Can the internal controllers handle a 51.8v battery

[Brendon1128]

I'm looking at upgrading my current li-ion (samsung 18650 cells) battery to a higher capacity one. Right now I have a 48v 15 ah brick battery. The new one I'm looking at is a 51.8v 26 ah triangle battery which would fit inside the bike frame's triangle. I like the design because it would keep a low center of gravity and maximize the capacity.

Would the extra 3.8v rating cause issues for my SP5 internal controller? According to the battery manufacturer, the charging cutoff is 58.8 volts.

Thanks

[Bikemad]

A 51.8V battery will work fine with the Smart Pie controller.

I suspect that your current "48V" battery is more likely to be a 52.8V or 51.8V pack.  If you look at the charger voltage you will probably find it is either 57.6~58.4V (if it's for a LiFePO₄ battery) or 58.8V (if it's for a Lithium Ion battery).

Be prepared for the 26Ah battery to have a capacity of nearer 22Ah as some sellers of lithium batteries often exaggerate the true capacity to make them appear more appealing.

I recently purchased a brand new 11.1V 5200mAh laptop battery (which also came with a three year guarantee) so that I could use four of the the six 2600mAh 18650 cells within it to power a high output 10 LED flashlight.
 
I discovered that their actual capacity was just short of 2200mAh when I performed an accurate discharge test at a rate of just 1 Amp on a fully charged cell. (From 4.2V right down to 3.0V!)

Fortunately there were no other bidders on this item, so I ended up paying just £4.98 delivered (approximately 7USD), so as far as I am concerned it was still a pretty good price for six brand new 2200mAh cells, although I don't suppose the guarantee will be of much use now that I've butchered the pack apart. 

Alan
 

[Dachawave]

And how will controller handle a li-on battery with 14S (14x3.7V) nominal 51.8V or maximum 58.8V ? How it will handle this maximum voltage ? Does will hurt the controller in future use ?

[Bikemad]

I have been using a homemade 14S 51.8V LiPo pack for many years with a variety of different GM controllers and have never experienced any problems with any of the standard controllers, but I have experienced controller failure caused by excessive current (97 Amps) on physically modified controllers.

The original GM controllers would not work if the battery's actual voltage was any higher than 60V, but some of the later controllers (SP4/5, MP4/5 and MP Edge) appear to work correctly right up to 63V, although I would not recommend running them at 63V because it would be right on the limit of the 63V capacitors used within the controller.

The current GM 48V LiFePO₄ batteries are actually 52.8V nominal as they are made up of 16 x 3.3V cells (16S).

My 48V10Ah GM LiFePO₄ battery charges up to 58.4V, which is only 0.4V less than my homemade 14S LiPo Pack, but some of the later LiFePO₄ packs seem to have a slightly lower charging voltage (57.6 instead of 58.4).
I suspect the charging voltage has been reduced slightly so as to only charge each of the 16 cells to a maximum of 3.6V (instead of the previous 3.65V per cell) purely to extend the working life of the battery and has nothing to do with protecting the controller itself.

Alan
 

[Ecobully]

I have 14S20A LiPo packs with my MP5 and they work fine hot off of the charger at both 58.8, and 57.4V. Most of the time I charge to 4.1V per cell when I don't need the capacity. Sometimes, only up to 4.0V per cell to prolong battery life.

I have run 16S20A LiPo charged up to 3.92V per cell and that was 62.7V, but the controller read it as 62.9V and it worked fine. Throttle response was ERRATIC! I recommend not going above 14S.

Please note, that regenerative braking will not work as any current passed back to the battery would exceed the 63V limitation.

Lastly, the MP5 works very well in its stock configuration with a 13S pack. The throttle modulation is much smoother than when using higher voltages--it's very twitchy and hard to modulate with anything above 13S LiIon/LiPo. Make sure that you are moving at a decent rate of speed before you go full throttle as most of that energy will be turned into heat.

[Brendon1128]

I see, I was curious too would there be much of a top speed difference between a 48v  (13s) battery vs a 51.8v (14s) battery on the Smart Pie? Or the Magic Pie?

[Ecobully]

50V (12S) ~ 25-27mph.
54V (13S) ~ 28-30mph.
59V (14S) ~ 30-32mph.
63V (15S) ~ 33-35mph.

This is on the MP5 with 26" wheel, Kenda city tires 55psi, 70lbs EVG eBike SX + 160lbs rider.

[Bikemad]

The difference in speed between the 13S and 14S packs is not a lot, but charging a 14S LiPo pack is much easier than a 13S LiPo pack as it can easily be reconfigured for charging as a single 7S2P pack and then charged using a 1~8 cell charger.

If the controllers were able to handle 67.2V, I would probably run 8S/16S packs using four Turnigy 4S 5000mAh hardcase packs in preference to my current 7S/14S packs, but unfortunately none of the GM controllers will allow me to use 16S LiPo at the fully charged voltage.

Alan
 

[Ecobully]

@Alan,

I feel the same way. I would have liked to run 16S as that is pretty easy to configure with high capacity LiPo packs ala HK Multistar packs.

Currently using their 6S + 4S + 4S with (2) serial XT90 harnesses leaving me with 14S with 20A capacity. I added balance extension cables and rewired them to be compatible with the BMS (I had to remove 2 ground wires). This is nice as I can remove the balance extensions and can use the LiPo packs individually when needed. I use the 4S packs in 6P configuration for camping with a pure sine wave inverter -- lasts all week long for my needs!

BTW, even though my BMS is "supposed" to balance the cells, it just trims off higher voltage cells to match the lowest voltage cell and not very efficient and sometimes lazy as I find my cells out of balance by about 0.07V at times. Easy fix is to just split the pack apart and toss them on a good RC balance charger which keeps it healthy for months.