# Will a diode in this configuration consume power?

#### Jeff262

Joined Sep 19, 2021
2
I am placing 2 12v lithium batteries in series to get 24v. the lithium batteries have a built in bms so if I charge them at 24v if one bms kicks in the other battery won't get charged fully so I want to charge each one separately by adding diodes will the diodes in this configuration consume power and need resistors to Balance out? The diodes are rectifier rated at 40 amps

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#### Papabravo

Joined Feb 24, 2006
17,306
In the diagram the diodes are reverse biased (cathode at a higher potential than anode). There is a small reverse bias leakage current, on the order of microamperes. Check the datasheet for the actual value. This current times whatever the charging voltage is will be the power dissipated. It should be negligible.

I fail to understand how this scheme will help you achieve your goal(s) since the diagram does not show any other details besides the batteries and the diodes. Where exactly is the BMS circuit and what exactly does it do under various circumstances.

#### Juhahoo

Joined Jun 3, 2019
250
There is always reverse current flowing, amount depending on the diode type. This particular Diode doesn't have data for that so you need to measure it.

#### Jeff262

Joined Sep 19, 2021
2
The bms, battery magament system. is just a circuit in the 12v pack that protects the cells from being over and under discharged and will shut down the pack in either case, if one pack has a slightly weak cell the charging will be terminated at that pack and the other battery will also stop charging since its bms will see a over current in the stronger pack. the point of the diodes are to isolated the batteries so I can charge them at 12v individually instead of charging both at the same time at 24v

#### Papabravo

Joined Feb 24, 2006
17,306
The bms, battery magament system. is just a circuit in the 12v pack that protects the cells from being over and under discharged and will shut down the pack in either case, if one pack has a slightly weak cell the charging will be terminated at that pack and the other battery will also stop charging since its bms will see a over current in the stronger pack. the point of the diodes are to isolated the batteries so I can charge them at 12v individually instead of charging both at the same time at 24v
I don't see how that will accomplish your goal. With 24V across both batteries the diodes serve no useful function. With 12V across the top battery, the bottom battery is floating and neither diode serves a useful function. With 12V across the bottom battery, the top battery is floating an neither diode serves a useful function. Did you come up with this idea on your own or is there a reference you can point to?

#### LowQCab

Joined Nov 6, 2012
1,343
In order to provide a solution for You,
You need to provide a Schematic, and any other info,