Battery calculations

[Motorhomer14]

Hi, guys, would like some help on my understanding of battery calculations. I am trying to understand it all and not sure if I am getting this right.

I have a NDS green power 100aH battery. When I look at RoadPro website they specify max charge current is 10 amps.

On NDS site I get the chart shown below.

From this if I am correct, 100 ah times 0.3c will be a 30Amp Max charge

At 0.1c which I assume is 10Amp charge it will take 10 hours to charge from 50% discharge.

Are my calculation correct

Capacity batter (Ah) X C rating = Max charge current

If so then I assume RoadPro are wrong and the Max charge current is 30A but ideal current would be 10A

Also what does the FM mean "0.3 C for FM"

 

[I2C]

Another site I visit specifically for solar power / 12v RVs (USA site), the experts on there always advise C/10 to C/12 for a battery so 10Amp seems to sound right to me. No idea what '0.3 C for FM' means, never seen that before.

 

[Motorhomer14]

0.3C is same as C/30 as far as I know, so I thought this was a percentage 30% of battery capacity.

 

[Wh05apk]

"At 0.1c which I assume is 10Amp charge it will take 10 hours to charge from 50% discharge."

Surely, if you have a 100ah battery and you are putting in 10amp, then from 50% you need to put in 50ah/10a = 5 hours?

 

[Motorhomer14]

"At 0.1c which I assume is 10Amp charge it will take 10 hours to charge from 50% discharge."

Surely, if you have a 100ah battery and you are putting in 10amp, then from 50% you need to put in 50ah/10a = 5 hours?

Logical maths yes, but going buy the chart no, Lead acid increase resistance as you charge it to full capacity. Chart says 10 hour. Also watched this guy testing battery it takes some time at 0.1C, was shocked at how little capacity he got from the stated ratting. I will be switching out this battery but would like to learn more about specifications

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[Raul]

Hi, guys, would like some help on my understanding of battery calculations. I am trying to understand it all and not sure if I am getting this right.

I have a NDS green power 100aH battery. When I look at RoadPro website they specify max charge current is 10 amps.

On NDS site I get the chart shown below.

From this if I am correct, 100 ah times 0.3c will be a 30Amp Max charge

At 0.1c which I assume is 10Amp charge it will take 10 hours to charge from 50% discharge.

Are my calculation correct

Capacity batter (Ah) X C rating = Max charge current

If so then I assume RoadPro are wrong and the Max charge current is 30A but ideal current would be 10A

Also what does the FM mean "0.3 C for FM"

View attachment 501282

The sweet spot for flooded is 0,1C or C/10. But, max can be as high as C/5 or 0,2C and minimum C/12 to prevent stratification. Gel and agm does not suffer with that, but will sulphate if charged to slow, like C/100.
AGM can take 1C - C/1 with ease, depending on construction and doping materials added. Pure lead takes 1C.
The figures quoted 0,3C or C/3 ( not C/30), are max figures in best condition 25C deg and plenty of time for absorb. When you force a high charge rate, you reach absorb faster and take longer to finish. Reduce charge rate and will get to absorb a little longer, but will finish quicker. Also temperature compensated charge is a must when you poor in C/5 -0,2C or more. Lead heats up quick due to the high internal resistance, and if charger does not throttle back, you degrade them fast. If you want a healthy charge, keep away from max charge rate. Only airplanes need to charge at 1C,
For us on earth C/5-0,2C is more than enough for lead.

 

[Motorhomer14]

The sweet spot for flooded is 0,1C or C/10. But, max can be as high as C/5 or 0,2C and minimum C/12 to prevent stratification. Gel and agm does not suffer with that, but will sulphate if charged to slow, like C/100.
AGM can take 1C - C/1 with ease, depending on construction and doping materials added. Pure lead takes 1C.
The figures quoted 0,3C or C/3 ( not C/30), are max figures in best condition 25C deg and plenty of time for absorb. When you force a high charge rate, you reach absorb faster and take longer to finish. Reduce charge rate and will get to absorb a little longer, but will finish quicker. Also temperature compensated charge is a must when you poor in C/5 -0,2C or more. Lead heats up quick due to the high internal resistance, and if charger does not throttle back, you degrade them fast. If you want a healthy charge, keep away from max charge rate. Only airplanes need to charge at 1C,
For us on earth C/5-0,2C is more than enough for lead.

Thanks I got most of that. Will re-read later when I have more time. So I assume the C rating is a percentage of the battery full capacity. So when they quote 0.3C max charge ratting on a 100aH battery this will be 30Amps. Max. (I understand this is not ideal) and so ideal at 0.1C will be 10 amps

 

[Raul]

You got it, 0,3C for a 100ah is 30A. This terminology is been brought up with Litium.
Lead, uses The old type C/3,3 for a 100ah equates to 30a. C being the capacity, divided by the value after the /.
A C/20 for a 100ah is 100 divided by 20 = 5a, or 0,05C. Most lead capacity, is quoted at C/20, a 5A draw till end of charge will yield the quoted capacity.

 

[Motorhomer14]

Thanks Guys