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   Rich Felker (dalias@hachyderm.io)'s status on Monday, 03-Mar-2025 07:56:00 JST Rich Felker

   Got the rest of the parts ordered for the UPS I'm building. Came to $39 counting batteries (went LiFePO4 for safety) but excluding the $7 PD module I already have, for 65Wh capacity which is probably all-day or more modem uptime.

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     Rich Felker (dalias@hachyderm.io)'s status on Monday, 03-Mar-2025 08:10:48 JST Rich Felker

     in reply to

     Went with 4S battery because this admits using 15V USB PD trigger as the charging source (desired charging voltage is 14.8-15.0 V) and has enough voltage across whole charge range to be in efficient range for the output DC-DC.

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     Rich Felker (dalias@hachyderm.io)'s status on Monday, 03-Mar-2025 08:24:20 JST Rich Felker

     in reply to

     • LisPi

     @lispi314 Yeah I probably will.

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     LisPi (lispi314@udongein.xyz)'s status on Monday, 03-Mar-2025 08:24:22 JST LisPi

     in reply to
     @dalias Going to do a build writeup and/or references recommendation?
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     Rich Felker (dalias@hachyderm.io)'s status on Wednesday, 05-Mar-2025 10:24:31 JST Rich Felker

     in reply to

     Got the parts! Everything looks good. Started taking measurements and in-notebook sketches of layout. My plan is for the whole unit to be around 165 x 78 x 40 mm in two part housing. One part is the battery pack and BMS, batteries lined up in one row side by side. The other has the USB-PD out module (73x37) and PD-trigger for power-in. The out module also has a barrel connector for barrel 15V if desired.

     The second part will be stackable, so if I ever need 2 or more things running off the same battery pack, I can add another out-only block on top, extending the long dimension.

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     Rich Felker (dalias@hachyderm.io)'s status on Wednesday, 05-Mar-2025 10:26:19 JST Rich Felker

     in reply to

     The 32700 form factor LiFePO4's turned out to be a really good choice for clean design - all the boards fit in roughly the same profile without needing to make anything an awkward shape.

   • Embed this notice
     cliffle@hachyderm.io's status on Wednesday, 05-Mar-2025 10:39:51 JST cliffle

     in reply to

     @dalias you doing a 4S pack?

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     Rich Felker (dalias@hachyderm.io)'s status on Wednesday, 05-Mar-2025 11:02:39 JST Rich Felker

     in reply to

     • cliffle

     @cliffle Yep, 4S LiFePO4. The voltage came out to be good for charging from USB-PD and for input to buck/boost PD output module.

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     Rich Felker (dalias@hachyderm.io)'s status on Thursday, 06-Mar-2025 01:24:47 JST Rich Felker

     in reply to

     Batteries packed. 🤞

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     Rich Felker (dalias@hachyderm.io)'s status on Thursday, 06-Mar-2025 11:45:50 JST Rich Felker

     in reply to

     Minor setback: these garbage PD trigger modules don't have diodes on the output, so the MCU that does PD negotiation gets/remains powered by the battery, then fails to realize it needs to do a PD handshake but feeds 13.5V back into the USB supply before negotiation. 🤬

     Tomorrow I'll splice a power diode inline. 14.3V input is probably better anyway. And I have to wait for a new spool of filament to dry anyway to make the PCB side housing.

     Otherwise it's working, and charged my phone like 15% while I was typing this.

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     Rich Felker (dalias@hachyderm.io)'s status on Thursday, 06-Mar-2025 22:57:36 JST Rich Felker

     in reply to

     Inline diode works as expected. It's a stupid & inefficient hack vs proper reverse current protection, but all that's practical to do without finding or making new PCBs. I'd love to find an off the shelf trigger module with builtin reverse current protection before publishing design tho. If anyone knows of one, let me know. (Boost for reach.)

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     Rich Felker (dalias@hachyderm.io)'s status on Friday, 07-Mar-2025 23:36:48 JST Rich Felker

     in reply to

     One more stupid setback: woke up with battery drained. I failed to actually check that the USB-PD adapter that came with the modem was charging the UPS. 🤦 It kept power cycling, probably tripping overcurrent charging the battery despite the label claiming it was rated high enough.

     So I'm just gonna put a 15V barrel adapter on it rather than buying a better USB-PD adapter or tying up one of my existing good ones. That cuts out the wasteful diode too.