LiPo Battery 20C vs 1C...and Do it yourself Protection PCB

[BournEE]

Dave did a vBlog on some lipo batteries he purchased from HobbyKing (the 5000 maH one). They had no PCB protection attached and they had a charge rating of 20C.

I loved the price of those batteries and was considering using them in a project but had second thoughts about doing my own protection PCB.

And then I read an educational article on Adafruit stating:

RC lithium ion batteries are meant for radio controlled cars, planes, UAVs, quad copters, etc. They are meant to give a lot of power at once, up to 20C and are designed to never 'cut off' so that the battery will be damaged instead of having the plane fall out of the sky.

Now this made me nervous about using the 20C in a small electronics project.

I am now considering buying the battery for $14.00 (1C with Protection PCB) instead of going the more cost effective route at $4.00 (20C and do-it-yourself protection ($4-$5))

Can anyone help with these two question:
1) Is 1C much better than 20C when dealing with hobby circuit projects?
2) Is it a bad idea to do your own protection and solder it onto the LiPo tabs?

you might save $5.00 between the two options.

Thank you.

[NiHaoMike]

It's often possible to reuse the protection board out of a dead cell phone battery. They'll work with any size battery of the correct voltage, although current would be limited to 1-2A or so.

[peter.mitchell]

You can purchase pre-made protection boards from a lot of places, http://www.ebay.com.au/itm/271069449737 being one example, generally they are fine to use, just note the maximum charge current and discharge current, as these will limit how much your circuitry can do.

Soldering to the tabs on a LiPo battery is fine, provided you do it very quickly, as the tabs run down into the cell, thus heating the cell. With bigger cells and thus bigger tabs you can usually drill a small hole, and use a bolt+nut+connector instead of soldering too.

[T4P]

I think the tabs were meant to be spot welded 
Or you could just simply bolt and nut it 

[BournEE]

Thats great guys...what about using the higher "C" charge values. Is it better to stick with a lower C or does this not have any issues.

[NiHaoMike]

Use pliers (and a rubber band) as a heatsink to prevent damage to the battery.

[SamD]

The tabs are in place for a specific reason: allowing the end-user to connect to the battery(s) via soldering without the need of a spot welder; I.E., the tabs are spot welded at the factory. Take a look at standard nicad cells; they're available with or without solder tabs- again, for this reason.

If you're unsure about the charging protocols related to Li-ion batteries, don't mess around with them- I say this not to sound peevish or otherwise but to caution you about the very real hazards of mistreating this battery chemistry. The stories of people burning down their houses, cars, etc. are very real. It's a sobering sight seeing a large pack catch fire and burn brightly.

[cwalex]

My experience with soldering hard to solder tabs on various things has been from virtually impossible with rosin based flux to doable and even easy with more aggressive acid based fluxes. The way I have had success is with a wide 2.4mm or larger tin tinned with 63/37 solder and a mild acid flux. Make sure you apply plenty of flux and use the flat side of the chisel tip to get really good surface area contact, make sure you can see that it has wetted properly and not balled up at all. You can then thoroughly clean the flux off (important) and it is easy to solder to from there. (I'm an amateur at this!!!, so you can do it too).

I would never use any acid based solder on a PCB though. OK maybe I would but I would thoroughly clean it...

Good luck

[Things]

I'm working on a DIY protection PCB for 3 6s5Ah packs in parallel, and let me just say, if you're looking to DIY a protection PCB, I'd highly recommend using a pre-made IC from someone like linear tech or TI to do your voltage monitoring, at least if you're using over 3 cells or so.

Designing your own circuit to measure individual cell voltage of a pack that's also powering the same circuitry turns out to be a huge pain due to isolation.

[peter.mitchell]

Thats great guys...what about using the higher "C" charge values. Is it better to stick with a lower C or does this not have any issues.

Generally, if you don't care about how long it takes to charge, so long as it isn't prohibitive, stick to 0.5C-1C, an hour or two isn't really that long of a charge time for anything I can think of.

My experience with soldering hard to solder tabs on various things has been from virtually impossible with rosin based flux to doable and even easy with more aggressive acid based fluxes.

...

Good luck

On packs with big tabs/hard to solder tabs, i usually just clean em up with some sand paper, then contact cleaner, heat-sink with a pair of pliers, have my tip very hot with a bit of solder on it, tin the tab starting with the most protruding edge as quickly as possible so the tab doesn't heat into the cell, allow to cool, then solder to the tinned section (should be very easy).

[cwalex]

Thats great guys...what about using the higher "C" charge values. Is it better to stick with a lower C or does this not have any issues.

My experience with soldering hard to solder tabs on various things has been from virtually impossible with rosin based flux to doable and even easy with more aggressive acid based fluxes.

...

Good luck

On packs with big tabs/hard to solder tabs, i usually just clean em up with some sand paper, then contact cleaner, heat-sink with a pair of pliers, have my tip very hot with a bit of solder on it, tin the tab starting with the most protruding edge as quickly as possible so the tab doesn't heat into the cell, allow to cool, then solder to the tinned section (should be very easy).

ahh, Sorry I forgot to mention ruffing up the tab with emery or or other rough material, I still found I needed a more aggessive flux on many occasions though. My technique is likely not as good as yours  . The JBC station has helped a LOT though!

[peter.mitchell]

If you're doing a bunch of cells at once, eg, making a pack of 10+ cells or getting ready to assemble, by the time you're done with tinning of the last one the first one is usually cool enough to solder, I don't like heating up cells too much so I try be quick and only put as much solder on as needed when tinning, otherwise you spend too much time on the tab and heat it too much.

ahh, Sorry I forgot to mention ruffing up the tab with emery or or other rough material, I still found I needed a more aggessive flux on many occasions though. My technique is likely not as good as yours  . The JBC station has helped a LOT though!

I don't usually need aggressive flux, but hey, maybe I just get lucky, and as for my technique being good, it's probably overkill, but hey it works for me so why the heck not?

[DarkPrince]

Thats great guys...what about using the higher "C" charge values. Is it better to stick with a lower C or does this not have any issues.

From what I understand the general rule of thumb is a charge rate always of 1C (unless the datasheet/manufacturer states it explicitly allowing higher rates). Higher rates I'd believe increase risk of a critical failure if not handled properly.

[peter.mitchell]

From what I understand the general rule of thumb is a charge rate always of 1C (unless the datasheet/manufacturer states it explicitly allowing higher rates). Higher rates I'd believe increase risk of a critical failure if not handled properly.

In smaller capacity batteries (200mah-1000mah range) you find a lot that the manufacturer states 0.5C, so i use that for safety, plus, the lower the charge rate the easier/cheaper the charging circuitry.

[DarkPrince]

From what I understand the general rule of thumb is a charge rate always of 1C (unless the datasheet/manufacturer states it explicitly allowing higher rates). Higher rates I'd believe increase risk of a critical failure if not handled properly.

In smaller capacity batteries (200mah-1000mah range) you find a lot that the manufacturer states 0.5C, so i use that for safety, plus, the lower the charge rate the easier/cheaper the charging circuitry.

Yeah that makes sense especially with the lower surface area inside the cell. Good to know about the smaller cells too... only deal with > 1000mAh usually with RC but do have a tiny 1-cell 400mAh (from memory) cell. Will consider for next charge.