Need help for a portable power pack

MSR01MSR01 Registered Users Posts: 1
I am new to solar and found this forum while researching for the portable power pack I want to build for my ham radio.  It should be as light as possible since I want to carry it in my backpack with the radio and also take a beating on what it means about batteries discharge and life span.  I also want to use solar power to recharge and maximize the utilization time.

The LiFePO seems quite attractive for that but I am very confused by the controller/charger.   My radio can put up to 100W RF output and for that it needs at least 20A @ 13.8VDC.   I normally only need that much juice for 30% of the time (only while transmitting).  For receiving it needs much less power. However, I also want to hook other stuff to the power pack such as my tablet and my phone to recharge them.  Both use very few power since they take just 5VDC @ ~2A (typical USB port).

I found several brands of batteries and  charger controllers but got stuck on this part.   I already have the solar panel, which is an Enerplex Commandr 20, two of them, that can put 20W, 19VDC @~1.1A each.  I am aware they will not be able to recharge the batteries while I'm using the radio but should at least extend the time I can use it if using full power.  If able to use the radio's minimum power (QRP @ 5 to 10W) things will be much better.    I'd like to be able to use the radio for three to four hours.  With the solar panels helping I would expect to add at least one more hour to that.  I believe the controller/charger must have what is called pass-through capability so the panels can provide energy to the battery while the radio is draining it?

My (initial) questions are:
1) do I have to use a controller/charger specially made for LiFePO batteries? - I read about some programmable ones.  I'm not looking for anything very sophisticated.
2) what should be the charger/controller's capacity?  At least 25A on the load port?
3) I read about MPPT types.  Are they worth the extra price?
4) I also read about battery packs with embedded balancing circuits. Do the charger/controllers have to be compatible with those?
5) if hes, how to know that?
6) what should be the ideal battery's capacity?
7) any brands and models you recommend?

I asked quite a bit of questions. Anything I forgot to consider?

Thanks much in advance!


  • BB.BB. Super Moderators, Administrators Posts: 30,760 admin
    You might want to look at Genasun for a charge controller:

    I would suggest a PWM controller (if you find one that meets your needs) unless you really need that extra 10-30% power or so in sub freezing weather--Or if you will, for example, have your station setup in the shade and the panels 20+ feet away in the sun (you put two or more panels in series/parallel for higher Vmp-array voltage and use the MPPT controller to take the high voltage/low current of the array and efficiently down convert to the low voltage/high current for charging the battery bank). MPPT controllers, in general, can have a computer interface (charging parameters, logs, etc. if you are interested).

    If you go with PWM charge controller, you do not need a sophisticated charging controller--LiFePO4 batteries just usually need a set voltage for charging (no temperature compensation).

    You can manually balance the cells--Probably good enough for your needs (short trips, re-balance at home if/when needed--Should not be a task that needs to be done very often--Save weight and complexity--Auto Balancing is more of interest for banks that are in 24 hours x 7 day service where you want to "forget" managing the bank for the next few years).

    You would need a larger charge controller that have 25+ amp load ports (Low Voltage Disconnect)--I would suggest using a small voltage monitor/alarm instead to let you know when to turn off the radio/loads (system will generally be attended?). Save weight and cubic inches.

    Say you want to use 60% of battery capacity (80% to 20% of capacity during typical cycling)--20 Amp load 30% of time, 1 amp 70% of time, for 4 hours, or ~4.97 amp average load, for 4 hours:
    • (20 amps * 0.30) + (1 amp * 0.70) = 12.7 Amps average
    • 12.7 amps * 4 hours * 1/0.60 battery capacity = ~85 Amp*Hour battery capacity minimum.
    Of course, there is running "better antenna" (directional antenna with higher gain on beam axis) and/or running at 1/2 power (~1/2 SU or 3 db drop in transmit power) to cut your battery bank/power requirements by ~1/2.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    There also are several threads here about LiFePO4 batteries.... very informative...  ps they are a long read
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • VicVic Solar Expert Posts: 3,017 ✭✭✭✭

    Hi MSR,

    These types of questions have come up,  here,  before.

    Even with Lithium batteries,  it seems quite possible that you are expecting to use quite a lot of power from the batteries,  with relatively limited recharge capability during your outings.

    Is it possible,  that you should consider  using a different radio  --  going to a QRP? radio?

    Many 100 watt transceivers waste a lot of power when their power is turned down to QRP values.  If you were to use a real QRP radio,  it will often be much,  much more efficient,  particularly if it is a CW-only rig.

    Just my drive-by Post    ...  errrr  ah   ...  Comment.  73   GL,  Vic

    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • oil pan 4oil pan 4 Solar Expert Posts: 766 ✭✭✭✭
    edited May 2016 #5
    I run the genasun on my 4 cell LiFePO4 pack.

    I have also considered running a 15 amp Morningstar MPPT set for the following:
    Gel battery setting (14.2V max) 
    No equalization
    Temperature compensation by passed/disabled with a 10.1Kohm resistor on the remote temperature sense terminals.

    You don't have to have a LiFePO4 specific charge controller but you do need one with enough features to put it in a LiFePO4 acceptable charging mode.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

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