Battery runtime tests: continuous vs. intermittent discharge

[Cemoi]

I assume that all battery runtime plots published on CPF (e.g. Silverfox's excellent NiMH shootout) show the behaviour of a battery discharged in a load in a continuous way.

I assume that because of the rebound effect, such (voltage as a function of time) curves would have small spikes each time the circuit is closed, if the battery is allowed to rest for a few minutes from time to time.

I'm wondering:
- Does a NiMH battery give more total Wh when discharged in several steps (separated by rest periods), vs. a continuous discharge?
- If the answer is yes: what is the discharge pattern (x minute discharge followed by y minute rest) which would give more Wh?

On the other hand, how is the rebound effect explained at the cell chemistry level? I searched for "rebound" on Isidor Buchmann's website but found no reply.

 

[Mr Happy]

Intermittent discharge does not seem to make much difference with NiMH cells. They perform very well with continuous discharge, even at high loads.

It does make a huge difference with alkaline and zinc-carbon cells though.

Alkaline and zinc-carbon cells contain an electrolyte paste to conduct the current between the two electrodes. When the cell is used, the electrolyte next to the electrodes gets "used up" quicker than it can be replenished, causing a temporary voltage sag and drop in output. However if the cell is allowed to rest the electrolyte has time to equalize, with various chemical species reacting and diffusing back into equilibrium. This effectively "recharges" the cell ready for another burst of output.

In an NiMH cell the same kind of thing happens, but it happens so fast that the cell can "keep up" with a continuous discharge and there is not much rebound effect.

 

[olo]

According to this paper, battery recovery effect is an artifact of the stochastic battery models and is not confirmed experimentally. Obviously we are comparing continuous and intermittent discharge with the same average power.

Instead of a battery recovery effect, our experimental results show the existence of the rate capacity effect, which is the reduction of usable battery capacity with higher discharge power, to be the dominant electrochemical phenomenon that should be considered for maximizing the runtime...

But Mr Happy is right about NiMH batteries - no difference there.

 

[Lynx_Arc]

According to this paper, battery recovery effect is an artifact of the stochastic battery models and is not confirmed experimentally. Obviously we are comparing continuous and intermittent discharge with the same average power.

But Mr Happy is right about NiMH batteries - no difference there.

The thread is 12 years old and Mr. Happy hasn't been around for over 6 years.

 

[hamhanded]

I appreciate olo's contribution even though this thread is old. I feel like necroposting shouldn't be too heavily frowned upon if the forum software is suggesting ancient threads at the bottom of each post, and it seems to do that pretty often for me.

For example: the very recent thread about re-wrapping a battery has a "Similar threads" suggestion that was last posted in 2005. Relevant is relevant, I say.

 

[Lynx_Arc]

I appreciate olo's contribution even though this thread is old. I feel like necroposting shouldn't be too heavily frowned upon if the forum software is suggesting ancient threads at the bottom of each post, and it seems to do that pretty often for me.

For example: the very recent thread about re-wrapping a battery has a "Similar threads" suggestion that was last posted in 2005. Relevant is relevant, I say.

My post is informative just in case they expected a reply from the OP as often people don't realize they are posting in a "dead" thread to begin with.