Date
1 - 20 of 22
Q: QDX powered by 18650 LiFePO3 cells?
Jim Strohm
Hi all
Has anybody tried powering a QDX with three 18650 LiFePO3 cells? The fully charged no-load voltage is about 12.15 VDC for three in series, and a partially charged voltage around 10V. I'm thinking that a QDX built for 12V will work fine with this, but I want to see first whether anybody has tried it yet. Thanks in advance. Jim N6OTQ |
|
William Smith
Sounds like it should work, but where are you finding those voltages? I'm seeing numbers up into the 14.6V range for charging, and 12V for pretty much discharged...
toggle quoted message
Show quoted text
Not that My Good Friend Google couldn't be wrong, but I'd be nervous... 73, Willie N1JBJ On Mar 22, 2023, at 8:13 PM, Jim Strohm <jim.strohm@...> wrote: |
|
Jim Strohm
Hi Willie I got the low voltage from what I've read, and the high voltage from three "freshly" charged cells I have here. But they were charged some months ago. I'll charge them again and see. Thanks and 73 Jim N6OTQ On Wed, Mar 22, 2023 at 7:22 PM William Smith <w_smith@...> wrote: Sounds like it should work, but where are you finding those voltages? I'm seeing numbers up into the 14.6V range for charging, and 12V for pretty much discharged... |
|
I power my QCX and QDX from 3 18650 cells when portable. They last plenty long for a decently long session. My battery pack with barrel connector on the end shorted against some keys the other day so be aware.
Joshua |
|
Each cell is rated at 4.2 volts fully charged ,so 12.6v is the full charged voltage of 3 cells in series. 4 cells total to 16.8 volts. Maybe that's where the confusion came in.. You can always add a couple series diodes to drop it if concerned about that voltage. Ron On Wed, Mar 22, 2023 at 5:54 PM Joshua KJ7LVZ <joshuajayg@...> wrote: I power my QCX and QDX from 3 18650 cells when portable. They last plenty long for a decently long session. My battery pack with barrel connector on the end shorted against some keys the other day so be aware. |
|
Jim Strohm
I was thinking more about using a 12V Zener diode, which won't steal any power once the voltage falls below 12V. Plain ol' diodes will always steal 0.7V / diode. N6OTQ On Wed, Mar 22, 2023 at 8:03 PM Ronald Taylor <wa7gil@...> wrote:
|
|
But Jim, a zener will require a dropping resistor which will steal power too. I think you’re best off with a couple silicon diodes and you can put a switch across them to short them out when the battery voltage gets to an acceptable lower level and then, no more power theft. I built a diode bank on a 12 position rotary switch so I could use a 4 cell lithium ion battery (16.8v) on my QCX Minis and just switch to lower settings as the voltage drops. Switch all of them out when it gets down to where you’re comfortable working and then let them continue to drop down from there to the safe discharge level. Ron On Wed, Mar 22, 2023 at 18:06 Jim Strohm <jim.strohm@...> wrote:
|
|
Colin Kaminski
I use 3 cell LiFePO4 for remote and shop power for all my QRP-Labs products. I use a boost converter for the 50w amps.
-- Colin - K6JTH http://tangokeys.com |
|
Jim Strohm
Hi Ron I have 4 18650 cells in my smart charger and they're coming up from 4.17V to 4.20V now. I'll look in the morning, then play with a fat 12V Zener and a fat resistor -- probably 25 ohms and 10watts, but it depends on what the junk box yields. I'll play with values to get a half-amp draw from three cells, and report back. These are all brand-new cells and have only been charged once here, and the only discharge cycling is from letting them sit next to the canned Ranch Style Beans (it's a Texas thing) for a few months. 73 Jim N6OTQ On Wed, Mar 22, 2023 at 8:44 PM Ronald Taylor <wa7gil@...> wrote:
|
|
We are already playing QRP, just commit to the simplicity and use 3.
|
|
Ok Jim. And in case you don’t know, it’s not good practice to leave lithium ion cells sitting around at full charge. They should be charged before use then used and then discharged or charged as required to get them to somewhere around their nominal 3.7 volts per cell for storage. Likewise they should not be stored at their safe discharge low voltage point either. Always store them at the mid voltage range for longest life. 73….Ron On Wed, Mar 22, 2023 at 19:18 Jim Strohm <jim.strohm@...> wrote:
|
|
Look at the super efficient buck-boost power regulator chip applied on the U4b board. On Wed, Mar 22, 2023 at 10:27 PM Ronald Taylor <wa7gil@...> wrote:
|
|
The Richtek chip used on the u4b outputs 5v but the Richtek chip RT2560Q offers a Vo of 12V Joe W2JEJ
|
|
AjaiDevMalik <friendlymercurian@...>
18650 LiFePO3 also exist along with other lithium-ion batteries is same/similar shape & size, but their chemistry and electrical properties are slightly different. LiFePO3 cells have a recommended voltage of 3.2 volts, so four cells (4S) are required in series for an approx.12 volt powered supply. Whereas only three (3S) Lithium-Ion Cells with an approx. Charged voltage of 4.2 volt each are normally used. This is very confusing, coz they require different BMS to work properly.
I too experimented with these cells, but was not very pleased to work with cylindrical cells, coz they require many accessories & tools for making battery packs for gadgets. So I opted to use the high capacity rectangular lithium polymer cells have terminals, which can be soldered allowing easy stacking of cells for making batteries. They are also available with higher AmpHr capacities, they are used in smartphones & powerbanks. I got these 10000 mAHr capacity lithium polymer cells (used in powerbanks) and made a 16.8 Volt, (4S) backup power supply. I too wanted to make a powerful battery, but then the other material was needed ~ housing/cabinet, nickel metal strips, machine for spot-welding, BMS & other hardware. This scheme was complicated, as it involved having cylindrical cells in parallel to achieve higher capacities. |
|
This is how I power my low band QDX, exclusively. Works acceptably to me for both portable and home purposes.
FWIW, on 80m I get @ 3.8w out, 40m @ 4.2w and 20m @ 3.9w. Bonus... at these levels I don't have to worry about the magic smoke escaping and temp stays low. |
|
Joe WB9SBD
Where did you get those cells?
toggle quoted message
Show quoted text
Joe WB9SBD On 3/22/2023 10:02 PM, AjaiDevMalik
wrote:
18650 LiFePO3 also exist along with other lithium-ion batteries is same/similar shape & size, but their chemistry and electrical properties are slightly different. LiFePO3 cells have a recommended voltage of 3.2 volts, so four cells (4S) are required in series for an approx.12 volt powered supply. Whereas only three (3S) Lithium-Ion Cells with an approx. Charged voltage of 4.2 volt each are normally used. This is very confusing, coz they require different BMS to work properly. |
|
Jim Strohm
On Thu, Mar 23, 2023 at 9:14 AM Joe WB9SBD <nss@...> wrote:
|
|
On Wed, Mar 22, 2023 at 09:44 PM, Ronald Taylor wrote:
you can put a switch across them to short them out when the battery voltage gets to an acceptable lower levelI recall that there was an article in (if I recall correctly) a non-ARRL ham publication about a circuit which would essentially do just that. 73, Don N2VGU |
|
Actually, a 78XX family regulator will have a fairly low drop when in "dropout" condition (VCEsat) but yet still maintain regulation when the battery voltage is higher. A low-dropout type will work the same way and stay in regulation longer during discharge.
73, Don N2VGU |
|
David Smith
Essentially, that what this is:
https://www.amazon.com/gp/product/B01M7Z9Z1N/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 I don't think you save much money/time/convenience trying to build something. I've powered my QDX for hours with this. 73 Dave KW4QY |
|