Battery Upgrade Project (Multiple Output Levels)

Fyfey96 · December 30, 2023

Hi All,

I have this battery pack, it's for my heated vest for scuba diving. It is only 2200mAh but I would like to have a higher capacity battery and would like to make my own battery pack.

I don't want to modify the existing one as it's brand new and don't want to duff the warranty.

The unit has 4 output modes as shown in the picture.

The button is pressed and held to turn on, then pressed to cycle through the modes.

What would be the best way to replicate this functionality? Do you think it's limiting the current? or changing voltage? I have a connector coming today and I can see what's happening with my multimeter.

I would also have the desire to have this wirelessly controlled too as it's worn under a drysuit and would be cool to change levels wirelessly. but that can come at a later stage.

Any suggestions as to what I can use for this project would be much appreciated.

Thanks

mariushm · December 30, 2023

Without opening it, I can not tell you exactly how changing between low / med / hi / max works ....

The chip will be a simple microcontroller that turns on output to the heated vest when you press the button for some time. Then, when you press the button a short duration, it switches modes ... the modes could just be a ratio between on time and off time ... for example max could mean always on , so the heated vest gets whatever voltage is in batteries, and medium could be something like 10 seconds on , 5 seconds off , and low could could be 10 seconds on , 10 seconds off ... something like that. It could be 100 ms on , 100 ms off or other shorter time intervals.

The power adapter is a simple generic 8.4v power supply - unless there's no charger chip inside the device, the actual voltage doesn't matter that much, it just has to be above the voltage required to charge the batteries.

Inside the device there will be two batteries in series , each battery a lithium-ion battery with nominal voltage 3.7v (maximum 4.2v when fully charged) so with two batteries in series, they'll be 7.4v nominal , 8.4v at maximum charge.

A basic charger IC inside the box would be able to take in this 8.4v from the power supply and charge the batteries inside.

So what you could do is replace the batteries with bigger capacity cells, or you could use 4 cells instead of 2 ... take 2 cells at a time and parallel them, then connect the two pairs in series.

Here's an example of what batteries may be in your device : https://uk.farnell.com/bak-technology/18650ca-2s-3j/battery-li-ion-2-25ah-7-4v/dp/2401854

It's just two 18650 2250 mAh cells in series - the picture is generic, from a 2600mAh pack

This one is as I explained above, 4 cells arranged as 2 groups in series, each group with 2 cells in parallel : https://uk.farnell.com/ansmann/2447-3049/battery-li-ion-5-2ah-7-4v/dp/2484236

It's made out from 4 2600 mAh cells - 2 in parallel give you 5200 mAh, and 2 in series increases the voltage from 3.7v to 7.4v

Fyfey96 · December 30, 2023

7 minutes ago, mariushm said:

Without opening it, I can not tell you exactly how changing between low / med / hi / max works ....

The chip will be a simple microcontroller that turns on output to the heated vest when you press the button for some time. Then, when you press the button a short duration, it switches modes ... the modes could just be a ratio between on time and off time ... for example max could mean always on , so the heated vest gets whatever voltage is in batteries, and medium could be something like 10 seconds on , 5 seconds off , and low could could be 10 seconds on , 10 seconds off ... something like that. It could be 100 ms on , 100 ms off or other shorter time intervals.

The power adapter is a simple generic 8.4v power supply - unless there's no charger chip inside the device, the actual voltage doesn't matter that much, it just has to be above the voltage required to charge the batteries.

Inside the device there will be two batteries in series , each battery a lithium-ion battery with nominal voltage 3.7v (maximum 4.2v when fully charged) so with two batteries in series, they'll be 7.4v nominal , 8.4v at maximum charge.

A basic charger IC inside the box would be able to take in this 8.4v from the power supply and charge the batteries inside.

So what you could do is replace the batteries with bigger capacity cells, or you could use 4 cells instead of 2 ... take 2 cells at a time and parallel them, then connect the two pairs in series.

Here's an example of what batteries may be in your device : https://uk.farnell.com/bak-technology/18650ca-2s-3j/battery-li-ion-2-25ah-7-4v/dp/2401854

It's just two 18650 2250 mAh cells in series - the picture is generic, from a 2600mAh pack

This one is as I explained above, 4 cells arranged as 2 groups in series, each group with 2 cells in parallel : https://uk.farnell.com/ansmann/2447-3049/battery-li-ion-5-2ah-7-4v/dp/2484236

It's made out from 4 2600 mAh cells - 2 in parallel give you 5200 mAh, and 2 in series increases the voltage from 3.7v to 7.4v

That's great thanks,

I already managed to figure out the batteries and what I will need for that but it's more the control I was trying to work out. I never thought of the on and off-time thing. That might be a good suggestion and would be a lot easier to do. When the plug arrrives later today I will test with my multimeter and see what its doing.

Thanks!

Fyfey96 · December 30, 2023

3 hours ago, mariushm said:

Without opening it, I can not tell you exactly how changing between low / med / hi / max works ....

The chip will be a simple microcontroller that turns on output to the heated vest when you press the button for some time. Then, when you press the button a short duration, it switches modes ... the modes could just be a ratio between on time and off time ... for example max could mean always on , so the heated vest gets whatever voltage is in batteries, and medium could be something like 10 seconds on , 5 seconds off , and low could could be 10 seconds on , 10 seconds off ... something like that. It could be 100 ms on , 100 ms off or other shorter time intervals.

The power adapter is a simple generic 8.4v power supply - unless there's no charger chip inside the device, the actual voltage doesn't matter that much, it just has to be above the voltage required to charge the batteries.

Inside the device there will be two batteries in series , each battery a lithium-ion battery with nominal voltage 3.7v (maximum 4.2v when fully charged) so with two batteries in series, they'll be 7.4v nominal , 8.4v at maximum charge.

A basic charger IC inside the box would be able to take in this 8.4v from the power supply and charge the batteries inside.

So what you could do is replace the batteries with bigger capacity cells, or you could use 4 cells instead of 2 ... take 2 cells at a time and parallel them, then connect the two pairs in series.

Here's an example of what batteries may be in your device : https://uk.farnell.com/bak-technology/18650ca-2s-3j/battery-li-ion-2-25ah-7-4v/dp/2401854

It's just two 18650 2250 mAh cells in series - the picture is generic, from a 2600mAh pack

This one is as I explained above, 4 cells arranged as 2 groups in series, each group with 2 cells in parallel : https://uk.farnell.com/ansmann/2447-3049/battery-li-ion-5-2ah-7-4v/dp/2484236

It's made out from 4 2600 mAh cells - 2 in parallel give you 5200 mAh, and 2 in series increases the voltage from 3.7v to 7.4v