[Milsurplus] RAK-RAL

Sat Oct 21 14:32:12 EDT 2023

Hi

If you head off shopping for affordable LiFePO4 batteries, be aware that some of them are not happy when run in series. You can parallel them just fine, just on 12+12 = 24 sort of stuff. 

Typical low end prices seem to be around the $250 to $300 range for 100AH / 12V retail versions. Various surplus alternatives exist. The surplus ones may or (more likely) may not come with a functioning BMS. Once you buy one of those, the cost of the surplus approach may or may not be as attractive. 

With lead acid you get about 50% of the “label capacity” in usable AH. Your 100AH battery gives you 50AH usable. Most LiFePO4’s are up in the 100% range. Your $250 100AH retail version is effectively the same as a pair of 100AH lead acid’s. 

Yes, you will need two 12V batteries to get to 24V. Doing some sort of custom 24 V stack from surplus parts still isn’t out of the running. You only need one BMS for that stack. 

At 24V / 1.5A for your filaments, a 24V 100AH setup is going to run over 60 hours. Toss in a transmitter that on for some percentage of the time and that will indeed drop. At 4 hours a day, you are past 2 weeks of operation in the “receive only” mode. Yes, the filament batteries are the “big deal”. 

Bob

> On Oct 21, 2023, at 2:12 PM, Bill Cromwell <wrcromwell at gmail.com> wrote:
> 
> Hi Bob,
> 
> The weak part of using battery power with the tube radios is the heaters. I use "12 Volt"
> SLAB batteries with two in series on the heaters of unmodified R-23 or BC variants. I get a few hours of operation between recharges. Practical. I get several weeks from my 90 Volt packs in daily operation. Practical. If I modify the screen supply those radios will operate on less than 45 Volts B+. Unmodified at 90 Volts the R-23 I am still using draws a bit less than 15 mA.
> 
> I would encourage anybody interested in battery operation to give it a go. I am still using SLABs because I am already invested in them. As they age out I intend to acquire the LiFePO4 battery packs. I would suggest anybody who wants to get started to start with those.
> 
> 73,
> 
> Bill  KU8H
> 
>> On Oct 21, 2023, at 12:23 PM, Bob Camp <kb8tq at n1k.org> wrote:
>> 
>> Hi
>> 
>> Lets’s see … hmmm …. surplus 3.6V LiFePO4 cells are all over the place. Wire up a hundred (gulp …) of them and you have a 360V plate supply. Toss in a few more and you are at 400 or 450. You won’t have a BMS (a 500V capable BMS is crazy expensive). You charge them each up and then interconnect them (even bigger gulp ….). Fortunately they seem to have very good shelf life. They also have a pretty flat discharge curve so the voltage doesn’t droop very fast at all. 
>> 
>> Even the little guys are in the “couple of amp hours” range. If you are running (say) 100 to 200 ma key down, that’s a *lot* of transmit time. Size wise, the filament battery likely takes up more room. At  < 50 cents a cell, not a totally insane way to get the job done cost wise. 
>> 
>> Yes, the whole “interconnect them” thing would take more than a bit of thinking in order to do it safely. 
>> 
>> Bob
>> 
>>> On Oct 21, 2023, at 10:38 AM, Bill Cromwell <wrcromwell at gmail.com> wrote:
>>> 
>>> Hi Charlie,
>>> 
>>> It has been my pleasure to be on the air when a power outage landed here.I have been moving to battery operation here full time. I have been using batteries for tube receivers for some time with a series stack of 9-Volt "transistor" batteries for ~90 Volts B+ with my R23 and it's six tubes. I do not yet have a battery supply for tube transmitters of more than one or two watts. I have not applied this to my RAK but I know what I will have to do. I see no reason why it will not give good service.
>>> 
>>> My motivation was the increased isolation from the AC power line and the noise that can be conducted into the receiver. It really does help. Operation without the electric utility is just icing on the cake.
>>> 
>>> 73,
>>> 
>>> Bill  KU8H
>>> 
>>>>> On Oct 20, 2023, at 8:04 PM, CL in NC via Milsurplus <milsurplus at mailman.qth.net> wrote:
>>>> 
>>>> I too have both the RAK and RAL receivers up an running.  The RAK on a homebrew supply, the RAL on the proper AC supply.  I cut my ham radio teeth on a regen receiver in the '60's, and there is something to be said when you start there and slowly work up to something more modern.  While I can't use the RAK during a power outage, I do have a couple VLF rigs that run on batteries, and I am probably the only person that looks forward to the power going out.  If the outage is big enough, all the noise on the VLF bands goes away, and you can hear some things like NDB's you could only hear at night, BC stations hundreds of miles away, and other mysterious sigs, but the lack of racket is amazing.
>>>> 
>>>> Charlie, W4MEC in NC
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