Hi there,

Ma says if someone put a primary cell battery (button type) 1V2 instead of a Rechargeable battery of the same type and voltage 1V5, the charging circuit will explode the battery. Why?
If the battery's voltage is higher than the load ...

Thank you

 

Primary cells are not designed for charging. If a charging current is applied (in reverse to the normal output current) then the abnormal chemical reaction in some types of primary cells can generate a gas which can eventually explode the cell if the pressure gets high enough.

I don't understand what the battery's voltage being higher than the load has to do with anything. This is about charging voltage which is always higher than the battery's normal output voltage.

 

Thanks crutschow,

I don't understand what the battery's voltage being higher than the load has to do with anything. This is about charging voltage which is always higher than the battery's normal output voltage.

Sorry, I made a mistake. In fact the primary cell battery is 1V5 (even more), the Rechargeable battery is 1V2 & the charging voltage is 1V3.

Almost when the primary cell battery is good its voltage is higher than the charging, so the current can't go in. Is in't ?

.

 

The 1.3V you measure when nothing is connected may not mean much. But you're right that the charger's voltage must overcome the battery's voltage in order to force current in.

When you connect the charger to the primary cell (which you should not do for any extended time), you can see whether the voltage rises slightly or falls slightly. That will tell you whether current is being forced in or pulled out. But again, don't leave it connected except to do your experiment.

 

The primary cell won't be at 1.5 forever.

May hold 1.5 until the end of life, but then what?

 

duplicate !

.

 

Thanks all,

The 1.3V you measure when nothing is connected may not mean much.

The 1.3V is when the Rechargeable battery is connected. I assume that a different level can be with the primary one.

The primary cell won't be at 1.5 forever.
May hold 1.5 until the end of life, but then what?

We put a new cell.

I guess that the device, a Weekly Digital Programmer (with the primary battery), can be stable for almost one year...