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[unbuiltnautilus]

I am thinking of changing battery packs in a troublesome submarine. Going from a 9.6v 5000mAh NiMh pack, which is heavy and causing stability issues, to a pair of 11.1v 2600mAh Samsung 18650 packs. This should give me something equivalent to the NiMh packs capacity connected in parallel, but with reduced all up weight, plus just a bit more voltage. Expected current drain is likely to be in the order of 5 amps.


The packs will be from Overlander, to a bespoke cell layout. Interestingly, Overlander seem to have an internal cell management PCB fitted. This seems to do away with a traditional balance lead. I will be using a Li-Ion compatible charger for ongoing charging.
Any thoughts, or better still practical feedback from users.


And though no doubt well intentioned, these are not LiPo packs, so any helpful advice about those types of cell will be wasted keyboard time.

[Taranis]

Apart from mobile phones my only experience with Lithium is my large quantity of Makita 18 volt units.
A lot of the early batteries died prematurely due to frequent over discharging so the more recent batteries monitor the cell voltage. Unfortunately they tend to only measure the first cell in the pack and if that reads low or faulty the charger refuses to charge them forever more.


Maybe the above is not relevant but I'm suggesting getting to know everything about that particular battery and if it has any form of inbuilt protection or requires a cut off voltage to be set.


EDIT looks like 2.5volts per cell is the maximum discharge

[Subculture]

Do you want the extra voltage for power? LifE PO4 would much more closely match the old pack voltage.

[unbuiltnautilus]

Do you want the extra voltage for power? LifE PO4 would much more closely match the old pack voltage.

Reduced weight is the first and foremost, but the slight increase in voltage will be a bonus.
As an aside, Overlanders packs come with balance leads, which makes life just that bit easier. I am still trying to get definitive info regarding max discharge currents per pack, info ranging from 2 amps to 15 amps per pack..just like brushless motors, lots of info, none of it matching! Still, I got round that problem by actually trying stuff, so more experimenting to follow.

[tsenecal]

if your current ESC is not "smart", you may want to either swap out your ESC to a model that understands LIPO/LIons or get an alarm to attach to the battery to keep the ESC from over discharging the battery.

[Subculture]

This website lists constant current for their batteries. Good prices too.

https://eu.nkon.nl/rechargeable/li-ion/18650-size.html

Could also look at a slightly bigger cell, which offers more capacity in a single pack- will work out cheaper.

https://eu.nkon.nl/rechargeable/li-ion/21700-20700-size/samsung-inr21700-50e.html

Do consider these batteries. You would need two packs four for 12.9 volts and equivalent capacity. A bit more bulk than the li-ions, but much tougher, and will last you years. they also have a very different discharge curve, more like nicads, which gives a good cue when you need to bring the boat in. Much more tolerant of discharge than lipos/Li-ion and safer.

https://eu.nkon.nl/rechargeable/li-ion/26650/a123-systems-anr26650m1b-a-grade-3-3v-a-grade.html

[unbuiltnautilus]

Very handy, cheers


On the subject of onboard monitors, I have access to budget units suitable for up to 8S, but they are configured for LiPo rather than LiIon, so not sure if they will help..also, bolted shut inside a sub, not sure how audible they will be with their low voltage alarms!!


Still, all starting to look promising. I like the look of the A123 cells, may consider them for the next project, which has much more room in it..

[Subculture]

Conventional Lipo monitors aren't very useful in a  sub. Instead of a sounder you need something that will blow ballast, cut motors or flash a bright led mounted somewhere it can be clearly seen. The other option would be telemetry if using something like 459mhz.

Ultimately you get best life from lithium batteries if you keep them between 20-80 of their capacity, so don't charge them up fully, or let them run too low.

[HMS Invisible]

...Overlander seem to have an internal cell management PCB fitted. This seems to do away with a traditional balance lead...

I had thought one function of the internal PCB was to prevent overdischarge mentioned in some replies.

According to Youtube ebike-related channels their battery Battery Management System (BMS) switches off power when ANY of the paralleled 18650 Lipo cells reaches a 3.0 volt threshold. Typically in 7s,10s,13s format. My ebike speed control is normal in that it provides some duplication of the BMS function with a 21.0 volt cut-off point for 7s3p wired (twenty one) 2.2Ah, 18650 no name brand cells.
The BMS acronym has become well enough understood within the ebike sphere. Hyperlink: Ebike BMS

I suggest contact the supplier to clarify if 5 amp is the nominal overcurrent function rather than the a maximum continuous rating per cell.

I do 40-80 with my phone battery