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DIY 5Ah 64wh LiFePO4 battery tutorial

Discussion in 'Amateur Radio News' started by OH8STN, Nov 20, 2017.

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  1. OH8STN

    OH8STN Ham Member QRZ Page

    Hello Operators.
    This is the third DIY build video in the portable power for amateur radio series. In this video, we build a 5Ah 64wh LiFePO4 battery pack for field communications. The pack has 2 cells in parallel, 4 cells in series. The BMS I chose, provides 10A current draw, upgradeable to 20-50A with a simple change of BMS.

    Like it's big brother the 10Ah Headway based pack we built previously, the Genasun GV-5 MPPT Solar charge controller has been integrated, giving us simultaneous charge and discharge capabilities, on the bench with an adjustable supply, or in the field with your solar panrl of choice.

    This pack would be most interesting for those with radios like the Elecraft kx2, Yaesu FT-817, mcHF, Elecraft KX3, Yaesu FT-857, or other popular radios used in the field.

    Video url:
    73
    Julian oh8stn
    IMG_20171120_170714_904.jpg
     
    W4BDK, WM9F and KQ6XA like this.
  2. W1YW

    W1YW Ham Member QRZ Page

    Excellent tutorial Julian!
     
  3. KC8VWM

    KC8VWM Ham Member QRZ Page

    I am using a 5 AH LiFePo4 battery pack with my FT-817 and these are vastly superior to any SLA type batteries I have used in the past.

    For one thing, the first thing you will notice is the power curve as it's discharging. It maintains a higher constant voltage for around 80% of the discharge cycle. This means your rig will have almost maximum voltage available for the majority of the time you are using it. The voltage doesn't start dropping off until you are approaching the last 20% of the remaining power in the battery and the BMS will cut off the pack when it reaches 10.5 volts.

    The LiFePo4 batteries are also much lighter compared to SLA batteries making them much easier to transport for SOTA and general outdoor QRP operation.

    LiFePo4 batteries can be recharged up to 2000 times whereas most SLA batteries may only last for 150 charge cycles. In terms of shelf life a typical SLA battery is rated between 1-3 years and a LiFePo4 battery is 7-10 years. So do the math if you want to figure out which battery is the better value for your money.

    If you have a good BMS in the pack, then you don't really have any need for any solar charge controller either. Adding a solar controller in front of the BMS just means you are losing a little charging efficiency. Most BMS circuits will easily handle the 22 volt input from the majority of solar panels and safely converts it to the voltage required to charge the battery cells. Check the BMS voltage range specifications you are using for more information.

    The BMS is going to cut off the charge voltage when the battery reaches 14.4 volts regardless if the solar panel continues to provide power or not. So the BMS circuit prevents you from mistakenly overcharging the battery and this means less babysitting is required because it's all done automatically for you.

    In terms of alternative charging methods, avoid any chargers that produce "pulse" type charging methods intended to desulfate wet lead acid battery cells. This also applies to many solar controllers on the market you may also be considering. The "spikes" these pulses produce can potentially damage LiFePo4 battery cells. Besides, LiFePo4 batteries don't sulfate like wet lead acid type batteries do in the first place so pulse charging them is a pointless endeavor and serves no purpose. Pretty much any common wallwart that produces a constant voltage between 14.5 and 18 volts with a current rating between 1 - 3 amps max is most suitable for charging the battery pack shown in this video. Remember, the BMS is doing all the charge regulating the battery needs, so no special charger is going to be required. The charging source needed is simply a constant supply of voltage and current and the built in BMS does all the rest.

    I would like to take this opportunity to thank Julian, OH8STN for providing this excellent LiFePo4 battery building tutorial.
     
    K6UMA, N9PBD, AA8GK and 2 others like this.
  4. N6YFM

    N6YFM XML Subscriber QRZ Page

    One of the things that mildly bugs me about the commercial packs, like Bioenno, and this DIY project, is that the voltage is really a nominal 12, with tiny drops for the wire feeding a 100 watt transceiver. But when we run our transceivers on a benchtop Astron, we are typically getting 13.6 to 14.0, which provides a stiffer transmit.
    For example, when using SLA standard batteries, on transmit, the voltage at the rig typically drops to 11. Most of this is due to voltage drop from the feed wires. You could solve this with AWG 2 Gauge battery jumper cable, but have you ever tried to fit those wires into the 4-pin molex connector on the back of your transceiver? Point made. One conductor is almost as large as the entire connector shell :)

    I wonder, hoping for comments, what people think about using 5 cells in series instead of 4, which should yield approx 14 or 15 volts, and then how hard it mightbe to design a BMS schematic change for the 5 cells in series, and how hard it might be to adjust or re-design a simple PWM Solar Charge Controller for theslightly higher battery voltage? We would also need at least one high current diode in series to keep the battery output below 14.5 volts.

    This would provide an excellent LFP battery pack that matches the voltage at the back of the transceiver that we typically get from a bench top power supply. (Our transceivers really do better on 14 than on 11 volts, and none of these battery backup power projects ever take that
    into account (start with 12v, forget to think about voltage drop in cables, voltage at back of rig is marginal at best). Most of us don't want to carry AWG 2 gauge cable between the battery and the transceiver. My tests with the typical small cable (factory supplied) on a transceiver
    power cord showed almost 3/4 of a volt drop on transmit.

    Yes, we would then have a non-standard charge controller, a non-standard BMS circuit board, and a non-standard auto battery. But we don't plan to use a DIY Ham project for an automobile, right?
    Let's be honest, we are trying to make a special purpose battery pack for using ham gear in the field. And those transceivers,
    power meters, tuners, and other accessories are all running around 13 to 14 volts in your home shack with an Astron.

    Comments, ideas? Maybe the low voltage is not a real problem on some brands of equipment, so 12 volt systems/batteries are good enough?

    Neal
    N6YFM
     
    Last edited: Nov 21, 2017
    KB3GWQ likes this.
  5. KW4HQ

    KW4HQ Ham Member QRZ Page

    Would the power supply in the shack charge these with powerpoles? Mine puts out 14.4v/25 amps. Wouldn't the bms cut it off safely?
     
  6. KC8VWM

    KC8VWM Ham Member QRZ Page

    No because 25 amps is far too much current.

    1 amp is sufficient.

    2 amps is ideal.

    3 amps is the maximum current the battery design can safely handle.
     
    OH8STN likes this.
  7. KC8VWM

    KC8VWM Ham Member QRZ Page

    12.8 is the nominal working voltage and it remains that way for approx. 80% of the discharge cycle. This 5 Ah battery pack is not suitable to operate a 100 watt rig that would require 20-22 amps while transmitting.
     
    KI5WW likes this.
  8. AG6ZZ

    AG6ZZ Ham Member QRZ Page

    A step up voltage circuit, which outputs a nominal voltage around 13.8V (plus or minus a little) should fix the voltage problem.
     
  9. K2TL

    K2TL Ham Member QRZ Page

  10. K6BRN

    K6BRN Premium Subscriber QRZ Page

    Charles (KC8VWM):

    N6YFM is quite correct. Bioenno specs their LiFePo batteries at 12 VDC working voltage, which would includes the drop induced by their charge/discharge controller and is NOT the native battery rest voltage.

    This will mean reduced output from HF rigs designed for 13.8-14V nominal - perhaps as much as 25% for the more sensitive base rigs. I would expect less output loss in mobile rigs optimized for lower input voltages.

    On an interesting note, the Bioenno 5 Amp-Hr LiFePo pack is rated at 9 amps discharge rate. Not 1, 2 or 3 amps. Their light weight, high energy density, flat discharge curve and deep cycle capability do make them very desirable for portable ops. But for full power HF rigs, the cost equation still favors a nice, reliable and light Honda EU1000is genertor, at 29 lbs/800-1000 watts output (pretty much forever)

    1200 Watt-Hr. LiFePo battery cost: $862 Weight: 28.2lbs

    900 Watt (continuous) Honda EU100ois generator: 29 lbs (runs 3.8 hours on 0.6 gal. of gas at rated load - 3,420 watt-hours, or 8+ hours at about half load)

    I do hope the cost will come down over time - it would mean a BIG boost to home solar effectiveness.

    DC to DC boost converters are notorious EMI generators and are not particularly efficient (80-90%). So if the charge controller is 90% efficient and the boot converter is 90% efficient, suddenly we are down to 0.9 x 0.9 = 81% efficiency - and that's the best case. It's best to avoid these in pure battery or battery/solar systems, if at all possible.

    Contrary to many claims, it seems that some LiFePo batteries can and do melt down with dangerous results: https://www.amazon.com/Battery-Tend...r&reviewerType=all_reviews#reviews-filter-bar

    Best Regards,

    Brian - K6BRN
     
    KC8VWM likes this.
  11. AA8GK

    AA8GK Ham Member QRZ Page

    Julian, you are a LiFePO4 MAN GOD!!!!! 72!!!!
     
  12. KK6QMS

    KK6QMS XML Subscriber QRZ Page

    Cost of materials? I have a Deltran BatteryTender brand LiFePo batt that I LOVE. BTL14A240C
    Was about $110 plus a charger- not cheap- but the weight savings and characteristics are great. My KX2 goes for days on it.
     
    N9PBD likes this.
  13. K6BRN

    K6BRN Premium Subscriber QRZ Page

    Peter:

    You might want to be a little careful with your Deltran/Batter Tender LiFePo battery. On occasion, they do burn up.

    https://www.amazon.com/Battery-Tend...r&reviewerType=all_reviews#reviews-filter-bar

    And yours comes with a warning:

    "MADE FOR ENGINE STARTING APPLICATIONS, NOT INTENDED FOR DEEP CYCLE APPLICATIONS"

    Not really suitable for ham field ops that require deep discharge (even 50%)

    Bioenno might be a little safer and more appropriate - designed for deep discharge:

    https://www.bioennopower.com/collec.../products/12v-15ah-lfp-battery-abs-blf-1215as

    Its a bit more capacity (15 vs. 14 amp-hrs.) and a bit more expensive ($150) but built specifically for deep discharge apps.

    Brian - K6BRN
     
    N5RES likes this.
  14. KK6QMS

    KK6QMS XML Subscriber QRZ Page

    That guy had it in an old motorcycle when it burned up. In fact all of the critical reviews/failures are from motorcycle users. Sounds like it was over charged/heated not over-taxed- just based on the idea his generator should be adequate to handle the current needs of the bike in operation. Had mine over 2 years and run it down to 9V a few times when I used to take my 857 /p. Has worked flawlessly and I just love it.
    In any event good info and I appreciate it.
    Clifford

     
  15. ZL2SCI

    ZL2SCI Ham Member QRZ Page

    Awesome thank you
     

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