Lead-Acid Battery Question

[rbscebu]

With gel type lead acid batteries, which is correct?

1. Charging = Exothermic
Discharging = Endothermic

2. Charging = Exothermic
Discharging = Neutral

3. Charging = Exothermic
Discharging = Exothermic

3. Charging = Neutral
Discharging = Neutral

4. Charging = Endothermic
Discharging = Endothermic

5. Charging = Endothermic
Discharging = Neutral

6. Charging = Endothermic
Discharging = Exothermic

 

[6zfshdb]

The answer will depend on the charge / discharge rate. Gel cell batteries are subject to thermal runaway. This occurs when the heat generated by charging exceeds what the battery can dissipate and results in cell rupture.

A lot of useful battery data is available here:

https://www.mpoweruk.com/performance.htm#temp

 

[Mikey-]

Read your text book.

 

[Bruce Arnold]

Lots of good information at the Battery University.

Sometimes, a question can be too specific. Without knowing why you ask, answers are going to be limited in scope.

If you're just curious, then I'm with @Mikey-

 

[harryS]

Emprirical observation. Exothermic for both.

The gel cell in my miata always got warm under charge. Exothermic.

As for discharge, there were many cold mornings that crappy little battery didn't turn over the engine. I'd get the dreaded clunk. But if I held the key on for few seconds, it would usually turn the starter on the 3rd or 4th try. The common theory is that the battery electrolyte warms up. That raises the voltage enough to spin the starter. Exothermic. Doesn't have to be a gel (AGM) cell, as it happens with any lead acid battery..

As rbscebu lives in Hawaii, he probably got to miss these cold lessons of automotive ownership.

 

[Trail Cruiser]

With gel type lead acid batteries, which is correct?

1. Charging = Exothermic
Discharging = Endothermic

2. Charging = Exothermic
Discharging = Neutral

3. Charging = Exothermic
Discharging = Exothermic

3. Charging = Neutral
Discharging = Neutral

4. Charging = Endothermic
Discharging = Endothermic

5. Charging = Endothermic
Discharging = Neutral

6. Charging = Endothermic
Discharging = Exothermic

Both produces heat. Would you classify them as exothermic?

There is such a thing called "efficiency" and the the efficiency lose is wasted as heat. There is efficiency loses in both charging and discharging a lead acid battery.

There are lots of sources you can read about. I'll give one example with tabulation of how much WH charged in and how nuch WH is discharged. https://electronics.stackexchange.c...-hour-wh-efficiency-for-lead-acid-batteries-a

 

[rbscebu]

Thank you all for your input.

The reason I was asking was to assist me in the design of the battery box for my ebike conversion project.This box will be made of 6mm thick plywood (a reasonably good heat insulator) and will sit on the bike's rear carry rack.

I was pretty sure that charging was exothermic as I have experienced that when charging the lead-acid battery on my motorcycle. I was not sure about heat generation during discharging. I will design the box with good ventilation to dissipate the heat build up in my 4 x 12V 16Ahr batteries.

BTW, I live Cebu, Philippines, not Hawaii.

 

[Alex M]

From observations, under normal conditions heat generation during discharging is minor, if not neutral. During extremely high discharge rate - don't know, don't want to know, would never subject my batteries to such an unncecessary torture.

Heat generation during charging could be minor as well, but there are heat losses - your charging current only partially goes into rearranging ions and electrons to store the charge, while a good chunk of that current is wasted, converted to heat, not necessarily by purely chemical reaction. Terms Exo or Endothemric normally refer to chemical reactions, not just any process when things are getting warmer or colder.

64Ah 12V led battery will give you less than 500Wh usable charge at horrible 40-45 lbs weight.

Also, in a hot climate gel batteries deteriorate much faster than wet cells - gel dries out, voids appear inside. People using batteries for daily deep discharging and charging, like RVs, prefer AGM and wet cells to gel. In fact, I haven't heard of anybody using gel in this application. Same for boaters - AGM or wet cells.

 

[rbscebu]

Alex M, thank you for your observations. That is what I needed to know.

Sorry about the confusion in using exo/endothermic. I was educated in UK English where those terms relate to any process (chemical or otherwise) that gives out or absorbs heat respectively. Obviously US English is different.

I also have read that gel batteries may tend to dry out in hotter climates. To an equal extent, I have read that gel batteries do not dry out as they are sealed from the outside atmosphere. In the Philippines, just about all ebike batteries areof the lead-acid gel type.

This is my first ebike project and my budget is limited. I was able to get my 4 x 12V 16Ahr gel batteries for about USD97 total. Similar AGM batteries were going to cost me more than twice as much. If this conversion project all works out to me liking, I will save up and look at getting Li-Ion batteries. Hopefully the gel batteries will have enough life to give me time to save.

My plywood battery box will have good ventilation holes in its bottom and I will charge the batteries with the battery box lid open. I hope that ventilation arrangement proves sufficient.

 

[Trail Cruiser]

Alex M, thank you for your observations. That is what I needed to know.

Sorry about the confusion in using exo/endothermic. I was educated in UK English where those terms relate to any process (chemical or otherwise) that gives out or absorbs heat respectively. Obviously US English is different.

I also have read that gel batteries may tend to dry out in hotter climates. To an equal extent, I have read that gel batteries do not dry out as they are sealed from the outside atmosphere.

This is my first ebike project and my budget is limited. I was able to get my 4 x 12V 16Ahr gel batteries for about USD97 total. Similar AGM batteries were going to cost me more than twice as much. If this conversion project all works out to me liking, I will save up and look at getting Li-Ion batteries. Hopefully the gel batteries will have enough life to give me time to save.

Mt plywood battery box will have good ventilation holes in its bottom and I will charge the batteries with the battery box lid open. I hope that ventilation arrangement proves sufficient.

Hi, sorry for the harsh words on my previous post. I have experience with lead acid powered old ebike. The casing that held the 2 batteries had no ventilation and there was minimal heat build up on charging and when using the ebike. I guess you don't have to worry about heat build up on he battery.



The motor will overheat first way way earlier before the battery does.

 

[Alex M]

I probably used an incorrect term - gel doesn't "dry out", i.e. evaporates into atmosphere. It just deteriorates from heat and current flow. Starter batteries are sometimes gel. Standby services like UPS, too. But not something that you want to charge and discharge by 50-70% several times a week. Nobody wants gel in their motorhomes, boats and off-grid homes. Well, maybe technology has advanced more than I am aware of...