BTW, in a recent iEARS (Intel Emergency Amateur Radio Services) net, Charles Congdon W1ZPB, led a discussion on batteries.? Here is the summary he sent out afterward:
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Friends:
??????????? On Tuesday¡¯s net we had a good discussion about making your own battery box and the care and feeding of lithium-ion batteries.??
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??????????? First, what you need to know is that there are about 6 different chemistries of lithium-ion batteries out there.?? Lithium polymer batteries (LiPo) are great for high-current applications (drones).? Other lithium chemistries are present in things like power drills, vape pens, and battery-powered scooters.? These chemistries are more likely to burn down your house if abused, charged incorrectly, etc.?? They also don¡¯t like being stored at a high state of charge.
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For radio Lithium iron phosphate (LiFePO4) is preferred as it is much more tolerant to abuse, can hold higher charge for longer without damage, and has a longer lifespan.?
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Here is an article that discusses lithium batteries and lithium battery safety in more depth:??.?? And here is one on LiFePO4 in particular:??
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?????? Here are more links detailing the differences in different lithium chemistries:
??????????? Here is the chart I have on all my LiFePO4 batteries:
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??????????? NOTE:?? This is no-load voltage, not voltage under load.?? Which is where Loren¡¯s advice comes into play:?? you really want to have an inline meter measuring energy (watts) you have taken from the battery, so you know how much of its total capacity you have consumed (nominal voltage times amp-hour rating).?? Stop when you have drawn 80%.
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??????????? Note that different battery chemistries, including different lithium chemistries, have different tables from the LiFePO4 table above.?? See this article for comparison/contrast:??
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??????????? Here are some discussions to discuss much of this in more depth:
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???????? Finally, there are other factors that need to be considered in order to keep the lithium battery healthy and safe to use (such as current protections, temperature protections, cell balancing, charger with the right profile, etc¡). ? With this many variables to track, this is why electronic BMS (Battery Management System) is an equally important component to consider for any battery solution.
??????? Having said all this, please keep in mind that even if all the correct steps are being followed to build a DIY battery, something can still go wrong.
If one is being built by yourself, you do so at your own risk.
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- Ideally, buy a commercial battery from a reputable vendor with known good internals (yes, 99% are made in China, but some are?much?better than others in terms of protection factors).?? Reviews including tear-downs of lots of batteries, some scary cheap, can be found here:??
- NEVER make a battery of your own from cells without a quality BMS that provides low and high-temperature charge protection [which you can test], high and low voltage and current protection, high and low state of charge protection, cell balancing, etc.?? Good commercial batteries will have such a BMS
- *Only* use the charger designed for that particular battery (the OEM charger), not a random fast or ¡°high¡± capacity charger.?? This is true whether we are talking about an E-bike, ¡°hoverboard,¡± or ham radio.?? The cheap ¡°just like the manufacturer charger only faster, stronger, etc.¡± can damage your battery.
- Do not buy ¡°reclaimed¡± cells (typically manually knocked out of a Tesla battery pack) ¨C buy quality grade-A cells
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????? And? yes, even if you do everything right, it¡¯s still at your own risk.?? Leaving these things in a closed car during a hot day once, charge below freezing once, over-charging or over-discharging because you have a poor BMS, a puncture or crush, and the battery may be permanently damaged (and in these batteries ¡°damage¡± = pulling the pin from a grenade ¨C these things damage the separator in the battery which will eventually lead to thermal runaway = super-fast and hot fire.? Maybe in minutes, maybe in hours, maybe in days or years)
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Hope this helps.
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73, Mike KK7ER
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