LiPo battery advice for a beginner

[rjoseph244510 14]

Hi guys

 

I’m just starting my journey into Tamiya and rc cars. I’ve purchased my first Tamiya kit (Egress) as a Christmas present to myself and plan to start building it on Boxing day.

 

I thought it wise to learn all I can before then and I’m currently on the subject of LiPo batteries / chargers. I have read countless articles and videos but there are still some really basic questions that I would really like answered.

 

1. If I decide to stop running my car for a few weeks/months what do I do with the battery? As I understand it, I need to discharge it to a safe voltage (ie place it in storage mode). Once I do that, can I simply unplug it from the charger, put it in a LiPo safe bag, and then put it on my garage shelf?

 

2. Where’s the best place to charge your LiPo battery? The thought of it exploding (even though this is apparently very rare) in my house scares me to death. Therefore, I’d be happier charging it in my garage (maybe in a ceramic pot / LiPo Safe bag). However, I read that you should never charge it unattended.

 

3. I understand that you shouldn’t let the battery drop below a certain level so save degradation. How do you know it’s not dropped below this level while driving the car? Does the ESC cut it off automatically when it reaches a certain voltage?

 

I fully understand and appreciate that these are probably silly questions to ask but I thought it’s better to find out from experienced users than experiment as i go along. Any help or advice would be fully appreciated.

 

Best regards

 

Rod

[Mad Ax 2704]

OK, first up - don't panic.  There's a lot of horror stories about LiPo batteries but if you treat them well and follow some basic precautions you should be OK.  LiPos will not usually catch fire unless they are damage, mistreated or are at the end of their life, in which case you should get some warning signs before they catch fire.

1) Your batteries should always be stored at a 'safe' voltage.  The longer a battery is stored at capacity, the more damage will be done.  I sometimes leave mine topped off for a day or two but if I'm not going to use them in that time they go back to storage charge.  Because I usually take more batteries than I need to an event, I estimate that some of my packs have had more cycles on the charger than they have in a car.  All good LiPo-compatible chargers should have a storage mode.

Note: this applies not just if you're not using the car for a few months.  After every run, unless you plan to go out again the next day, put the battery to storage.  It's a good habit to get into and if you don't, it's very easy to forget.  I once charged up all of my packs for a big event that was cancelled due to bad weather.  I put the packs away full because I thought I might go for a run in the next day or two.  I got busy and then forgot about them for 6 months.  When I came back to them, every single pack had puffed (more on this later).  That was a very expensive mistake.

Store your batteries in a LiPo safe bag or other fireproof container.  Ammunition boxes are popular.  Make sure you store them in something vented - a battery failure can release flammable gases which may explode in a sealed container.

2) Charge your battery wherever you feel comfortable, but always use a LiPo-safe bag or other fireproof container.  It won't stop your battery venting noxious gases or catching fire but it will minimise the risks of things catching fire.  If you can charge on a concrete floor or a paving slab, all the better, but I usually don't.  Note that a LiPo fire can expel a long jet of hot flame, so a patio slab won't help if it's surrounded by wood dust from a lathe, etc.  (I say this because my garage is usually foot-deep in wood shavings and dust).  Never charging unattended is good advice, however if I was to attend my batteries before race day then I would spend my Sunday evenings sitting in a chilly workshop.  I'd rather be in the warm reading.  This may come back to bite me one day when my workshop burns down.

The main reason not to charge in the house is the gas released during a fire or failure.  It is toxic, very thick and very smelly.  It took several weeks to get the smell out of my workshop after I destroyed some old batteries.  I'd hate to have that in my house.

3) The easiest way is to use a LiPo-safe ESC and make sure it is properly configured.  Most are automatic but always read the instructions before assuming it is safe.  This will prevent your battery from going below the safe voltage.  Some ESCs will cut off immediately, some will reduce available power.  With the second type it can be hard to tell.

Other points to note:

LiPos don't usually explode.  They either vent (releasing flammable gas which can ignite or explode) or they catch fire.  It's a chemical fire, it burns very hot and fierce and it won't go out until the internal fuel source is expended.  It will even burn underwater.  A NiMH, on the other hand, will explode if overcharged.  It will destroy your chassis if it's strapped in, and I expect it would make a mess of your hand if you were holding it.  LiPos don't have exclusivity on danger.

LiPos have a service life.  It will vary depending on quality and use, but after a time you'll notice it takes longer to balance.  This is a sign that it's getting ready to dispose of.  I have had packs that have started to take a while to balance, and in a matter of weeks they have puffed under charge.  If your battery isn't balancing as quickly as it did, consider it a 'danger' battery and never charge it unattended.

Puffing is bad.  Over time, the battery breaks down internally, releasing gas.  Because the cell is sealed in a plastic sack, the gas can't escape, so the cell 'puffs'.  Literally, like the Stay Puft monster.  This is a sign that your battery is nearing the end of its life.  Again, consider it a danger battery if you see signs of expansion.  It's harder to tell in car batteries because they are contained in hard cases, however once the case starts to split it's time to think about replacements.

Heat is very bad for LiPo batteries.  If a battery gets hot during use, you are pulling too much current or have other problems.  Heat will cause your battery to puff, vent or catch fire.  I expect it was heat (caused by excess current) in my Top Force that caused the pack to puff during a race.  (Literally, when I took the car off the track and undid the battery straps, the pack was under so much internal pressure it ejected itself from the car.  When I retrieved it it was 3 times its original size).  Heat during charging is very very bad and should result in you switching off the charger, disconnecting the plugs and making sure there's nothing flammable around the charging sack.

Damage is also bad.  A lot of aircraft LiPo fires are due to crashes or hard landings that puncture the membranes inside the cells.  Car packs are more resilient because they have hard cases.  You can use soft case batteries in cars but only if the battery compartment is good.  Soft case LiPos are banned at most race events.

I think that's about it.  I've had a lot of LiPos over the years and have never once regretted the switch from NiMH.  Yes, there are drawbacks and safety concerns but a bit of caution should protect you and your property from harm and the benefits in terms of run-time and reliability are vast.

Have fun

[rjoseph244510 14]

Hi Mad Ax

Wow, thank you so so much for taking so much time in your reply. Your have really helped to alleviate my queries and concerns. I really appreciate it.

Just to clarify, let's say I take my car out on the 1st of the month. When I return home I attach it to my charger and place it in storage mode. If I don't plan to take my car out again for two whole months, am I OK to simply place the battery in a LiPo safe bag on my garage floor (ie ceramic pot) for the two months? Do I have to periodically check (eg twice a week) on the batteries to make sure that are still at storage level and haven't dropped?

Again, any help or advice would be fully appreciated.

Best regards

Rod Joseph

[Wooders28 2947]

It's good you're taking time to ask questions.👍

I've 20+ lipos , always storage charge after use (after letting it cool down, if ive been hammering it with a low turn motor), and I normally check mine every 6 months ,ish , by just plugging them into the charger and do a storage charge, normally a couple of seconds and the charger comes up, DONE. (Or whatever your charger does when it's finished)

If you have a digest through this page, I think you'll know more than most.

 

https://rogershobbycenter.com/lipoguide/

 

[rjoseph244510 14]

Thanks Wooders28, much appreciated!

Best regards

Rod

[Juls1 1209]

So for your own reference. 
 

a safe storage voltage is 3.8-4.0V per cell, 

for a 2S That means 7.6-8.0v

with regard to esc discharge cutoffs, ideally you want a esc that will do this for you, 

generally that cutoff will be about 3.2-3.4v some esc’s will be set for 3.0v this is ok if the pack cells are very equal and balanced well but if not there is potential for damage to the weakest cell. If you don’t have a cutoff esc you can still use the car with lipo just stop playing the moment the pack dumps (suddenly slows) I generally don’t recommend that for crawlers as often the current drain is so slight you may not notice the dump until it’s a bit late or you might be like “just need to drive back to car, keep going we are nearly there” 

alternatively you can buy small plug in device called a lipo alarm, basically it plugs into the balance port and gives a shrieking racket if the voltage of any cell gets low. 
 

if you have a balance charger, and good maintainence schedule then lipo battery’s are very safe, it is recommended to do it somewhere that fire can’t escape/escalate but generally that’s not necessary. It’s important to regularly check your pack charging, keep a eye on the time and how much mah is going in the pack, Often when one cell is going bad balance charge times will gradually increase while the charger keeps trying to equal the voltages at low input current. 
 

finally your packs will give you a sign if they are not happy, they will get really puffy. A little bit of puffing is ok, a lot is not. Generally if the pack is puffing you’ll also notice longer charge times, a battery checker will also show you significant shifts in voltage between cells after use, if there is a 0.4v difference after a run alarm bells should be ringing, generally this will be  accompanied by shorter run times and poorer performance. 
 

packs puffed up to heck? What to do? Discharge the pack as low as posssible, (0 if you can) cut the plugs off, chuck in a bucket of super salty water for a week. Battery should be inert at this stage then put it in the trash. If you can’t get the pack discharged below 3.0v per cell you might have to leave it in the salty solution for a few weeks. 
 

Juls.

[Juggular 3296]

5 hours ago, Mad Ax said:

I've had a lot of LiPos over the years and have never once regretted the switch from NiMH. 

The same here.  

LiPo just gives out a lot more amp (flow) than NiMH.  Maintains higher voltage on heavy discharge too.  

I charge my LiPos on my desk.  Most new LiPo chargers won't allow you to overcharge.  You don't want to use old "dumb" chargers that would trickle charge overnight. 

Most new chargers would have a "storage charge" function.  Imax B6, for example, would actually discharge a fully charged pack down to 60%, if you "storage charge."  Of course, it will bring it back up to 60%, if it's undercharged.  You don't have to know if it's blow or above 60%, because the charger will make the pack ready for storage."  As mentioned, don't let it stay fully charged, don't let it stay drained.  My rule of thumb is 8 hours.  If you are going to use it in 8 hours, it's fine.  If you don't use it within that time, storage charge (to discharge), and charge again when you are going to use it.  

If it's at "storage voltage," LiPos actually do okay for longer.  But like Wooders28 said, do another "storage charge" every 6 months.  

ESCs like Hobbywing 1060 (for brushed motors) has either "LiPo" or "NiMH" battery option.  It will cut off at respective voltages, depending on how you connect the jumper tabs.  

Some ESC will allow you to set it, some don't.  

If you are using TBLE02S ESC, it is set only for NiMH.  That's too much drain for LiPo, so it'd be a good idea to spend $3 and get a voltage cutoff alarm.  It's small, cheap and loud.  Once you know that it takes 30 minutes for the alarm to go off, just run it for 20 or 25 minutes.  That way, you don't have to bother with plugging the alarm every time. (It's called @Jonathon Gillham method)  I still recommend plugging in the alarm at least 5 times under various circumstances, so you'd get a feel for how long it takes.  If you change the motor, plug in the alarm again for 5 runs.  Each car, each motor, even each terrain is different.  

LiPo fire is rare.  It's one of those things you hear about all the time, but you don't see it every day.  But fireproof bag is always a good idea.  You can get a $4 bag, and it can do a reasonable job of containing the jet.  Don't have clutter near where you charge (since I charge on my desk, paper is everywhere though--don't do what I do!).  Have a fire extinguisher, if you don't have one already.  I have 3 arm-sized ones like below.  But you can get a small spray can too.  Every kitchen should have one, even if they never charge batteries.  After all the precautions, probably nothing would happen.  But if it did, you can take care of it.  

People panic and don't even use the extinguishers they have.  They used one blanket.  When that didn't quite kill the flame, then they poured one drink, and then another drink.  Until the end the extinguisher was never used.  This was a fuel fire, not a battery fire.  But the lesson is to use the extinguisher, if there ever was a fire. 

I think it's interesting how Nitro car folks don't really talk about fire.  Nitro fuel is highly flammable (I've got gallons of it, I never lost any sleep over it).  I worried about all this before I got into LiPo.  But LiPo flaming up doesn't happen often.  Of course more often than NiCd and NiMH, but not as much as you'd think.  Tamiya doesn't sell LiPo, because they aim to sell to children.  Children might plug it into their grandpa's old trickle charger and leave it for 12 hours.  

(1) Don't over-charge or (2) over-discharge, (3) don't give it a hard impact, and (4) "storage charge" after each run.  That's not that hard for adults.   

Also, you might want to consider XT-60 or Deans plugs.  Tamiya connectors are designed for 1A (but will do 2A bursts).  It was designed for NiCD's 1A discharge rate.  LiPo can do a lot more, most ESCs can do 60A burst and newer ESCs can do 120A.  Even some Tamiya kits come with Deans.  So Tamiya knows their 1A connector is not adequate.  The question is; are they going to swallow their pride and go with XT60 that's free, or pay Deans for license fees, or invent their own and get a backlash from RC community that's already using either Deans or XT60.  

At any rate, if you hadn't used LiPo before, you will also see why many folks don't go back to NiMH.  

 

[Jonathon Gillham 3053]

Thanks @Juggular, I may have peaked knowing there is a method named after me!

Lipo's are far better and I can't add to the advice already given about them.

I still have a few NiMH as I have a 6yo who doesn't plan and say "Dad, can we race our cars after school".  He gets home and then may or may not ask to run the cars, so lipo's aren't ideal as then I have to charge them by which time a 6yo can lose interest.  The NiMH can be charged and then left charged, and while they lose charge over time they usually are good enough for a run around the garden.  I will always have a couple of NiMH for this reason, even though we have a bunch of lipos.  They also save the lipos from being used for bashing or running my nitro starter box - all my lipos are meant for racing and are really expensive.  They degrade over time so need replacing.  Since I don't use them at home I get a couple of seasons out of them before they are noticeably slower, puff or the charger refuses to charge them due to cell errors.  

[Jamess 4]

Others have already describe in great detail, and I also have learned a lot. Anyway, I always handle my 4S lipo very carefully. If I don’t use it, I will discharge to 15.2v-16v before storing them.

[Mad Ax 2704]

9 hours ago, Juggular said:

(since I charge on my desk, paper is everywhere though--don't do what I do!)

To be honest, I expect there's a lot of this in the LiPo user fraternity.  Currently my charging area is on a set of wooden shelves that are screwed to a plywood stud wall, inside which is my home office / studio.  Although the workshop is block built, the office / studio is wooden floor, wooden walls and wooden ceiling.  On top of that wooden ceiling is my entire RC collection, and above that is the wood and felt workshop roof.

If the shelves caught fire, it wouldn't take long for the studio wall to catch and pretty soon the entire workshop would be destroyed.

I do have a plan to empty and re-fill the workshop, move some of the workbenches and generally tidy it all up, but I have a full-time job and a child, so spare time is a thing that other people have.

[Jonnythefox87 38]

9 hours ago, Juggular said:

The same here.  

LiPo just gives out a lot more amp (flow) than NiMH.  Maintains higher voltage on heavy discharge too.  

I charge my LiPos on my desk.  Most new LiPo chargers won't allow you to overcharge.  You don't want to use old "dumb" chargers that would trickle charge overnight. 

Most new chargers would have a "storage charge" function.  Imax B6, for example, would actually discharge a fully charged pack down to 60%, if you "storage charge."  Of course, it will bring it back up to 60%, if it's undercharged.  You don't have to know if it's blow or above 60%, because the charger will make the pack ready for storage."  As mentioned, don't let it stay fully charged, don't let it stay drained.  My rule of thumb is 8 hours.  If you are going to use it in 8 hours, it's fine.  If you don't use it within that time, storage charge (to discharge), and charge again when you are going to use it.  

If it's at "storage voltage," LiPos actually do okay for longer.  But like Wooders28 said, do another "storage charge" every 6 months.  

ESCs like Hobbywing 1060 (for brushed motors) has either "LiPo" or "NiMH" battery option.  It will cut off at respective voltages, depending on how you connect the jumper tabs.  

Some ESC will allow you to set it, some don't.  

If you are using TBLE02S ESC, it is set only for NiMH.  That's too much drain for LiPo, so it'd be a good idea to spend $3 and get a voltage cutoff alarm.  It's small, cheap and loud.  Once you know that it takes 30 minutes for the alarm to go off, just run it for 20 or 25 minutes.  That way, you don't have to bother with plugging the alarm every time. (It's called @Jonathon Gillham method)  I still recommend plugging in the alarm at least 5 times under various circumstances, so you'd get a feel for how long it takes.  If you change the motor, plug in the alarm again for 5 runs.  Each car, each motor, even each terrain is different.  

LiPo fire is rare.  It's one of those things you hear about all the time, but you don't see it every day.  But fireproof bag is always a good idea.  You can get a $4 bag, and it can do a reasonable job of containing the jet.  Don't have clutter near where you charge (since I charge on my desk, paper is everywhere though--don't do what I do!).  Have a fire extinguisher, if you don't have one already.  I have 3 arm-sized ones like below.  But you can get a small spray can too.  Every kitchen should have one, even if they never charge batteries.  After all the precautions, probably nothing would happen.  But if it did, you can take care of it.  

People panic and don't even use the extinguishers they have.  They used one blanket.  When that didn't quite kill the flame, then they poured one drink, and then another drink.  Until the end the extinguisher was never used.  This was a fuel fire, not a battery fire.  But the lesson is to use the extinguisher, if there ever was a fire. 

I think it's interesting how Nitro car folks don't really talk about fire.  Nitro fuel is highly flammable (I've got gallons of it, I never lost any sleep over it).  I worried about all this before I got into LiPo.  But LiPo flaming up doesn't happen often.  Of course more often than NiCd and NiMH, but not as much as you'd think.  Tamiya doesn't sell LiPo, because they aim to sell to children.  Children might plug it into their grandpa's old trickle charger and leave it for 12 hours.  

(1) Don't over-charge or (2) over-discharge, (3) don't give it a hard impact, and (4) "storage charge" after each run.  That's not that hard for adults.   

Also, you might want to consider XT-60 or Deans plugs.  Tamiya connectors are designed for 1A (but will do 2A bursts).  It was designed for NiCD's 1A discharge rate.  LiPo can do a lot more, most ESCs can do 60A burst and newer ESCs can do 120A.  Even some Tamiya kits come with Deans.  So Tamiya knows their 1A connector is not adequate.  The question is; are they going to swallow their pride and go with XT60 that's free, or pay Deans for license fees, or invent their own and get a backlash from RC community that's already using either Deans or XT60.  

At any rate, if you hadn't used LiPo before, you will also see why many folks don't go back to NiMH.  

 

With these voltage cut off alarms, does it matter what esc you have? I have a TBLE02S so will definitely be investing in one, for example would this be the kind of thing I'm looking for 

https://www.modelsport.co.uk/index.php?product_id=406668&gclid=Cj0KCQiA2vjuBRCqARIsAJL5a-KXdyDSeURbR-Es4c5rHBfRjmHYA0y7vB2nw7ww34kOlI9K8wE29VYaAiiSEALw_wcB

[Wooders28 2947]

15 minutes ago, Jonnythefox87 said:

With these voltage cut off alarms, does it matter what esc you have? I have a TBLE02S so will definitely be investing in one, for example would this be the kind of thing I'm looking for 

https://www.modelsport.co.uk/index.php?product_id=406668&gclid=Cj0KCQiA2vjuBRCqARIsAJL5a-KXdyDSeURbR-Es4c5rHBfRjmHYA0y7vB2nw7ww34kOlI9K8wE29VYaAiiSEALw_wcB

The alarms plug into the balance lead on the Lipo,(and alarms like a smoke alarm) , so don't have anything to do the Esc, eg:- you could run a torch off the Lipo and it would alarm when the voltage dropped to the preset value.

It does mean you need to run a balance lead, could be an issue running shorty lipos with 4 / 5mm ports, but not impossible.

I ran one of these when I first got a cheap brushless esc, (to check the cut off voltage), i dont like a 3v cut off, the esc just looks for 6v (on 2s) so could be 3.01 / 2.99v. I've found if you set it around 3.4/3.6v, (depending on the motor) the battery is pretty much at storage charge.

 

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F273474735869

[rjoseph244510 14]

Wow. I honestly can't say thanks enough for all the help, advice and tips you guys have provided!

Best regards

Rod

[Mad Ax 2704]

I've got a couple of LiPo alarms with voltage LEDs on.  Very useful for checking cell voltage after time in storage without having to hook up to the charger, also useful if I've got a 3S on the workbench powering a test rig.  I accidentally left one plugged in a few months ago and I came back to the workshop next morning to find it bleeping - the LED had drained one of the cells and had been bleeping out loud for who knows how long.  However that pack had previously had a problem with a dumping cell (which is why I only use it as a workbench power pack), so that might explain why it dropped so quickly with just an alarm plugged in.

Anyway, I have a Mod Clod that was running a Traxxas EVX 4S / twin motor brushed setup.  It was a pre-LiPo ESC, so I used a LiPo alarm on each of 2 2S stick packs.  The EVX seems to pull a lot of current and on my initial test run the packs dropped below warning voltage after just a couple of wheelies.  Unfortunately something in the LiPo alarms interfered really bad with the radio and the whole thing went barmy.  Fortunately it flipped itself upside down before it could race off and damage parked cars or run over any snoozing kittens.

Since then I don't use LiPo alarms on runners.

I also replaced the EVX with a later LiPo-safe one, but I still rarely run it as it seems to dump packs within just a few wheelies.  There must be something not 100% with that setup.

[Jonnythefox87 38]

I’m planning to buy a second truck in the not too distant future, sounds like I may as well buy a new ESC that supports a lipo. 
How would I be able to tell if an ESC has a voltage cutoff built in?

[Juggular 3296]

31 minutes ago, Jonnythefox87 said:

I’m planning to buy a second truck in the not too distant future, sounds like I may as well buy a new ESC that supports a lipo. 
How would I be able to tell if an ESC has a voltage cutoff built in?

It could be advertised as such. 

Or you can look up the manual.  Most manufacturers would have manuals online.  

Like this Hobbywing 10BL120 ESC for Sensored Brushless motors. 

As you can see, it allows you to set the cutoff voltage.  

 

[nbTMM 411]

The ESC advertising literature and/or downloadable user manual will tell you what cutoff voltages you can program in to it. If it doesn't have the ability to program the cutoff voltage, chances are it is unsuitable for LiPos. Some ESCs have you set the cut off on a 'per cell' basis and automatically detect how many cells there by measuring the battery voltage at turn on. Other ESCs require you to set the overall voltage for the pack. Both do the same thing however as the ESC can only monitor the voltage of the whole pack, not individual cells.

Setting the LiPo cutoff voltage is probably the single most misunderstood part of safe usage of LiPos. 3.0Volts is the absolute minimum you should ever discharge a LiPo cell to however if you have a 2 cell pack that does NOT mean that you should set your LiPo cutoff to 6.0V. This is because the cells in a multi-cell pack are never perfectly matched, so if you set the cutoff to 6.0V, one cell would be >3.0V and the other <3.0V which is no good.

To understand what is a reasonable cutoff voltage you must first understand the relationship between voltage and the state of charge of a battery. It is non-linear and goes something like this:
>4.2V - permanently damaged, possibly unsafe to continue using, dispose of battery appropriately.
4.2V - 100% charge 
4.0V - 80% charge 
3.8V - 40% charge 
3.7V - 20% charge
3.6V - 10% charge 
3.0V - 0% charge
<3.0V - permanently damaged, possibly unsafe to continue using, dispose of battery appropriately.

I would set the battery cut off to 3.5 or 3.6V per cell. So for a 2S battery you program your ESC cutoff to 7.0-7.2V or 10.5-10.8V for a 3S pack. As you can see from the above, once a cell dips below 3.6V, it is over 90% discharged anyway.
This gives you about a 10% safety margin in matching between the cells in the pack, so if the pack advertises that it is 5000mAh but one cell happens to be 5200mAh and the other 4700mAh you will still be OK. When the ESC cutoff kicks in at 7.0-7.2V, although your underperforming 4700mAh cell will be lower in voltage as more % of it's capacity has been spent, it should still be above 3.0V.
Most reputable brand packs will have cells matched to better than 10%.
Setting your cutoff lower than that won't give you appreciably longer run time and greatly increases the risk of over-discharging and damaging one of the cells in the pack if the capacity of the cells are not matched to better than 10%.

If you have a very powerful motor, this can cause the battery voltage to sag under load and prematurely trigger the ESC cutoff. If you consistently measure your pack at say 3.8V per cell after cutoff is triggered, then maybe you might (with caution!) set your cutoff 0.2V per cell lower to compensate.

You should check the cell voltages at the end of each run to keep an eye on how your pack is doing as some cells decrease in capacity faster than others as they age. A perfectly matched pack may no longer be perfectly matched after you've cycled it 50 times. If you notice any cells getting lower than 3.2V by the end of the run, consider increasing your ESC cutoff voltage, or retiring the pack as the matching between cells is becoming too poor for the pack to be serviceable.

Storage charge should be about 3.8V per cell, or about 40-50% charge. LiPo cells degrade/age faster when stored at 100% charge . Storing at 40-50% gives longer lifespan and reduces the risk of fire as there is less energy to fuel a runaway discharge event. It also leaves enough charge so that the pack can sit on a shelf for a long time (at least a year) before it self-discharges all the way to 0% and becomes unusable.

A charger with a discharging function can be useful if you charge a battery and then decide later not to run it, or your car breaks down mid-run and leaves the battery mostly charged. Otherwise you can get away with a charger that has a storage function but can only charge - run the battery down in the car and then charge it back up to storage and put it away.

I charge/discharge batteries just on the bench in the open but always supervised for the entire charge. My theory is that if it's going to smoke up on the charger it's better for me to notice it immediately a few metres away and/or set off my smoke alarm.
Don't be lazy and store batteries completely discharged or leave them installed in cars. Let them cool for a bit if they are hot, then do a storage charge and put them away in a fire bag. It is however better to put away a completely discharged battery and do a storage charge later if you don't have the time to be supervising an immediate storage charge. The golden rule is never leave charging batteries unattended. Fire bags are not as good as you being there to pull the plug if things go bad.

[Oneball1971 117]

Jumping in on this very informative Lipo discussion: C Rating, what's the average number rating are we looking for?

[OOZZEE 30]

On 11/28/2019 at 6:47 AM, Wooders28 said:

It's good you're taking time to ask questions.👍

I've 20+ lipos , always storage charge after use (after letting it cool down, if ive been hammering it with a low turn motor), and I normally check mine every 6 months ,ish , by just plugging them into the charger and do a storage charge, normally a couple of seconds and the charger comes up, DONE. (Or whatever your charger does when it's finished)

If you have a digest through this page, I think you'll know more than most.

 

https://rogershobbycenter.com/lipoguide/

 

the one bit of information that I struggle to find is what amperage should we discharge them at to go into storage mode, set at the lowest rating a 5000mah battery can take 18 hours to discharge to storage( from full charge ) I am using an Ultra Power UP6+ and an ISDT Q6 pro with an independent power supply. any advise appreciated.

 

 

 

[Wooders28 2947]

47 minutes ago, OOZZEE said:

the one bit of information that I struggle to find is what amperage should we discharge them at to go into storage mode, set at the lowest rating a 5000mah battery can take 18 hours to discharge to storage( from full charge ) I am using an Ultra Power UP6+ and an ISDT Q6 pro with an independent power supply. any advise appreciated.

 

 

 

A Lipo C rating let's you know the max discharge rate, normally 2 rates, the lower is continuous and the higher is a burst for 10 seconds. "C" stands for Capacity, and a bit of algebra, to work out the rating (and people say you don't use this stuff when you leave school.. 🙄). If your 5000mah (5Ah) Lipo is 50C /70C , then 5 x 50 = 250 Amps discharge continuous and 350 Amps for 10 seconds.

I discharge my 3800 mah/110C lipos with a 6.5t brushless motor in around 6 minutes. 3800mah means it can provide 3.8 amps for an hour, 6 mins is 1/10 of an hour,  so an average discharge rate of 38 amps (but think the motor can pull 90Amps) 

A charger needs to get rid of a fair bit of energy, I think they do that through a resistor (?) I bought an LRP pulsar pro charger on the basis of it being a 5A discharge rate, my old Imax b6 was 1A discharge, so would be 5hrs for a fully  charged 5000mah, and the charger auto cut off after 2hrs! (Which happened if I charged lipos, and then I couldn't run).

I try and set Lipo cut off voltages to just under the storage charge (3.6v) so the charger has to balance charge, and doesn't take too long to balance them upto 3.8v.

[Jonathon Gillham 3053]

On 11/30/2019 at 9:31 AM, Oneball1971 said:

Jumping in on this very informative Lipo discussion: C Rating, what's the average number rating are we looking for?

I only use (buy, but then you know, they get used for everything) my lipos for racing so mine all have 100C or more continuous.  In theory.  C ratings aren't really a science on most batteries, more a marketing thing as there doesn't appear to be a standard for it even though, you know science, there should be.  This is where the brand comes in and that old chestnut - you get what you pay for.

My Orion lipos have never let me down, they always provide plenty of power throughout the full 6 min race.  They are rated either 110C or 120C.  Others have found that the Gens Ace which are rated around 50C are as good, but then they are a reputable brand as well.  As @Wooders28 explained above, even a 5000mah at 25C is more than most motors will draw anyway, but the problem is the inflated values that manufacturers give.  I have also read (on the internet, so it must be true, but you know...) that the current technology means that the claimed 100C + rates are impossible.  I don't know if thats true or not as I'm not a scientist.  Give me 2 more beers and I'll have an opinion though.

I have experienced when a battery can't provide the power as well.  I had a programmable brushless set up in a TT02B and on NiMH (about 12C - 15C) it reached a point (quickly) where no matter what I did to the programming the car didn't get any faster.  Then I put a decent lipo (Racing Performer 5800mah, 100C) and the thing was a rocketship.  The battery does make a difference, but only if your motor is asking more than a "worse" one can supply.

I would get as high as you can afford and think you'll need (if you're running a silvercan then you don't need much, but mod motors with programmable ESC will need a lot) but take that with a grain of salt and buy reputable brands, eg that 50C Gens Ace will be better than a 110C no-name in the bargain bin.

 

On 11/30/2019 at 9:59 AM, OOZZEE said:

the one bit of information that I struggle to find is what amperage should we discharge them at to go into storage mode, set at the lowest rating a 5000mah battery can take 18 hours to discharge to storage( from full charge ) I am using an Ultra Power UP6+ and an ISDT Q6 pro with an independent power supply. any advise appreciated.

 

 

 

I have the same problem as my chargers only have a 1A discharge rate but a few minutes running in the backyard will get them to storage voltage easily.  

[gt6++ 23]

I changed over to lipo just because I barely get out to run the my cars and it seemed that every time my NIMH batteries would never hold a charge from sitting for so long. 

From what I understood at the time was since lipo doesn't have any "charge memory"  there was less loss over storage time.

Otherwise I much prefer the ease and peace of mind of storing and charging NIMH.   

[Wooders28 2947]

15 hours ago, gt6++ said:

From what I understood at the time was since lipo doesn't have any "charge memory"  there was less loss over storage time.

When mine are in storage charge, they loose a little bit, but not a great deal over 6 months, (some have been sat longer than that, so I'll need to dig those out and check the voltages)

What you shouldn't do, is leave a Lipo charged, I sometimes charge one the night before ,if I'm racing early the next day, but that's about as long as I'll leave them.

[nbTMM 411]

C ratings are marketing bs for the most part. All they really ascertain is that one pack with a certain C rating from a particular manufacturer isn't as good as another pack with a higher C rating from the same manufacturer. 
In the following link is some real world testing, showing that some batteries marketed as 70-100C can't even do 35C with a reasonable voltage drop, while the best packs around can do about 50C max.
Funny that the four packs that passed the 50C test were rated 65-75C, and most of the packs rated >75C performed very poorly. Goes to show that most of the vendors trying to sell you a >75C pack either have no idea what they are selling or figure that they can pull the wool over the eyes of their customers.
https://www.rcgroups.com/forums/showpost.php?p=42381735&postcount=7579

Turnigy packs seem to do consistently well in various 3rd party testing, and their Graphene packs are top tier in the above test. Venom and Gens Ace seem like good quality batteries from what I've seen, but are a little overpriced (at least in my part of the world). Maxamps and SMC are bottom tier rubbish with a lot of marketing hype - avoid at all costs.

That said, unless you run a fairly 'hot' motor or are a super competitive racer, you don't need much C from your battery.
Most RTR setups are lucky to demand more than 20C. That's why the more powerful RTR cars move to more cells and lower kv motors - it allows the manufacturers to put more power into a car without requiring more current from the batteries. So customers can put trash batteries in them without taking a large hit to performance or puffing batteries.

On the other hand if you are running a 7000kV motor and 120A esc in your 1/10 touring car then a quality battery capable of 30C+ may help.

A pack being able to perform at extreme levels, even if your car doesn't need it to, also speaks volumes for the ability of the manufacturer to source quality cells and manufacture the packs properly, which could lead to longer lasting and safer packs. 

[Falcon#5 453]

For racing I used to think the higher the C rating the better.

All my LiPo are the same brand. Have about 15 or so of them in various mAh and C.

What I found though is the lower C rating batteries were smoother to drive and less snappy than the higher ones.

So stopped buying the 100C+ and prefer to run around the 50C mark.

I have some old ones that are 30C and have raced and bashed with them no probs.

If you are competitive, racing high kV motors, on a high grip track, then the higher C rating may help with your track times.

Otherwise save your money and buy the lower C rated LiPo.