each one of these separately or do you use more than one charger to save the time?

How long does it take to fully charge your set of 4 batteries?

Thanks
Alex

 

[alexk-il]

I've got one at the moment in my Peugeot pack, the only one out of 24...its the always the first to hit LVC and the last to fully charge.

How many charges had this cell survived before getting weak? Just an estimation would be ok.

Thanks
Alex

 

[alexk-il]

Hmmm... They do have some nice batteries, however the disclaimer is scary:
"When charging Battery Pack, please put battery in a fire proof container".

Warnings for Using Batteries

 

[tangent]

Really interesting. Do you know what the chemistry of the LIPO is? Is it marked on the battery anywhere?

 

[NRG]

How many charges had this cell survived before getting weak? Just an estimation would be ok.

Thanks
Alex

About 50 Alex before I noticed it getting lazy. Its had another 50 or so since, all the others still OK...I'm just unlucky with this one I guess but as I know its there I can manage it...