# Battery charge and discharge currents

#### treez

Hi
We are required to power a load which itself is in parallel with a 72Ah Lithium Battery.
That is, we are tasked with making a power supply which will provide the 48V, at 240Amps to the load.

Normally, the battery provides power to the load by itself.
Since the load is 48V, 240Amps, does it not sound to you like the battery is under-spec’d at 72Ah?
Also, we have been told that when our power supply is powering the load, it must not put more than 90A into the battery. This seems odd. Howcome the battery cannot be charged with more than 90A, when it is said to supply 240Amps when powering the load?

#### d123

Hi,

A battery I looked at - only 10,000mAh and 3.7V, 37millohms, says it can pulse discharge 100A but definitely not be charged with more than 10A within its temp range for charging. Maybe it can briefly pulse out e.g. 720A but over C/whatever it is is forbidden as it will damage the cell and/or electrodes.

treez

### treez

points: 2

#### FvM

##### Super Moderator
Staff member
"we have been told", "it is said". Instead of retelling hearsay information, won't it be appropriate to look at battery specifications?

treez

### treez

points: 2

#### Easy peasy

What is the internal resistance of the battery - this will limit charging current - depending on applied volts differential

Also a shunt on the batt could be used ( separate from a total load shunt ) to monitor batt current ( both in & out ) and use this information to limit Vout of the power supplies such that Ibatt charge is 90A or less, even though more than this is going to the load + batt ...

treez

### treez

points: 2

#### biswaIITH

##### Full Member level 3
Hi
We are required to power a load which itself is in parallel with a 72Ah Lithium Battery.
That is, we are tasked with making a power supply which will provide the 48V, at 240Amps to the load.

Normally, the battery provides power to the load by itself.
Since the load is 48V, 240Amps, does it not sound to you like the battery is under-spec’d at 72Ah?
Also, we have been told that when our power supply is powering the load, it must not put more than 90A into the battery. This seems odd. Howcome the battery cannot be charged with more than 90A, when it is said to supply 240Amps when powering the load?
If 72Ah battery is required to deliver 240A to the load, then it is definitely under-spec'd. Maximum discharge current(peak not continuous) up-to 2C is generally considered safe. Continuous discharge with higher C rate will reduce the life span of battery .However, you can refer manufacturer's datasheet before making a conclusion.

Again 90A charging current for 72Ah is also not safe. Usually all manufacturers recommend a 0.3C to 0.4 C normal charging & around 1C for fast charging(For few cycles)..

d123

points: 2