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Rolling your own LiFePO4


Tom Visser

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Here is my first attempt at making a small LiFePO4 battery pack.

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The parts shown are:

$10.95 Pelican 1010 Mico Case

$31.60 (4x) LiFePO4 26650 3400mAh cells

$6.45 PCB-LFP12.8V2A Protection Circuit Module

$31.95 H01280007-US-D1 LiFePO4 12.8V 0.7A Charger

$7.04 (8x) Keystone 87 C Battery Holders

some solder, some hookup wire, glue, and a spare 2.5mm female jack

Total cost was under $90. For a 3.2Ah battery pack, this may not seem like a great deal. If you take out the cost of the charger, it is around $60. A Sony NP-F970 is $103 from B&H and is 6300mAh @ 7.2V, so these batteries probably have about the same power, only the custom pack I just built operates at about twice the voltage... somewhere in the neighborhood of 14 to 15V+ depending on the charge status.

You cannot operate rechargeable lithium batteries directly, otherwise you risk over discharging them and permanently ruining the cell. The PCB provides a buffer between the batteries and your load, so that it prevents the cells from becoming catastrophically discharged. They also provide the function of preventing overcharging in multi-cell packs... so that a battery specific smart charger can be used and the PCB will monitor the voltage of individual cells and prevent any single cell from becoming overcharged.

The other type of commercially available protection circuit is called the CMB or charge management board. The CMB has some advantages, it allows the cells to be charged and discharged simultaneously. You can use cheaper "dumb" DC chargers, as the board itself will directly manage charge voltages. Often times they will have cell balancing and fuel gauge features, although this is not a feature specific to the CMB as some PCBs also have this feature. The only disadvantage would be cost and size.

Presumably the real value of using LiFePO4 is long term costs as supposedly they can be used for a much larger number of charge/discharge cycles. There are some other advantages such as safety, as they do not explode under certain conditions that could cause Lithium Ion chemistries to fantastically combust.

I'm charging my pack right now. It wouldn't pass DC out the socket, that is either because the batteries were shipped without a significant charge (I hope) and the PCB was simply doing its job and cutting off the discharge voltage or I blew up the PCB when I forgot to insulate the circuit board as it sat underneath the cells :(

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Ok, this is mildly frustrating. The pack will power up a Lectro D4T, but it will not power up my Zaxcom Micplexer and 2 QRX. I tried connecting directly to a single QRX, and it still wouldn't power up. The QRX has a habit of blowing fuses on my Nagra VI if I forget to power them off before starting up the power sequence next time and those are rated at 500mA (now up to 650mA actually). The D4T is an energy hog itself, so don't really understand why this is happening. The PCB is rated for 2A output. Maybe I have to buy a bigger PCB, I know the batteries themselves are rated for 16.5A rate. I guess I'll try ordering a PCM that is rated for higher output, but I would have though that 2A was plenty. Maybe I did damage the PCB in my mistake hooking it up initially... Anyways, I'll time how long I can run the D4T, and should give me a good estimate of real world capacity.

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Neat idea, to use a small pelicase for that. What's the purpose? For in your bag?

Yes, basically just need to power my wireless. I don't need super high capacities, as I'm pretty happy with the 14Ah battery from Nagra, but wanted something that could last a day powering a couple of wireless devices as you can see in my picture.

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Nice work. To test if it's the PCB I guess you could take the output of your cells straight to your QRX (through a fuse or circuit breaker of course). It looks like the PCB's I see on eBay all the time, and I've had a couple duds. (I've been making li-ion batteries for a while).

Love the little pelican case!

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D4T went for about 7 hours or so on a charge, not too shabby for a device that draws a lot of power. Now if I could just crack the QRX challenge... I'm not willing to spend overnight freight as I'm flying out for work on Friday, but will renew my attention to this project in another week or so, and probably work on something a bit more elegant / space efficient than the Pelican. I'm digging the C-battery style clips. You don't have to solder tabs onto the cells and makes battery swaps, either for routine maintenance or even in-the-field battery changes possible.

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  • 2 weeks later...

Here's a little update, replaced the other PCB, which honestly, I think I damaged during the initial installation, with this unit, which is more or less a similar type of board, except it is rated for 7A discharge limit. My Lectro D4T, Zaxcom MicPlexer, and 2 Zaxcom QIFB are probably only drawing about 1A while running, perhaps a momentary higher level surge on initial powerup. Everything is working fine with this PCB, keeping fingers crossed that I get a half day runtime out of the pack. It was a couple dollars more expensive than the original board.

http://www.batteryspace.com/pcbprotectioncircuitmodulefor4cells128vlifepo3batterypackat7aimit.aspx

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Here's a little update, replaced the other PCB, which honestly, I think I damaged during the initial installation, with this unit, which is more or less a similar type of board, except it is rated for 7A discharge limit. My Lectro D4T, Zaxcom MicPlexer, and 2 Zaxcom QIFB are probably only drawing about 1A while running, perhaps a momentary higher level surge on initial powerup. Everything is working fine with this PCB, keeping fingers crossed that I get a half day runtime out of the pack. It was a couple dollars more expensive than the original board.

http://www.batterysp...ckat7aimit.aspx

4392.jpg

Tom, did you source everything from BatterySpace? If you could, I'd like to see where you placed everything in the Pelican box. I'm pretty handy and love the idea of rolling my own battery packs.

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Tom, did you source everything from BatterySpace? If you could, I'd like to see where you placed everything in the Pelican box. I'm pretty handy and love the idea of rolling my own battery packs.

All the battery components were from Battery Space. The C-cell holders were from Mouser. The Pelican, I already had.

It's sort of a shame that Pelican didn't make an exact sized case that was a bit thinner, as it is much thicker than is really necessary for this application. The way the cells barely fit in the case, makes a relatively large hollow space under the cells where you can store the PCB circuit.

The solder pads on the PCB include battery+, battery-, plug+, plug-, B1, B2, and B3. The "B" pads are leads between the 4 batteries and how the circuit determines individual cell cut-off voltages.

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I was wondering how you insulated the PCB. Thanks, this helps a lot.

For the AC charger, did you hack the additional clips that came with the charger to make the inside hook up? (I'm talking about the black barrel jack that goes from the outside of the case and wires to the PCB by the look of it)

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I was wondering how you insulated the PCB. Thanks, this helps a lot.

For the AC charger, did you hack the additional clips that came with the charger to make the inside hook up? (I'm talking about the black barrel jack that goes from the outside of the case and wires to the PCB by the look of it)

Yes, that's correct. If I do a version 2, it will be either the weather sealed Switchcraft threaded jack or the "Trailtech" waterproof locking connector that Batteryspace sells.

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Hey Tom, and anyone interested, i have been using these batteries for the past year,

http://www.sales-battery.com/External_laptop_battery.html

They power my bag with a 788t, 2 Lectro SR and a Sennheiser G3 (with battery eliminator) for anything between 80% and a full day.

They run at 12, 16 and 19v. Plus a usb out to charge your phone. And for the price they come with a charger each.

They are very handy, I even use them on the cart as a UPS kinda power when i know i have access to power but don't want a surprise cut.

And in the bag they are very light and slim too.

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Hey Tom, and anyone interested, i have been using these batteries for the past year,

http://www.sales-bat...op_battery.html

They power my bag with a 788t, 2 Lectro SR and a Sennheiser G3 (with battery eliminator) for anything between 80% and a full day.

They run at 12, 16 and 19v. Plus a usb out to charge your phone. And for the price they come with a charger each.

They are very handy, I even use them on the cart as a UPS kinda power when i know i have access to power but don't want a surprise cut.

And in the bag they are very light and slim too.

16V @ 4A, not too shabby. Is charging them a big pain in the butt?

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OK I cant believe that Im the only person to bring this up, but your tape measurer is awesome and I want one!

It was a gift from the GF. "Professional Sound" my ass... sometimes the tape measure spools out all over the floor and I have to rewind it back in by hand.

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tom, what's that sort of zaxpaq that holds your qrx100 and d4t?

thanks,v.

Zaxcom is selling a new 3 unit ZaxPaq. Contact them or your dealer to purchase. The D4 will only fit if you remove the metal insert, as of course it was not designed specifically to hold Lectro gear.

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