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| DIY Power Bank technical questions |
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| drummerdimitri:
--- Quote from: Siwastaja on May 31, 2019, 11:00:49 am ---8A * 5 V * 8 hours / 0.90 (eff) = 355Wh 355Wh/16hours = 22W charging power. At 5V, 4.4A -> impossible with standard 5V USB. An external 12V charger would probably be the best. This would then be another synchronous buck. Integrated li-ion charger ICs with synchronous buck FET drivers do exist. Some can control input back-to-back FETs, which is desirable unless you can 100% guarantee mechanically that the 12V charger input is inaccessible, since unlimited battery voltage flows through the synch buck to the charger input. --- End quote --- I have decided to make a 12V pack with a 3s6p configuration. Will I need 6 protection boards or just one since they are all in parallel? |
| Siwastaja:
Paralleled cells act like one bigger cell. Just measure each voltage individually so they are within about 50mV before doing the initial connection, to prevent excessive current from flowing when you make the connection. Make sure the parallel connection cannot accidentally break (and later reconnect). |
| drummerdimitri:
Yes of course i will charge them all to 4.2V prior to welding them in the configuration mentioned. So you're saying one protection board is all I need then right? |
| viperidae:
You'll find you won't need 2A if you don't have fast charge negotiation. Most phones won't pull more than about 1.2A USB micro is only rated at 1.8A max |
| drummerdimitri:
--- Quote from: viperidae on June 01, 2019, 07:33:14 am ---You'll find you won't need 2A if you don't have fast charge negotiation. Most phones won't pull more than about 1.2A USB micro is only rated at 1.8A max --- End quote --- Sure however I have to design it for worst case scenarios with large tablets in mind so 2A per port would be more than enough and leave some headroom. |
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