Since the mid 1990s my "go to" handie-talking has been the venerable Yaesu FT-530. Reasonably popular at the time, this radio has endured, possessing pretty much all of the features that I would want in a handie-talkie such as dual-band operation, reasonably high power (2-5 watts), the ability to receive out-of-band (NOAA weather, for example), and decent battery life.
When I got this radio I immediately got higher-capacity battery packs - first NiCd, then NiMH - to allow longer-duration operation over the original 600 mAH battery pack. I also have a "shell" to allow operation from alkaline cells - the 10 cells allowing the radio to operate in spite of the significant voltage drop when transmitting due to their internal resistance.
Switching to LiIon cells:
Over time, the original NiCd and NiMH cells faded and in the early 2000s, I updated the battery back to LiIon cells, using four cylindrical "18650" cells, providing around 2.5 rated amp-hours using the cell technology then available. In 2009, these cells had also faded in their usable capacity so I "refreshed" the pack once again with "prismatic" LiIon cells - this time using foil-wrapped cells to better-utilize the volumetric capacity within the battery cases.
Flashing forward to 2019, these decade-old cells had begun to show their age, so it was time to rebuild the pack yet again - this time, documenting how the pack was put together.
"Re-celling" with prismatics:
In 2009, I looked around for cells that would better-fit within the original "high capacity" battery case better than the 18650 cylindrical cells and after a bit of searching, I found the model number 703562-2C sold by Batteryspace.com (information on that cell may be found here) - a 1.5 amp-hour foil-pouch cell that is 7mm thick 35mm wide and 65mm long and weighing only grams each (about 0.9 oz). Taking careful measurements, I determined that four of these cells - and the protection circuit - would fit in the case and wired in series-parallel, a 7.2 volt, 3 amp-hour pack could be assembled. Amazingly enough, these cells are still being sold, available for less than $7.00 each plus shipping.
When using these cells - which are essentially foil pouches with explosive lithium compounds inside - it is imperative that one must take several precautions, including:
Warnings and weasel words:
Because Lithium-Ion cells - and other cells - can be dangerous, and there is the possibility of damage or injury, I must insert a few warnings at this point:
The rebuild:
Starting out with some "large" battery packs that I'd been using with my FT-530 (e.g. a "high capacity" pack, about twice the length of the original packs) I carefully removed the original contents - including the 2.5mm charging connector, and disconnecting/removing the metal connections for the "drop-in" charger. Because we will NOT be able to use the original charger, we will not be needing these.
Having on-hand the four LiIon cells required (e.g. 703562-2C sold by Batteryspace.com - information on that cell may be found here) and a suitable "protection circuit"(also available from Batteryspace.com) I set to work.
To prevent abrasion and possible shorting, each cell must be physically insulated from each other: We do not want to have the possibility of the cells rubbing against each other - or the possibility of unwanted electrical contact. For this, I'd used the thin cardboard such as that from a cereal box or a box of crackers when I first constructed the battery in 2009, but this time I used various thicknesses of Nomex (tm) sheet - a nearly-indestructible paper-like insulation material: This is probably overkill as the thin cardboard had worked fine, but I decided to use it because I'd had it on-hand from another project, having obtained it via EvilBay.
As it turned out, the width and length of the cells was narrower and quite a bit shorter than the inside of the battery case: If I could have found cells that were a better "fit" and no thicker I could have managed more than a 3 amp-hour (nominal) capacity for the battery pack. These cells' thickness by themselves doesn't give much margin for the internal space within the case itself, but by staggering the centers of these cells a bit there is more room for expansion of the cells in their normal change in size as they are cycled and as they age.
Clear RTV (silicone) sealant/adhesive is used to hold everything together: A thin layer is used between the two parallel cells to hold the Nomex sheet in place - and to hold the two cells together and more RTV is used to hold the two sets of cells at an offset. The use of RTV is suggested as it is flexible and has some "give" - something that is absolutely necessary with these types of cells to avoid damage during their normal use.
Charging:
One cannot use the original NiCd or NiMH charger for the "new" battery - instead, a constant-voltage, current-limited supply is used. While this sounds complicated, I simply used an LM317 adjustable voltage regulator - the circuit being taken from the standard data sheet with the exception that a 5k, 10-turn potentiometer is used to set the voltage, and there is an LED (with series resistor) placed across the output as an indication of applied voltage.
To charge, the regulated supply is set (nominally) to 8.2 volts and allowed to charge for 6-8 hours when powered from a 1-2 amp power supply, after which time the battery should be removed from the voltage source: In the interest of longevity one should NOT apply charging voltage continuously as maintaining a battery at "full charge voltage" accelerates chemical degradation.
To further-promote longevity of the battery it has been suggested by battery manufacturers and other "experts"1 that the charge voltage be reduced from the nominal 4.2 volt/cell value - a value of 4.05 volts/cell (or 8.1 volts charging) will double the lifetime (in terms of charge cycles) and slow the inevitable degradation over time: This is likely one of the reasons why I got about 10 years out of the original set when a typical LiIon cell/battery will last about 5 years.
What about capacity loss from not "fully charging" the battery? Charging to 4.05 volts/cell will yield about 80-85% of capacity as a full charge, but it is not uncommon for a new LiIon cell - charged to the full 4.2 volts/cell - to lose 15-20% after the first year, so in the long run, the net loss is mitigated, anyway, also offset by the slower degradation of the cell over time by this same reduction in voltage.
Footnotes:
1 - "How to Prolong Lithium-Based batteries" - https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
This page stolen from ka7oei.blogspot.com
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When I got this radio I immediately got higher-capacity battery packs - first NiCd, then NiMH - to allow longer-duration operation over the original 600 mAH battery pack. I also have a "shell" to allow operation from alkaline cells - the 10 cells allowing the radio to operate in spite of the significant voltage drop when transmitting due to their internal resistance.
Switching to LiIon cells:
Over time, the original NiCd and NiMH cells faded and in the early 2000s, I updated the battery back to LiIon cells, using four cylindrical "18650" cells, providing around 2.5 rated amp-hours using the cell technology then available. In 2009, these cells had also faded in their usable capacity so I "refreshed" the pack once again with "prismatic" LiIon cells - this time using foil-wrapped cells to better-utilize the volumetric capacity within the battery cases.
Flashing forward to 2019, these decade-old cells had begun to show their age, so it was time to rebuild the pack yet again - this time, documenting how the pack was put together.
"Re-celling" with prismatics:
 |
| Figure 1: The 10 year old pack. The old cells have started to "puff up" - a sign that they need to be replaced. Click on the image for a larger version |
When using these cells - which are essentially foil pouches with explosive lithium compounds inside - it is imperative that one must take several precautions, including:
- The use of a "protection" circuit. Especially when using cells in series, you MUST include a circuit that prevents either cell from being overcharged or overdischarged: Either state can (and will!) damage the cell, making it more prone to "rapid, explosive self-disassembly".
- Include current limiting. A typical "protection circuit" will usually offer overcurrent protection in the event that the terminals accidentally get shorted - and this is a good thing as these cells can produce tens of amps of short-circuit current. The circuit I used does do this, but there is also a "thermal fuse" included as well for redundancy. For this radio, 3-5 amps of protection is adequate and will prevent catastrophic results.
- Allow room for expansion. These foil-pouch cells will expand slightly with normal use and over time and they should not be packed tightly into the available space - this, to prevent the battery case from being forced apart when this happens, but also to prevent the cells from being crushed/damaged by their own expansion and posing a hazard.
Warnings and weasel words:
Because Lithium-Ion cells - and other cells - can be dangerous, and there is the possibility of damage or injury, I must insert a few warnings at this point:
- If you wish to rebuild/build your own battery pack using LiIon - or other types of cells - it is up to you to take the required safety precautions when doing so, and to accept the risk should fire, explosion, damage, injury or even death result.
- While I can offer advice on how to rebuild battery packs using these cells, I cannot control the quality of the cells, the safety and usability of the build or the way that it is used and implemented. It is up to you to do due diligence when it comes to safely constructing/using cells and educating yourself on the best way to do - or not do it!
- Appropriate care must be taken in the use and maintenance of this and other battery/cell types. It is up to you to determine the most appropriate and safest way to do this.
- I cannot be responsible for your actions or the results of those actions or any damage/injury that might result. As mentioned above, make sure that you do your own research, and take due care to ensure the safety in the construction and use of a battery pack.
The rebuild:
 |
| Figure 2: The four LiIon cells to be used for the rebuild. Click on the image for a larger version. |
Having on-hand the four LiIon cells required (e.g. 703562-2C sold by Batteryspace.com - information on that cell may be found here) and a suitable "protection circuit"(also available from Batteryspace.com) I set to work.
 |
| Figure 3: The four cells installed within the case. 2 mil Nomex sheets have been placed between the two parallel cells with a 20 mil Nomex sheet between the two series sets of cells. Click on the image for a larger version. |
As it turned out, the width and length of the cells was narrower and quite a bit shorter than the inside of the battery case: If I could have found cells that were a better "fit" and no thicker I could have managed more than a 3 amp-hour (nominal) capacity for the battery pack. These cells' thickness by themselves doesn't give much margin for the internal space within the case itself, but by staggering the centers of these cells a bit there is more room for expansion of the cells in their normal change in size as they are cycled and as they age.
 |
| Figure 4: The completed, rebuilt LiIon battery pack. Click on the image for a larger version. |
Charging:
One cannot use the original NiCd or NiMH charger for the "new" battery - instead, a constant-voltage, current-limited supply is used. While this sounds complicated, I simply used an LM317 adjustable voltage regulator - the circuit being taken from the standard data sheet with the exception that a 5k, 10-turn potentiometer is used to set the voltage, and there is an LED (with series resistor) placed across the output as an indication of applied voltage.
To charge, the regulated supply is set (nominally) to 8.2 volts and allowed to charge for 6-8 hours when powered from a 1-2 amp power supply, after which time the battery should be removed from the voltage source: In the interest of longevity one should NOT apply charging voltage continuously as maintaining a battery at "full charge voltage" accelerates chemical degradation.
To further-promote longevity of the battery it has been suggested by battery manufacturers and other "experts"1 that the charge voltage be reduced from the nominal 4.2 volt/cell value - a value of 4.05 volts/cell (or 8.1 volts charging) will double the lifetime (in terms of charge cycles) and slow the inevitable degradation over time: This is likely one of the reasons why I got about 10 years out of the original set when a typical LiIon cell/battery will last about 5 years.
What about capacity loss from not "fully charging" the battery? Charging to 4.05 volts/cell will yield about 80-85% of capacity as a full charge, but it is not uncommon for a new LiIon cell - charged to the full 4.2 volts/cell - to lose 15-20% after the first year, so in the long run, the net loss is mitigated, anyway, also offset by the slower degradation of the cell over time by this same reduction in voltage.
Footnotes:
1 - "How to Prolong Lithium-Based batteries" - https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
This page stolen from ka7oei.blogspot.com
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