[Elecraft] Charging LiFePO4 Batteries

[Wes Stewart]

Despite your earlier response, allow me to offer a suggestion.  I've written 
about this too before but I'll summarize again.  I used for a number of years a 
HB analog charger on a 90 AH AGM battery to run most of my station.  This was 
built using an Astron 35M power supply for the raw DC, heatsink and series pass 
transistors.  The regulator board was removed and substituted by a modified A&A 
Engineering "smart charger" board.  I think these are obsolete now, but the 
heart of them is the uC3906 IC.  I set mine up for a bulk charge rate of 25A 
(~C/4).  I'm not going to design it for you but I imagine the IC can do the 
trick for this battery chemistry.

  On 7/12/2016 12:57 PM, Clay Autery wrote:
> Thanks Jim!!!
>
>
> Here is what I take from that....  Say, you have a 100+ Ah battery and a
> 10 amp max charge current (limited) on the charger.  (And assuming the
> charger meets other requirements for CC/CV voltage during CC and the
> desired Voltage during CV (trickle current cell balancing).
>
> Assuming a K3s/P3 for instance with only the 100W internal PA...
>
> During Transmit, the rig pulls anywhere up to about 15 amps or so on
> peaks (my experience).
> On receive, the rig is pulling well less than 1.5 amps...
>
> So, on receive... MOST of the time, the charger will be charging the
> battery....  and when at rest, even with the rig on say overnight (I
> seldom do this), the battery will easily reach full charge and enter CV
> cycle which is where the cell balancing happens.
>
> On a contest where the TX duty cycle is much higher.... say 50+%, The
> battery will be averaging somewhere around it's 10 Hr charge current in
> power draw...  So, for the duration of the contest (or high duty cycle
> session) the battery will remain in the CC charge cycle.
>
> At the conclusion of the high duty cycle use, the battery will continue
> in CC until it is fully charged and thence to CV for maintenance/cell
> balance...
>
> I don't think there is going to be anything super tough about this one...
>
> IF a commercial solution doesn't present, I will proceed on the path of
> finding/building a linear supply that will provide at least the required
> voltage and trim (if necessary) it with a well-designed linear regulator
> circuit to the CC voltage required.  Add a second linear regulator that
> provides the CV voltage....  Then add a sense/feedback circuit that
> monitors the battery for the event/events that signals the need to
> switch from CC to CV or CV to CC...
>
> Seems pretty doable...  unless I am missing something...
>
>
> 73,
>
> _____________________
> Clay Autery, KY5G
> MONTAC Enterprises
> (318) 518-1389
>
> On 7/12/2016 2:16 PM, Jim Brown wrote:
>> This is what I got from Kevin.  We also spoke on the phone.
>>
>> On the phone, Kevin clarified that as long as the charger was "proper"
>> for LiFePO4 chemistry and charge current was safely limited, an
>> LiFePO4 battery will NOT be damaged if charged during discharge. His
>> only concern was that the battery might not reach full charge simply
>> because more current was being drawn than was being supplied by the
>> charger.
>>
>> SO -- the bottom line is that LiFePO4 batteries ARE suitable for use
>> as the main power source in a station where a charger is always
>> connected as long as the charger has the proper charging
>> characteristics for the LiFePO4 in use.  In general, battery life is
>> maximized if the maximum charging current is no greater than the 4-10
>> hour discharge current. For example, a 10A charger is sold by Bioenno
>> with their 40 - 100Ah batteries. Higher charging currents reduce
>> battery life.
>>
>> Kevin also said that they have taken our concerns seriously with
>> respect to RFI from chargers, and that they have begun working on
>> sourcing chargers that are RF quiet. He noted that it typically takes
>> 3-6 months to find potential candidates, evaluate them, and get them
>> in inventory. I've volunteered to evaluate them in my station for noise.
>>
>> Bioenno also works with Powerwerx, so they are generally aware of
>> connector issues. He said that they are using the larger connector as
>> standard because some of their customers need the larger connector
>> with the higher current rating.  The grey SB50 connectors used in the
>> ham world are rated for 50A.
>>
>> 73, Jim K9YC