COUP-DE-FOUET (Battery phenomenon)

[HiTech]

Well when I first started testing my AGMs, I found a tiny voltage drop and then slight recovery of voltage when first applying a constant heavy load. I wondered if it was just variation in my instruments. Turns out it is real, and there is not a proven answer as to why it happens.

COUP-DE-FOUET

Jim

[HiTech]

camperpaul wrote:
I first observed this phenomenon in the '60s, so just to satisfy my own curiosity, I did some experimentation.

My observations:

1. When a heavy load was applied, tiny bubbles would form on the plates.
   
   
2. The bubbles would reduce the plate area exposed to the electrolyte.
   
   
3. This would increase the internal resistance of the cell.
   
   
4. The increased internal cell resistance would cause a brief drop in measured output voltage.
   
   
5. After a short time the tiny bubbles would come together making larger bubbles.
   
   
6. This would allow more plate area to come in contact with the electrolyte.
   
   
7. This reduced the internal cell resistance, allowing the measured cell voltage to return to 'normal'.

Interesting!!

Jim

[nevadanick]

Its always been that way. Forever as far as i know that when you tried starting your car and the battery wouldnt turn it over enough to start you waited a few minutes and tried again as it would always have a bit more power.

[camperpaul]

I first observed this phenomenon in the '60s, so just to satisfy my own curiosity, I did some experimentation.

My observations:

1. When a heavy load was applied, tiny bubbles would form on the plates.
   
   
2. The bubbles would reduce the plate area exposed to the electrolyte.
   
   
3. This would increase the internal resistance of the cell.
   
   
4. The increased internal cell resistance would cause a brief drop in measured output voltage.
   
   
5. After a short time the tiny bubbles would come together making larger bubbles.
   
   
6. This would allow more plate area to come in contact with the electrolyte.
   
   
7. This reduced the internal cell resistance, allowing the measured cell voltage to return to 'normal'.

[HiTech]

🙂

[mena661]

HiTech wrote:
We pigs like the mud. I grew up a shop rat and I'm proud of it. 🙂

Jim

Hear! Hear!

[HiTech]

We pigs like the mud. I grew up a shop rat and I'm proud of it. 🙂

Jim

[mena661]

HiTech wrote:
Nobody else found this increase in voltage on a discharging battery at all odd?

Jim

Most AGM's owners are set and forget types. You're pretty much the only one getting into the mud with this battery type.

[HiTech]

Jim you seem to be the only other one who has seen this. I just saw it again. It is subtle (hundredths digit) on newer batteries but it is supposed to show up more easily on older batteries. Nobody else found this increase in voltage on a discharging battery at all odd?

Jim

[HiTech]

It is an interesting problem with say an inverter and an old battery. The initial dip can trip the low voltage cut out, even though the bank could actually sustain the load for some time if it could get past that brief dip.

The way around is to bring on loads a little more gradually, if possible.

Jim

[JiminDenver]

Jim
I just noticed this with the LED test I'm running. My battery was at 12.83 when I checked it last night and first thing this morning it was sitting a 12.7v. A few minutes ago I checked it and the voltage had climbed to 12.81v