LiPo, the big guide thread *updated March '10* *

[Spoonmeister]

I know lipos don't like water BUT if I got a Maxamps skin kit then sealed the battery in it would it resist going pop when it got wet? (I'm talking splashed, not submerged)

[HappyLad]

I know lipos don't like water BUT if I got a Maxamps skin kit then sealed the battery in it would it resist going pop when it got wet? (I'm talking splashed, not submerged)

I'm not sure that getting LiPo's wet is a problem.....

The cells are sealed, no water is going to get into them. The only thing I can see there being a potential issue with is corrosion of the soldered tags. I've a 3 cell LiPo that ended up in sea water. I rinsed it off and let it dry out and it still works fine

[Spoonmeister]

K, cheers.

Its just I want my E-Revo to still be [almost] waterproof after I get lipo's

[Kpowell911]

thanks for the guide i learnt alot

[Tug]

been running lipos for a bit in my mlst.

stupidly left a pack plugged in overnight (but switched off) and my charger refused to recharge the pack ( low voltage)....so it had been sitting for a bit till i was told on another forum that if the pack hasnt 'swelled up' , it is possible to revive the pack by chargeing the lipo on a nimh setting at 0.1a.

had nothing to lose ( but maybe my face, nothing much lost there! ) so i gave it a try, charged it till the voltage in the pack came up to around 6.5/7v keeping an eye on it the whole time for any 'swelling' of the cells, then continued to balance charge the pack on a normal lipo setting (1300mah pack i charged it at 0.8a just to be safe), charged up/balanced as normal.

yet to try it, but i thought this might be useful info for this thread?

You might get them working again, but capacity will now drop off with every cycle.

[windmill84]

Yeah, all you need is a 2 cell LiPo cutoff.

LiPo packs are multiples of 3.7v instead of NiMH/NiCD which is 1.2v per cell.

7.4v is a 2 cell LiPo.

11.1v is a 3 cell LiPo.

a 6 cell LiPo would be 22.2v and be absolutely massive in terms of size, it would be a big pack for a plane.

so out of a 7.4V lipo battery you only get to use 1.4 of the volts because each cell cant go lower than 3V?? is that right?

it just doesnt sound like you get to use much of the battery. how long a run time will you get out of 1.4V then on average? it sounds like you'd only get about 5 mins if that!

[HootMaRoot]

so out of a 7.4V lipo battery you only get to use 1.4 of the volts because each cell cant go lower than 3V?? is that right?

it just doesnt sound like you get to use much of the battery. how long a run time will you get out of 1.4V then on average? it sounds like you'd only get about 5 mins if that!

you get a lot longer run times than you do from NiMh cell's

in my 1/8 TC i runn a 4000kv motor and a 4000mah batt 11.1V and get just over 30min run time but i also have the cut of set @ 3.1V/cell

[windmill84]

you get a lot longer run times than you do from NiMh cell's

in my 1/8 TC i runn a 4000kv motor and a 4000mah batt 11.1V and get just over 30min run time but i also have the cut of set @ 3.1V/cell

oh right, thats quite a good run time then. it just sounds like a waste because out of 7.4V you can only use 1.4V of them! imagine how long you could run for if you could use the whole 7.4V! they need to hurry up and find a way of letting us use all that power!

[HootMaRoot]

oh right, thats quite a good run time then. it just sounds like a waste because out of 7.4V you can only use 1.4V of them! imagine how long you could run for if you could use the whole 7.4V! they need to hurry up and find a way of letting us use all that power!

if a lipo cell drops under 3V per cell it will wreck the LiPo. in the long run lipo's are a far better kind of battery to invest in as you get longer run times and almost the same voltage output through out the run

[Garry]

7.4v is the nominal voltage for a pack, and voltage is just an expression of power. You can't mention voltage without mentioning capacity.

Without getting bogged down with C-ratings, a charged 2S pack is 8.44v, and can't be discharged below 6v. That means you've got 2.44v to play with before you'll have to stop. Now, the size of the cells determines how long you can use all that 8.44v before it starts to drop off. A 5000mAh pack can deliver twice as much drive time than a 2500mAh pack, but both will drive for the same speed. And average drive times are much better than NiMH because less energy is wasted in the form of heat, resistance etc.

Think of it this way, voltage is how hard the boxer hits you, capacity is how long he can punch you before he gets tired

[windmill84]

7.4v is the nominal voltage for a pack, and voltage is just an expression of power. You can't mention voltage without mentioning capacity.

Without getting bogged down with C-ratings, a charged 2S pack is 8.44v, and can't be discharged below 6v. That means you've got 2.44v to play with before you'll have to stop. Now, the size of the cells determines how long you can use all that 8.44v before it starts to drop off. A 5000mAh pack can deliver twice as much drive time than a 2500mAh pack, but both will drive for the same speed. And average drive times are much better than NiMH because less energy is wasted in the form of heat, resistance etc.

Think of it this way, voltage is how hard the boxer hits you, capacity is how long he can punch you before he gets tired

cheers garry, yet again another great explanation

[cbr6fs]

Seems like a few questions have come up about this lately, as LiPo's get more popular and chargers get more powerful i guess this is only going to become a more regular question.

I took pretty much every thing i've learned about parallel charging from the post listed below.

I have asked and been given the permission of the original author to repost it in this forum.

The link to the original thread is included below though and it's well worth wading through the original thread as pretty much everything about LiPo charging is covered there.

So here is Julian's post:

Hi!

I did notice that some people do not know about the advantages of charging multiple packs at the same time on only one charger, wired in parallel.

Instead, many even bother with charging in series.

Therefore, I want to make this thread.

Attention: Do not charge Nixx packs in parallel!

When does charging in parallel makes sense?

-When I have multiple packs with the same cell count.

-When I want to charge them at the same time, thus reducing overall charge time, or avoiding the hassle of starting multiple charging processes.

-When the packs have slightly different states of charge (<30%, to be safe).

-When the charger can provide the current needed for parallel charging, but not the voltage needed for series charging.

What are the advantages of parallel charging?

-No need to care about different capacities or slightly different states of charge.

-Reduced balancing times.

-Simple wiring, fits for a multitude of packs.

When does charging in series make sense?

-When I have multiple packs of the same capacity constantly wired together in series, making a bigger pack

-When the pack's state of charge is nearly identical.

-When the charger can provide the voltage needed for series charging, but not the current needed for parallel charging.

How do I wire packs in parallel?

That is very simple: Just connect every contact of one pack with the corresponding contact of the next pack.

The positive contact is connected to the positive contact, the negative contact is connected to the negative contact.

Simple, isn't it?

And the balancing contacts?

The first balancing contact is connected to the first balancing contact, the second balancing contact is connected to the second balancing contact, and so on.

One can see, that this adapter board has enough contacts to also work with 6s packs. So one board fits all pack cell counts from 1-6s. No need to build different adapters for different packs.

The board in red shrink wrap is a little difficult to solder, but there is a simple alternative:

One can easily see how the contacts are connected.

The pin row headers take the balancing plugs of the packs, and the female header takes the balancing cable coming from the charger or balancer.

Here in another nice image how it can be done:

http://www.rcgroups.....postcount=1895

One can see clearly which contact goes where.

This is another neat example:

http://www.rcgroups.....9#post10883849

Note: Long cables mean no harm, but they can in some cases mean a longer charging and balancing time.

Here one can see a harness in detail:

http://www.rcgroups.....&postcount=274

Another neat example, using real balance plugs instead of row headers:

http://www.rcgroups.....&postcount=122

http://www.rcgroups.....mentid=2254168

http://www.rcgroups.....5#post11255155

Dieter from KD-Modelltechnik presented the neatest solution I have seen so far in a german forum. The PCBs are not for sale, though. The images should be self-explanatory:

But this is not all: When one only charges with small currents <2A, it is not even necessary to connect the packs' main leads. The balancing cables can cope with this current, so just one pack's main lead has to be connected to the charger.

I have charged up to 5 slowflyer packs 2s 900mAh this way.

One can even use the provided standard adapter for parallel charging. It must only be ensured, that the contacts of all balance ports are connected in parallel. Better check with a multimeter first.

It is very convenient: Just connect all packs at once, and start charging. No need to bother with starting 5 separate charges.

One can see, that just one pack is connected to the actual charge cable. The charge current spreads out to all other packs via the balancing cables.

Here is a very neat setup from Mark:

http://www.rcgroups.....50&postcount=5

He can charge 11 packs at a time.

Note how he connected the main leads to the outer balancing contacts.

This is a very good solution, provided one always charges packs with the same cell number on a given adapter/harness.

If you want to charge with more current, wire the packs like this:

http://www.rcgroups.....7#post10909267

How is the charge current calculated?

Simply add the currents of the single packs.

Say, one wants to charge a 1Ah, a 2Ah, and a 3Ah pack together, each with 1C.

1A+2A+3A=6A.

So these packs are charged with 6A.

There may, however, be the issue, that the packs connected in parallel have a different inner resistance (IR). The older a pack, the higher the IR. This means, that such a pack will not accept the charge current as willingly as a brand-new pack with a very low IR.

Now in the hypothetical situation that one has a lazy old 5000mAh pack connected in parallel with a brand spanking new 500mAh pack, and decides to charge at 1C with 5.5Ah, the chances are good that the small pack will see more than its share of 500mA.

My advice is this:

Know your packs and their health. If you are pushing for the maximum rated charge current of the packs, be sure to connect only those in parallel that are not way off concerning age, capacity, and general health.

If you, however, slowly charge with a small current over night, I do not see a problem.

More on this subject.

Generally, when one has the time, I advise to charge LiPos as slow as possible. Let's say, you want to charge your lipos over night. In this case, there is no need to charge than at 1C or even 2C.

If you have 12h time, use it. Set the current to 1/10C.

I do this all the time. Less current means less problems, less thermal stress for the chargers and power supplys, less risk of anything malfunctioning.

Questions that might arise:

- How come this works with packs of different capacities?

This is because they are connected in parallel. This way, they will always have the same voltage. It is not possible to overcharge a single pack.

Although all pipes have different shapes and volumes, they are always filled to the same level. The same applies to the packs' voltage levels.

- What happens if I connect packs with different states of charge?

A current will flow between the packs. However, this current is not very high, even if one pack is full and the other depleted. Yet, it should be avoided to connect packs with a state of charge differing over 50%

Here is a site that explains everything in a nutshell with great diagrams:

http://sites.google.....allel-charging

Please note: A troll named "cstratton" frequently claims in this thread, that parallel charging is dangerous.

Although he has no data to back up his claims, he does neither accept the data collected by users, which suggest parallel charging is perfectly safe, nor numerous experiences by credible users, which suggest the same.

It is up to the reader to decide whom to believe.

Thanks to Julian for his permission to repost and if you found the post useful please visit the original thread and say thanks.

http://www.rcgroups....hlight=parallel

Cheers

Mark

[cbr6fs]

Couple of good vids here as well.

Cheers

Mark

[cbr6fs]

Mods,

Anyway we could make this a sticky please?

[Garry]

Yep, great thread. Pinned.

[Dave1985]

Great thread as I was one having questions about this sort of thing.

Thanks Mark for yesterdays help!

[cbr6fs]

It is a fantastic post and really helped me understand a lot on LiPo charging, so i thought copying it over would help in the future.

Thanks for stickying it Garry

No worries Dave any time.

[Nick]

Excellent thread!!

I'm going to do this for sure.

[Nick]

I found another useful topic here about balancing packs in series (rather than parallel):

http://monster.traxx...ad.php?t=498097

Mind boggling but going to try and get my head around it!

[daveTheRave]

Hi All

Having dug around the forums a bit I'm thinking about getting one of these

http://www.unitedhobbies.com/hobbyking/store/uh_viewitem.asp?idproduct=9515

Looks like great value for money.

I'm not sure if it will be compatible with my current setup though, would I need a different charger?

This is the one I have at the moment

http://www.modelsport.co.uk/?CallFunction=ShowSpecification&ItemID=32526

The maximum charger rate is 4.0A and from reading this thread it seems that to charge at 1C I would need to charge at 5.0A. Or is it possible to charge at 4.0A for longer?

I'm currently using a 3200 version of this

http://www.modelsport.co.uk/?CallFunction=Category&CategoryID=99206010&ManufacturerID=1160

with this motor and esc

http://www.modelsport.co.uk/?CallFunction=ShowSpecification&ItemID=34310

in a cat SX kit. I love it!

Would the Turnigy 5000 30C battery be ok with that motor and esc or would it be to much?

Thanks

[Garry]

That charger, ESC and motor will be fine with that battery pack (it'll charge at 4A, but just take longer than approx 1 hour to charge), but its a 3S pack, and the CAT SX was designed for 2S max, so theres not much chance of it fitting in under the upper deck.

[daveTheRave]

That charger, ESC and motor will be fine with that battery pack (it'll charge at 4A, but just take longer than approx 1 hour to charge), but its a 3S pack, and the CAT SX was designed for 2S max, so theres not much chance of it fitting in under the upper deck.

Hmm thanks for the advice Garry. I've just got my measuring stick out and it looks like the dimensions of the space in my cat sx (leaving 1.5mm clearance for the drive belt) are

140 x 49 x 24mm

the dimensions of the Turnigy 5000 30C battery are

143 x 49 x 24mm

I wonder how squashy the end of the packaging is, do you think I could get away with that 3mm lack of space, hmmmm.

Has anyone got one they could measure?

Thanks, much appreciated!

Edited February 18, 2010 by daveTheRave

[daveTheRave]

I've continued the discussion on the Turnigy 5000 pack & fitting it in my Cat here.

[TheGava]

Great thread!! Helped me loads, just this morning got my SCT running on FTX 4800 20c lipoS... Wow it moves, also charging up 5000mah nimh to see the difference!! Electric is so quiet compared to the baja... Well at least the neighbours will be happy haha

[stealthrc]

Just some questions that needs answering, where do you charge your lipo, is it safe to charge in the house, do you use lipo bag. I have used a small lipo before for my helicopter but no experience with bigger batteries.