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Badcrumble

LiFe Battery queries

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Hi all,

I have seen an old thread on here about Tamiya LiFe batteries and they are now pretty non-existent apart from the one that can be used in the new Star Unit Lunchbox.

The thread suggested these as an alternative.

http://www.broadtech.hk/eagleshop/shop/ShopProductDetail.aspx?id=3371V2U

I have also found these more locally

https://www.nexusmodels.co.uk/hacker-topfuel-life-battery-3s-2100mah-30c-52100351.html

Then I saw this. The specs seem similar to me but it is marketed towards the drone market.

https://hobbyking.com/en_us/zippy-compact-2100mah-3s1p-30c-lifepo4-pack.html

Does the 9.9v rating of the top-fuel or zippy batteries mean they going to be more powerful for car running than the one at Broadtech?

Is it the discharge rate (30C) that differentiates this battery from one that seems identical but is marked up as for a transmitter?

https://hobbyking.com/en_us/turnigy-nano-tech-1500mah-life-3s-9-9v-transmitter-pack-taranis-compatible-1.html

If memory serves, the mAh figure relates to  capacity = runtime? In which case something like this ought to give more power for longer (than a standard 3300mAh nimh stickpack)?

https://hobbyking.com/en_us/zippy-compact-4200mah-3s1p-30c-lifepo4-pack.html

I’m sure the easy answer is just go LiPo but the scare stories mean they have a low Wife Acceptability Factor and as I don’t get to run that often, keeping stuff on charge isn’t really an option.

This is all a bit beyond me so any help would be appreciated.

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A 3-cell/'3S' (9.9V) battery will definitely make the car more powerful than a 2-cell/'2S' (6.6V) battery. Just make sure your motor and ESC are rated for 10.8V (fully charged voltage of a 3s life pack). The mAh rating is indeed the capacity of the battery - more capacity = more runtime. Be aware however than if you use a 3S battery, the electronics will draw more power so a 3S 4200mAh battery will have less runtime than a 2S 4200mAh battery. Higher mAh packs also tends to be heavier and physically larger, as will packs with more cells. The nano-tech pack is physically smaller, lighter and has lower capacity. I'd say the reason for the low discharge rate (1C) is because of the low-current plug installed on it.

All batteries are inherently unsafe, as they can store a lot of energy, and if abused all that energy can be released suddenly resulting in a lot of heat and possibly a fire. LiPos are primarily less safe than NiMH because the energy density is slightly higher (mAh higher for same physical size) and they typically have much lower internal resistance, so will happily release a huge amount of energy quickly. A LiPo pack might happily provide 500-1000Amps of current if shorted out, whereas a NiMH might only do 50-100A. Lifepo and NiMH can cause fires, but you have to try much harder. Lipo and Lifepo are more sensitive to improper charging, over-charging, over-discharging and degrade more quickly when stored for long periods at an improper voltage compared to NiMH. LiFePo4 sit somewhere between NiMH and LiPo with respect to energy density, power delivery and therefore safety. 

Not sure what you meant by 'keeping stuff on charge isn't an option'? With LiPo you store the batteries at about 40% charge (~3.8V/cell), as this gives the longest shelf life and some buffer so the battery doesn't self discharge to 0% if storage long term (up to 1year). If a LiPo cell goes below 0% (3.0V) charge, it is permanently damaged and attempting to recharge it is risky. The car needs to have an appropriate cut-off so it stops before the battery voltage gets too low. Storing at 100% (4.2V) long term will also drastically reduce the lifespan of a LiPo.
When it's time to use it you put it on the charger and bring it up to 100% which takes about 30mins to an hour for most batteries. All LiPo battery chargers automatically stop charging when the battery hits 100% (4.2V/cell). Balance charging is typically performed to make sure that all the cells in the pack are charged to equal voltage and no single cell is brought above 4.2v which could damage it.
After use you should immediately charge (or discharge) the LiPo to the storage charge of 3.8V/cell and put away in a fire safe bag. Typically LiPo fires only happen if the battery is charged improperly (non-balance charger), charged or discharged at an excessive rate, or is continued to be used after being physically damaged or after accidental over-discharge. Because the risk is elevated when charging a lipo, you should never leave a charging lipo unattended.

Technically Lifepo batteries should the treated the same as lipo to ensure maximum lifespan and safety, the voltages of interest are just 2.5/3.3/3.6 instead of 3.0/3.8/4.2. Using a Lifepo in a transmitter is somewhat at odds with the whole storage charge philosophy so I'm not sure how we ended up with lifepos being primarily sold for RC transmitters. I use NiMH in my transmitter.


When treated properly and put in a fire safe bag while charging/storing, the risks of lipos are minimised. The exact same battery technology is used in phones and laptops, the only difference is that those batteries permanently have battery monitoring circuitry attached to them to prevent them being charged/discharged improperly, and people generally don't often crash their phones/laptops at high speed, physically damaging the battery. With RC batteries the responsibility is put onto the user to ensure that the battery isn't charged/discharged improperly and inevitably people get it wrong and cause fires.

NiMH are generally much more tolerant of abuse (over charge, over discharge, stored at 100% charge) so are a better option if you don't have time or patience to charge/store batteries properly. They however self discharge at a much higher rate so you should charge them fully every few months to prevent them over-discharging while sitting on the shelf and degrading.

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Thank you @nbTMM for your comprehensive reply, I hadn't seen your response until now. Really much appreciated.

As you can tell, I've a lot to learn on the electrics front and I really only want to take the plunge once I know what I'm getting myself into.

Only after posting had I thought about the ESC rating! 

 

 

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LiFe used to be called A123 cells but afaik these days they're more famous as 18650 aka "Tesla cells"

When Tesla builds them into an array of 7000 and plugged into a Supercharger, there's close monitoring & reticulated coolant keeping them cool under high charge current. Latest iteration I hear uses the car's Aircon to superchill the coolant to allow even higher charging currents. 

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