Hacker News Reader

Comment by beefield | Hacker News Reader

Now, who would start to standardize lithium ion battery packs for different voltages? It would be quite nice to have a pile of packs of 12V that you can slap together to get the voltages 24, 36 and 48 as you need and all your tools from power drill to chainsaw, lawnmower and ebike could use the same packs - regardless of the brand.

(I assume there are some technical challenges regarding balancing a 1Ah pack with 80Ah pack when someone is going to slap them together to get 24V, but those can't be unsolvable.)

View on HN

We already have standardized voltages, they're a defining feature of each chemistry. What Makita markets as 18V batteries and DeWalt calls 20V are actually the same battery with the same voltage range.

And regarding combining a 12V 1Ah pack and 80Ah pack together to create a 24V pack, you would end up with a 24V 1Ah pack, as by that time the first pack will have been emptied and you need to recharge it, while the other pack still has 79Ah remaining.

Getting into FPV drones was super interesting because battery tech plays a huge part in the hobby. Rather than voltages, everything is normalized to number of LiPo cells in series, e.g. 1S, 2S, 4S.

Drone accessories also accept a super wide voltage range so they can be mostly powered by whatever battery packs you have laying around (excepting support for 6S, which is kinda rare).

However moving past drones, you'll start seeing other battery chemistries with different voltage ranges. Li-Ion can be discharged further than LiPo. LiFePO4 tops out at 3.6V, rather 4.2V. And so on.

This has me wondering how to engineer a circuit to have the 80Ah constantly charging/balancing with the 1Ah to maintain both the full voltage and capacity capabilities of both cells without shorting out the leads to the load. Of course, the peak power/current is still limited by the 1Ah cell. I guess the simple way is just put the cells in parallel and use a boost converter.

This whole strand of consideration serves no purpose since nowadays if a hardware designer wanted specific voltages they'd use a buck/boost converter with the effect that any battery can output any voltage at any current up to its total safe power output limit, with losses so minimal that they are negligible.

You use a battery controller that balances the cell voltages by doing either charge redistribution or plain current bypass.

I use a number of Makita "36V" tools, like their XCU04Z chainsaw [1]. Like their other yard tools and circular saws and other more power-hungry tools, you clip on two of their 18V LXT battery packs. If you don't need the chainsaw, you can clip one of them on a drill or angle grinder or whatever that only needs 18V.

Unfortunately, this endorsement is complicated because they just introduced their "40V" XGT line that's not backwards compatible with the LXT. [2] It's really 36V, just 10 series 21700 cells instead of one, two, or three parallel banks of 5 series 18650 cells.

You can get adapters to use your Makita (or red or yellow or orange or green whatever brand you favor) batteries on any other tool brand, but I haven't seen 2xLXT to XGT adapters yet; the form factor is difficult. Perhaps a lanyard with the batteries in a backpack or holster, and a smaller adapter at the tool...

Edit: On searching, apparently back in 2020 they filed a patent for a 2x18 to 40V adapter: [3] [4] but I haven't found a released product. The image looks like it could fit nicely in that leaf blower, but it would be absurd on an impact wrench or similar.

[1] https://www.makitatools.com/products/details/XCU04Z

[2] https://makitauk.com/xgt-qa

[3] https://i.redd.it/zd8ubj3ualq41.png

[4] https://www.reddit.com/r/Tools/comments/fu6vwk/someone_dug_a...

Dewalt has 20v and 60v batteries. the 60v batteries can also power 20v tools, and can be ganged together to power 120v tools.

That said, I suspect power tools are a different animal because of current.

I see some indication that some dewalt 60v tools can pull 2400 watts.

Reply on news.ycombinator.com