Am I reading this block diagram right?

Submitted ⁨⁨1⁩ ⁨day⁩ ago⁩ by ⁨Strayce@lemmy.sdf.org⁩ to ⁨askelectronics@discuss.tchncs.de⁩

https://lemmy.sdf.org/pictrs/image/4366292f-ab7d-438c-9939-3da4311a5916.png

From the service manual for the Yamaha DX-100 FM synthesiser. The way this looks to me, both the 12v DC power supply, and 9v DC battery power get routed through exactly the same voltage regulator.

So it should be possible to just straight replace the 6x C-cells with 3x 18650s without needing to make any other changes, right?

I know exactly enough electronics to be dangerous, which is why I’m double checking here in case I’ve failed to account for something.

I’m aware that fresh 18650s put out a little over 4v, but I seriously doubt the vReg tops out at exactly 12v. I can disassemble the unit and check part numbers etc if necessary but I was really hoping to avoid that as it’s quite a chore.

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ignotum@lemmy.world ⁨1⁩ ⁨day⁩ ago
Lithium batteries are a bit finicky, they self-discharge, and the rate varies from cell to cell, so if you have three cells in series at 4V, some of them will drop in voltage faster than the others over time

When you then charge them in series like that, it’ll charge until the three cells combined are at 12V, but that might mean that one is at 4V, the second is 3.9V, and the last is 4.1V

This drift keeps happening over time, and eventually one cell will end up at a dangerously high voltage, potentially catching fire

That’s why with lithium batteries, you need a monitoring circuit that keeps the voltages of the cells balanced

So i would not advice you to simply swap them in like that, you could charge the cells in an external charger and then use them in the device, but remove or isolate the 12V supply so it doesn’t charge them while installed

NiMH batteries might be a better fit, they basically self-balance i believe, but you’d need 10 cells in series to reach 12V

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- Strayce@lemmy.sdf.org ⁨1⁩ ⁨day⁩ ago
  It looks to me like the circuit already isolates the batteries when the 12v supply is plugged in anyway, but regardless I would definitely be charging them external to the device. I have a dedicated charger already so it would be quicker and easier to use that and just swap in a new set as needed. I’ll be 3D printing adapter housings such as this, so adding a diode into that assembly should be easy enough. Thanks for your advice!
  
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Nawor3565@lemmy.blahaj.zone ⁨1⁩ ⁨day⁩ ago
Master degree in EE here. It will almost certainly be fine to swap those batteries like that, I would be more cautious if it was some cheap Temu device but for a vintage Yamaha you’ll be fine.

One thing I will caution you about though, the synth almost certainly lacks under-voltage protection and could drain your 18650s below their minimum voltage. Make sure your cells have built-in protection or add some of your own.

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SillyDude@lemmy.zip ⁨1⁩ ⁨day⁩ ago
If you can I would open it up, find the voltage regulator, then look up its specs. 12.6v might be pushing it a bit but still within spec. Adding a little heatsink if it can fit would set you up a lot better to then run 12.6v frequently.

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