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...

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:
>
> 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

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. 

Joshua

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:

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. 

Joshua

 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:

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

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:

 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:

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

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:

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:

 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:

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

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:

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:

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:

 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:

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

Where did you get those cells?

Joe WB9SBD