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3446 posts

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  #2193276 7-Mar-2019 22:08
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The controller will stop it overcharging once its full, but the amount of power you put in at once can damage the battery

 

Both discharging too fast and charging too fast cause problems.   

 

 

 

When charging, the battery will create gas - the casing is sealed to prevent that gas escaping. Eventually the pressure causes it to condense back into liquid.  
If you charge it too fast then it creates too much pressure and can damage the battery, as well as makes the plates less efficient. 

 

The controller doesnt know the capacity of the battery and maximum rate its designed to accept charge- it just puts as much power as it can in, until it reaches the "full" voltage level by stopping the charge and doing occasional voltage tests , then it stops the charging when the voltage reads full. 

 

More expensive controllers will do multistage charging etc but they are beyond the basic requirements of this project. They too though dont know the capacity of the battery. 

 

 

 

Maximum charge rate is typically C10 for a sealed lead acid battery. That means total capacity over 10 hours or in this case 0.7amps for a 7ah battery. 

Discharging too fast also affects the battery. I use much bigger batteries such as 120ah capacity. 
A 120ah battery discharged at C10 (12amps per hour over 10 hours) will have a much bigger capacity if discharged slower at C100 (discharged over 100 hours) where it is rated for 150ah of capacity. 

 

 

 

Unsealed batteries like car batteries are designed for cranking amps where they deliver more amps immediately - and can be recharged faster because the gas exits the vent on top. You then refill a car battery with a small amount of water twice a year to replace the lost gas. They are discharged only a shallow amount and are recharged in a couple of minutes quite quickly. 

 

This also makes them unsuitable for solar or deep cycle usage where they are better to be sealed. 

 

 





Ray Taylor
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www.ruralkiwi.com

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3636 posts

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  #2193319 8-Mar-2019 07:02
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I guess the limiting factor for charging rate would be the size of the solar panel... if the solar panel can only deliver 0.7A and you have a 7AH SLA battery you can't charge too fast.

 

But why use lead-acid batteries? Why not use LiPo? A cheap power bank does all the voltage regulation and charging control for you. Or you could roll your own. Charging controller. Buck converter to step up to 5V (or 12V if necessary) to feed the RPi. A single cheap 18650 battery gives 2-3Ah.

 

 


 
 
 
 




89 posts

Master Geek


  #2193339 8-Mar-2019 08:07
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raytaylor:

 

The controller will stop it overcharging once its full, but the amount of power you put in at once can damage the battery

 

Both discharging too fast and charging too fast cause problems.   

 

 

 

When charging, the battery will create gas - the casing is sealed to prevent that gas escaping. Eventually the pressure causes it to condense back into liquid.  
If you charge it too fast then it creates too much pressure and can damage the battery, as well as makes the plates less efficient. 

 

The controller doesnt know the capacity of the battery and maximum rate its designed to accept charge- it just puts as much power as it can in, until it reaches the "full" voltage level by stopping the charge and doing occasional voltage tests , then it stops the charging when the voltage reads full. 

 

More expensive controllers will do multistage charging etc but they are beyond the basic requirements of this project. They too though dont know the capacity of the battery. 

 

 

 

Maximum charge rate is typically C10 for a sealed lead acid battery. That means total capacity over 10 hours or in this case 0.7amps for a 7ah battery. 

Discharging too fast also affects the battery. I use much bigger batteries such as 120ah capacity. 
A 120ah battery discharged at C10 (12amps per hour over 10 hours) will have a much bigger capacity if discharged slower at C100 (discharged over 100 hours) where it is rated for 150ah of capacity. 

 

 

 

Unsealed batteries like car batteries are designed for cranking amps where they deliver more amps immediately - and can be recharged faster because the gas exits the vent on top. You then refill a car battery with a small amount of water twice a year to replace the lost gas. They are discharged only a shallow amount and are recharged in a couple of minutes quite quickly. 

 

This also makes them unsuitable for solar or deep cycle usage where they are better to be sealed. 

 

 

 



Some good information. thanks :)




89 posts

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  #2193342 8-Mar-2019 08:10
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frankv:

 

I guess the limiting factor for charging rate would be the size of the solar panel... if the solar panel can only deliver 0.7A and you have a 7AH SLA battery you can't charge too fast.

 

But why use lead-acid batteries? Why not use LiPo? A cheap power bank does all the voltage regulation and charging control for you. Or you could roll your own. Charging controller. Buck converter to step up to 5V (or 12V if necessary) to feed the RPi. A single cheap 18650 battery gives 2-3Ah.

 



I was looking at a usb powerbank.
The problem with most of them is (from my reading) they have a low amp cutoff where if the device isn't pulling enough amps it turns off to prevent loss
The controller I will be using for the pi runs on less than that which means it will stop working when it turns the PI off

"Can I Use a 5V USB Rechargeable Battery?

 

Yes, There seem to be a lot of these coming onto the market, typically used to recharge your mobile phone or tablet whilst on the go.

 

Plug these into the USB power socket on the Sleepy Pi 2 (NOT the Raspberry Pi) which will pipe the power straight through the regulator giving you the lowest possible power consumption. Don’t use the power jack as that is meant for voltages above 5V.

 

However be aware that some of these batteries have a minimum current draw; typically 50mA which they use to work out whether they are charging anything or not. If they think there’s no load, then they will switch off. When running the Sleepy Pi 2  with the Raspberry Pi asleep, the current draw will be well below this threshold and they will switch off, which means no power to the system and it will never wake."


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