Low Voltage Cut Out

[bstedh]

Does anyone have a simple circuit to add low voltage cut out and or battery balance to series batteries for an extra layer of protection in a mod?

Also for single cell's as I would like my mod to shut down at a set level to extend the usable life of the battery.

I have heard several times to add battery protection into your mod but have not found any circuits to do this other than the same ones the batteries have.

 

[WillyB]

This is as far as I would go for extra protection.

2920L300DR Littelfuse PTC Resettable Fuses

Very low additional resistance. 3A hold, and 5A trip sounds about right.

 

[bstedh]

That's good for helping with shorts but I am having a low voltage issue with two 14500's in series with my VV. One cell is draining to the point that the batteries pcb is shutting it down and I don't want to push it that far.

 

[Dalton63841]

Perhaps you can modify something from here: voltage cut off switch - RC Groups

 

[CapeCAD]

A resistor divider or resistor/zener diode on the enable pin should work.

For a single cell, a resistor/zener with a breakdown voltage at your minimum will work.

 

[bstedh]

Ok, my basic electronics are a little rusty. I believe if i use this zener with an LED I can at least have an indicator that will tell me if the voltage drops below 3.3V on an individual cell.

1N5226B-TPCT-ND

Here is a multi cell monitor circuit. My big question is will current follow the red path or the blue path. If it follows the blue path due to the higher potential this will not work.

Oh yea one of the diodes are backwards. I was to lazzy to re-draw it =]

 

[CapeCAD]

This modification to the picture in another one of your posts demonstrates what I meant. You can use the enable pin to set the minimum voltage.

You can also insert the Diode and resistor at the enable pin even if your switch is on the input as you have drawn it (I got carried away with the safety/enable switches).

The diode will keep the enable from going high unless the input voltage is greater than the breakdown voltage. The resistor will hold it low when the switch is off and decrease the current required to enable.

 

[bstedh]

I would wan't a 6.6V zener in this configuration correct?
Also the drawback to this on my weller mod is that I don't have a location available for a master switch =] That was the main reason I wasn't using the control pin. I am starting to lean towards just drilling a couple of small holes in the mod body so I can stick the multimeter leads in to get voltage readings of each battery and load. I would only need to drill two holes. one on the bottom and one at the switch.

On my next mod I think I will follow this as an example.

 

[CapeCAD]

I would wan't a 6.6V zener in this configuration correct?
Also the drawback to this on my weller mod is that I don't have a location available for a master switch =] That was the main reason I wasn't using the control pin. I am starting to lean towards just drilling a couple of small holes in the mod body so I can stick the multimeter leads in to get voltage readings of each battery and load. I would only need to drill two holes. one on the bottom and one at the switch.

On my next mod I think I will follow this as an example.

Yes, a 6.6V zener would work and you can just add the zener and a ~680k resistor to your current setup to keep enable low at less than 6.6V

 

[clutchjunkie]

Awesome, this is just what I needed for my Lipo powered mods. Any extra safety is a good thing.

 

[WillyB]

That's good for helping with shorts but I am having a low voltage issue with two 14500's in series with my VV. One cell is draining to the point that the batteries pcb is shutting it down and I don't want to push it that far.

What voltage you vaping at?

I'm assuming it's the lead cell. Do you swap positions after a re-charge?

 

[bstedh]

What voltage you vaping at?

I'm assuming it's the lead cell. Do you swap positions after a re-charge?

I am not sure what voltage I am vaping at as I don't have a means of testing under load until I drill a couple of holes. [on the todo list] I am guessing I am mostly running about 3.8~3.5 with my 1.25 dual coils and ~4 with my 2.0ohm cartos and just over 4 with my standards. I think My preferred vape is 8.5~9.5 watts but I won't know for sure until I am able to get my voltage under load.

I haven't played around with the batteries much since I discovered the issue as it was the same time I finished my "Really Ugly Stick" an I have been vapping exclusively on it to test it out. I should be able to get some more detailed info on what is happening after this weekend as I will be going back to my VV and will have test point holes drilled out.

Also I haven't been paying any attention to what position which battery was in but that is something I will also track as I test it out. I will probably mark them with a 1 and 2 to identify them.

 

[bstedh]

Awesome, this is just what I needed for my Lipo powered mods. Any extra safety is a good thing.

With all of the battery safety posts I have seen lately a little protection for the masses is a good thing.

 

[breaktru]

Just my 1.5 cents: Half way thru battery use, I swap the battery positions.

 

[asnider123]

Hi Bstedh .. thanks for the reference from the poorvari thread, just the info I was looking for. Zeners are one of those things which I have had no experience, but this will soon be remedied.

In all the references I have seen about LEDs and zeners and cutoff voltages, it seems that the zeners used are always considerably lower voltage than is the desired cutoff voltage. It seems it is the combination of voltage drops of each component (the LED, the current limiting resistor, and the zener itself) .. it's all theoretical to me.

For example: one RC site suggests a 3.9v zener, an hi-output led, a fixed resistor and a trim pot to calibrate it. Oddly, the zener is put in backwards (I don't understand it exactly). Then just hook it up to a variable ps and calibrate the cutoff where you want. Light dims as it approaches cutoff, goes out completely when time to replace batts.

Thanks again for the inspiring thread.

Alan

 

[asnider123]

Just my 1.5 cents: Half way thru battery use, I swap the battery positions.

Hi Breaktru .. which battery is the lead battery? Electrons flow from minus to plus, so I assume the lead battery is really the last one. Correct?

 

[breaktru]

Hi Breaktru .. which battery is the lead battery? Electrons flow from minus to plus, so I assume the lead battery is really the last one. Correct?

What I have experienced is the battery closes to the Neg, always drains the most (lowest reading)

 

[asnider123]

What I have experienced is the battery closes to the Neg, always drains the most (lowest reading)

Rotating 1/2 way through is a good idea. Thanks

 

[bstedh]

Hi Bstedh .. thanks for the reference from the poorvari thread, just the info I was looking for. Zeners are one of those things which I have had no experience, but this will soon be remedied.

In all the references I have seen about LEDs and zeners and cutoff voltages, it seems that the zeners used are always considerably lower voltage than is the desired cutoff voltage. It seems it is the combination of voltage drops of each component (the LED, the current limiting resistor, and the zener itself) .. it's all theoretical to me.

For example: one RC site suggests a 3.9v zener, an hi-output led, a fixed resistor and a trim pot to calibrate it. Oddly, the zener is put in backwards (I don't understand it exactly). Then just hook it up to a variable ps and calibrate the cutoff where you want. Light dims as it approaches cutoff, goes out completely when time to replace batts.

Thanks again for the inspiring thread.

Alan

Find the wiki on zener diodes it will give you good information. I had to look it up to refresh my memory because it has been so long. Basically a zener diode is used because like a regular diode it only conducts in one direction. However they are designed so that when the current is running to it backwards there is a breakdown point where it will start to conduct at a specific voltage.

I am starting to miss the days when I could design these simple circuits without even thinking about it. Todays pluck and chuck trouble shooting has really deteriorated my knowledge.

 

[bstedh]

I think I will get into the habit of rotating the batteries several times while I am using it as they come out of my mod really easy.